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First physics from the ALICE electromagnetic calorimeters

First physics from the ALICE electromagnetic calorimeters.  0 and  spectra Neutral-charged correlations. Gustavo Conesa Balbastre for the ALICE collaboration. First physics from electromagnetic calorimeters.

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First physics from the ALICE electromagnetic calorimeters

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  1. First physics from the ALICE electromagnetic calorimeters 0 and  spectra Neutral-charged correlations Gustavo Conesa Balbastre for the ALICE collaboration

  2. First physics from electromagnetic calorimeters • Calorimeters offer the unique capability to identify photons, electrons and hadrons (neutral mesons) in a wide momentum range 0<pT<100 GeV/c • Elementary QCD calculation in pp • perturbative: NLO, NNLO for various processes including exclusive processes with photon in final state • Non perturbative: structure function, fragmentation function, initial and final state effects • Reference data for AA • Medium generated effects in AA • Medium color density: quenching of high pt hadrons, photons unaffected (?), modification of FF, • Additional photon sources: thermal, jet conversion, bremsstrahlung • The observables • 0, , direct photon spectra • Correlation with hadron correlation • -jet • Q vs g quenching

  3. RHIC experience: Direct photons 0 and  in AA collisions [PHENIX, QM2009] Neutral meson spectra at RHIC was the first evidence of a parton energy loss in a quark matter. RAA scales with Npart. What expects us at LHC?

  4. RHIC experience: -hadron and hadron-hadron correlations -h correlations [PHENIX, QM2008] h-h correlations [STAR] Suppression of away-side peak in central Au-Au collisions proves a parton energy loss in a quark matter.

  5. ALICE: The dedicated HI Experiment

  6. ALICE setup for 2010 Full TPC+ITS =360, |TPC|<0.9, |ITS|<1.2 4/10 EMCAL =40, ||<0.7 4 5 3 6 2 7 1 8 0 9 17 16 10 15 11 14 12 13 0 4 3/5 PHOS =60, ||<0.12 1 3 2

  7. PHOton Spectrometer: PHOS • High granularity and resolution spectrometer: • 10,752 (17,920)lead-tungstate crystals(PbWO4), 3(5) modules (5664 crystals per module) • crystal size:22  22  180 mm3 • depth in radiation length:20 • Distance to IP:4.4 m • Acceptance: • pseudo-rapidity [-0.12,0.12] • azimuthal angle60º(100o) • For E > 10 GeV, E/E < 1.5% and x = [0.5,2.5] mm • Focus on low and moderate pT • High resolution 0 and  • Thermal photons CPV (not installed yet) Crystals EMC

  8. Pb/Sc Shashlik • 4k (11K) channels • 4 Super Modules for 2009-2010 runs • Complete (10 SM) for 2011? runs EMCAL Module: 2x2 towers 12 Modules per strip module 24 Strip Modules per Super Module • Coverage =1.4, =40o (107o) • Distance to IP: 4.3 m • Granularity  = = 0.014 • Resolution E/E=11%/√E, x=[3,50] mm • Focus on moderate to high pT • 0 and  • prompt direct photon • jet

  9. DCAL • Same towers than the EMCAL, shorter Super Modules in . • Including PHOS, acceptance is =1.4, =60º • To be installed for 2012 runs • Focus on /0/jet-jet correlations

  10. Scope of first physics • Inclusive spectrum of 0 production in pp collisions at 900 GeV and 7 TeV in mid-rapidity and pT range from 0.3-0.5 to 20-30 GeV/c • Measure inclusive spectrum of ,  and other neutral mesons production in pp collisions at 7 TeV in pT range from 3-5 to 15-20 GeV/c • Physics: • Constrain pQCD and non perturbative aspects of QCD • Provide reference spectrum for Pb-Pb collisions at 2.76 and 5.5 TeV

  11. Neutral meson measurement in ALICE • ALICE provides 3 independent ways to identify 0 and  mesons, through invariant mass analysis of photon pairs and external conversion electrons: • H->    (both on PHOS or EMCAL) • H->    e+e- (CTS, PHOS or EMCAL) • H->    e+e- e+e- (CTS) • Performance plots, p+p at 7 TeV, coming next

  12. PHOS h-> +  0 • 175 million minimum bias events. • Cluster selection (better tuning under study). • Ecl>0.3 GeV • Ncell3 • 0 plots lines: • Red line: fit to combinatorial. • Blue points: histogram minus combinatorial fit. • Blue line: - fit of blue points.

  13. PHOS h-> + Estimation of decalibration and comparison with MC Current PHOS decalibration is 7% 0 reconstruction efficiency Efficiency limited to < 30-40 GeV when the 2 photons merge into a single cluster in the calorimeter.

  14. PHOS h-> + raw yield • 175 million Minimum Bias events. • We identify 0 up to 20 GeV, we expect to arrive to 30 GeV.

  15. EMCAL h-> + 188 million minimum bias events. Cluster selection (better tuning under study) Ecl>0.3 GeV Ncell2  0

  16. EMCAL h-> + 0 width vs pT in real data and MC Still important decalibration in EMCAL, we are working to get the MC values. Reconstruction efficiency descends fast after 6-7 GeV because of the large cell size / clusterizer, being our measurement limit actually about 10 GeV We are working in a new clusterization procedure that will allow us to arrive to 20 GeV. Data MC Data

  17. EMCAL h-> + • 188 million minimum bias events • pT reach 10 GeV due to size of cells and clusterizer used. • We plan to improve clusterizer and arrive to 20 GeV.

  18. h-> + -> e+e-e+e-, data candidate

  19. CTS h-> + -> e+e-e+e- • For pT > 1 GeV • Photon conversion probability of about 8% • Photon reconstruction efficiency is of 70% with close to 100% purity

  20. CTS h-> + -> e+e-e+e-, raw yields For ~108 minimum bias p+p events at 7 TeV, the accessible pT range is: 0 : 0.3-0.4 to 10 GeV/c  : 0.6 to 6 GeV/c

  21. PHOS-CTS h-> + -> e+e-  0 Events per 5 MeV/c2 Events per 10 MeV/c2 pp @ √s= 7 TeV pp @ √s= 7 TeV 140 million p+p events at 7 TeV • p0can be identified with pT>0.5 GeV/c • is visible with pT>2 GeV/c

  22. PHOS-CTS h-> + -> e+e- pp @ √s= 7 TeV pp @ √s= 7 TeV

  23. EMCAL-CTS h-> + -> e+e- • 140 million minimum bias events. • Non linearity correction not applied yet • masks the  Events per 5 MeV/c2 pp @ √s= 7 TeV

  24. EM Cluster - Hadron correlation analysis See Yaxian’s presentation performance 01/09/2010 performance 01/09/2010 pp @ √s= 7 TeV pp @ √s= 7 TeV • Correlation of Charged Tracks / PHOS clusters / EMCAL clusters with charged hadrons measured in TPC+ITS. • Left Plot: Near (mainly 0 for EM calorimeters) and away side correlation shows a jet-like structure • Right plot: Applying isolation cuts to clusters or 0, the away side correlation remains: single pi0 - jets and/or direct-photon - jet ? • Consolidate the isolation cut, extract kT, FF.

  25. Summary • ALICE has identifed 0 and  neutral mesons with its calorimeters and central tracking system. • The agreement between the analysis seems to converge, but work is needed, specially on calibration and non linearity effects in the calorimeters. • For the end of the p+p collisions at 7 TeV data taking period at LHC we expect to measure 0 in the range 0.3 < pT <30 GeV and  in the range 0.6 < pT < 10 GeV. • We are getting ready for and looking forward to Pb+Pb collisions in a couple of months …

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