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Resonance results by the ALICE detector in pp and in Pb-Pb collisions at LHC energies

Resonance results by the ALICE detector in pp and in Pb-Pb collisions at LHC energies. Introduction – Resonances in medium ALICE performances Results in p-p @ 7 TeV (about 25-155X 10 6 of MB events) K*(892) 0 , (1020), Σ*(1385) ± , (1232) ++ , (1530) 0

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Resonance results by the ALICE detector in pp and in Pb-Pb collisions at LHC energies

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  1. Resonance results by the ALICE detector in pp and in Pb-Pb collisions at LHC energies • Introduction – Resonances in medium • ALICE performances • Results in p-p @ 7 TeV (about 25-155X 106 of MB events) • K*(892)0, (1020), Σ*(1385)±,(1232)++, (1530)0 • Results for (1020) in Pb-Pb collisions @ 2.76 ATeV (about 6x106 MB events) • Conclusions and Prospects • Badalà - INFN Sezione di Catania • for the ALICE collaboration 1 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  2. Resonance in heavy-ion collisions Resonances lifetimes of about a few fm/cresonance~ fireball t~10 fm/c Resonances may give information on the nuclear matter dynamics and chiral properties Regeneration and rescattering effectsTimescale chemical-kinetic freeze-out Modification of width, mass and branching ratio Space-time evolution of ultrarelativistic heavy ion collision 2 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  3. Resonances in p-p Collisions Decay of resonances large fraction of the final-state particles early step in understanding p-p collisions at LHC, i.e. opportunity to test QCD in a new energy domain • In general, resonance production in p-p collisions helps in • establishing the underlying event structure and the baseline for heavy-ion collisions • constraining QCD-inspired models (PYTHIA, PHOJET,etc…) • understanding hadronic production processes 3 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  4. ALICE Detector: Size: 16 x 26 meters Weight: 10,000 tons material budget 4

  5. Particle identification : Basic identification strategy: fit response function in pT bin TOF  ≈ 90 ps TPC dE/dx ≈5-6% pT range of separation within 3σ (GeV/c) For resonances, V0 and cascade analysis PID by a cut (3-5 ) on the relative difference between: TPC signal and Bethe-Bloch function TOF signal and integrated time 5 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  6. Resonance Reconstruction Reconstruction based on primary tracks or particles (cut on DCA) , K, p identified via TPC and TOF detectors (1232)++  p++ (1520)0  p + K- (1385)±  0 + p± (1530)0  - + p+  identified bysecondarytracks, with opposite charges, within a fiducial volume, + “V0 topology” K+ K*  identified by three secondary tracks, within a fiducial volume, + “Cascade topology” p- (1020) - 0 6 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  7. Signal extraction:  and *  (|y| ≤ 0.5) Ξ*(|y| ≤ 0.8) • Fit: poly + Voigtian (i.e. Breit-Wigner convoluted with Gaussian) • take into account inv. mass resolution (for  estimated by MC ~ 1 MeV/c2) • Raw counts: Voigtian full integral A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011 7

  8. Signal extraction: K* Subtract background estimated by like-sign (2√N++N--) Fit: Breit-Wigner + straight line Raw counts: BW full integral Rapidity range: |y| ≤ 0.5 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  9. Signal extraction: ++ Subtract background estimated by event mixing Fit: relativistic p wave Breit Wigner*phase space factor+linear background Raw counts: BW full integral Rapidity range: |y| ≤ 0.5 Invariant mass shifted to low values, alredy observed at RHIC energies. (STAR coll. Phys. Rev. C78(2008)044906) This could be originated from N interactions with medium Counts/(0.02 GeV/c2) A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  10. Signal extraction: * • Fit: Gaussian + negative power law • Subtract background function • Raw counts: bin count - 3σ around peak center. • Rapidity range: |y| ≤ 0.8 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  11. Reconstruction efficiency of K* ,  and * Branching ratio limits Ξ* efficiency includes also reconstruction efficiency for previous decay steps (Ξ decay reconstruction) A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  12. Systematics PID cuts topological selection (Ξ*) background subtraction material budget track selection normalization Corrected spectra of K* ,  and * Fit: Levy / Tsallis function A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  13.  resonance : comparison with 900 GeV dNφ/dy increases proportionally to dNch/dy from 900 GeV to 7 TeV uncert = √(stat2+syst2) • φ @ 900 GeV : ALICE Collaboration, Eur. Phys. Journal C 71 (2011), 1594 • Charged multiplicity @ 900 GeV and 7 TeV:ALICE Collaboration, Eur. Phys. Journal C 68 (2010), 345 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  14.  KK and μμ Slope KK consistent with slope μμ (2.5<y<4.1, 1<pT<5 GeV/c) Preliminary LHCb results, KK (2.44<y<4.06, 0.8<pT<5 GeV/c) LHCb-CONF-2010-014 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  15. Comparison with MC :  resonance Yellow band: data systematics A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  16. Comparison with MC : K* resonance All pT: good agreement with PYTHIA D6T Yellow band: data systematics A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  17. Comparison with MC : * resonance All pT: underestimated Yellow band: data systematics A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  18. Particle ratios A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  19.  in Pb-Pb collisions • Smaller signal / background • tighter Particle ID cuts with TPC and TOF • require TOF for tracks with pT > 600 MeV/c • subtract like-sign background • Fit: Voigtian + polynomial • Raw counts: Voigtian full integral Extracted φ signal in 14 bins for 0.5 ≤ pT ≤ 5 GeV/c Counts / 1 MeV/c2 A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  20. Conclusions and Prospects • In p-p collisions at 7 TeVperformances for K*(892)0,  (1020), (1385)± and (1530)0, (1232) resonance signals have been shown. Good agreement of their characteristics (mass, width) with PDG value or previous measurements at lower energies. • Measured dN/dpT for φ, K* and Ξ* at mid-rapidity in pp collisions at √s = 7 TeV. •  spectrum compared with the one measured at 900 GeV and withthe one measured in forward direction by the μμ decay channel. Good agreement was found. • Measured spectra have been compared with MC • φwell reproduced by PYTHIA D6T below 2 GeV/c, by PHOJET above • K*well reproduced by PYTHIA D6T • Ξ* underestimated by a factor ~5 in all cases • Particle ratios as /K* or K*/K don't increase with respect to lower collision energy values, even φ /π saturates. >>> Extracted φ raw counts spectrum for different centrality in Pb-Pb collisions at √sNN = 2.76 TeV. Yield will be soon available. A.Badalà-EPIC-Bari(Italy)- 6-8 July 2011

  21. Backup slides

  22. Ratios : THERMUS Predictions • Ratio proportional with the T • Ratio inversely proportional with the mass difference ΔS=0 ΔJ=1 ΔB=0 S. Wheaton, J. Cleymans and M. Hauer, Comput. Phys. Commun. 180, 84 (2009) 22 22

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