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Study of the K*(892) 0 signal in pp ALICE events

Study of the K*(892) 0 signal in pp ALICE events. Giuseppe Lo Re INFN-CNAF, Bologna (Italy) ACAT03, 12/3/2003. Summary. Physics motivations Computing tools ALICE simulations for pp collisions Conclusions and outlook. Physics motivations.

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Study of the K*(892) 0 signal in pp ALICE events

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  1. Study of the K*(892)0 signal in pp ALICE events Giuseppe Lo Re INFN-CNAF, Bologna (Italy) ACAT03, 12/3/2003 ACAT03 - Giuseppe Lo Re

  2. Summary • Physics motivations • Computing tools • ALICE simulations for pp collisions • Conclusions and outlook ACAT03 - Giuseppe Lo Re

  3. Physics motivations ACAT03 - Giuseppe Lo Re

  4. Modifications of properties of mesons resonances and their production rate give information on the nuclear medium and possible QGP phase transition ACAT03 - Giuseppe Lo Re

  5. Resonances which decay into strongly inte- racting hadrons may not be reconstructed due to rescattering of daughters inside the system. • The study of such resonances may also probe the role of the rescattering phase between chemical freeze-out and kinetic freeze-out (regeneration mechanism) • Finally, the study of K*(892) is also interesting due to its strange quark content. • Combined measurements of K*(892) and  mesons are particularly useful in this respect. ACAT03 - Giuseppe Lo Re

  6. K0*(892) signal in Pb+Pb @160 AGeV (NA49 Collaboration) K0*(892) signal in Au+Au @ snn=130 GeV (STAR Collaboration) ACAT03 - Giuseppe Lo Re

  7. Computing tools • AliRoot/ROOT framework for simulation and analysis • 550 Pb+Pb HIJING (peripheral) events • 4x104 PYTHIA pp minimum-bias events • Full reconstruction in TPC+ITS • Use of AliEN to handle pp events ACAT03 - Giuseppe Lo Re

  8. AliEn is the ALICE implementation of a distributed computing infrastructure. • 1% native code, 99% Open Source packages and perl modules • used over about 30 sites • during last years 16,000 jobs have been succesfully run uner AliEn and more than 20TB of data produced We used AliEn used both for production, reconstruction and analysis of pp events for the reconstruction of the k*(892)0 http://alien.cern.ch ACAT03 - Giuseppe Lo Re

  9. Production Reconstruction ACAT03 - Giuseppe Lo Re

  10. ACAT03 - Giuseppe Lo Re

  11. AliEn job submition system already incorporate the “job splitting” feature. Example of jdl file used for our analysis jobs Executable="Analysis.sh"; Packages="AliRoot::3.09.07"; InputFile="LF:/alice/cern.ch/user/g/glore/k0Starpp.C"; Arguments="--macro k0Starpp.C"; InputData={"LF:/alice/simulation/2002-04/V3.08.Rev.01/00005/*/galice.root", "LF:/alice/simulation/2002-04/V3.08.Rev.01/00005/*/galiceSDR.root", "LF:/alice/simulation/2003-02/V3.09.06/00147/*/tpc.tracks.root"}; Split="event"; OutputFile={"its.tracks.slow.root","its.clusters.slow.root","hm.root"}; Email="giuseppe.lore@cnaf.infn.it"; ACAT03 - Giuseppe Lo Re

  12. ALICE simulations for K*(892)0 • PYTHIA generates 1.7 K*(892)0 (14 TeV cms energy) with 70 k*π- combinations per event • Several factors reduce them during reconstrution • Geometrical acceptance (-0.9<η<0.9) • Branching ration of K*(892)0 in k+π- (2/3) • Tracking efficiency (overall for low pT tracks and for k+ which decay inside the TCP) • At the end there are 0.02 K*(892)0 (our findable candidates)with 1.4 combinations per event ACAT03 - Giuseppe Lo Re

  13. Ideal particle identification K*(892)0/evt S/B (2) S/S+B 0.02 0.10 11.1 M=894.9±2.4 Γ=59.1±11.6 Kinematical cuts used: Angles of daughters w.r.t. parent: k < 2 rad,  < 1 rad After kinematical cuts: Found K*(892)0/evt S/B (2) Rec.Eff. S/S+B 0.018 0.102 98 % 11.1 ACAT03 - Giuseppe Lo Re

  14. Additional cut introduced by means of the Armenteros-Podolanski plot (, qt) ql(+) - ql(-)  = qt(+) ql(+) + ql(-) q(+) PK*(892) ql(+) (, qt) pairs from different parent particles fall into different elliptical loci qt(-) ql(-) q(-) ACAT03 - Giuseppe Lo Re

  15. K*(892) Combinatorial background Cut on Armenteros plot: -0.12<α<0.67 0.25<qT<0.33 After cut on Armenteros: Found K*(892)0 /evt S/B (2) Rec.Eff. S/S+B 0.014 0.146 79 % 8.9 ACAT03 - Giuseppe Lo Re

  16. Missing particle identification • Particle identification open task in ALICE • It has to combine information from several subdetectors (mainly ITS, TPC, TOF, TRD) • We explored the worst scenario considering all the possible pos/neg pair combinations arising from (π+,k+,p) x (π-,k-,p) ACAT03 - Giuseppe Lo Re

  17. The true combinations (left) are e embedded in a large combinatorial background and there is a strong contamination from other resonances, overall ρ(770) and ω(782). ACAT03 - Giuseppe Lo Re

  18. Cuts used: • Armenteros: • -0.12<α<0.67 • 0.25<qT<0.33 • p pos track • p > 1.6 GeV/c • With these cuts we obtain S/B=0.06. To extract the signal we need to use the mixed events techiques. M=895±2 Γ=59±11 ACAT03 - Giuseppe Lo Re

  19. Conclusions and outlook • We carried out a detailed simulation study of K*(892)0 in pp collisions at 14 TeV in the c.m.s. • The two extreme hypotheses have been considered as far as particle identification is concerned • Even without PID and with a no so large amount of events K*(892)0 study is feasible in ALICE • AliEn has been successfully used both for production and analysis To be done: • Increase statistics profitting by next ALICE production (ADC will start at the beginning of 2004) • Check how PID will affect the pp results ACAT03 - Giuseppe Lo Re

  20. ACAT03 - Giuseppe Lo Re

  21. STAR results @ 200 AGeV pp Transverse mass spectrum, yields and particle ratios extracted from the data. Results from STAR point out that no reduction of such resonance is observed in AA collisions despite expected losses due to rescattering effects. Quark Matter, 2002 ACAT03 - Giuseppe Lo Re

  22. No. of K*(892)0 in central (b=3 fm) Pb+Pb collisions vs energy ACAT03 - Giuseppe Lo Re

  23. True pairs vs combinatorial background as a function of b ACAT03 - Giuseppe Lo Re

  24. After reconstruction: pt-range Findable K*(892)0 /evt S/B (2)) > 0 6.0 5 x 10-4 >3 GeV/c 0.5 5 x 10-3 ACAT03 - Giuseppe Lo Re

  25. All pairs True signal Before cuts: S/B = 5 x 10-3 ACAT03 - Giuseppe Lo Re

  26. Closest distance between tracks All pairs True signal ACAT03 - Giuseppe Lo Re

  27. Momenta of daughters All pairs True signal ACAT03 - Giuseppe Lo Re

  28. Summary of cuts for Pb-Pb: Transverse momenta of daughters: p > 1.5 GeV/c pk > 1.7 GeV/c Impact parameters of tracks: d,k < 150 m Closest distance between tracks: dpn < 200 m Angles of daughters wrt parent: k < 0.14 rad,  < 0.3 rad Relative angle between tracks: rel < 0.5 rad Overall effect of cuts: S/B from 0.005 to about 0.1 0.14 K*(892)/evt 27% rec. efficiency ACAT03 - Giuseppe Lo Re

  29. Combinatorial background evaluated by the mixed event spectrum ACAT03 - Giuseppe Lo Re

  30. Evolution of difference signal with the statistics ACAT03 - Giuseppe Lo Re

  31. Centroid at (0.887 0.017) GeV/c2 S/(S+B) = 2.5 for 550 events ACAT03 - Giuseppe Lo Re

  32. True signal Addition of Armenteros cut: 0.07 K*(892)/evt S/B = 0.23 Rec.Eff = 15% ACAT03 - Giuseppe Lo Re

  33. All pairs True signal Invariant mass spectra ACAT03 - Giuseppe Lo Re

  34. S/(S+B) = 2.7 for 550 events ACAT03 - Giuseppe Lo Re

  35. ACAT03 - Giuseppe Lo Re

  36. ACAT03 - Giuseppe Lo Re

  37. ACAT03 - Giuseppe Lo Re

  38. True signal Overall signal Verificare se conviene metterla  = (52 ± 2 ) MeV  = (60 ± 10 ) MeV ACAT03 - Giuseppe Lo Re

  39. ACAT03 - Giuseppe Lo Re

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