Participation of JINR team in the physics of ALICE experiment at LHC (CERN) A.Vodopianov JINR Scientific Council 21 January 2005

ALICE Collaboration ~ 1000 Members (63% from CERN MS) ~30 Countries ~80 Institutes

The ALICE Experiment ITS Low p t tracking Vertexing ITS Low p t tracking Vertexing TPC Tracking, dE/dx TPC Tracking, dE/dx TRD Electron ID TRD Electron ID TOF PID ( K, p, p ) TOF PID ( K, p, p ) HMPID PID high p t HMPID PID high p t PHOS g,  0 PHOS g,  0 MUON m + m - pairs MUON m + m - pairs PMD g multiplicity PMD g multiplicity

JINR participation in ALICE construction Dimuon Spectrometer:  Design of the Dipole Magnet;  Construction of the Yoke of the Dipole Magnet;  Participation in test beam data analysis;  Physics Simulation; Photon Spectrometer (PHOS):  Delivery of PWO crystals (collaboration w/ Kharkov, Ukraine);  Participation in beam tests at CERN;  Beam test data analysis;  Preparation for beam tests at BNL; Transition Radiation Detector (TRD):  Construction and tests of 100 drift chambers;  Participation in beam tests at CERN;  Physics Simulation;

TRD: Chamber production in Heidelberg, GSI, Dubna, Bucharest Chamber production lab in JINR Electronics and MCM bonding at FZ Karlsruhe Chamber production in Heidelberg

for photons, neutral mesons and  -jet tagging PbW0 4 : Very dense: X 0 < 0.9 cm Good energy resolution: stochastic 2.7%/E 1/2 noise 2.5%/E constant 1.3% Photon Spectrometer PbW0 4 crystal single arm em calorimeter – dense, high granularity crystals; novel material: PbW0 4 ; – ~ 18 k channels; ~ 8m 2 ; – cooled to -25 o C;

Dimuon Spectrometer Study the production of the J/ ,  ', ,  ' and  '’ decaying in 2 muons, 2.4 <  < 4 Resolution of 70 MeV at the J/  and 100 MeV at the  Dipole Magnet: bending power 3 Tm Complex absorber/small angle shield system to minimize background (90 cm from vertex) RPC Trigger Chambers 5 stations of high granularity pad tracking chambers, over 1200k channels

Dipole Magnet assembled and successfully tested, November 2004

t = - 3 fm/c t = 0 t = 1 fm/c t = 5 fm/c t = 10 fm/c t = 40 fm/c Heavy Ion Collision hard collisions pre-equilibrium QGP hadron gas freeze-out

Study of Quark-Gluon Plasma is the main goal of ALICE experiment

Signatures of quark-gluon plasma  Dilepton enhancement (Shuryak, 1978)  Strangeness enhancement (Muller & Rafelski, 1982)  J/Ψ suppression (Matsui, Satz, 1986)  Pion interferometry (Pratt; Bertsch, 1986)  Elliptic flow (Ollitrault, 1992)  Jet quenching (Gyulassy & Wang, 1992)  Net baryon and charge fluctuations (Jeon & Koch; Asakawa, Heinz & Muller, 2000)  Quark number scaling of hadron elliptic flows (Voloshin 2002)  ……………

Experimental Facilities AGS ( )  Beam: E lab < 15 GeV/N,  s ~ 4 GeV/N  Users: 400 Experiments: 4 big, several small SPS( )  Beam: E lab < 200 GeV/N,  s < 20 GeV/N  Users: 600Experiments: 6-7 big, several small RHIC(>2000)  Beam:  s < 200 GeV/N  Users: 1000  Experiments: 2 big, 2 small LHC(>2007)  Beam:  s < 5500 GeV/N  Users: 1000  Experiments: 1 dedicated HI, 3 pp expts X 5X 10X 30

LHC as Ion Collider Running conditions: + other collision systems: pA, lighter ions (Sn, Kr, Ar, O) & energies 5.5 TeV). Collision system PbPb pp /L 0 (%) 10 7 Run time (s/year)  geom. (b) L 0 (cm -2 s -1 ) √s NN (TeV) * ** *L max (ALICE) = ** L int (ALICE) ~ 0.7 nb -1 /year

From SPS to RHIC to LHC ‘hotter – bigger – longer lived’ <0.2~0.5~1  0 (fm/c) 4–101.5–4.0<1  QGP (fm/c) 2x10 4 7x V f (fm 3 ) 15–404–54–52.5  (GeV/fm 3 ) 2–8x dN ch /dy s 1/2 (GeV) LHCRHICSPS Central collisions Formation time τ 0 3 times shorter than RHIC Lifetime of QGP τ QGP factor 3 longer than RHIC Initial energy density ε 0 3 to 10 higher than RHIC

ALICE Physics Goals ALICE PPR, 2004, J. Phys. G: Nucl. Part. Phys. 30, ➮ Heavy ion observables in ALICE  Particle multiplicities  Particle spectra  Particle correlations  Fluctuations  Jet physics  Direct photons  Dileptons  Heavy-quark and quarkonium production ➮ p-p and p-A physics in ALICE ➮ Physics of ultra-peripheral heavy ion collisions ➮ Contribution of ALICE to cosmic-ray physics

Charmonium (J/ ,  c,  ') production (theory & experiment) The production of J/  and other charmonium states would be suppressed because of: -- dissociation by impact of gluons at the pre-resonance stage. (D. Kharzeev et al. Z. Phys. C 74 (1997) 307.) -- an absorbtion via the interaction in the hot and dense nuclear matter. (N.Armesto et al. Phys.Rev. C 59(1999) 395; J.Geiss et al. Phys.Lett. B 447 (1999) 31) -- Debye screening of the quark colour charge in the QGP stage, (T.Matsui, H.Satz. Phys.Lett. B178(1986) or in the pre-QGP stage (mixed phase) via creation of the percolation clusters in the parton percolation model (favorable in last few years) (M.Nardi, H.Zatz. Phys.Lett. B 442(1998)14; S.Digal, S.Fortunato, H.Satz. BI-TP 2003/30.)..

Parton percolation model: The expected evolution of nuclear collision. Partonic cluster structure in the transverse collision plane. Full QGP stage is reached if the temperature and the density is sufficient, otherwise in the pre-equilibrium stage the local clusters only with QGP inside are created by the percolation mechanizm, i.e. the mixed phase (of partons and hadrons) appears. The Lorentz-contraction makes the nuclei as two thin disks during 0.1 fm at RHIC. Parton density increases with overlapping of partons and creation of percolation clusters - the condensate of deconfined partons. The percolation condition is n p = N  r 2 /  R 2  where N is number of partons with size r ( r is found from the uncertainty relation  r 2   /, k T - partron momentum), R is nuclear radius (R » r)

The fractional cluster size and its derivative as function of the parton density n. The cluster size shows the critical behavior, since it increases suddenly near the critical parton density n p, i.e. percolation condition starts from some experimental ones : A - number, energy, centrality of the A-A collision. Charmonium suppression. The tipical time of fm needs for formation of the charmonium and also of the parton condensate. If the charmonium is created inside the percolation cluster it can be dissociated by the colour charge screening if r s < r ch, where r s and r ch are the screening and charmonium radii respectively. The charmonium radii are: r J/   (0.9 GeV) -1, r   (0.6GeV) -1,r  ’  (0.45 GeV) -1. The screening radius is r s = 1/Q s, Q s is screening scale depending from the parton dencity.

Charmonium dissociation as function of centrality. The measured J/p suppression as function of centrality from NA-50 experiment at SPS. S/S n     The screening scale Q s has the critical behaviour from the centrality (N part is the number of nucleon - participants). The charmonium dissociation has two steps in the SPS: for  and  c at N part  150 (blue arrow) and for J/  at N part  250 ( green arrow) No such behaviour is predicted at the RHIC and particulaly at the LHC. S =  (J/  )/  (DY) S n = S for p-A collisions described by the normal absorptions in the nuclear matter (‘normal’ suppression). Two drops of ‘anomalous’ suppression in Pb-Pb are seen at N part  150 and at N part  250 in correspondence to the prediction. There is also prediction of strong  suppression but the experimental results are still absent.

J/    +  - and     detection in ALICE Effective mass spectra of (     ) pairs Muon pairs will be detected in the ALICE forward muon spectrometer in the pseudorapidity interval 2.5 <  < 4 and with the mass resolutions about 70 (100) MeV/c 2 for J/  (  ). The simulation was carried out for 10% more central Pb-Pb events by the fast code including acceptance cuts and detector efficiencies and resolutions. The statistics corresponds to the one month running time at the luminosity of 5  cm -2 s  10 5 J   at S/B = 0.72, 1800   at S/B = 7.1, 540   at S/B = 2.5, 260   at S/B = 1.5. All other muon sources (the decays of , K, D, B) were included in the simulation. The trigger cut for muon p t > 1.0 GeV/c was used.

J/   e + e - detection in ALICE. To study J/  e + e - (at |  | < 1) the TRD and TPC will be used. To find the suppression factor the comparison with a production of open charm particles is supposed (selection of Drell-Yan process is problematical). The preliminary simulation was done for 5  10 5 Pb-Pb central events using the TRD for electron identification. J/  S/B = 0.5 (e+e-) J/  production at 2.5 < p t < 4 GeV/c J/  J/  production from B meson decay (must be taken into account because they are not suppressed)

Light vector mesons production ( , ,  ) (theory & experiment) -- The enhancement of  yield ( N  /(N  +N  ) ) in central Pb-Pb events as compared to p-p and p-A interactions: up to factor 10 because the supression of Okubo-Zweig-Iizuka rule and a large abundance of strange quarks in the QGP, (A.Shor. Phys.Rev.Lett. 54 (1985) 1122). up to factors 3-4 because the secondary collisions in the nuclear matter (if QGP is not reached). (P.Koch et al. Z.Phys. C 47 (1990) 477). The experimental result is 3.0±0.7 for Pb-Pb at E beam =158 A GeV (NA-49, CERN, SPS)..

Light vector mesons production( , ,  ) (theory & experiment) -- The significant decrease of  and  masses (by factor up to 150 MeV/c 2 ) because partial chiral symmetry restoration in the QGP stage (small effect is for  since the isospin structure differs from the  one). The effect may be seen in leptonic decay mode (no interactions in the nuclear matter) and only for  e + e - in ALICE (  peak is not seen in the level of high combinatorial background since the width is too large). ( M.Asakava, C.M.Ko. Phys,Lett. B 332 (1994) 33) The experimental result shows an evidence of the mass shift for  0  e + e - in Pb-Pb at 160 A GeV (NA-45, CERN, SPS)..

Light vector mesons production( , ,  ) (theory & experiment) --The increase of  width by factor 2-3 because of: - Decrease of kaon mass as a consequence of chiral symmetry restoration near the temperature of phase transition to QGP. (D.Lissauer and E.Shuryak. Phys.Lett. B 253 (1991) 15) -- Rescattering of kaons from  decays in the hot and dense nuclear matter. (C.Jonson et al. Phys. Journ. C 18 (2001) 645) The effect may be seen in ALICE by studing of  K + K - decays or by comparison of this decay mode with the  e + e -. There is no experimental evidence for this effect. But 30% difference was found in the slope of pt spectra for  meson obtained from (K + K - ) or (  +  - ) decay modes (in the Pb-Pb at 158 A GeV, CERN SPS). This effect may be explained by the rescattering of kaons in the nuclear matter.

Light vector mesons detection in ALICE. To detect the  e+e-,  e+e-,  K+K- decays the ITS, TPC, TOF and TRD of ALICE will be used for tracking and particle identificatuon. The simulation was done for the ITS, TPC and TOF using the GEANT-3, HIJING model and the last experimental data (the TRD will be included as well). To select the resonance peaks from very high combinatorial background the special cuts were used. Background before the cuts   After the specials cut (S/B = 0.05) For 5  10 7 Pb-Pb central events (one month ALICE run)

Light vector mesons detction in ALICE. To study the  K + K - decays the ITS, TPC and TOF were applied for the simulation To select the resonance peaks from the combinatorial background the cuts were used for p t of (K + K - ) pair. For 10 6 Pb-Pb central events. S/B = 0.06  signal after (K+K+) background subtraction with the gaussian fit. The fit results are for the  : mass =  0.04 MeV/c 2, widht = 4.43  0.12 MeV/c 2

Momentum correlations (HBT) Formalism: CF=1+(-1) S  cos q  x  where S = j 2, j - spin 4vectors: q = p 1 - p 2,  x = x 1 - x 2 S(Qinv) yield of pairs from same event B(Qinv) pairs from “mixed” event N normalization factor, used to normalize the CF to be unity at large, l - ‘longitudional’ (beam) direction; o - ‘outward’ direction parallel to transverse pair velocity; s - ‘sideward’ direction transverse to ‘longitudional’ and ‘outward’ In practice: Projections of the momentum difference q l, q o, q s are used to the correspondence axis: Following to Richard Hanbury-Brown and Robert Twiss (HBT) method for an estimation of star sizes JINR physicists G.I.Kopylov & M.I.Podgorecky suggested to study the space - time parameters of sources producing identical particles using the correlation function with Bose- Einstein interferometric effect : (space-time sizes )

Transport models and hydro calculations strongly overestimate out and long radii at RHIC. The RHIC data thus points to a new physics: Explosive fireball decay ? Momentum correlations (HBT) HBT radii decrease with k T (strong flow) HBT radii increase with increasing centrality (geometrical radius also increases R O / R S ~ 1 (short emission duration) No significant changes in correlation radii AGS  SPS  RHIC (5 - 6 fm) RHIC correlations results & “HBT Puzzle” HBT and the QGP · Pratt PRD 1314 (`86): fireball + EOS (Equation of State):  ~ 90 fm/c ( long emission duration) · Bertsch NPA 173 (89) QGP + cascade:  ~ 12 fm/c (long emission duration) · Hydro calculation of Rischke &Gyulassy NPA 608 (1996) 479: Rout/Rside ~ · Soff, Bass, Dumitru (PRL86) microscopic transport + hydro with phase transition: Still expect Rout/Rside>1 AGS: SPSRHIC (  - time of emission duration)

Momentum correlations (HBT) Simulations of particle correlations in ALICE. The different particles systems that can be study by ALICE simulation chain using Lednicky’s algorithm. It performs the calculation of the weight of particle pair according with quantum statistic and FSI effects.

Influence of particles identification and resolutions effects in ALICE detectors: TPC, ITS, TOF on correlation functions was studied using HIJING model and Lednitsky’s algorithm for calculation of particle correlations. To study particle correlations the ITS, TPC, TOF and TRD of ALICE will be used for tracking and particle identification. The simulation was done for the ITS, TPC and TOF using the GEANT code. Example: Qinv for CF of (π,π). Perfect PID, resolution effects in TPC only, PID by dE/dx in TPC and impact parameter of the track Momentum correlations (HBT) Example: Qinv for CF of (K+,K-). Perfect PID, resolution effects in TPC only

HBT for direct photons The direct photon interferometry is important for investigation of the very early phase of heavy ion collisions. The following correlation function is considerd: (WA98, CERN. M.Aggarwal et al. Phys.Rev.Lett (2004)) 1) The radius R inv = 5.4  0.8 fm is near to the one for charged pions. 2)The yield of direct photons was extracted from the equation Yield of direct photons versus p T. The results show dominant contribution to the hadronic phase of the direct photon emission.

Detection of Upsilons in p-Pb and Pb-p collisions at ALICE muon spectrometer. Analysis of minibias events. bb̃ BGR & Signal Pb-p p-Pb

Analysis ( p t m > 3GeV/c) bb̃ BGR & Signal p-Pb Pb-p

ALICE COMPUTING 2003 JINR team took responsibility to organize the Physics Data Challenge for all ALICE Institutes situated in Russia; Physics Data Challenge: March - August events processed; LHC Computing GRID (LCG) activity (deployment, test)

Configuration of AliEn sites in Russia 04Q2 – >4 AliEn operators at work stations CERN server INR IHEP SPbSUPNPIKIAEJINR ITEP

Brief analysis of currently available data on Physics Data Challenge (2004) Processed jobs by JINR ~ 2500 (2.0%) Erroneous jobs on JINR site ~ 404 possible explanation – the RAM capacity of 2 processors batch node (512MB) is insufficient for processing of two AliRoot jobs. Large swap. About 10 times more computing power and disk space will be needed for data analysis in 2008!!!

Participation of JINR team in ALICE physics was presented on seminars, workshops and conferences: 2003: 1.M.K.Suleimanov, …, A.A.Kuznetsov, A.S.Vodopianov, Analysis of the characteristics of nucleus-nucleus collisions depending on the centrality, Talk presented on VIII International Conference on Nucleus-Nucleus Collisions, June 2003, Moscow, Russia. 2004: 1.A. Vodopianov, Status of the ALICE detector (Invited talk), International Workshop “Quantum Fields and Particles –3”, Baku, September B.Batyunya, …, S.Zaporozhets. Simulation of  ->K+K- detection in ALICE experiment. Presentation on XVII International Seminar on High Energy Physics Problems, Dubna, Yu. Kharlov, …, Yu.Bugaenko, V.Korenkov, V.Mitsyn, G.Shabratova et al, Participation nof Russian Sites in the Data Challenge of Alice Experiment in CHEP-04 “Computing in High Energy and Nuclear Physics” 2004, Interlaken, Switzerland, September A.Zinchenko, G.Chabratova, V.Pismennaya, A.Vodopianov. Development of Algorithms for Cluster Finding and Track Reconstruction in the Forward Muon Spectrometer of ALICE experiment. CHEP-04 “Computing in High Energy and Nuclear Physics” 2004, Interlaken, Switzerland, September 2004.

Participation of young physicists in ALICE JINR team Romaina2 persons; Russia3 persons; Ukraine1 person;

Joint Workshop on ALICE physics with physicists of Laboratory of Theoretical Physics will take place spring 2005

CONCLUSION Participation of JINR team in ALICE physics is based on: 1.Contribution to design and construction of particular ALICE sub- detectors; 2.Long term participation in the physics and detector simulation; 3.Practical knowledge and experience in using of distributed computing (GRIID & LCG) for data analysis. Achievements of JINR team are recognized by ALICE. JINR team has leading positions in some physics tasks. End 2004 four physics groups were named in ALICE (beginning!). Convener of one of these groups is JINR physicist Y. Belikov. JINR team presents scientific results on workshops & conferences. It is planned that the most of the data analysis carried by JINR, will be done at Dubna. Computing power has to be increased by about 10 times.