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Dilepton and medium effect on particle properties

Dilepton and medium effect on particle properties. Zhangbu Xu. Outline 共振态在 QGP 态下的性质 双轻子谱 探测方法. Medium Effect in Dense Nuclear Matter. Brown-Rho Scaling  Broadening Low Mass Dilepton measuring  properties. R. Rapp, et al. Last Call for RHIC Predictions

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Dilepton and medium effect on particle properties

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  1. Dilepton and medium effect on particle properties Zhangbu Xu • Outline • 共振态在QGP态下的性质 • 双轻子谱 • 探测方法

  2. Medium Effect in Dense Nuclear Matter • Brown-Rho Scaling •  Broadening • Low Mass Dilepton measuring  properties R. Rapp, et al Last Call for RHIC Predictions Nucl.Phys. A661 (1999) 205-260 • Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)手征对称

  3. With the establishment of the hydrogen bubble-chamber, entirely new possibilities for research into high-energy physics present themselves. Results have already been apparent in the form of newly-discovered elementary particles. The first, very short-lived, so called, "resonance particle" was found in 1960. The Nobel Prize in Physics 1968 First time Invariant Mass was used (bump hunting) A little bit of history  (1952?) (1385) (1960) (892) (1961) (1405)   1411 (1967)

  4. ISR K*0 from p+p Collisions Measurement Technique 强子道的测量 • Mixed-event, Like-sign Background subtraction • P-Wave Breit-Wigner function or Modified BW

  5. K*  K K* K* measured K* lost  K K*   K* K K K K* measured Kinetic freeze-out Chemical freeze-out All that Matters: X-section作用截面 Different by 5 Rescattering>Regeneration at later stage 强子衰变道: 散射(大于)再产生

  6. 重核子碰撞的时空演化 • Stages in the collision 1. Pre-equilibrium Hard parton scattering processes 2. Equilibration After t≤ 1 fm/c partons materialise and either hadronise or rescatter. 3. Thermal quark-gluon plasma Hydrodynamic expansion 4. Hadronization (phase transition) Quark coalescence + gluon fragmentation … or … String fragmentation 5. Hadron gas Hadrons continue to interact 6. Particle freeze-out • Chemical freeze-out 化学冻结 粒子数不再变化 • Thermal freeze-out热冻结不再有强相互作用 p, K, N, … t p, K, N, … tf tf 6. t(eH) Hadron gas t(eQ) 5. t0 = th 6. Mixed phase Hadron gas t0 = tq 4. QGP 5. 3. 4. 2. 1. 1. Hadron formation. Parton formation and thermalisation. z A A a) Without QGP b) With QGP

  7. 共振态有化学冻结吗? STAR PHENIX Strangeness Enhancement Resonance Suppression Au+Au, p+p, Thermal Fit; Feed-down K. Schweda, O. Barannikova

  8. M. Bleicher et al. J. Phys. G 25 (1999) 1859 σ(Kπ) σ(ππ) Resonance driven by Cross Section K. Schweda, P. Fachini, C. Markert, H. Zhang Statistical and systematic errors added in quadrature • Finite Interaction Cross Section Breakdown of Ideal fluid? • Different Cross Section regeneration or rescattering ? • Different Cross Section Flow at hadron stage

  9. 质量 or 重子/介子? • RCP flattens at intermediate pT • Two groups (2<pt<6GeV/c): - ,K0s, K, K*, f mesons - p,L, X, W baryons • Meson/Baryon Effect!Collective velocity is not the only scale • quark coalescence ? 介子共振态的特征: 质量大

  10. Quark Contents Constituent Quark Scaling? n=20.3 K+K*? s+uK*? C. Nonaka, B. Muller et al. , Phys.Rev.C69:031902,2004

  11. + - Invariant Mass Distribution pp AuAu 40% to 80% STAR Preliminary STAR Preliminary sNN = 200 GeV 0.2  pT  0.8 GeV/c |y|  0.5 0 f0K0S  K*0 0 f0 K0S  K*0 0.2  pT  0.9 GeV/c |y|  0.5 Statistical error only Statistical error only • 2.1106 Au+Au minimum biasevents and 4.7106 pp events • Breit-Wigner  fixed width 0  = 150 MeV and f0  = 75 MeV  fixedf0 masse  0.98 GeV (AuAu) and 0.96 GeV (pp) • 0 mass = 0.698 ± 0.013 GeV (AuAu) • 0 mass = 0.729 ± 0.006 GeV (pp) P. Fachini (STAR)

  12. RHIC The Lost Sword (Fable, 《呂氏春秋》~250B.C.) <qq>, TQGP <qq>, TQGP The Sword A+A Collisions Moving Boat Freeze-out Ferry Hadrons Mark Detecting Signals Jumping into water Chiral Symmetry Restoration e+e-, thermal Radiation g+ge+e-

  13. Medium Effect in Dense Nuclear Matter • Brown-Rho Scaling • Rho Broadening • Low Mass Dilepton measuring  properties R. Rapp, et al Last Call for RHIC Predictions Nucl.Phys. A661 (1999) 205-260 • Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)

  14. q l s  q l How to Probe Early Stage? • Modification in medium • Decay quicklymatter exists 10-23s • Small or no FSIleptons, photons Golden:   J/ Small Branching Ratio(10-4), Low Production Rate

  15. NA49 at SPS A central Pb+Pb Collision 1 cm slice centred on beam-axis B = 1.1 T B = 1.5 T NA49 Pb+Pb 158 GeV/A

  16. f-Production: Hadronic versus Leptonic Decay Channel • Different decay channels: • NA49: F K-K+ • NA50: F -+ • Transverse momentum spectrum • fit: 1/mTdn/dmT ~ exp(-mT/T) (NA49: 3.0<y<3.8) significant differences in slopes and yields Dieter Röhrich, QM02

  17. K l+l- K  K+K-  c=50fm AMPT, STAR Nucl-th/0202086  Vector Meson at RHIC 130GeV • AMPT: (l+l-)/(K+K-)=1.5 • Experiments’ comparison

  18. The NA45 experiment 95% of charged hadrons do not produced Cherenkov light Ring Imaging Cherenkov (RICH) Radiator chosen to select electrons Time Projection Chamber Used for charged particle tracking

  19. Dileptons at SPS • Conventional cocktail of particles • Underpredicts dilepton production • Mass shifted??

  20. The NA50/NA60 experiment NA50: di-muon spectrometer Note: absorber to remove all hadrons absorber muon spectrometer ET E0 event selection

  21. 双轻子的质量和动量谱斜率 Phys. Rev. Lett. 96 (2006) 162302 drop -Teff rises in low mass region  radial flow of a hadronic source - drop at M~1 GeV suggests partonic nature of equilibrated particles~thermal radiation? - note: yield goes like (dN ch /dy)2 S. Damjanovic, Quark Matter 2008 21

  22. PHENIX from Above

  23. West Arm tracking: DC,PC1, PC2, PC3 electron ID: RICH, EMCal Photons EMCal East Arm tracking: DC, PC1, TEC, PC3 hadron& electron ID: RICH,TEC, TOF, EMC photons: EMCal PHENIX Setup • Other Detectors • Vertex & centrality: • ZDC, BBC, • MVD • South Arm • tracking: • MuTr • muon ID: • MuID accumulated ~200 106 Au-Au full heavy ion program and first spin physics including electron & muon pairs

  24. Measured p+p Mee • Cocktail filtered in PHENIX acceptance • Charm, Bottom, DY contributions from PYTHIA • Excellent agreement! arXiv:0802.0050

  25. Thermal contribution perhaps if ccbar mass spectrum softened by rescatt. Au+Au Mee compared to Cocktail • Data and Cocktail absolutely normalized • Cocktail normalized to Au+Au measurements • Except ccbar • Low mass excess • 150 < Mee < 750 • X 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) • Intermediate mass agreement arXiv:0706.3034

  26. 0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c 0.7 < pT < 1.5 GeV/c 1.5 < pT < 8 GeV/c • Still significant at high pT PT Dependence of Au+Au Mee PHENIX Preliminary QM08 • Low Mass excess is a low pT enhancement • Huge excess at lowest pT • Late Phase info PHENIX Preliminary

  27. STAR Upgrades MTD MRPC ToF barrel EMC barrel EMC End Cap BBCRPSD FMS F0S PMD • DAQ1000 • TPC FEE • MTD • Soft  finished HFT: Si-pixels; IST: Si-strips; FGT: GEM-layers Integrated Tracking Upgrades ongoing

  28. STAR的目标 Measuring the dilepton → To study: 1. vector meson production and in-medium effect 2. heavy Quarkonian production (suppression) Focus on the dilepton spectra at low mass region Electrons may come from the following sources at low mass region: γ conversion π0, η Dalitz decays ρωΦ vector meson decays

  29. What STAR Can Do? Future upgraded detectors: μVertex detector Full TOF Electrons PID Reject electrons not from primary vertex (gamma conversion) Simulation: γconversion and π0, η Dalitz decay background How can μVertex detector deal with γconversion subtraction?

  30. Electron Identification Before, using TPC dE/dx only to separate electrons from hadrons is complicated TOF detector lights up this study A prototype TOF tray (TOFr) installed this year |1/β-1|<0.03 With TOF PID cut, electron band can be separated from others readily!

  31. Dilepton Assume electrons can be identified with full TOF Total bkgd: ~10-4/25MeV (ω) ~2∙10-5/25MeV (Φ) Dalitz decay bkgd: ~5∙10-6/25MeV (ω) ~5∙10-7/25MeV (Φ)

  32. Background Rejection Electrons from gamma conversion L.J.Ruan Require TPC+SVT+μVertex ~98% electrons from gamma conversion rejected Dalitz decays become dominant sources!!! Great thanks to Kai!

  33. Upgraded TOF for dileptons • Background: g  e+e- • HFT discriminates background • Need low mass detector • Statistics comparable to NA60 • Charm background

  34. Vacuum Engineering Big Bang 强作用下的宇称破缺

  35. D. Kharzeev, QM08

  36. Conclusions • Vector Meson Resonances are sensitive tools to study new state of matter • An important physics program STAR will pursue • TOF+TPC+SVT+ μVertexSTAR RHIC II Upgrade

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