ee production from pBe to PbAu Harald Appelshuser

e+e- production from p-Be to Pb-Au Harald Appelshäuser Institut für Kernphysik Universität Frankfurt for the CERES Collaboration Harald Appelshäuser Hard Probes Lisbon 2004

e+e- production from p-Be to Pb-Au • Introduction • The CERES experiment at the SPS • Electron pair analysis • Recent results from run 2000 158 AGe. V/c Pb-Au Harald Appelshäuser Hard Probes Lisbon 2004

Electromagnetic Radiation 1) formation phase DY, qg… 2) hot and dense medium thermal radiation, medium modifications (r)… 3) hadron decays p 0, h, w, f. . Penetrating probes …but a 2 ~ 10 -5 1) and 3) also in pp, new physics in 2) Harald Appelshäuser Hard Probes Lisbon 2004

Dilepton mass spectrum (schematic) NA 50, NA 60 (m pairs): HMR and IMR: • J/y suppression • open charm enhancement… • NA 60: + low mass CERES (e pairs): Low mass region, r, w, f: • chiral symmetry restoration • thermal radiation… Harald Appelshäuser Hard Probes Lisbon 2004

CERES history Eur. Phys. J. C 4 (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 Hard Probes Lisbon 2004

CERES history Phys. Rev. Lett. 75 (1995) 1272 HI-induced reactions: pt > 0. 2 Ge. V/c qee > 35 mrad 2. 1<h<2. 65 <d. Nch/dh> = 125 • significant enhancement in the low mass region • E = 5. 0 +/- 0. 7(stat) +/- 2. 0 (syst) for mee>0. 2 Ge. V/c 2 Harald Appelshäuser Hard Probes Lisbon 2004

CERES history CERES coll. NPA 661(1999), PLB 422(1998), NPA 715 (2003) Pb-Au at 158 AGe. V/c: combined 95/96 data • E = 2. 4 +/- 0. 2(stat) +/- 0. 6(syst) for mee>0. 2 Ge. V/c 2 w. r. t. HI-cocktail thermal particle yields (f!) and mass dependence of flow Harald Appelshäuser Hard Probes Lisbon 2004

CERES history Pb-Au at 158 AGe. V/c: combined 95/96 data enhanced vacuum-r due to pp-annihilation modified r-spectral function Brown-Rho scaling calculations: R. Rapp Harald Appelshäuser Hard Probes Lisbon 2004

CERES history CERES coll. PRL 91 (2003) 042301 with TPC (Run 1999): Pb-Au at 40 AGe. V/c E = 5. 9 +/- 1. 5 (stat) +/- 1. 2 (syst)+/- 1. 8 (decays) for mee> 0. 2 Ge. V/c 2 enhanced vacuum-r due to pp-annihilation modified r-spectral function Brown-Rho scaling T vs. m. B effects? Harald Appelshäuser Hard Probes Lisbon 2004

The upgraded CERES experiment Radial TPC RICHes Silicon Drift Detectors acceptance: 8 < q < 15 deg 2. 1 < h < 2. 65 Harald Appelshäuser Hard Probes Lisbon 2004

Silicon Drift Detectors SDD 1 and SDD 2: • charged particle tracking • vertex reconstruction Run 2000 Pb-Au Harald Appelshäuser Hard Probes Lisbon 2004 s=205 mm

RICH 1 and RICH 2: electron ID via ring signature field-free operation allows combined mode Harald Appelshäuser Hard Probes Lisbon 2004

Time Projection Chamber radial TPC: • charged particle tracking • momentum determination • electron ID via d. E/dx Harald Appelshäuser Hard Probes Lisbon 2004

TPC tracking efficiency TPC efficiency (MC) pt ~ 0. 1 Ge. V/c radial TPC: • charged particle tracking • momentum determination TPC efficiency (MC) plab (Ge. V/c) • electron ID via d. E/dx q (rad) Harald Appelshäuser Hard Probes Lisbon 2004

Momentum and mass resolution Ks 0 p+ p- m. K 0 = 497. 2 +/- 0. 6 Me. V/c 2 s = 14. 6 Me. V/c 2 mass resolution ~4% at f Harald Appelshäuser Hard Probes Lisbon 2004

Electron pair analysis Data set from Run 2000: Pb-Au 80 AGe. V/c s/sgeo= 30% 0. 5 M Events Pb-Au 158 AGe. V/c s/sgeo= 30% 3. 0 M Events Pb-Au 158 AGe. V/c s/sgeo= 8% 30. 0 M Events Harald Appelshäuser Hard Probes Lisbon 2004

Electron pair analysis 1. charged particle tracking 2. electron identification 3. rejection of combinatorial background Harald Appelshäuser Hard Probes Lisbon 2004

Charged particle tracking sq(mrad) sf(mrad) Angular matching of TPC and SDD tracks pt(Ge. V/c) vertex condition suppresses late conversions Harald Appelshäuser Hard Probes Lisbon 2004 pt(Ge. V/c)

Charged particle tracking Angular matching of TPC and SDD tracks Study of hadronic observables: f KK, L pp, D Kp, r pp HBT event-by-event fluctuations azimuthal anisotropies … K 0 I T T N NO Harald Appelshäuser Hard Probes Lisbon 2004 S I H ! ! ! K ppp K+, - L A T

Electron identification Ring signature in RICH: Energy loss d. E/dx in TPC: s(d. E/dx) / (d. E/dx) = 10% e p Harald Appelshäuser Hard Probes Lisbon 2004

Electron identification RICH TPC e. g. at 1. 5 Ge. V/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 Hard Probes Lisbon 2004

Background rejection Dominant sources are p 0 -Dalitz and g-conversions 1. Dalitz recognition: • Rejection of tracks which form a pair Qee < 35 mrad • Tracks which form a pair mee < 0. 2 Ge. V/c 2 excluded from further pairing …still a large number of tracks remaining from unrecognized p 0 -Dalitz pairs and g-conversions! Harald Appelshäuser Hard Probes Lisbon 2004

Background rejection 2. on the remaining tracks: kinematical and topological cuts TPC SDD • conversion and Dalitz tracks are soft • the lost partner must be close-by Harald Appelshäuser Hard Probes Lisbon 2004

Background rejection 2. on the remaining tracks: kinematical and topological cuts • pt-cut: limits acceptance at low mass and pair pt traditional: pt>0. 2 Ge. V/c mt, ee > 0. 4 Ge. V better: pt>0. 1 Ge. V/c mt, ee > 0. 2 Ge. V Harald Appelshäuser Hard Probes Lisbon 2004

Background rejection 2. on the remaining tracks: kinematical and topological cuts • energy loss in SDD: Harald Appelshäuser Hard Probes Lisbon 2004 • V-track signature in TPC:

Invariant mass distributions pt > 0. 2 Ge. V/c pt>0. 2 Ge. V/c mee<0. 2 Ge. V/c 2: S = 2844+/- 113, B/S = 1. 8 mee>0. 2 Ge. V/c 2: S = 2174+/-182, B/S = 13 Harald Appelshäuser Hard Probes Lisbon 2004 counts/100 Me. V/c 2 ~1. 8 x 107 Pb-Au events at 158 AGe. V/c: pt > 0. 1 Ge. V/c signal mixed-event bg pt>0. 1 Ge. V/c mee<0. 2 Ge. V/c 2: S = 18030+/-347, B/S = 2. 8 mee>0. 2 Ge. V/c 2: S = 5511+/-351, B/S = 20

Invariant mass distributions pt > 0. 2 Ge. V/c pt>0. 2 Ge. V/c mee<0. 2 Ge. V/c 2: S = 2844+/- 113, B/S = 1. 8 mee>0. 2 Ge. V/c 2: S = 2174+/-182, B/S = 13 Harald Appelshäuser Hard Probes Lisbon 2004 counts/100 Me. V/c 2 ~1. 8 x 107 Pb-Au events at 158 AGe. V/c: pt > 0. 1 Ge. V/c signal mixed-event bg pt>0. 1 Ge. V/c mee<0. 2 Ge. V/c 2: S = 18030+/-347, B/S = 2. 8 mee>0. 2 Ge. V/c 2: S = 5511+/-351, B/S = 20

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 correlation Harald Appelshäuser Hard Probes Lisbon 2004

Electron pair analysis combinatorial background pt>0. 2 Ge. V/c for subtraction: same-event BG for mee< 0. 2 Ge. V/c normalized mixed-event BG for mee> 0. 2 Ge. V/c Harald Appelshäuser Hard Probes Lisbon 2004 pt>0. 1 Ge. V/c

Mass spectrum Run 2000 Pb-Au 158 AGe. V/c: • mixed-event background • normalization to cocktail at p 0 -Dalitz Enhancement for mee>0. 2 Ge. V/c 2: E = 3. 3 +/- 0. 3 (stat) …no systematic errors yet! A. Marin (QM 04) J. Phys. G 30 (2004) Harald Appelshäuser Hard Probes Lisbon 2004

Mass spectrum Run 2000 Pb-Au 158 AGe. V/c: modified r-spectral function (Rapp, Wambach) Brown-Rho scaling thermal radiation (Kämpfer et al. ) discrimination soon possible A. Marin (QM 04) J. Phys. G 30 (2004) Harald Appelshäuser Hard Probes Lisbon 2004

Transverse momentum spectra mee<0. 2 Ge. V/c 2 0. 2<mee<0. 7 Ge. V/c 2 mee>0. 7 Ge. V/c 2 pt, ee (Ge. V/c) modified r-spectral function S. Yurevitch, Ph. D in preparation Brown-Rho scaling • enhancement located at low pt (known from 95/96) Harald Appelshäuser Hard Probes Lisbon 2004

Centrality dependence mee<0. 2 Ge. V/c 2 0. 2<mee<0. 6 Ge. V/c 2 mee>0. 6 Ge. V/c 2 <d. Nch/dh> • pair yield increases stronger than linear with <Npart> Harald Appelshäuser Hard Probes Lisbon 2004

Centrality dependence mee<0. 2 Ge. V/c 2 0. 2<mee<0. 6 Ge. V/c 2 mee>0. 6 Ge. V/c 2 NA 60 In-In <d. Nch/dh> • pair yield increases stronger than linear with <Npart> • most central point confirmed by 2000 data Harald Appelshäuser Hard Probes Lisbon 2004

pt>0. 1 Ge. V/c mass spectrum Run 2000 Pb-Au 158 AGe. V/c: • both spectra normalized to p 0 -Dalitz • spectra agree for mee>0. 7 Ge. V/c 2 • pt > 0. 1 Ge. V/c adds sensitivity to low masses and pair pt (mt>0. 2 Ge. V) Harald Appelshäuser Hard Probes Lisbon 2004

Mass spectrum and hadronic cocktail Run 2000 Pb-Au 158 AGe. V/c: with pt>0. 1 Ge. V/c selection: • Enhancement extends to p 0 -peak • E = 5. 6 +/- 0. 4 (stat) for m>0. 2 Ge. V/c 2 S. Yurevitch, Ph. D in prep. Harald Appelshäuser Hard Probes Lisbon 2004

Mass spectrum and models Run 2000 Pb-Au 158 AGe. V/c: modified r-spectral function Brown-Rho scaling Low-mass enhancement over models? S. Yurevitch, Ph. D in prep. Harald Appelshäuser Hard Probes Lisbon 2004

Transverse momentum spectra mee<0. 2 Ge. V/c 2 0. 2<mee<0. 7 Ge. V/c 2 mee>0. 7 Ge. V/c 2 modified r-spectral function Brown-Rho scaling S. Yurevitch, Ph. D in preparation • Enhancement located at low pt • Larger enhancement due to improved low pt acceptance Harald Appelshäuser Hard Probes Lisbon 2004

Summary and outlook • preliminary results of e+e- production in 158 AGe. V/c Pb-Au from run 2000 have been presented • low mass enhancement with pt>0. 2 Ge. V/c consistent with highest centrality in 95/96 • larger enhancement observed with pt>0. 1 Ge. V/c selection • new data production just finished – larger significance expected (r/w, f) • evaluation of efficiency and systematic errors Harald Appelshäuser Hard Probes Lisbon 2004

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. Radomiski, 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 Hard Probes Lisbon 2004

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, Ph. D thesis, nucl-ex/0203004 Harald Appelshäuser Hard Probes Lisbon 2004

Estimate of combinatorial background pt > 0. 2 Ge. V/c Harald Appelshäuser Hard Probes Lisbon 2004 pt > 0. 1 Ge. V/c