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Future Measurements of Photons and Di-leptons at RHIC/RHICII

Discusses high-pT photons, low-mass vector meson, and thermal dilepton measurements at RHIC/RHICII. Explores heavy flavor decay, heavy quarkonia, and detection improvements for precise measurements.

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Future Measurements of Photons and Di-leptons at RHIC/RHICII

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  1. Future Measurements of Photons and Di-leptons at RHIC/RHICII LijuanRuan (Brookhaven National Laboratory) Outline: • high pT photons • low mass vector meson and thermal dilepton measurements • dilepton from heavy flavor decay: heavy flavor production mechanism and a base line for intermediate mass dilepton thermal radiation • heavy quarkonia Lijuan Ruan (RHIC & AGS User Meeting)

  2. Why photons and di-leptons EM probes: do not interact with the medium strongly, carry the direct information (medium properties) when it was produced Lijuan Ruan (RHIC & AGS User Meeting)

  3. High pT photons at STAR and PHENIX Both STAR and PEHNIX have the -h correlation measurements. The current measurements with big statistical and systematic uncertainties can not distinguish different energy loss mechanisms. PHENIX: Vale QM2009 STAR: Hamed QM2008 Lijuan Ruan (RHIC & AGS User Meeting)

  4. Future improvements •  v2 measurements • -identified hadron correlation: • measure flavor separated quark and gluon fragmentation function • 3. -jet reconstruction should also be feasible Lijuan Ruan (RHIC & AGS User Meeting)

  5. arXiv:0706.3034 PLB670,313 (2009) PHENIX low mass dielectrons p+p NORMALIZED TO mee<100 MeV low mass w AuAu f pp and AuAu normalized to p0 Dalitz region (~ same # of particles) p+p: agree with the expected background from hadron decays Au+Au: large Enhancement in 0.15-0.75 GeV/c2 J/y intermediate mass y’ pp Au+Au: S/B ratio is: ~ 1/100 in ,  mass region DreesQM2009 Lijuan Ruan (RHIC & AGS User Meeting)

  6. What still need to be done for low invariant mass region • Do we observe the chiral symmetry restoration: vector meson? • How do we know the initial temperature of QGP? The understanding requires precise measurement in pp, dAu and AuAu collisions • More luminosity to decrease statistical errors • Detector upgrades to reject the combinatorial background, reduce systematic errors • Precise measurement of all the cocktail contributions (charm, heavy quarkonia …) to get thermal photon/dilepton information • New measurements Lijuan Ruan (RHIC & AGS User Meeting)

  7. Improve the measurement with statistics Cu+Cu d+Au raw data DreesQM2009 Axel Drees • Cu+Cu data finalized soon • Cover low Npart range • High statistics pp data (4x) • Continuum between J/ and  • Even better reference including bottom • High statistics d+Au • Cold nuclear matter effects • 500 GeV data with HBD! • RHIC II lumonosity Lijuan Ruan (RHIC & AGS User Meeting) 7

  8. Improvedilepton continuum with detector upgrade signal electron e- partner positron needed for rejection Cherenkov blobs e+ qpair opening angle ~ 1 m HBD Need tools to reject photon conversions and Dalitz decays Hadron blind detector To identify open charm Silicon Vertex Detector (VTX) DreesQM2009 Axel Drees • HBD is fully operational • Proof of principle in 2007 • Taking data right now with p+p • Expect large Au+Au data set in 2010 • Vertex detector (VTX) will be installed for 2011 Lijuan Ruan (RHIC & AGS User Meeting) 8

  9. STAR just starts it bright journey Clean electron PID can be obtained up to PT < 3 GeV/c. Run9: phiee; reference di-lepton mass spectrum in 200 GeV 300 M p+p collisions Run10: 200 GeV Au+Au collisions Run8-10: low material budget similar to PHENIX TOF upgrade: ||<0.9, full azimuthal coverage Run9: 86 trays (72% of the full coverage) in operation. Run10: 100% coverage Lijuan Ruan (RHIC & AGS User Meeting)

  10. ee and KK PHENIX: HiroshimaQM2009 STAR Phys. Rev. Lett. 99 (2007) 112301 TPC+TOF configuration in run10: 300 M Au+Au events: ee 25 sigma significance; S/B = 1/25 - 1/10 Measure mass, width, line shape and yield and v2 It’s important to have both measurements in one experiment. Run8-10: low material budget similar to PHENIX Lijuan Ruan (RHIC & AGS User Meeting)

  11. (770)ee and  STAR Phys. Rev. Lett. 92 (2004) 92301 The mass shift observed in  in 200 GeV p+p and Au+Au collisions, more shift in peripheral Au+Au collisions (phase space, Bose-Einstein correlations, dynamical effects in the medium). In run10, STAR should be able to measure ee:mass, width, line shape Run8-10: low material budget similar to PHENIX Lijuan Ruan (RHIC & AGS User Meeting)

  12. a1(1260) measurement Spontaneous chiral symmetry breaking leads to the mass difference for vector meson  and axial-vector meson a1; In the hot dense medium, due to chiral symmetry restoration, there are several different scenarios, such as dropping mass, melting, etc. a1 should be tried and feasible at STAR with TOF. R. Barate et al. [ALEPH Collaboration], Eur. Phys. J. C 4, 409 (1998);R. Rapp, Pramana 60, 675 (2003) [arXiv: hep-ph/0201101].G. David, R. Rapp and Z. Xu, Phys. Rept. 462, 176 (2008). Lijuan Ruan (RHIC & AGS User Meeting)

  13. Dilepton capability using TOF + HFT PXL at 2.5 and 8 cm TPC+TOF+SSD+HFT ~ 200M central Au+Au events : 22Kand 6K vector meson pairs for one year RHIC running, Accuracy comparable to NA60 presented at QM05 in central InIn collisions; HFT provides precise D and B measurements  provides a baseline for the possible intermediate di-lepton thermal radiation. Lijuan Ruan (RHIC & AGS User Meeting)

  14. Future heavy flavor measurement projection STAR with HFT: 500 M PHENIX with VTX: 0.4 nb-1 Precise D,B measurements leave room for the possible intermediate di-lepton thermal radiation. Also the resonance in the sQGP also need precise ee from ccbar measurements. Lijuan Ruan (RHIC & AGS User Meeting)

  15. Distinguish heavy flavor and initial lepton pair production: e muon correlation L.Ruan et al., 0904.3774; Z. Xu, BNL LDRD project 07-007 EngelmoreQM2009 e correlation simulation with Muon Telescope Detector at STAR from ccbar: S/B=2 (Meu>3 GeV/c2 and pT(e)<2 GeV/c) S/B=8 with electron pairing and tof association Lijuan Ruan (RHIC & AGS User Meeting)

  16. Large mass dilepton: J/ STAR Preliminary 60% direct J/psi • J/ has been proposed as a smoking gun for QGP. • many measurements from RHIC: pT, rapidity dependence in different system at 200 GeV • Q: do we understand J/ production mechanism in pp collisions? • A: Not really PHENIX: Leitch, Silva QM2009; STAR: 0904.0439 F. Karsch, D. Kharzeev and H. Satz, PLB 637, 75 (2006);B. Alessandro et al. (NA50), Eur. Phys. J. C 39 (2005) 335; R. Arnaldi et al. (NA60), Quark Matter 2005; PHENIX: Phys.Rev.Lett.98, 232301,2007. Lijuan Ruan (RHIC & AGS User Meeting)

  17. Recent measurements on J/ STAR Preliminary • High pt J/-h correlations constrain B contribution • Using nuclear modification factors to understand production mechanism and medium properties • Spin alignment • What else can we do? STAR Preliminary PHENIX: Leitch QM2009; STAR: 0904.0439 Lijuan Ruan (RHIC & AGS User Meeting)

  18. The future measurements at RHIC/RHICII STAR preliminary with FMS To understand the production mechanism at high pT and medium properties; using medium to understand the J/ production mechanism in p+p • Different collision system: Au+Au (RAA) • J/ v2 • Cold nuclear medium effect: d+Au • Forward/backward measurements • Different energy: p+p 500 GeV • Correlations • Higher states: c, ’ • Spin alignment of J/ and ’ • Upsilon(1S,2S,3S) c→J/ +  PHENIX: Leitch, Silva QM2009 STAR: Perkins QM2009 Lijuan Ruan (RHIC & AGS User Meeting)

  19. Upsilon Upsilon: the journey is starting … PHENIX: Leitch, Silva, Atomssa QM2009 STAR: H. Liu QM2009 Lijuan Ruan (RHIC & AGS User Meeting)

  20. Improve mass resolution simulation L.Ruan et al., 0904.3774; Z. Xu, BNL LDRD project 07-007 STAR Muon Telescope Detector PHENIX FVTX Uprade PHENIX VTX Uprade Lijuan Ruan (RHIC & AGS User Meeting)

  21. STAR: Future dramatic improvement of J / at low pT EMC+TOF+HFT (large acceptance): J/ production Different states predicted to melt at different T in color medium Charmonia(J/), bottonia() dE/dx after TOF cut pT (e)>1.5 GeV/c Quarkonium dissociation temperatures – Digal, Karsch, Satz PHENIX Acceptance: |h|<0.35, f=2*p/2 STAR TOF-Upgrade Acceptance: |h|<0.9, f=2*p J/y yields from 1 billion minbias Au+Au events: 43.8x10-9/0.040x109*292*0.5*1.8*0.5=144,0000.3% v2 error sJ/y spp N Nbine y RAA Lijuan Ruan (RHIC & AGS User Meeting)

  22. High luminosity for Υ & J/ STAR high pT J/ Lijuan Ruan (RHIC & AGS User Meeting)

  23. Summary With high luminosity, detector, daq and trigger upgrade, the following measurements with good precision: Lijuan Ruan (RHIC & AGS User Meeting)

  24. Backup Lijuan Ruan (RHIC & AGS User Meeting)

  25. Photon and dilepton spectra thermal production rates for photons and dileptons: Boltzmann factor Electromagnetic correlation function; Can be measured in e+e- annihination M<1.5 GeV, vector meson properties M>1.5, QGP thermal radiation G. David, R. Rapp and Z. Xu, Phys. Rept. 462, 176 (2008). Lijuan Ruan (RHIC & AGS User Meeting)

  26. Electron identification from TOF from STAR Clean electron PID can be obtained up to PT < 3 GeV/c. (STAR Collaboration, PRL94(2005)062301) Run9: phi->ee; low pt J/psi; reference di-lepton spectrum in 200 GeV 300 M p+p collisions Run10: 200 GeV Au+Au collisions Low material, material budget similar to PHENIX Lijuan Ruan (RHIC & AGS User Meeting)

  27. HFT: Reject gamma conversion PXL at 2.5 and 8 cm • Background: g  e+e- • HFT discriminates background ! • Dalitz decay is dominate backgound: 50-70% can be rejected through the TPC (invariant mass, opening angle cut) Lijuan Ruan (RHIC & AGS User Meeting)

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