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Inclusive production of neutral mesons in ALICE

Inclusive production of neutral mesons in ALICE. Adam Matyja for the ALICE Collaboration Subatech, Nantes. Outline Motivation Experimental apparatus Results Summary. Cracow Epiphany Conference On the first year of the LHC 10 - 12 January 2011 Kraków, Poland. Motivation.

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Inclusive production of neutral mesons in ALICE

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  1. Inclusive production of neutral mesons in ALICE Adam Matyja for the ALICE Collaboration Subatech, Nantes Outline • Motivation • Experimental apparatus • Results • Summary Cracow Epiphany Conference On the first year of the LHC 10 - 12 January 2011 Kraków, Poland

  2. Motivation • Electromagnetic calorimeters offer a possibility to identify photons and neutral mesons in a wide pT range • Charged hadrons identification limited to low pT • Inclusive meson production spectrum is a good probe for pQCD and necessary for direct photons search • Neutral hadrons, detected via their photonic decays, carry information about medium • Studies of transport properties of quark-gluon matter • Initial gluon density  constraint of parameters of theoretical models in both perturbative (NLO, NNLO) and non-perturbative regime (structure function, fragmentation function) • Measurements in pp collisions give reference data to compare with AA • 's from neutral meson decays are background for other processes •  - jet studies

  3. Motivation Experience from RHIC arXiv:0806.0261v1 (2008) • 0,  and direct photons in AA collisions from PHENIX • The first evidence of a parton energy loss in a quark-gluon matter • RAA scales with Npart PHENIX, QM2008 What is expected at LHC energies?

  4. Motivation /0ratio in pp and AA collisions PHENIX, PRC 75, 024909 (2007) • Ratio is universal for a wide energy range • Needed for nuclear transport models • ALICE capabilities: • Large pT region • Both pp and Pb-Pb measurement f(mT)=(mT+a)-n, a=1.2, n=10-14

  5. Experimental apparatus ALICE detector EMCAL CTS = ITS + TPC PHOS

  6. Experimental apparatus EMCal • Shashlik technology • Tower - 77 layers: • Pb - 1.4 mm • Scintillator - 1.7 mm • Size - 6  6  25 cm3 • Module (2  2 towers) • Geometry • 4/10 Super Modules are installed • Next 6 are being installed in Dec. 2010 - Jan. 2011 • 24  48 towers in each Super Module • Coverage: || < 0.7, 80o <  < 120o • Distance to IP: 4.5 m • Material budget from IP: 0.8 X0 • Energy range: 0 < E < 250 GeV • Energy resolution: 12 Modules per Strip Module 24 Strip Modules per Super Module 10 Super Modules in EMCal

  7. Experimental apparatus PHOS • Technology • Crystal of lead tungstate (PbWO4) • Size: 2.2  2.2  18 cm3 • Geometry • 3/5 Super Modules are installed • 1 more expected in 2012 • 64  56 crystals in each Super Module • Coverage: • || < 0.13 • 260o <  < 320o • Distance to IP: 4.6 m • Material budget from IP: 0.2 X0 • Energy range: 0 < E < 100 GeV • Energy resolution: CPV (not installed yet) Crystals CPV - charged particle veto

  8. Experimental apparatus CTS = ITS + TPC • TPC: • Diameter  Length: 5 m  5 m • Acceptance:  = 2, ||<0.9 • Readout chambers: 72 • Pad readout (3 types): 557 568 • Drift field: 400 V/cm • Maximum drift time: 94 s • Central electrode HV: 100 kV • Gas: • Active volume: 90 m3 • Ne-CO2-N2: 85.7% - 9.5% - 4.8% • ITS: • Layout • 2 layers of pixel detectors • 2 layers of drift detectors • 2 layers of strip detectors • Acceptance:  = 2, ||<0.9 5 m 2.5 m 2.5 m CTS energy resolution: E/E  2%

  9. Results Method • Three ways of neutral meson (, 0) measurement via invariant mass analysis in ALICE → photon pairs or external conversion electrons • h →  +  (PHOS, EMCAL) • h →  (→e+ e-) +  (→e+ e-) (CTS) Reconstructed 0 candidate through conversions Distribution of conversions

  10. Results Data sample • ALICE minimum bias trigger • ALICE has collected: • about 9 M pp minimum bias events @ s = 900 GeV (0.15 nb-1) • about 800 M pp minimum bias events @ s = 7 TeV (11 nb-1) • Reconstruction of data just after being transferred to GRID after the end of each run • Presented analysis based on subset of data sample • about 8 M pp minimum bias events @ s = 900 GeV (0.12 nb-1) • about 360 M pp minimum bias events @ s = 7 TeV (4.3 nb-1) - PHOS • about 100 M pp minimum bias events @ s = 7 TeV (1.2 nb-1) - CTS

  11. Results Analysis selection • Event selection: • Correct event type and interaction trigger  pp interaction • At least 1 hit in SPD or beam-beam interaction by V0 detectors  MB event • Beam-gas events suppressed offline • Primary vertex: |Z| < 10 cm • Photon candidate selection: • PHOS • Ncells 3 • Ecl > 0.3 GeV • |A| < 1 (0) or |A| < 0.7 () • EMCal • Ncells 2 • Ecl > 0.5 GeV (0) or Ecl > 0.3 GeV () • |A| < 1 (0) or |A| < 0.6 () A = (E1 - E2)/(E1 + E2)

  12. Results Calibration • PHOS • Pre-calibration: adjusting the high voltage bias to provide the same gain • Accuracy: 20-50 % • Equalization of the mean deposited energy per channel by events from pp collisions • Accuracy: 6.5 % • Equalization of 0 peak channel-by-channel • Not enough statistics yet • Goal accuracy: 1 % • EMCAL • Pre-calibration: adjusting the high voltage bias to provide the same gain • Accuracy: 20 % • Calibration with cosmic rays before installation • Calibration with pp data using MIP signals • Equalization of 0 peak channel-by-channel • Current accuracy: 7 % • Goal accuracy: 1 %

  13. Results 0→   invariant mass in pp PHOS PHOS EMCAL EMCAL EMCAL

  14. Results 0→   →e+e- e+e-invariant mass in pp CTS Data Combinatorial background

  15. Results  and  invariant mass in pp PHOS PHOS → → EMCAL →0 EMCAL EMCAL → →

  16. Results  →   →e+e- e+e-invariant mass in pp CTS CTS CTS CTS Data Combinatorial background

  17. Results 0peakand width • DATA • MC/MCwith realistic calibration and non-linearity (calibration ongoing) Notice different ranges! EMCAL PHOS CTS EMCAL PHOS CTS above pT6 GeV/c cluster unfolding Measured 0 mass consistent with PDG value → good energy linearity

  18. Results  peakand width PHOS EMCAL CTS PHOS EMCAL CTS Measured  mass consistent with PDG value → good energy linearity

  19. Results Raw 0 and  spectra in PHOS 0 spectra  spectrum Range 0.5 < pT < 5 GeV/c for pp @ s = 900 GeV Range 0.5 < pT < 20 GeV/c for pp @ s = 7 TeV Range 5 < pT < 10 GeV/c for pp @ s = 7 TeV

  20. Results Raw 0 and  spectra in EMCAL 0 spectrum  spectrum Range 0.5 < pT < 20 GeV/c for pp @ s = 7 TeV Range 2.5 < pT < 20 GeV/c for pp @ s = 7 TeV

  21. Results Raw 0 and  spectra in CTS 0range 0.4 < pT < 7 GeV/c for pp @ s = 7 TeV  range 0.6 < pT < 6 GeV/c for pp @ s = 7 TeV

  22. Results Systematic uncertainties Raw spectra in CTS • Material budget: - 6.2 % • Minimum pT of the electron/positron: < 2 % • dE/dx of the electron/positron: < 1 % • 2 for the photon reconstruction: < 2 % • Track reconstruction in the TPC: < 2 % • Energy assymetry of meson decay products: 1 - 2 % • Backgrond calculations: 2 - 7 % • Signal integration: < 0.5 % Total: 5 - 13 % in wide range + 3.3 Raw spectra in PHOS • Absolute energy scale and decalibration: • 6.5 % decalibration leads to systematic error 5 % • Energy non-linearity: • 17 % @ pT = 1 GeV/c • < 2 % @ pT > 1.5 GeV/c • Geometrical acceptance: 2 % • Raw spectrum extraction from invariant mass peaks: 2 % • Conversion probability: 3.3 % • Particle identification: 3 % Total: 10 % @ pT > 1.5 GeV/c

  23. Results 0 production spectrum, pp @ 900 GeV L = 0.12 nb-1 Data points normalized for the cross section  = 50  10 mb Tsallis fit with: T = 0.15 N = 8.5 NLO: CTEQ5M, KKP P. Aurenche et al., Eur. Phys. J C13, 347 (2000)

  24. Results 0 production spectrum, pp @ 7 TeV LPHOS = 4.3 nb-1 Data points normalized for the cross section  = 67  10 mb Tsallis fit for PHOS with: T = 0.14 N = 6.8 LCTS = 1.2 nb-1 NLO: CTEQ5M, KKP P. Aurenche et al., Eur. Phys. J C13, 347 (2000)

  25. Results /0ratio in pp @ 7 TeV (CTS) World data taken from Phys RevC 75(2007) 0224909 Good agreement with PYTHIA predictions and world data measured in hadron-hadron collisions

  26. Results 0 in Pb-Pb • PHOS data @ 2.76 A TeV • 1.7 M minimum bias events • Cluster energy E>0.3 GeV • |A| < 0.7 • No track extrapolated to clusters in PHOS within 10cm • Requirement on dispersion axis • Combinatorial background described by event mixing • 0 peak well visible above background • Analysis ongoing

  27. Summary and Outlook • Neutral mesons 0 and  are observed in ALICE calorimeters and CTS • Good agreement between independent analyses • Production spectra are measured in pp collisions • 0 spectrum @ 900 GeV up to pT = 5 GeV/c @ 7 TeV up to pT = 25 GeV/c •  meson spectrum observed in pp collisons • 3 < pT < 20 GeV/c in EMCAL • 5 < pT < 10 GeV/c in PHOS • 0.6 < pT < 6 GeV/c in CTS • 0/  ratio in good agreement with previous mesurements • 0 meson visible in Pb-Pb @ s = 2.76 A TeV • Ongoing analyses with Pb-Pb @ s = 2.76 A TeV in a wide range 1 < pT < 10 GeV/c • RAA measurement • RCP measurement • New components of the ALICE detector will be inserted soon

  28. Same towers as for EMCal, but shorter Super Modules in  Acceptance (including PHOS):  = 1.4  = 60o To be installed in 2012 Experimental apparatus DCal DCal-3 DCal-2 DCal-1

  29. BACKUP

  30. Results Calculation of event rate • N0 - number of detected 0 in selected pT-bin (raw spectrum) • L - luminosity • T - run time • Br - branching ratio • Ceff - geometrical acceptance • Crec - reconstruction efficiency • Cconv - correction due to conversion loss • Ctrig - trigger bias correction

  31. Results Reconstruction efficiency y = 1,  = 2 MC with single 0 or  and flat pT distribution EMCAL 0 PHOS 0 PHOS 

  32. Results Reconstruction efficiency |y| < 0.9,  = 2 MC with single 0 and flat pT distribution CTS 0

  33. Motivation Theory predictions pp → 0 X pp →  X • Cross section in pp LO pQCD: Pythia 6 NLO pQCD + CTEQ5M + KPP Bands indicate possible uncertainties in QCD scale P.Aurenche, et al,., Eur. Phys. J. C13,347 (2000)

  34. Motivation Expected event rates in pp pp → 0 X, 0 →   pp →  X,  →   • ALICE PHOS Pythia 6 NLO pQCD + CTEQ5M + KPP Expected pT range of neutral meson spectrum pT < 25 GeV/c for 0 pT < 20 GeV/c for 

  35. Combined analysis (CTS+PHOS/EMCal) h →  (→e+ e-) +  PHOS + CTS EMCAL + CTS PHOS + CTS

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