Measurement of Electro- magnetic radiation at PHENIX Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration

Measurement of Electro-Measurement of Electro-magnetic radiation at PHENIXmagnetic radiation at PHENIX

Takao SakaguchiTakao Sakaguchi

Brookhaven National LaboratoryBrookhaven National Laboratory

for the PHENIX Collaborationfor the PHENIX Collaboration

2007/02/12 For WWND072007/02/12 For WWND07 Takao Sakaguchi, BNLTakao Sakaguchi, BNL 22

What is this?What is this? Quotes from the literature.Quotes from the literature.

Direct radiation from the matter produced, and no strong interaction afteDirect radiation from the matter produced, and no strong interaction after producedr produced

J/J/, , , , , , are NOT electromagnetic probe in this sense. Of course, they ar are NOT electromagnetic probe in this sense. Of course, they are closely related to dilepton or photon production. They decay into electrons e closely related to dilepton or photon production. They decay into electrons that don’t strongly interact matter.that don’t strongly interact matter.

Direct (thermal) photons, dileptons, direct electrons(?)Direct (thermal) photons, dileptons, direct electrons(?)

Production ProcessProduction Process Compton and annihilation (LO)Compton and annihilation (LO) Fragmentation (NLO)Fragmentation (NLO)

Photons come from all the stages.Photons come from all the stages. Transparent in the strongly interacting mediumTransparent in the strongly interacting medium Carry thermodynamical information of the stateCarry thermodynamical information of the state

Temperature, Degree of freedomTemperature, Degree of freedom

…Since the mean free path of the produced photons is considerably larger than the size of the nuclear volume, photons produced throughout all stages of the collision will be observable in the final state. …., thereby provide evidence for the possible formation of a quark gluon plasma (QGP). (WA70, 1996)

Photons and dileptons are potentially more direct probes of the early collision stages since they escape from the impact zone nearly undisturbed by final-state interactions and have their largest emission rates in hot and dense matter. Moreover, according to the vector dominance model, dilepton production is mediated in the hadronic phase by the light neutral vector mesons ρ, ω, and φ which mark the low-mass region by distinctive resonance peaks. (CERES, 2005)

Measurement of direct photon production allows more definitive discrimination between initial- and final-state suppression due to the fact that photons, once produced, are essentially unaffected by the surrounding matter. Hence photons produced directly in initial parton scatterings are not quenched unless the initial parton distributions are suppressed in the nucleus.. (PHENIX, 2005)

Electromagnetic radiation in URHICElectromagnetic radiation in URHIC

direct

fragment


Sources of RadiationSources of Radiation Thermal radiationThermal radiation from QGP (1<p from QGP (1<pTT<3G<3G

eV)eV) 5-10% of 5-10% of ’s from all the hadron decays’s from all the hadron decays Compton, annihilation of quarksCompton, annihilation of quarks Annihilation also can be seen in dilepton sAnnihilation also can be seen in dilepton s

pectrapectra

Hadron-gas interactionHadron-gas interaction (p (pTT<1GeV/c): <1GeV/c): (() ) ((), ), K* K* K K

A compilation on photons,PRC 69(2004)014903

)0(Im23

Mfpd

dRE em

Bem

)0(Im324

MfMpd

dRem

Bemee

fB: Bose dist. em: photon self energy

photons

dileptons


Sources of Radiation (jet driven)Sources of Radiation (jet driven) Compton scattering of hard scattered Compton scattering of hard scattered

and thermal partonsand thermal partons (Jet-photon conv (Jet-photon conversion)ersion)

A prediction: J-P A prediction: J-P pQCD in 2<p pQCD in 2<pTT<3<3GeV/c, and ~50% @ 5GeVGeV/c, and ~50% @ 5GeV

Another prediction: J-P Another prediction: J-P pQCD even pQCD even at 5GeVat 5GeV

Bremsstrahlung from hard scattered Bremsstrahlung from hard scattered partonspartons in medium in medium A comparison of Run2 data and Jet-

photon conversion calculation

C. Gale, NPA774(2006)335 R. Fries et al., PRC72, 041902(2005)

Hard scattered partons interact with thermal partons in matter


Same sources seen in dileptonsSame sources seen in dileptons Comparison of “High pComparison of “High pTT low mass” and “High mass, low p low mass” and “High mass, low pTT” ”

dilepton will disentangle interplay of various contributionsdilepton will disentangle interplay of various contributions

High pT, low mass High mass, low pTS. Turbide, QM2006


Dileptons in Au+Au collisionsDileptons in Au+Au collisions 200GeV Au+Au Minimum bias200GeV Au+Au Minimum bias

870M events870M events pTpTee>0.3GeV/c>0.3GeV/c

Compared with various contributionCompared with various contributionss Fit the pion spectra Fit the pion spectra Other mesons estimated from Other mesons estimated from 00

Ex. Ex. //00 = 0.45 ±0.10 = 0.45 ±0.10 J/J/ yield is adjusted to reflect yield is adjusted to reflect realreal

suppressionsuppression Filtered into the Ideal PHENIX Filtered into the Ideal PHENIX

acceptanceacceptance Charm contribution generated Charm contribution generated usingusing

PYTHIA PYTHIA Scaled by NScaled by Ncollcoll Doesn’t consider charm Doesn’t consider charm

suppressionsuppression

No additional scaling between No additional scaling between cocktail and datacocktail and data ie. Not scaled by 1/Nie. Not scaled by 1/N00

Low “energy” photons


PHENIX preliminaryPHENIX preliminary

PeripheralColl

CentralCollCP NYield

NYieldR

)/(

)/(

DileptonsDileptons in IMR in IMR(1-3GeV/c(1-3GeV/c22))

PHENIX Preliminary

Possible IMRPossible IMR(1100-2900)(1100-2900) Sources Sources Correlated Charm pairCorrelated Charm pairss Thermal SourcesThermal Sources

Similar to high pSimilar to high pTT (p(pTT>3GeV/c) >3GeV/c) single single electron suppression patternelectron suppression pattern Attributed to charm suppressionAttributed to charm suppression Different from low pDifferent from low pTT (p (pTT>0.3GeV/c) si>0.3GeV/c) si

ngle electronsngle electrons Thermal sources probably underlying iThermal sources probably underlying i

n this region, but not identified.n this region, but not identified.

Shape Comparison OnlyShape Comparison Only

Y(1100-2900)/Y(0-100)

RCP for IMRRCP for IMR, RAA for single particles


How about low mass region?How about low mass region? Ratio of Yield in 150-300MeV/cRatio of Yield in 150-300MeV/c22 to 0-100MeV/c to 0-100MeV/c22 region. region. Lines: NLines: N00(decaying into ee)/Npart(decaying into ee)/Npart An excess over An excess over 00 contribution is seen contribution is seen

Hadron gas interactionHadron gas interaction Mean pT of the distribution is lower than the expected QGP contributionMean pT of the distribution is lower than the expected QGP contribution

Very low “energy” photons.


Direct photons in p+p collisionsDirect photons in p+p collisions p+p cross-section at s=200GeV is well e

stablished with PHENIX Year-5 data set. Statistically improved from the published

Run3 result

Reference for Au+Au collisions

Data parameterized by a fitting function to Data parameterized by a fitting function to interpolate to the pinterpolate to the pTT of Au+Au points of Au+Au points

Measured p+p yield is higher than NLO pMeasured p+p yield is higher than NLO pQCD calculation by more than 20%.QCD calculation by more than 20%.

Data/fit


Direct photons in 200GeV Au+AuDirect photons in 200GeV Au+Au

Blue line: Ncoll scaled p+p cross-section 900M events900M events

Reached up to 18GeReached up to 18GeV/cV/c

Qualitatively well deQualitatively well described by NLO pQCscribed by NLO pQCD calculationsD calculations


RAA with pQCD

RAA with p+p data

Direct photon RDirect photon RAAAA in 200GeV Au+Au in 200GeV Au+Au Used p+p data is the denoUsed p+p data is the deno

minatorminator NLO pQCD as denominatNLO pQCD as denominat

or is shown as well for a ror is shown as well for a referenceeference

For pT<10GeV, RFor pT<10GeV, RAAAA is con is consistent with sistent with NNcollcoll scaled p+ scaled p+p reference.p reference.

RRAAAA seems to decrease at seems to decrease at very high-pvery high-pT T (especially for (especially for central)central)

Difference of NLO pQCD Difference of NLO pQCD calculation and p+p data acalculation and p+p data affects quite a bit.ffects quite a bit.


Comparison with some modelsComparison with some models

Turbide et al. Turbide et al. (Phys. Rev. C72 (2005) (Phys. Rev. C72 (2005) 014906 + Private communication.)014906 + Private communication.) AMY formalism for jet-quenching AMY formalism for jet-quenching

effect for fragmentation photons.effect for fragmentation photons. Systematically data points are belSystematically data points are bel

ow theoretical prediction.ow theoretical prediction.

F. Arleo F. Arleo (JHEP 0609 (2006) 015)(JHEP 0609 (2006) 015) High-pHigh-pTT suppression due to isospi suppression due to isospi

n effect, in addition to jet-quenchin effect, in addition to jet-quenching and shadowing.ng and shadowing.

BDMPS for jet-quenching.BDMPS for jet-quenching. Medium induced jet-photon is not Medium induced jet-photon is not

taken into account.taken into account. The suppression of very high-pThe suppression of very high-pTT p p

hoton is well reproduced.hoton is well reproduced.


What is expected from structure function?What is expected from structure function?

100 xT

Au+Au minimum bias

Structure function ratios drop by ~20% from x=0.1 to 0.2?

Eskola,Kolhinen,Ruuskanen Nucl. Phys. B535(1998)351

gq ->q is main contribution


What is expected from isospin effect?What is expected from isospin effect? Werner Vogelsang provided direct photon cross-section in p+p, pWerner Vogelsang provided direct photon cross-section in p+p, p

+n and n+n at 200 and 62.4GeV+n and n+n at 200 and 62.4GeV

Minimum bias Au+Au can be calculated by: Minimum bias Au+Au can be calculated by:

)Z)-(A Z)-2Z(A (Z)(1/A /N nn2

pnpp22

collAA


What is RWhat is RAAAA for pure hard scattering for pure hard scattering Consistent with F. Arleo’s work.Consistent with F. Arleo’s work.

Werner’s comment: The isospin effect has to be bigger than for 0, because for 0 the qg channel is proportional to g(x1)*(u+d+ubar+dbar)(x2), among other things, which is flavor and isospin "blind"…

62GeV Direct photon would be a go62GeV Direct photon would be a good measure of the effectod measure of the effect The effect could be seen in lower pThe effect could be seen in lower p

T region, where the analysis is rathT region, where the analysis is rather establisheder established

Interplay of jet-photon conversion aInterplay of jet-photon conversion and isospin effect in 4-6GeV/c region nd isospin effect in 4-6GeV/c region would be, thoughwould be, though

One message: RAA<1 for direct photons does not necessarily mean that our messageof “0 suppression at high pT” changes

100 xT


Direct photon vDirect photon v22 ~a photon source detector~~a photon source detector~

ppTT>3GeV/c>3GeV/c N-N and jet fragmentation (vN-N and jet fragmentation (v22>0)>0) Jet-photon conversion, in-medium bJet-photon conversion, in-medium b

remsstrahlung (vremsstrahlung (v22<0)<0) Higher the pHigher the pTT gets, lower the v gets, lower the v22 bec bec

ome.ome.

ppTT<4GeV/c<4GeV/c Thermal photon vThermal photon v22 based on hydro c based on hydro c

alculation (roughly 20-30% centralitalculation (roughly 20-30% centrality)y)

Quark flow ~ photon flowQuark flow ~ photon flow Dilepton vDilepton v22 is also predicted, and is i is also predicted, and is i

n the same ordern the same order

annihilationcomptonscattering

Bremsstrahlung (energy loss)

jet

jet fragment photon

v2 > 0

v2 < 0

Chatterjee, et al., PRL 96, 202302(2006)

Turbide, et al., PRL96, 032303(2006)


Direct photon vDirect photon v22 in Au+Au collisions in Au+Au collisions• Hadron decay photon subtracted

from inclusive photon v2.

• Reached up to ~8GeV/c (~4GeV/c in Run2)

• Tends to be positive?

PHENIX PreliminarysNN=200GeV Au+Au

PHENIX PreliminarysNN=200GeV Au+Au

Finalizing systematic errors..

1

).().().( 22

2

R

bkgdvinclvRdirv


SummarySummary Direct photons and dileptons are closely related, and can be compeDirect photons and dileptons are closely related, and can be compe

nsated each othernsated each other Can cover broad energy (kinetic) range of EM radiation.Can cover broad energy (kinetic) range of EM radiation. Different production mechanism can be disentangledDifferent production mechanism can be disentangled

Dielectrons in 1-3GeV/cDielectrons in 1-3GeV/c22 is explainable by a charm contribution is explainable by a charm contribution

An excess in low mass, low pAn excess in low mass, low pTT region is seen in dielectrons region is seen in dielectrons

High pT Direct photons in Au+Au reached up to 18GeV/cHigh pT Direct photons in Au+Au reached up to 18GeV/c Several effects that interplay each other can be disentangled in 62GeV Several effects that interplay each other can be disentangled in 62GeV

Au+Au analysisAu+Au analysis

Direct photon v2 is measured up to 8GeV/cDirect photon v2 is measured up to 8GeV/c Tends to be positive?Tends to be positive? Final results in preparationFinal results in preparation

Documents

Measurement of Electro- magnetic radiation at PHENIX Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration