Conveners
Parallel: A4 - Initial State I
- Kari J. Eskola (University of Jyvaskyla)
Parallel: B4 - Initial State II
- Jamal Jalilian-Marian (Baruch College)
Parallel: C4 - Initial State III
- Wei Li (Rice University (US))
Parallel: D4 - Initial State IV
- Jacquelyn Noronha-Hostler (Rutgers University)
Parallel: E4 - Initial State V
- Anthony Robert Timmins (University of Houston (US))
Parallel: F4 - New Theoretical Developments I
- Raju Venugopalan (Brookhaven National Laboratory)
Parallel: G4 - New Experimental Developments
- Harald Appelshaeuser (Goethe University Frankfurt (DE))
Parallel: H4 - New Theoretical Developments II
- Hannah Elfner
Evidence for the production of top quarks in heavy ion collisions is reported in a data sample of lead-lead collisions recorded in 2018 by the CMS experiment at a nucleon-nucleon center-of-mass energy of $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = 5.02$ TeV, corresponding to an integrated luminosity of $1.7\pm0.1\,\text{nb}^{-1}$. Top quark pair ($\mathrm{t\bar{t}}$) production is measured in...
Nuclear dynamics at short distances among nucleons is one of the most outstanding phenomena in nuclear physics. Understanding the role of QCD in generating nuclear forces is important for uncovering the underlying physics of Short-Range Correlations (SRCs). In recent years, SRCs have been observed from light to heavy nuclei using fixed target experiments at Jefferson lab via high energy...
Deep inelastic scattering (DIS) total cross section data at small-x as measured by the HERA experiments is well described by Balitsky-Kovchegov (BK) evolution in the leading order dipole picture [1-3]. Recently the full Next-to-Leading Order (NLO) dipole picture total cross sections have become available for DIS [4-6], and a working factorization scheme has been deviced which substracts the...
The Colour Glass Condensate effective field theory is a useful framework for studying heavy ion collisions at ultrarelativistic energies, such as those reached at the Large Hadron Collider at CERN. In this framework, we study the rapidity evolution of Wilson lines that appear explicitly in cross section expressions. The next-to-leading order BK (Balitsky-Kovchegov) equation for the 2-point...
This talk presents ATLAS measurements of the azimuthal anisotropy for charged particles in 8.16 TeV $p$+Pb collisions up to a $p_T$ of 50 GeV. The measurements are performed via the two-particle correlation method and the statistics are enhanced at high-$p_T$ by selecting events triggered by a high-$p_T$ jet. Restrictions on other particles are imposed to suppress the contribution from jets....
An important phenomenological consequence of the phenomenon of gluon saturation is the suppression of back-to-back hadron and jet pairs produced in the forward region of pA collisions. We present a new calculation of this process within the dilute-dense formalism of the color glass condensate (CGC) effective theory. Following Ref. [1], we collide a large-$x$, dilute probe, described in terms...
We investigate the scattering of a quark jet on a high-energy heavy nucleus using the time-dependent light-front Hamiltonian approach. We present the real-time evolution of the quark-jet in a strong classical color field of the incoming nucleus described by the Color Glass Condensate effective theory. We calculate the cross section, the differential cross section, and the quark jet...
Studies of jet energy loss and momentum broadening with photon-jet momentum and angular correlations will be presented, with PbPb data at 5.02 TeV collected by the CMS detector. Photon-jet events provide a means of probing in-medium jet energy loss with good constraints on the initial parton kinematics and flavor. Studies of momentum and angular correlations in photon-jet events can enable...
Flow results in small systems at RHIC and the LHC indicate QGP droplets are
formed in these collision systems. Measurements of jet $R_{pA}$ on the other
hand are consistent with no modification to the jets produced. However,
non-zero $v_n$ values for high momentum particles, which in A+A collisions
are attributed to path-length dependent energy loss, have been observed in
small systems....
At the LHC energies Multiple Parton Interactions (MPI) are expected to affect not only processes involving soft particle production, but also the hard momentum scales relevant for the production of heavy quarks, such as charm and beauty. Quarkonium measurements in high-multiplicity proton-proton (pp) collisions can shed light on the role of MPI at such hard momentum scales, as well as on the...
Charmonium is considered a valuable probe to study the medium produced in
collisions involving nuclei and/or nucleons. With the recent observations of
collective behavior of produced particles in small system collisions,
measurements of the modification of charmonium in these systems have become
increasingly relevant. In this talk we will present the PHENIX results of
J/ measurements at...
The strong electromagnetic fields generated by ultra-relativistic heavy ions provide the possibility to study photon-induced processes at the LHC in new kinematic regions. ALICE has measured the exclusive and the coherent production of J/$\psi$ in p-Pb and Pb-Pb collisions at a center-of-mass energy of 5.02 TeV. These collisions correspond to photon-proton and photon-Pb interactions,...
Measurements of two-particle correlations in $pp$ collisions have demonstrated long-range azimuthal correlations between charged particle pairs, commonly interpreted as arising from a single particle azimuthal anisotropy. To better understand the origin and nature of these collective signatures, ATLAS presents studies in $pp$ collisions with a novel handle on the event geometry, and in...
W and Z bosons are created in the hard scattering processes occurring in the initial stage of heavy-ion collisions and they are insensitive to the presence of a strongly-interacting medium. This makes them clean probes of the initial-state effects of the collision, such as the nuclear modification of the parton distribution functions (nPDFs). The measurement of the electroweak-boson production...
Observations of flow-like signals in small-system collisions, $pp$ and $p$/$d$+A, have led to a resurgence of interest and measurements, the results of which have perhaps permanently challenged the naive picture of initial geometry and subsequent early-time dynamics for these systems. In the wake of this renewed interest, jet and high-$p_\mathrm{T}$ particle measurements in small systems are...
Fully coherent energy loss (FCEL), predicted from first principle QCD calculations, affects the yields of hadrons in proton-nucleus collisions at all energies. The FCEL effects on quarkonia have been succesfully compared to existing measurements over the last few years. In this talk, our approach is generalized systematically to $2\to 2$ processes allowing for the first computation of FCEL...
Dijet processes can be used in several ways to probe the nuclear initial state. Exclusive dijet photoproduction in ultra-peripheral heavy-ion collisions has recently been suggested as a probe of the gluon Wigner distribution. In particular, the angular correlation of exclusive dijets can asses the azimuthal anisotropy of the gluon distribution in the nuclear target. In this talk we present,...
We present the first computation of the next-to-leading order (NLO) impact factors for inclusive dijet and photon+dijet production in e+A DIS at small $x$ in the framework of the Color Glass Condensate (CGC) effective field theory. When combined with the recent derivation of JIMWLK small $x$ evolution to next-to-leading logarithm in $x$ accuracy, these results provide us with a prediction of...
ATLAS measurements of flow harmonics ($v_n$) and their fluctuations in Pb+Pb and Xe+Xe collisions covering a wide range of transverse momenta, pseudorapidity and collision centrality are presented. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV, Pb+Pb collisions at 5.02 TeV, and $p$+Pb collisions at 5.02 and 8.16 TeV. The $v_{n}$ are measured up to $n=6$ using the...
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma using the QCD effective kinetic theory in longitudinally expanding systems. We find that chemical equilibration takes place after hydrodynamization, but well before local thermalization. By relating the transport properties of QGP and the system size we estimate that hadronic collisions with final state multiplicities...
We establish a non-equilibrium QCD evolution model with light quark and gluon degrees of freedom. By including both elastic and inelastic scattering for quarks and gluon, the model is proficient to describe kinetic and chemical equilibration of quark-gluon plasma, and thus connect the initial (semi-) hard production of partons at early times with the hydrodynamic description of a...
One of the greatest uncertainties in heavy-ion collisions is the description of the initial state. Different models predict a wide range of initial energy density distributions based on their underlying assumptions. Final flow harmonics are sensitive to these differences in the initial state due to the nearly linear mapping between eccentricities and anisotropic flow harmonics. The Trento...
Whether, how, and to what extent solutions of Bjorken-expanding systems become insensitive to aspects of their initial conditions is of importance for heavy-ion collisions. In this talk I will present attractor solutions in hydrodynamics, kinetic theory and holography, whereby we show that in hydrodynamics and kinetic theory the attractor extends to arbitrarily early times, whereas in...
We consider the following conundrum: On one hand the proton as a quantum object is in a pure state and is described by a completely coherent wave function with zero entropy. On the other hand in high energy experiments (DIS) when probed by a small external probe, it behaves like an incoherent ensemble of (quasi-free)
partons.
In this talk, we define the "entropy of ignorance" which...
The splitting processes of bremsstrahlung and pair-production in a medium are coherent over large distances in the high energy limit leading to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. Avoiding soft-emission approximations and working in the large-Nc limit, we consider corrections to the LPM effect from cases where the coherence lengths of two consecutive splittings...
The interplay between the small x limit of QCD amplitudes and QCD factorization at moderate x has been studied extensively in recent years. It was finally shown that semiclassical formulations of small x physics can have the form of an infinite twist framework involving Transverse Momentum Dependent (TMD) distributions in the eikonal limit. In this work, we demonstrate that small x...
We compute for the first time the spectrum for emitting 1, 2, and 3 soft and collinear gluons from a hard scattering process in full QCD. This result is important because 1) all current energy loss calculations assume QED-like independent emissions of multiple gluons, which obviously misses all correlations from the non-Abelian nature of QCD, and 2) the average high-p$_{\mathrm{T}}$ parton...
We revisit the [calculation of multiple parton scattering of a heavy quark in nuclei][1] within [the framework of recently improved high-twist factorization formalism][2], in which gauge invariance is ensured by a delicate setup of the initial partons’ transverse momenta. We derive [a new result for the heavy quark radiative energy loss in deeply inelastic scattering][3]. By taking the...
The proposed high luminosity high energy Electron Ion Collider (EIC) will explore the proton/nuclear structure, search for gluon saturation and precisely determine the nuclear parton distribution functions (nPDFs) in a wide x-$Q^{2}$ phase space. Heavy flavor and jet measurements at the future EIC will allow us to better constrain the nPDFs within the poorly constrained high Bjorken-x region,...
The largely unknown parton distribution functions of nuclei and the similarities observed between high-multiplicity pp and pPb events compared to PbPb, often described by means of hydrodynamics, are the main motivations for an extended pPb data taking program during LHC Run 3 and Run 4.
The future increase in luminosity combined with the LHCb unique and improved detector capabilities in the...
A Large Ion Collider Experiment plans intensive use of silicon technologies for extensions of the experiment, beyond the currently ongoing upgrade during the Long Shutdown 2 of the LHC. For Run 4, we will discuss the plans for the installation of three new layers of the Inner Tracking system, based on wafer-sized sensors sufficiently thinned to be rolled to a cylinder. This will lead to an...
The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). A new timing layer is designed to measure minimum ionizing particles (MIPs) with a time resolution of ~30 ps and hermetic coverage up to a pseudo-rapidity of $|\eta|$=3. The precision...
The STAR Collaboration designs, constructs, and installs a suite of new detectors in the forward rapidity region (2.5<$\eta$<4) over the next two years, enabling a program of novel measurements in pp, pA, and AA collisions. This extension of STAR’s kinematic reach will allow detailed studies of cold QCD physics at both very high and very low partonic momentum fraction, i.e., when the...
A solid hadronization model is essential for understanding hadronic observables in high-energy nuclear collisions, while still remains a challenge due to its non-perturbative nature. We have developed an advanced hadronization model for heavy quarks [1] and studied their suppression, flow and hadron chemistry in heavy-ion collisions. A complete set of both $s$ and $p$-wave hadronic states are...
The jet transport coefficient $\hat{q}$ is the leading property of a strongly interacting medium that effects jet propagation. It introduces momentum transverse to a jet parton’s direction, changing its virtuality and thus controls the modification of hard jets in a dense extended medium. In this talk, we present the first unquenched lattice QCD calculation of $\hat{q}$. The calculation is...
We study the response of a Bjorken-expanding quark-gluon plasma (QGP) to the passage of an energetic parton through it. We compute the non-equilibrium stress-energy tensor induced by such moving energetic parton using linearized Boltzmann equation under the relaxation time approximation. At large distances and large Bjorken time, the QGP exhibits hydrodynamic response, meaning the disturbance...
We calculate the double differential cross section for production of a quark parton and a photon in proton-nucleus collisions using a newly proposed formalism which generalizes the Color Glass Condensate approach by including large x gluons of the target. We investigate transverse momentum, rapidity and A dependence of azimuthal angular correlations between the produced parton and the photon...
A new mechanism of photon emission in the quark-gluon plasma is proposed. Photon dispersion relation in the presence of the CP-odd topological regions generated by the chiral anomaly acquires an imaginary mass. It allows photon radiation through the decay $q→q\gamma$ and annihilation $q \bar q→\gamma$ processes closely related to the chiral Cherenkov radiation. Unlike previous proposals this...
