f production in proton-nucleus and indium-indium collisions

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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. - PowerPoint PPT Presentation

Text of f production in proton-nucleus and indium-indium collisions

  • f production in proton-nucleus and indium-indium collisionsMichele FlorisUniversity and INFN, Cagliari, Italy. on behalf of the NA60 Collaboration ISMD 2005, Kromeriz, Czech Republic, August, 14th 2005. OutlineMotivationApparatus Collected dataResults in p-AResults in In-In Ongoing work for fKK

  • MotivationThe study of f meson production in heavy ion collisions carries information about strangeness production Two channels have been studied: f mmMuons not influenced by the mediumPrevious SPS measurements: NA50Acceptance limited to high pT f KKBetter mass resolutionNo physical BGPrevious SPS measurements: NA49Broad pT coverage, but dominated by low pTThe discrepancy between the values of the inverse slope T measured by these experiments led to the so-called f puzzleNew measurements from NA60 in In-In collisionsNA60 measures the mm channel with very good pT coverageHas access to the fKK channel

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  • The NA60 experiment17mThe vertex region:Fixed target dimuon experiment at the CERN SPSApparatus composed of 4 main detectorsZero degree calorimeter(centrality measurements)Muon SpectrometerAnalysis strategyCreate sample of matched muonsSubtract combinatorial BG via event mixingEstimate fakes via overlay MCFit experimental spectra with expected sources Hadronic cocktail (Genesis)IMR continuum (open charm and Drell-Yan or empirical)

  • Data TakingTwo samples discussed in this talkp-A Collisions (400 GeV protons)Six targets, three nuclei (Be, In, Pb)Microstrips silicon vertex detector4 days in 2002, 600 000 dimuons collected (at low beam intensity: 13 x 108 protons/burst)New high statistics sample collected in 2004, still to be analyzedIn-In collisions (158 GeV ions)Seven indium targetsSilicon pixels vertex detector5-week-long run in 2003, very good statistics (~ 230 million dimuon triggers on tape)~ 50% statistics discussed in this talk

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  • Detector performanceDimuon mass resolution at M ~ 1 GeV:In-In: ~ 23 MeV (independent of centrality)p-A: ~ 30 MeVPrevious dimuon experiments: ~ 80 MeV

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  • f production in proton-nucleus collisionsMass spectra described as a superposition of the low mass resonances decays into muons + charm + DYFit to the mass spectra to extract the f/w ratio

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  • f production in indium-indium collisions4 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/w and the continuumArbitrarily normalize to the w

    Total sample: 570 000 events after BG subtraction 50% of the full statisticsS/B = 1/4

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  • Peripheral BinPeripheral bin studied in three pT binsThe normalizations of the hadron decay cocktail and of the continuum are independently fit in each pT binh/w and f/w ratios are nearly pT independentThe peripheral bin is well described in terms of expected sources but:Too many low pT r mesonsPeripheral In-In is not quite pp, its more like CC or OOEffect of pion annhilation cannot be neglected

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  • / cross section ratio Vacuum rVacuum 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 w yieldVacuum r +Cocktail rCocktail r

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  • / cross section ratio Centrality DependenceAs a function of centrality:We restrict analysis topT > 1 GeV

    Increase of a factor ~2 from peripheral to central collisions

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  • / comparison to NA50 f / (r+w)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 isolateNA50 points converted to the window pT>1.1 GeV/c assuming T=228 MeV

    sr= 1.2 sw used (lower limit for NA50 f/w ratio)

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  • / comparison to NA49 f/pIf we set the ratio w/p to 0.070.08, as suggested by statistical models, then the NA60 f yield is a factor 1.52 higher than the NA49 value

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  • f transverse momentum spectrumWe 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 ybackgroundtotalf

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  • 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 feasiblef pT spectrum versus y and centrality

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  • Comparison to NA49/NA50The disagreement between NA49 and NA50 is not due to the different decay channelAverage 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

  • f KK, Analysis strategyf KK can be studied using charged tracks reconstructed in vertex telescopeBrute force method (no PID):Assume all tracks are kaonsMake invariant mass from all track pairsHuge combinatorial BG Subtracted by event mixing techniqueKinematical cutsSingle tracksh avoid phase space boundariespT and p improve Signal/BGPairOpening angle improve Signal/BG

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  • f KK, StatusSubtractionDetailed Monte Carlo (Venus) studies (full detector description)First attempts to get a signal out of the dataMCSemi-peripheral In-In collisions

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  • SummaryNA60 is well suited to help understanding the f puzzle New In-In measurementsBetter pT coverage than previous mm experimentsCapability to measure fKK f/w ratio:Rise with Npart consistent with NA49 and NA50Absolute values between NA49 and NA50Inverse slope T of the f pT-distribution:Agreement between NA49 and NA60The difference between NA49 and NA50 is not due to the different channels probedfKK Full MC simulation shows the feasibility of the studyFinal tuning still needed for background subtraction in real data

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  • The NA60 Collaboration56 people13 institutes 8 countriesR.Arnaldi, R. Averbeck, K. Banicz, K.Borer, J. Buytaert, J.Castor, B.Chaurand, W. Chen, B.Cheynis, C.Cical, A. Colla, P.Cortese, S. Damjanovic, A. David, A.deFalco, N. de Marco, A.Devaux, A. Drees, L.Ducroux, H. Enyo, 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.Loureno, 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. Whrihttp://na60.cern.ch/

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  • BACKUP

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  • Measuring DimuonsMWPC &trigger hodosMWPC &trigger hodosToroidalmagnetIron WallHadron absorberTargetLast triggerstationLimiting Factor: Enegy loss Multiple Scattering

    Tracking before the hadron absorberVertex Detector High multiplicity+High luminosity Rad-hard silicon pixels

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  • Concept of NA60Concept 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 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 determined2.5 T dipole magnetbeam trackervertex tracker

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  • Peripheral bin0.5 < pT < 1.0 GeV/cpT > 1.0 GeV/cpT < 0.5 GeV/cSignalCocktail

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  • f pT spectra vs multiplicityClear increase of the extracted slope parameter T with multiplicity

    Purely statistical errors

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  • Fit of the f pT distribution in different pT rangesDifferential fitsFix fit interval at DpT=0.8 GeV and move the extremes Dynamic range of 40 MeV in Teff (all centralities)Flat trend for peripheral collisionsIndication for flow in In-In collisions

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  • Combinatorial Background from ,K decaysAgreement of data and mixed CB over several orders of magnitude Accuracy of agreement ~1%

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  • Muon track matching 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)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.

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  • Example of overlay MC: the fFake-match contribution localized in mass (and pT) space = 23 MeV fake = 110 MeV

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  • Comparison of data to RW, BR and Vacuum rVacuum r +Cocktail rCocktail r

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  • Mass spectrum in semi-central In-In collisionsComplicated continuum under the w in more central collisionsHowever, the excellent mass resolution of NA60 allows us to extract a robust w yield

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  • Comparison of data to RW, BR and Vacuum rPredictions for In-In by Rapp et al (2003) for = 140, covering all scenarios Theoretical yields, folded with acceptance of NA60 and normalized to data in mass interval < 0.9 GeV Only broadening of