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Highlights from the NA60 Experiment

Highlights from the NA60 Experiment. Alessandro De Falco University and INFN Cagliari on behalf of the NA60 collaboration SQM08, Beijing, China. Outline. The NA60 Experiment Detector Concept Phi Meson Production in In-In Collisions Analysis details

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Highlights from the NA60 Experiment

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  1. Highlights from the NA60 Experiment Alessandro De Falco University and INFN Cagliari on behalf of the NA60 collaboration SQM08, Beijing, China Alessandro De Falco (NA60) SQM08

  2. Outline • The NA60 Experiment • Detector Concept • Phi Meson Production in In-In Collisions • Analysis details • pT, y and decay angular distributions • f yield • Raw spectra from fKK analysis • Eta meson production in In-In collisions • Highlights from IMR • Origin of excess: prompt or charm? • pT spectra of excess • T vs mass Alessandro De Falco (NA60) SQM08

  3. 2.5 T dipole magnet muon trigger and tracking (NA50) beam tracker vertex tracker magnetic field targets hadron absorber <1m >10m Origin of muons can be accurately determined Improved dimuon mass resolution (~20 MeV/c2 at  instead of 80 MeV/c2) Additional bend by the dipole field extends the dimuon coverage down to low pt High luminosity mm experiment: possible with radiation tolerant detectors and high speed DAQ The NA60 detector layout 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 Alessandro De Falco (NA60) SQM08

  4. Data sample • In-In collisions at 158 AGeV Incident beam energy • 5 weeks in Oct.-Nov. 2003 • ~ 4 ∙ 1012 ions delivered • ~ 230 million dimuon triggers • Data analysis • Select events with only one reconstructed vertex in target region (avoid re-interactions) • Match muon tracks from Muon Spectrometer with charged tracks from Vertex Tracker (candidates selected using weighted distance squared  matching c2) • Subtract Background Alessandro De Falco (NA60) SQM08

  5. 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  fpuzzle:in-medium effects on f and kaons +kaon absorption and rescattering leading to reduced yield and hardened pT spectrum in hadronic channel? • 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% Alessandro De Falco (NA60) SQM08

  6. We select the events on the f peak and use two side mass windows to estimate the pT,y and decay angle distribution of the continuum under the peak 5 centrality bins Extraction of differential spectra 4000 A data set only Systematic error: variation of analysis cuts and parameters Acceptance: Overlay Monte Carlo tuned to data with an iterative process Alessandro De Falco (NA60) SQM08

  7. reflected a = 0.1 ± 0.1 ± 0.1 s = 1.13 ± 0.06 ± 0.05 All centralities All centralities Fitted with • = 0, independent of centrality Rapidity and cosq distributions s constant vs centrality Agreement with previous measurements in other colliding systems at the same energy Alessandro De Falco (NA60) SQM08

  8. 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) f transverse mass distributions Alessandro De Falco (NA60) SQM08

  9. T slopes in In-In and Pb-Pb collisions 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? Alessandro De Falco (NA60) SQM08

  10. 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% f cross section and yield Alessandro De Falco (NA60) SQM08

  11. 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 f Yield: Alternative Method f multiplicity extracted from the measured ratio J/y multiplicity is corrected for nuclear and anomalous suppression Alternative method with independent systematics! Total systematic error ~ 13% Alessandro De Falco (NA60) SQM08

  12. Yield integrated in centrality: • Direct method: • J/y Calibration: f Yield: Results 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 Alessandro De Falco (NA60) SQM08

  13. f yields In-In - comparison to other systems CERES Pb-Pb KK CERES Pb-Pb ee f/Npart in central In-In collisions in the muon channel exceeds the corresponding values in Pb-Pb collisions in the KK channel Unambiguous comparison to NA50 in full phase space not feasible due to the observed differences in the T value An extrapolation with the extreme hypoteses T=220 MeV and T=300 MeV leads to values with respect to In-In that are larger than a factor of 2 Alessandro De Falco (NA60) SQM08

  14. fKK in In-In collisions • No PID Huge combinatorial background • Event mixing technique • Residual background present in spectra • Data taken mainly with dimuon trigger: high multiplicity more populated 0.6 < pT < 1.8 GeV/c <Npart> = 39 <Npart> = 75 <Npart> = 132 S/B~1/300 S/B~1/400 S/B~1/100 Alessandro De Falco (NA60) SQM08

  15. fKK: mass spectra vs pT <Npart> = 132 Despite of the residual background a pT distribution can be extracted in most central bins starting from pT>0.9 GeV/c Enough statistics up to ~2.5 GeV/c Still ongoing analysis Alessandro De Falco (NA60) SQM08

  16. Raw pT spectrum in the fKK channel Not corrected for the acceptance <Npart> = 132 Alessandro De Falco (NA60) SQM08

  17. h increases by a factor of 1.34 from most peripheral to most central In-In collisions h production in In-In collisions Strangeness content of h = 40% (for f it is 100%) f enhancement from peripheral to central In-In collisions What about h enhancement? Alessandro De Falco (NA60) SQM08

  18. RCP: h vs f f increases by a factor of 3, while h increases by a factor of 1.34 from most peripheral to most central In-In collisions Alessandro De Falco (NA60) SQM08

  19. To describe the strange particle yield, an additional parameter gS is introduced in the canonical partition function gS suppresses the phase space of particles composed of valence s or s quarks Taking from the SM that f production is primary Statistical model Becattini et al.: For central In-In gS~0.8 gS vs Npart Phys.Rev.C73:044905,2006 Alessandro De Falco (NA60) SQM08

  20. h/Npart calculated from gS Strangeness content of h = 40%. One expects In case of feed-down from other resonances: The largest contribution to secondary h yield owes to p1(1400) and a0 which are NOT gS suppressed Knowing the centrality dependence of gS we can calculate what one should expect for the RCP of h production if there would not be any feed down from higher resonances and compare to the measured values. Alessandro De Falco (NA60) SQM08

  21. RCP data vs expectation for primary production The measured values of the eta RCP (red points) agree within errors with the expectations for the primary production of the h Alessandro De Falco (NA60) SQM08

  22. NA38/NA50 proton-nucleus data centralcollisions M (GeV/c2) IMR: previous measurements • NA38/NA50 was able to describe the IMR dimuon spectra in p-A (Al, Cu, Ag, W) collisions at 450 GeV as the sum of Drell-Yan and Open Charm contributions. • The yield observed by NA50 in heavy-ion collisions (S-U, Pb-Pb) exceeds the sum of DY and Open Charm decays, extrapolated from the p-A data (factor ~2 excess for central Pb-Pb) • What is the origin of this excess? Alessandro De Falco (NA60) SQM08

  23. Offset and mass distributions measurement of muon offsets Dm:distance between interaction vertex and track impact point isolation of excess by subtraction of measured open charm and expected Drell-Yan charm not enhanced; excess prompt; 2.4 × DY excess similar to open charmsteeper than Drell-Yan Alessandro De Falco (NA60) SQM08 23

  24. Excess/DY vs pT The process responsible for the production of excess dimuons is significantly softer than Drell-Yan dimuons Alessandro De Falco (NA60) SQM08

  25. IMR excess pT and mT spectra The pT spectra in 3 different mass windows are clearly different while Drell-Yan pT spectra and mass spectra factorize, the primordial kT=0.8 GeV/c being independent of mass for pT>0.5 GeV/c mT spectra fitted by the function T=199 ± 21 ± 3 MeV T=193 ± 16 ± 2 MeV T=171 ± 21 ± 3 MeV Alessandro De Falco (NA60) SQM08

  26. Centrality integrated mT spectra Phys. Rev. Lett. 100 (2008) 022302 steepening at low mT; not observed for hadrons (like f) monotonic flattening of spectra with mass up to M=1 GeV, followed by a steepening above signs for mass-dependent radial flow? fit mT spectra for pT>0.4 GeVwith Alessandro De Falco (NA60) SQM08

  27. Evolution of inverse slope Teff with mass Phys. Rev. Lett. 100 (2008) 022302 Strong rise of Teff with dimuon mass, followed by a sudden drop for M>1 GeV Rise consistent withradial flow of a hadronic source(here pp→r→mm) , taking the freeze-out ρ as the reference Drop signals sudden transition tolow-flowsource, i.e.source of partonic origin (here qq→mm) Alessandro De Falco (NA60) SQM08

  28. Summary • f puzzle: • Yield in leptonic channel in In-In larger than in hadronic channel in Pb-Pb • Dependence of T slope on pT suggests NA49 vs NA50 T difference larger than expected from radial flow • Physical origin of effect? • New NA60 data on fKK to come soon! • PbPb measurements in a NA60-like experiment? • h production: only primary • Intermediate mass region • Prompt excess • Drell-Yan process does not reproduce mass spectrum • Excess softer than Drell-Yan • T slope dependence on mass suggests a source of partonic origin Alessandro De Falco (NA60) SQM08

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