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

January 2011, Cracow Epiphany Conference Adam Matyja Motivation Electromagnetic calorimeters offer a possibility to identify photons and neutral mesons in a wide p T range  Charged hadrons identification limited to low p T 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

January 2011, Cracow Epiphany Conference Adam Matyja Experience from RHIC  0,  and direct photons in AA collisions from PHENIX The first evidence of a parton energy loss in a quark-gluon matter R AA scales with N part What is expected at LHC energies? arXiv: v1 (2008) PHENIX, QM2008 Motivation

January 2011, Cracow Epiphany Conference Adam Matyja  /  0 ratio in pp and AA collisions Ratio is universal for a wide energy range Needed for nuclear transport models PHENIX, PRC 75, (2007) f(m T )=(m T +a) -n, a=1.2, n=10-14 ALICE capabilities: Large p T region Both pp and Pb-Pb measurement Motivation

January 2011, Cracow Epiphany Conference Adam Matyja ALICE detector EMCAL PHOS CTS = ITS + TPC Experimental apparatus

January 2011, Cracow Epiphany Conference Adam Matyja EMCal 12 Modules per Strip Module 24 Strip Modules per Super Module Shashlik technology  Tower - 77 layers: Pb mm Scintillator mm Size - 6  6  25 cm 3  Module (2  2 towers) Geometry  4/10 Super Modules are installed Next 6 are being installed in Dec Jan  24  48 towers in each Super Module Coverage: |  | < 0.7, 80 o <  < 120 o Distance to IP: 4.5 m Material budget from IP: 0.8 X 0 Energy range: 0 < E < 250 GeV Energy resolution: 10 Super Modules in EMCal Experimental apparatus

January 2011, Cracow Epiphany Conference Adam Matyja PHOS Technology  Crystal of lead tungstate (PbWO 4 )  Size: 2.2  2.2  18 cm 3 Geometry  3/5 Super Modules are installed 1 more expected in 2012  64  56 crystals in each Super Module Coverage:  |  | < 0.13  260 o <  < 320 o Distance to IP: 4.6 m Material budget from IP: 0.2 X 0 Energy range: 0 < E < 100 GeV Energy resolution: CPV (not installed yet) Crystals Experimental apparatus CPV - charged particle veto

January 2011, Cracow Epiphany Conference Adam Matyja CTS = ITS + TPC 5 m 2.5 m CTS energy resolution:  E/E  2% TPC:  Diameter  Length : 5 m  5 m  Acceptance:  = 2 , |  |<0.9  Readout chambers: 72  Pad readout (3 types):  Drift field: 400 V/cm  Maximum drift time: 94  s  Central electrode HV: 100 kV  Gas: Active volume: 90 m 3 Ne-CO 2 -N 2 : 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 Experimental apparatus

January 2011, Cracow Epiphany Conference Adam Matyja 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) Distribution of conversions Reconstructed  0 candidate through conversions Results

January 2011, Cracow Epiphany Conference Adam Matyja Data sample ALICE minimum bias trigger ALICE has collected:  about 9 M pp minimum bias  s = 900 GeV (0.15 nb -1 )  about 800 M pp minimum bias  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  s = 900 GeV (0.12 nb -1 )  about 360 M pp minimum bias  s = 7 TeV (4.3 nb -1 ) - PHOS  about 100 M pp minimum bias  s = 7 TeV (1.2 nb -1 ) - CTS Results

January 2011, Cracow Epiphany Conference Adam Matyja 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 N cells  3 E cl > 0.3 GeV |A| < 1 (  0 ) or |A| < 0.7 (  )  EMCal N cells  2 E cl > 0.5 GeV (  0 ) or E cl > 0.3 GeV (  ) |A| < 1 (  0 ) or |A| < 0.6 (  ) Results A = (E 1 - E 2 )/(E 1 + E 2 )

January 2011, Cracow Epiphany Conference Adam Matyja Calibration PHOS  Pre-calibration: adjusting the high voltage bias to provide the same gain Accuracy: %  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 % Results

January 2011, Cracow Epiphany Conference Adam Matyja  0 →   invariant mass in pp PHOS EMCAL Results

January 2011, Cracow Epiphany Conference Adam Matyja  0 →   →e + e - e + e - invariant mass in pp Results CTS Data Combinatorial background

January 2011, Cracow Epiphany Conference Adam Matyja  and  invariant mass in pp EMCAL PHOS Results →0→0  → 

January 2011, Cracow Epiphany Conference Adam Matyja  →   →e + e - e + e - invariant mass in pp Results CTS Data Combinatorial background

January 2011, Cracow Epiphany Conference Adam Matyja  0 peak and width PHOS EMCAL MC/MC with realistic calibration and non-linearity (calibration ongoing) Measured  0 mass consistent with PDG value → good energy linearity above p T  6 GeV/c cluster unfolding Notice different ranges! Results CTS DATA

January 2011, Cracow Epiphany Conference Adam Matyja  peak and width EMCAL PHOS Measured  mass consistent with PDG value → good energy linearity Results CTS

January 2011, Cracow Epiphany Conference Adam Matyja Raw  0 and  spectra in PHOS Range 0.5 < p T < 5 GeV/c for  s = 900 GeV Range 0.5 < p T < 20 GeV/c for  s = 7 TeV Range 5 < p T < 10 GeV/c for  s = 7 TeV  0 spectra  spectrum Results

January 2011, Cracow Epiphany Conference Adam Matyja Raw  0 and  spectra in EMCAL Range 0.5 < p T < 20 GeV/c for  s = 7 TeV Range 2.5 < p T < 20 GeV/c for  s = 7 TeV  0 spectrum  spectrum Results

January 2011, Cracow Epiphany Conference Adam Matyja Raw  0 and  spectra in CTS  0 range 0.4 < p T < 7 GeV/c for  s = 7 TeV  range 0.6 < p T < 6 GeV/c for  s = 7 TeV Results

January 2011, Cracow Epiphany Conference Adam Matyja Systematic uncertainties Raw spectra in PHOS Absolute energy scale and decalibration:  6.5 % decalibration leads to systematic error 5 % Energy non-linearity:  17 p T = 1 GeV/c  1.5 GeV/c Geometrical acceptance: 2 % Raw spectrum extraction from invariant mass peaks: 2 % Conversion probability: 3.3 % Particle identification: 3 % Total: 10 p T > 1.5 GeV/c Results Raw spectra in CTS Material budget: % Minimum p T 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: % Backgrond calculations: % Signal integration: < 0.5 % Total: % in wide range + 3.3

January 2011, Cracow Epiphany Conference Adam Matyja  0 production spectrum, 900 GeV L = 0.12 nb -1 Tsallis fit with: T = 0.15 N = 8.5 Data points normalized for the cross section  = 50  10 mb NLO: CTEQ5M, KKP Results P. Aurenche et al., Eur. Phys. J C13, 347 (2000)

January 2011, Cracow Epiphany Conference Adam Matyja  0 production spectrum, 7 TeV L PHOS = 4.3 nb -1 Tsallis fit for PHOS with: T = 0.14 N = 6.8 Data points normalized for the cross section  = 67  10 mb NLO: CTEQ5M, KKP Results L CTS = 1.2 nb -1 P. Aurenche et al., Eur. Phys. J C13, 347 (2000)

January 2011, Cracow Epiphany Conference Adam Matyja  /  0 ratio in 7 TeV (CTS) Results World data taken from Phys RevC 75(2007) Good agreement with PYTHIA predictions and world data measured in hadron-hadron collisions

January 2011, Cracow Epiphany Conference Adam Matyja  0 in Pb-Pb PHOS 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 Results

January 2011, Cracow Epiphany Conference Adam Matyja 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   GeV up to p T = 5 7 TeV up to p T = 25 GeV/c  meson spectrum observed in pp collisons  3 < p T < 20 GeV/c in EMCAL  5 < p T < 10 GeV/c in PHOS  0.6 < p T < 6 GeV/c in CTS  0 /  ratio in good agreement with previous mesurements  0 meson visible in  s = 2.76 A TeV Ongoing analyses with  s = 2.76 A TeV in a wide range 1 < p T < 10 GeV/c  R AA measurement  R CP measurement New components of the ALICE detector will be inserted soon

January 2011, Cracow Epiphany Conference Adam Matyja DCal Same towers as for EMCal, but shorter Super Modules in  Acceptance (including PHOS):   = 1.4   = 60 o To be installed in 2012 Experimental apparatus DCal-1 DCal-2 DCal-3

January 2011, Cracow Epiphany Conference Adam Matyja BACKUP

January 2011, Cracow Epiphany Conference Adam Matyja Calculation of event rate N  0 - number of detected  0 in selected p T -bin (raw spectrum) L - luminosity T - run time Br - branching ratio C eff - geometrical acceptance C rec - reconstruction efficiency C conv - correction due to conversion loss C trig - trigger bias correction Results

January 2011, Cracow Epiphany Conference Adam Matyja Reconstruction efficiency MC with single  0 or  and flat p T distribution EMCAL  0 PHOS  PHOS  0  y = 1,  = 2  Results

January 2011, Cracow Epiphany Conference Adam Matyja Reconstruction efficiency MC with single  0 and flat p T distribution |y| < 0.9,  = 2  Results CTS  0

January 2011, Cracow Epiphany Conference Adam Matyja Theory predictions Cross section in pp pp →  0 X NLO pQCD + CTEQ5M + KPP Bands indicate possible uncertainties in QCD scale P.Aurenche, et al,., Eur. Phys. J. C13,347 (2000) LO pQCD: Pythia 6 pp →  X Motivation

January 2011, Cracow Epiphany Conference Adam Matyja Expected event rates in pp ALICE PHOS pp →  0 X,  0 →   pp →  X,  →   Expected p T range of neutral meson spectrum p T < 25 GeV/c for  0 p T < 20 GeV/c for  Motivation Pythia 6 NLO pQCD + CTEQ5M + KPP

January 2011, Cracow Epiphany Conference Adam Matyja Combined analysis (CTS+PHOS/EMCal) h →  (→e + e - ) +  PHOS + CTS EMCAL + CTS