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Identified particle studies at the LHC with the ALICE experiment

Identified particle studies at the LHC with the ALICE experiment. P. Foka a on behalf of Panos Christakoglou b,c for the ALICE Collaboration a GSI b NIKHEF c Utrecht University. Introduction.

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Identified particle studies at the LHC with the ALICE experiment

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  1. Identified particle studies at the LHC with the ALICE experiment P. Fokaa on behalf of Panos Christakogloub,c for the ALICE Collaboration a GSI b NIKHEF c Utrecht University Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  2. Introduction • ALICE is designed to study the physics of the strongly interacting matter, the Quark Gluon Plasma, produced in nucleus-nucleus collisions at the LHC • The physics program of ALICE has already started with the study of proton-proton collisions at unprecedented high energies: • calibrate and prepare our detectors for the future heavy-ion collisions, • the measured properties of these collisions will set the baseline for the nucleus-nucleus collisions, • what are the properties of high multiplicity events (collectivity, flow)? • In this talk: results from pp collisions at √s = 0.9 and 7 TeV • identified particles • pbar/p ratio Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  3. ALICE @ the LHC Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  4. PID in ALICE • PID for hadrons in the central barrel (|η| < 0.9) • ITS: Excellent (3σ) separation from ~50 MeV/c for π • TPC: π from 200 MeV/c, Κ from 300 MeV/c • TOF: K from 500 MeV/c up to 2.5 GeV/c, p up to 3.5 GeV/c • HMPID: intermediate to high momenta (up to 5 GeV/c) • Photons with the dedicated spectrometer (PHOS - |η| < 0.12) • Electrons in the central barrel: • ITS + TPC for low momentum • TRD from P ~ 1GeV/c (beauty measurements feasible even @1GeV/c!) • Muons reconstructed in the forward region (muon arm: -4 < η < -2.4) • Strange particles identified via their topology For more details see the talk of Orlando Villalobos PID – momentum reach Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  5. ITS commissioning • Design goals • Optimal resolution for primary vertex and track impact parameter • Minimize distance of innermost layer from beam axis (<r>≈ 3.9 cm) and material budget • Maximum occupancy (central PbPb) < few % • dE/dx information in the 4 outermost layers for particle ID in 1/β2 region • Installed in 2007. • Successfully commissioned during the cosmics runs in 2008 and 2009. For more details see the talk of Emanuelle Biolcati dE/dx resolution ~ 13% Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  6. TPC commissioning • Main TPC characteristics • Cylindrical in shape, with an active volume that has an inner radius of about 85 cm, an outer radius of about 250 cm, and an overall length along the beam direction of 500 cm (largest TPC ever built) • Cylindrical field cage filled with ~90 m3 of Ne/CO2/N2 gas mixture (90:10:5) • Drift time of ~90 μs • Many (>90) 3D points (+dE/dx) per track • Since August 2009 more than 750 million events (cosmics, krypton, and laser) recorded, with and without B-field. • First round of calibrations (dE/dx, momentum, alignment, gain) completed before collisions. Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  7. TPC particle identification September 2009 (cosmic) December 2009 (cosmic) J. Alme et al. (ALICE TPC), arXiv:1001.1950 (subm. to NIM) dE/dx resolution ~ 5-6% Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  8. TOF • 18 sectors, 2π covering in |η| < 0.9 • Granularity: 2.5x3.5 cm2 at ∼3.7 m from the primary vertex; • Fully installed • 95% channels operational • Resolution at present ∼90 ps Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  9. p K p 6 ways to measure Kaons • Kaons from kinks • K0s decaying into a pair of pions • ITS, TPC, TOF, HMPID π- kinks Kaon pT distributions stable & decays HMPID K → m n K0S → pp • Data collected in December 2009 pp @ √s = 900 GeV • Good agreement between the 3 detectors (ITS, TPC, TOF) • Shows that detectors’ calibration/understanding and analysis methods are OK • Statistics not sufficient for more differential studies Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  10. Identified particle spectra – Tsallis fit Combined spectra (ITS+TPC+TOF) • pp @ LHC: multiplicity ≈ AA collisions at lower √s • Does collective behavior develop with multiplicity? • Tsallis Blast Wave (PRC79 051901, 2009) • Boltzmann-Gibbs statistics replaced by “Tsallis statistics” • Adds one parameter q (quantifies degree of non equilibrium) • ITS included in these plots • Provides a significant reduction of the extrapolation to zero pt • Constrains models (e.g. flow) ~250K collision candidates at 900GeV (December 2009) > 100M collision candidates at 7TeV (March2010 - …) Ongoing study @ 7TeV (possibility for differential analysis – high statistics) Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  11. Prospects for the spectra measurements Baryo-chemical potential μB and Chemical freeze-out Temperature Tch I.Kraus et al., in arXiv0711.0974 [hep-ph] Expectations at LHC: Tch =161±4 MeV μB =0.8+1.2-0.6 MeV A.Andronic et al., Last Call for Predictions, in arXiv0711.0974 [hep-ph] I.Kraus et al., J.Phys.G32 (2006) S495 A.Andronic et al., Nucl. Phys. A772 (2006) 167 J.Rafelski et al., Eur. J. Phys. C45 (2006) 61 (non equilibrium) But the ratios can be used for other studies as well… Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  12. Baryon number transport – Motivation • Where does the conserved baryon number (BN) reappear after the pp collision? • G.C. Rossi and G. Veneziano, Nucl. Phys B123 (1977) 507. • B.Z. Kopeliovich and B. Zakharov, Z. Phys. C43 (1989) 241. • Different approaches based on theory: • Baryon considered as bound quark-diquark state within QGSM. BN transport implies breaking the diquark pair. • Gluonic mechanism aka String Junction (SJ). BN transport implies the stopping of the SJ. d u u String Junction u d • BN transport (asymmetry) even at large rapidity gaps (large energies). • Veneziano: Probability exponentially suppressed with aJ ~ 0.5 (aJ: J intercept) • Kopeliovich: Probability constant with rapidity u Conventional approach - QGSM • Within QGSM one expects no BN transport (an asymmetry ~0) at LHC energies • No BN transported at mid-rapidity from the fragmentation region u d Δy = ybeam – ybaryon = ‘rapidity loss’ SJ LHC’s large rapidity gap between the incoming protons (yp-max = ±9.6) will give us the opportunity to distinguish between the different models. u Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  13. p+p Au+Au 20% central BRAHMS: Phys. Lett. B607 (2005) 42 p+p - Au+Au @√s = 200GeV PYTHIA HIJING-B Baryon number transport – Experimental results Lessons from RHIC Lessons from HERA STAR: Phys.Rev.Lett.86 (2001) 4778 AuAu@√sNN = 130 GeV A. Falkiewicz: DIS2008, London • Proton excess at mid-rapidity can be attributed to the BN transport from the beam at RHIC energies • No sign of any rapidity or pt dependence • PYTHIA systematically overestimates the proton ratio • HIJING-B (includes a SJ formalism) describes the experimental data • Initially reported an asymmetry of ~8% for Δy ~ 7. • Results never published due to large systematic uncertainties caused by the high beam-gas rate. • Results reported at the DIS2008 are compatible with an asymmetry for Λs ~0 Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  14. Baryon number transport – Corrections Bendiscioli and Kharzeev, Riv.Nuovo Cim.17N6, 1-142 (1994) • Fluka in full agreement with the data • Clear disagreement between the experimentally measured values and the input curves of GEANT3-GEANT4 (data points lower by a factor of 2-3 depending on the momentum). • Recent physics lists provided by the G4 team reproduce the data points Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  15. Baryon number transport – Transverse momentum dependence • Results show no sign of any transverse momentum dependence for both energies. • Experimental points are compared with different model predictions that include variation of BN transport mechanisms: • PYTHIA tunes having a standard prescription for transferring the BN over large rapidity intervals (D6T, ATLAS-CSC, Perugia-0), describe the data well. • Perugia-SOFT underestimates the data points • HIJING-B clearly underestimates the pt dependence (particularly at the lower energy) K. Aamodt et al. [ALICE Collaboration], Phys. Rev. Lett. 105, 072002 (2010) Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  16. Baryon number transport – Energy dependence K. Aamodt et al. [ALICE Collaboration], Phys. Rev. Lett. 105, 072002 (2010) • Energy dependence of the ratio parameterized based on the contribution of different diagrams describing the p(bar) production (pair production at mid-rapidity and BN transfer) • Intercept of the Pomeron set to 1.2 based on fit on the energy dependence of the multiplicity. • Junction intercept fixed to 0.5 • The curve describes the (high energy) points well. • The lower ISR points are overestimated due to the contribution of yet another diagram which is suppressed at high energies. Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  17. Conclusion • ALICE in a very good shape • Most detectors perform close to specs • Physicist perform also close to specs • Pbar/p ratio published in PRL • Identified particle spectra paper under internal review • The identified particle spectra coming from different analyses/detectors agree remarkably well between each other. • Differential analysis (e.g. vs multiplicity) feasible with the large stats 7TeV sample  ongoing • The pbar/p ratio has been measured at both 0.9 and 7TeV • The data points favor the existence of the string junction with the value of the intercept of the J being 0.5 (Veneziano) • Models with additional transfer (QGSM with ε = 0.9, HIJING/B) are disfavored. Still ALICE being mainly a HI experiment, we look forward to November/December Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  18. BACKUP Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  19. ITS calibration and PID (SDD + SSD) • Charge distribution measured on all the SDD modules • ~95% of the detector included in the readout during data taking • Charge distribution measured on all the SSD modules • 90% of the detector active in 2009, (<1.5% bad strips) • S/N ~40 For more details see the talk of Emanuelle Biolcati dE/dx resolution ~ 13% Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

  20. Identified particle spectra • Data collected in December 2009 pp @ √s = 900 GeV • Good agreement between the 3 detectors (ITS, TPC, TOF) • Shows that detectors’ calibration/understanding and analysis methods are OK • Statistics not sufficient for more differential studies Panos.Christakoglou@cern.ch - Quark Confinement and the Hadron Spectrum IX

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