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f production in proton-nucleus and indium-indium collisions

f production in proton-nucleus and indium-indium collisions. Outline Motivation Apparatus Collected data Results in p-A Results in In-In Ongoing work for f  KK. Michele Floris University and INFN, Cagliari, Italy. on behalf of the NA60 Collaboration.

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f production in proton-nucleus and indium-indium collisions

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  1. f production in proton-nucleus and indium-indium collisions • Outline • Motivation • Apparatus • Collected data • Results in p-A • Results in In-In • Ongoing work for fKK Michele Floris University and INFN, Cagliari, Italy. on behalf of the NA60 Collaboration ISMD 2005, Kromeriz, Czech Republic, August, 14th 2005.

  2. Motivation • The study of f meson production in heavy ion collisions carries information about strangeness production • Two channels have been studied: • fmm • Muons not influenced by the medium • Previous SPS measurements: NA50 • Acceptance limited to high pT • f KK • Better mass resolution • No physical BG • Previous SPS measurements: NA49 • Broad pT coverage, but dominated by low pT • The discrepancy between the values of the inverse slope T measured by these experiments led to the so-called f puzzle • New measurements from NA60 in In-In collisions • NA60 measures the mm channel with very good pT coverage • Has access to the fKK channel ISMD 2005

  3. The NA60 experiment • Fixed target dimuon experiment at the CERN SPS • Apparatus composed of 4 main detectors Zero degree calorimeter (centrality measurements) 17m Muon Spectrometer The vertex region: • Analysisstrategy • Create sample of matched muons • Subtract combinatorial BG via event mixing • Estimate fakes via overlay MC • Fit experimental spectra with expected sources • Hadronic cocktail (Genesis) • IMR continuum (open charm and Drell-Yan or empirical)

  4. Data Taking • Two samples discussed in this talk • p-A Collisions (400 GeV protons) • Six targets, three nuclei (Be, In, Pb) • Microstrips silicon vertex detector • 4 days in 2002, 600 000 dimuons collected (at “low” beam intensity: 1–3 x 108 protons/burst) • New high statistics sample collected in 2004, still to be analyzed • In-In collisions (158 GeV ions) • Seven indium targets • Silicon pixels vertex detector • 5-week-long run in 2003, very good statistics (~ 230 million dimuon triggers on tape) • ~ 50% statistics discussed in this talk ISMD 2005

  5. Detector performance The acceptance of NA60 extends, all the way down to small M and pT Clear separation of all targets (Z vertex resolution ~ 600–900 mm in p-A, better than 200 mm in In-In) A (%) Transverse vertexingwith 20 µm accuracy 7 In targets target boxwindows Beam tracker station z-vertex (cm) In Pb p beam 400 GeV 3 x Be Be Indium beam 158 A GeV Dimuon mass resolution at M ~ 1 GeV: In-In: ~ 23 MeV (independent of centrality) p-A: ~ 30 MeV Previous dimuon experiments: ~ 80 MeV ISMD 2005

  6. f production in proton-nucleus collisions w f r BG+charm • Mass spectra described as a • superposition of the low mass • resonances decays into • muons + charm + DY • Fit to the mass spectra to • extract the f/w ratio ISMD 2005

  7. f production in indium-indium collisions peripheralall pT Signal Cocktail • 4 Centrality bins: • Npart estimated from a Glauber fit to the EZDC spectrum • Fit input: • Hadron cocktail (genesis) • Low-level (empirical) continuum source with exponential fall-off • (to mimic continuum under the vector mesons) • Parameters allowed to vary: • h/w, r/w, f/wand the continuum • Arbitrarily normalize to the w • Total sample: • 570 000 events after BG subtraction • 50% of the full statistics • S/B = 1/4 ISMD 2005

  8. Peripheral Bin Peripheral bin studied in three pT bins • The normalizations of the hadron decay cocktail and of the continuum are independently fit in each pT bin • h/w and f/w ratios are nearly pT independent • The peripheral bin is well described in terms of expected sources but: • “Too many” low pT r mesons • Peripheral In-In is not quite pp, it’s more like CC or OO • Effect of pion annhilation cannot be neglected ISMD 2005

  9. / cross section ratio – Vacuum r Vacuum r + Cocktail r Cocktail r Vacuum r contribution (pp annihilation) important at low pT even in peripheral collisions Effect becomes dramatic in more central collisions  complicated continuum below the w However, the excellent mass resolution of NA60 allows us to extract a robust wyield ISMD 2005

  10. / cross section ratio – Centrality Dependence As a function of centrality: • We restrict analysis to • pT > 1 GeV • Increase of a factor ~2 from peripheral to central collisions ISMD 2005

  11. / comparison to NA50 f / (r+w) NA50 points converted to the windowpT>1.1 GeV/c assuming T=228 MeV sr= 1.2 swused (lower limit for NA50f/w ratio) A direct comparison is impossible, due to the contribution from pion annihilation, which must be even higher in Pb-Pb collisions, and which NA50 cannot isolate ISMD 2005

  12. / comparison to NA49 f/p Same trend as a function of Npartw/p constant If we set the ratio w/p to 0.07–0.08, as suggested by statistical models, then the NA60f yield is a factor 1.5–2 higher than the NA49 value ISMD 2005

  13. f transverse momentum spectrum total f background 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 ISMD 2005

  14. 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 ISMD 2005

  15. Comparison to NA49/NA50 The In-In measurement of NA60follows the NA49 systematics, Pb-Pb In-In Si-Si C-C pp • Average NA60 value • All pT: 253 ± 2 MeV • NA50 range (mT > 1.65 GeV/c): 244 ± 5 MeV • NA49 range (pT < 1.5 GeV/c): 260 ± 5 MeV •  Only small variations… The disagreement between NA49 and NA50 is not due to the different decay channel

  16. f KK, Analysis strategy MC pT (GeV/c) • f KK can be studied using charged tracks reconstructed in vertex telescope • Brute force method (no PID): • Assume all tracks are kaons • Make invariant mass from all track pairs • Huge combinatorial BG • Subtracted by event mixing technique • Kinematical cuts • Single tracks • h  avoid phase space boundaries • pT and p  improve Signal/BG • Pair • Opening angle  improve Signal/BG ISMD 2005

  17. f KK, Status MC Measured spectrum Combinatorial BG DATA Signal Something yet to be tuned (BG?) Very clean signal! • Detailed Monte Carlo (Venus) studies (full detector description) • First attempts to get a signal out of the data MC Subtraction Semi-peripheral In-In collisions ISMD 2005

  18. Summary • NA60 is well suited to help understanding the “f puzzle” • New In-In measurements • Better pT coverage than previous mm experiments • Capability to measure fKK • f/w ratio: • Rise with Npart consistent with NA49 and NA50 • Absolute values between NA49 and NA50 • Inverse slope T of the f pT-distribution: • Agreement between NA49 and NA60 • The difference between NA49 and NA50 is not due to the different channels probed • fKK • Full MC simulation shows the feasibility of the study • Final tuning still needed for background subtraction in real data ISMD 2005

  19. The NA60 Collaboration CERN Heidelberg Bern Palaiseau BNL BNL Riken Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon http://na60.cern.ch/ 56 people 13 institutes 8 countries R. Arnaldi, R. Averbeck, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen,B. Cheynis, C. Cicalò, A. Colla, P. Cortese, S. Damjanovic, A. David, A. de Falco, N. de Marco,A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A. Grigorian, J.Y. Grossiord,N. Guettet, A. Guichard, H. Gulkanian, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço,J. Lozano, F. Manso, P. Martins, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho,G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht, R. Tieulent, G. Usai, H. Vardanyan, R. Veenhof, D. Walker and H. Wöhri ISMD 2005

  20. BACKUP ISMD 2005

  21. Measuring Dimuons MWPC & trigger hodos MWPC & trigger hodos Hadron absorber Toroidal magnet Iron Wall Target Last trigger station Vertex Detector High multiplicity + High luminosity Tracking before the hadron absorber • Limiting Factor: • Enegy loss • Multiple Scattering Rad-hard silicon pixels ISMD 2005

  22. Concept of NA60 muon trigger and tracking iron wall magnetic field targets hadron absorber muon other 2.5 T dipole magnet vertex tracker beam tracker Concept of NA60: place a silicon tracking telescope in the vertex region to measure the muons before they suffer multiple scattering in the absorberand match them to muon measured in the spectrometer Improved kinematics (~20 MeV/c2 at  instead of 80 MeV/c2 in NA50)Origin of muons can be accurately determined ISMD 2005

  23. Peripheral bin pT < 0.5 GeV/c 0.5 < pT < 1.0 GeV/c pT > 1.0 GeV/c Signal Cocktail ISMD 2005

  24. f pT spectra vs multiplicity Clear increase of the extracted slope parameter T with multiplicity Purely statistical errors ISMD 2005

  25. Fit of the f pT distribution in different pT ranges • Differential” fits • Fix fit interval at DpT=0.8 GeV and move the extremes • Dynamic range of 40 MeV in Teff (all centralities) • Flat trend for peripheral collisions • Indication for flow in In-In collisions ISMD 2005

  26. Combinatorial Background from ,K→ decays Agreement of data and mixed CB over several orders of magnitude Accuracy of agreement ~1% ISMD 2005

  27. Muon track matching Matching between the muons in the Muon Spectrometer (MS) and the tracks in the Vertex Telescope (VT) is done using the weighted distance (2) in slopes and inverse momenta. For each candidate a global fit through the MS and VT is performed, to improve kinematics. A certain fraction of muons is matched to closest non-muon tracks (fakes). Only events with 2< 3 are selected. Fake matches are subtracted by a mixed-events technique (CB) and an overlay MC method (only for signal pairs, see below) ISMD 2005

  28. Example of overlay MC: the f Fake-match contribution localized in mass (and pT) space  = 23 MeV fake = 110 MeV ISMD 2005

  29. Comparison of data to RW, BR and Vacuum r Vacuum r + Cocktail r Cocktail r ISMD 2005

  30. 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 ISMD 2005

  31. Comparison of data to RW, BR and Vacuum r Predictions for In-In by Rapp et al (2003) for <dNch/d > = 140, covering all scenarios Theoretical yields, folded with acceptance of NA60 and normalized to data in mass interval < 0.9 GeV Only broadening of (RW) observed, no mass shift (BR) ISMD 2005

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