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Resonances production from the NA60 experiment

Resonances production from the NA60 experiment. Results for the f m + m - channel in In-In collisions Results for the f K + K - channel in In-In collisions Comparison between the hadronic and leptonic channels Comparison between In-In and other systems

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Resonances production from the NA60 experiment

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  1. Resonances production from the NA60 experiment • Results for the fm+m-channel in In-In collisions • Results for the fK+K-channel in In-In collisions • Comparison between the hadronic and leptonic channels • Comparison between In-In and other systems • r production in In-In collisions Eur.Phys.J.C64:1 (2009) Phys.Lett.B699:325 (2011) Alessandro De Falco (University and INFN Cagliari) Resonance Workshop at UT Austin March 5-7 2012 Alessandro De Falco

  2. The f puzzle Historic facts on NA49 fKK vs NA50 fmm Yields in hadronic channel lower than in leptonic channel by factor ~4 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? • CERES hadronic yield and inverse slope similar to NA49. Within large errors leptonic yield also compatible with NA49  No f puzzle? Alessandro De Falco

  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

  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 for dimuons • 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

  5. 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 Mmm (GeV/c2) 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

  6. Yield integrated in centrality: • Direct method: • J/y Calibration: fmm: Multiplicity Multiplicity determined either directly with the cross section measurement or extracted using the J/y (corrected for the nuclear and anomalous suppression) 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

  7. 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mm: transverse mass distributions Alessandro De Falco

  8. 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 (mm, pT < 1.6 GeV)‏ NA49 Pb-Pb (KK, pT < 1.6 GeV)‏ NA50 Pb-Pb (mm, pT > 1.1 GeV)‏ NA60 In-In (mm, pT > 1.1 GeV)‏ NA49 Pb-Pb (KK, pT < 1.6 GeV)‏ NA50 Pb-Pb (mm, 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

  9. dN/dMKK MC f mass spectrum s=7.8 MeV MKK (GeV/c2) fKK in In-In collisions • No PID: all tracks assumed to be kaons Huge combinatorial background • Events are accepted if there is one and only one vertex • All triggers are taken (dominated by dimuon trigger) • Event mixing technique • Cuts on tracks: c2<3, pT > 0.2 GeV/c, 2.9 < y < 3.7 • Cut on pairs: 0.005 < qKK < 0.15 • Acceptance correction evaluated with an overlay Monte Carlo • The expected mass resolution is 7.8 MeV (20 MeV in muons) Alessandro De Falco

  10. fKK in In-In collisions • Residual background present in spectra • Mass spectra fitted with a function that describes the MC f mass peak + the BKG Several functions used to describe the residual background. Differences taken into account in the systematic error • Different selections are applied to check the consistency of the results • Peak position and width correctly reproduced when left as free parameters, independent of centrality Alessandro De Falco

  11. fKK: mT distributions • pT and mT distributions are obtained fitting the mass spectra in pT slices • High background at low pT: fit limited to pT>0.9 GeV/c • Spectra normalized to the multiplicity in 4p (discussed in next slides) • Due to limited statistics in the peripheral data, the pT distributions can be extracted only in the two most central bins • Systematic error on T of ~ 5 MeV • Clear agreement between the mT distributions measured in In-In collisions in the hadronic and dileptonic channels Phys.Lett.B699:325 (2011) Spectra normalized to multiplicity Alessandro De Falco

  12. Yield vs Npart in KK compared to mm • Multiplicity obtained for pT>0.9 GeV/c for each centrality bin • Data corrected for the integrated acceptance in 4p and branching ratioTeff from KK in (semi)central collisions, from mm in (semi)peripheral collisions f multiplicity vs Npart in the kaon channel in agreement with the results in muons Alessandro De Falco

  13. Sensitivity to rescattering-absorption Modelslike AMPT predicteffects due to rescattering/absorptionconcentratedatlowpT Common coverage of the NA60 mm and KK chanels for mT– m0> 0.34 GeV The localTeffvalue in thisregionwoulddiffer by 30-50 MeVin the twochannels Fractionallossin kaonswould be 35-50%Notseen in NA60 data For lowermT:Extreme hypothesis: assume Teffvaluemeasured by NA49 in Pb-Pb (330 MeV) for formT– m0< 0.34 GeV Thisvariationwouldlead to a reduction of the fyield in kaons by 12% RESCATTERING-ABSORPTION MODEST OR ABSENT IN In-In mm KK Alessandro De Falco

  14. T and <f>/Npartin central collisions • Inverse slope: increase fast at low Npart, less pronounced at high Npartlower value observed by NA50 • Yield per participant: in In-In collisions the dilepton and hadron channels, differences within 22% in full pT<f>/Npart in In-In exceeds the one measured in Pb-Pb (KK) by about 30%NA50 point higher by a factor of 2 • Suppression of the kaon channel in Pb-Pb below experimental sensitivity in In-In? Alessandro De Falco

  15. Eur.Phys.J.C 49 (2007) 235 Peripheral (Nch<30) In-In collisions Well described by meson decay ‘cocktail’: η, η’, ρ, ω, f and contributions(Genesis generator developed within CERESand adapted for dimuons by NA60). A. Uras, QM2011 p-A Similar cocktail describes NA60 p-A collisions, 400 GeV data Alessandro De Falco

  16. More central In-In collisions • Clear excess of data above decay ‘cocktail’ describing peripheral events • Excess isolated subtracting the measured decay cocktail (without r) independently for each centrality bin, based on local criteria for h,w,f (2-3% accuracy) • Advantages: • no need for reference data (pA, peripheral collisions, models) • Less uncertainties (e.g. strangeness enhancement: h,f) Phys. Rev. Lett. 96 (2006) 162302 Alessandro De Falco 16

  17. No cocktail rand noDDsubtracted NA60 LMR excess dimuons Evolution of the excess with centralitystudied with precision with a rather fine binning in multiplicity • Eur.Phys.J.C 49 (2007) 235 data – cocktail (all pT) • Clear excessabove the cocktail ,centeredat the nominalr poleand rising with centrality • monotonic broadening with centrality • “melting” of the r

  18. Centrality dependence of LMR excess NA60, In-In 158A GeV Eur.Phys.J.C 49 (2007) 235 r peak: R=C-1/2(L+U) continuum: 3/2(L+U)cocktail ρ is fixed by ρ/ω=1.0 Excess rises faster than linear with multiplicity: compatible with emission from annihilation processes • rapid initial increase of total - already 3 at dNch/dh=Npart=50 • strong increase of continuum (by a factor of >10) • Precision measurement of excess yield (r-clock): • -the most precise constraint in the fireball lifetime (6.5±0.5 fm/c) in heavy ion collisions to date! Alessandro De Falco

  19. LMR excess: r dropping mass vs broadening Rapp-Wambach: hadronic model predicting strong broadening/no mass shift Brown/Rho scaling: dropping mass due to dropping of chiral condensate Predictions for In-In by Rapp et al (2003) for dNch/d = 140, covering all scenarios Theoretical yields normalized to data in mass interval < 0.9 GeV After acceptance filtering,data and predictions displayspectral functions, averaged over space-time and momenta Only broadening of (RW) observed, no mass shift (BR)

  20. Excess mass spectrum up to 2.5 GeV • All known sources (hadro-cocktail, open charm, DY) subtracted • Acceptance corrected spectrum (pT>0.2 GeV) • Absolute normalization → comparison to theory in absolute terms! • thermalpp g mm(M<1 GeV) • && thermalqq g mm(M >1 GeV) suggested dominant by Teff vs M (supported by R/R, D/Z) • also multipion processes (H/R) • Eur. Phys. J. C 59 (2009) 607 • Planck-like mass spectrum; falling exponentially • Agreement with theoretical models up to 2.5 GeV! Alessandro De Falco • 20 20 • 20

  21. Dimuon mT distributions • Phys. Rev. Lett. 100 (2008) 022302 • Eur. Phys. J. C 59 (2009) 607 • all mT spectra exponential for mT-M > 0.1 GeV; <0.1 GeV ?? • IMR • LMR • fit with 1/mT dN/mT ~ exp(-mT/Teff)

  22. 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

  23. Low mass dimuons in the LHC era: ALICE arXiv:1112.2222 • Dimuon mass spectrum in p-p collisions at 7 TeV described by hadronic cocktail + open charmMass resolution at the f peak of about 60 MeV Alessandro De Falco

  24. w,f pT-differential cross sections arXiv:1112.2222 f w Alessandro De Falco

  25. Summary • f production in In-In (kaons vs muons):results in the KK channel agree with the ones in mm both for T and multiplicity Compared to Pb-Pb central collisions:-TEFF values in In-In significantly lower than kaon points in Pb-Pb (NA49/ CERES) higher than NA50(mm) points in Pb-Pb- <f>/NPART in In-In much lower than the NA50 result slightly higher than results in kaon pairs and dielectrons - mm vs KK in Pb-Pb still leave room for a physical effectHowever, CERES measurements in kaons and dielectrons agree • Excess in dilepton emission:Good agreement with models of thermal emissionFaster than linear scaling with NchargedPlanck-like mass spectraTeff rising with mass in LMR and, after sharp drop, flat in IMR No f puzzle in In-In collisions Alessandro De Falco

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