Leptons and Heavy Flavors at RHIC

Leptons and Heavy Flavors at RHIC Y. Akiba　（KEK) RHIC/AGS User’s Meeting August 10, 2001

Outline • Lepton and heavy flavor physics at RHIC • Run-1(year2000) results • Outlook for Run-2 data • Summary

Lepton and heavy flavor physics at RHIC • Lepton (e, m), lepton pairs (ee, mm), and heavy flabors (c, b) are probes of early stage of nucleus-nucleus collisions • charm production • gluon density • gluon shadowing • charm pt distribution • intrinsic <kt>, multiple parton scattering • dE/dx of charm quark in hot matter • J/Y suppression • deconfinement • Drell-Yang process • quark, anti-quark density • shadowing • Thermal radiation from the QGP • Thermal lepton pair (ee, mm) • Thermal direct photon (g  ee) (conversion) • r, f, w  e+e- • medium modification of vector mesons • Heavy flavor and lepton measurement are related • Open charm, bottom production is measured by its semi-leptonic decay (e, m) • Dilepton pair (ee, mm, em) from charm decay • J/Y is measured by its ee, mm decay

Space Time evolution of Au+Au collisions parton-parton interactons Drell-Yan　（ee, mm） (M>6 GeV) Direct photon　（gee）(pt>3GeV/c) Charm production（e,m,ee,em,mm) Two Au nuclei collide Quark/gluon energy loss Energy loss of c-quark Formation of Hot & Dense matter deconfinement J/Y suppression (ee,mm) Thermal radiation from QGP Thermal photon (g ee) Thermal lepton pair(ee,mm) MT ~ 1 – 3 GeV Statistical formation of charmonium J/Y enhancement? Hadronization time Light vector mesons (ee) (Mf, Mr, Gr,…) Chiral symmetry restoration Hadron gas Thermal photon (gee) Thermal lepton pair(ee,mm) MT ~ 1 GeV Thermal radiation from hadron gas e,g,m from decay of light hadrons(p,h,K,…) Freeze Out The entire space-time evolution can be probed by lepton and heavy flavors

Physics from lepton pairs Medium modification of r, w, f Thermal lepton pairs Deconfinement by J/y suppression lepton pairs from c-cbar decay High mass Drell-Yan pair Baseline with Upsilon

Charm production at RHIC energy • Charm production cross section in p+p is not known at RHIC energy • The cross section can be estimated by tuning PYTHIA (LO pQCD) calculation with fixed target data. A large (~5) K-factor is required. • Extrapolation to RHIC (p+p) • scc = 200-400 mb at s1/2 = 130 GeV • scc = 400-800 mb at s1/2 = 200 GeV • If charm production scaled with number of binary N-N collisions, a large number of charm pairs are produced in single Au+Au collision • <Ncc> is 10 to 20 in central Au+Au collision at 200 GeV! • Deviation from the Binary scaling • Gluon shadowing/saturation? • Thermal charm production?

Single electron from charm • Because of a large charm production at RHIC, charm can be indirectly measured from its semi-leptonic decay. • At ISR, single electron signal is observed at e/p ~ 2x10-4 in pt>1.5 GeV/c • At RHIC energy, single electron signal from c-qark decay is expected at a level of e/p ~ 3-4x10-4 in p+p • Since high pt pions are suppressed relative to Nbinary scaling, the e/p ratio can be as high as 10-3 in Au+Au collision. This means that charm can be the dominant souce of electron in pt>1-2 GeV/c. • At higher pt (pt>3-4 GeV/c), electrons from b decay can be dominant.

J/Y production • “Anomalous J/Y suppression” was observed by NA50 in Pb+Pb collisons at s1/2 ~17 GeV • What happens in Au+Au at the RHIC energy? • Complete suppression? • J/Y enhancement at RHIC? • re-generation from large (~10-20) number of cc pairs produced in one event NA50 In QGP, J／Y can not be formed because of color screening In normal vacuum, a cc pair is bound to form a J／Y ｐ＋A Pb+Pb

Light vector mesons e+ r,w,f e- • Enhancement of low mass di-electron was observed by CERES in S+Au and Pb+Au collisons at s1/2 ~20 GeV • What happens at the RHIC energy? • Precise measurement of r, w, f with high mass resolution. Properties of r, w, f in the hot matter can be probed by their ee decay

PHENIX Experiment Two central electron/photon/hadron spectrometers Two forward muon spectrometers PHENIX - only RHIC experiment specifically designed to measure leptons. Electrons are measued by the two central arms. Muons are measured by the two forward arms. In Run-1, a part of central arm is operational for electron measurement.

Electron measurement in PHENIX in RUN-1 • Half of the West arm was used for electron measurement. • DC and PC1 (W) • tracking • RICH(W) • electron ID • PBSC EMCAL (W): • electron ID (E/p ratio) • Search for single electrons from heavy quark decay • Muon system was not available in Run-1

High pt electron measured by PHENIX RUN 12280 SEQ 0014 EVENT 850 PHENIX South Side East Arm West Arm RICH EMCal DC DC RICH ring (6 PMT hit) PC1 PC1 RICH RICH TEC PC3 6 PMT RICH ring 2.55 GeV/c track 2.5 GeV EMCal hit electron candidate TOF EMCal EMCal EMCal hit (2.5GeV) View from North Side Electron was selected by RICH, DC and EMCal

Electron Identification in PHENIX 0.8GeV<p<0.9GeV • Electrons are identified by RICH and EMCAL • A clear peak in energy/momentum (E/p) ratio is seen at 1.0 after RICH hit is required • EMCAL E/p cut cleans up the rest of the background. • Random background is also subtracted. All charged With RICH hit Random background E/p ratio

Electron Spectra from RUN-1 • PHENIX measured electron spectra is up to 4 GeV/c. • The electron spectra include “trivial” background from p0 Dalitz decay and photon conversion. • The amount of the background can be calculated from the pion spectrum measured by the same experiment.

Comparison: data - cocktail • Analysis in progress to explain the inclusive electron data from know sources of electron. • Excellent agreement　between data and cocktail simulation for peripheral collisions. • Dominant source in the cocktail • p0 Dalitz decay • photon conversion • Charm contribution relevant in pt>1.5 GeV/c • The coktail agrees with the peripheral data with and without charm component within statistics. • Analysis is in progress in search for charm-like component in central collisions • If charm production scales as Nbinary, charm contribution is larger in central collisions.

Electron Pairs in PHENIX in RUN-1 • Di-electron mass distribution is measured up to 3 GeV in RUN-1 by PHENIX • Only one of e+ or e- was required to hit EMCAL • Most of the pairs are combinatorial background. • The statistics is not sufficient to measure J/Y. (Less than a few J/Y are expected.)

PHENIX in RUN-2 • Two central arms completed • 4 times more acceptance for single electrons • Much larger pair acceptance • South Muon Arm completed • Improved DAQ system • Data logging rate > 20 MB/s • Level-2 software triggers to select rare events • Single high pt electron • Single high pt muon • J/Y ee • J/Y mm

Electron pairs in PHENX (RUN2) ～16M central Au+Au events in central arms of PHENIX(simulation) • Good Measurement of J/Y • ~10K at y=0 • Very good S/N ratio • Measurement of light vector mesons • Large combinatorial background • S/N ~1/10 for f • S/N ~ 1/15 for w • High mass resolution • r/w/f separation • Modification of Mf, Gf • Look for low mass pair enhancement • Can measure r if there is a large enhancement by ppree J/Y

Muon Pairs in PHENIX (Run2) • 1.2 < h < 2.2 (south), full f coverage • tracking with 3 stations of chambers in magnetic field • muon ID with 5 layers of steel absorber and Iarocci tubes • low energy cutoff at 2 GeV • 5 times of J/Y acceptance of the central arms PHENIX South Muon arm

Lepton measurement by PHENIX in RUN-2

Electrons and Muons _ cc p+p s = 200 GeV 320 pb-1 _ bb /K Yield per 1 GeV/c2 Mem[GeV] Mem[GeV] • Excellent additional way to measure heavy quark production. • Signal can be seen in Mem > 4 GeV • Large statistics is needed to see the signal

Summary • Lepton and heavy Flavors are clean probes to the early stage of the collisions • In RUN-1, PHENIX measured inclusive electron spectra in Au+Au at 130 GeV. • demonstrate its ability to identify electron in very high multiplicity event • Analysis is in progress to observe electrons from heavy quark decay • Exciting new results should come from RUN-2 • Measurement of ce, cm • Measurement of J/Yee, mm • Measurement of w, f  ee • And more!

Leptons and Heavy Flavors at RHIC