1 Measurements of Leptonic and Photonic Probes in Au+Au Collisions at PHENIX Run-2 Takashi Matsumoto for the PHENIX collaboration at RHIC & AGS Annual User’s Meeting PHENIX

2 Topics Covered in This Talk Part 1 What is PHENIX? Overview of experimental setup and physics. Part 2 Electron measurements in PHENIX. Results : Leptonic probes in Au+Au. Part 3 Photon measurements in PHENIX in Au+Au. Results : Photonic probes. Other Topics from PHENIX Global/hadron -> by Kensuke Homma in next session. pp results -> by Xie Wei on Saturday.

What is PHENIX? Overview of experimental setup and physics. Part 1

4 Physics in PHENIX Search for a new state of matter, quark-gluon plasma (QGP). what is happening in heavy ion collision at RHIC energy? How do we get the information about the earliest stage of the collision and hot/dense phase? Hadrons and global variables. Particle production. Achieved energy density, etc. Leptons and photons. Carry the “direct” information without affected by strong interaction. Difficult, but important The preliminary results from PHENIX Run2 presented in this talk focused on leptons and photons.

5 PHENIX Experiment Capability of measuring the photons and leptons using 2 central arms and 2 muon arms. Capability to achieve different kind of measurements at the same time. e + e -, K + K - J/  e + e -, J/    +  - Photon measurement in 3 different ways. 2 direct measurements  e + e -

6 PHENIX Setup Central arms cover ||<0.35, d  =90°x 2 Measurements of Vertex and Collision timing Beam-Beam Counters (BBC) Zero Degree Calorimeters (ZDC) Coincidence between BBC and ZDC produce minimum bias trigger Tracking Drift Chambers (DC) Pad Chambers (PC) Electron identification Ring Imaging Cherenkov Detectors (RICH) Electro-Magnetic Calorimeters (EMCal) Lead Scintillator Calorimeters (PbSc) Lead Glass Calorimeters (PbGl) Photon identification Electro-Magnetic Calorimeters

7 0-5% 15-20% % 0-5% 5-10% Centrality Determination Event characterization in terms of impact parameter (b) in Au+Au collisions. Large : peripheral collision Small : central collision Coincidence between BBC and ZDC. Determine collision centrality. 92 % of inelastic cross section can be seen. Extract variables using Glauber Model Number of participants (N_part). Number of nucleons participate in a collision. Represents centrality. Related with soft physics. Number of binary collisions (N_binary). Number of Nucleon-Nucleon collisions. Related with hard physics. Incoherent sum of N-N collisions becomes a baseline for A-A collisions. peripheralcentral b To ZDC To BBC spectator

8 Electron Identification Ring Imaging Cherenkov counter Track - Ring association 3 PMT hits Ring shape cut e + e - candidate net e + e - Electromagnetic Calorimeter Energy – Momentum matching Track – Hit position association Timing cut charged tracks Background Energy / momentum z direction [cm] phi direction [cm] Distance between track and ring

9 Photon Measurements Direct measurement. 2 types of Electromagnetic Calorimeter. PbSc calorimeter. covering ¾ acceptance. PbGl calorimeter. covering ¼ acceptance. Indirect measurement. Measurements of photons through their conversion into e + e - pairs. Photon converter located around beam pipe

Part 2 Results : Leptonic probes Single electron results Dielectron continuum results  results J/  results

11 Single Electron (Charm Measurement) Direct method: Reconstruction of D-meson (e.g. D 0  Kp). Very challenging without measurement of displaced vertex ++ Indirect method: Measure leptons from semi-leptonic decay of charm. This method is used by PHENIX at RHIC Motivation Measurements of Heavy flavor (charm and beauty) production through semi-leptonic decay. -> non-photonic decay. Background:  0 dalitz decay, photon conversion…

12 Single Electron Spectra from Non-photonic Source Spectra (130 and 200 GeV) with binary scaled PYTHIA calculation of electron spectra from semi- leptonic charm decay. Our data are consistent with binary scaling in all centrality classes within current statistical and systematic errors.

13 Discussion of Single Electron Result NA50 has inferred a factor of ~3 charm enhancement at lower energy. We do not see this large effect at RHIC. PHENIX observes a factor of ~3-5 suppression in high p T  0 relative to binary scaling (See Kensuke Homma’s talk). We do not see this large effect in the single electrons. Initial state high p T suppression excluded? Smaller energy loss for heavy quark ? (dead cone effect) NA50 - Eur. Phys. Jour. C14, 443 (2000). N part Enhancement of Open Charm Yield Binary Scaling PHENIX Preliminary

14 Dielectron Continuum Motivation Is there excess in low and intermediate mass region, due to In-medium mass modification of mesons ? Contribution from charm ? Background subtracted invariant mass spectra of e + e - Expected meson decay contributions. PYTHIA charm calculation scaled by number of binary collisions. Black curve is sum of above two contribution. dN/dm ( GeV/c 2 ) = 13.4  7.2(stat) –8.4 (sys) x10 -5 dN/dm ( GeV/c 2 ) = 0.38  2.60(stat) –0.81 (sys) x10 -5 PHENIX will measure this as soon as we get statistics.

15 measurement ( e + e -, K + K - ) Motivation Is there medium modification? Restoration of chiral symmetry Mass and natural width Difference between leptonic (e) and hadronic (K) probe Simultaneous measurements of two probes Strangeness production  e + e - ( AuAu minimum bias) Signal = 101  47   K + K - ( AuAu minimum bias) Signal = 1135  120 PHENIX preliminary Yield Mass (GeV/c 2 ) Yield PHENIX preliminary

16 dN/dy for   ee  KK Au +Au minimum bias data. Corrected for vacuum PDG branching fraction.  BR  e + e - = 2.9 x  BR  K + K - = 0.49 There is no difference of dN/dy between   e + e - measurements and K + K - measurements within current errors.

17 J/  measurements ( J/  e + e - ) Motivation. Screening effect in deconfined matter Melt the J/ y produced in the initial collision Suppression of the yield above normal nuclear effect will be seen N J/ is obtained in 3 centrality bin. 0-20% : 5.9  2.4(stat)  0.7(sys) 20-40% : 4.5  2.1(stat)  0.5(sys) 40-90% : 3.5  1.9 (stat)  0.5(sys) Systematical error of N J/ is estimated using several kind of fitting models.

18 B dN/dy for J/  B dN/dy was measured as a function of number of participants % : (3.9  1.6  1.0) x % : (2.5  1.2  0.7) x % : (6.9  3.7  1.9) x B dN/dy per binary collision was calculated % (N binary 791): (4.9  2.0  1.3) x % (N binary 297): (8.5  4.0  2.2) x % (N binary 45) : (1.5  0.8  0.6) x comparison p - p data from PHENIX run2 NA50 data Absorption measured at other experiment 7.1mb NA50 S-U 4.4mb NA50 p-A,S-U (from QM2002) Statistics are limited. But BdN/dy per binary seems to decrease in most central collisions Combine with single electron data  constraint to model?

Part 3 Results : Photonic probes photon measurements given by PbGl calorimeter PbSc calorimeter Converter method

20 Question Is there photon excess compared to hadron decay background? Sources of photon Carry the information of matter. Initial collision. Thermal radiation. Background.  0 decay, etc. Photon Sources

21 Inclusive Photon Measurement Inclusive photon spectra for different centrality (PbGl). Comparison of peripheral spectra between PbGl and PbSc.  Two analyses are consistent. PHENIX preliminary

22 Inclusive Photon Measurement (  e + e - ) Inclusive photon spectra Black bar and green band show Statistical and systematic uncertainties. Study of Systematic error is ongoing. Spectrum is consistent to PbGl result within current error bars. Pt[GeV/c] (1/(2  Pt))·dN/(dydpt) Work in Progress Min. Bias Au+Au √s NN =200GeV

23 Direct Photon Measurements ((/ 0 ) measured / (/ 0 ) simulated ) What was done ? Measure the inclusive photon spectrum. Measure the  0 spectrum. Decay photon simulator (input is  0 spectrum). Assume mT scaling to get contribution of , Compare the measured photon and simulated photon from hadron decay. No excess is observed within current error bars.

24 Summary PHENIX has shown its capability to measure leptonic and photonic probes in Run2. Leptonic probes Single electron from non-photonic source scales to the binary collision within current statistical and systematical errors. We have made first lepton pair measurement. Dielectron continuum. e + e -, K + K -. J/ e + e - Photonic probes 3 different analyses have been done to obtain inclusive photon spectra. There is no excess above hadronic decay background within current errors. Analysis are preliminary and ongoing. Another data set of LVL2 triggered event is being analyzed More will come in final form soon!!

Back up

26 Single electron spectrum from non-photonic source

27 Single electron Motivation Measurements of Heavy flavor (charm and beauty) production through semi-leptonic decay. Gluon-gluon fusion in initial stage of collision? Charm yield : Baseline of charmonium analysis Converter method (Electron from non-photonic source ) Shape of Electron spectrum Without converter Photonic +non-photonic With converter Photonic source dominate Difference can be seen!! Spectrum of electron from non-photonic source subtraction

28 Invariant Mass Spectrum of e+e- pairs Conversion peak is clearly seen. Combinatorial B.G. can be estimated correctly. Due to our tracking algorithm, Reconstructed invariant mass of conversion pairs are shifted to higher value. Red : Real Black : Combinatorial BG Conversion at MVD outer shell Dalitz and Conversion near beam pipe Combinatorial BG