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EM Probes at RHIC II

EM Probes at RHIC II. Zhangbu Xu (BNL) For the RHIC-2 EM-Probes Working Group (co-convenors: G. David, R. Rapp, XZB). http://www.phenix.bnl.gov/WWW/publish/david/rhicii_em Talks by members at April Workshop R. Rapp (Nov. PAC meeting) Simulations from individuals

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EM Probes at RHIC II

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  1. EM Probes at RHIC II Zhangbu Xu (BNL) For the RHIC-2 EM-Probes Working Group (co-convenors: G. David, R. Rapp, XZB) http://www.phenix.bnl.gov/WWW/publish/david/rhicii_em Talks by members at April Workshop R. Rapp (Nov. PAC meeting) Simulations from individuals First Draft of Working Group Document RHIC II Workshop, 11/11/05

  2. Outline 1. Motivations: • Chiral Symmetry Restoration • QGP Radiation -- Temperature 2. Experimental Measurements • Vector Meson In-medium Properties • Thermal Dilepton Spectra • Direct Photons 3. Challenges: • Chiral partners? • Understanding backgrounds • What do we learn from SPS results 4. Conclusions RHIC II Workshop, 11/11/05

  3. Search for Chiral Symmetry Restoration scholar.google.com: 4,130www.google.com: 76,700 Responsible for >90% mass of the visible world RHIC II Workshop, 11/11/05

  4. QCD Phase Diagram A thermodynamic state is specified by a set of values of all the thermodynamic parameters necessary for the description of the system. --- statistical mechanics by K. Huang Temperature (T), chemical potential (m), pressure(P) … • Chemical/thermal Equilibrium at certain stage of the evolution • At the predicted QCD phase boundary • persistent from SPS to RHIC • Below the phase boundary atAGS and SIS • Can we put a point above? RHIC II Workshop, 11/11/05

  5. RHIC The Lost Sword 刻舟求剑 (Fable, 《呂氏春秋》~250B.C.) Experimental Signatures • Vector Meson Properties • Thermal Dileptons • Direct Photons RHIC II Workshop, 11/11/05

  6. at Tc: Chiral Restoration EM Emission and Chiral Symmetry [Brown-rho, Rapp…] nucl-th/0409054 RHIC II Workshop, 11/11/05

  7. Low-Mass Vector Mesons at RHIC • hadron liquid close to Tc: r, w “melt”, f more robust? • baryon+antibaryons important Energy Scan!! RHIC II Workshop, 11/11/05

  8. R. Rapp, hep-ph/0010101 Dilepton from HI smooth transition HG → QGP liquid? Integrated yields from several stages RHIC II Workshop, 11/11/05

  9. QGP Temperature and Composition Direct Photons Intermed.-Mass Dileptons • thermal window: q0 , Mee≈ 2GeV • photons: jet-QGP interactions compromise T-sensitivity • less so for dileptons; charm? Energy Scan RHIC II Workshop, 11/11/05

  10. Detector Upgrades • PHENIX • Hadron Blind Detector (HBD)reject g conversion and Dalitz decay • Silicon Vertex Tracking DetectorMeasure charm background • STAR • Time-of-Flight TPC+TOF+EMC Electron/muon Identification • Heavy Flavor Tracker (HFT)TPC+HFT reject g conversion, Dalitz decay and HFe • Data Acquisition System (1KHz minbias rate) RHIC II Workshop, 11/11/05

  11. Measuring Low Mass Electron Pairs in PHENIX • Hardware • Compensate magnetic field with an inner coil to • preserve e+e- pair opening angle (foreseen in • original design  B0 for r  50-60cm) • Compact HBDin inner region • Strategy • Identify signal electrons with p > 200 MeV/c from • vector mesons in the outer PHENIX detectors • Identify low momentum electrons with p < 200 MeV/c • (mainly from Dalitz pairs and conversions) in the HBD • Reject pair if opening angle < 200 mrad • (for ~ 90% rejection). Requirements * Electron efficiency  90% * Double hit recognition  90% * Modest  rejection ~ 200 C. Woody, RHICII EM probes group meeting, 04/30/05 RHIC II Workshop, 11/11/05

  12. Resulting Low Mass Pair Spectrum with the HBD • Combinatorial background is • reduced by more than two • orders of magnitude • limited by combinatorial • background from open charm • A precision measurement of • charm using the Silicon • Vertex Tracking Detector. C. Woody, RHICII EM probes group meeting, 04/30/05 RHIC II Workshop, 11/11/05

  13. Rates for Vector Meson Production • Consider Run 8 (200 GeV Au x Au, 4x Design Luminosity) : • Lpeak = 30 x 1026 cm-2 s-1 • L ave store= 8 x 1026 cm-2 s-1 • 20 KHz peak min. bias rate • 5.4 KHz avg min. bias rate • 10 week dedicated HBD run (central field in  configuration) • eRHIC x ePHENIX = 0.5 x 0.5 = 0.25 Lower energy 30GeVg2 = 44 • f’s produced in |h| < 0.5 • e+,e- into PHENIX central • arm acceptance • pT,e > 200 MeV/c 8.2 x 109 min. bias events produced N fe+e-= 1.5 x 10-5 / min.bias event f:w:r (e+e-PHENIX) = 1 : 0.9 : 0.7 N fe+e-= 1.2 x 105 produced in PHENIX acceptance C. Woody, RHICII EM probes group meeting, 04/30/05 RHIC II Workshop, 11/11/05

  14. STAR MRPC-TOFr Electron PID electrons Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!! 2 in azimuth, |eta|<1 STAR Collaboration, PRL 94, 2005, 062301 Clean electron PID can be obtained up to PT< 3 GeV/c.  This is used to measure the semileptonic decay of open charm. Hadron rejection power at 10-5. M. Shao et al., nucl-ex/0505026 Higher pT: TPC+TOF+EMC RHIC II Workshop, 11/11/05

  15. g e+e- Reject g conversion • Background: g  e+e- • HFT discriminates background ! • Need low mass detector • Also: DD  e+e- RHIC II Workshop, 11/11/05

  16. Mass(e+e-)<0.15 GeV/c2 Angle pT (GeV/c) Dalitz Decay TPC e+e- invariant mass γ conversion π0Dalitz decay Find the pair from Dalitz,reject both leptons RHIC II Workshop, 11/11/05

  17. Charm Spectrum Measurement • Au + Au, 50M central events • D0 K + p • Stat. uncertainties small • We can subtract DDbar  e+e- • Alternative Approach: reject electrons event-by-event • (~50% for electron pair) • HFT resolution <10m RHIC II Workshop, 11/11/05

  18. STAR Dilepton Capability TOF: vector meson TOF+HFT: thermal radiation RHIC II Workshop, 11/11/05

  19. Rate Estimate Assume: (pp) (AuAu) TOF match+PID eff ≈ 80% TPC+HFT eff ≈ 60% (?) From PDG: Acceptance: N fe+e- = 8 x 10-4 / min.bias event Preliminary estimation for the requested data RHIC II Workshop, 11/11/05

  20. Muon ID at low pT p e m STAR Preliminary: 0.15<pT<0.25 GeV/c, DCA<3cm • less Dalitz decay and g conversion (<x10), Decays from p,K rejected by HFT DCA Dilepton mass: 0.2<m<0.6 GeV RHIC II Workshop, 11/11/05

  21. Direct Photons • Direct Measurement of direct photons All g – known sources • Virtual photon (via low-mass dilepton) • gg HBT RHIC II Workshop, 11/11/05

  22. Rdirect S/B=~1 g g h h calculated from Dalitz formula Rh p0 Here we are… Rp0 p0 measured with EMCal measured ÷ Rdata VirtualDirect Photons RHIC II Workshop, 11/11/05

  23. ( + 1 ) Comparison to Conventional result Conventional method:gall-gph RHIC II Workshop, 11/11/05

  24. gg HBT • Thermal model for direct photon production • Assuming l=1 • EMC+TPC efficiencies:50%+(5—9%) • 16 million Au+Au events Sandweiss/Chikanian (Yale) RHIC II Workshop, 11/11/05

  25. Challenges • Lack of measurements of Chiral Partners • Backgrounds on dilepton, direct photon measurements • What we learn from SPS Measurements RHIC II Workshop, 11/11/05

  26. Chiral Partner (r  a1) h1 3 πB.R. = 0.1 h1  ρπB.R. = 0.9 Mass = 1.170 GeV/c2 Γ = 360 MeV/c2 UrQMD minimum bias Au+Au at √sNN= 200 GeV rp+p- Cocktail P. Fachini 3σ signal a1  gπ±54M events ! Interesting but difficult (Type B) RHIC II Workshop, 11/11/05

  27. Vector MesonCSR • Experimental observation of modification of Vector Spectral Function significant by itself • Model calculation of V-A Spectral Function:Calculate vector and axialvector spectral functions as a function of temperature and density (including as many of the constraints, Weinberg sum rule) in a chirally invariant model. • Compare results with Lattice QCD • Detailed Experimental-Thoery comparison vs energy/density scanPerform detailed comparisons of the in-medium effects on the vector correlator with dilepton data (centrality, excitation function, mass and q_t-spectra), which requires a realistic expansion model (e.g. hydro/transport). RHIC II Workshop, 11/11/05

  28. Charm Background in PHENIX Dilepton crude charm RHIC 2 subtracted spectrum thickness of line represents statistical error 15% at m=2GeV Needs ~+-2% QGP Vacuum Vector mesons R. Seto, RHICII EM probes group meeting, 04/30/05 Mass (GeV) RHIC II Workshop, 11/11/05

  29. Charm/Dalitz Background in STAR DDbar  e+e- correlations can be measured (<+-10%) Dalitz rejection: Inner Detector tracking: SSD+HFT+Vertexin progress RHIC II Workshop, 11/11/05

  30. Direct Photons Temperature • pQCD+QGP+HG+Jet • Extract temperature difficult • Energy Scan important • Detailed model comparison RHIC II Workshop, 11/11/05

  31. e+ g* g g g e- p0 p0 p0 p0 e+ g g* g g e- Residual Correlation from pp HBT Similar effect for virtual photons? Negligible with HBD Background = 4x signal Subtract from known p±p± HBT Sandweiss/Chikanian (Yale) in progress RHIC II Workshop, 11/11/05

  32. Recent Advances at SPS: Power of Precision drop. mass (norm.) drop. mass (norm.) drop. mass (norm.) [RR+Wambach ’99] NA60 • r -meson “melting” , dropping mass? • address: absolute norm., pt-dep., M > 0.9GeV (4p→m+m-!) • “cocktail-r“ (+smooth signal)? vector dominance? • precision data essential to rule out models RHIC II Workshop, 11/11/05

  33. Direct Photons Central Pb(158AGeV)+Pb [Turbide,RR+Gale’04] [Liu+ RR’05] Dileptons Electromagnetic Probes at SPS Medium Effects! 10% QGP HG: 4p→m+m- 30% QGP [RR+ Shuryak ’99] RHIC II Workshop, 11/11/05

  34. What needed at the SPS? Experimentally: • Low-mass e+e-: drop. mass vs. broad., energy scan [run time] • Cronin enhancement vs. temperature [systematic p-A] • Isolation of charm dileptons [vertex detector] • Redundancy Physics: • QGP subdominant ?! • early thermalization (v2) ?! RHIC II (dedicated QCDLab) has it all RHIC II Workshop, 11/11/05

  35. Conclusion • EM probes are directly sensitive to the chiral symmetry properties and to the temperatures of the partonic system • There are three major measurementsrelated to the questions above • Each with complemental/redundant techniques • Challenges:not only confirm a theory, but rule out incorrect ones requires precision data in M, qt , centrality and √s • RHIC (detectors) positioned to meet the challenges:- Dalitz suppression / charm ID; redundancy - energy-scan (006-200GeV!?) • Theory Homework: chiral theory with baryons, sQGP, g/dilepton components, … RHIC II Workshop, 11/11/05

  36. Am I too negative? 哀兵必胜“pessimistic” troops win Continue pushing our detectors to their limits Understand the strength and weakness Am I too positive?I don’t think of all the misery, but of all the beauty that still remains. – Anne Frank Continue exploration of techniques and simulations Understand and reduce the background Remarks CHARM DILEPTON I believe we can fly, RHIC II will provide us with wings RHIC II Workshop, 11/11/05

  37. at Tc: Chiral Restoration • Low-Mass Dilepton Rate: r -meson dominated! ImPem ~ [ImDr+ImDw /10+ImDf /5] • Axialvector Channel:p±g invariant mass-spectra ~ Im Da1(M) ?! 2.2 EM Emission and Chiral Symmetry ~ “r - a1(1260)” (chiral partners) Axial-/Vector in Vacuum pQCD cont. RHIC II Workshop, 11/11/05

  38. Spectral Functions Chiral Condensate cm - [Bielefeld] T=1.4Tc ‹qq› [Tokyo] 1.0 T/Tc QCD Phase Diagram Introduction I:EM-Probes -- The Basic Questions • Thermalization at RHIC study the phase diagram: • (highest) temperature of the matter • chiral symmetry restoration (mass generation!) • medium effects on spectral properties above + below Tc Inevitable consequences of QGP, link to lattice QCD RHIC II Workshop, 11/11/05

  39. Dilepton Radiation ratio to pert. qq rate _ Mee/mq (ii) Heavy Partons + Multiple Bound States → based on finite-T lattice potentials approach to “zero-binding line”  ~ stable-massr-resonance [Shuryak,Zahed, Brown, …] • thermal parton scattering through bound states? • composite interactions? quark scaling? RHIC II Workshop, 11/11/05

  40. Cocktail comparison • Data and cocktail absolutely normalized • Cocktail from hadronic sources • Charm from PYTHIA • Predictions are filtered in PHENIX acceptance • Good agreement in p0 Dalitz • Continuum:hint for enhancement not significant within systematics • What happens to charm? • Single e  pt suppression • angular correlation??? • LARGE SYSTEMATICS! RHIC II Workshop, 11/11/05

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