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f Meson Production in In-In Collisions and the f Puzzle

f Meson Production in In-In Collisions and the f Puzzle

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f Meson Production in In-In Collisions and the f Puzzle

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  1. f Meson Production in In-In Collisions and the f Puzzle Michele Floris1 for the NA60 Collaboration Quark Matter 2008, Jaipur, India February 5th, 2008 1University and INFN, Cagliari, Italy

  2. Outline • The f puzzle in heavy ion collisions • The NA60 experiment • f yield: InIn vs PbPb • w yield in InIn • f mT spectra: InIn vs PbPb • f KK: a first look • Summary Quark Matter 2008 - Jaipur

  3. The f puzzle Historic facts on NA49 fKK vs NA50 fmm Yields in hadronic channel lower than in leptonic channel by factor >2 in central collisions Inverse slopes in central collisions Hadronic (low pT) ~ 300 MeV Leptonic (high pT) ~ 230 MeV More recently: • CERES hadronic yield and inverse slope similar to NA49. Within large errors leptonic yield also compatible with NA49  No f puzzle? • New NA50 analysis confirms previous results within 8% (See D. Jouan, SessionXXIII)  fpuzzle:in-medium effects on f and kaons +kaon absorption and rescattering leading to reduced yield and hardened pT spectrum in hadronic channel? Quark Matter 2008 - Jaipur

  4. The NA60 Experiment 2.5 T dipole magnet muon trigger and tracking (NA50) beam tracker vertex tracker magnetic field targets Zero degree calorimeter (centrality measurements) 17m Muon Spectrometer hadron absorber <1m >10m The vertex region (2 detectors): • Fixed target dimuon experiment at the CERN SPS • Apparatus composed of 4 main detectors Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorber and match them (in both angles and momentum) to the tracks measured in the spectrometer Origin of muonscan be accurately determined Improved dimuon mass resolution (~20 MeV/c2 at  instead of 80 MeV/c2) High luminositymm experiment: possible with radiation tolerant detectors and high speed DAQ Quark Matter 2008 - Jaipur

  5. Data Sample InIn collisions at 158 AGeV 5 weeks in Oct.-Nov. 2003 ~ 4 ∙ 1012 ions delivered ~ 230 million dimuon triggers Data analysis Events with only one reconstructed vertex in target region (avoid re-interactions) Match muon tracks from Muon Spectrometer with charged tracks from Vertex Subtract combinatorial Background and Fake Matches • f events: • Subtract continuum below the f by means of side windows • Effective statistics: 12000 f mesons • Statistics up to pT = 3 GeV • Present results: up to pT = 2.6 GeV, 4000 A setup only Quark Matter 2008 - Jaipur

  6. Centrality Selection and Acceptance Correction 5 Centrality Bins Selected using charged tracks density Acceptance Correction Overlay Monte Carlo f kinematics tuned with an iterative procedure in the 5 centrality bins  1D Acceptance correction for differential spectra (within ~5%) f mmAcc x Rec. Eff. Acc. x Rec. Eff. Acceptance down to 0 pT Quark Matter 2008 - Jaipur

  7. Rapidity and cos qCS distributions s = 1.13 ± 0.06 ± 0.05 a = -0.2 ± 0.2 ± 0.2 reflected All centralities All centralities pT, rapidity and decay angular distributions (in the Collins-Soper, Gottfried-Jackson and Helicity frames) measured in the 5 centrality bins  full characterization of the f kinematics See also NA60@SQM07 Quark Matter 2008 - Jaipur

  8. f Cross Section and Yield Beam Counters Monte Carlo Beam Counters (DAQ-vetoed) • Effective Target Length • Beam Absorption • Transverse Size Dedicated Runs f multiplicity Eur. Phys. J. C13 69 (2000) Total Systematic Uncertainties ~ 10% Quark Matter 2008 - Jaipur

  9. f Yield: Alternative Method • Measured in same exp • Once corrected for nuclear/anomalous abs • scales with Ncoll J/y J/y cross section x BRmm in a nucleon-nucleon collision Total number of binary collisions in a given centrality bin Inelastic nucleon-nucleon cross section Average J/y multiplicity in a nucleon-nucleon collision f yield defined as: Effective number of interactions estimated from observed counts of reference process Alternative method with independent systematics! Total systematic error ~ 13% Quark Matter 2008 - Jaipur

  10. f Yield: Results • Yield integrated in centrality: • Direct method: • J/y Calibration: Results in full phase space and corrected for BRmm = 2.86 · 10-4 Centrality Dependence (average of the 2 methods) f scales faster than Npart Box: stat+syst. error Box: stat+syst. error Quark Matter 2008 - Jaipur

  11. f yields In-In - comparison to Pb-Pb NA60 vs NA49 (full phase space): Also fmm in In-In higher than NA49 yield (like NA50) NA60 vs NA50 (NA50 kinematic range): fmm: Npart scaling almost within errors - system size dependence - saturation in central collisions Ceres PbPb f KK 3 < ylab < 4 |cosqCS| < 0.5 mT > 1.5 GeV NA60 In-In NA50 Pb-Pb NA49 Pb-Pb NA60 In-In NA49 p-p Box: stat+syst. error Box: stat+syst. error Difference in fmm and fKK yields seems confirmed - related to a real physics mechanism (kaon absorption)? Quark Matter 2008 - Jaipur

  12. Further crosscheck: w Yield w yield: determined as the f yield The w yield scales with Npart Box: stat+syst. error Box: stat+syst. error Previously all NA60 results M < 1 GeV normalized to w  Now absolute calibration Quark Matter 2008 - Jaipur

  13. w yield: comparison to existing measurements NA60 Preliminary Particle ratios in 4p r/w = 1 sw,r/sp Convert w/Npart w/p = 0.069 ± 0.004 ± 0.007 NA60 w: follows the general trend f/w ratio insensitive to systematic uncertainties Factor 2 reduction in <f> Same change in <w> Completely out of systematics Absolute normalization robust Quark Matter 2008 - Jaipur

  14. f mT Distributions Box: stat+syst. error Spectra fitted with the function: • Depends on the fit range in presence of radial flow • Effective temperature (larger T at low pT) Quark Matter 2008 - Jaipur

  15. T slopes: InIn vs PbPb NA60 fits at high pT(NA50 range) NA60 fits at low pT (NA49 range) NA60 In-In (pT < 1.6 GeV)‏ NA49 Pb-Pb (pT < 1.6 GeV)‏ NA50 Pb-Pb (pT > 1.1 GeV)‏ NA60 In-In (pT > 1.1 GeV)‏ NA49 Pb-Pb (pT < 1.6 GeV)‏ NA50 Pb-Pb (pT > 1.1 GeV)‏ Ceres Pb-Pb (KK, pT > 0.75 GeV) Ceres Pb-Pb (ee, pT < 1.5 GeV) Box: stat+syst. error Box: stat+syst. error NA60low vs high pT: maximal difference in T slopes only ~ 15 MeV presumably related to radial flow well below difference between NA50 and NA49 (~ 70 MeV) in the most central bin  significant extra hardening of hadronic channel beyond radial flow? Quark Matter 2008 - Jaipur

  16. f KK: Promising Signal No PID Huge CB (S/B ~ 1/400 at the f peak)‏ Event Mixing technique Effective statistics: ~500 events Analysis on-going  First results to come soon! Real Mixed Very Promising! Quark Matter 2008 - Jaipur

  17. Summary Measurement of fµµ in InIn confirms f puzzle: • Yield in leptonic channel larger than in hadronic channel • Dependence of T slope on pT suggests NA49 vs NA50 T difference larger than expected from radial flow • Qualitatively consistent with expectations from kaon rescattering/absorption and/or in-medium effects on f and kaons Quantitative size of effect? • New NA60 data on fKK to come soon! • PbPb measurements in a NA60-like experiment? Quark Matter 2008 - Jaipur