単電子および電子対測定の 物理、現状、展望 蜂谷 崇 広島大学 /PHENIX collaboration

2004/11/5Workshop at RCNP2 Physics Motivation Search for the new State of Matter (quark-gluon-plasma) and study its properties. Leptonic Observables Why do we want to measure leptonic observable? Heavy flavor (Charm): Single Electrons (c  D  e + X) Quarkonia: J/   e + e -, Light vector mesons:   K + K -,   e + e -, ,  also Dielectron Continuum: Low and Intermediate Mass Region Photons: Direct (prompt and thermal) photons via its conversions Pair wise observable

2004/11/5Workshop at RCNP3 J/  measurement

2004/11/5Workshop at RCNP4 Motivation of J/  measurement Debye color screening will lead to a suppression of charmonium production in heavy ion collisions. one of the earliest probe of the QGP Predictions of enhanced J/  production at RHIC energy from recombination in final state interaction. NA50 measured J/  at SPS energy. They found an anormalous suppression. Systematic study is needed to disentangle the compete effect.

2004/11/5Workshop at RCNP5 PHENIX Experiment Two central spectrometers , e  and hadrons |  | < 0.35,  =  /2  2 Two fwd spectrometers  1.2 < |  | < 2.4 BBC DC&PC RICH EMCAL

2004/11/5Workshop at RCNP6 Electron Measurement All charged tracks BG Net e ± e ± real. Electrons are measured by DC→PC1→RICH→EMCal Electron Identification :  Cherenkov light in RICH Number of Hit PMT Ring shape  Energy – Momentum matching e+ EM Calorimeter PC2 Mirror PC3 RICH PC1 DC X Cherenkov light in RICH Ring in RICH

2004/11/5Workshop at RCNP7 J/  in p+p at  s = 200 GeV baseline measurement good agreement with: –lower  s data and phenomenological extrapolation –Run 2 and Run 3 data p+p  J/  +X at  s = 200 GeV PHENIX PRL 92, (2004) p+p  J/  +X at  s = 200 GeV (Run 3) PHENIX preliminary

2004/11/5Workshop at RCNP8 J/  in d+Au Nuclear Effects Modification of the parton distribution functions: Gluon shadowing -> reduction of production at low x. 3 rapidity ranges in PHENIX probe different momentum fraction of Au partons South (y < -1.2) : large X 2 (in gold) Central (y ~ 0) : intermediate North (y > 1.2) : small X 2 (in gold) Predicted Gluon Shadowing in d+Au From Eskola, Kolhinen, Vogt Nucl. Phys. A696 (2001)

2004/11/5Workshop at RCNP9 J/  production in d+Au is compared in p+p d  Au J/  in pp and dAu collisions at RHIC

2004/11/5Workshop at RCNP10 S.B. Klein and R. Vogt, nucl-th/ Low x 2 (shadowing) indication for (weak) shadowing and absorption more statistics desirable to disentangle nuclear effects (and distinguish models ) d  Au J/  d+Au/p+p vs rapidity Rapidity

2004/11/5Workshop at RCNP11 J /  in Au + Au at  s NN =200 GeV (run2) Need more statistics –inconsistent with large enhancement scenarios SPS NA50 normalized to p+p point Au+Au  J/   e  e  at  s NN = 200 GeV PHENIX PRC 69, (2004) normal nuclear absorption 0-20 % central N coll = % central N coll = % central N coll = 45 PRC 69, (2004)

2004/11/5Workshop at RCNP12 Coming attraction of J/  analysis Au + Au analysis Run2 25 M (MB) + 25M (LVL2) events Run4 1.6 B events with healthy detector times larger statistics Bdn/dy/N binary Accurate study of the centrality dependence We see the clear J/  signal. Au + Au

2004/11/5Workshop at RCNP13 Current Status of J/  J/  has been measured in p+p, d+Au, Au+Au Nuclear effects are studied in d+Au –Weak shadowing –Smaller absorption than expected (  > 0.92) –Statistics is limited---- Need more data. We have 1.6B MB data in Run 4 (Au+Au) –Quantitative study of J/  production in Au+Au

2004/11/5Workshop at RCNP14 Light vector meson measurement

2004/11/5Workshop at RCNP15 Motivation of light vector meson (LVM) measurement Looking for (partial) Chiral symmetry restoration –LVM has Short lifetime ~ few fm/c è Decay inside medium. –Mass modification of vector mesons is expected. Au + Au and d +Au collisions –Distinguish between hot and cold partonic matter –Probing nuclear effects Quark mass in vacuum m u ~ m d ~ 5 MeV/c 2 m s ~ 100 MeV/c 2 Effective quark mass in hadron m u ~ m d ~ 300 MeV/c 2 m s ~ 500 MeV/c 2 T.Hatsuda and S.Lee (Phys.Rev.C )

2004/11/5Workshop at RCNP16  measurement in  d+Au at  s NN = 200 GeV Fit is to relativistic Breit-Wigner convoluted with a Gaussian (detecter) –N  ~120 in e + e – mode and N  = 207  16 in K + K – mode –Both measurements are consistent with PDG M inv (GeV/c 2 ) Combinatorial Background Yield   e+e-  e+e-   K+K-  K+K-

2004/11/5Workshop at RCNP17 Minimum-bias m T distribution of   yields in d-Au collisions in K + K - and e + e – channels are consistent. K + K – channel dN/dy = / (stat) ( , ) (syst.) e + e – channel dN/dy=.056 .015(stat)  50%(syst) dN/dy K+K–K+K– e+e–e+e– PHENIX Preliminary dAu  KK dAu  ee 1/2  m T dN/dm T dy (GeV/c 2 ) -2 M T (GeV/c 2 ) PHENIX Preliminary

2004/11/5Workshop at RCNP18  measurement in  Au+Au at  s NN = 200 GeV Clear signal in KK channel No clear signal in ee channel, due to small statistics Mass centroid and width is consistent with PDG No-dependence with centrality Yield nucl-ex/

2004/11/5Workshop at RCNP19 , ,  in near future Full statistics available in RUN3 d+Au. –Background subtracted mass spectra –Amount of data is twice Large statistics in Run 4 Au+Au dataset , ,   signal in  M ee spectrum can be seen work in progress   e + e – invariant mass Yield

2004/11/5Workshop at RCNP20 Current Status of LVM  is measured in both K + K – and e + e – channel in d+Au  yields in d-Au collisions in K + K – and e + e – channels are consistent.  Mass centroid and width is consistent with PDG  is measured in K + K – channel in Au+Au –Not so clear signal in e + e – channel –Mass centroid and width is consistent with PDG –Not depend on centrality We have more statistics in both d+Au and Au+Au –In d+Au, data can be twice –In Au+Au, 1.6B min. bias data in run 4 (20M in run2)

2004/11/5Workshop at RCNP21 Heavy Flavor Measurement using Single Electrons

2004/11/5Workshop at RCNP22 Motivation of Heavy flavor Measurement Charm is produced through mainly gluon-gluon fusion in heavy ion collisions Sensitive to gluon density in initial stage of the collisions Charm is propagated through hot and dense medium created in the collisions Energy loss of charms via gluon radiation (dead cone effect?, else … ) Charm can be produced thermally at very high temperature Sensitive to state of the matter Charm measurements bring us an important baseline of J/ 

2004/11/5Workshop at RCNP23 Heavy flavor in p+p, d+Au and Au+Au p + p measurement –Test pQCD calculation –Baseline measurement for d+Au and Au+Au d + Au measurement –Normal nuclear effect Cronin effect Gluon shadowing Au + Au measurement –Total yield Expected to scale with binary collision –Spectral shape at higher p T Study charm energy loss in dense medium –Charm Flow V2 measurement  Sakai-san’s Talk

2004/11/5Workshop at RCNP24 Charm Measurement Direct method: Reconstruction of D-meson (e.g. D 0  K  ). Very challenging without measurement of displaced vertex. Indirect method: Measure leptons from semi- leptonic decays of charm. This method is used by PHENIX at RHIC ++

2004/11/5Workshop at RCNP25 Non-PHOTONIC signal Charm decays Bottom decays Background Photon conversions :  0, ,  ’, ,  Dalitz decays  0  ee ,   ee , etc) Conversion of direct photons Di-electron decays of , ,  Thermal di-leptons Kaon decays (weak decay) Most of the backgrounds are PHOTONIC Source of Electrons All back grounds should be subtracted to extract the signal All electrons measured in experiment are EM force origin and Weak force origin PHOTONIC

2004/11/5Workshop at RCNP26 Extraction of Non-photonic Electrons (Heavy flavor Electrons) Converter method Comparison of electron yield with and without the converter allows to separate the photonic and the non-photonic electrons. Cocktail method Light hadron cocktail. Major source (  0 ) is measured by the PHENIX spectra. Other mesons are estimated by m t scaling assumption and asymptotic ratios from lower energy data. Photon conversion from material in PHENIX acceptance. Photon Converter

2004/11/5Workshop at RCNP27 Result (from PHENIX) p+p (reference for all other system) d+Au (nuclear effect) Au+Au (Suppression? Enhancement?)

2004/11/5Workshop at RCNP28 PHENIX PRELIMINARY Non-Photonic Electrons in p+p at  s = 200 GeV 200 GeV pp non- photonic electron spectrum from cocktail subtraction method PYTHIA tuned to low energy data Data is harder than PYTHIA charm + bottom above p t =1.5 GeV/c

2004/11/5Workshop at RCNP29 Non-Photonic Electrons in d+Au at  s NN =200GeV 200 GeV dAu non- photonic single electron spectrum from converter method Data divided by T AB Spectacular agreement within stated errors No indication for strong cold-nuclear matter effects PHENIX PRELIMINARY 1/T AB 1/T AB EdN/dp 3 [mb GeV -2 ]

2004/11/5Workshop at RCNP30 PHENIX PRELIMINARY 1/T AB 1/T AB EdN/dp 3 [mb GeV -2 ] Centrality Dependence in d+Au at  s NN = 200 GeV

2004/11/5Workshop at RCNP31 Status in p+p and d + Au In p + p, the spectra are described by PYTHA at low p T. –Spectra are “ harder ” than PYTHIA at p T > 1.5 GeV/c: Non-photonic electrons in d+Au agree well with pp fit and binary scaling. –for whole p T range and all centrality bins. –No indication for strong nuclear effect What happened in Au + Au ?

2004/11/5Workshop at RCNP32 1/T AA 1/T AB EdN/dp 3 [mb GeV -2 ] Non-photonic Electron in Au+Au at  s NN = 200 GeV 200 GeV Au+Au non-photonic single electron spectrum from converter method Data is divided by T AA and overlaid with PHENIX pp fit At low p t the pp fit is in good agreement

2004/11/5Workshop at RCNP33 1/T AA 1/T AB EdN/dp 3 [mb GeV -2 ] Centrality Dependence in Au+Au at  s NN = 200 GeV Consistent with binary scaling Small statistics for high p T

2004/11/5Workshop at RCNP34 N collision Scaling in Au+Au Quantitative study of binary scaling. Fit dN/dy (0.8<p T <4.0) = A (N coll )   =1  complete binary scaling  =  ( – ) without p+p =  with p+p Non-photonic (charm) electron production is consistent with number of binary collisions scaling. nucl-ex/ N coll

2004/11/5Workshop at RCNP35 PHENIX measures  cc = 622  57  160  b in Au+Au at 200GeV (MB) NLO calculation shows  cc = 300~450  b Total cross section is consistent with pQCD calculation Charm Cross Section

2004/11/5Workshop at RCNP36 Coming attraction Converter vs Cocktail method –The p T distributions are in good agreement. –The converter is good for lower p T, the cocktail is good for higher p T –Energy loss effect can be studied by cocktail method. Systematic study is now proceeding. –p+p at  s NN 200GeV in Run2 –p+p and d+Au at  s NN 200GeV in Run3 (much more statistics) –Au+Au at  s NN =62.4GeV and 200GeV (much more statistics) Converter vs Cocktail Work in progress PHENIX Preliminary p+p and d+Au at  s NN =200GeV Au+Au at  s NN =62.4GeV

2004/11/5Workshop at RCNP37 Status in Au + Au Total non-photonic electron yield in Au+Au agree well with binary scaling. –Total cross section  cc = 622  57  160  b –  =  ( – ) without p+p –Small statistics for high p T measurement Systematic study is now in progross. –Refine Au+Au data by cocktail method. –P + p, d + Au and Au + Au measurement with higher statistics PHENIX detector upgrade –Silicon vertex to reconstruct displaced vertices D → K  B → J/  K –Hadron blind detector High electron identification capability

2004/11/5Workshop at RCNP38 Summary PHENIX measured leptonic observables  j/  in p+p, ｄ＋ Au, Au+Au at  s NN = 200GeV.  Light vector mesons in d+Au and Au+Au. + Both   K + K –,   e + e – are measured in d+Au.  Non-photonic electrons in p+p, d+Au, Au+Au  Total charm production in Au+Au is consistent with binary scaliing.  no indication for strong enhancement / suppression of charm cross section in nuclear collision. Systematic study with wide range of system and kinematic now begins  Much more statistics in Run 4  Detector upgrade will provide new opportunity