PHENIXにおける 最新のレプトン対測定結果 小沢恭一郎 東大・理 Open Questions Formation of hot and dense matter is established. Still, we have many important questions to answer. Is the matter deconfined? How does Heavy-flavor act? Heavy flavor measurements Is Chiral symmetry restored? J/y suppression Vector meson Radiation? Mass shift? Di-lepton continuum 9/15/2007 Heavy Ion Cafe @ Hongo 2 @SPS CERES 9/15/2007 Heavy Ion Cafe @ Hongo 4 CERES 2 9/15/2007 Heavy Ion Cafe @ Hongo 5 NA60 and : fix yields such as to get, after subtraction, a smooth underlying continuum : () set upper limit, defined by “saturating” the measured yield in the mass region close to 0.2 GeV/c2 (lower limit for excess). () use yield measured for pT > 1.4 GeV/c 9/15/2007 Heavy Ion Cafe @ Hongo 6 What’s this? [van Hees+RR ‘06] • absolute norm., melting r • M>0.9GeV: “4p”→mm; and ?! 9/15/2007 Heavy Ion Cafe @ Hongo • baryon effects essential 7 Model 2 Contributions included in our calculation: QGP quasi-particle picture, (Schneider et al. (2002)) In-medium Rho spectral function (Eletsky et. al. (2001)) In-medium Omega spectral function (Martell & Ellis (2004)) In-medium Phi not (yet) included Renk, Ruppert (2006) (Results were obtained by folding with the schematic acceptance matrix, not the full MC acceptance simulation.) 9/15/2007 Heavy Ion Cafe @ Hongo 8 φ・ω @RHIC Chiral Symmetry in Hadronic matter Mass shift and/or modification of vector mesons are expected Lepton decays become good probes Not interacting “strongly.” However, we only see integrated information from all stages of collisions. R. Rapp (Nucl. Phys A661(1999) 238c QGP, Mixed, Hadron gas Comparisons between lepton decays and hadron decays in several collision systems are important 9/15/2007 Hadron gas QGP Integrated Heavy Ion Cafe @ Hongo information After Freeze Out 10 Observables in vector meson measurements Line shape Direct measurements Yield Q value of → KK is small Should be sensitive to mass changes in either or K BR( ee) BR( KK ) Lissauer and Shuryak, Phys. Lett. B253, 15 (1991). pT slope 9/15/2007 Difference between hadron decays and lepton decays It could show the difference of collision stage. Heavy Ion Cafe @ Hongo T.Hatsuda and S.Lee (Phys.Rev.C46-R34-38, 1992) 11 Measurement ● ● ωφ Au＋Au p+p J/y Dalitz Conversion g After BG subtraction Raw spectrum Invariant mass spectrum of e+e- in PHENIX (Combinatorial BG included) 0 1 2 3 [GeV/c2] Clear , , and J/y peaks with very good mass resolution!! 9/15/2007 Heavy Ion Cafe @ Hongo 12 : hadron and lepton decays Main issue: K+K- and e+eseem not consistent Many efforts are on-going to understand the difference btw K and e. We have to prove that the difference is not made artificially. Analysis in d+Au and p+p data is important as baseline. 9/15/2007 Heavy Ion Cafe @ Hongo 13 Baseline - dAu Counts per 10 MeV/c2 d – Au collisions at √sNN = 200 GeV e+eCombinatorial Background N~120 PHENIX Preliminary PHENIX Preliminary e+e- invariant mass (GeV/c2) To settle cold nuclear matter effect, Both e+e- and K+K- are measured in d-Au collisions and results are compared. 9/15/2007 K+K- Heavy Ion Cafe @ Hongo S = 786 ± 34, S/B = 1/0.47 K+K- invariant mass (GeV/c2) 14 dN/dy in dAu dN/dy is compared between ee and KK. KK channel dN/dy = 0.0468 +/- 0.0092(stat) (+0.0095,-0.0092) (syst.) ee channel dN/dy=.056.015(stat) 50%(syst) dN/dy dN/dy No significant difference between ee and KK within statistical and systematic errors. 9/15/2007 Heavy Ion Cafe @ Hongo KK ee PHENIX preliminary 15 p+p omega phi ds/dy Extracted by integration OMEGA: 3.50037 +/- 0.175942 (stat) +/- 0.875 (sys) 4.37554 (upper sys) 2.62521 (lower sys) PHI: 0.369182 +/- 0.0195987 (stat) +/- 0.0894 (sys) 0.458564 (upper sys) 0.2798 (lower sys) 9/15/2007 来島 Heavy Ion Cafe @ Hongo 16 spectra Spectra of meson are measured in several collision systems. p+p d+Au Au+Au Results are mainly obtained using hadron decays. Analysis for electron decay mode is underway. 9/15/2007 Heavy Ion Cafe @ Hongo 17 New approaches for and No PID method for K+K- in p+p It works very well especially in high pT region Combinatorial BG is decreased Improved BG estimation in Au+Au p0g 9/15/2007 Heavy Ion Cafe @ Hongo 18 Next steps Analysis for run4 should be completed soon Improved statistics and background in run7 Improved understanding for dAu Figure out how to analyze r mesons (short lived) r→ p+p- at STAR (Phys. Rev. Lett. 92, 092301) Try many measurements to figure out chiral symmetry restoration 9/15/2007 Line shape? Yield? Slope? Ratio between hadron and electron or and Ratio to p0 Heavy Ion Cafe @ Hongo 19 electron positron continuum electron-positron continuum Broadening of r meson makes continuum on the invariant mass of electron-positron pair prediction In addition, thermal radiation by the system via quark anti-quark annihilation also makes continuum and it carries direct information from the matter. A Matter is formed Deconfinement Thermalized Experimentally, combinatorial background is very large and must be subtracted properly. Also, useful for charm measurements 9/15/2007 Heavy Ion Cafe @ Hongo R. Rapp, nucl-ex 0204003 21 Results submitted to Phys. Rev. Lett arXiv:0706.3034 Clear enhancement is observed in the mass region below . 9/15/2007 Heavy Ion Cafe @ Hongo 22 pp – AuAu comparison p+p MULTIPLIED Ncoll p+p NORMALIZED TO mby ee<100 MeV 9/15/2007 Heavy Ion Cafe @ Hongo 23 Centrality Dependence LOW MASS • p0 production scales with Npart • If in-medium enhancement from pp or qq annihilation yield should increase faster than proportional to Npart INTERMEDIATE MASS • p0 production scales with Npart • charm follows binary scaling 9/15/2007 Heavy Ion Cafe @ Hongo yield should increase proportional to Ncoll 24 Further analysis Comparison with CuCu Comparison with SPS Finalizing pp Reasonable normalization of pp Npart for low mass? Ncoll for charm? Improved statistics in run7 Cu+Cu pT dependence reaction plane dependence Use HBD to suppress background 9/15/2007 Heavy Ion Cafe @ Hongo 25 Hadron Blind Detector g e+ e po g e+ e - Background is made by combination of non-correlated e+e- pair, e+e- from Dalitz and g rejected by new detector “combinatorial pairs” signal electron partner positron needed for rejection all signal Dalitz rejector Hadron Blind Detector 9/15/2007 Heavy Ion Cafe @ Hongo 26 photon 9/15/2007 Heavy Ion Cafe @ Hongo 27 Thermal photon Direct photon Directly emitted from the medium Not from hadron Hard photon Turbide, Rapp, Gale, Phys. Rev. C 69 (014903), 2004 Initial pQCD Thermal photon Hadron gas QGP After subtraction of large background from hadron decays, 9/15/2007 Window for thermal photons from QGP in this calculation: pT = 1 - 3 GeV/c pQCD calculation should be confirmed in High pT region Heavy Ion Cafe @ Hongo 28 Idea - * g + ee Any source of real g emits virtual g with very low mass Dalitz decay p0 g g p0 Compton q g g q q g g e+ e- g* g* e+ eq Use lepton pairs to measure virtual g and extrapolate to real g PHENIX can measure low mass e+e- pairs hadron decays and direct photon g*direct g*incl. can be measured. *In the analysis, Mee distribution for Dalitz and direct photon is calculated theoretically. Therefore, the ratio of Nee in two different mass region is converted to the ratio between direct and inclusive photons. The systematic error is reduced. 9/15/2007 Heavy Ion Cafe @ Hongo 29 * g direct / * g inclusive Significant 10% excess of verylow-mass virtual direct photons ~25 % systematic error : ~20 % from measured /p0 ratio ~10 % from g inclusive ~5 % acceptance 9/15/2007 Heavy Ion Cafe @ Hongo 30 * g direct / * g inclusive Significant 10% excess of verylow-mass virtual direct photons Results agrees well with Conventional result One can extract the direct photon yield from the inclusive photon yield. g*direct g* 9/15/2007 Heavy Ion Cafe @ Hongo gdirect = incl. gincl. 31 Direct photon yield Direct photon yield is calculated from the inclusive photon yield. 9/15/2007 Heavy Ion Cafe @ Hongo 32 Direct photon yield Direct photon yield is calculated from the inclusive photon yield. Compare to NLO pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) Excess above the calculation It might include contribution from thermal photons Reference measurement needed pp and dAu Using same analysis method 9/15/2007 Heavy Ion Cafe @ Hongo 33 Thermal photon? Compare to NLO pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) excess above pQCD Compare to thermal model D. d’Enterria, D. Perresounko nucl-th/0503054 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c 9/15/2007 data above thermal at high pT Heavy Ion Cafe @ Hongo 34 ｐ＋ｐ 9/15/2007 Heavy Ion Cafe @ Hongo 山口 35 Recalculation of Rg* in p+p PHENIX Preliminary Stat.errors on simulation are included in sys.errors on Rg*. 9/15/2007 It should be reduced. Heavy Ion Cafe @ Hongo 36 Comparison of Rg* with Run4-central result PHENIX Preliminary 9/15/2007 Heavy Ion Cafe @ Hongo 37 Summary So many interesting analysis topics are ongoing at PHENIX Measurement for chiral symmetry is underway. Such as, Heavy flavor measurements, J/y, , and lepton pair continuum First result will publish soon. Enhancement is observed in e+econtinuum! Interesting results in Direct photon measurements. We are still in an exciting time! 9/15/2007 Heavy Ion Cafe @ Hongo 38
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