1. 06/10/2008Alessandro De Falco (NA60) SQM081 Highlights from the NA60 Experiment Alessandro De Falco University and INFN Cagliari on behalf of the NA60 collaboration SQM08, Beijing, China

2. 06/10/2008Alessandro De Falco (NA60) SQM082 Outline The NA60 Experiment – Detector Concept Phi Meson Production in In-In Collisions – Analysis details – p T, y and decay angular distributions –  yield –Raw spectra from   KK analysis Eta meson production in In-In collisions Highlights from IMR –Origin of excess: prompt or charm? –p T spectra of excess –T vs mass

3. 06/10/2008Alessandro De Falco (NA60) SQM083 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 Origin of muons can be accurately determined Improved dimuon mass resolution (~20 MeV/c 2 at  instead of 80 MeV/c 2 ) Additional bend by the dipole field extends the dimuon coverage down to low pt High luminosity  experiment: possible with radiation tolerant detectors and high speed DAQ 2.5 T dipole magnet hadron absorber targets beam tracker vertex tracker muon trigger and tracking (NA50) magnetic field >10m<1m

4. 06/10/2008Alessandro De Falco (NA60) SQM084 Data sample In-In collisions at 158 AGeV Incident beam energy –5 weeks in Oct.-Nov. 2003 –~ 4 ∙ 10 12 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  2 ) –Subtract Background

5. 06/10/2008Alessandro De Falco (NA60) SQM085 The  puzzle Historic facts on NA49   KK vs NA50    Yields in hadronic channel lower than in leptonic channel by factor >2 in central collisions Inverse slopes in central collisions Hadronic (low p T )~ 300 MeV Leptonic (high p T )~ 230 MeV   puzzle: in-medium effects on  and kaons + kaon absorption and rescattering leading to reduced yield and hardened p T 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  puzzle? –New NA50 analysis confirms previous results within 8%

6. 06/10/2008Alessandro De Falco (NA60) SQM086 We select the events on the  peak and use two side mass windows to estimate the p T,y and decay angle distribution of the continuum under the peak Systematic error: variation of analysis cuts and parameters 5 centrality bins 4000 A data set only Extraction of differential spectra Acceptance: Overlay Monte Carlo tuned to data with an iterative process

7. 06/10/2008Alessandro De Falco (NA60) SQM087 All centralities  = 0.1 ± 0.1 ± 0.1 Fitted with  = 0, independent of centrality All centralities  = 1.13 ± 0.06 ± 0.05 reflected Rapidity and cos  distributions  constant vs centrality Agreement with previous measurements in other colliding systems at the same energy

8. 06/10/2008Alessandro De Falco (NA60) SQM088  transverse mass distributions 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 p T )

9. 06/10/2008Alessandro De Falco (NA60) SQM089 T slopes in In-In and Pb-Pb collisions NA60 In-In(p T < 1.6 GeV)‏ NA49 Pb-Pb(p T < 1.6 GeV)‏ NA50 Pb-Pb(p T > 1.1 GeV)‏ NA60 fits at low p T (NA49 range) Box: stat+syst. error NA60 In-In (p T > 1.1 GeV)‏ NA49 Pb-Pb (p T < 1.6 GeV)‏ NA50 Pb-Pb (p T > 1.1 GeV)‏ Box: stat+syst. error NA60 low vs high p T : 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? NA60 fits at high p T (NA50 range) Ceres Pb-Pb(KK, p T > 0.75 GeV)Ceres Pb-Pb(ee, p T < 1.5 GeV)

10. 06/10/2008Alessandro De Falco (NA60) SQM0810  cross section and yield Beam Counters Effective Target Length Beam Absorption Transverse Size Monte Carlo Dedicated Runs Beam Counters (DAQ-vetoed) Total Systematic Uncertainties ~ 10%  multiplicity Eur. Phys. J. C13 69 (2000)

11. 06/10/2008Alessandro De Falco (NA60) SQM0811  Yield: Alternative Method  multiplicity extracted from the measured ratio Alternative method with independent systematics! Total systematic error ~ 13% Total number of binary collisions in a given centrality bin J/  cross section x BR  in a nucleon-nucleon collision Inelastic nucleon-nucleon cross section J/  multiplicity is corrected for nuclear and anomalous suppression

12. 06/10/2008Alessandro De Falco (NA60) SQM0812  Yield: Results Yield integrated in centrality: Direct method: J/  Calibration: Results in full phase space and corrected for BR  = 2.86 · 10 -4 Centrality Dependence (average of the 2 methods) Box: stat+syst. error  scales faster than N part

13. 06/10/2008Alessandro De Falco (NA60) SQM0813  yields In-In - comparison to other systems  N part 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 CERES Pb-Pb KK CERES Pb-Pb ee

14. 06/10/2008Alessandro De Falco (NA60) SQM0814   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 S/B~1/400S/B~1/300 S/B~1/100 = 39 = 75 = 132

15. 06/10/2008Alessandro De Falco (NA60) SQM0815   KK: mass spectra vs p T Despite of the residual background a p T distribution can be extracted in most central bins starting from p T >0.9 GeV/c Enough statistics up to ~2.5 GeV/c Still ongoing analysis = 132

16. 06/10/2008Alessandro De Falco (NA60) SQM0816 Raw pT spectrum in the   KK channel Not corrected for the acceptance = 132

17. 06/10/2008Alessandro De Falco (NA60) SQM0817  production in In-In collisions Strangeness content of  = 40% (for  it is 100%)  enhancement from peripheral to central In-In collisions What about  enhancement?  increases by a factor of 1.34 from most peripheral to most central In-In collisions

18. 06/10/2008Alessandro De Falco (NA60) SQM0818 R CP :  vs   increases by a factor of 3, while  increases by a factor of 1.34 from most peripheral to most central In-In collisions

19. 06/10/2008Alessandro De Falco (NA60) SQM0819 To describe the strange particle yield, an additional parameter  S is introduced in the canonical partition function  S suppresses the phase space of particles composed of valence s or s quarks Statistical model Becattini et al.: For central In-In  S ~0.8 Taking from the SM that  production is primary  S vs N part Phys.Rev.C73:044905,2006

20. 06/10/2008Alessandro De Falco (NA60) SQM0820 Strangeness content of  = 40%. One expects In case of feed-down from other resonances: The largest contribution to secondary  yield owes to  1 (1400) and a 0 which are NOT  S suppressed Knowing the centrality dependence of  S we can calculate what one should expect for the R CP of  production if there would not be any feed down from higher resonances and compare to the measured values.  /N part calculated from  S

21. 06/10/2008Alessandro De Falco (NA60) SQM0821 The measured values of the eta R CP (red points) agree within errors with the expectations for the primary production of the   R CP data vs expectation for primary production

22. 06/10/2008Alessandro De Falco (NA60) SQM0822 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? NA38/NA50 proton-nucleus data central collisions M (GeV/c 2 )

23. 06/10/2008Alessandro De Falco (NA60) SQM0823 Offset and mass distributions 23 measurement of muon offsets  : distance between interaction vertex and track impact point charm not enhanced; excess prompt; 2.4 × DY excess similar to open charm steeper than Drell-Yan isolation of excess by subtraction of measured open charm and expected Drell-Yan

24. 06/10/2008Alessandro De Falco (NA60) SQM0824 Excess/DY vs p T The process responsible for the production of excess dimuons is significantly softer than Drell-Yan dimuons

25. 06/10/2008Alessandro De Falco (NA60) SQM0825 IMR excess p T and m T spectra The p T spectra in 3 different mass windows are clearly different while Drell-Yan p T spectra and mass spectra factorize, the primordial k T =0.8 GeV/c being independent of mass T=199 ± 21 ± 3 MeV T=193 ± 16 ± 2 MeV T=171 ± 21 ± 3 MeV m T spectra fitted by the function for p T >0.5 GeV/c

26. 06/10/2008Alessandro De Falco (NA60) SQM0826 Centrality integrated m T spectra steepening at low m T ; not observed for hadrons (like  fit m T spectra for p T >0.4 GeV with monotonic flattening of spectra with mass up to M=1 GeV, followed by a steepening above signs for mass-dependent radial flow? Phys. Rev. Lett. 100 (2008) 022302

27. 06/10/2008Alessandro De Falco (NA60) SQM0827 Evolution of inverse slope T eff with mass Strong rise of T eff with dimuon mass, followed by a sudden drop for M>1 GeV Rise consistent with radial flow of a hadronic source (here  →  →  ), taking the freeze-out ρ as the reference Drop signals sudden transition to low-flow source, i.e. source of partonic origin (here qq→  ) Phys. Rev. Lett. 100 (2008) 022302

28. 06/10/2008Alessandro De Falco (NA60) SQM0828 Summary  puzzle: –Yield in leptonic channel in In-In larger than in hadronic channel in Pb-Pb –Dependence of T slope on p T suggests NA49 vs NA50 T difference larger than expected from radial flow –Physical origin of effect? –New NA60 data on  KK to come soon! –PbPb measurements in a NA60-like experiment?  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