The 2nd International Conference on the Initial Stages in High-Energy Nuclear Collisions

Embassy Suites Napa Valley, California

Embassy Suites Napa Valley, California

Mateusz Ploskon (Lawrence Berkeley National Lab. (US))

International Conference on the Initial Stages in High-Energy Nuclear Collisions

Focus of the conference:

  • partonic structure of protons and nuclei
  • the conditions at the initial stages of the nuclear collisions
  • complementarity of proton-ion and electron-ion collisions
  • role and nature of fluctuations of initial conditions in pp, pA, eA and AA collision and the subsequent system evolution 
  • determination of viscosity and other physical properties of the created system
    • 1
      Speaker: Mateusz Ploskon
    • Wednesday AM-1
      Convener: Peter Martin Jacobs (Lawrence Berkeley National Lab. (US))
      • 2
        PHENIX Highlights
        Speaker: Dr shengli huang (PHENIX Collaboration)
      • 3
        STAR Highlights
        Speaker: Helen Caines (Yale University (US))
      • 4
        Proton-ion physics with LHCb - results and prospects
        Speaker: Christian Urs Elsasser (Universitaet Zuerich (CH))
      • 5
        CMS Highlights
        Speaker: Julia Velkovska (Vanderbilt University (US))
    • 10:40 AM
    • Wednesday AM-2
      Convener: Urs Wiedemann (CERN)
      • 6
        ATLAS Highlights
        Speaker: Aaron Angerami (Columbia University (US))
      • 7
        ALICE Highlights
        Speaker: Constantinos Loizides (Lawrence Berkeley National Lab. (US))
      • 8
        Overview/outlook CGC
        Speaker: Raju Venugopalan (Brookhaven National Laboratory)
      • 9
        Factorization in Saturation Physics
        Speaker: Bowen Xiao (Central China Normal University)
      • 10
        Particle correlations from CGC
        Speaker: Adrian Dumitru (Baruch College (City University of New York))
    • 1:15 PM
    • Wednesday PM-1
      Convener: Peter Alan Steinberg (Brookhaven National Laboratory (US))
      • 11
        pQCD and saturation (EKRT model)
        Speaker: Risto Paatelainen (Jyvaskyla University)
      • 12
        Thermal radiation - theory
        Speaker: Ralf Rapp (Texas A&M University)
      • 13
        Thermal radiation - experiment
        Speaker: Axel Drees (Stony Brook University)
      • 14
        Photons as a signature of early time non-equilibrium dynamics
        Speaker: Larry McLerran (BNL)
    • 4:10 PM
    • Wednesday PM-2
      Convener: Dirk Rischke (University Frankfurt)
      • 15
        Thermalization process in ultra-relativistic heavy-ion collisions
        Speaker: Jürgen Berges (Heidelberg University)
      • 16
        Speaker: Thomas Epelbaum (McGill University)
      • 17
        Anisotropic hydrodynamics
        Speaker: Wojciech Florkowski (Institute of nuclear Physics, Krakow)
      • 18
        Bottom-up thermalization and heavy-ion collisions
        It is a commonly held belief that weak coupling dynamics are in contradiction with the apparently fast thermalization observed in heavy-ion collisions at RHIC and at the LHC. This belief is based on parametric estimates and naturalness arguments in the Bottom-up picture of thermalization of Baier, Mueller, Schiff, and Son. In my talk, I will discuss elevating this parametric picture into a numerical one through simulations in an effective kinetic theory. I discuss how the numerical factors play an important role and show that the Bottom-Up scenario results in rapid thermalization at realistic couplings.
        Speaker: Eero Aleksi Kurkela (CERN)
    • End of the day discussion
      Conveners: Peter Martin Jacobs (Lawrence Berkeley National Lab. (US)) , Urs Wiedemann (CERN)
    • 7:15 PM
    • Thursday AM-1
      Convener: Carsten Greiner (University of Frankfurt)
      • 19
        Heavy-flavor in pp, pA and AA -overview
        Speaker: Andrea Dainese (INFN - Padova (IT))
      • 20
        Theoretical aspects of quarkonia production in pA collisions
        Speaker: Jianwei Qiu (Brookhaven National Lab)
      • 21
        Quarkonia at RHIC
        Speaker: Grazyna Odyniec (LBNL)
      • 22
        Quarkonia at the LHC
        Speaker: Roberta Arnaldi (Universita e INFN (IT))
    • 10:40 AM
    • Thursday AM-2
      Convener: Barbara Jacak (Stony Brook University)
      • 23
        Impact of fluctuations of IS for system evolution
        Speaker: Dr Jean-Yves Ollitrault (CNRS)
      • 24
        Azimuthal Anisotropy Distributions
        Speaker: Art Poskanzer (LBNL)
      • 25
        Continuous description of fluctuating eccentricities
        "We consider the initial energy density in the transverse plane of a high energy nucleus-nucleus collision as a random field $\rho(x)$, whose probability distribution $P[\rho]$, the only ingredient of the present description, encodes all possible sources of fluctuations. We argue that it is essentially a local Gaussian, with a short-range 2-point function, and that the fluctuations relevant for the calculation of the eccentricities that drive the anisotropic flow have small relative amplitudes. In fact, this 2-point function, together with the average density, contains all the information needed to calculate the eccentricities and their variances, and we derive general model independent expressions for these quantities. The short wavelength fluctuations are shown to play no role in these calculations, except for a renormalization of the short range part of the 2-point function. As an illustration, we compare to a commonly used model of independent sources, and recover the known results of this model."
        Speaker: Blaizot Jean-Paul (CNRS)
      • 26
        Correlations between harmonics
        Speaker: Dr Jiangyong Jia (State University of New York (US))
      • 27
        Hydro-fluctuations in heavy ion collisions and connections to their treatment in cosmology
        Speaker: Urs Wiedemann (CERN)
    • 1:10 PM
    • Thursday PM-1
      Convener: Axel Drees (Stony Brook University)
      • 28
        Viscosity/entropy density ratio in pA vs AA
        Speaker: Paul Romatschke (University of Colorado, Boulder)
      • 29
        Flow results from BES at RHIC
        Speaker: Alexander Schmah (Lawrence Berkeley National Lab)
      • 30
        High order cumulants of azimuthal anisotropy in pA collisions from initial state physics
        In this talk, using the hybrid formalism of the CGC to describe p+A collisions at high energies, we compute the azimuthal structure of the m-particle correlation function. We show that within the conventional CGC, the "flow" coefficient v_2{2} is real, while v_2{4} is complex (v_2^4{4} is negative). The analogous pattern holds for higher order cumulants. We argue that this result is also true for the so-called "glasma" graph. Phenomenological consequences of this finding are discussed. We also consider the case of anisotropic fluctuations of the saturation momentum of the target nucleus, and show that within this approach, v_2^4{4} changes sign as a functions of the anisotropy strength. This might explain the change of sign of c_2{4} as a function of multiplicity observed experimentally in p+Pb collisions at LHC energy.
        Speaker: Vladimir Skokov (Western Michigan University)
      • 31
        Speaker: Klaus Werner
    • 4:10 PM
    • Thursday PM-2
      Convener: Ralf Averbeck (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
      • 32
        Recent results on flow and correlations from the ATLAS experiment
        Measurements of soft particle production have provided valuable insight on properties of the evolution of the quark-gluon plasma in Pb+Pb collisions at the LHC. In particular, measurements of flow harmonics using the azimuthal angle distributions of low-pT particles directly test hydrodynamic model descriptions of its evolution. The large acceptance of the ATLAS detector enables the measurement of event-by-event flow and the correlations between different harmonics. Results will be presented from a variety of two-particle and multi-particle measurements in Pb+Pb and proton-Pb collisions.
        Speaker: Soumya Mohapatra (Columbia University (US))
      • 33
        Review of flow results from ALICE
        We will present recent results on azimuthal flow from the ALICE detector at the LHC. A variety of studies on flow fluctuations in heavy-ion collisions will be shown, and recent searches for the chiral magnetic effect and chiral magnetic wave. Recently published results on identified particle flow and searches for flow in smaller systems will be highlighted, and possible future studies for running period 2. All of these results will be discussed in the context of the initial state, and what we have learned so far.
        Speaker: Anthony Robert Timmins (University of Houston (US))
      • 34
        PHENIX Measurements of Anisotropic Flow in Heavy-Ion Collisions at RHIC energies
        "The anisotropic flow coefficients $v_n$ can provide constraints crucial for precision extraction of the specific shear viscosity eta/s, of the plasma (QGP) produced in heavy-ion collisions at RHIC. A significant recent attention has been given to theoretical studies of $v_n$ (odd and even) and the associated initial [fluctuating] eccentricities which drive $v_n$. In recent experiments, the PHENIX Collaboration has made detailed differential measurements of $v_n$ (odd and even) relative to the participant event planes $\Psi_n$ as a function of transverse momentum, centrality, collision system (Au+Au, Cu+Cu, Cu+Au), beam energy for different particle species. The results from these measurements will be presented and discussed. Detailed comparisons to LHC data will be shown as appropriate."
        Speaker: Arkadiy Taranenko (Department of Chemistry, Stony Brook University)
      • 35
        Initial-state fluctuations from transverse momentum and pseudorapidity dependent event plane fluctuations with CMS
        Various aspects of anisotropic collective flow in a system emerging in ultrarelativistic heavy-ion collisions have been studied by the method of two-particle correlations. A key assumption that is usually applied is that the Fourier coefficients of two-particle azimuthal distributions can be factorized into a product of single-particle anisotropy Fourier harmonics. Recent hydrodynamic studies indicate that due to the lumpy, fluctuating initial state, a pT-dependent event plane angle fluctuation will be induced, leading to a breakdown of the factorization assumption. Systematic study for this underlying effect is conducted using CMS data for 5.02 TeV pPb and 2.76 TeV PbPb collisions. Significant pT-dependent factorization breakdown in central PbPb collisions is observed. The data are compared to viscous hydrodynamic calculations with different initial-state conditions and eta/s values. Implication on constraining the transverse granularity of initial-state fluctuations using factorization data will be discussed. Furthermore, the effect of factorization breakdown for correlating two particles at different pseudorapidities will be discussed. This aspect of the measurement will provide important insight on the longitudinal dynamics of QGP fireball created in heavy-ion collisions.
        Speaker: Mr Wei Li (Rice University (US))
    • Discussion: Collectivity
      Conveners: Alexander Schmah (Lawrence Berkeley National Lab) , Dr Jean-Yves Ollitrault (CNRS) , Raimond Snellings (NIKHEF (NL))
    • Ultra-peripheral collisions
      Convener: Federico Antinori (Universita e INFN (IT))
      • 36
        Theoretical overview of UP Collisions
        Speaker: Tuomas Lappi (University of Jyvaskyla)
      • 37
        UPC experimental overview - RHIC
        Speaker: Spencer Klein (Lawrence Berkeley National Laboratory)
      • 38
        UPC experimental - LHC
        Speaker: Eugenio Scapparone (INFN-Bologna(IT))
    • 10:15 AM
    • Cabernet-1
      Convener: Xin Dong (Lawrence Berkeley National Lab)
      • 39
        Charmonium production in p-Pb collisions with ALICE at the LHC
        "Charmonia are considered as a key observable for deconfinement in nucleus-nucleus (A-A) collisions at LHC energies. Measurements in proton-nucleus (p-A) collisions provide crucial information to study nuclear effects which are also present in the absence of the Quark-Gluon Plasma. Charmonium production has been measured by ALICE in proton-proton, p-Pb and Pb-Pb collisions down to p_T = 0 both via their dimuon decay in the forward muon spectrometer and with dielectrons in the central barrel. In this talk, results on the inclusive J/psi and psi(2S) production in p-Pb collisions at sqrt{s_{NN}}~= 5.02 TeV at forward (p going direction), backward (Pb going direction) rapidity and midrapidity as a function of transverse momentum will be presented. At forward and backward rapidities, measurements as function of event activity will be shown. Finally, comparisons with theoretical models will be carried out and further prospects will be discussed."
        Speaker: Mr Michael Andreas Winn (Ruprecht-Karls-Universitaet Heidelberg (DE))
      • 40
        Bottomonium production at forward rapidity with ALICE at the LHC
        "The measurement in hadron collisions of bottomonia ($b\bar{b}$ mesons) is a powerful tool to investigate their properties and those of the surrounding medium. According to the color-screening model, bottomonia give important information about the deconfined medium called Quark-Gluon Plasma (QGP) that is produced in ultrarelativistic heavy-ion collisions. On the other hand, cold nuclear matter (CNM) effects can also modify the bottomonium production even in absence of deconfined matter: its study in pA collisions is therefore essential to disentangle these effects from the hot ones. Last, in pp collisions high precision data serve as crucial test of different models of quarkonium hadroproduction and provide the reference for the measurements in AA and pA collisions. In the ALICE Muon Spectrometer, bottomonium is measured at forward rapidity ($2.5 < y < 4$) and down to $p_{\mathrm{T}} = 0$ exploiting the dimuon decay channel. The latest results of bottomonium production in pp, Pb--Pb and p--Pb collisions are discussed and compared to available theoretical calculations."
        Speaker: Massimiliano Marchisone (Turin University and INFN)
      • 41
        Charmonium photoproduction in ultra-peripheral Pb-Pb collisions with ALICE at the LHC
        "The photoproduction of vector mesons in Ultra-Peripheral Collisions (UPC) is a powerful tool to probe the nuclear gluon distribution in the nucleus, for which there is considerable uncertainty in the low-x region. The first measurements of coherent photoproduced J/ψ and ψ(2S) in Pb-Pb collisions at √sNN = 2.76 TeV, performed with the ALICE detector, are presented. The J/ψ is identified via its dimuon decay in the forward rapidity region and via dimuon and dielectron decay at midrapidity, while the ψ(2S) is measured at midrapidity in three different decay channels (dilepton, e+e- + π+π- and μ+μ- + π+π-). The measured cross section is compared to STARLIGHT and QCD based models, in order to investigate nuclear gluon shadowing."
        Speaker: Daniele De Gruttola (Universita e INFN (IT))
      • 42
        Results from ultra-peripheral collisions from CMS
        The nature of the initial state can be studied in photon-nucleus collisions at the LHC. Ultra-peripheral collisions (UPCs) of heavy ions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius. At TeV energies, the strong electromagnetic field due to the coherent action of the Z=82 proton charges generates a large flux of photons, which can be used for high-energy photoproduction studies. Heavy vector mesons (for example J/psi, Psi', Upsilon) produced in electromagnetic interactions provide direct information on the parton distribution functions in the nucleus at very low values of Bjorken-x. These events are characterized by a very low hadron multiplicity. The wide pseudorapidity coverage of the CMS detectors is used to separate such events from very peripheral nuclear interactions. The CMS experiment has excellent capabilities for the measurement of the heavy vector mesons in the dimuon decay channel using the tracker and the muon chambers. This analysis demonstrates CMS's capabilities for measuring J/psi, psi' and the two-photon process in ultra-peripheral collisions, using the 2011 PbPb and 2013 pPb data. The measured coherent J/psi photoproduction cross section in ultra-peripheral Pb-Pb collisions will be presented. The prospects for future measurements using the data to be collected in the 2015 PbPb run will be described.
        Speaker: Pat Kenny (University of Kansas (US))
      • 43
        Weak boson results from CMS
        The weak bosons, Z and W, do not participate in the strong interaction, and thus constitute clean probes of the initial state of nuclear collisions. Detected trough their leptonic decay channels, they provide constraints on the nuclear parton distribution functions (PDF). In particular the W boson proves a unique constraint on the sea quark distributions. We report on CMS measurements of weak boson production in pp, pPb and PbPb. Particular emphasis is place on measurements of the 35 /nb of pPb data collected at the beginning of 2013. This provides access to a Bjorken x region, 10^-3 -- 1, which is lacking precision experimental measurements needed by nuclear PDF parametrizations. The Z boson nuclear modification factors as a function of transverse momentum and rapidity will be shown, together with forward to backward ratios. The W boson yields, charge asymmetries, and forward to backward ratios in pPb collisions will also be reported. With a production cross section an order of magnitude larger than the Z, the W allows precise comparisons to theoretical predictions. Comparisons to PDFs are made for both Z and W measurements.
        Speaker: Manuel Calderon De La Barca Sanchez (University of California Davis (US))
      • 44
        Recent results on elector-weak probes in lead-lead and proton-lead collisions from the ATLAS Detector at the LHC
        Photons and weak bosons do not interact strongly with the dense and hot medium formed in the nuclei collisions, thus should be sensitive to the nuclear modification of parton distribution functions (nPDFs). In particular, proton-lead collisions provide an excellent opportunity to test nPDFs in a less dense environment than lead-lead. The ATLAS detector, optimized for searching new physics in proton-proton collisions, is especially well equipped to measure photons, Z and W bosons in the high occupancy environment produced in heavy ion collisions. Using the full data samples of 2.76 TeV lead-lead and 5.02 TeV proton-lead collisions we will present recent results on the prompt photon, Z and W boson yields as a function of centrality, transverse momentum and rapidity, from the ATLAS experiment. The binary collision scaling of the yields will be discussed in detail.
        Speaker: Alexander Milov (Weizmann Institute of Science (IL))
      • 45
        Direct virtual photon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at STAR
        One important physics goal of ultra-relativistic heavy-ion collisions is to study the fundamental properties of a hot, dense medium created in these collisions. This medium is expected to emit thermal radiation in the form of direct photons and dileptons. Once produced, photons and leptons traverse the strongly interacting medium with minimal interactions. The fully installed Time-of-Flight Detector in 2010 enables clean electron identification from low to intermediate transverse momentum ($p_{T}$). In this talk, we will present the direct virtual photon production for $1 < p_{T} < 10$ GeV/$c$ derived from the dielectron continuum in the dielectron invariant mass region $0.1 < M_{ee} < 0.3$ GeV/$c^{2}$ from one billion $\sqrt{s_{NN}}$ = 200 GeV Au+Au minimum bias events taken in years 2010 and 2011. Comparisons to model calculations including hadronic and partonic thermal radiation will be made for the direct virtual photon in Au+Au collisions.
        Speaker: CHI YANG (USTC)
    • Sauvignon-1
      Convener: Matthew Luzum
      • 46
        Initial state angular asymmetries in high energy p+A collisions: spontaneous breaking of rotational symmetry by a color electric field and C-odd fluctuations
        "We present a simple model for generating initial-state azimuthal asymmetries in pA collisions due to scattering on an anisotropic dense target. Here the scenario where rotational symmetry is broken due to the formation of a condensate for the electric field $\vec{E}$ in the target is explored. This leads to an angular correlation with the direction of $\vec E$; the parity even angular harmonics are generated through the C-even real part of the dipole S-matrix. Parity odd harmonics are generated by the C-odd imaginary part (odderon) due to coupling to coherent target fluctuations which again break rotational invariance. We perform a first qualitative extraction of the amplitude and cutoff of C-odd fluctuations in the dense target and show how the existence of multiple $\vec{E}$-field domains in the target allows us to study two- and four-particle cumulants. A. Dumitru and A. V. Giannini, ``Initial state angular asymmetries in high energy p+A collisions: spontaneous breaking of rotational symmetry by a color electric field and C-odd fluctuations,'' arXiv:1406.5781 [hep-ph]."
        Speaker: André Giannini
      • 47
        Initial state fluctuations and anisotropic flows within an event by event transport approach.
        "We study the build up of the elliptic flow $v_2$ and high order harmonics $v_n$ within a transport approach at fixed shear viscosity to entropy density ratio $\eta/s$ and with initial state fluctuations. We investigate the effect of a temperature dependent $\eta/s$ on $v_n$ and their correlations with the initial eccentricities $\epsilon_n$ at RHIC energies for Au+Au collisions at $\sqrt{s}=200 \,GeV$ and LHC energies for $Pb+Pb$ collisions at $\sqrt{s}=2.76 \,TeV$. We find that for the two different beam energies considered the suppression of all $v_n(p_T)$ due to the viscosity of the medium have different contributions coming from the cross over or QGP phase. Moreover, we discuss the correlation between the initial spatial anisotropies $\epsilon_n$ and flow coefficients $v_n$ for different centralities. We observe that at LHC energy all $v_n$ are strongly correlated with initial eccentricity $\epsilon_n$. While such a correlation for $v_3$ and $v_4$ significantly weakens for non central collisions and/or lower energy."
        Speaker: Salvatore Plumari (University of Catania (Italy))
      • 48
        Charge-dependent correlations from event-by-event anomalous hydrodynamics
        "Recently, it is found that triangle anomalies manifest themselves in macroscopic transport effects. For example, a chirality asymmetry in the presence of a magnetic field generates an electric current along the magnetic field. This is called the Chiral Magnetic Effect (CME). Experimentally, STAR[1] and PHENIX [2] at the Relativistic Heavy Ion Collider and ALICE[3] from the Large Hadron Collider reported experimental observation of charge-dependent fluctuations that are expected from the CME, although the interpretation is still under debate. The main difficulty is that there has been no calculations from anomalous hydrodynamics that can be compared to the experimental results. In order to do this, event-by-event simulations are necessary, because the initial chiral-charge distributions are random and the measured quantities involve multi-particle correlations. For the purpose of establishing whether the observed effect is coming from anomalous transport quantitatively, we develop a numerical code for 3+1 dimensional anomalous hydrodynamic simulations on an event-by-event basis[4]. We develop a model of the initial condition that captures the statistical nature of random chiral-charge distributions, and we perform simulations for hundreds of thousands of events. We then calculate the correlation functions that are measured in experiments, and discuss how the anomalous transports affect the observables. [1] B. I. Abelev et al. [STAR Collaboration], Phys. Rev. Lett. 103, 251601 (2009); B. I. Abelev et al. [STAR Collaboration], Phys. Rev. C 81, 054908 (2010). [2] A. Ajitanand, S. Esumi, R. Lacey [PHENIX Collaboration], Proc. of the RBRC Workshops, vol. 96, 2010. [3] P. Christakoglou [ALICE Collaboration], J. Phys. G: Nucl. Part. Phys. 38 124165 (2011). [4] Y. Hirono, M. Hongo, T. Hirano, and D. E. Kharzeev, in preparation."
        Speaker: Yuji Hirono (Stony Brook University)
      • 49
        Eigenmode Analysis of Anisotropic Flow
        "Authors: Rajeev S. Bhalerao, Jean-Yves Ollitrault, Subrata Pal and Derek Teaney Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India CNRS, URA2306, Inst. de physique theorique de Saclay, F-91191 Gif-sur-Yvette, France Dept. of Physics & Astronomy, State University of New York, Stony Brook, NY 11794, USA Methods currently used to analyze anisotropic flow, $v_n$, in relativistic heavy-ion collisions, (event-plane, cumulants, etc.) were devised before the importance of event-to-event flow fluctuations was recognized. We argue that flow fluctuations can be obtained directly from data by fully exploiting the information contained in the two-particle correlation matrix $\left \langle \cos n \Delta \phi \right \rangle$, where $\Delta \phi$ is the azimuthal separation between two particles (from different pseudorapidity bins, in general), and $\langle\cdots\rangle$ denotes an average over pairs of particles in an event and then over events in a centrality class. Our new method uses the eigenmodes and eigenvalues of the two-particle correlation matrix. It can be used to extract information on the pseudorapidity- and transverse momentum-dependence of multiplicity and flow fluctuations. We test the applicability of this method with Monte-Carlo simulations using the transport model AMPT, as well as the ALICE data."
        Speaker: Rajeev Bhalerao (Tata Inst. of Fundamental Research)
      • 50
        Collective flow in small systems from parton scatterings
        "We show that the incoherent elastic scattering of partons, as present in a multi-phase transport model (AMPT), with a modest parton-parton cross-section of $\sigma$=1.5-3 mb, naturally explains the long-range two-particle azimuthal correlations as observed in p+p and p+Pb collisions for all measured $N_{track}$ and $p_T$ bins at the Large Hadron Collider. We calculate the elliptic, $v_2$, and triangular, $v_3$, Fourier coefficients of the two-particle azimuthal correlation function in p+Pb and peripheral Pb+Pb collisions. Our results for $v_3$ are in a good agreement with the CMS data. The $v_2$ coefficient is very well described in p+Pb collisions and is underestimated for higher $p_T$ in Pb+Pb collisions. The characteristic mass ordering of $v_2$ in p+Pb is reproduced whereas for $v_3$ such ordering is not observed. We further predict the pseudorapidity dependence of the two-particle azimuthal correlation function. Predictions for the higher order Fourier coefficients, $v_4$ and $v_5$, in p+Pb are also presented. Our numerical results indicate an emergence of collectivity in p+p, p+Pb and peripheral Pb+Pb collisions from parton scatterings. References: [1] Guo-Liang Ma and Adam Bzdak, arXiv:1404.4129. [2] Adam Bzdak and Guo-Liang Ma, arXiv:1406.2804."
        Speaker: Guo-Liang Ma (Shanghai Institute of Applied Physics (SINAP) Chinese Academy of Sciences)
      • 51
        Azimuthal quadrupole correlation from gluon interference in 200 GeV and 7 TeV p+p collisions
        "The BFKL multi-Pomeron model of Levin and Rezaeian [1] was shown to produce a v2-like anisotropy in the single gluon azimuthal emission from proton + proton (p+p) collisions as result of gluon interference from multi-parton showers. This anisotropy produces a quadrupole correlation among the emitted gluon pairs. However, several parameters in the model were not estimated in [1], preventing quantitative predictions which can be compared with measurements. In this presentation [2] I will show how the Levin and Rezaeian model can be applied to data and will show results for the long-range pseudorapidity, same-side correlations reported by the CMS collaboration for high multiplicity p+p collisions at 7 TeV [3]. Comparisons with recent quadrupole correlation data for 200 GeV p+p collisions from STAR is also discussed. The multi Pomeron exchange probabilities in the model were estimated by fitting the p+p minimum-bias multiplicity frequency distributions. The model predictions also depend on the saturation scale in p+p collisions which is estimated using simple scaling rules. The calculations show that the multi-parton shower, gluon interference mechanism for generating the long-range pseudorapidity, azimuthal quadrupole correlation is not excluded by the data. In addition, the model accurately describes the energy/multiplicity dependence of the p+p quadrupole correlation. Extension of this model to p+A and A+A collisions will also be discussed. [1] E. Levin and A. Rezaeian, Phys. Rev. D 84, 034031 (2011). [2] R. L. Ray, Phys. Rev. D 90, 054013 (2014). [3] CMS, J. High Energy Phys. 09 (2010) 091; arXiv:1009.4122."
        Speaker: Ray Lanny (University of Texas at Austin)
      • 52
        Collective excitations in anisotropic quark-gluon-plasma
        "The quark-gluon plasma at the early stage of relativistic heavy-ion collisions is strongly anisotropic. We systematically study spectrum of collective excitations of such a plasma which is a fundamental characteristic of any many-body system. We demonstrate how the spectrum evolves when the momentum distribution of plasma constituents changes from the extremely prolate – infinitely elongated along the beam direction, through the isotropic one to the extremely oblate – infinitely squeezed in the beam direction. We discuss when unstable modes show up and when they disappear; their role in the plasma dynamics is also considered. Based on: Plasmons in Anisotropic Quark-Gluon Plasma M. Carrington, K. Deja, St. Mrówczyński arXiv:1407.2764 [hep-ph] Phys.Rev. C (in print)"
        Speaker: Katarzyna Deja (National Centre for Nuclear Research)
    • 1:00 PM
    • Cabernet-2
      Convener: Julia Velkovska (Vanderbilt University (US))
      • 53
        Light messengers from heavy quarks - Measurements of leptons from heavy-flavor decays with ALICE at the LHC
        "Light messengers from heavy quarks - Measurements of leptons from heavy-flavor decays with ALICE at the LHC R. Averbeck (GSI) for the ALICE Collaboration Hadrons carrying heavy flavor, i.e. charm or beauty quarks, are unique probes in hadronic collisions at high energies. Given their large masses charm and beauty quark-antiquark pairs are produced almost exclusively via hard parton scattering process in the initial phase of the collisions. Therefore, the measurement of heavy-flavor hadron production cross sections in pp collisions at the LHC serves as a sensitive test for perturbative quantum chromodynamics at the high energy frontier. In p-Pb collisions the yields and kinematical distributions of heavy-flavor hadrons are subject to cold nuclear matter effects such as modifications of the parton densities in nuclei with respect to nucleons, i.e. shadowing or saturation at low Bjorken x, k_T broadening, or energy loss in cold nuclear matter. Heavy-flavor measurements in pp and p-Pb collisions help to characterize the initial state of heavy-ion collisions and provide a mandatory reference for corresponding studies in Pb-Pb collisions, where the quarks propagate through the hot and dense medium and interact with its constituents. The resulting medium modifications of the heavy-flavor momentum distributions can provide unique information on the interaction of partons with the medium and, furthermore, can help to constrain the transport properties of the medium. ALICE is well suited for heavy-flavor measurements at the LHC, not only through the full reconstruction of hadronic D-meson decays at mid rapidity but also via the measurement of electrons (muons) from semileptonic heavy-flavor hadron decays at mid (forward/backward) rapidity. An overview of the lepton measurements with ALICE will be given. Special emphasis will be put on recent results from pp and p-Pb collisions relevant for the characterization of the initial state in Pb-Pb collisions, such as lepton production cross sections, nuclear modification factors, and correlations with hadrons."
        Speaker: Ralf Averbeck (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
      • 54
        Heavy-flavour production as a function of multiplicity in pp and p-Pb collisions with the ALICE detector at the LHC
        "The measurement of heavy-flavour production cross sections in pp collisions at the LHC represents a test for pQCD calculations and provides a reference for heavy-ion studies. The study of heavy-flavour production as a function of multiplicity of charged particles produced in the collisions could give insight into the role of multi-parton interactions (MPI) and on the interplay between hard and soft mechanisms for particle production. In p-Pb collisions, heavy-flavour measurements allow us to estimate the relevance of initial state effects due to the presence of the nucleus in the collisions. Cold nuclear matter effects can also be studied for different multiplicity classes to understand their relation with the number of particles produced in the collisions and with the collision geometry. The talk will be focused on the measurement of open heavy-flavour production as a function of charged-particle multiplicity in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt {s_{\rm NN}}$ = 5.02 TeV recorded with the ALICE detector in 2010 and 2013, respectively. D-mesons are reconstructed from their hadronic decay channels in the central rapidity region, and their yields are measured in different multiplicity and $p_{\rm T}$ intervals. The per-event yield of D-mesons, in different multiplicity intervals, normalised to its multiplicity-integrated value, will be compared for pp and p-Pb collisions to study the effect of MPI on open charm production in both collisions system. Also the D meson transverse momentum distributions in p-Pb collisions relative to pp collisions, in different multiplicity classes, will be shown. The results on D mesons will be also compared to the same observable measured for the J/$\psi$ mesons, in order to investigate whether similar or different production mechanisms related to multi-parton interactions and event activity play a role for open and hidden charm production at the LHC."
        Speaker: Davide Caffarri (CERN)
      • 55
        Heavy Flavor Results in Cold Nuclear Matter from PHENIX
        Charm and bottom quarks, formed primarily from gluon fusion in the initial hard scatterings at RHIC, provide a rich probe with which to study the many interesting physics effects present in p(d)+A collisions including energy loss, gluon saturation, and nuclear parton distribution modification. By measuring the production of both open heavy flavor and closed heavy flavor, in the form of quarkonia, over a broad range in pT and rapidity we hope to be able to disentangle these often competing effects. This talk will review the current set of measurements on heavy flavor production in d+Au collisions from PHENIX, as well as prospects for future p+A running.
        Speaker: Darren McGlinchey (University of Colorado)
      • 56
        Flow Measurements and selection of body-body and tip-tip enhanced samples in U+U collisions at STAR
        The azimuthal anisotropy of particle production is commonly used in high-energy nuclear collisions to study the early evolution of the expanding system. The prolate shape of uranium nuclei provides the possibility to study how the initial geometry of the nuclei affects the azimuthal distributions. It also provides a unique opportunity to understand the initial conditions for particle production at mid-rapidity in heavy ion collisions. In this talk, the two- and four- particle cumulant, $v_2$($v_2{2}$ and $v_2{4}$), from U+U collisions at $\sqrt{s_{NN}}=$ 193 GeV and Au+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV for inclusive charged hadrons will be presented. The STAR Zero Degree Calorimeter is used to subdivide the 0-1% centrality bin into even finer centralities. Differences were observed between the multiplicity dependence of $v_2{2}$ for most central Au+Au and U+U collisions. Data was compared with both Monte Carlo Glauber and IP-Glasma models and it was seen that IP-Glasma model does a better job of describing data. It has also been demonstrated that ZDC and multiplicity in combination provide a way to select body-body or tip-tip enhanced samples of central U+U collisions. We will also present preliminary $v_3{2}$ results for inclusive charged hadrons from Au+Au and U+U collisions.
        Speaker: Hui Wang (Brookhaven National Lab)
      • 57
        Correlation results from CMS
        Latest results of particle correlations in pPb and PbPb collisions at the LHC from the CMS experiment will be presented. In particular, focus will be given to the studies of long-range two-particle correlations (known as the "Ridge") observed in high-multiplicity pPb collisions and their implications to collective phenomena in small systems. These correlations are studied as a function of transverse momentum, pseudorapidity, and event multiplicity, for both inclusive charged particles and neutral strange hadrons. Furthermore, multiparticle correlations are employed to investigate the collective nature of the observed novel correlations.
        Speaker: Zhenyu Chen (Rice University (US))
      • 58
        Femtoscopy in d-Au collisions
        The HBT analysis for pions emitted in d-Au collisions at 200GeV is discussed. The HBT radii are calculated and compared to experiment. Predictions are made for HBT parameters that can be observed in asymmetric p-Pb or d-Au collisions. Azimuthal angle sensitive HBT analysis in d-Au collisions yields a pronounced azimuthal angle dependence of the radii.
        Speaker: Piotr Bozek
      • 59
        Quantum coherence measurements using two-, three-, and four-pion Bose-Einstein correlations
        "Coherence of pions in the final state is known to suppress Bose-Einstein correlations. The amount of suppression increases for higher order correlations. We present a new method to measure the coherent fraction of pions using multi-pion Bose-Einstein correlations. The comparison of two-, three-, and four-pion correlations allows for a more unambiguous measure of the coherent fraction. We present the measurements in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV with ALICE at the LHC. We also show how the methodology can be extended for future measurements in smaller systems such as pp and p-Pb."
        Speaker: Dhevan Raja Gangadharan (Lawrence Berkeley National Lab. (US))
    • Sauvignon-2
      Convener: Adrian Dumitru (Baruch College (City University of New York))
      • 60
        The Balitsky-JIMWLK evolution equation at next-to-leading order
        Scattering amplitudes of proton-Nucleus or Nucleus-Nucleus collisions at high-energy are described by matrix elements of Wilson line operators - in finite gauge factors ordered along the straight lines of the fast moving particles. The energy dependence of such amplitudes is obtained by the evolution equation of Wilson lines with respect to the rapidity parameter - the Balitsky-JIMWLK evolution equation. Most of the current phenomenology of high-energy and high-density QCD is based on the leading-order evolution equation with only running coupling corrections. In my talk I will present the derivation of the Balitsky-JIMWLK evolution equation at the next-to-leading order.
        Speaker: Giovanni Antonio Chirilli (Ohio State University)
      • 61
        Particle production at NLO in pA collisions: the wave function approach
        We present a derivation, within the wave function approach at next-to-leading accuracy, of single-inclusive hadron production in pA collisions considering a dilute projectile composed of collinear partons on a dense target - the hybrid formalism. The separation of collinear divergencies, absorbed into the DGLAP evolution of parton densities and fragmentation functions, and soft divergencies is shown explicitly. Our analysis differs from previous ones in two points. First we are careful to specify unambiguously the rapidity interval that has to be included in the evolution of the leading order eikonal scattering amplitude. This is important, since varying this interval by a number of order unity changes the next to leading order correction, which the calculation is meant to determine. Second, we introduce the explicit requirement that fast fluctuations in the projectile wave function which only exist a short time are not resolved by the target. This Yoffe time cutoff also strongly affects the next-to-leading order terms. Our final result is unambiguous and differs at NLO from the results available in the literature.
        Speaker: Tolga Altinoluk (Universidade de Santiago de Compostela)
      • 62
        The shape of the proton at high energies
        We present an event-by-event study of the spatial structure of the fluctuating gluon fields inside a proton as well as their x-dependence using the JIMWLK renormalization group equation. We discuss how event-by-event fluctuations of the protons internal structure can generate the observed azimuthal anisotropies in p+A collisions and how these fluctuations can be constrained from e+p/A experiments.
        Speaker: Soeren Schlichting (Brookhaven National Lab)
      • 63
        High-energy parton in unstable QGP
        The momentum distribution of quark-gluon plasma at the early stage of relativistic heavy-ion collisions is anisotropic and consequently, the system is unstable due chromomagnetic plasma modes. We consider a high-energy parton, which flies across such an unstable plasma, showing that the parton typically loses its energy but the energy can be also gained depending on initial conditions. The energy transfer is studied as an initial value problem. We have checked that in the limit of equilibrium plasma the highly-energetic parton loses the energy and the well-known formula of the collisional energy-loss is reproduced. Consequences of our findings for a phenomenology of jet quenching in relativistic heavy-ion collisions are discussed.
        Speaker: Stanislaw Mrowczynski (Jan Kochanowski University)
      • 64
        Chemical and mechanical equilibration of the quark-gluon plasma
        "In this talk, I discuss the equilibration of the quark-gluon plasma produced by ultrarelativistic heavy ion collisions. In particular, starting from initial conditions which are highly anysotropic and far from equilibrium which are then evolved by means of simulation code based on the relativistic transport Boltzmann equation, I discuss the mechanical equilibration, namely the isotropization of longitudinal and transverse pressures, and the chemical equilibration, namely the evolution of the system from a pure glue ensemble to a quark-gluon mixture via inelastic QCD processes. For the latter the role of the quasiparticle nature of quarks and gluons for temperatures not too close to the critical temperature will be emphasized."
        Speaker: Marco Ruggieri
      • 65
        Ghosts in Non-equilibrium Quark-Gluon Plasma
        "The quark-gluon plasma at the early stage of relativistic heavy-ion collisions is out of equilibrium. The Keldysh-Schwinger formalism provides a natural framework to describe such a plasma, in particular when the plasma is weakly coupled and perturbative methods are applicable. However, a perturbative computation of various QCD characteristics requires Faddeev-Popov ghosts to cancel unphysical degrees which are present in a wide class of covariant gauges. The question thus arises how to introduce the ghosts for non-equilibrium QCD. Using the functional methods, we derive a relation analogous to the Slavnov-Taylor identity which expresses the ghost propagator of the Keldysh-Schwinger formalism through the gluon one. Then we show that the ghost propagator obtained in this way allows one to construct a gauge invariant perturbative expansion of various characteristics of non-equilibrium quark-gluon plasma. Based on: A. Czajka, St. Mrówczyński, Phys. Rev. D89 (2014) 085035"
        Speaker: Alina Czajka (Jan Kochanowski University)
      • 66
        The event structure in PP collisions at the LHC energies.
        In the recent years advances have been made in the use of event structure selection to the study of pp collisions. The recent results obtained by applying event structure events generated by Pythia will be discussed
        Speaker: Guy Paic (Universidad Nacional Autonoma (MX))
    • 4:40 PM
    • Cabernet-3
      Convener: Grazyna Odyniec (Department of Physics)
      • 67
        Measurement of low-mass dielectrons in p-Pb collisions with ALICE
        "Low-mass dielectrons are an important probe for the hot and dense medium which is created in ultrarelativistic heavy-ion collisions. Since leptons do not interact strongly, they carry information from all collision stages with negligible final state interaction. While pp collisions provide a reference measurement for a medium-free environment, the impact of cold nuclear matter effects on the dielectron characteristics can be studied in p-Pb collisions. \\ The latest results of the dielectron measurements at mid-rapidity in minimum bias p-Pb collisions at $\sqrt{s} =5.02$ TeV with the ALICE detector will be presented. The dielectron invariant mass and transverse momentum distributions will be compared to expectations from hadronic sources."
        Speaker: Theo Alexander Broker (Johann-Wolfgang-Goethe Univ. (DE))
      • 68
        Leading-order anisotropic hydrodynamics
        "In ultrarelativistic heavy-ion collisions nuclear matter is heated to a temperature exceeding that necessary to create a quark-gluon plasma (QGP). Traditionally, second order viscous hydrodynamics has been used to reproduce the soft collective flow of the QGP and hadronic spectra; however, due to rapid longitudinal expansion in the early stages of evolution, the system may possess substantial pressure anisotropies which are a consequence of large viscous corrections. These large corrections violate the viscous hydrodynamics assumption of small deviation from local equilibrium. They may lead to unphysical results, and, comparing to the exact 0+1 solutions of the Boltzmann equation, they often badly reproduce the longitudinal pressure (especially for initial stages) and provide the wrong asymptotic behavior. In order to more accurately treat systems possessing large pressure anisotropies, a new approach called anisotropic hydrodynamics was recently developed.  In this approach, the pressure anisotropy is treated non-perturbatively at leading order in the hydrodynamic expansion.  This allows one to match with second order viscous hydrodynamics in the close to equilibrium limit and to also have a striking agreement with the exact solution for large anisotropies.  I am presenting the latest formulation of leading-order anisotropic hydrodynamics which uses (1) an ellipsoidal ansatz for the underlying distribution function, allowing non trivial transverse dynamics; and (2), dynamical equations resulting from the second moment of the Boltzmann equation. References [1] L. Tinti and W. Florkowski, Projection method and new formulation of leading-order anisotropic hydrodynamics, Phys. Rev. C 89, 034907, arXiv:1312.6614. [2] W. Florkowski, R. Ryblewski, L. Tinti, and M. Strickland, Leading-order anisotropic hydrodynamics for systems with massive particles, Phys. Rev. C 89, 054909, arXiv:1403.1223."
        Speaker: Leonardo Tinti (Jan Kochanowski University)
      • 69
        Transport coefficients for bulk viscous evolution in the relaxation-time approximation
        "We derive the form of the viscous corrections to the phase-space distribution function due to bulk viscous pressure and shear stress using the iterative Chapman-Enskog method. We then calculate the transport coefficients necessary for the second-order hydrodynamic evolution of the bulk viscous pressure and the shear stress tensor. We demonstrate that the transport coefficients obtained using the Chapman-Enskog method are different than those obtained previously using 14-moment approximation for finite particle mass. Specializing to the case of boost-invariant and transversally homogeneous longitudinal expansion, we show that the transport coefficients obtained using the Chapman-Enskog method result in better agreement with the exact solution of the Boltzmann equation compared to results obtained in the 14-moment approximation. Finally, we demonstrate that, within second-order viscous hydrodynamics, the inclusion of the full set of kinetic coefficients, particularly the shear-bulk couplings, is necessary to properly describe the time evolution of the bulk pressure. Talk based on: A.Jaiswal, R.Ryblewski, M.Strickland, arXiv:1407.7231, submitted to PRC G.S. Denicol, W.Florkowski, R.Ryblewski, M.Strickland, arXiv:1407.4767, accepted to PRC"
        Speaker: Dr Radoslaw Ryblewski (Institute of Nuclear Physics PAS)
      • 70
        Anisotropic hydrodynamics for conformal Gubser flow
        We derive equations of motion for a system undergoing boost-invariant longitudinal and azimuthally symmetric transverse Gubser flow using leading order anisotropic hydrodynamics. This is accomplished by assuming that the one-particle distribution function is ellipsoidally symmetric in the momenta conjugate to the de Sitter coordinates used to parametrize the Gubser flow. We then demonstrate that the $SO(3)_q$ symmetry in de Sitter space further constrains the anisotropy tensor to be of spheroidal form. The resulting system of two coupled ordinary differential equations for the de Sitter space momentum scale and anisotropy parameter are solved numerically and compared to a recently obtained exact solution of the relaxation time approximation Boltzmann equation subject to Gubser flow. We show that anisotropic hydrodynamics describes the spatio-temporal evolution of the system better than all currently known dissipative hydrodynamics approaches. In addition, we prove that anisotropic hydrodynamics gives the exact solution of the relaxation-time approximation Boltzmann equation in the ideal, $\eta/s \rightarrow 0$, and free-streaming, $\eta/s \rightarrow \infty$, limits. In collaboration with: Radoslaw Ryblewski (H. Niewodniczan´ski Institute of Nuclear Physics), Michael Strickland (Kent State University)
        Speaker: Mohammad Nopoush (Kent State University)
      • 71
        Bulk viscosity-driven suppression of shear viscosity effects on the flow harmonics at RHIC
        The interplay between shear and bulk viscosities on the flow harmonics, vn's, at RHIC is investigated using the newly developed relativistic 2+1 hydrodynamical code v-USPhydro that includes bulk and shear viscosity effects both in the hydrodynamic evolution and also at freeze-out. While shear viscosity is known to attenuate the flow harmonics, we find that the inclusion of bulk viscosity decreases the shear viscosity-induced suppression of the flow harmonics bringing them closer to their values in ideal hydrodynamical calculations. Depending on the value of the bulk viscosity to entropy density ratio, ζ/s, in the quark-gluon plasma, the bulk viscosity-driven suppression of shear viscosity effects on the flow harmonics may require a re-evaluation of the previous estimates of the shear viscosity to entropy density ratio, η/s, of the quark-gluon plasma previously extracted by comparing hydrodynamic calculations to heavy ion data. This work is based on the published work: Phys. Rev. C 90, 034907 (2014).
        Speaker: Jacquelyn Noronha Hostler (Columbia University)
      • 72
        A Multiplicity Selection Effect on the Long-range Dihadron Correlation Measurement in d+Au Collisions at RHIC
        A long-range (large |\Delta\eta|) two-particle azimuthal (\Delta\phi) correlation (“ridge”) was observed in high-multiplicity p+p and p+Pb collisions at the LHC. Subtraction of two-particle correlations in high- and low-multiplicity events reveals a back-to-back double ridge (\Delta\phi=0 or \pi). A similar double ridge was observed in d+Au collisions with the same technique by the PHENIX experiment at RHIC. This talk reports results of the ridge in d+Au collisions with the STAR detector at RHIC. The dihadron correlations are studied for different multiplicity and zero-degree neutral energy classes. It is found that the ridge on the away-side (around \Delta\phi=\pi) in d+Au collisions is strongly influenced by jet-like correlations. The mid-rapidity jet correlated particle yields differ between low- and high-multiplicity d+Au collisions. With the STAR detector's large acceptance, the near-side (\Delta\phi=0) ridge correlated yield \Delta\eta and multiplicity dependences are studied. The long-range near-side ridge is observed on the Au-going side for high-multiplicity events. In a Fourier decomposition of the dihadron correlations, the second Fourier coefficients are observed to be the same for low- and high-multiplicity, d- and Au-going side, despite the large multiplicity difference and near-side ridge appearance difference. This near-side ridge yield difference is found to be due to the large negative first Fourier coefficients in the low-multiplicity and d-going side. We will discuss the implications of the STAR data on the theoretical explanations for the ridge mechanism in d+Au collisions.
        Speaker: Li Yi
    • Sauvignon-3
      Convener: Guilherme Teixeira De Almeida Milhano (Instituto Superior Tecnico (PT))
      • 73
        Centrality dependence of baryon-pair production in heavy-ion collisions at different energies
        We consider the experimental ratios of multistrange to strange antibaryon production as a function of centrality. The predictions of the well-stablished Quark-Gluon String Model fail to describe the experimental data on overline(Xi)+/overline(Lambda) and, especially, \overline(Omega)+/\overline(Lambda), for the case of heavy-ion collisions at high centralities. This significant disagreement between experimental data and model predictions could be interpreted as the signal of Quark-Gluon Plasma (QGP) formation, making of the overline(Omega)+ production a possible QGP signature.
        Speaker: Carlos Merino (University of Santiago de Compostela (Spain))
      • 74
        Gluon spectral functions and transport coefficients in Yang–Mills theory
        We study non-perturbative gluon spectral functions at finite temperature in quenched QCD with the maximum entropy method. We also provide a closed loop equation for the spectral function of the energy-momentum tensor in terms of the gluon spectral function. This setup is then used to compute the shear viscosity over entropy density ratio eta/s in a temperature range from about 0.4 Tc to 4.5 Tc. The ratio eta/s has a minimum at about 1.25 Tc with the value of about 0.115. We also discuss extensions of the present results to QCD.
        Speaker: Fister Leonard (IPhT, CEA Saclay)
      • 75
        3+1D Structure of Nuclear Collisions From Classical Gluon Fields
        We discuss the energy momentum tensor of the gluon field created in high energy collisions of nuclei at early times. We show how early radial and directed flow are created as a consequence of the non-abelian Gauss, Ampere and Faraday Laws. We find that even in a boost-invariant setup the global structure of the event is non-trivial and exhibits angular momentum. We conclude with a discussion of possible observable consequences.
        Speaker: Rainer Fries (Texas A&M University)
      • 76
        Holographic non-conformal hydrodynamization
        "We numerically solve the collision of shock-waves in a holographic model with a non-trivial scalar field. We adjust the scalar field potential such that the bulk space-time coincides with AdS in the infrared and in the ultraviolet with different AdS radius. This introduces a non-trivial running of the dual gauge theory coupling constant which we choose at our convenience. We study the effect of this non-conformality on the the hydrodynamization of the system and focus on the effect of the non-trivial equation of state and the effect of bulk viscosity."
        Speaker: maximilian attems (University of Barcelona)
      • 77
        Numerical solution of the next to leading order BK equation
        "The Color Glass Condensate (CGC) effective field theory provides a consistent framework to describe high energy hadronic interactions where a small-x part of the hadron wave function is probed. In recent years it has been succesfully applied to phenomenology at leading order accuracy, see e.g. Ref. [1]. However the next to leading order corrections are potentially large, and thus an important next step to test the saturation picture of the CGC is to bring the CGC calculations to next to leading order accuracy. First steps in this direction have been taken by calculating the photon impact factor and the single inclusive cross sections at NLO [2,3]. An essential part of a fully consistent NLO CGC calculation is the solution to the NLO BK evolution equation which is derived in Ref. [4] but has not been numerically solved so far. We present the first numerical solution to the NLO BK equation in transverse coordinate space. We show that the solution has a problematic short distance behavior due to the nonconformal double logarithmic term in the kernel. We also study the energy evolution of the so called conformal dipole whose NLO evolution equation, derived in Ref. [5], is conformally invariant except for the running of the coupling. We find that the problematic small distance behavior is only partially cured by the conformally symmetric evolution equation. [1] T. Lappi, H. Mäntysaari, Phys.Rev. D88 (2013) 114020, arXiv:1309.6963 [hep-ph] [2] G. A. Chirilli, B..W. Xiao, F. Yuan, Phys. Rev. D86 (2012) 054005, arXiv:1203.6139 [hep-ph] [3] G. Beuf, Phys. Rev. D85 (2012) 034039, arXiv:1112.4501 [hep-ph] [4] I. Balitsky, G. A. Chirilli, Phys. Rev. D77 (2008) 014019, arXiv:0710.4330 [hep-ph] [5] I. Balitsky, G. A. Chirilli, Nucl. Phys. B822 (2009) 45, arXiv:0903.5326 [hep-ph]"
        Speaker: Mr Heikki Mäntysaari (University of Jyväskylä)
      • 78
        Production of strange particles in jets and the underlying event in p--Pb and Pb--Pb collisions measured with ALICE at the LHC
        "The $p_{\rm T}$ dependence of the baryon/meson yield ratio in hadronic and nuclear collisions is sensitive to the collective expansion of the system, partonic recombination into hadrons, jet fragmentation and hadronization. This ratio for inclusive yields in the region $2 < p_{\rm T} < 6$~GeV/$c$ is significantly enhanced in large systems (Pb--Pb, p--Pb) relative to that in proton--proton collisions. However, the origin of the enhancement remains an open question. In this talk we explore the connection between baryon yield enhancement and jet production, through measurement of the $p_{\rm T}$-differential spectrum of ${\rm K}_{\rm S}^{0}$ and $\Lambda$ in p--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$~TeV, both inclusively and within energetic jets. The results show that jet fragmentation in p--Pb collisions is similar to that in pp collisions, without evidence of baryon yield enhancement, and that the baryon yield enhancement arises solely from the dynamics of the underlying event in complex collision systems."
        Speaker: Xiaoming Zhang (Lawrence Berkeley National Lab. (US))
    • Saturday AM-1
      Convener: Larry McLerran (B)
      • 79
        Forward production measurements with LHCb
        Speaker: Bo.Bo Liu (Universita e INFN (IT))
      • 80
        The proton and nuclei in 3D
        Speaker: elke-caroline Aschenauer (BNL)
      • 81
        The experimental future of e+A physics
        Speaker: Matthew Lamont (BNL)
    • 10:40 AM
    • Saturday AM-2
      Convener: Ernst Sichtermann (Lawrence Berkeley National Laboratory)
      • 82
        Back-to-back jets in pp,pA and their complementarity in eA collisions
        Speakers: Cyrille Marquet (CPHT - Ecole Polytechnique) , Feng Yuan (LBNL)
      • 83
        The impact of e+A collisions on nuclear PDFs.
        e+A collisions can bring useful information to questions that A+A cannot (fully) answer. In particular, they can shed light on the distribution of partons within nuclei. This is most relevant in the case of the gluon, which suffers from huge uncertainties in the small-x regime. We show how to implement data from e+A collisions into existing nPDFs and the impact these collisions have on said distributions.
        Speaker: Manoel R. Moldes
      • 84
        The EMC effect - JLAB experimental findings and plans
        Speaker: John Arrington (Argonne National Laboratory)
      • 85
        Future at the LHC: LHeC, FCC
        Speaker: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
    • 12:50 PM
    • Saturday PM-1
      Convener: Xin-Nian Wang (Lawrence Berkeley National Lab. (US))
      • 86
        Jet measurements in p+Pb and Pb+Pb with the ATLAS Experiment at the LHC
        Jets provide a powerful tool for probing the dynamics of the quark-gluon plasma created in Pb+Pb collisions at the LHC. The modification of high-pT jets as they propagate in the quark-gluon plasma provides insight on structure of the plasma at short-length scale. Such modifications have been observed in a variety of measurements of single jet, dijet, photon-jet and charged-particle fragmentation functions. Recent results of jet modifications in proton-lead and Pb+Pb collisions will be presented.
        Speaker: Peter Alan Steinberg (Brookhaven National Laboratory (US))
      • 87
        Jet and charged hadron results from CMS
        To precisely understand the effect of the hot and dense medium produced in central PbPb collisions on the production of jets and hadrons, initial-state effects such as the nuclear modification of the parton distribution functions (nPDF) must also be understood. These initial-state nuclear effects may be accessed by measuring the distributions of charged particles, inclusive jets, and dijet pairs in pPb collisions, where the effects of the medium produced in PbPb collisions are expected to be largely absent. In this talk, the nuclear modification factor of both jets and of charged-particles in pPb (RpPb) collisions are presented. The spectra of both jets and charged-particles in pPb collisions at 5.02 TeV have been measured with the CMS detector at the CERN LHC using high statistics samples. The RpPb of charged particles is determined by dividing the measured pPb spectrum by a pp reference spectrum constructed using interpolation methods, or alternatively from PYTHIA simulations.
        Speaker: Dr Yaxian Mao (Vanderbilt University (US))
      • 88
        Quantifying Cold Nuclear Matter Effects on Jet Observables in p-Pb Collisions
        Jet quenching is a signature of the Quark Gluon Plasma (QGP) produced in heavy ion collisions. As a result of partonic energy loss in the medium, the jet spectrum in Pb-Pb collisions is suppressed compared to the same spectrum measured in pp collisions scaled by the number of binary collisions. However, the jets can be influenced by all stages of the collision. To disentangle the final state QGP effects from the initial state, the jet spectrum in p-Pb collisions is measured. In addition, the substructure and fragmentation behavior of jets are also explored in p-Pb collisions for modifications due to cold nuclear matter effects. Jets are reconstructed from charged tracks in the ALICE central tracking system combined with clusters in the electromagnetic calorimeter. To quantify the cold nuclear matter effects, observables in p-Pb are compared to MC simulations at the same center of mass energy, 5.02 TeV.
        Speaker: Megan Elizabeth Connors (Yale University (US))
      • 89
        Jet vs. Jettiness - the event shape in p+A and e+A collisions
        Jet is known as the "footprint" of high energy quark and gluon produced in high energy scattering, and has been an excellent probe for short-distance dynamics of QCD and potential new physics. Jet quenching is recognized as a key evidence for the discovery of quark-gluon plasma in relativistic heavy ion collisions. However, quantifying the jet quenching in a hot and dense medium is challenging due to the definition of the jet itself and its phase space limitation. In this talk, I propose to use the jettiness, a more inclusive observable for global event shape, to quantify the jet quenching phenomenon and QCD radiation and energy loss in p+A and e+A collisions, and to discuss the complementary between the jet and jettiness as observables, and between p+A and e+A scattering.
        Speaker: Jianwei Qiu (Brookhaven National Lab)
      • 90
        Aspects of centrality determination in asymmetric nuclear collisions
        Speaker: Dr Andreas Morsch (CERN)
    • 4:30 PM
    • Discussion: Measurements in pA collisions - open questions
      Conveners: Dr Andreas Morsch (CERN) , Gunther Roland (MIT)
      • 91
        Centrality in jet studies in pA collisions: the need to understand kinematical biases
        Speaker: Guilherme Teixeira De Almeida Milhano (Instituto Superior Tecnico (PT))
      • 92
        Hard scatterings and multiplicity biases
        Speaker: Peter Alan Steinberg (Brookhaven National Laboratory (US))
      • 93
        A centrality detector concept.
        Parameters describing the initial state of the heavy ion interaction are commonly denoted by the term "centrality". Centrality includes the impact parameter of the interaction, number of participating nucleons and spatial orientation of colliding nuclei. In all present heavy ion experiments centrality is measured indirectly, by detecting the number of particles or the energy of the particles produced in the interactions, typically at high rapidity. Centrality parameters are associated to the measured detector response using the Glauber model. This approach suffers from systematic uncertainties related to the assumptions about the particle production mechanism and limitations of the Glauber model. In the collider based experiments there is a unique possibility to measure centrality parameters by registering spectator fragments remaining from the collision. This approach does not require model assumptions and relies on the fact that spectators and participants are related via the total number of nucleons in the colliding species. This article describes the concept of a centrality detector for heavy ion experiment, which measures the total mass number of all fragments by measuring their deflection in the magnetic field of the collider elements.
        Speaker: Alexander Milov (Weizmann Institute of Science (IL))
      • 94
        Remarks / discussion starter
        Speaker: Gunther Roland (MIT)
    • 8:00 PM
    • Sunday AM-1
      Convener: Nestor Armesto Perez (Universidade de Santiago de Compostela (ES))
      • 95
        Parton cascade description of ultrarelativistic heavy-ion collisions
        An updated version of the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS) is presented, which allows interactions among all partons: gluons, light quarks, and heavy quarks with elastic and inelastic collisions. We introduce the improved Gunion-Bertsch matrix element, which cures problems of the original Gunion-Bertsch result in characteristic regions of the phase space. With th this new important properties of the quark-gluon-plasma in heavy-ion collisions such as the thermalization time of the plasma and the shear viscosity over entropy density ratio are calculated within the microscopic transport model BAMPS. Furthermore, we compare our results of the nuclear modification factor and elliptic flow to experimental data at RHIC and LHC. In addition, thermalization of gluons with the onset of Bose-Einstein condenstation will be presented for color glass condenstate initial conditions. The times of the completion of the gluon condensation are calculated, which scale inversely with the energy density.
        Speaker: Carsten Greiner (University of Frankfurt)
      • 96
        From End to beginning - Constraining the Initial State from Final-State Beginnings
        Speaker: Scott Pratt (Michigan State University)
      • 97
        "Trento" new fast IS generator
        Speaker: Prof. Steffen A. Bass (Duke University)
      • 98
        Initial State Bremsstrahlung versus Final State Hydrodynamics in pA Collisions
        Recent azimuthal correlation data from d+Au and Au+Au collisions at RHIC energies and cumulant azimuthal harmonics in p+Pb and PbPb at LHC energies display very similar size and characteristics challenging the uniqueness of local equilibrium hydrodynamical interpretation of these data. We show that in p+A collisions the azimuthal harmonics arising from initial-state non-abelian interference effects associated with multiple projectile and target beam jets are remarkably similar to the measured data in experiments and predictions from final state perfect fluid models. The corresponding GLVB model description for pA collisions [1] will be shortly summarized and discussed. [1] M. Gyulassy, P. Levai, I. Vitev, T.S. Biro, Phys. Rev. D90 (2014) 054025.
        Speaker: Peter Levai (Hungarian Academy of Sciences (HU))
    • 10:40 AM
    • Sunday AM-2
      Convener: Jim Thomas (Lawrence Berkeley National Lab. (US))
      • 99
        Strong coupling QGP thermalization with longitudinal dynamics
        This talk will give an overview of recent attempts to use holography to understand the thermalization of heavy-ion collisions. For this I will argue that the AdS/CFT duality may improve our understanding of some aspects of these collisions, in particular focusing on the longitudinal dynamics. This may provide a distinctive way to probe the results from these strong coupled methods. In the end I will show some preliminary results allowing to make a direct comparison with experimental data.
        Speaker: Wilke van der Schee (Utrecht University)
      • 100
        Outlook - collectivity aspects
        Speaker: Matthew Luzum
      • 101
        Outlook - experimental perspective
        Speaker: James Lawrence Nagle (University of Colorado at Boulder)
      • 102
        Closing remarks
    • 1:00 PM