PHENIX Detector

Central ArmsCoverage (E&W) -0.35< y < 0.35 30o <|f |< 120o

A complex apparatus to measure: Hadrons, Muons, Electrons, Photons

Muon ArmsCoverage (N&S) 1.2< |y| <2.3 -180o < f < 180o

View From Beam

View From Side

For the Quark Matter 2006 Conference at Shanghai, China, Nov 13-20, 2006

System SizeSystem Size and energy dependence and energy dependence of of pphoton production measured hoton production measured withwith the PHENIX experiment at RHIC the PHENIX experiment at RHIC

Takao Sakaguchi, Brookhaven National Laboratory, for the PHENIX Collaboration

Nuclear Effect

Prompt Prompt and and 00 production in production in -Be, p-Be, -Be, p-Be, -Cu, p-Cu (T-Cu, p-Cu (T

evatron E706) evatron E706)

Cronin effect both in Cronin effect both in and and 00!!: k: kTT broadening, broadening, 00: k: kTT bro bro

adening + recombinatioadening + recombinationn

PRD72, 032003(2005)

Center-of-mass energy, and xT region:•RHIC: sNN=200GeV, xT ~0.04-0.25•E706: sNN=32-40GeV, xT~0.2-0.5

CERN (WA98) resultsCERN (WA98) resultsA dedicated experiments for direct photon search A dedicated experiments for direct photon search in relativistic heavy Ion collisions. in relativistic heavy Ion collisions.

((PRL 85 (2000) 3595)PRL 85 (2000) 3595)ssNNNN=17.3GeV=17.3GeV

Data can be either explained by kT-smearing or Data can be either explained by kT-smearing or higher initial temperaturehigher initial temperatureAny data did not see pT>4GeV, where pQCD phAny data did not see pT>4GeV, where pQCD photons dominateotons dominateNo information on kT does not allow us to resolvNo information on kT does not allow us to resolve the issue.e the issue.Recent data points at ~100MeV available from WRecent data points at ~100MeV available from WA98. A98. By analysis of correlation strength in interferometBy analysis of correlation strength in interferometry,ry,

PRL93(2004)022301PRL93(2004)022301WA98 data and theoretical interpretationPRC69(2004)014903

Good thing about photons!

•Compton scattering of quarks and gluons: q(q)gq(q)•Annihilation of quarks: qqg•NLO: Bremsstrahlung, NNLO: Fragment…

No strong interaction once produced! Best probe bringing thermodynamical Information out of the system (Initial temperature, degree of freedom, time profile, etc.)

What we learn from system and energy dependence of photon production?

•Photon: hard + soft + hard-soft interplay•Results from different systems disentangle photon sources•Results from different energies give different signal to background ratios

Leading order (LO)

Next to Leading order (NLO)

Au+Au sNN=200GeV•Brand New high pT direct photon spectra up to 18GeV/c

•NLO pQCD calculation works relatively well.•Intermediate pT region show is of interest (5-10GeV/c)

•For pT<3GeV/c, thermal photon contribution looks dominant

•Jet-Photon conversion can describe the data for pT>3GeV/c

•Uncertainty of p+p and d+Au result can overcome these contributions

•Upcoming data disentangles the fraction of soft and hard component

•AuAu 62GeV•CuCu 200, 64GeV Initial hard scatte

ring: p+p 200GeV

•Calculable by NLO pQCD (pT>5GeV/c)

•Comparison with p+p 200GeV collisions data

•Calculation agrees data within error

Estimate of background photons from sources listed above is also essential

The baseline in this collision energy

Good thing about CERN:less Jet production cross-section-> less pi0 background

PHENIX Data! : d+A 200GeV

•Expect kT broadening as is seen in E706

•Probably, some hint is here

•Still in work to reduce systematic error

A compilation on photons, PRC 69(2004)014903

1.Jet-Photon conversion due to secondary scattering of hard-scattered parton (4<pT<7GeV/c)1. A prediction says almost same amount as pQCD contributi

on is expected2.Thermal photon production in QGP(1<pT<3GeV)

1. ~10% of ’s from hadron decays3.Hadron-gas interaction (pT<1GeV/c)

1. () (), K* KPRC 72(2005)014906

nucl-th/0507018

)0(Im23

Mfpd

dRE em

Bem

)0(Im324

MfMpd

dRem

Bemee

fB: Bose dist. em: photon self energy

photons

dileptons

Possible contribution in heavy ion collisions (Au+Au, CuCu)

Different Ncoll andNpart dependence!

NLO pQCD: L.E.Gordon and W. Vogelsang, PRD48(1993)3136

pQCD is LO!

Low to Mid-pT region data (/0 double ratio)

p+p Data to fit function used for making RAA

Latest direct photon spectra

RAA’s

/0 double ratio