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di-electrons at SPS

di-electrons at SPS. Harald Appelshäuser Institut für Kernphysik Universität Frankfurt for the CERES Collaboration. di-electrons at SPS. introduction CERES experiment at the SPS electron pair analysis recent results from run2000 158 AGeV/c Pb-Au.

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di-electrons at SPS

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  1. di-electrons at SPS Harald Appelshäuser Institut für Kernphysik Universität Frankfurt for the CERES Collaboration Harald Appelshäuser Hirschegg Workshop 2005

  2. di-electrons at SPS • introduction • CERES experiment at the SPS • electron pair analysis • recent results from run2000 158 AGeV/c Pb-Au Harald Appelshäuser Hirschegg Workshop 2005

  3. dilepton mass spectrum (schematic) • NA50, NA60(m pairs): • HMR and IMR: • J/y suppression • open charm enhancement • thermal radiation • NA60: +low mass • CERES(e pairs): • low mass region, r,w,f: • chiral symmetry restoration • thermal radiation Harald Appelshäuser Hirschegg Workshop 2005

  4. CERES history Eur.Phys.J. C4 (1998) 231, 249 p-induced reactions: • consistent with expectations from • known hadronic sources • the hadronic cocktail: our best knowledge of cross sections, form factors, branching ratios… in the absence of new physics, folded with detector acceptance and resolution Harald Appelshäuser Hirschegg Workshop 2005

  5. CERES history Phys. Rev. Lett. 75 (1995) 1272 HI-induced reactions: pt > 0.2 GeV/c qee > 35 mrad 2.1<h<2.65 <dNch/dh> = 125 • significant enhancement • in the low mass region • E = 5.0 +/- 0.7(stat) +/- 2.0 (syst) • for mee>0.2 GeV/c2 Harald Appelshäuser Hirschegg Workshop 2005

  6. CERES history CERES coll. NPA 661(1999), PLB 422(1998), NPA 715 (2003) Pb-Au at 158 AGeV/c: combined 95/96 data • E = 2.4 +/- 0.2(stat) +/- 0.6(syst) • for mee>0.2 GeV/c2 • w.r.t. HI-cocktail: thermal particle yields (f!) and mass dependence of flow Harald Appelshäuser Hirschegg Workshop 2005

  7. CERES history enhanced vacuum-r due to pp-annihilation modified r-spectral function Brown-Rho scaling Pb-Au at 158 AGeV/c: combined 95/96 data calculations: R. Rapp Harald Appelshäuser Hirschegg Workshop 2005

  8. CERES history enhanced vacuum-r due to pp-annihilation modified r-spectral function Brown-Rho scaling CERES coll. PRL 91 (2003) 042301 Pb-Au at 40 AGeV/c: E = 5.9 +/- 1.5 (stat) +/- 1.2 (syst)+/- 1.8 (decays) for mee> 0.2 GeV/c2 T vs. mB? Harald Appelshäuser Hirschegg Workshop 2005

  9. the upgraded CERES experiment radial TPC RICHes Silicon Drift Detectors acceptance: 8 < q < 15 deg 2.1 < h < 2.65 Harald Appelshäuser Hirschegg Workshop 2005

  10. Silicon Drift Detectors s=205 mm Run 2000 Pb-Au SDD1 and SDD2: • charged particle tracking • vertex reconstruction Harald Appelshäuser Hirschegg Workshop 2005

  11. RICH RICH1 and RICH2: electron ID via ring signature field-free operation allows combined mode Harald Appelshäuser Hirschegg Workshop 2005

  12. Time Projection Chamber • radial TPC: • charged particle tracking • momentum determination • electron ID via dE/dx Harald Appelshäuser Hirschegg Workshop 2005

  13. TPC tracking efficiency pt ~ 0.1 GeV/c • radial TPC: • charged particle tracking • momentum determination • electron ID via dE/dx TPC efficiency (MC) plab (GeV/c) TPC efficiency (MC) q (rad) Harald Appelshäuser Hirschegg Workshop 2005

  14. momentum and mass resolution Ks0 p+p- (with SDD vertex) mK0 = 498.7 +/- 0.1 MeV/c2 s = 11.3 MeV/c2 W. Ludolphs PhD in prep.  mass resolution ~4% for fee Harald Appelshäuser Hirschegg Workshop 2005

  15. electron pair analysis data set from Run 2000: Pb-Au 80 AGeV/c s/sgeo= 30% 0.5M Events Pb-Au 158 AGeV/c s/sgeo= 30% 3 M Events Pb-Au 158 AGeV/c s/sgeo= 8% 30 M Events Harald Appelshäuser Hirschegg Workshop 2005

  16. electron pair analysis • charged particle tracking • electron identification • rejection of combinatorial background Harald Appelshäuser Hirschegg Workshop 2005

  17. charged particle tracking angular matching of TPC and SDD tracks: sf(mrad) sq(mrad) pt(GeV/c) pt(GeV/c) vertex condition suppresses late conversions Harald Appelshäuser Hirschegg Workshop 2005

  18. electron identification ring signature in RICH: energy loss dE/dx in TPC: s(dE/dx) / (dE/dx) = 10% e p Harald Appelshäuser Hirschegg Workshop 2005

  19. electron identification RICH TPC e.g. at 1.5 GeV/c:0.03 (TPC) x 0.003 (RICH) =10-4 p-efficiency at 0.9 (TPC) x 0.65 (RICH) =60% e-efficiency Harald Appelshäuser Hirschegg Workshop 2005

  20. background rejection Dalitz recognition: • rejection of tracks which form a pair Qee < 35 mrad • tracks which form a pair mee < 0.2 GeV/c2 excluded • from further pairing dominant sources are p0-Dalitz and g-conversions …still a large number of tracks remaining from unrecognizedp0-Dalitz pairs and g-conversions! Harald Appelshäuser Hirschegg Workshop 2005

  21. background rejection RICH TPC SDD on the remaining tracks: kinematical and topological cuts • conversion and Dalitz tracks are soft • the lost partner must be close-by Harald Appelshäuser Hirschegg Workshop 2005

  22. background rejection traditional: pt>0.2 GeV/c  mt,ee > 0.4 GeV kinematical cut: • single-lepton pt-cut •  acceptance loss at low mass and pair pt better: pt>0.1 GeV/c  mt,ee > 0.2 GeV Harald Appelshäuser Hirschegg Workshop 2005

  23. background rejection energy loss in SDD: V-track signature in TPC: topological cuts: • search for remnants of the lost partner Harald Appelshäuser Hirschegg Workshop 2005

  24. invariant mass distributions pt > 0.2 GeV/c pt > 0.1 GeV/c counts/100 MeV/c2 counts/100 MeV/c2 pt>0.2 GeV/c: mee<0.2 GeV/c2: S = 2844+/- 113,B/S = 1.8 mee>0.2 GeV/c2: S = 2174+/-182,B/S = 13 pt>0.1 GeV/c: mee<0.2 GeV/c2: S = 18030+/-347,B/S = 2.8 mee>0.2 GeV/c2: S = 5511+/-351,B/S = 20 ~1.8x107 Pb-Au events at 158 AGeV/c: signal mixed-event bg Harald Appelshäuser Hirschegg Workshop 2005

  25. electron pair analysis Signal S: • combination of unlike-sign pairs from the same event Background B: • like-sign combinations from the same event • (+) same-event correlations (partially) contained • (-) if not S>>B, finite statistics contributes • unlike-sign (or like-sign) combinations from mixed events • (+) no statistical limitation • (-) normalization, no correlations Harald Appelshäuser Hirschegg Workshop 2005

  26. electron pair analysis combinatorial background pt>0.1 GeV/c pt>0.2 GeV/c • for BG subtraction: • same-event BG for mee< 0.2 GeV/c • normalized mixed-event BG for mee> 0.2 GeV/c Harald Appelshäuser Hirschegg Workshop 2005

  27. mass spectrum Run 2000 Pb-Au 158 AGeV/c: • normalization to cocktail at p0-Dalitz Enhancement for mee>0.2 GeV/c2: E =3.3 +/- 0.3 (stat) …no systematic errors yet! A.Marin (QM04) J.Phys.G30 (2004) Harald Appelshäuser Hirschegg Workshop 2005

  28. mass spectrum modified r-spectral function (Rapp, Wambach) Brown-Rho scaling discrimination soon possible Run 2000 Pb-Au 158 AGeV/c: thermal radiation (Kämpfer et al.) A.Marin (QM04) J.Phys.G30 (2004) Harald Appelshäuser Hirschegg Workshop 2005

  29. centrality dependence mee<0.2 GeV/c2 0.2<mee<0.6 GeV/c2 mee>0.6 GeV/c2 <dNch/dh> • pair yield increases stronger than linear with <dNch/dh> Harald Appelshäuser Hirschegg Workshop 2005

  30. multiplicity dependence NA60 In-In NA60 In-In mee<0.2 GeV/c2 0.2<mee<0.6 GeV/c2 mee>0.6 GeV/c2 <dNch/dh> • pair yield increases stronger than linear with <dNch/dh> • most central point confirmed by 2000 data Harald Appelshäuser Hirschegg Workshop 2005

  31. pt>0.1 GeV/c mass spectrum Run 2000 Pb-Au 158 AGeV/c: • both spectra normalized to p0-Dalitz • spectra agree for mee>0.7 GeV/c2 • pt > 0.1 GeV/c adds sensitivity to low • masses and pair pt (mt>0.2 GeV) Harald Appelshäuser Hirschegg Workshop 2005

  32. pt>0.1 GeV/c mass spectrum Run 2000 Pb-Au 158 AGeV/c: with pt>0.1 GeV/c selection: • enhancement extends to p0-peak • E = 5.6 +/- 0.4 (stat) • for m>0.2 GeV/c2 S. Yurevitch, PhD in prep. Harald Appelshäuser Hirschegg Workshop 2005

  33. pt>0.1 GeV/c mass spectrum low-mass enhancement over models? Run 2000 Pb-Au 158 AGeV/c: modified r-spectral function Brown-Rho scaling S. Yurevitch, PhD in prep. Harald Appelshäuser Hirschegg Workshop 2005

  34. mass spectrum and models low pt enhancement over models? WA98 direct photonsPRL85 (2000) calculations: Turbide, Rapp, Gale PRC (2004) Run 2000 Pb-Au 158 AGeV/c: modified r-spectral function Brown-Rho scaling S. Yurevitch, PhD in prep. Harald Appelshäuser Hirschegg Workshop 2005

  35. transverse momentum spectra modified r B-R scaling cocktail mee < 0.2 GeV/c2 : pt > 0.2 GeV/c pt > 0.1 GeV/c Harald Appelshäuser Hirschegg Workshop 2005

  36. transverse momentum spectra modified r B-R scaling cocktail 0.2 < mee < 0.7 GeV/c2 : pt > 0.1 GeV/c pt > 0.2 GeV/c • enhancement located at low pt • larger enhancement due to increased low pt acceptance Harald Appelshäuser Hirschegg Workshop 2005

  37. transverse momentum spectra modified r B-R scaling cocktail mee > 0.7 GeV/c2 : pt > 0.1 GeV/c pt > 0.2 GeV/c • moderate enhancement at high masses Harald Appelshäuser Hirschegg Workshop 2005

  38. thermal source parametrization Thomas, Gallmeister, Zschocke, Kämpfer • inclusion of colder source describes • pt > 0.1 GeV/c data • same source is consistent with low pt photons • pt > 0.1 and pt > 0.2 GeV/c data are • not described simultaneously Harald Appelshäuser Hirschegg Workshop 2005

  39. soft dileptons from DCC Koch, Randrup, Wang, Kluger, APCTP Seoul, Korea, 1997 nucl-th/9712061 • rapid cooling of chirally restored • state leads to a misaligned vacuum • (Disoriented Chiral Condensate) • system will decay into normal • vacuum by emission of soft pions annihilation of soft pions may be significant source of low pt,ee dileptons pairs with mee ~ 2mp Harald Appelshäuser Hirschegg Workshop 2005

  40. soft dileptons from DCC Koch, Randrup, Wang, Kluger, APCTP Seoul, Korea, 1997 nucl-th/9712061 • DCC source is softer than thermal source • only visible at small mee and pair pt Harald Appelshäuser Hirschegg Workshop 2005

  41. low mass enhancement at SPS NA60 5.6 • low mass dilepton enhancement • most pronounced at mid-rapidity • and small mt • complementary information from • ee and mm experiments Axel Drees, Hard Probes 2004 Harald Appelshäuser Hirschegg Workshop 2005

  42. summary and outlook • preliminary results of e+e- production in 158 AGeV/c Pb-Au • from run2000 have been presented • low mass enhancement with pt>0.2 GeV/c consistent with • highest centrality in 95/96 • larger enhancement observed with pt>0.1 GeV/c selection • new data production just finished – larger significance • expected (r/w, f) • evaluation of efficiency and systematic errors Harald Appelshäuser Hirschegg Workshop 2005

  43. CERES Collaboration D. Adamova, G. Agakichiev, D. Antonczyk, A. Andronic, H. Appelshäuser, V. Belaga, J. Bielcikova, P. Braun-Munzinger, O. Busch, A. Castillo, A. Cherlin, S. Damjanovic, T. Dietel, L. Dietrich, A. Drees, S. Esumi, K. Filimonov, K. Fomenko, Z. Fraenkel, C. Garabatos, P. Glässel, G. Hering, J. Holeczek, V. Kushpil, B. Lenkeit, W. Ludolphs, A. Maas, A. Marin, J. Milosevic, A. Milov, D. Miskowiec, R. Ortega, Yu. Panebrattsev, O. Petchenova, V. Petracek, A. Pfeiffer, S. Radomski, J. Rak, Ravinovich, P. Rehak, W. Schmitz, J. Schukraft, H. Sako, S. Shimansky, S. Sedykh, J. Stachel, M. Sumbera, H. Tilsner, I. Tserruya, G. Tsiledakis, T. Wienold, B. Windelband, J.P. Wessels, J.P. Wurm, W. Xie, S. Yurevich, V. Yurevitch NPI ASCR, Rez, Czech Republic GSI Darmstadt, Germany Frankfurt University, Germany Heidelberg University, Germany JINR Dubna, Russia Weizmann Institute, Rehovot, Israel SUNY at Stony Brook, USA CERN, Switzerland BNL, Upton, USA Münster University, Germany MPI Heidelberg, Germany Harald Appelshäuser Hirschegg Workshop 2005

  44. Mass spectrum Comparison to 96 data: s/stot = 8% s/stot = 30% E(96) = 3.7 +/- 1.0 (stat) +/- 1.5 (syst) E(00) = 5.6 +/- 0.4 (stat) +/- ? 96 data: G. Hering, PhD thesis, nucl-ex/0203004 Harald Appelshäuser Hirschegg Workshop 2005

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