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

2007/02/12 For WWND07 Takao Sakaguchi, BNL2 What is this? What is this? Quotes from the literature. Quotes from the literature. Direct radiation from the matter produced, and no strong interaction after produced Direct radiation from the matter produced, and no strong interaction after produced J/ , , ,  are NOT electromagnetic probe in this sense. Of course, they are closely related to dilepton or photon production. They decay into electrons that don ’ t strongly interact matter. J/ , , ,  are NOT electromagnetic probe in this sense. Of course, they are closely related to dilepton or photon production. They decay into electrons that don ’ t strongly interact matter. Direct (thermal) photons, dileptons, direct electrons(?) Direct (thermal) photons, dileptons, direct electrons(?) Production Process Production 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 medium Transparent in the strongly interacting medium Carry thermodynamical information of the state Carry thermodynamical information of the state Temperature, Degree of freedom Temperature, 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 URHIC direct fragment

2007/02/12 For WWND07 Takao Sakaguchi, BNL3 Sources of Radiation Thermal radiation from QGP (1<p T <3GeV) Thermal radiation from QGP (1<p T <3GeV) 5-10% of  ’ s from all the hadron decays 5-10% of  ’ s from all the hadron decays Compton, annihilation of quarks Compton, annihilation of quarks Annihilation also can be seen in dilepton spectra Annihilation also can be seen in dilepton spectra Hadron-gas interaction (p T <1GeV/c):  (  )   (  ),  K*  K  Hadron-gas interaction (p T <1GeV/c):  (  )   (  ),  K*  K  A compilation on photons, PRC 69(2004) f B : Bose dist.  em : photon self energy photons dileptons

2007/02/12 For WWND07 Takao Sakaguchi, BNL4 Sources of Radiation (jet driven) Compton scattering of hard scattered and thermal partons (Jet-photon conversion) Compton scattering of hard scattered and thermal partons (Jet-photon conversion) A prediction: J-P  pQCD in 2<p T <3GeV/c, and 5GeV A prediction: J-P  pQCD in 2<p T <3GeV/c, and 5GeV Another prediction: J-P  pQCD even at 5GeV Another prediction: J-P  pQCD even at 5GeV Bremsstrahlung from hard scattered partons in medium Bremsstrahlung from hard scattered partons in medium A comparison of Run2 data and Jet- photon conversion calculation C. Gale, NPA774(2006)335 R. Fries et al., PRC72, (2005) Hard scattered partons interact with thermal partons in matter

2007/02/12 For WWND07 Takao Sakaguchi, BNL5 Same sources seen in dileptons Comparison of “High p T low mass” and “High mass, low p T ” dilepton will disentangle interplay of various contributions Comparison of “High p T low mass” and “High mass, low p T ” dilepton will disentangle interplay of various contributions High p T, low massHigh mass, low p T S. Turbide, QM2006

2007/02/12 For WWND07 Takao Sakaguchi, BNL6 Dileptons in Au+Au collisions 200GeV Au+Au Minimum bias 200GeV Au+Au Minimum bias 870M events 870M events pT e >0.3GeV/c pT e >0.3GeV/c Compared with various contributions Compared with various contributions Fit the pion spectra Fit the pion spectra Other mesons estimated from  0 Other mesons estimated from  0 Ex.  /  0 = 0.45 ±0.10 Ex.  /  0 = 0.45 ±0.10 J/  yield is adjusted to reflect real suppression J/  yield is adjusted to reflect real suppression Filtered into the Ideal PHENIX acceptance Filtered into the Ideal PHENIX acceptance Charm contribution generated using PYTHIA Charm contribution generated using PYTHIA Scaled by N coll Scaled by N coll Doesn’t consider charm suppression Doesn’t consider charm suppression No additional scaling between cocktail and data No additional scaling between cocktail and data ie. Not scaled by 1/N  0 ie. Not scaled by 1/N  0 Low “energy” photons

2007/02/12 For WWND07 Takao Sakaguchi, BNL7 PHENIX preliminary Dileptons in IMR(1-3GeV/c 2 ) PHENIX Preliminary Possible IMR( ) Sources Possible IMR( ) Sources Correlated Charm pairs Correlated Charm pairs Thermal Sources Thermal Sources Similar to high p T (p T >3GeV/c) single electron suppression pattern Similar to high p T (p T >3GeV/c) single electron suppression pattern Attributed to charm suppression Attributed to charm suppression Different from low p T (p T >0.3GeV/c) single electrons Different from low p T (p T >0.3GeV/c) single electrons Thermal sources probably underlying in this region, but not identified. Thermal sources probably underlying in this region, but not identified. Shape Comparison Only Shape Comparison Only Y( )/Y(0-100) R CP for IMRR CP for IMR, R AA for single particles

2007/02/12 For WWND07 Takao Sakaguchi, BNL8 How about low mass region? Ratio of Yield in MeV/c 2 to 0-100MeV/c 2 region. Ratio of Yield in MeV/c 2 to 0-100MeV/c 2 region. Lines: N  0 (decaying into ee)/Npart Lines: N  0 (decaying into ee)/Npart An excess over  0 contribution is seen An excess over  0 contribution is seen Hadron gas interaction Hadron gas interaction Mean pT of the distribution is lower than the expected QGP contribution Mean pT of the distribution is lower than the expected QGP contribution Very low “energy” photons.

2007/02/12 For WWND07 Takao Sakaguchi, BNL9 Direct photons in p+p collisions p+p cross-section at  s=200GeV is well established 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 interpolate to the p T of Au+Au points Data parameterized by a fitting function to interpolate to the p T of Au+Au points Measured p+p yield is higher than NLO pQCD calculation by more than 20%. Measured p+p yield is higher than NLO pQCD calculation by more than 20%. Data/fit

2007/02/12 For WWND07 Takao Sakaguchi, BNL10 Direct photons in 200GeV Au+Au Blue line: N coll scaled p+p cross-section 900M events 900M events Reached up to 18GeV/c Reached up to 18GeV/c Qualitatively well described by NLO pQCD calculations Qualitatively well described by NLO pQCD calculations

2007/02/12 For WWND07 Takao Sakaguchi, BNL11 R AA with pQCD R AA with p+p data Direct photon R AA in 200GeV Au+Au Used p+p data is the denominator Used p+p data is the denominator NLO pQCD as denominator is shown as well for a reference NLO pQCD as denominator is shown as well for a reference For pT<10GeV, R AA is consistent with N coll scaled p+p reference. For pT<10GeV, R AA is consistent with N coll scaled p+p reference. R AA seems to decrease at very high-p T (especially for central) R AA seems to decrease at very high-p T (especially for central) Difference of NLO pQCD calculation and p+p data affects quite a bit. Difference of NLO pQCD calculation and p+p data affects quite a bit.

2007/02/12 For WWND07 Takao Sakaguchi, BNL12 Comparison with some models Turbide et al. (Phys. Rev. C72 (2005) Private communication.) Turbide et al. (Phys. Rev. C72 (2005) Private communication.) AMY formalism for jet-quenching effect for fragmentation photons. AMY formalism for jet-quenching effect for fragmentation photons. Systematically data points are below theoretical prediction. Systematically data points are below theoretical prediction. F. Arleo (JHEP 0609 (2006) 015) F. Arleo (JHEP 0609 (2006) 015) High-p T suppression due to isospin effect, in addition to jet- quenching and shadowing. High-p T suppression due to isospin effect, in addition to jet- quenching and shadowing. BDMPS for jet-quenching. BDMPS for jet-quenching. Medium induced jet-photon is not taken into account. Medium induced jet-photon is not taken into account. The suppression of very high-p T photon is well reproduced. The suppression of very high-p T photon is well reproduced.

2007/02/12 For WWND07 Takao Sakaguchi, BNL13 What is expected from structure function? 100 x T 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

2007/02/12 For WWND07 Takao Sakaguchi, BNL14 What is expected from isospin effect? Werner Vogelsang provided direct photon cross-section in p+p, p+n and n+n at 200 and 62.4GeV Werner Vogelsang provided direct photon cross-section in p+p, p+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:

2007/02/12 For WWND07 Takao Sakaguchi, BNL15 What is R AA 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(x 1 )*(u+d+ubar+dbar)(x 2 ), among other things, which is flavor and isospin "blind"… 62GeV Direct photon would be a good measure of the effect 62GeV Direct photon would be a good measure of the effect The effect could be seen in lower pT region, where the analysis is rather established The effect could be seen in lower pT region, where the analysis is rather established Interplay of jet-photon conversion and isospin effect in 4-6GeV/c region would be, though Interplay of jet-photon conversion and isospin effect in 4-6GeV/c region would be, though One message: R AA <1 for direct photons does not necessarily mean that our message of “  0 suppression at high p T ” changes 100 x T

2007/02/12 For WWND07 Takao Sakaguchi, BNL16 Direct photon v 2 ~a photon source detector~ p T >3GeV/c p T >3GeV/c N-N and jet fragmentation (v 2 >0) N-N and jet fragmentation (v 2 >0) Jet-photon conversion, in-medium bremsstrahlung (v 2 <0) Jet-photon conversion, in-medium bremsstrahlung (v 2 <0) Higher the p T gets, lower the v 2 become. Higher the p T gets, lower the v 2 become. p T <4GeV/c p T <4GeV/c Thermal photon v 2 based on hydro calculation (roughly 20-30% centrality) Thermal photon v 2 based on hydro calculation (roughly 20-30% centrality) Quark flow ~ photon flow Quark flow ~ photon flow Dilepton v 2 is also predicted, and is in the same order Dilepton v 2 is also predicted, and is in the same order annihilation compton scattering Bremsstrahlung (energy loss) jet jet fragment photon v 2 > 0 v 2 < 0 Chatterjee, et al., PRL 96, (2006) Turbide, et al., PRL96, (2006)

2007/02/12 For WWND07 Takao Sakaguchi, BNL17 Direct photon v 2 in Au+Au collisions Hadron decay photon subtracted from inclusive photon v 2. Reached up to ~8GeV/c (~4GeV/c in Run2) Tends to be positive? PHENIX Preliminary  s NN =200GeV Au+Au PHENIX Preliminary  s NN =200GeV Au+Au Finalizing systematic errors..

2007/02/12 For WWND07 Takao Sakaguchi, BNL18 Summary Direct photons and dileptons are closely related, and can be compensated each other Direct photons and dileptons are closely related, and can be compensated 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 disentangled Different production mechanism can be disentangled Dielectrons in 1-3GeV/c 2 is explainable by a charm contribution Dielectrons in 1-3GeV/c 2 is explainable by a charm contribution An excess in low mass, low p T region is seen in dielectrons An excess in low mass, low p T region is seen in dielectrons High pT Direct photons in Au+Au reached up to 18GeV/c High pT Direct photons in Au+Au reached up to 18GeV/c Several effects that interplay each other can be disentangled in 62GeV Au+Au analysis Several effects that interplay each other can be disentangled in 62GeV Au+Au analysis Direct photon v2 is measured up to 8GeV/c Direct photon v2 is measured up to 8GeV/c Tends to be positive? Tends to be positive? Final results in preparation Final results in preparation