Prospects in ALICE for  mesons Daniel Tapia Takaki (Birmingham, UK) for the ALICE Collaboration International Conference on STRANGENESS IN QUARK MATTER Levoca, Slovakia – June 2007

24th June SQMDaniel Tapia Takaki (Birmingham)2  Resonances in ALICE  ALICE Detector & PID capabilities  Simulation method & MC predictions   signal and background predictions  Conclusions Structure of Talk

24th June SQMDaniel Tapia Takaki (Birmingham)3 Resonances in ALICE ALICE is a general-purpose heavy-ion (HI) experiment designed to study the physics of strongly interacting matter and the Quark Gluon Plasma (QGP) in nucleus-nucleus collisions at the CERN LHC. Resonances are a useful probe with which to study the QGP. (see Wed afternoon session). ALICE will allow the study of resonance production in pp and Pb-Pb collisions. This talk is devoted to the prospects of  meson production at the ALICE experiment. ALICE: Physics Performance Report, Vol. II. B. Alessandro et al., ALICE Collaboration. J. Phys. G: Nucl. Part. Phys , (See A. Badala talk on Thursday)

24th June SQMDaniel Tapia Takaki (Birmingham)4 Interest in  production Interesting due to its quark content. It is sensitive to strangeness production. It interacts weakly with non-strange hadrons in the hadronic phase due to its small cross section. Several theoretical predictions suggest changes in the  mass and width due to medium-induced effects. The  in hadronic and leptonic mode. The dileptons will have a different medium interaction. Proposed as a probe of chiral symmetry restoration.

24th June SQMDaniel Tapia Takaki (Birmingham)5 Interest in  production in pp collisions Production of the  can be measured early in the running of LHC, because of its narrow width, which gives it good S/B. –Interesting for itself, as one more hadronic measurement. Could be done at several energies.  measurements not very high precision at Tevatron, so even “low” energy points from LHC startup are interesting. M  = 1019 ± 2 (stat) MeV/c 2  =6.5 ± 0.7 (stat) MeV/c  ->K + K - events vs μ N Φ /N h vs μ T. Alexopoulos, et al., Z. Phys. C. 67, (1995) Tevatron experiment E735, √s = 1.8 TeV

24th June SQMDaniel Tapia Takaki (Birmingham)6 ITS Low p t tracking Vertexing ITS Low p t tracking Vertexing TPC Tracking, dEdx TPC Tracking, dEdx TRD Electron ID TRD Electron ID TOF PID TOF PID HMPID PID high p t HMPID PID high p t PHOS ,  0 PHOS ,  0 MUON  -pairs MUON  -pairs PMD  multiplicity PMD  multiplicity The ALICE experiment ITS - Tracking, vertex finding and PID by dE/dx. Time Projection Chamber, used for tracking and particle identification (PID) by dE/dx. TRD – tracking and electron identification. TOF – Tracking and hadron identification by Time of Flight. ALICE studies both pp and Pb-Pb collisions.

24th June SQMDaniel Tapia Takaki (Birmingham) p (GeV/c) p (GeV/c) TRD e /  PHOS  /   TPC + ITS (dE/dx)  /K K/p e /  HMPID (RICH) TOF ALICE Particle Identification capabilities Particle ID from low to high momenta. ALICE can combine the single detector PID information. Alice uses ~ all known techniques!

24th June SQMDaniel Tapia Takaki (Birmingham)8 Detector simulation & MC predictions The simulation of the pp (Pb-Pb) physics is generated by PYTHIA (HIJING). The output is then passed to the ALICE simulation and reconstruction algorithm – using the ALICE offline computing framework known as AliRoot. Results from fast-simulation (pp) and detailed simulation (Pb-Pb) are presented. PYTHIA’s prediction for pp mb at ALICE. Rapidity distribution for the  meson at the generation level.

24th June SQMDaniel Tapia Takaki (Birmingham)9 Background estimation A good estimation of the shape and size backgrounds is essential for the study of resonances measurement. Like-sign and mixed events are popular techniques. Both methods were implemented in AliRoot. Mass (GeV/c 2 ) PYTHIA pp 14 TeV cms energy 4 x 10 6 events – No PID was used. K + K - spectrum ~ 1 hr nominal run. Inv. Mass with no PID.

24th June SQMDaniel Tapia Takaki (Birmingham)10 Background estimation (2) Same-event background Like-sign same-event Same-event background Like-sign same-event Same-event background Like-sign same-event Mixed event Either method works well. This agrees with reported results. Physical Review C (2005). K + K - spectrum Ratio of same-event background to Like-sign same event inv. Mass. 2 x 10 6 events. PYTHIA pp 14 TeV cms energy

24th June SQMDaniel Tapia Takaki (Birmingham)11 Mass Same event Mixed event K + K + pairs K - K - pairs Background estimation (3) The ratio of same to mixed event for the K + K + and K - K - pairs. The signal can be obtained subtracting the background from either method. K + K + pairs K - K - pairs Ratio of Like-sign same event to mixed event mass distribution. PYTHIA pp 14 TeV cms energy 2 x 10 6 events.

24th June SQMDaniel Tapia Takaki (Birmingham)12 Like-sign Signal – background subtracted PYTHIA pp 14 TeV cms energy ΦK+K-ΦK+K- 2 x10 6 PYTHIA mb pp events. Fast-simulation results. Perfect PID. Background subtracted Reconstructed mass and width consistent with generated. Number of  found consistent with the number generated.

24th June SQMDaniel Tapia Takaki (Birmingham)13 Results in Proton-Proton collisions with no PID PYTHIA mb 14 TeV cms energy ALICE should be able to measure the  meson early in the LHC running - even before the PID system become available. Mass (GeV/c 2 ) 2.4<P t <2.6 GeV ΦK+K-ΦK+K- K + K - spectrum 4 x 10 6 events – No PID was used. ~ 1 hr nominal run. Inv. Mass with no PID. 2.4<P t <2.6 GeV

24th June SQMDaniel Tapia Takaki (Birmingham)14  meson in Pb-Pb collisions 4,000 HIJING central Pb-Pb events. Detailed simulation method. Perfect PID ΦK+K-ΦK+K- K + K - spectrum HIJING 5.5 TeV ~ 1/2 min nominal run. Reconstructed transverse-momentum K - K +   K + K -

24th June SQMDaniel Tapia Takaki (Birmingham)15 Conclusions The ALICE experiment will allow the study of resonances in great detail. It has excellent PID. A study of the  meson in hadronic (and leptonic) decay channels will be possible. Like-sign and mixing-event were tested for background subtraction. They give consistent result. The  analysis might be one of the first resonance measurements in ALICE because of its good S/B ratio. ALICE should be able to study the  meson in pp collisions before the PID system become available. In Pb-Pb collisions the  meson can also be measured (even with small statistics).