Photon Analysis Strategiesat ALICE

Kenta Shigaki(Hiroshima University )

ALICE Asian WorkshopNovember 5, 2009

Yonsei University, Seoul

physics prospects at ALICE/LHC– physics outcomes (and standing issues) at RHIC– global understanding of new state of matter

importance of photons in wide pT range

physics via photons – goals, prospects, status– neutral mesons, pQCD photons, thermal photons

first year physics strategies data import strategy summary and concluding remarks

Presentation Outline

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 2/21

dense: energy loss of (even heavy) quarks– jet quenching (high pT suppression)

– jet modification partonic: quarks’ degrees of freedom,

screening– constituent quark number scaling of collective

motion– J/ suppression

strongly coupled: perfect fluidity– hydro-dynamical collective motion

hot: thermally radiative– thermal (virtual) photons

RHIC Outcomes: New State of Matter

Nov. 5, 2009

The matter may melt and/or regenerate J/’s

The matter is dense

The matter modifies jets The matter is hot

The matter is strongly coupled

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 3/21

partonic density– jet quenching/modification at very high pT

– J/, suppression/regeneration initial temperature and space-time evolution

– thermal photons– thermal photon correlation

chiral symmetry restoration– mass states of light vector mesons

i.e. global understanding via penetrating probes

LHC to overcome physics issues

Standing Issues to Overcome

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 4/21

Photon Collection from HI Collisions

Nov. 5, 2009

Pre-equilibrium

ThermalizationQGP phase?

Mixed phaseHadronization (Freeze-out) + Expansion

Compton/AnnihillationFragmentation

Prompt PhotonJet-Photon Conversion

Jet-Bremsstrahlung (QGP)

Jet+MediumThermal Photon (QGP)Thermal Photon (HG)

Thermal Photon

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 5/21

ALICE photon spectrometer: PHOS– photons, nuetral mesons, jet tagging

+ L0, L1 trigger capability wide coverage from 100 MeV to 100 GeV

– high eneregy resolution, high granularity /E ~ 3 %/E [GeV] up to 100 GeV PbWO4 crystals of 22 (1.0 RMoliere)×22×180 (20 X0)

mm3

APD + charge sensitive pre-amplifier readout cooled and controlled at 250.1 C

– || < 0.12, = 100 at 4.6 m 56×64×5 modules; 17,920 channels, 12.5 t

– 3 (out of 5) modules installed and cooled

Precise Photon Measurement at ALICE

Nov. 5, 2009

thermal ~ eE/T

hadron decays

jet-medium interaction jet-photon conversion bremsstrahlung

pQCD processes ~ pTn

compton scattering annihilation fragmentation

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 6/21

LHC start-up schedule– 2008/09 first beam– 2009/12 p+p, s = 0.9, 2.2 TeV– 2010 p+p, s = 10 TeV, 1032 cm2s1

– 2010/10 Pb+Pb, sNN = 3.9 TeV, 5×1025 cm2s1

expectations in initial years– p+p s = 14 TeV, 1031 cm2s1 (ALICE), 107 s/y

s = 5.5 TeV, 1031 cm2s1, 106 s/y×1 y

– Pb+Pb sNN = 5.5 TeV, 1027 cm2s1, 106 s/y

– p+Pb sNN = 8.8 TeV, 1029 cm2s1, 106 s/y×1 y

– Ar+Ar sNN = 6.3 TeV, 1029 cm2s1, 106 s/y×1 y

Boundary Condition: LHC Schedule

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 7/21

higher pT reach + stronger suppression than RHIC– clearer measurement of quark energy loss

e.g. quark flavor/spin dependent suppression?

“day-1” ALICE physics program– enough acceptance with initial 3 PHOS modules

Physics #1: Neutral Meson Quenching

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 8/21

assumptions:– 10 TeV p+p;

5×1028 cm2s1;180 days×10%

– 0 in NLO/CTEQ6M/KKP;particle ratios from PYTHIA

– 3/5 PHOS geom. coverage (~ high pT limit) only

Statistics + pT Reach in 1st p+p Run

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 9/21

assumptions:– 3.9 TeV Pb+Pb;

5×1025 cm2s1;30 days×10%;~ 10% central (b < 5 fm)

– NLO pQCD×PYTHIA×N-N binary scaling (1,150 for central Pb+Pb)×suppression (0.1)

– 3/5 PHOS geom. coverage (~ high pT limit) only

Statistics + pT Reach in 1st Pb+Pb Run

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 10/21

statistics not really an issue

LHC First Year versus Years at RHIC

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 11/21

Real Feasibility Issue: Significance

Nov. 5, 2009

single particle + HIJING “hybrid” approach– NLO pQCD×PYTHIA×N-N binary

scaling×suppression– mass reconstruction in AliRoot

e.g. 0 in ~ 10% central Pb+Pb at 3.9 TeV– 5×1025 cm-2 s-1, 30 days, 10% uptime; RAA = 0.1

for details, ref. H.Torii, this afternoon for multiplicity effect studies, ref. H.Sakaguchi,

Saturday

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 12/21

direct photon universality in p+p and p+p

– also pQCD prediction– good probe of PDF

possibly new physics in any enhancement

Physics #2: p+p (p+p) Universality

Nov. 5, 2009

Preliminary

Tn

xFs

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 13/21

direct photon at RHIC: consistent with pQCD– consistent with simple p+p superposition– consistent w/ and w/o nuclear modification of

PDF– consistent w/ and w/o string fragmentation

quenching hard photons at ALICE/LHC

– # prompt photons ~ # decay photons at > 60 GeV

– large rate up to very high pT

Physics #3: pQCD Photon in A+A

Nov. 5, 2009

K.J.Eskola et al.,NPB535 (1998) 351

F.Arleo,hep-ph/0601075 (2006)

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 14/21

significant suppression of pQCD photons expected– independent measurement of quark energy

loss– less background for thermal photon

measurement

Quenched String Fragmentation

Nov. 5, 2009

~ 60 % suppression at 10 GeV/c

F.Arleo,hep-ph/0707.2320 (2007)

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 15/21

unique probe of central part of hot matter ref. H.Z.Zhang, this afternoon ref. Y.Miake, earlier in this session

H.Z.Zhang et al. PRL98(2007)212301 + slides at ATHIC08

Physics #4: Transparent Hard Tagging

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki

single hadron di-hadron gamma-hadron

small zT

16/21

quark jet identification via associated photon– gluon jet naively quenched more than quark jet

test of quenching mechanism

– high pT photon/0 separation essential

Quark/Gluon Jet Identification

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki

single 0

PYTHIA 14 TeV

di-jetPYTHIA 5.5

TeV

gamma-jetPYTHIA 5.5

TeV

quark jet

gluon jet

quark jet

quark jet

gluon jet

gluon jet

17/21

Photon Physics #5: Thermal Photons

Nov. 5, 2009

RHIC outcome– radiation at 300 – 500 MeV (!) implied

indirect measurement via * cf. critical temperature ~ 170 MeV

– models not strongly constrained

LHC prospect– direct measurement of thermal photons

higher temperature + longer life time reduced background due to quenching ALICE-PHOS detector

– understanding of thermal properties of partonic system

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 18/21

Direct/Thermal Photon Feasibility

Nov. 5, 2009

expected signal/background ratio– 4 ~ 10 % (3 GeV/c) – 25 ~ 50 % (10 GeV/c)

expected systematic error with PHOS– 8.9 % (2 GeV/c) – 5.7 % (10 GeV/c)

detailed study still needed ref. H.Torii, this afternoon

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 19/21

2010/02: p+p particle production – first paper– (low pT) neutral mesons

taskforce in PWG4; co-convener H.Torii T.Iwasaki

2010/08: p+p baseline for Pb+Pb– p+p high statistics neutral mesons (and direct

photons) H.Torii + grad. students

2011/02: Pb+Pb quark energy loss– Pb+Pb neutral mesons

K.Shigaki + grad. students

2011/06: Pb+Pb thermo-dynamics– Pb+Pb direct/thermal photons

First Year Physics Strategies

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 20/21

ALICE data rate expectation– triggered data 2.5 PB/yr– event summary data (ESD) ~ 600 TB/yr– analysis object data (AOD) ~ 60 TB/yr

at least PWG4 AOD (~ 15 TB/yr ?) to Hiroshima T2– ~ 4 Mbps full time in average; feasible– need to keep AOD updated; frequency unknown

all AOD in Asia desirable?– Hiroshima + KISTI ?

massive ESD import unrealistic– any use of sampled ESD?

Data Import Strategy (for Discussion)

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 21/21

physics prospects at LHC after RHIC discoveries– global understanding of hot partonic matter– ALICE at LHC starting in months (finally!)

key analyses: photons in very wide pT range

– high pT neutral mesons and direct/thermal photons

– both in p+p and Pb+Pb ultimate challenge: low/int. pT thermal photons in Pb+Pb

analysis strategies laid out; need to materialize! data import strategy discussions being called goal: photon physics from very beginning of

LHC!

Summary and Concluding Remarks

Nov. 5, 2009

ALICE Asian Workshop – Photon Analysis Strategies at ALICE – K.Shigaki 22/21