V Workshop on Particle Correlations and Femtoscopy

14 Oct 2009, 09:00 → 17 Oct 2009, 13:30 Europe/Zurich

TH Auditorium (CERN)

The Fifth Workshop on Particle Correlations and Femtoscopy (WPCF2009) continues the tradition of bringing together experts in the experimental and theoretical physics of measuring source shapes and sizes in high energy collisions through particle momentum correlations. The workshop will cover the problems of the evolution of quark/hadronic matter formed in high energy collisions and of the methods to extract the information on this evolution by the analysis of the data on final state particles. The conference is to be held on the CERN site in Meyrin, and the participants will be accommodated at the CERN hostel.

more information Map-to-Balladins.pdf WPCF-local.pdf

Slides StatusOfLHC.pdf.pdf

WPCF '09 Poster wpcf09_poster.jpg

Wednesday 14 October

Recent results from SPS and RHIC

Title: WPCF 09
Description: WPCF 09 - A.Kisiel -TH Audit
Community: ALICE
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Convener: Prof. Sandra Padula (Instituto de Fisica Teorica (IFT)-Universidade Estadual Paulista)

1 HBT systematics from AGS to LHC

The investigation of momentum correlations of identical bosons yields information about the spatial and temporal evolution of the particle emitting source in heavy ion collisions. A well-established technique to study space-time dimensions in such processes is the Hanbury-Brown Twiss (HBT) interferometry. Particularly interesting are the rapidity dependence of the HBT source parameters and the mean free path of pions at thermal freeze-out that can be derived from them. These parameters are studied as a function of the beam energy in search for a universal freeze-out criterion. So far, systematic uncertainties in the AGS to SPS regime did not allow to derive satisfactory conclusions from the measured excitation function of the HBT parameters. Recently, a re-analysis of the CERES data sets for 80 and 158 AGeV, employing an improved calibration procedure of the CERES TPC, has been performed. The results will be compared to the previously published data and discussed in the context of a universal pion freeze-out scenario, which will also include predictions for the approaching experiments at the LHC.

Speaker: Simone Schuchmann (Institut fuer Kernphysik-Johann-Wolfgang-Goethe Univ.-Unknown)

Slides WPFC_talk_SimoneSchuchmann.pdf

2 Recent femtoscopic results in Au+Au and p+p collisions from PHENIX at RHIC

Recent results for charged kaon and pion femtoscopic analysis in PHENIX will be summarized. Bose-Einstein correlations of charged kaons are used to probe Au+Au collisions at sqrt(s(NN)) = 200 GeV, and compared to charged pion probes which have a larger hadronic scattering cross section. Three dimensional Gaussian source radii were extracted, along with a one-dimensional kaon emission source function. The centrality dependence of the three Gaussian radii are well described by a single linear function of N(part)**(1/3) - with zero intercept. Imaging analysis shows a deviation of the kaon source function from a Gaussian with a heavy tail at r > 10 fm, although the bulk emission of kaons at lower radius is well-described by a Gaussian. The presence of a non-Gaussian tail in the kaon source indicates that the particle emission region in a heavy ion collision is extended, and that similar measurements with pions are not solely due to the decay of long-lived resonances. Measuring similar correlations in smaller systems with significant correlations due to local energy and momentum conservation, such as p+p collisions is also required to put such measurements into a proper context. PHENIX preliminary measurements of HBT analysis for charged pions from sqrt(s) = 200 GeV p+p collisions will be presented and compared to Au+Au results of pions and kaons. The current status of other PHENIX preliminary femtoscopic correlation measurements will also be discussed.

Speaker: Tamas Csorgo (MTA KFKI RMKI and Harvard University)

Paper http://arxiv.org/abs/0907.5002 http://link.aps.org/abstract/PRL/v103/e142301

Slides 2009-10-14-Csorgo-WPCF-v2.pdf 2009-10-14-Csorgo-WPCF-v2.ppt

3 Two-pion Source Imaging with the STAR experiment

Three-dimensional pion source images have been successfully extracted from relativistic heavy-ion collisions at RHIC and CERN recently. The extraction exploits the use of the 3D source imaging technique of Danielewicz, Pratt and Brown. The STAR collaboration has acquired much better statistics data in recent years thus extending the application of imaging techniques to pion correlation functions obtained with various pion pair kT and collision centrality selections. This permits the systematic extraction of dynamical parameters of the pion source evolution. The STAR program for extracting the pion source images at various kT and centrality bins with improved statistics will be presented in conjunction with model calculations.

Speaker: Dr Michal Sumbera (Nuclear Physics Institute ASCR-Acad. of Sciences of the Czech Re)

Slides Sumber_WPCF09.pdf Sumber_WPCF09.ppt

10:30 coffee break

4 NA49 Results on fluctuations

Strong experimental and theoretical efforts are devoted to the study of the QCD phase diagram looking for the phase transition from hadronic to partonic matter. Event-by-event fluctuations of different observables are considered as a signal for the first order phase transition and should shed light on the predicted existence and location of the critical endpoint of the first order transition line. We present experimental NA49 results and model comparisons for <p_t> fluctuations, multiplicity fluctuations as well as the energy and centrality dependence of particle yield ratio fluctuations. Details of the data analysis together with the estimation of the expected effect from a critical point will be discussed. The energy dependence of <p_t> and multiplicity fluctuations shows no conclusive indication of the critical point. In addition, we will argue that the new results on the centrality dependence of event-by-event p/pi fluctuations strongly hint to resonances as their origin.

Speaker: Mr Dmytro Kresan (Gesell. fuer Schwerionforschung mbH (GSI))

Slides Kresan_2009-10-14.ppt

5 Fluctuations and correlations in NA61

The NA61 program with respect of fluctuation and correlation studies in nuclear collisions will be presented. The main goal of this program is to search for the critical point of strongly interacting matter via two-dimensional scan in collision energy and system size.

Speaker: Marek Gazdzicki (Frankfurt University)

Slides draft9.odp draft9.pdf

6 Measurement of Azimuthal Anisotropy with the New Reaction Plane Detector in the PHENIX experiment

Azimuthal anisotropy of particle emission with respect to the reaction plane is one of the most important global observables in relativistic nucleus-nucleus collisions at RHIC. The observation of a large anisotropy which follows specific scaling relations over a broad range of particle species is considered as evidence for the probable formation of a hot and dense partonic matter in Au+Au collisions at RHIC. The accurate measurement of the reaction plane is a key factor in the study of azimuthal anisotropy. In order to improve the resolution of such measurements in the PHENIX experiment at RHIC, we designed and fabricated a new Reaction Plane Detector (RxP). RxP worked very well during the PHENIX Run7 period and demonstrated the design performance. As a result of the upgrade, the reaction plane resolution was improved by a factor of two. This allows us to improve the precision of the measurements of azimuthal anisotropy for high-pT identified hadrons up to p_T of 6 GeV/c and v_4 up to p_T of 3 GeV/c and to perform a more detailed study of rare particles, such as Deuteron or Phi.

Speaker: Yoshimasa Ikeda (University of Tsukuba, for the PHENIX collaboration)

Slides wpcf09_ike.pdf

7 New Results from SPS and RHIC

Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy ion collisions. These domains are predicted to lead to charge separation of quarks along the system's orbital momentum axis. We investigate a three particle azimuthal correlator which is a P even observable, but directly sensitive to the charge separation effect. We report measurements of charged hadrons near center-of-mass rapidity with this observable in Au+Au and Cu+Cu collisions at psNN=200 GeV/c using the STAR detector. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. Consistency cross checks for different data sets, detectors and kinematic regions are performed. A signal consistent with several expectations from the theory is detected. We compare our results to the predictions of existing event generators, and discuss possible contributions from other effects that are not related to parity violation. New ideas, future experimental and analysis plans are discussed.

Speaker: Alexei Chikanian

Slides Chikanian-VWPC_2009_draft8.pdf Chikanian-VWPC_2009_draft8.ppt

12:50 lunch break

TH Colloquium

8 RHIC and the Quark-Gluon Plasma -- from qualitative discovery to quantitative characterization

Heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) produce an extremely hot and dense, but shortlived state of thermalized, strongly interacting matter, the quark-gluon plasma. The discoveries of strong anisotropic collective flow in the soft particle sector, strong suppression of high-pt particles and of jet-like correlations in the hard sector, and of a quark-coalescence pattern for hadron production at intermediate transverse momenta have provided compelling qualitative evidence for the formation of thermalized partonic matter which evolves like an almost perfect liquid, without constraints from color confinement, that is strongly coupled and extremely opaque to hard colored probes, and that reacts collectively to the energy deposited by such probes. I will describe the second stage of RHIC experiments and theoretical developments that aim to turn these qualitative discoveries into quantitative statements about the properties (initial temperature, shear and bulk viscosity, jet quenching parameter, etc.) of the Quark-Gluon Plasma, pointing out similarities and complementarities to the impending heavy-ion program at the LHC.

Speaker: Mr Ulrich Heinz (The Ohio State University)

Slides Heinz_THColl.pdf.pdf

15:00 coffee break

Dynamics and the Equation of State (1/2)

Convener: Yorigo Hama (Universidade de Sao Paulo, Instituto de Fisica)

9 Effects of a phase transition on HBT correlations in an integrated Boltzmann+Hydrodynamics approach

A systematic study of HBT radii of pions, produced in heavy ion collisions in the intermediate energy regime (SPS), from an integrated (3+1)d Boltzmann+hydrodynamics approach is presented. The calculations in this hybrid approach, incorporating an hydrodynamic stage into the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport model, allow for a comparison of different equations of state (EoS) retaining the same initial conditions and final freeze-out. The results are also compared to the pure cascade transport model calculations in the context of the available data. Furthermore, the effect of different treatments of the hydrodynamic freeze-out procedure on the HBT radii are investigated. It is found that the HBT radii are essentially insensitive to the details of the freeze-out prescription as long as the final state interactions in the cascade are taken into account. The HBT radii $R_L$ and $R_O$ and the $R_O/R_S$ ratio are sensitive to the EoS that is employed during the hydrodynamic evolution. We conclude that the increased lifetime in case of a phase transition to a QGP (via a Bag Model equation of state) is not supported by the available data. References: Q.f. Li, J. Steinheimer, H. Petersen, M. Bleicher and H. Steocker, ``Effects of a phase transition on HBT correlations in an integrated Boltzmann+Hydrodynamics approach,'' arXiv:0812.0375 [nucl-th], Physics Letters B (2009) in print

Speakers: Dr Hannah Petersen (University of Frankfurt), Marcus Bleicher (Uni Frankfurt)

Slides petersen_wpcf09.ppt

10 Transverse hydrodynamics with sudden hadronization and freeze-out

The physical scenario for ultrarelativistic heavy-ion collisions is analyzed where the early dynamics of the system is dominated by the purely transverse hydrodynamic expansion (transverse hydrodynamics [1,2,3]). The local isotropization of the system in the momentum space is described in the schematic way with the help of the Landau matching conditions. The isotropization process is followed by the fast hadronization implemented by THERMINATOR. The model is used to calculate the transverse-momentum spectra, the elliptic flow, and the HBT radii of pions and kaons. A good agreement between the model results and the data is obtained [4]. Our results indicate that the evolution of matter at the early stages of the heavy-ion collisions may proceed far from the local thermal equilibrium. In fact, the purely transverse expansion favors fast building of the transverse radial and elliptic flow. This, in turn, helps to reduce the timescales characterizing the expansion and leads to good description of the HBT radii. [1] A. Bialas, M. Chojnacki, and W. Florkowski, Phys.Lett. B661:325-329, 2008. [2] M. Chojnacki and W. Florkowski, Acta Phys.Polon. B39:721-738, 2008. [3] R. Ryblewski and W. Florkowski, Phys.Rev.C77:064906, 2008 [4] R. Ryblewski and W. Florkowski, in preparation

Speaker: Mr Radosław Ryblewski (Institute of Nuclear Physics PAS)

Slides CERN_RR.pdf

11 Study of identical and non-identical particle correlations at RHIC energies within microscopic models.

Microscopic transport models are found to reproduce well many features of ultra-relativistic heavy-ion collisions. Our aim is to study the femtoscopic correlations of different particle systems: pion-pion, pion-kaon, pion-proton, and pion-Xi within the quark-gluon string model (QGSM) and ultra-relativistic quantum molecular dynamics (UrQMD) model. We are extracting space-time sizes and asymmetries of particle emission and comparing the extracted characteristics with the available experimental data as well as with the freeze-out parameters obtained from the microscopic models.

Speaker: Mr Mads Stormo Nilsson (Department of Physics, University of Oslo)

Slides WPCF.pdf

17:00 coffee break

12 Observables from a 3+1D relativistic hydro solution

In the last several years it has been revealed that the matter produced in the collisions of the Relativistic Heavy Ion Collider (RHIC) is a nearly perfect fluid, i.e. it can be described with perfect fluid hydrodynamics. There was a long search for exact hydrodynamic models (solutions of the partial differential equations of hydrodynamics) and several models proved to be applicable. There are 1+3 dimensional models, as well as relativistic models - but no 1+3 dimensional and relativistic model has been tested yet. We extract observables for the first time from a 1+3 dimensional relativistic hydro model. We use the relativistic, ellipsoidally symmetric model of Csorgo, Csernai, Hama and Kodama. We calculate momentum distribution, elliptic flow and correlation radii and compare them to RHIC data.

Speaker: Dr Mate Csanad (Eotvos University, Department of Atomic Physics)

Paper http://arxiv.org/abs/0909.4842

Slides csanad_wpcf09.pdf csanad_wpcf09.ppt

13 Azimuthally asymmetric BudaLund hydrodynamic model and fits to spectra, elliptic flow and asHBT

We present the extension of the Buda-Lund hydrodynamic model from high energy central collisions to peripherial ones. Spectra and the elliptic flow of indentified particles are described along with the azimuthal dependence of two-particle correlation function radii in the ellipsoidally symmetric generalization of the model. Theoretical predictions were tested against RHIC data. From fits to data of 20-30\% centrality class source parameters characterizing these non-central ultra-relativistic heavy ion reactions were extracted. In the simultaneous fits we used azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX in Au+Au reactions at center of mass energy of 200 AGeV. In the same reactions PHENIX extracted transverse momentum dependent elliptic flow distributions, as well. STAR data were used for azimuthally variable two-particle correlation function radii. The results show that the central temperature in 20-30\% centrality reactions is lower, then that in central ones, $T_{0} = 173 \pm 2(stat) MeV$. We have found that the flow is stronger in reaction plane then out of plane. Hence, the almond shape of the reaction zone initially elongated out of plane gets elongated in-plane transverse direction by the time the particle emission reaches its maximal value. The effect is reflected by the geometrical radii in the two perpendicular directions at that time, as well, $R_g (in-plane) = 7.8 \pm 0.2(stat) fm , \ R_g (out-plane) = 7.2 \pm 0.2(stat) fm$. This is the first time that an in-plane extended source has been reconstructed from a simultaneous fit to identified particle spectra, elliptic flow and azimuthally sensitive HBT data in 200 AGeV Au+Au collisions at RHIC. Values for the strength of transverse flow, width of emission time, as well as for the longitudinal rapidity extension are provided, too. [1] M.~Csan\'ad, T.~Cs\"{o}rg\H{o}, B.~ L\"orstad, Nucl. Phys. A {\bf 742}, 80 (2004)[arXiv:nucl-th/0310040] [2] M.~Csan\'ad, T.~Cs\"{o}rg\H{o}, B.~ L\"orstad and A.~Ster, Nukleonika \ {\bf 49}, S45 (2004). [arXiv:nucl-th/0402037] [3] B.~Tomasik, AIP Conf. Proc. {\bf 828},\ 464 (2006). [arXiv:nucl-th/0509100] [4] T.~Cs\"{o}rg\H{o}, J. Phys. Conf. Ser. {\bf 50}, 259 (2006). [arXiv: nucl-th/0505019] [5] M.~Csan\'ad, B.~Tomasik, T.~Cs\"{o}rg\H{o}, Eur. Phys. J. A {\bf 37}, 111 (2008) [arXiv:nucl-th/0801.4434] [6] M.~Csan\'ad et al., Eur. Phys. J. A {\bf 38}, 363 (2008). [arXiv:nucl-th/0512078]

Speaker: Andras Ster (Res. Inst. Particle &amp; Nucl. Phys. - Hungarian Academy of Science)

Slides ster_wpcf09.pdf ster_wpcf09.ppt

14 Significant in-medium reduction of the mass of $\eta\prime$ mesons in $\sqrt{s_\mathrm{NN}}=200\ \mathrm{GeV}$ Au+Au collisions

It is argued that the $\mathrm{U_A}(1)$ or chiral symmetry may temporarily be restored in a hot and dense medium that is created in high energy heavy ion collisions. As a consequence, the mass of the $\eta\prime$(958) mesons may be reduced to its quark model value, and the abundancy of the $\eta\prime$ mesons at low $p_T$ may be significantly enhanced. PHENIX and STAR data on the intercept parameter of the two-pion Bose-Einstein correlation functions in $\sqrt{s_{NN}}= 200$ GeV Au+Au collisions were analysed in terms of various models of hadronic abundances. To describe these data, an in-medium $\eta\prime$ mass reduction of at least 200 MeV was needed in each case [1]. [1] http://arxiv.org/abs/0905.2803

Speaker: Mr Robert Vertesi (MTA KFKI RMKI)

Paper http://arxiv.org/pdf/0905.2803

Slides WPCF09_vertesi.pptx

Slides (pdf) WPCF09_vertesi.pdf

Slides (ppt) WPCF09_vertesi.ppt

Thursday 15 October

Dynamics and the Equation of State (2/2)

Convener: Prof. Wojciech Florkowski (IFJ PAN Krakow / UJK Kielce)

15 Azimuthally sensitive photon HBT interferometry at RHIC

Azimuthally sensitive HBT interferometry can complement elliptic flow measurements by constraining the spatial deformation of the source and its time evolution. Performing these measurements on photons allows us to access the fireball evolution at earlier times than with hadrons. Using ideal hydrodynamics to model the space-time evolution of the collision fireball, we explore theoretically various aspects of 2-photon intensity interferometry with transverse momenta up to 2 GeV, in particular the azimuthal angle dependence of the HBT radii in non-central collisions. We find interesting differences in the structure of the photon correlation function when compared to that of hadrons, caused by the masslessness of the photon. We highlight the dual nature of thermal photon emission, in both central and non-central collisions, resulting from the superposition of QGP and hadron resonance gas photon production. This signature is present in both the thermal photon source function and the HBT radii extracted from Gaussian fits of the 2-photon correlation function. We find that the azimuthal oscillation amplitude of the sideward HBT radius for photons tracks the source eccentricity not only at KT=0 (as is the case for pions), but for all KT. This allows to reconstruct the time-evolution of the source eccentricity from the KT-dependence of the sideward oscillation amplitude.

Speaker: Prof. Ulrich Heinz (The Ohio State University)

Slides WPCF09_Heinz.pdf

16 Lattice based Equation of State and its effect on the hydrodynamical evolution

At low temperatures the hadron resonance gas model is expected to give a fair description of thermodynamic quantities even if the lattice QCD calculation leads to significantly different result. In this talk I show that he discrepancies are significantly reduced if we take into account the larger values of quark mass, i.e. larger hadron masses, used in lattice calculations as well as the finite spacing errors. Thus, I propose thatelow the critical temperature, T_c, the physical EoS is close to the hadron resonance gas EoS, and present a parametrization interpolating consistently between hadron resonance gas EoS below and lattice EoS above T_c. In the second part of the talk I show how such an Equation of State affects the evolution of the system and compare it with old calculations done using an Equation of State with a first order phase transition.

Speaker: Pasi Huovinen (Johann Wolfgang Goethe-Universität)

Slides Huovinen_wpcf.pdf

17 Viscosity and HBT

Finite viscosity affects the evolution of the fireball created in energetic nuclear collisions. A recent attempt of the CERES experiment to extract viscosity from pion source radii in central lead-gold collisions at the CERN SPS will be presented. The unexpected result, the limitations of the method, and the possible ways out will be discussed.

Speaker: Dariusz Miskowiec (Gesellschaft fuer Schwerionenforschung mbH (GSI))

Slides 2009-10-15.pdf 2009-10-15.ppt

10:30 coffee break

18 Elliptic flow fluctuations and non-flow correlations in 200 GeV Au+Au collisions

We present the latest results of the determination of the contribution of non-flow effects to the elliptic flow fluctuations in 200 GeV Au+Au collisions, measured by PHOBOS. In a hydrodynamical scenario, fluctuations in the shape of the initial collision region naturally lead to corresponding fluctuations in the elliptic flow signal. Measurements of elliptic flow fluctuations should therefore shed light on the connection between observed flow, the initial geometry and the hydrodynamic evolution of the system. However, non-flow correlations can lead to a broadening of the observed event-by-event v2 distribution and thereby modify the observed v2 fluctuation signal. We have developed an analysis procedure to quantify the contribution of non-flow correlations to the flow signal. This analysis crucially relies on the large pseudorapidity coverage of the PHOBOS multiplicity array. The flow signal is disentangled from the non-flow contributions, by a systematic study of two-particle azimuthal correlations at different rapidity gaps.

Speaker: Constantinos Loizides (Massachusetts Institute of Technology (MIT))

Slides wpcf09-loizides-v0.pdf

19 Further study on the ridge effect in hydrodynamic model

In a recent paper [1], the hydrodynamic code NeXSPheRIO was used in conjunction with STAR analysis methods to study two-particle correlations as function of \Delta\eta and \Delta\phi. Both the ridge-like near-side and double-hump away-side structures were obtained. The appearance of the ridge-like structure is related to the combined effect of high-energy density tubes in the initial conditions and the transverse expansion of the fluid. As far as the near-side ridge is concerned, this statement can easily be accepted, if some high-density tubes are located close to the surface of the hot matter. As for the less trivial away-side structure, made of double ridges placed symmetrically with respect to the high-pT trigger in the most central collisions, it is hard to understand. A closer look at the flow produced in the neighborhood of such a tube, showed that actually the ridge structure in our hydrodynamics, both nearside and the away-side, is due to a peculiar flow effect of interference between the peripheral high-energy tubes and the backgound hot matter in expansion. The pT-dependence of the two-particle correlation function in \Delta\phi, produced by this mechanism, is similar to the PHENIX data [3]. We have further studied this mechanism, computing the three-particle correlation, which may discriminate between this and the popular Mach cone mechanism [4]. References: [1] J. Takahashi et al. arXiv:0902.4870. [2] R. Andrade, F. Grassi, Y. Hama and W.-L. Qian, communication to ISMD2009. [3] A.Adare et al., Phys.Rev.C77 (2008)011901(R); Phys.Rev.C78 (2008) 014901. [4] J. Casalderrey-Solana, E.V. Shurayk, D. Teaney, hep-ph/0602183; J. Ruppert and T. Renk, Acta Phys. Polon. Supp. 1, 633 (2008).

Speaker: Y. Hama (Instituto de Fisica - USP)

Slides Hama_wpcf09.pdf

20 RHIC observes plasma viscosity and hadronic dissipation

Reduction of the elliptic flow of charged particles has been proposed as a measure of the shear viscosity coefficient in the Quark Gluon Plasma. We complete these studies by introducing independent shear and bulk viscosities in the hadronic phase of the hydrodynamic expansion. We show that most of the effect of the reduction of elliptic flow due to dissipation comes from the hadronic phase. Only a combination of the charged particle elliptic flow results with the predictions on HBT radii, spectra and identified transverse momentum elliptic flow of identified particles (pions, protons, strange particles) indicates a non-zero viscosity coefficient eta/s=0.16 in the QGP phase. Quantitative estimates of QGP shear viscosity should take into account late dissipative effects using viscous hydrodynamics in the hadronic phase or a hadronic cascade model.

Speaker: Piotr Bozek (Institute of Nuclear Physics PAN, Krakow and Rzeszow University, Poland)

Slides Bozek-WPCF.pdf

21 Long-Range Multiplicity and Transverse Momentum Correlations in pp Collisions in ALICE at the LHC

In pp collisions at the LHC, collective effects due to colour-string interactions (screening/annealing/fusion/percolation are the mechanisms proposed by different models) could take place, resulting in the appearance of the so-called long-range correlations. In the present work long-range correlations are studied in an event-by-event charged particle analysis, performed on MC PYTHIA simulations for pp collisions at Fermilab and LHC energies. Two parameter sets corresponding to different contributions of gluon string formation and fusion processes are used. The results are compared to the available experimental data and predictions for ALICE at the LHC are discussed. It is also shown that the long-range correlations, obtained in pp collisions using charged particle multiplicity and/or transverse momentum information in two separate rapidity intervals, allow the definition of a specific type of pp events that might be characterized as ”very central”. In such events, particle emitting sources with maximal energy density, corresponding to clusters of fused strings, may be formed.

Speaker: Dr Grigory Feofilov (V. Fock Institute for Physics of Saint-Petersburg State University)

Slides feofilov-cern-15-Oct-09.pdf feofilov-cern-15-Oct-09.ppt

12:50 lunch break

Non-identical correlations and squeezed states

Convener: Boris Tomasik (Univerzita Mateja Bela)

22 Non-identical particle femtoscopy at RHIC energies in hydrodynamics with statistical hadronization

Non-identical particle femtoscopy probes not only the size of the emitting system, but also the emission asymmetries between particles of different mass, which are intimately related with the collective behavior of matter. We apply the technique to the simulations from the THERMINATOR+Lhyquid model of the heavy-ion collisions at RHIC. We present predictions for all common pair combinations and discuss their interpretation. Emphasis is put on extracting unique information about collective behavior of matter from the non-identical correlations and understanding the role of particles coming from decays of hadronic resonances. We also present, in detail, the technical aspects of the non-identical particle femtoscopy technique applied to data from the heavy-ion collisions. We list the sources of systematic errors coming from the method itself and the usual assumptions. We suggest most robust analysis methods and discuss their limitations.

Speaker: Adam Kisiel (CERN)

Slides

• Kisiel_wpcf2009.odp
• Kisiel_wpcf2009.pdf
• Kisiel_wpcf2009.ppt

23 Recent STAR results of pion-proton femtoscopy

Correlations between non-identical particles at small relative velocity probe asymmetries in the average space-time emission points at freezeout. Such asymmetries may arise from long-lived resonances, bulk collective effects, or differences in the freezeout scenario for the different particle species. STAR has extracted pion-proton correlation functions from a high-statistics dataset of Au+Au collisions at $\sqrt{s_{NN}}=200GeV$. We present femtoscopic analysis using spherical-harmonics decomposition of this data for pions and protons, for collisions of different centrality. Preliminary quantitative results extracted from this data are presented for the first time.

Speaker: Mr Marcin Zawisza (Warsaw University of Technology)

Slides mzawisza.pdf

24 pi+- Xi-+ Correlations and the Xi*(1530) Puzzle.

The analysis of the preliminary RHIC data on $\pi^{+}-\Xi^{-}$ correlation function is carried out. The $\Xi^*(1530)$ resonance is reasonably described. The value of the fireball radius has been estimated and the sensitivity to the $\pi^{+}-\Xi^{-}$ $S$-wave scattering lengths has been tested.

Speaker: Dr Ludmila Malinina (JINR and SINP MSU)

Slides for_WPCF09_1.pdf for_WPCF09_2.ppt

25 Baryon-baryon correlations

The analysis of two-particle correlations provides a powerful tool to study the properties of hot and dense matter created in heavy-ion collisions at ultra-relativistic energies. Applied to identical and non-identical hadron pairs, it makes the study of space-time evolution of the source in femtoscopic scale possible. Baryon femtoscopy allows extraction of the radii of produced sources which can be compared to those deduced from identical pion studies, providing complete information about source characteristics. By analyzing the momentum correlations it is possible to access information about source characteristics which cannot be measured directly. Identical baryon correlations reflect the properties of the quantum statistics (QS) and of the final state interactions (FSI): Coulomb and strong. Non-identical baryon pairs are sensitive to the final state interactions only. The correlation functions obtained for identical and non-identical baryon pairs are planned to be presented. The results will be compared to theoretical predictions as well.

Speaker: Dr Hanna Zbroszczyk (Warsaw Univesroty Of Technology)

Slides zbroszczyk.pdf

16:00 coffee break

26 Squeezed Hadronic Correlations

Squeezed correlations of particle-antiparticle pairs are predicted to appear in case the masses of those particles are modified in the hot and dense medium formed in high energy heavy ion collisions. If discovered experimentally, they would be an unequivocal evidence of such modification by means of hadronic probes. Previous studies have shown that, for a uniformly distributed, momentum-independent shift in the hadronic masses, the particle-antiparticle squeezed correlations were expected to lead to sizable signals. We briefly recall those results here, for $K^+ K^-$ and of $\phi \phi$ pairs, with in-medium reduced masses. Next, we discuss results of squeezing effects on particle-antiparticle correlations of $D$-mesons, whose detection and identification are expected to be more easily performed in future upgrades of experiments at the BNL/RHIC accelerator. The suggested observable to be searched for is the squeezed correlation function of D-meson pairs, plotted in terms of their average momentum, $K_{_{12}}=\frac{1}{2} (k_{_1} + k_{_2})$, for large values of their relative momentum, $q_{_{12}}=(k_{_1} - k_{_2})$. We show also for this case that the effects of squeezing on particle-antiparticle correlations survive finite size and flow effects, with enough strength to be observed experimentally. We investigate the dependence of the maximum of the squeezed correlation on the asymptotic particle mass, as well as on their emission temperatures.

Speaker: Dr Sandra Padula (Instituto de Fisica Teorica (IFT)-Universidade Estadual Paulista, Brazil)

Slides WPCF2009-SSPadula.pdf

27 Particle-antiparticle back-to-back correlation measurement in $\sqrt{s_{NN}}=200$ GeV Au+Au collisions

for the PHENIX Collaboration The collision of energetic nuclei forms a hot and dense partonic matter. Determining the nature of the phase transition associated with the production of the observed hadrons is an important task. Experimental data on direction-dependent correlation length (HBT radii) studies seem to exclude the possibility of a strong first order phase transition in $\sqrt{s_{NN}}=200$ GeV Au+Au collisions, while lattice QCD calculations favorize a cross-over type of hadron formation. A novel type of correlations, hypothesized in the late 1980's and fully highlighted in the last decade, is sensitive to the medium effects on the produced hadrons. This type of quantum mechanical correlations, called back-to-back correlations, or squeezed back-to-back correlations, was predicted among particle-antiparticle pairs, both $\pi^+\pi^-$, $K^+K^-$, or $p\bar{p}$ pairs, if their masses are modified by the medium due to hadronic interactions or chiral dynamics. Observation and exploring the properties of such correlation effect would thus provide a unique insight into the freeze-out dynamics of the hot and dense partonic matter created in heavy ion collisions. The experimental details and the latest status of the PHENIX measurement of this type of particle-antiparticle back-to-back correlations will be presented.

Speaker: Marton Nagy (MTA KFKI RMKI)

Slides mn_wpcf09.pdf.pdf

28 Implications of HBT analyses

Two problems important for the HBT method are discussed. The relation of the measured momentum distributions to theWigner function of the final hadrons and the relation of this Wigner function to the emission function. It is found that for the profile of each homogeneity region all the even cumulants and no odd cumulant can be unambiguously measured. Moreover, if the centers of all the homogeneity regions are known, the profile of all the interaction region can be unambiguously measured. Obtaining further information about the emission function requires additional assumptions. A few important cases are discussed.

Speaker: Kacper Zalewski (Institute of Physics, Jagellonian University)

Slides Zalewski-CERN09.pdf

19:00 Conference Dinner

Friday 16 October

09:00 Excursion

12:00 lunch break

TH Phenomenology Seminar

29 Heavy Ion's Mini-me: Strong Radial Flow in p+p Collisions at RHIC

The phenomenon of collective, hydrodynamic-like flow plays a central role in the present understanding of the new state of matter (the quark-gluon plasma) produced in high-energy collisions between gold nuclei at the Relativistic Heavy Ion Collider (RHIC). It has long been assumed that collisions between protons produce insufficient particle multiplicity and energy density to produce a collective, bulk system; thus, these collisions are a natural ``reference'' against which to compare signals from heavy systems, measured at the same energy, in the same detectors, and with identical techniques. Significant differences in bulk signals from these systems have, indeed, been observed. These differences are usually taken to confirm the assumption that proton collisions produce no flow. We challenge this interpretation, and the assumption in general. We show that, when simple effects of conservation law-induced phasespace constraints are taken into account, the single-particle spectra and two-pion correlation functions exhibit radial flow signals quantitatively identical to those seen in Au+Au collisions. We discuss possible driving physics behind--and potential implications of--this surprising finding, as well as future measurements at RHIC and the LHC.

Speaker: Prof. Mike Lisa (Ohio State University)

Slides WPCF2009-EMCICs_noBackups.pdf WPCF2009-EMCICs_noBackups.pptx

Collectivity in p+p

Convener: Prof. Ullrich Heinz (The Ohio State University)

30 Extracting source sizes from two-pion correlation functions at sqrt(s) 14TeV

Two pion correlation functions are used to extract source sizes from events at sqrt(s) 14 TeV in proton-proton collisions.

Speaker: Mr Nicolas Bock Garcia (Dept. Phys., High Energy Phys. Grp.-Ohio State University-Unknow)

Slides Bock_WPCF09.pdf.pdf

31 The meaning of the time scale ∆t in Bose−Einstein correlations

The time scale ∆t parameter, which appears in the Bose-Einstein Correlations (BEC) and treated in term of the Heisenberg uncertainty relations, is reexamined. Arguments are given for the role of ∆t as a measure of the particles’ emission time rather than representing the strength property of the correlated particles. In heavy ion collisions ∆t measures the emission time duration of the particles produced from a nucleus of atomic number A which is shown to be $\Delta t = \frac{m_{\pi}\alpha^2}{hc^2}A^{2/3}$ where a ≃1 fm that is, proportional to the nucleus surface area. This finding agrees rather well with the experimental ∆t values deduced from the BEC analyzes of heavy ion collisions.

Speaker: Prof. Gideon Alexander (Tel-Aviv University)

Slides Gideon-WPCF2009t.pdf Gideon-WPCF2009t.ppt

32 Recent L3 results on BEC at LEP, improved description of the tau-model

Bose-Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various parametrizations. A good description is achieved using a Levy stable distribution in conjunction with a hadronization model having highly correlated conguration and momentum space, the tau-model. Using these results, the time evolution of particle emission in two-jet events is reconstructed. Previous studies have found an elongated shape of the source along the event axis while tau-model prefers a spherical shape. Elongaton is also found using the tau-model equations modified ad hoc to allow elongation. Hence new theoretical improvements of the tau model are needed.

Speaker: Dr Tamas Novak (MTA RMKI KFKI - Budapest, KRF - Gyöngyös)

Slides novak2.pdf novak_wpcf09.pdf

16:30 coffee break

33 Femtoscopic signatures of collective behavior

Femtoscopy measures space-time characteristics of the particle emitting source created in relativistic heavy-ion collisions. It is argued that collective behavior of matter (radial flow) produces specific femtoscopic signatures. Some of them, like the mT dependence of the pion "HBT radii" can be explained by the alternative scenario of temperature gradients. We identify the ones that can invalidate such alternatives, such as non-identical particle correlations and mT scaling for particles of higher mass. Studies with a simple rescattering code show that as the interaction cross-section is increased the system develops collective behavior and becomes more thermalized at the same time, the two effects being the natural consequence of increased number of particle rescatterings. Repeating calculations with a more realistic rescattering model confirmed all of these conclusions.

Speaker: Prof. Tom Humanic (Ohio State University)

Slides Humanic_wpcf2009.odp Humanic_wpcf2009.pdf

34 Does interferometry probe thermalization?

Hydrodynamical models have generally failed to describe interferometry radii measured at RHIC. In order to investigate this "HBT puzzle", we carry out a systematic study of HBT radii in ultrarelativistic heavy-ion collisions within a two-dimensional transport model. We compute the out and side radii as a function of the transverse momentum for various values of the Knudsen number, which measures the degree of thermalization in the system. In the case of central collisions, we show that the large difference between the side and out radii, which is seen in hydrodynamical models but not in data (HBT puzzle), appears only for unrealistically small values of the Knudsen number. For realistic values of the Knudsen number, our result for the ratio Ro/Rs is much closer to data than standard hydrodynamical results. The transverse momentum dependence of the radii, which is usually said to reflect collective flow, also has a very limited sensitivity to the degree of thermalization. Finally, we study the azimuthal oscillations of Ro, Rs, and R_{os} for non central collisions. Their amplitudes depend very little on the Knudsen number. In particular, the azimuthal dependence of Rs is found to reflect the initial eccentricity of the overlap area.

Speaker: Prof. Jean-Yves Ollitrault (Institut de Physique Theorique - CEA Saclay)

Slides ollitrault-WCPF.pdf ollitrault-WCPF.ppt

35 Imaging of fragmented fireball and in non-central collisions

We calculate the images of particle-emitting sources which might result from the scenario where fireball fragments at the phase transition. This can happen due to sudden appearance of the bulk viscisity or via spinodal decomposition. We discuss the constraints on the fragmented source from data by PHENIX collaboration. We also study the images which result from summing up of many randomly oriented sources in non-central collisions and compare them with an image obtained from azimuthally symmetric averaged source.

Speaker: Boris Tomášik (Univerzita Mateja Bela - Banska Bystrica - Slovakia)

Slides tomasik_WPCF.ppt.ppt

36 Multiplicity fluctuations as signature of the temperature fluctuations

Recently experiments in high-energy nuclear collisions have observed fluctuations of multiplicity which exhibit spectacular and unexpected features as functions of the number of participants (in particular they show that the scaled variance of the multiplicity distribution, Var(N)/<N>, increases when proceeding from the central towards peripheral collisions, i.e., when the number of participants decreases. None of the present models can account for the experimental results. In [1] we have described the observed behavior without resorting to any specific dynamical picture but, instead, by attributing it to some nonstatistical,intrinsic fluctuations existing in a hadronizing system produced in high energy heavy ion collisions. To account for such fluctuations we propose to use a special version of statistical model based on nonextensive Tsallis statistics in which fluctuations of the temperature are known to be directly connected with the nonextensivity parameter q, with |q-1| being a direct measure of fluctuations, namely q = 1 + Var(1/T)/<1/T>^2 (in the limit of vanishing fluctuationsfor, q -> 1, one recovers the usual Boltzmann-Gibbs statistical approach [2]). We evaluate the nonextensivity parameter q and its dependence on the hadronizing system size from the experimentally observed collision centrality dependence of the mean multiplicity, <N>, and its variance, Var(N). We attribute the observed system size dependence of q to the finiteness of the hadronizing source with q = 1 corresponding to an infinite, thermalized source with a fixed temperature, and with q > 1 (which is observed) corresponding to a finite source in which both the temperature and energy fluctuate. The possible fate of such fluctuations at LHC energies is discussed. [1] G.Wilk and Z.Wlodarczyk, Phys. Rev. C79 (2009) 054903. [2] G.Wilk and Z.Włodarczyk, Eur. Phys. J. A40 (2009) 299.

Speaker: Prof. Grzegorz Wilk (The Andrzej Soltan Institute for Nuclear Studies, Warsaw, Poland)

Slides wpcf2009_wilk.pdf

Saturday 17 October

LHC predictions

Convener: Prof. Jan Rak (JYFL/HIP)

37 Energy dependance of interferometry scales in ultra-relativistic heavy ion collisions

A study of the energy behavior of the hadronic spectra and pion interferometry scales is conducted for the top SPS, RHIC and LHC energies within the hydrokinetic approach. The latter allows one to describe evolution of quark-gluon and hadron matter as well as continuous particle emission from the fluid in agreement with the underlying kinetic equations. The main mechanisms that lead to the paradoxical, at first sight, behavior of the interferometry scales, are exposed. In particular, a decrease of $R_{out}/R_{side}$ ratio with growing energy happens due to pre-thermal collective transverse flows and a strengthening of positive correlations between space and time positions of emitted pions. Also the results obtained within hydrokinetic model as for kaon intensity interferometry at RHIC are presented.

Speaker: Prof. Yuriy Sinyukov (Bogolyubov Institute for Theoretical Physics)

Slides

• EndSlides.pdf
• EndSlides.ppt
• WPCF2009_Sinyukov.pdf
• WPCF2009_Sinyukov.ppt

38 Influence of jets on femtoscopic correlation radii in ultra-relativistic heavy ion collisions

The influence of jet production on femtoscopic momentum correlations in ultra-relativistic heavy ion collisions is analyzed in the frame of HYDJET++ Monte-Carlo model. Non-trivial energy dependence of the correlation radii from RHIC to LHC due to jets is predicted.

Speaker: Igor Lokhtin (SINP MSU)

Slides Lokhtin-WPCF09.odp Lokhtin-WPCF09.pdf

39 Initial source size and transverse momentum fluctuations in the event-by-event relativistic heavy- ion collisions

We investigate the initial transverse size of the source, which comes directly from the Glauber treatment of the earliest stage of relativistic heavy-ion collisions. After the hydrodynamic evolution stage the fluctuations in the transverse velocity flow at the hadronic freeze-out are transformed into the even-by-event fluctuations of the average transverse momentum. The Glauber phase is simulated by GLISSANDO and followed by a realistic hydrodynamic evolution stage. The statistical hadronization is performed by the THERMINATOR. We describe the pT fluctuations at RHIC, in particular the magnitude of the effect, its centrality dependence, and the weak dependence on the incident energy. The results show that the observed event-by-event p_T fluctuations are mainly caused by the initial source size fluctuations

Speaker: Mikołaj Chojnacki (Institute of Nuclear Physics, Krakow - Poland)

Slides 2009-10-17_3_Chojnacki.pdf

10:30 coffee break

40 Elliptic flow measurements at ALICE

soon to follow...

Speaker: Naomi Van Der Kolk (NIKHEF-Unknown-Unknown)

Slides NvanderKolk.ppt.pdf NvanderKolk.ppt.ppt

41 Effects of Hadronic Rescattering on HBT Radii for PP Collisions at the LHC

I will present the results of a femtoscopic analysis on Monte Carlo pp data, at multiple expected LHC energies, which has been run through a hadronic rescattering afterburner. Through these results, the expected effect of hadron rescattering on expected HBT radii will be shown.

Speaker: David Truesdale (Ohio State University)

Slides PP_Rescattering.pdf

42 Jet-like heavy-flavour particle correlations in ALICE

The energy loss of partons is predicted to be a sensitive probe of the QCD matter created in high energy nucleus-nucleus collisions since its magnitude depends strongly on the colour charge density of the matter traversed. In particular, the understanding of the flavour dependent coupling of quarks and the modification of their fragmentation function give essential information on the properties of the medium. Due to their large mass, heavy quarks are believed to be predominantly produced in the initial state of the collision and, therefore, probe the complete space-time evolution of the expanding medium. Recent RHIC results on single electron production in nucleus-nucleus collisions have shown that the yield at high transverse momentum is suppressed to the same level as observed for light-quark hadrons, which was not expected due to the dead-cone effect. Heavy-quark particle azimuthal angular correlations allow studying the fragmentation function of charm and bottom quarks separately, where high-pT decay electrons are associated with open charmed mesons. The precision on secondary vertex finding in the ALICE Inner Tracker System will play a key role for the reconstruction of the decay products. First simulation studies and current experimental preparations in the ALICE experiment will be presented.

Speaker: Dr Andre Mischke (Utrecht University)

Slides MischkeWPCF2009.pdf MischkeWPCF2009.ppt

43 Azimuthally-sensitive femtoscopy: an excitation function worth pursuing

The reaction plane-dependence of pion HBT correlations has been measured at the AGS, SPS and RHIC facilities. Though very few data points exist over this two orders of magnitude in energy, an intriguing behaviour is observed. In particular, contrary to generic expectations of a monotonic energy dependence of the freezeout anisotropy, a "step" or perhaps even a dip-like behaviour appears. We will speculate on the possible implications of this observation and discuss plans at RHIC to more fully explore the energy landscape over the next few years. We will also present transport calculations showing strong sensitivity of the excitation function to the underlying physics, including a sensitivity to the onset of a first order phase transition at lower energies.

Speaker: Prof. Mike Lisa (Ohio State University)

Slides lisaWPCF2009asHBT_noBackups.pdf lisaWPCF2009asHBT_noBackups.pptx