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Photon physics in ALICE D.Peressounko RRC Kurchatov institute for the ALICE collaboration

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Photons in heavy ion collision Photon physics with ALICE 2 Direct photons: photons not originated in hadron decays. - prompt photons: photons created in collisions of incoming partons and in parton fragmentation - thermal photons: thermal emission of hot matter Isolated photons: photons without hadron activity in some cone prompt isolated thermal Spectrum: temperature, fireball lifetime R AA : control of initial state Collective flow: flow development on early stages HBT: space-time dimensions of hot matter Jet tagging: calibrated jets, fragmentation function modification in matter

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ALICE setup for 2010 3 4/11 EMCAL =40 , | |

Isolated direct photons Photon physics with ALICE 15 Y. Mao et al., Eur.Phys.J.C57:613-619,2008 IC: R =0.3, (p T )=2 GeV/c IC: R =0.2, p T >2 GeV/c G. Conesa et al., ALICE-INT-2005-014, NIM A 580 (2007) 1446 2 PHOS modules 5 PHOS modules

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16 Photon physics with ALICE Isolated photons: jet tagging xEzxEz p out kTkT p Ta X E = -p T h p T / |p T | 2 p Tt Direct access of jet modification & medium response Clean way to measure Fragmentation Functions: approximate z with x E - Caveat: k T smeares relation z x E Systematic control on geometrical bias Look at modification of FF in AA collisions with respect to pp

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17 Photon physics with ALICE Gamma-jet correlations: PHENIX A. Adare et al (PHENIX) PRC 80, 024908 (2009) M.Connor @ Hard Probes 2010

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18 Photon physics with ALICE Correlation function with direct photons Started analysis First results are promising Y.Mao @ Hot Quarks 2010

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19 Correction functions with isolated triggers 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. performance 01/09/2010 performance 01/09/2010 pp @ s= 7 TeV Photon physics with ALICE Y.Mao @ Hot Quarks 2010

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Photons provide the possibility to study a large variety of characteristics of heavy-ion collisions ALICE measures photons in detectors based on different technologies which provide reliable cross-check Ongoing analyses look promising. 20 Photon physics with ALICE Conclusions

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Backup slides 21 Photon physics with ALICE

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-h correlation in pp and AA Photon physics with ALICE 22 xEzxEz p out kTkT p Ta X E = -p T h p T / |p T | 2 EPJC (2008) 57: Y. Mao background photons background soft hadrons XEXE D AA = CF AA /CF pp p Tt PYQUEN

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-hadron correlations Photon physics with ALICE 23 G. Conesa, Proceedings of Science, PoS (HIGH-pTLHC) 003 All associated charged hadrons with p T > 2 GeV/c PYTHIA pp collisions s=14 TeV

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Isolated Spectra in EMCAL 24 pp @ 14 TeV PbPb @ 5.5 TeV PbPb @ 5.5 TeV, qhat = 50 pp = PYTHIA PbPb =PYTHIA (signal) +HIJING (UE) Full reconstruction in ALICE -jet (signal); jet-jet ( 0 hadron background) Photon physics with ALICE

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Influence of isolation on different sources Pythia MSUB(14) =1 : Annihila5on ON Pythia MSUB(29) =1 : Compton ON PYTHIA6.420 : * UE Perugia hard : more ISR/FSR, less MPI & beam remnants * UE Perugia sol : less ISR/FSR, more MPI & beam remnants 80% 100% of Compton and annihila5on photons 60% of fragmenta5on photons 70% 85% of total photons 20% 1% of 0 25 Photon physics with ALICE Raphaelle Ichou, Ph.D thesis 2010

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PHOton Spectrometer: PHOS High granularity and resolution spectrometer: 10,752 (17,920) lead-tungstate crystals (PbWO 4 ), 3(5) modules (56 64 crystals per module) crystal size: 22 22 180 mm 3 depth in radiation length: 20 Distance to IP: 4.4 m Acceptance: pseudo-rapidity [-0.12,0.12] azimuthal angle 60(100 o ) For E > 10 GeV, E/E < 1.5% and x = [0.5,2.5] mm Focus on low and moderate p T High resolution 0 and Thermal photons 26/25 CPV (not installed yet) Crystals EMC Photon physics with ALICE

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27/25 Module: 2x2 towers Coverage =1.4, =40 o (107 o ) Granularity = = 0.014 Resolution E/E=11%/E, x =[3,50] Focus on moderate to high p T 0 and prompt direct photon jet Pb/Sc Shashlik 13K channels 4 SM for 2009-2010 runs Complete for 2011? runs EMCAL Photon physics with ALICE