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f production in p-A and In-In collisions

f production in p-A and In-In collisions. Alessandro De Falco – University and INFN Cagliari, Italy F or the NA60 collaboration. Motivation Apparatus Collected data Results for f  mm Ongoing work for f  KK. Quark Matter 2005 – August 4-9 – Budapest. Motivation.

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f production in p-A and In-In collisions

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  1. f production in p-A and In-In collisions Alessandro De Falco – University and INFN Cagliari, Italy For the NA60 collaboration • Motivation • Apparatus • Collected data • Results for f  mm • Ongoing work for f  KK Quark Matter 2005 – August 4-9 – Budapest

  2. Motivation • The study of f meson production in heavy ion collisions carries information about strangeness enhancement • Previous measurements offproduction at the SPS: • NA49 studied the f  KK channel • Good mass resolution • Broad pT coverage, dominated by low pT • NA50 studied the f  mm channel • Muons insensitive to medium • Acceptance limited to high pT • NA49 and NA50 observed different T slope values,as a function of Npart  f puzzle • NA60 is well placed to help solving the f puzzle: • it can cleanly measure the mm channel down to zero pT • and has access to f  KK

  3. ~ 1m Muon Spectrometer Iron wall MWPC’s Hadron absorber Toroidal Magnet m Target area beam m Trigger Hodoscopes Dipole field2.5 T • Matching in coordinate • and momentum space • Improved dimuon mass resolution TARGET BOX  MUON FILTER BEAM BEAMTRACKER VERTEX TELESCOPE IC not to scale ZDC dimuon studies vs.collision centrality  ZDC Layout of the NA60 apparatus

  4. Transverse vertexingwith 20 µm accuracy 7 In targets target boxwindows Beam tracker station z-vertex (cm) A(%) • pT coverage: the dipole field in the target region leads to much better acceptances at low mass and low pT than previous dimuon measurements Indium beam 158 A GeV Detector performance • Vertexing: clear separation of the individual targets • Z vertex resolution: ~ 600–900 mm in p-A; < 200 mm in Indium-Indium p beam 400 GeV In Pb 3 x Be Be

  5. p-A data: event selection • Data collected in 4 days during 2002 run • statistics in 2004 is around 100 times higher • Muons in the spectrometer are matched to the tracks in the vertex telescope • The combinatorial background due to uncorrelated p and K decaysis estimated through an event mixing technique(matching improves S / B by up to a factor ~ 4) • ~ 15000 OS dimuons in final sample w matching f

  6. w f r BG+charm Mass spectra in p-Be, p-In, p-Pb • Mass spectra described as a superposition of light meson decays + charm + Drell-Yan • A fit to the mass spectra allows us to extract the f/w ratio

  7. opposite-sign pairscombinatorial backgroundsignal + fakes opposite-sign pairscombinatorial backgroundsignal pairs (inc. fakes) In-In data selection • Data sample: 570 000 events after background subtraction (around 50% of the total statistics) • Overall Signal to Background ratio = 1 / 4 • Fake matches (tracks in the muon spectrometer incorrectly matched to the tracks in the vertex telescope) estimated superimposing simulated dimuons on real datatracks • fmass resolution: 23 MeV (not depending on centrality) signal + fakesfakessignal

  8. peripheralall pT Signal Cocktail Extraction of f/w cross section ratio vs. Npart • Mass spectra are obtained in four centrality bins, using the charged track multiplicity • Corresponding Npart values areevaluated from the EZDC spectrum • Detector acceptances and efficiencies are accounted throughMC simulations • GENESIS code describes the light meson decays • Empirical continuum source added • Mass spectra are fit with the expected sources leaving as free parameters h/w, r/w, f/w and the continuum normalization w f h-D h w-D r

  9. Peripheral collisions in 3 pT bins pT < 0.5 GeV/c 0.5 < pT < 1.0 GeV/c pT > 1.0 GeV/c Signal Cocktail • The normalizations of the hadron decay cocktail and of the continuum are independently fit in each pT bin • h/wandf/wratios: nearly pT independent • In general, the peripheral bin is very well described in terms of expected sources (but there are “too many” low pTr mesons)

  10. Vacuum +cocktail r Cocktail r Vacuum +cocktail r Cocktail r Cocktail r Vacuum +cocktail r rmass spectra in peripheral collisions Vacuum r contribution (pp annihilation) important at low pTeven in Indium-Indium peripheral collisions

  11. Mass spectrum in semi-central In-In collisions Complicated continuum under the w in more central collisions… However, the excellent mass resolution of NA60 allows us to extract a robust w yield, in particular at high pT

  12. f/w cross section ratio vs. Npart • f/wobtained for pT > 1 GeV/c • Increase by a factor ~ 2 from peripheral to central collisions f/w

  13. f/w comparison between NA60 and NA50 • A direct comparison is impossible, due to the contribution from pion annihilation, which NA50 cannot isolate. • This contribution must be even higher in Pb-Pb collisions. • NA50 points converted to the window pT>1.1 GeV/c assuming T = 228 MeV • sr= 1.2 swused(lower limit for NA50 f/w) f/w

  14. f/w NA60 ratio compared with NA49 f/p • Same trend as a function of Npart w/p constant • If we set the ratio w/p to 0.07–0.08, as suggested by statistical models, then the NA60 f yield is a factor 1.5–2 higher than the NA49 value

  15. Extraction off pT spectra • Continuum under f subtracted using 2 side windows defined symmetrically around the fpeak • The net pT spectrum is corrected for the acceptance using a 2-D acceptance correction (y vs. pT)

  16. f pT spectra vs. rapidity and multiplicity Characterized by the extracted inverse pT slope parameter, T No significant variation with rapidity Clear increase with multiplicity pT distributionvs. rapidity pT distributionvs. multiplicity Only statistical errors

  17. NA49 Pb-Pb Pb-Pb In-In NA60 In-In NA50 Pb-Pb Si-Si C-C NA49 pp pp The In-In measurement of NA60follows the NA49 systematics, contrary to the NA50 Pb-Pb point It seems that the difference between NA50 and NA49is not due to the different decay channels probed f T parameter: NA60 versus NA50 and NA49 Average T(f) for In-In collisions: 1) all pT : 253 2 MeV 2) pT < 1.50 GeV (NA49 range) : 260  5 MeV 3) mT > 1.65 GeV (NA50 range) : 244  5 MeV

  18. MC All tracks K from f pT (GeV/c) Preliminary study of the f  KK channel • Consider all charged tracks associated to a vertex • Assume they are kaons (no particle id.) • Extract the invariant mass spectrum • Subtract the (huge) combinatorial background with event mixing technique • Carefully select candidate charged tracks,using pseudo-rapidity, pT, p and opening angle • to stay away from acceptance borders • to improve signal over background ratio

  19. pT (GeV/c) Extraction of f  KK signal from Monte Carlo opposite sign background • 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 MC (VENUS)semi-peripheral

  20. f  KK mass spectrum in In-In collisions • 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 semi-peripheral bin

  21. Summary and Outlook • f/wratio: • Rise with Npart consistent with NA49 and NA50 • Absolute values between NA49 and NA50 • Inverse slope T of the f pT distribution: • Our f  mm values agree with NA49: the difference between NA49 and NA50is not due to the different decay channels probed • f  KK • Full MC simulation shows feasibility of the study • Final tuning still needed for background subtraction in real data • f flow also under study

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