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

3/12/2003 ACAT03 - Giuseppe Lo Re Summary Physics motivations Physics motivations Computing tools Computing tools ALICE simulations for pp collisions ALICE simulations for pp collisions Conclusions and outlook Conclusions and outlook

3/12/2003 ACAT03 - Giuseppe Lo Re Physics motivations

3/12/2003 ACAT03 - Giuseppe Lo Re Resonance Mass c  (fm) Decay  (770) +-+-  (782) +-+- K*(892) k+-k+- f0(980) +-+-  (1020) kk Modifications of properties of mesons resonances and their production rate give information on the nuclear medium and possible QGP phase transition Modifications of properties of mesons resonances and their production rate give information on the nuclear medium and possible QGP phase transition

3/12/2003 ACAT03 - Giuseppe Lo Re 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.

3/12/2003 ACAT03 - Giuseppe Lo Re K 0 * (892) signal in  s nn =130 GeV (STAR Collaboration) K 0 * (892) signal in AGeV (NA49 Collaboration)

3/12/2003 ACAT03 - Giuseppe Lo Re 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 Computing tools

3/12/2003 ACAT03 - Giuseppe Lo Re We used AliEn used both for production, reconstruction and analysis of pp events for the reconstruction of the k*(892) 0 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

3/12/2003 ACAT03 - Giuseppe Lo Re Production Reconstruction

3/12/2003 ACAT03 - Giuseppe Lo Re

3/12/2003 ACAT03 - Giuseppe Lo Re Example of jdl file used for our analysis jobs Executable="Analysis.sh"; Packages="AliRoot:: "; InputFile="LF:/alice/cern.ch/user/g/glore/k0Starpp.C"; Arguments="--macro k0Starpp.C"; InputData={"LF:/alice/simulation/ /V3.08.Rev.01/00005/*/galice.root", "LF:/alice/simulation/ /V3.08.Rev.01/00005/*/galiceSDR.root", "LF:/alice/simulation/ /V /00147/*/tpc.tracks.root"}; Split="event"; OutputFile={"its.tracks.slow.root","its.clusters.slow.root","hm.root"}; AliEn job submition system already incorporate the “job splitting” feature.

3/12/2003 ACAT03 - Giuseppe Lo Re PYTHIA generates 1.7 K*(892) 0 (14 TeV cms energy) with 70 k*π - combinations per event PYTHIA generates 1.7 K*(892) 0 (14 TeV cms energy) with 70 k*π - combinations per event Several factors reduce them during reconstrution Several factors reduce them during reconstrution Geometrical acceptance (-0.9<η<0.9) Geometrical acceptance (-0.9<η<0.9) Branching ration of K*(892) 0 in k + π - (2/3) Branching ration of K*(892) 0 in k + π - (2/3) Tracking efficiency (overall for low p T tracks and for k + which decay inside the TCP) Tracking efficiency (overall for low p T 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 At the end there are 0.02 K*(892) 0 (our findable candidates) with 1.4 combinations per event ALICE simulations for K*(892) 0

3/12/2003 ACAT03 - Giuseppe Lo Re Ideal particle identification After kinematical cuts: Found K*(892) 0 /evt S/B (  2  ) Rec.Eff. S/  S+B % 11.1 Kinematical cuts used: Angles of daughters w.r.t. parent:  k < 2 rad,  < 1 rad K*(892)0/evt S/B (  2  ) S/  S+B M=894.9±2.4 Γ=59.1±11.6

3/12/2003 ACAT03 - Giuseppe Lo Re q(+) q(-) q t (-) P K*(892) q t (+) q l (+) q l (-) q l (+) - q l (-) q l (+) + q l (-)  = ( , q t ) pairs from different parent particles fall into different elliptical loci Additional cut introduced by means of the Armenteros-Podolanski plot ( , qt)

3/12/2003 ACAT03 - Giuseppe Lo Re K*(892) Combinatorial background After cut on Armenteros: Found K*(892)0 /evt S/B (  2  ) Rec.Eff. S/  S+B % 8.9 Cut on Armenteros plot: -0.12<α< <q T <0.33

3/12/2003 ACAT03 - Giuseppe Lo Re Particle identification open task in ALICE Particle identification open task in ALICE It has to combine information from several subdetectors (mainly ITS, TPC, TOF, TRD) 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) We explored the worst scenario considering all the possible pos/neg pair combinations arising from (π +,k +,p) x (π -,k -,p) Missing particle identification

3/12/2003 ACAT03 - Giuseppe Lo Re 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).

3/12/2003 ACAT03 - Giuseppe Lo Re Cuts used: Armenteros: -0.12<α< <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

3/12/2003 ACAT03 - Giuseppe Lo Re 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

3/12/2003 ACAT03 - Giuseppe Lo Re

3/12/2003 ACAT03 - Giuseppe Lo Re STAR 200 AGeV Quark Matter, 2002 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.

3/12/2003 ACAT03 - Giuseppe Lo Re No. of K * (892) 0 in central (b=3 fm) Pb+Pb collisions vs energy

3/12/2003 ACAT03 - Giuseppe Lo Re b (fm)K*(892)0/evtRatio signal/combinatorial x x x x x x 10-5 True pairs vs combinatorial background as a function of b

3/12/2003 ACAT03 - Giuseppe Lo Re After reconstruction : pt-range Findable K*(892) 0 /evt S/B (  2  )) > x >3 GeV/c x 10 -3

3/12/2003 ACAT03 - Giuseppe Lo Re Before cuts: S/B = 5 x True signal All pairs

3/12/2003 ACAT03 - Giuseppe Lo Re Closest distance between tracks All pairsTrue signal

3/12/2003 ACAT03 - Giuseppe Lo Re Momenta of daughters All pairs True signal

3/12/2003 ACAT03 - Giuseppe Lo Re Summary of cuts for Pb-Pb: Transverse momenta of daughters: p  > 1.5 GeV/c p k > 1.7 GeV/c Impact parameters of tracks: d ,k < 150  m Closest distance between tracks: d pn < 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 to about K*(892)/evt 27% rec. efficiency

3/12/2003 ACAT03 - Giuseppe Lo Re Combinatorial background evaluated by the mixed event spectrum

3/12/2003 ACAT03 - Giuseppe Lo Re Evolution of difference signal with the statistics

3/12/2003 ACAT03 - Giuseppe Lo Re Centroid at (0.887  0.017) GeV/c 2 S/  (S+B) = 2.5 for 550 events

3/12/2003 ACAT03 - Giuseppe Lo Re True signal Addition of Armenteros cut: 0.07 K*(892)/evt S/B = 0.23 Rec.Eff = 15%

3/12/2003 ACAT03 - Giuseppe Lo Re Invariant mass spectra All pairs True signal

3/12/2003 ACAT03 - Giuseppe Lo Re S/  (S+B) = 2.7 for 550 events

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3/12/2003 ACAT03 - Giuseppe Lo Re True signalOverall signal  = (52 ± 2 ) MeV  = (60 ± 10 ) MeV Verificare se conviene metterla

3/12/2003 ACAT03 - Giuseppe Lo Re