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Study of short-lived resonances in ALICE

Study of short-lived resonances in ALICE. A. Badal à – INFN Sezione di Catania- Italy for the ALICE Collaboration. Contents Physics motivations ALICE detector Results on strange resonances (K*(892), (1520),(1020),..) from simulated p-p events @ 900 GeV and @14 TeV Summary.

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Study of short-lived resonances in ALICE

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  1. Study of short-lived resonances in ALICE A. Badalà – INFN Sezione di Catania- Italy for the ALICE Collaboration • Contents • Physics motivations • ALICE detector • Results on strange resonances (K*(892),(1520),(1020),..) from simulated p-p events @ 900 GeV and @14 TeV • Summary

  2. Resonances c  (fm) (770) +- 1.3 f0(980) +- 2.6 K*(892)0 K 3.9 (1520) Kp 13 (1020)  K+K- 44  Resonances are strongly decaying particles which have lifetimes of about a few fm/c (i.e resonance~ fireball ) Partial chiral symmetry restoration Interaction of the resonances and/or their daughters with fireball medium Modifications of properties of resonances (peak,width) Why short-lived resonances? Resonances may give information on the dynamics and on the chiral property of the hot and dense matter which is produced in the collision 2 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  3. NA60 RESULTS In-In@ 158AGeV A significant excess of +- pairs is observed above the yield expected from neutral meson decay. Its shape is consistent with a contribution from +-  annihilation Models based on in-medium  broadening scenario seem able to reproduce data, while moving mass models seem ruled out R. Arnaldi et al. (NA60 Collaboration) Phys. Rev. Lett. 96(2006)162302 Resonances as a probe of chiral symmetry restoration The best probes are resonances reconstructed by their leptonic decay channel since leptons are less likely to rescatter in the hadronic medium Resonance mass shift and width broadening have been suggested as a signature of chiral symmetry restoration 3 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  4. Resonances from jets Recently suggestion to study chiral symmetry restoration by comparing resonance production in event classes based on azimuthal distribution respect to jet direction First attempt has been done studying h(high pt)-(1020) correlations C. Markert, 23rd Winter Workshop on Nuclear Dynamics Big Sky, Montana, USA High pT resonances from the away side jet could be modified by the partonic medium, but they are so fast to have low probability to be affected by the hadronic medium 4 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  5. Interactions of resonances in hadronic nuclear medium • The yields of resonances detected by their hadronic decay can be influenced by effects of rescattering and regeneration which depends on: • the time between the chemical and the thermal freeze-out • the lifetime of the resonances • the interaction cross-section of the decay particles. Due to the rescattering , resonances may not be reconstructed Pseudo-elastic collisions may regenerate resonances Rescattering Regeneration No interaction The resonances may probe the timescale between the chemical and the kinetic freeze-out 5 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  6. p+p and Au+Au @ sNN=200 GeV Resonance/non-resonance ratio B.I. Abelev (Star Collaboration) nucl-ex 0604019 At RHIC energies thermal models are able to reproduce the ratios of stable particles Deviations from these ratios have be used to estimate the time interval between thermal and chemical freeze-out  (UrQMD) = 13±3 fm/c Suppression of K* and * Lower limit (<4 fm/c, T=160 MeV) from measured K*/K and */ ratio by a thermal model with a rescattering phase (G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 and C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045) 6 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  7. Main observables concerning the study of resonances in pp and AA collisions (*) Extraction of the signal/yields (*) Mass and widths of resonances (*) Transverse momentum and transverse mass spectra (*) Particle ratios Elliptic flow Nuclear modification factors: RCP and RAA 7

  8. Elliptic flow Baryons For KET >1 GeV, mesons and baryons scale separately Mesons S. Adare et al. (Phenix coll.) nucl-ex 0608033 Universal scaling is observed for mesons and baryons when quark number scaling is employed A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  9. Elliptic flow for resonances Measurement of flow for meson and baryon resonances is of great interest to further validate the picture sorting of this scaling i.e. that partonic collectivity dominates the transverse expansion dynamics. Au-Au @200 GeV Mass  meson ~ Mass proton v2 of  mesons confirms this universal scaling S. Afanasiev et al. (PHENIX Coll. ) nucl-ex 0703024 9 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  10. Nuclear Modification Ratios (RCP) for resonances RHIC results have shown as, in the intermediate pt region, nuclear modification factors depend on the constituent quarks rather than on particle mass. Recent suggestion by Maiani et al. (Phys. Lett. B645(2007)138) to use this observable to solve the problem of the real quark composition of some resonances as the fo(980)( or ?) 10 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  11. MUON-ARM μ-pairs ALICE(ALargeIonColliderExperiment) HMPID PID (RICH) @ high pT TOF PID EMCAL Jets reconstruction TRD Electron ID PMD γ multiplicity ITS Low pT tracking Vertexing TPC Tracking, dE/dx PHOS γ, π0 11 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  12. Pb-Pb p-p Reconstruction of short-lived resonances is improved by optimal performance on: vertex reconstruction Primary vertex in ALICE is reconstructed by means of tracklets in the two innermost pixel layers and by a Kalman vertex procedure for p-p events < 40 m ~ 5 m 12 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  13. Reconstruction of short-lived resonances is improved by optimal performance on: primary vertex reconstruction tracking efficiency ITS + TPC In ALICE Kalman filter strategy allows a good tracking performance down to very low momenta 13 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  14. pt/pt(%) pt(GeV/c) Reconstruction of short-lived resonances is improved by optimal performance on: primary vertex reconstruction tracking efficiency momentum resolution pt/pt <0.7% for pt<2 GeV/c pt/pt ~ 3 % at 100 GeV/c 14 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  15. Reconstruction of short-lived resonances is largely improved by optimal performance on: primary vertex reconstruction tracking efficiency momentum resolution track impact parameter particle identification with ITS and TPC at low momenta… and TOF at high momenta… 15 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  16. Particle Identification stable hadrons (p, K, p): 100 MeV < p < 5 GeV (few 10 GeV) dE/dx in silicon (ITS) and gas (TPC) + Time-of-Flight (TOF) + Cerenkov (RICH) decay topology (K0, K+, K-, L) K and L decays up to at least 10 GeV leptons (e, m), photons, p0, h electrons in TRD: p > 1 GeV, muons: p > 5 GeV, p0 in PHOS: 1 < p < 80 GeV 16 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  17. Study of short-life resonances in ALICE Several activities are going on in ALICE concerning the study of such resonances, both in pp and AA collisions, with contributions from several groups. (Other contributions to this conference from P.Ganoti and D. Tapia-Takaki). Resonance K*(892) Φ(1020)*(1520) Decay channel (B.R.) K (~100%)K+K- (49%)N K (45%) Width [MeV/c2] 50.8 4.5 15.6 Life time [fm/c] 3.9 44 13 • Software code development • Test distributed analysis of events • Optimization of reconstruction tools • Background estimation • Efficiency evaluation 17 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  18. Results from p-p events @ 900 GeV and 14 TeV • Events of PYTHIA were generated and fully reconstructed using • Realistic simulation of the detector response for the whole ALICE assembly • Realistic clusters and tracks reconstruction 2 Data Sets 2 x 105 minimum bias p-p PHYTIA events @ 900 GeV. Running scenario at LHC startup 1.5 x 106 minimum bias p-p PHYTIA events @ 14 TeV (about 0.2% 1-year data taking) PDC06 data, distributed GRID analysis 18 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  19. Study of the combinatorial background by the mixed-event technique Studied dependence on event selection criteria ●Charged multiplicity ●z-vertex location Only events with Δm<5 and Δzv < 3 cm mixed Multiplicity Comparison of the event mixing background to the “true” combinatorial backgroung ‘True’ background = (Signal) – (True pairs) z-vertex 19 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  20. K* K* Like-sign technique also explored p-p@900 GeV Unlike sign Like-sign Comparison of the like-sign background to the “true” combinatorial background 20 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  21. Perfect PID Realistic PID PID influence on K*(892) reconstruction True Found p-p@900 GeV Maxprob > 0.7 (K) No PID (π) No thresh on maxprob Maxprob > 0.7 (K) Maxprob > 0.7 (π) Perfect PID Realistic PID True K* = 4306 Found K* = 4139 S/B = 0.11 S/√B = 20.28 True K* = 7599 Found K* = 7488 S/B = 0.138 S/√B = 30.68

  22. True  (± 2σ) = 186 Found  (±2σ) = 168 S/B = 2.87 S/√B = 13.86 True Λ (± 2σ) = 146 Found Λ (± 2σ) = 128 S/B = 1.23 S/√B = 19.5   * (1020) and *(1520) with realistic PID p-p@900 GeV * 22 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  23. Results for p-p collisions @14 TeV 1.5 x 106 PYTHIA events Detailed analysis for K*(892)0 on PID perfomances Found K*(±2)=89182 True K*(±2)=85360 K* Mass resolution ~ 3MeV/c2 23 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  24. pT= 0 - 0.5 pT= 1.5 - 2 pT= 3.5 - 4 K*(892)0 pT-analysis with realistic PID p-p@14 TeV 24 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  25. Correction matrix 25 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  26. (1020) and *(1520) with realistic PID p-p@14 TeV Mass resolution 1.2 MeV/c2 (1020) (1520) (1020) (1520) True *=3879 Found *=3649 True =4893 Found =4967 26 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  27. Summary ● Short-lived resonances in pp collisions @ LHC energies could be studied in ALICE from the very beginning ● With a small sample of events [O(105)] @ 900 GeV and realistic PID: ●Extraction of yields at least for K*(892), Φ(1020), Λ*(1520) ●Rough pT - distribution for K*(892) up to 1.5 GeV/c ●Particle ratios Φ/K*, Λ*/K*, Φ/Λ* measurable ● Analysis of O(106) pp events at 14 TeV fully reconstructed on the GRID ●Resonance yields with large statistics ●pT-analysis ● Correction matrix (y,pT) ● Extension to other resonances is in progress. K*(892)0 A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  28. EXTRA SLIDES

  29. Practical limit for 2 x105 events K*(892) pt-distribution @ 900 GeV pT-spectrum for realistic PID 2 x 105 events  3500 K* A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  30. K*(892) yield Exp.data PYTHIA Resonance yield Overall number of particles + antiparticles generated by PYTHIA@900 GeV: 1.34 K*(892)/event 0.08 (1520)/event 0.23 Φ(1020)/event A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  31. (780)

  32. (1020)

  33. K*(892)0 1 GeV/c<pt<2 GeV/c 2 GeV/c<pt<3 GeV/c

  34. Signal extraction (unlike-sign) Inside same event, correlations between K+ and π- candidates K- and π+ candidates Evaluate invariant mass spectrum Example: K*(892)  Kπ (~100%) Mixed-event technique Combinatorial background: Like-sign technique

  35. ALICE PID A common BAYESIAN approach is adopted by every ALICE detector performing PID; The probability w(i|s) to be a particle of type i (i = e,,, K, p...) if a signal s (dE/dx, TOF,...) is detected, is: r(s|i)(Detector response function) conditional probability density functions to get a signal s in a detector, if a particle of i-type hits the detector Ci (particle concentration) a priori probability to find a particle of type i in the detector Probability to be a particle of i-type (i = e, , , K, p, … ), if we observe a vector S= {sITS, sTPC, sTOF, …} of PID signals in different detectors is: Combinated response function

  36. Mass resolution ~4000 HIJING events Mass resolution ~3 MeV

  37. Temperature and lifetime from (1520) / and K*/K G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 Dependence of the two ratios K*/K and (1520)/, on the chemical freeze-out temperature and time interval between chemical and kineticfreeze-out.Model: termally produced particle yields + rescattering phase. Then regeneration is not taken into account. preliminary 0-20% most central Au+Au C. Market, J. Phys. G. Nucl. Part. Phys. 31 (2005) 1045. (1520)/ = 0.034  0.011  0.013 K*(892)/K = 0.19  0.05 results between : T= 175 MeV =>  = 4-6 fm/c  = 0 fm/c => T= 110-130 MeV  > 4 fm/c for T=160 MeV

  38. 14  PID in the relativistic rise K p pT (GeV/c) Identified particle spectra ALICE has unique capabilities to reconstruct and to identify particles: Global tracking (ITS-TPC-TRD) (pt/pt ~ 3% at 100 GeV/c) + dE/dx (low pT + relativ. rise), TOF, HMPID, PHOS, … Reconstruction by invariant mass and topological decay , K, p: 0.1- 0.15 <pt< 50 GeV/c Estimated pt range for particle identification for 107 central Pb-Pb events (1-year data taking) Weak or strong decaying particles: up to 10-15 GeV/c

  39. ALICE performance on: primary vertex reconstruction tracking efficiency momentum resolution track impact parameter Pb-Pb p-p  <100 m @ pt> 1GeV/c A. Badalà- SQM07- Levoča – 24/06/-29/06/07

  40. Preparation of tools for K*(892)± analysis K*(892)± KS0 + π± B.R. ~33% Total B.R. ~ 23 % π+ + π- B.R. ~ 69% K*+ p-p@900 GeV

  41. Nuclear Modification Ratios (RCP) for resonances RHIC results have shown as, in the intermediate pt region, nuclear modification factors depend on the constituent quarks rather than on particle mass. L. Maiani et al., Phys. Lett. B645(2007)138 A two components recombination/fragmentation model shows clear distinction for the Rcp of the f0(980) resonance with or content. A. Badalà- SQM07- Levoča – 24/06/-29/06/07

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