photon physics in alice
DESCRIPTION
Photon physics in ALICE. D.Peressounko RRC “Kurchatov institute” for the ALICE collaboration. Photons in heavy ion collision. Direct photons: photons not originated in hadron decays. - prompt photons : photons created in collisions of - PowerPoint PPT PresentationTRANSCRIPT
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Photon physics in ALICE
D.PeressounkoRRC “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
g prompt
g isolated g thermal
Spectrum: temperature, fireball lifetime
RAA: control of initial state
Collective flow: flow development on early stagesHBT: 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, ||<0.7
0
1
2345
6
7
9
8
1112 13 14
15
17
0
12
3
4
1610
3/5 PHOS=60, ||<0.12
Full TPC+ITS=360, |TPC|<0.9, |ITS|<1.2
Photon physics with ALICE
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4Photon physics with ALICE
Calorimeters: PHOS and EMCALPHOS EMCAL
sE/E (%)
sx (mm)
Rip (cm)
222
12.13.33.1
EE
22
44.026.3
E
460
222
8.43.117.1
EE
428
E3.55.1
sE/E (%)
sx (mm)
Rip (cm)
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5Photon physics with ALICE
Conversion method
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6Photon physics with ALICE
Spectrum of direct photons: PHENIX
Tini = 300 to 600 MeV t0 = 0.15 to 0.5 fm/c D.d’Enterria, D.Peressounko, Eur.Phys.J.C 46 (2006)
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Spectrum of direct photons: ALICE
Photon physics with ALICE 7
[[1] N. Armesto, (ed.) et al. F.Arleo et al, J.Phys.G35:054001, 2008 2+1 hydro, Tin=650 MeV, reach RHG EOS pQCD: CTEQ6.5M + nDSg, AKK+wc=50 GeV[[2] F. Arleo et al.,(Yellow Report)hep-ph/0311131 pQCD:CTEQ5M,KKP(BFGII for g), EKS98+Eloss(0 for g)[[3] S.Tubide et al., Phys.Rev.C72:014906,2005
To estimate expected systematic error extrapolate PHENIX results to ALICE accounting S/Bg ratio, difference in amount of material, resolutions etc.
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8Photon physics with ALICE
Direct photon HBT
Most probable yield
The lowest yield
Correlation method: Predictions
hadronic gasQGP
sumpQCD
M.M. Aggarwal et al.,Phys.Rev.Lett.93:022301,(2004)
86Kr+natNi @ 60 AMeV
181Ta+197Au @ 40 AMeV
M.Marques et al., (TAPS collaboration) PRL 73 (1994) 34.
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9Photon physics with ALICE
Direct photon HBT in ALICE/PHOS, MC simulations
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10Photon physics with ALICE
Direct photons and hadron RAA in AA collisions: RHIC
[PHENIX, QM2009]
Direct photons scale as with Npart and provide calibration of the initial state of AA collisions.
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Photon physics with ALICE 11
Direct photon RAA in ALICE
F. Arleo et al. Yellow report, CERN-2004-009-D, hep-ph/0311131
~measurable level
So far ALICE collected ~15 nb-1
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12Photon physics with ALICE
Isolated photons22 R
g TT pp
i
In pp collisions:
In PbPb collisions
cutTT pp
i
Due to underlying event one should use fixed cut
Due to limited acceptance of ALICE use R = 0.4
hep-ex/0609031
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13Photon physics with ALICE
Isolation of fragmentation photons
‐ The fragmentation channel dominates al low pT‐ After ~ 35 GeV the Compton channel dominates.
IsolatedAll direct photons
- Increase the Compton (and annihilation) contributions.‐ Decrease strongly the fragmentationchannel
Raphaelle Ichou, Ph.D thesis 2010
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14Photon physics with ALICE
Isolated photons: spectrum
Raphaelle Ichou, Ph.D thesis 2010
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Isolated direct photons
Photon physics with ALICE15
Y. Mao et al., Eur.Phys.J.C57:613-619,2008
IC: R =0.3, S(pT)=2 GeV/c IC: R =0.2, pT>2 GeV/c
G. Conesa et al., ALICE-INT-2005-014, NIM A 580 (2007) 1446
2 PHOS modules5 PHOS modules
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16Photon physics with ALICE
Isolated photons: jet tagging
xEzpout kT
pTa
XE= -pTh · pTg / |
pTg|2
pTt
• Direct access of jet modification & medium response • Clean way to measure Fragmentation Functions: approximate z with xE
- Caveat: kT smeares relation z<-> xE
• Systematic control on geometrical bias
Look at modification of FF in AA collisions with respect to pp
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17Photon 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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18Photon physics with ALICE
Correlation function with direct photons
• Started analysis• First results are promising…
Y.Mao @ Hot Quarks 2010
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19Photon physics with ALICE
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.
performance01/09/2010
performance01/09/2010 pp @ √s= 7 TeVpp @ √s= 7 TeV
Y.Mao @ Hot Quarks 2010
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20Photon physics with ALICE
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.
Conclusions
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21Photon physics with ALICE
Backup slides
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g-h correlation in pp and AA
Photon physics with ALICE22
xEzpout kT
pTa
XE= -pTh · pTg / |
pTg|2
EPJC (2008) 57: Y. Mao
background photonsbackground soft hadrons
XE
DAA = CFAA/CFpp
pTt
PYQUEN
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g-hadron correlations
Photon physics with ALICE23
G. Conesa, Proceedings of Science, PoS (HIGH-pTLHC) 003
All associated charged hadrons with pT > 2 GeV/cPYTHIA pp collisions √s=14 TeV
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Photon physics with ALICE
Isolated Spectra in EMCAL
24
pp @ √14 TeV PbPb @ √5.5 TeV PbPb @ √5.5 TeV, qhat = 50
pp = PYTHIAPbPb =PYTHIA (signal) +HIJING (UE) Full reconstruction in ALICE
g-jet (signal); jet-jet (0 –hadron background)
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25Photon physics with ALICE
Influence of isolation on different sources
Pythia MSUB(14) =1 : Annihila5on ONPythia MSUB(29) =1 : Compton ONPYTHIA6.420 :* UE Perugia hard :more ISR/FSR, less MPI & beam remnants* UE Perugia sol :less ISR/FSR, more MPI & beam remnants
• 80%‐100% of Compton andannihila5on photons• 60% of fragmenta5onphotons• 70%‐85% of total photons• 20%‐1% of π0
Raphaelle Ichou, Ph.D thesis 2010
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Photon physics with ALICE
PHOton Spectrometer: PHOS
High granularity and resolution spectrometer: 10,752 (17,920) lead-tungstate crystals
(PbWO4), 3(5) modules (5664 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 angle 60º(100o)
For E > 10 GeV, E/E < 1.5% and sx = [0.5,2.5] mm
Focus on low and moderate pT
High resolution 0 and Thermal photons
26/25
CPV (not installed yet)
CrystalsEMC
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Photon physics with ALICE 27/25
Module:2x2
towers
• Coverage =1.4, =40o (107o)
• Granularity = = 0.014• Resolution E/E=11%/√E, sx=[3,50]• Focus on moderate to high
pT0 and prompt direct
photonjet
Pb/Sc Shashlik– 13K channels– 4 SM for 2009-2010
runs– Complete for 2011?
runs
EMCAL