Identified particles in pp and Pb-Pb collisions at LHC energies with the ALICE Detector

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1 Identified particles in pp and Pb-Pb collisions at LHC energies with the ALICE Detector Michele Floris on behalf of ALICE Collaboration CERN, Geneva, Switzerland 26/05/2011 Quark Matter 2011

2 Outline What I will cover Low to intermediate p T Spectra and Yields Cascades Resonances More on identified particles High P T PID (Raa) See H. Appelshaeuser (25 May) Anisotropic flow PID See R. Snellings (24 May) Brief reminder: PID in ALICE Results in pp collsions at s = 900 GeV and 7 TeV Results in Pb-Pb collisions at s NN = 2.76 TeV Outlook 26 May 2011 M. Floris - QM2011 2

3 PID in ALICE Inner tracking system Low pt standalone tracker PID: de/dx in the silicon (up to 4 samples) TPC Standalone and global (+ITS) tracks PID: de/dx in the gas (up to 159 samples) Time of Flight Matching of tracks extrapolated from TPC PID: TOF, stot ~ 85 ps (PbPb) 120 ps (pp) Topological ID + Invariant Mass Resonances, Cascades, V0s, Kinks PID: indirect cuts to improve S/B See A. Kalweit (23 May) See L. Milano (Poster) 26 May 2011 M. Floris - QM2011 3

4 s = 7 TeV New Results

5 p/k/p spectra K + p + p Different techniques used Minimum p T = 0.1 / 0.2 / 0.3 GeV/c for p/k/p (small extrapolation for yields and <p T > calculation) MC models: poor description of data Ratios similar at different energies K/p p/p 26 May 2011 M. Floris - QM2011 5

6 <p T > and K/p p/p ratios Modest increase of <p T > Harder spectra Integrated and p T differential particle ratios ~ independent of energy between 0.9 and 7 TeV See M Chojnacki (23 May) 26 May 2011 M. Floris - QM2011 6

7 Resonances f/k - K*/K S 0 K * (892) 0 Kp f (1020) KK X * (1530) Xp Invariant mass studies Ratios ~ constant vs s See A Pulvirenti (23 May) f (1020) mm (fwd rapidity) Slope consistent with f KK See A De Falco(23 May) 26 May 2011 M. Floris - QM2011 7

8 Cascades W X Measured via topological identification MC models underestimate strangeness production (factor 10 for the W in the measured range) X: ALICE and CMS agree (taking into account NSD/INEL) See DD Chinellato (23 May) 26 May 2011 M. Floris - QM2011 8

9 Thermal Fits Fit to 900 GeV data (arxiv: ) T = 161 MeV R = R c = 1.37 fm g s = 1 (fixed) m B = 2.6 MeV THERMUS: Comput. Phys. Commun 180, 84, May 2011 M. Floris - QM2011 9

10 L/K 0S 900 GeV h < 1 y < 0.75 PbPb Results s = 2.76 TeV - very good agreement between STAR (200 GeV) and ALICE (900 GeV) - very different from CDF (630/1800) and UA1 (630) for p T > 1.5 GeV - UA1(630) and CDF(630) don t agree either to be further investigated (different triggers, acceptance, feed-down correction?)

11 PbPb: Centrality & Crosschecks Centrality bins: See A. Toia (24 May) K +/- vs K 0 s p in the relativistic rise: nice continuation of low p T analysis Agreement of charged kaons and K 0 s See A. Kalweit (23 May) 26 May 2011 M. Floris - QM

12 Baryon/Meson ratio: L / K S 0 Baryons produced more easily at intermediate p T Baryon/meson ratio increases with centrality Recombination? Enhancement stronger that at RHIC (L feed down corrected in this study) Maximum of L/K slightly pushed towards higher p T than at RHIC: higher radial flow? Dramatic shift of baryon enhancement, O(1-2) GeV predicted by some models (e.g. EPJC C34, s279, 2004) not seen See J Belikov (23 May) 26 May 2011 M. Floris - QM

13 p/k/p Spectra Combined analysis in Inner Tracking System Time Projection Chamber TOF p T Range: GeV/c (p) GeV/c (K) GeV/c (p) Blast wave fits to individual particles to extract yields 26 May 2011 M. Floris - QM

14 Comparison to RHIC (0-5% Central) positive negative At RHIC: STAR proton data generally not feed-down corrected. Large feed down correction Consistent picture with feed-down corrected spectra At LHC: ALICE spectra are feed-down corrected Harder spectra, flatter p at low pt Strong push on the p due to radial flow? STAR, PRL97, (2006) STAR, PRC 79, (2009) PHENIX, PRC69, (2004) 26 May 2011 M. Floris - QM

15 Mean p T Mean p T increases linearly with mass Higher than at RHIC (harder spectra, more flow?) For the same dn/dh higher mean p T than at RHIC 26 May 2011 M. Floris - QM

16 Blast wave fits PRC48, 2462 (1993). Blast wave fits radial flow ~ 10% higher than at RHIC Fit Range: pions GeV kaons GeV protons GeV T depends on the pions and fit-range (effect of resonances to be investigated) 26 May 2011 M. Floris - QM

17 p/p ratio vs p T p/p: similar trend at RHIC Saturates at higher p T than at RHIC similar to L/K 0 Stronger push from radial flow? STAR, PRC 79, (2009) PHENIX, PRC69, (2004) 26 May 2011 M. Floris - QM

18 L and p comparison Lambda very similar to protons in shape and yield Feed-down correction: p corrected for weak decays L corrected for f.d. from the X this was similar at RHIC, if one compares feed-down corrected spectra STAR, PRL98, (2007) PHENIX, PRC69, (2004) 26 May 2011 M. Floris - QM

19 Integrated yields ratios p + /p - p/p All +/- ratios are compatible with 1 at all centralities, as expected at LHC energies K + /K - STAR, PRC 79, (2009) 26 May 2011 M. Floris - QM

20 Integrated ratios vs Centrality STAR (Not feed-down corrected) p/p - K - /p - ALICE, BRAHMS, PHENIX (feed-down corrected) Predictions for the LHC Ratio Data (1) (2) p/p + p/p and K/p ratios are very similar at RHIC energies p/p K/p K/p STAR, PRC 79, (2009 PHENIX, PRC69, (2004 BRAHMS, PRC72, (2005 (1) A. Andronic et al, Nucl. Phys. A (2006) (2) J. Cleymans et al, PRC74, (2006) T = 164 MeV, m B = 1 MeV T = (170±5) MeV and μ B =1+4 MeV

21 Outlook: much more to come! Strangeness Resonances Anti- and Hyper-Nuclei Counts / 1 MeV/c 2 Raw Counts See N Sharma (Poster) See B Doenigus (Poster) 26 May 2011 M. Floris - QM

22 Summary ALICE has very good capabilities for the measurement of identified particles pp Collisions Measurements at s = 900 GeV and 7 TeV Particle ratios independent of energy PbPb Collision Spectral shapes show much stronger radial flow than at RHIC Baryon/meson anomaly: enhancement slightly higher and pushed to higher p T than at RHIC p/p 0.05 in pp and PbPb collisions Difficult to understand in a thermal model prediction with T = MeV 26 May 2011 M. Floris - QM

23 The ALICE Collaboration 33 countries, 116 institutes, 1000 members

24 Geant3 vs Fluka Efficiencies 26 May 2011 M. Floris - QM

25 K/p ratio vs p T (0-5% central) K/p ratio vs p T is very similar at RHIC and LHC energies STAR, PRC 79, (2009) PHENIX, PRC69, (2004) 26 May 2011 M. Floris - QM

26 Thermal RHIC A. Andronic, (Mon 23) 26 May 2011 M. Floris - QM

27 R. Stock May May 2011 M. Floris - QM

28 Negative Spectra 26 May 2011 M. Floris - QM

29 Feed-down correction Distance of closest approach fitted with MC templates 26 May 2011 M. Floris - QM

30 Blast Wave E d 3 N e (u m p m )/T fo pds dp 3 m s dn m rdrm T K T cosh R p 1 I T sinh 0 0 m T dm T T fo T fo r tanh 1 T T S R 0.5, 1, 2 Free parameters: T fo,, E.Schnedermann, J.Sollfrank, and U.Heinz, Phys. Rev. C48, 2462(1993). 26 May 2011 M. Floris - QM

31 Lambda at RHIC PRL (2004) 26 May 2011 M. Floris - QM

32 Hydro + Hadronic Cascade VISHNU: PRC 83, (2011) 26 May 2011 M. Floris - QM

33 R.J.Fries and B.Muller, Eur. Phys. J C34, s279 s285 (2004) 26 May 2011 M. Floris - QM

34 v 2 for identified particles See R. Snellings (24 May) 26 May 2011 M. Floris - QM