Thermal photon and Dilepton results from PHENIX Takao Sakaguchi Brookhaven National Laboratory

Photon production and rate Photon production rate can be written by photon self energy and Bose distribution At higher p T (E>>T), the slope of the distribution tells the temperature of the system – When including hard component, one may have to use Tsallis function instead of Bose L. McLerran and B. Schenke, Absolute yield is dependent on production processes included – Self energy is weakly dependent on E/T – In order to compare with data, time/temperature profile of the system (simple Bjorken picture, fireball model, etc..) Experimental side – Measure absolute yield as a function of E – Ideally, one would like to measure the yield directly as a function of time, and separately for different processes, but it’s impossible – However, other differential measurements (flow, HBT, etc.) may help to disentangles the processes  em : photon self energy 6/9/2015 QGP case: Kapusta, Lichard, Seibert, PRD47, 4171 (1991) Baier, Nakkagawa, Niegawa, Redlich, PRD45, 4323 (1992) 2 T. Photon workshop

3 Photon production in a nutshell (fm/c) log t hadron decays sQGP hard scatt jet Brems. jet-thermal parton-medium interaction hadron gas EE Rate Hadron Gas sQGP Jet-Thermal Jet Brems. Hard Scatt 6/9/2015 Jet in-medium bremsstrahlung Jet-photon conversion Magnetic field, Glasma? Schematics by the courtesy of Gabor David

Disentangling various photon sources SourcespTpT v2v2 v3v3 v n t-dep. Hadron-gasLow p T Positive and sizable QGPMid p T Positive and small Primordial (jets) High p T ~zero Jet-Brems.Mid p T Positive? Jet-photon conversion Mid p T Negative? Magnetic fieldAll p T Positive down to p T =0 Zero 6/9/ T. Photon workshop More differential measurements would disentangle the photon production sources

Start from baseline ~rate~ 6/9/ T. Photon workshop

External conversion of photons Look for external conversion of photons at the HBD Measure the ratio of inclusive to background photons by: Tag photons as coming from  0 decay other decays accounted for with a cocktail (as in the internal analysis) 6/9/2015T. Photon workshop 6 HBD conversions Dalitz arXiv: , PRC91, (2015)

6/9/2015 External conversion technique PRL104, : p+p and AuAu from virtual photon (Run4 data) PRL 98, : pp in EMCal (Run2003 data) PRD 86, : pp in EMCal (Run2006 data) PRL 109, : AuAu in EMCal (Run2004 data) Using external photon conversion method achieved good agreement with previous results. Latest result on direct photons arXiv: , PRC91, (2015) 7 T. Photon workshop Min. Bias

6/9/ T. Photon workshop Thermal photon spectra Thermal photon spectra are obtained by subtracting hard photons from all direct photon spectra – Hard photon contribution is estimated from p+p times Ncoll Fitting to low p T region gives T~240MeV/c, almost independent of centrality The Slope parameter reflects the convolution of the instantaneous rates with the time-dependent temperature. – One has to assume time profile to obtain the temperature at given time. arXiv: , PRC91, (2015)

6/9/2015 T. Photon workshop 9 Integrated thermal photon yield N part dependence of integrated yield has same slope even as the integration range is varied – dN/dy ~N part  :  = 1.48+/ (stat) +/ (syst) – dN/dy ~N qp  :  = 1.31+/ (stat) +/ (syst) Possible difference between data and model may be from more HG contribution in data? PRC (Shen, Heinz) arXiv: , PRC91, (2015)

Flow measurement 6/9/ T. Photon workshop

Measurement of direct photon v n |  rxn -  meas | =~1.5 (event plane from RxN) – RXN is a dedicated reaction plane detector Measure inclusive photon v n and subtract hadron- decay photon v n – Decay photon v n obtained from a MC calculation using  0 v n as input – v n for other hadrons are obtained by KE T -scaling + m T scaling 6/9/2015 (GeV/c) T p (GeV/c) T p  inc.  dec. v2v2 v3v3 0-60% centrality AuAu 200GeV 11 T. Photon workshop

Recent result on photon v 2 and v 3 Some centrality dependence in v 2, weak dependence in v 3 – Similar trend as for charged hadrons (PRL 107, (2011)) and  0. General trend to note: v 3 ~ v 2 /2 6/9/ T. Photon workshop

Puzzle on direct photons remains Large yield – Emission from the early stage where temperature is high Large elliptic flow (v 2 ) – Emission from the late stage where the collectivity is sufficiently built up 6/9/ T. Photon workshop

Comparison of spectra and flow with latest models ~ Taking 20-40% centrality ~ 6/9/ T. Photon workshop

HG+QGP+pQCD H. vHees et al., PRC 84, (2011) Included Hadron Gas interaction (HG), QGP and pQCD contribution with fireball time profile – HG includes resonance decays and hadron-hadron scattering that produce photons Blue shift of the HG spectra is included Two lines in the v 2 calculation correspond to different parameterization of pQCD component No v 3 (should be possible) 6/9/ T. Photon workshop

PHSD model Parton-hadron string dynamics O. Linnyk et al., PRC 89, (2014) Including as much hadron- hadron interactions as possible in HG phase, using Boltzmann transport Thermal photon from QGP is also included – qg, qbar incoherent scattering + LPM Latest paper ( ) describes v 3 for 0-20% very nicely, but no calculation so far for % 6/9/ T. Photon workshop

A latest Hydro model C. Shen et al., PRC 91, (2015) Thermal photon contribution calculated by 3+1D Hydro including viscous correction Two Initial conditions are considered v 2 and v 3 are for thermal + pQCD photons Blue shift effect is naturally included in the hydro-evolution 6/9/ T. Photon workshop

Slow chemical freezeout A. Monnai, PRC90, (2014) We assumed that this calculation is for Minimum Bias – More details in Akihiko’s talk. Slowing chemical freezeout would gain more time for developing larger flow Both spectra and v 2 are from this contribution only – Neither pQCD nor HG contribution is included – No v 3 yet 6/9/ T. Photon workshop

Semi-QGP Photons from semi-QGP is assessed together with HG – C. Gale et al., PRL114, priv.comm. with Y Hidaka and J-F. Paquet Definition of semi-QGP is the QGP around T c – Photon contributions are evaluated at each T – T-dep. Polyakov loop is taken into account, and summed over T i >T>T c Annihilation and Compton processes around the hadronization time are naturally included – More in Shu Lin’s talk Add some v 2 and v 3 on top of HG contribution – Still HG contribution is large (~80% of total v 2 is from HG) 6/9/ T. Photon workshop

Initial strong magnetic field Initial strong magnetic field produces anisotropy of photon emission – Emission duration should be very short -> small yield – G. Baser et al., PRL109, (2012), – B. Mueller et al., PRD 89, (2014) Baser’s model is from weakly coupled scenario – Minimum bias (20-40% roughly corresponds to Minbias) – Conformal anomaly  magnetic field effect – Conventional  thermal photons calculated by Lattice QCD Mueller’s model is from strongly coupled scenario – This rate may also be small 6/9/ T. Photon workshop v 3 =0!

Possibility of improvement on flow result Statistical error can be reduced with additional dataset Systematic uncertainty may or may not be reduced – Event plane resolution  hard.. – Photons from hadron decay Needs more precise measurement of R , and v n of inclusive photons and  0 (hard, but may be possible to some extent) Some cancellation of systematic uncertainty is possible by taking ratio of quantities – v 2 /v 3 for instance 6/9/2015T. Photon workshop 21

Measurement of ratio of v 2 to v 3 Overall trends both for  +/- and direct photons are well described by the calculation – Based on arXiv: , private communication for RHIC energy Systematic error estimate is currently very conservative – Working on better understanding of systematic errors 6/9/ T. Photon workshop

Dilepton news 6/9/ T. Photon workshop

Run-10 Au+Au dileptons at √s NN =200 GeV with the HBD 6/9/ Semi-centralSemi-peripheralPeripheral T. Photon workshop I. Tserruya from TPD2014

6/9/2015 T. Photon workshop Central collisions 0-10% Quantitative understanding of the background verified by the like-sign spectra. Combinatorial background determined using the mixed event technique and taking into account flow. Correlated components (cross pairs, jet pairs and e-h pairs) independently simulated and absolutely normalized. Background shape reproduced at sub-percent level for masses m > 150 MeV/c 2 25 I. Tserruya from TPD2014

Cocktail is not simple either For charm contribution estimate, we’ve been using PYTHIA Total cross-section will be different depending on the event generator In order to properly describe the mass distribution in 1.5<m<3GeV/c 2, the total cross-section has to be changed between PYTHIA and 6/9/2015T. Photon workshop 26 Plot from Yosuke Watanabe

Summary Direct photon spectra and its flow (v 2 and v 3 ) have been measured in 200GeV Au+Au collisions Thermal component of direct photon spectra was extracted – Temperature was found to be constant over centrality – Integrated yield was found to scale with: N part  :  = 1.48+/ (stat) +/ (syst) N qp  :  = 1.31+/ (stat) +/ (syst) Sizable v 2 and v 3 have been measured Simultaneous comparison of spectra, v 2, and v 3 between data and models suggests the late time emission is significant Dilepton analysis is in good progress – Both correlated and uncorrelated background are investigated in detail – Cocktail simulation has also been revisited for finalizing the result 6/9/ T. Photon workshop