Single Electron Measurements at RHIC-PHENIX T. Hachiya Hiroshima University For the PHENIX Collaboration

2 Motivation 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 can be seen. (PHENIX observed high pT suppressions in hadron measurements) Charm can be produced thermally at very high temperature Sensitive to state of the matter Charm measurements bring us an important baseline of J/  measurement

3 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 decay of charm. This method is used by PHENIX at RHIC ++

4 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

5 Photon conversions : Dalitz decays of  0, ,  ’, ,   0  ee ,   ee , etc) Kaon decays Conversion of direct photons Di-electron decays of , ,  Thermal di-leptons Most of the background are PHOTONIC Source of Electrons Background Charm decays Beauty decays Those are Non-PHOTONIC signal Signal  0   e+e-e+e-

6 PHENIX Run 2  Amount of data 20 times larger statistics  All detectors work in Central arm spectrometers Acceptance is 4 times as large  Special run with a photon converter 1.7 % radiation length of brass and placed around beam pipe The converter can increase electrons only from photonic source by a fixed factor By comparing the data with and without the converter, We can separate electron from non-photonic and photonic source  Complementary to cocktail method Photon Converter e+e+ e-e-

7 Photon Converter Method Single electron spectra : data with the converter data w/o the converter If all electrons are from photonic source, the ratio is constant. But the data shows that electron yield approach at high p T each other. It is an evidence for non-photonic electrons NeNe 00 1.1% 1.7% Dalitz : 0.8% X 0 equivalent 0 With converter Conversion in converter W/O converter Conversion from pipe and MVD 0.8% Non-photonic

8 Electrons from Non-photonic Source Back ground subtracted single electron spectra at  s NN =200GeV 200GeV data is higher than 130GeV data. Spectral shape at 200GeV is similar to that at 130GeV The data is in good agreement with PYTHIA calculation  cc (130GeV)=330  b   cc (200GeV)=650  b

9 Centrality Dependence Single electrons in each centrality class are in reasonable agreement with PYTHIA calculation scaled by binary collision

10 Observations Our data is consistent with binary scaling within our current statistical and systematic uncertainties. NA50 at SPS has inferred a factor of ~3 charm enhancement from intermediate mass di-muon measurement. 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. We do not see this large effect in the single electrons. Initial state high pt 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

11 Summary & Outlook  PHENIX measured single electrons from non-photonic source at  s NN =130GeV and 200GeV  The single electrons are in good agreement with PYTHIA charm calculation using number of binary collision scaling within current statistic and systematic uncertainties  Refine the converter method and cross-check by the cocktail calculation  Finalize single electron spectra from non-photonic source  Comparison to single electron in p+p and d+Au at  s NN =200GeV (RHIC Run2 and Run3)

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13 Inclusive Electrons at  s=130GeV 1.5M M.B. events are analyzed. The back ground from random association is estimated by event mixing method Spectra are fully corrected with acceptance and efficiency loss Back ground electrons from photonic source are included

14  conversion  0   ee    ee, 3  0   ee,  0 ee   ee,  ee   ee  ’   ee Cocktail Calculation p T distribution of  0 are constrained with PHENIX  0 and   measurement p T spectra of ,  ’  and  are estimated with m T scaling p T = sqrt(p T 2 + M had 2 – M  2 ) Hadrons are relatively normalized by  0 at high p T from the other measurement at SPS, FNAL, ISR, RHIC Material in acceptance are studied for photon conversion Signal above cocktail calculation can be seen at high p T

15 Data / Background Ratio of Electrons  conversions and  0 dalitz are ~ 80% of photonic source  is ~ 20% Contribution from the other hadrons are very small Top figure shows data/background ratio in M.B event sample. The data shows excess above background in p T > 0.6[GeV/c]. Most of the systematic uncertainty comes from single electron measurement and cocktail calculation. -> need reference point in run2

16 Single Electron Spectra at  s NN =130GeV PYTHIA direct  (J. Alam et al. PRC 63(2001)021901) b c PHENIX: PRL 88(2002) Single electron spectra after background (photonic source) is subtracted for central and M.B collisions at  s NN =130GeV Electrons from charm and beauty decays calculated by PYTHIA are overlaid -- PYTHIA parameter is tuned to fit low energy data -- scaled to Au+Au using number of binary collision. Charm in PYTHIA are in reasonably agreement with data (within relatively large uncertainty) The contribution from thermal dileptons and direct  is neglected -- We may over-estimate the charm yield.

17 Charm Cross Section Single electron cross section is compared with ISR data Charm cross section is compared with fixed target charm data. Solid curve : PYTHIA shaded Band : NLO pQCD Assuming binary scaling, PHENIX data are consistent with  s systematics (within large uncertainties)  By fitting the PYTHIA electron spectrum to the data for pt>0.8[GeV/c], we obtained charm yield Ncc per event.  The charm cross section per binary NN collision is obtained as  T AA is nuclear overlap integral ~ NN integrated luminosity per event T AA (0-10%)=22.6±1.6/mb T AA (0-92%)=6.2±0.4/mb  Charm cross section derived from the single electron PHENIX PYTHIA ISR NLO pQCD (M. Mangano et al., NPB405(1993)507) PHENIX: PRL 88(2002)192303

18 Cocktail Calculation p T distribution of  0 are constrained with PHENIX  0 and   measurement p T spectra of ,  ’  and  are estimated with m T scaling p T = sqrt(p T 2 + M had 2 – M  2 ) Systematic uncertainty in cocktail calculation is assigned 50 % in each ratio PHENIX DATA η η' ρ ω φ

19 Photon conversions : Dalitz decays of  0, ,  ’, ,   0  ee ,   ee , etc) Kaon decays Conversion of direct photons Di-electron decays of , ,  Thermal di-leptons Most of the background are PHOTONIC Charm decays Beauty decays Those are Non-PHOTONIC signal Source of Electrons Background Signal  0   e+e-e+e-  conversion  0   ee    ee, 3  0   ee,  0 ee   ee,  ee   ee  ’   ee

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21 Outline Motivation Charm and electron measurements PHENIX experiment: how to measure electrons Run-1: Au +  s NN = 130 GeV single electrons from charm decays (c  D  e + X) Run-2: Au +  s NN = 200 GeV single electrons refined Summary and outlook

22 PHENIX Experiment Two central spectrometers , e  and hadrons Coverage: |  | < 0.35  =  /2  2 M.B. Trigger and Centrality Beam Beam Counter Zero Degree Calorimeter Collision vertex Beam Beam Counter BBC DC&PC RICH EMCAL