A. Kisiel

THERMINATOR: THERMal heavy-IoN generATOR☆☆☆

THERMINATOR is a Monte Carlo event generator designed for studying of particle production in relativistic heavy-ion collisions performed at such experimental facilities as the SPS, RHIC, or LHC. The program implements thermal models of particle production with single freeze-out. It performs the following tasks: (1) generation of stable particles and unstable resonances at the chosen freeze-out hypersurface with the local phase-space density of particles given by the statistical distribution factors, (2) subsequent space–time evolution and decays of hadronic resonances in cascades, (3) calculation of the transverse-momentum spectra and numerous other observables related to the space–time evolution. The geometry of the freeze-out hypersurface and the collective velocity of expansion may be chosen from two successful models, the Cracow single-freeze-out model and the Blast-Wave model. All particles from the Particle Data Tables are used. The code is written in the object-oriented c++ language and complies to the standards of the ROOT environment. Program summary Program title:THERMINATOR Catalogue identifier:ADXL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADXL_v1_0 Program obtainable from: CPC Program Library, Queens University of Belfast, N. Ireland RAM required to execute with typical data:50 Mbytes Number of processors used:1 Computer(s) for which the program has been designed: PC, Pentium III, IV, or Athlon, 512 MB RAM not hardware dependent (any computer with the c++ compiler and the ROOT environment [R. Brun, F. Rademakers, Nucl. Instrum. Methods A 389 (1997) 81, http://root.cern.ch] Operating system(s) for which the program has been designed:Linux: Mandrake 9.0, Debian 3.0, SuSE 9.0, Red Hat FEDORA 3, etc., Windows XP with Cygwin ver. 1.5.13-1 and gcc ver. 3.3.3 (cygwin special)—not system dependent External routines/libraries used: ROOT ver. 4.02.00 Programming language:c++ Size of the package: (324 KB directory 40 KB compressed distribution archive), without the ROOT libraries (see http://root.cern.ch for details on the ROOT [R. Brun, F. Rademakers, Nucl. Instrum. Methods A 389 (1997) 81, http://root.cern.ch] requirements). The output files created by the code need 1.1 GB for each 500 events. Distribution format: tar gzip file Number of lines in distributed program, including test data, etc.: 6534 Number of bytes in ditribution program, including test data, etc.:41 828 Nature of the physical problem: Statistical models have proved to be very useful in the description of soft physics in relativistic heavy-ion collisions [P. Braun-Munzinger, K. Redlich, J. Stachel, 2003, nucl-th/0304013. [2]]. In particular, with a few physical input parameters, such as the temperature, chemical potentials, and velocity of the collective flow, the models reproduce the observed particle abundances [P. Koch, J. Rafelski, South Afr. J. Phys. 9 (1986) 8; J. Cleymans, H. Satz, Z. Phys. C 57 (1993) 135, hep-ph/9207204; J. Sollfrank et al., Z. Phys. C 61 (1994) 659; P. Braun-Munzinger et al., Phys. Lett. B 344 (1995) 43, nucl-th/9410026; P. Braun-Munzinger et al., Phys. Lett. B 365 (1996) 1, nucl-th/9508020; J. Cleymans et al., Z. Phys. C 74 (1997) 319, nucl-th/9603004; F. Becattini, J. Phys. G 23 (1997) 1933, hep-ph/9708248; G.D. Yen, M.I. Gorenstein, Phys. Rev. C 59 (1999) 2788, nucl-th/9808012; P. Braun-Munzinger, I. Heppe, J. Stachel, Phys. Lett. B 465 (1999) 15, nucl-th/9903010; J. Cleymans, K. Redlich, Phys. Rev. C 60 (1999) 054908, nucl-th/9903063; F. Becattini et al., Phys. Rev. C 64 (2001) 024901, hep-ph/0002267; P. Braun-Munzinger et al., Phys. Lett. B 518 (2001) 41, hep-ph/0105229; W. Florkowski, W. Broniowski, M. Michalec, Acta Phys. Polon. B 33 (2002) 761, nucl-th/0106009], the transverse-momentum spectra [W. Broniowski, W. Florkowski, Phys. Rev. Lett. 87 (2001) 272302, nucl-th/0106050], balance functions [W. Florkowski, W. Broniowski, P. Bozek, J. Phys. G 30 (2004) S1321, nucl-th/0403038. [17]; P. Bozek, W. Broniowski, W. Florkowski, Acta Phys. Hung. A 22 (2005) 149, nucl-th/0310062. [18]], or the elliptic flow [W. Broniowski, A. Baran, W. Florkowski, AIP Conf. Proc. 660 (2003) 185, nucl-th/0212053. [19]; W. Florkowski, W. Broniowski, A. Baran, 2004, nucl-th/0412077. [20]] in both non-strange and strange sectors. The key element of the approach is the inclusion of the complete list of hadronic resonances, which at the rather high temperature at freeze-out, ∼165 MeV, contribute very significantly to the observed quantities. Their two- and three-body decays, taken from the tables, proceed in cascades, ultimately producing the stable particles observed in detectors. At the moment there exist several codes to compute the abundances of particles (the publicly available programs for this purpose are SHARE [G. Torrieri et al., 2004, nucl-th/0404083] and THERMUS [S. Wheaton, J. Cleymans, 2004, hep-ph/0407174]), which is a rather simple task, since the abundances are insensitive to the geometry of the fireball and its expansion. On the other hand, the calculation of the transverse-momentum spectra of particles is much more complicated due to the sensitivity to these phenomena. THERMINATOR deals with this problem, offering the full information on the space–time positions and momenta of the produced particles. As a result, the program allows to compute very efficiently the transverse-momentum spectra of identified particles and examine implications of the assumed expansion model. THERMINATOR allows easily for the departure from symmetries typically assumed in other approaches. This opens the possibility to study the dependence of physical quantities on rapidity and the azimuthal angle. The contribution of the resonances to various observables may be traced conveniently, and their role in the statistical approach may be verified. As a Monte Carlo event generator written in the object-oriented c++ language in the ROOT [R. Brun, F. Rademakers, Nucl. Instrum. Methods A 389 (1997) 81, http://root.cern.ch] environment, THERMINATOR can be straightforwardly interfaced to the standard software routinely used in the data analysis for relativistic heavy-ion colliders, such as SPS, RHIC, and, in the future, LHC. In this way the inclusion of experimental acceptance, kinematic cuts, or interfacing with other programs poses no difficulty. Method of solving the problem:THERMINATOR uses the particle data tables [Particle Data Group, K. Hagiwara et al., Phys. Rev. D 66 (2002) 010001] in the universal input form used by the SHARE [G. Torrieri et al., 2004, nucl-th/0404083] package. The user decides for the thermal parameters and the preferred expansion model. The optimum thermal parameters may be taken, e.g., as those obtained with the help of SHARE [G. Torrieri et al., 2004, nucl-th/0404083] or THERMUS [S. Wheaton, J. Cleymans, 2004, hep-ph/0407174]. At the moment there are two different expansion models implemented in the code: the model of Ref. [W. Broniowski, W. Florkowski, Phys. Rev. Lett. 87 (2001) 272302, nucl-th/0106050], based on the so-called Buda–Lund [T. Csorgo, B. Lorstad, Phys. Rev. C 54 (1996) 1390, hep-ph/9509213] parameterization, and the Blast-Wave model [E. Schnedermann, J. Sollfrank, U.W. Heinz, Phys. Rev. C 48 (1993) 2462, nucl-th/9307020; F. Retiere, M.A. Lisa, Phys. Rev. C 70 (2004) 044907, nucl-th/0312024]. The positions and velocities of the particles are randomly generated on the hypersurface according to the statistical (Bose–Einstein of Fermi–Dirac) distribution factors. All particles, stable and unstable, are included. The particles move along classical trajectories from their initial positions, with velocities composed of the thermal motion and the collective expansion of the system. Stable particles just stream freely, while the resonances decay after some (randomly generated) time, which is controlled by the particles lifetime. The decays are two-body or three-body, and their implementation involves simple kinematic formulas. The decays can proceed in cascades, down to the stage where only stable particles are present. All particles have tags indicating their parent. The secondary rescatterings are not considered in this approach. Full history of the event is stored in an output file, allowing for a detailed examination of the space–time evolutions and the calculation of the transverse-momentum spectra. Additional comment: The ongoing analyses of the SPS and the RHIC data as well as the future heavy-ion program at LHC will certainly benefit from THERMINATOR as a tool for generating events in a simple statistical model. The Monte Carlo code written in c++ and using the standard ROOT [R. Brun, F. Rademakers, Nucl. Instrum. Methods A 389 (1997) 81, http://root.cern.ch] environment can be easily adapted to purposes directly linked to experimental data analyses. The space–time tracking capability will allow, in the framework of the statistical approach, to better understand the physics of relativistic heavy-ion collisions. THERMINATOR calculates the particle spectra and other observables related to the space–time evolution of the system. It provides a c++ framework which may be easily developed for detailed analyses of more involved observables such as, e.g., correlation functions or HBT radii. Typical running time: The generation of 500 events from scratch takes about 1 hour 15 minutes on a PC with Athlon-Barthon 2.5 GHz under Red Hat Fedora 3. Each subsequent 500 events take about 1 hour. To store 500 events about 1.1 GB disk storage is needed, depending on the kinematic range. After converting the output to the ROOT TTree format, 900 MB may be freed.

Uniform Description of Soft Observables in Heavy-Ion Collisions at {radical}(s{sub NN})=200 GeV

We investigate the role of the initial condition used for the hydrodynamic evolution of the system formed in ultra-relativistic heavy-ion collisions and find that an appropriate choice motivated by the models of early-stage dynamics, specifically a simple two-dimensional Gaussian profile, leads to a uniform description of soft observables measured in the Relativistic Heavy-Ion Collider (RHIC). In particular, the transverse-momentum spectra, the elliptic-flow, and the Hanbury-Brown--Twiss correlation radii, including the ratio R_out/R_side as well as the dependence of the radii on the azimuthal angle (azHBT), are properly described. We use the perfect-fluid hydrodynamics with a realistic equation of state based on lattice calculations and the hadronic gas at high and low temperatures, respectively. We also show that the inclusion of the partonic free-streaming in the early stage allows to delay the start of the hydrodynamical description to comfortable times of the order of 1 fm/c. Free streaming broadens the initial energy-density profile, but generates the initial transverse and elliptic flow. The data may be described equally well when the hydrodynamics is started early, or with a delay due to partonic free-streaming.

Femtoscopy in hydrodynamics-inspired models with resonances

Effects of the choice of the freeze-out hypersurface and resonance decays on the Hanbury-Brown-Twiss (HBT) interferometry in relativistic heavy-ion collisions are studied in detail within a class of models with single freeze-out. The Monte-Carlo method, as implemented in THERMINATOR, is used to generate hadronic events describing production of particles from a thermalized and expanding source. All well-established hadronic resonances are included in the analysis as their role is crucial at large freeze-out temperatures. We find that presence of the the short-lived resonances increase the pionic HBT radii by about 1 fm. We use the two-particle method to extract the correlation functions, which allows us to study the Coulomb effects. We find that the pion HBT data from the Relativistic Heavy Ion Collider are fully compatible with the single freeze-out scenario, pointing at the shape of the freeze-out hypersurface where the transverse radius is decreasing with time. Results for the single-particle spectra for this situation are also presented. Finally, we present predictions for the kaon femtoscopy.

The STAR silicon strip detector (SSD)

Abstract The STAR Silicon Strip Detector (SSD) completes the three layers of the Silicon Vertex Tracker (SVT) to make an inner tracking system located inside the Time Projection Chamber (TPC). This additional fourth layer provides two-dimensional hit position and energy loss measurements for charged particles, improving the extrapolation of TPC tracks through SVT hits. To match the high multiplicity of central Au+Au collisions at RHIC the double-sided silicon strip technology was chosen which makes the SSD a half-million channels detector. Dedicated electronics have been designed for both readout and control. Also a novel technique of bonding, the Tape Automated Bonding, was used to fulfill the large number of bounds to be done. All aspects of the SSD are shortly described here and test performances of produced detection modules as well as simulated results on hit reconstruction are given.The STAR Silicon Strip Detector (SSD) completes the three layers of the Silicon Vertex Tracker (SVT) to make an inner tracking system located inside the Time Projection Chamber (TPC). This additional fourth layer provides two dimensional hit position and energy loss measurements for charged particles, improving the extrapolation of TPC tracks through SVT hits. To match the high multiplicity of central Au+Au collisions at RHIC the double sided silicon strip technology was chosen which makes the SSD a half million channels detector. Dedicated electronics have been designed for both readout and control. Also a novel technique of bonding, the Tape Automated Bonding (TAB), was used to fullfill the large number of bounds to be done. All aspects of the SSD are shortly described here and test performances of produced detection modules as well as simulated results on hit reconstruction are given.

Extracting baryon-antibaryon strong-interaction potentials frompΛ¯femtoscopic correlation functions

The STAR experiment has measured

Pion, kaon, and proton femtoscopy in Pb-Pb collisions at s NN = 2.76 TeV modeled in (3+1)D hydrodynamics

p\Lambda

Signatures of collective flow in high multiplicity pp collisions

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Operation and calibration of the Silicon Drift Detectors of the ALICE experiment during the 2008 cosmic ray data taking period

\bar{p}\bar{\Lambda}

Non-identical particle femtoscopy in models with single freeze-out

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Describing transverse dynamics and space-time evolution at RHIC in a hydrodynamic model with statistical hadronization

\bar{p}\Lambda