Single Electron Measurements at RHIC-PHENIX

1. 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. p+ Charm Measurement Indirect method: Measure leptons from semi-leptonic decay of charm. This method is used by PHENIX at RHIC Direct method: Reconstruction of D-meson (e.g. D0Kp). Very challenging without measurement of displaced vertex

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

5. Charm decays • Beauty decays Those are Non-PHOTONIC signal p0  g g Signal e+e- Source of Electrons • Photon conversions : • Dalitz decays of p0,h,h’,w,f (p0eeg, heeg, etc) • Kaon decays • Conversion of direct photons • Di-electron decays of r,w,f • Thermal di-leptons Most of the background arePHOTONIC Background

6. Photon Converter 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 e+ e-

7. Ne 1.7% 1.1% 0.8% With converter Conversion in converter W/O converter Conversion from pipe and MVD Dalitz : 0.8% X0 equivalent Non-photonic 0 0 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 pT each other. • It is an evidence for non-photonic electrons

8. Electrons from Non-photonic Source • Back ground subtracted • single electron spectra at • sNN=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. NA50 - Eur. Phys. Jour. C14, 443 (2000). Binary Scaling PHENIX Preliminary Enhancement of Open Charm Yield N part 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 pTp0 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)

11. Summary & Outlook • PHENIX measured single electrons from non-photonic source • at sNN=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 sNN=200GeV (RHIC Run2 and Run3)

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. gconversion p0 gee h gee, 3p0 w ee, p0ee f ee, hee r ee h’  gee Cocktail Calculation • pT distribution of 0 are constrained with PHENIX 0 and  measurement • pT spectra of , ’  and  are • estimated with mT scaling • pT = sqrt(pT2 + Mhad2 – M2) • Hadrons are relatively normalized by • 0 at high pT 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 pT

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 pT > 0.6[GeV/c]. • Most of the systematic • uncertainty comes from • single electron measurement • and cocktail calculation. • -> need reference point in run2

16. PHENIX: PRL 88(2002)192303 c PYTHIA b direct g (J. Alam et al. PRC 63(2001)021901) Single Electron Spectra at sNN=130GeV • Single electron spectra after • background (photonic source) • is subtracted for central and • M.B collisions at sNN=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. PHENIX: PRL 88(2002)192303 NLO pQCD (M. Mangano et al., NPB405(1993)507) PHENIX PYTHIA ISR Charm Cross Section • 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 • TAA is nuclear overlap integral ~ NN integrated luminosity per event TAA(0-10%)=22.6±1.6/mb TAA(0-92%)=6.2±0.4/mb • Charm cross section derived from the single electron • 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)

18. η η' ρ ω φ Cocktail Calculation • pT distribution of 0 are constrained with PHENIX 0 and  measurement • pT spectra of , ’  and  are • estimated with mT scaling • pT = sqrt(pT2 + Mhad2 – M2) • Systematic uncertainty in cocktail calculation is assigned 50 % • in each ratio PHENIX DATA

19. p0  g g gconversion e+e- p0 gee h gee, 3p0 w ee, p0ee f ee, hee r ee h’  gee Signal Source of Electrons Background • Photon conversions : • Dalitz decays of p0,h,h’,w,f (p0eeg, heeg, etc) • Kaon decays • Conversion of direct photons • Di-electron decays of r,w,f • Thermal di-leptons Most of the background arePHOTONIC • Charm decays • Beauty decays Those are Non-PHOTONIC signal

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

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