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Experience from analyzing pp collisions in ALICE Konstantin Mikhaylov ITEP, Moscow

Experience from analyzing pp collisions in ALICE Konstantin Mikhaylov ITEP, Moscow. K.Mikhaylov, ITEP Alice Week, CERN October 2008 1. Simulations: software and input.

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Experience from analyzing pp collisions in ALICE Konstantin Mikhaylov ITEP, Moscow

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  1. Experience from analyzing pp collisions in ALICE Konstantin Mikhaylov ITEP, Moscow K.Mikhaylov, ITEP Alice Week, CERN October 2008 1

  2. Simulations: software and input • Aliroot v4-14-Rev-01,AliFemto from svn/trunk • PDC2007: PYTHIA pp 14 TeV • (the pp events simulated at the request of the V0 group with no ITS refit requirement: • /alice/sim/PDC_07/LHC07f/1600*) • AliRoot local analysis (~2*106 events)‏ • 1Dπ+π+ correlations • 0.1 < PT < 1.0 GeV/c • Standard cut on splitting-merging • Influence of Vz, Multiplicity, Particle collection on the correlation function • Pythia direct analysis (read galice.root ~7*105 events)‏ • 1Dπ+π+ correlations • 0.1 < PT < 1.0 GeV/c, |η|<1 K.Mikhaylov, ITEP Alice Week, CERN October 2008 2

  3. AliFemto Simple Analysis K.Mikhaylov, ITEP Alice Week, CERN October 2008 3

  4. PYTHIA direct events • π+π+ correlation function • Cuts: • 0.1 < PT < 1.0 GeV/c • -1. < η < +1 • CF=Real/Mixed • Energy and Momentum Conservation- • Induced Correlations: • Due to energy-momentum conservation • probability of two particle emitted • at same direction is smaller • than in opposite direction K.Mikhaylov, ITEP Alice Week, CERN October 2008 4

  5. PYTHIA and ALIFEMTO We created the correlation which does not exist in PYTHIA. Does it come from mixing procedure? K.Mikhaylov, ITEP Alice Week, CERN October 2008 5

  6. Vz: ALIFEMTO and PYTHIA ALIFEMTO PYTHIA Reconstruction? K.Mikhaylov, ITEP Alice Week, CERN October 2008 6

  7. Acceptance for mixed events TPC size is equal 2.5m Collision point distribution is Gaussian with sigma ~5.5cm Does it important for correlation function(mixing)? Blue is real pair with Z=0 (both particles are in acceptance). Red is mixed pair with different Z's (one is in acceptance and other is out of acceptance). We create the correlation! Solution: mix only events which have a very similar z-vertex position! Z TPC K.Mikhaylov, ITEP Alice Week, CERN October 2008 7

  8. K.Safarik. Physics Forum. Alice Week. Oct 2008 Acceptance • Events at any position in the chosen vertex range have to accept the whole phase space () accessed in the analysis • Trade-off between statistics (vtx-range) and accessible phase space • || < 1.0  |vtx-z| < 6 cm • || < 1.4  |vtx-z| < 10 cm Tracking efficiency correction  vtx-z (cm)‏

  9. Cut on Vz(±2.5cm)‏ mec->SetVertZPos(-2.5,2.5); K.Mikhaylov, ITEP Alice Week, CERN October 2008 9

  10. AliFemto ConfigFemtoAnalysis.C ConfigFemtoAnalysis.C //#### Old #### //Simple Analysis: AliFemtoSimpleAnalysis* an =new AliFemtoSimpleAnalysis(); //#### New: STAR Vz, multiplicity mixing procedure#### //With z-vertex mixing: AliFemtoVertexMultAnalysis *an = new AliFemtoVertexMultAnalysis(NbinsVz, -15.6, 15.6,NbinsMulti, 2, 100); an->SetNumEventsToMix(10);//Number of events to mix an->SetMinSizePartCollection(2);//Minimum number of particles in event after all cuts //Test with different cut parameters //#1 NbinsVz=20 ,NbinsMulti=1 //#2 NbinsVz=1, NbinsMulti=10 //#3 Combined : NbinsVz=20 and NbinsMulti=10 K.Mikhaylov, ITEP Alice Week, CERN October 2008 10

  11. Mixing: Z-vertex (20 bins)‏ AliFemtoVertexMultAnalysis *an = new AliFemtoVertexMultAnalysis(20, -15.6, 15.6, 1, 2, 100); an->SetNumEventsToMix(10); an->SetMinSizePartCollection(2); K.Mikhaylov, ITEP Alice Week, CERN October 2008 11

  12. Mixing: Multiplicity(10 bins) AliFemtoVertexMultAnalysis *an = new AliFemtoVertexMultAnalysis(1, -15.6, 15.6, 10, 2, 100);//10 bins on multiplicity an->SetNumEventsToMix(10); an->SetMinSizePartCollection(2); K.Mikhaylov, ITEP Alice Week, CERN October 2008 12

  13. Combined: Vz+Mult (20+10bins)‏ AliFemtoVertexMultAnalysis *an = new AliFemtoVertexMultAnalysis(20, -15.6, 15.6, 10, 2, 100); an->SetNumEventsToMix(10); an->SetMinSizePartCollection(2); K.Mikhaylov, ITEP Alice Week, CERN October 2008 13

  14. Conclusion • Vz,mutiplicity mixing procedure is very important • Only events with at least two particle should be taken into analysis • Vz mixing is most important in case of pp collision at 14TeV K.Mikhaylov, ITEP Alice Week, CERN October 2008 14

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