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Leptonic and Charged Kaon Decay of the f Meson in Heavy-Ion Collisions at CERN-SPS

This study measures the leptonic and charged kaon decay modes of the f meson in heavy-ion collisions, providing insights into the transition from hadronic to quark matter and the restoration of chiral symmetry. The results show the modification of vector meson properties, strangeness enhancement as a signature of quark-gluon plasma formation, and possible in-medium modifications of the rho meson.

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Leptonic and Charged Kaon Decay of the f Meson in Heavy-Ion Collisions at CERN-SPS

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  1. Leptonic and Charged Kaon Decay Modes of the f meson Measured in Heavy-Ion Collisions at CERN-SPS A. Marín (GSI) Ceres Collaboration

  2. Motivation • Transition from hadronic to quark matter • Chiral symmetry will be restored • Modification of vector meson properties (r,w,f) • Strangeness Enhancement: signature of QGP formation

  3. Light Vector Mesons R. Rapp • baryon effects importanteven atrB,tot= 0:sensitivetorBtot • walso melts,fmore robust ↔ OZIRule

  4. The f puzzle: Pb+Au 158AGeV • Difference observed in yields (factor 2-4) and slopes • (D.Röhrich J.Phys.G. 27(2001)355) • NA49: fgK+K- T=(305±15)MeV 2f/(p++p-) 12.2(13)10-3 • NA50: fgm+m- T=(218±6)MeV • Thermal Model : 2f/(p++p-) 19.10-3 (J.Stachel et al., PLB 465(1999)15) • Reason: D. Lissauer, E.V.Shuryak, PLB 253 (1991) 15 • F. Klingl,T.Waas,W.Weise, PLB 431 (1998) 254 • Rescattering of K? • Modification of the mass/width of the f meson? Or the K? Measurement of both decay channels in the same experiment CERES

  5. The CERES Setup 2000 Run: 30x106 events s/s geo=7% 3x106 events s/sgeo=20% Sidc: vertex reconstruction, anglemeasurement Rich: electron ID TPC: momentum and electron-ID (smass~3.8% at f gee)

  6. s=205 mm Run 2000 Pb-Au The Sidc detectors • Two 4" silicon wafers • Charged particle tracking • Vertex reconstruction • Angle measurement

  7. The RICH detectors Rich1 Rich2 • Electron identification • Hough transformation algorithm for ring recognition • Use of Rich1/2 in combined mode (no Bfield)

  8. The CERES TPC • radial-drift TPC: • charged particle tracking • momentum determination • electron ID via dE/dx

  9. Momentum and mass resolution mass resolution ~3.8% at f(includes bremsstrahlung contribution) - sp/p=2% ⊕ 1%.p(GeV)

  10. Centrality and Ncharge of 2000 data D.Miskowiec, nucl-ex/0511010 Measurement done at 7% centrality

  11. Analysis steps: fg e+e- • Charged particle tracking • Electron identification • Rejection of combinatorial background

  12. Electron identification with TPC dE/dx Energy loss dE/dx in TPC e p s(dE/dx)/(dE/dx)<10% for all tracks used

  13. Electron identification: TPC and RICH e.g. at 1.0 GeV/c: 4x104p-rejection factor 68% e-efficiency

  14. Background rejection Dominant sources are p0-Dalitz and g-conversions • Dalitz recognition: • Rejection of tracks which form a pair Qee < 35 mrad • Tracks which form a pair mee < 0.2 GeV/c2excluded • from further pairing • …still a large number of tracks remaining from • unrecognizedp0-Dalitz pairs and g-conversions!

  15. Invariant mass fg e+e- • Invariant mass for opposite sign pairs with pt>0.2 GeV/c • me+e-2 = 2 . pe+ .pe- (1- cos qe+e-) • Background subtraction using mixed events normalized to like sign background

  16. Invariant mass fg e+e- • f : mass 0.9-1.1 GeV/c2 • 229 ± 53 Counts • S/B=1/12 Physics Background: in-medium modified rho dilepton yield from QGP 35% contribution in f peak (R. Rapp) Decay cocktail Decay cocktail+rho+QGP

  17. Transverse Momentum Distribution fg e+e- T = 306 ± 82 (stat) MeV dN/dy=2.19±0.52(stat)±0.34(syst) at 2.1<y<2.65

  18. Invariant mass fg K+K- • All charged particles asigned the Kaon mass (no PID) • Selection of target tracks with matched SDD-TPC tracks • Single track cuts: 0.13<q<0.24 rad, pt>0.250 GeV/c • Opening angle vs pt cut following the f , Armenteros cut 1.5 GeV/c < pt < 1.75 GeV/c 2.2<y<2.4

  19. fg K+K-: Acceptance and efficiency Includes losses due to decay on flight of charged kaons

  20. fg K+K- : Transverse Momentum Distribution T = 273 ± 9(stat) ±10(sys) MeV dN/dy = 2.05 ± 0.14(stat) ±0.25(syst) at 2.0<y<2.4

  21. Comparison between two decay channels Different rapidity dNf/dy 2-2.4=0.93.(dNf/dy)2.1-2.65 (from NA49, PLB 491(2000) 59 ) K+K-: dN/dy=2.05±0.14(stat)±0.25(syst) T = 273± 9(stat)±10(sys) MeV e+e- : dN/dy=2.04±0.49(stat)±0.32(syst) T = 306 ± 82(stat) MeV Results in both channels in close agreement dN/dy (fge+e-)/dN/dy(fgK+ K-)<1.6 at 95% CL Ceres Collaboration: nucl-ex/0512007

  22. Comparison to NA49/NA50 results Different measurement conditions: NA49 CERES Correction centrality: 4% 7% h-4%/h-7% CERES rapidity: 3.4 2.2 dN/dy NA49 Scaling factor: F=1.17 ± 0.12 CERES results in K+K- and e+e- decay channels agree with NA49 results NA49 and NA50:D.Röhrich, J.Phys.G.27(2001)355 CERES: nucl-ex/0512007

  23. Expectations from AMPT model and UrQMD AMPT: medium modifications and rescatering UrQMD: K rescattering > 0.63 at 95% CL S.C. Johnson et al. Eur.Phys.J C18(2001) 645 S.Pal at al., Nucl. Phys.A 707(2002) 525 Differences in yields between the two channels up 40-50% (UrQMD) or up to 70% (AMPT) at low pt cannot be ruled out by CERES

  24. Conclusions • For the first time in heavy-ion collisions the leptonic and charged kaon decay channels of the f meson are measured in the same experiment • The measured rapidity densities and transverse momentum spectra are in agreement in both decay channels • The data rule out a possible enhancement of the f yield in the leptonic over hadronic channel by a factor larger than 1.6 at 95% CL. • CERES results are in agreement with NA49 results • Possible differences of maximum 40-50% as expected by models like UrQMD or up to 70% at lowest pt as expected by AMPT model cannot be ruled out by CERES results.

  25. Ceres Collaboration • D. Adamova, G. Agakichiev, D. Antonczyk, A. Andronic, H. Appelshäuser, V. Belaga, • J. Bielcikova, P. BraunMunzinger, 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. Manafov, A. Marin, J. Milosevic, A. Milov, D. Miskowiec, R. Ortega, • Yu. Panebrattsev, O. Petchenova, V. Petracek, A. Pfeiffer, M. Ploskon, S. Radomski, • J. Rak, I. 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. Yurevich • 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

  26. Extra

  27. Main experimental difficulties in low e+e- Ne+e-/Nch ~10-5: Electromagnetic decays are rare Ring Imaging Cherencov Detectors gamma ~31 Aditional e-PID via TPC-dE/dx vs momentum Ne+e-/Ng~10-5:large gamma background Minimize radiation length in the acceptance Still large combinatorial background g g e+e- p0gg e+e- • Reconstruction of pair with small opening angle • Good efficiency for low momentum tracks

  28. The f meson • mf= 1019.456 MeV • Gf = 4.26 MeV (~45 fm) • BR ( fgK+K-) = 49.1% • BR ( fge+e-) = 2.98 x 10-4 Measurement of both decay channels in the same experiment CERES

  29. Armenteros Cut

  30. Opening Angle vs pt Cut

  31. Background rejection V-track signature in TPC energy loss in SDD

  32. fg e+e-: Acceptance and efficiency

  33. Counts in each pt bin (dilepton channel) • Pt bin Counts Background • 0.0-0.4 GeV/c 51.4+-29 802 • 0.4-1.0 GeV/c 109.9+-41 1568 • 1.0-2.0 GeV/c 67.6+-24 501

  34. f transverse momentum spectrum We select the events on the f peak and use two side mass windows to estimate the pT distribution of the continuum under the peak Then we correct for the acceptance, calculated (by Monte Carlo) as a 2-dim matrix: pT and y

  35. only statistical errors shown fitted curves: C exp(-mT/T) f pT spectrum versus y and centrality • There is no significant variation of the extracted inverse slope parameter, T, with rapidity • There is a clear increase from peripheral to central collisions • With full statistics, extension up to pT > 3 GeV/c should be feasible

  36. T(f): NA60 versus NA50 and NA49 Average T(f) In-In values 1) all pT252 ± 3 MeV 2) pT < 1.5 GeV (NA49 range)256 ± 6 MeV 3) mT > 1.65 GeV (NA50 range)245 ± 5 MeV  Always ~ 250 MeV NA49 Pb-Pb T (MeV) NA50 Pb-Pb NA60 In-In Systematic errors still under investigationExpected to be less than 10 MeV

  37. Extraction of f  KK signal from Monte Carlo • Full simulation of In-In collisions (VENUS) • Tracks in the same event are combined to build the mass spectrum • Tracks from different events are mixed if events belong to the same centrality class and their vertices are closer than 2sx, 2sy, 2sz • Gaussian fit gives the mass and peak width Extracted values agree very well with the inputs of the simulation

  38. fKK mass spectrum in InIn collisions (NA60-QM05) • The real data follows the same analysis procedure • Statistics sufficient to extract the f pT distribution in 4 centrality bins • … but the background is not yet under sufficient control

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