1. Latest results from NA60 P. Cortese for the NA60 Collaboration Università del Piemonte orientale – Alessandria and INFN Europhysics Conference on High Energy Physics Manchester, 19-25 July 2007

2. EPS HEP 2007P. Cortese for the NA60 Collaboration LMRIMRHMR Intermediate mass excess, connected with thermal dilepton production? central collisions J/  suppression in Pb-Pb, connected with deconfinement? Low-mass excess observed by CERES is, connected with chiral symmetry restoration? Physics motivation Detailed study of in-medium modification of ρ meson Intermediate mass excess: prompt or charm? J/ψ production in p-A and In-In

3. EPS HEP 2007P. Cortese for the NA60 Collaboration The NA60 Experiment A silicon tracking telescope in the vertex region allows to: measure the muons before they suffer multiple scattering in the absorber match them (in coordinate and momentum space) to the tracks measured in the spectrometer Origin of muons can be accurately determined Mass resolution @  :~20 MeV/c 2 (vs. 80 MeV/c 2 ) Mass resolution @ J/  :~70 MeV/c 2 (vs. 105 MeV/c 2 ) High luminosity  experiment: possible thanks to: radiation tolerant detectors – selective trigger – high speed DAQ 2.5 T dipole magnet hadron absorber targets beam tracker vertex tracker muon trigger and tracking (NA50) magnetic field >10m<1m ZDC prompt Open Charm (or  ,K   ) Muon Other

4. EPS HEP 2007P. Cortese for the NA60 Collaboration For the first time,  and  peaks clearly visible in dilepton channel; even  μμ seen Mass resolution: 20 MeV at the ω position Progress over CERES statistics: factor >1000 resolution: factor 2-5 Net sample: 440 000 events Low-mass data sample In-In @158 A·GeVBeam intensity=10 7 s -1 230 M trigger with two settings of the muon spectrometer magnet: 6500 A and 4000 A ~50% contain a dimuon, out of them ~60% are matched

5. EPS HEP 2007P. Cortese for the NA60 Collaboration R. Arnaldi et al. (NA60), PRL 96 (2006) 162302 Peripheral collisions: well reproduced by the hadronic cocktail (η, η’, ρ, ω,  ) Central collisions: excess is present isolation of excess by subtraction of the measured decay cocktail (without ρ), based solely on local criteria for the major sources  and  : fixed in such a way to get, after subtraction, a smooth underlying continuum  : yield fixed at p T >1 GeV/c Excess dimuons

6. EPS HEP 2007P. Cortese for the NA60 Collaboration no cocktail  and no DD subtracted clear excess above the cocktail  (bound to the  with  /  = 1.2) excess centered at the nominal  pole rising with centrality all p T Centrality dependence of the excess mass spectra S. Damjanovic et al.(NA60), EPJ C 49 (2007) 235R

7. EPS HEP 2007P. Cortese for the NA60 Collaboration Quantify the contributions of peak and of the broad symmetric continuum with a mass interval “C” around the peak (0.64 <M<0.84 GeV) and two equal side bins “L” and “U” “continuum” = 3/2(L+U) “peak” = C-1/2(L+U) non trivial changes of all three variables at dN ch /dy>100? Excess shape vs centrality peak/  continuum/  peak/continuum

8. EPS HEP 2007P. Cortese for the NA60 Collaboration Predictions by Rapp (2003) for different scenarios Theoretical yields normalized to data for m<0.9 GeV Data and predictions are shown, after acceptance filtering, roughly mirror the  spectral function, averaged over space-time and momenta Only broadening of  (RW) observed, no mass shift (BR) Comparison with theory

9. EPS HEP 2007P. Cortese for the NA60 Collaboration Van Hees and Rapp, PRL97(2006) 102301 Ruppert,Gale,Renk,Lichard and Kapusta, arXiv:0706.1934 Dusling and Zahed, PRC75(2007) 024908 Manifestation of hadron-parton duality? All the results available so far favour broadening with no mass shift Attempts to make mass shifts comptible with data failed so far (see e.g. vanHees and Rapp, hep-ph/0604269) m> 1 GeV: Dominantly hadronic Dominantly partonic Both hadronic and partonic Recent theoretical developments

10. EPS HEP 2007P. Cortese for the NA60 Collaboration Can p T distributions of the excess help in distinguishing between the various scenarios? 2-d acceptance correction (m-p T ), using measured y distributions Flat cos  distribution, as measured  Small centrality dependence, significant mass dependance p T distributions of the excess

11. EPS HEP 2007P. Cortese for the NA60 Collaboration Steepening at low m T : analogy with pion spectra? Not present for the  Fit m T spectra for p T >0.4 GeV with Flattening of spectra with increasing mass (up to m=1 GeV) Above 1 GeV, steepening Mass-dependent radial flow? Transverse mass distributions

12. EPS HEP 2007P. Cortese for the NA60 Collaboration Strong rise of T eff with dimuon mass, followed by a sudden drop for M>1 GeV Rise reminiscent of radial flow of a hadronic source But: thermal dimuons are emitted continuously during fireball expansion (reduced flow), while hadrons are emitted at final freeze- out (maximal flow); how can T eff be similar? Systematic errors studied in great detail (CB, cocktail subtraction, acceptance, y and cos CS distributions)  <= statistical errors. Subtraction of DY for LMR: T eff decreases by few MeV Look at the  region in more detail Inverse slope parameter T eff vs mass

13. EPS HEP 2007P. Cortese for the NA60 Collaboration T eff of peak higher by  70 MeV with respect to the continuum Identify the “  peak” with the freeze-out  in the dilute final stage, when it does not experience further in-medium influences Subtraction of the “hot  ” can be performed m T spectra of  and continuum

14. EPS HEP 2007P. Cortese for the NA60 Collaboration Rise consistent with radial flow of a hadronic source (here ππ→ρ→μμ) Drop signals sudden transition to low-flow source, i.e. source of partonic origin? (here qq→μμ) Break hadron-parton duality? Radial flow of thermal dimuons

15. EPS HEP 2007P. Cortese for the NA60 Collaboration  IMR dimuon spectra in p-A at 450 GeV are described as the sum of Drell-Yan and Open Charm contributions.  The yield observed in heavy-ion collisions (S-U, Pb-Pb) exceeds the sum of DY and Open Charm decays (factor ~2 excess for central Pb-Pb). NA38/NA50 proton-nucleus data central collisions M (GeV/c 2 ) NA50/NA38 measurements of IMR dimuons σ cc (450GeV)=36.2  9.1 μb

16. EPS HEP 2007P. Cortese for the NA60 Collaboration  offset = 40  m < c  (123  m for D 0 ) NA60 measures the (transverse) offset of the muon production point with respect to the interaction vertex J/  muons We use a muon offset   weighted by the error matrix of the fit (eliminate momentum dependence) Then  Good enough to separate prompt production from open charm decays NA60: disentangle prompt and displaced sources

17. EPS HEP 2007P. Cortese for the NA60 Collaboration 4000 A,  2 < 3 Fit of the offset distribution, leaving the normalization of the prompt and open charm contributions as free parameters  2.4 times more prompt dimuons are required with respect to expected Drell-Yan The charm contribution is slightly lower than the extrapolation of NA50 p-A data (which is in turn higher by a factor  2 than the world average) Systematic errors smaller than statistical errors (estimated by comparing various data sets and matching definitions) Fit results show yield with respect to expectations DY: PYTHIA with K=1.9 (consistent with NA3 and NA50) DD:  cc = 13.6  b/nucleon, from dimuon production in p-A (NA50) Excess in the IMR is prompt

18. EPS HEP 2007P. Cortese for the NA60 Collaboration Acceptance correction done differentially in m and p T, assuming flat cos  distribution and rapidity similar to Drell-Yan (  y  1) Syst. errors  DY and DD normalization factors Fit in 0.5<P T <2 GeV/c Excess is prompt with mass shape Steeper than Drell-Yan Similar to open charm (as for PbPb in NA50) T eff much lower than in the low-mass region  disappearance of radial flow? Mass and pT dependence of the excess

19. EPS HEP 2007P. Cortese for the NA60 Collaboration Acceptance corrected The excess is mainly concentrated at low p T Comparing pT shapes in the IMR

20. EPS HEP 2007P. Cortese for the NA60 Collaboration Excess/N participants (arb. scale) acceptance corrected The excess clearly rises faster than the number of participants (probably) faster than the number of collisions Centrality dependence of the IMR excess

21. EPS HEP 2007P. Cortese for the NA60 Collaboration Previous knowledge 1986 – 1992: NA38 experiment (light ions and protons) 1994 – 2000: NA50 experiment (Pb ions and protons) At CERN SPS energy (  s ~ 20 GeV/nucleon)  Study the onset of deconfinement (Matsui and Satz, 1986) Main topics (to be) studied Normal vs anomalous suppression  needs accurate p-A data Scaling variables(s) for the onset of the anomaly  needs comparison between different colliding systems J/  vs  c vs  ’ suppression  needs high statistics (  ’)  needs a sophisticated apparatus (  c  J/   )  Issues presently addressed by NA60 from H. Satz, hep-ph/0609197 J/ψ suppression in nuclear collisions

22. EPS HEP 2007P. Cortese for the NA60 Collaboration Nuclear absorption Nuclear absorption cross section  J/  abs =4.18  0.35 mb extracted from p-A data NA60: first pA data at 158 GeV (avoid systematics related to energy/kinematic rescaling) J/  is suppressed beyond nuclear absorption Rescaled to 158 GeV Calculate the expected J/  yield in case of pure nuclear absorption and compare to In-In, as a function of centrality J/ψ suppression – from pA to In-In

23. EPS HEP 2007P. Cortese for the NA60 Collaboration (  J/  /  DY ) meas /(  J/  /  DY ) nucl. abs (dN J/  /dE zdc ) meas /(dN J/  /dE zdc ) nucl. abs Small statistical errors Systematic errors ~10% centrality independent large for very central events In-In and Pb-Pb suppression patterns compatible in the common N part region Anomalous suppression sets in at 50 < N part <100, corresponding to  Bj ~ 1.5 GeV/fm 3 (  0 =1 fm/c) Results and comparison with PbPb R. Arnaldi et al. (NA60),arXiv:0706.4361, accepted by PRL

24. EPS HEP 2007P. Cortese for the NA60 Collaboration Size of the anomalous suppression reasonably reproduced Quantitative description not satisfactory R.Rapp, EPJ C43(2005) 91 S. Digal et al. EPJ C32(2004) 547 A. Capella et al. EPJ C42(2005) 419 J/  suppression apparently does not depend on collisions energy Many competing mechanisms involved  theoretical interpretation not straightforward Comparison with theoretical predictions and RHIC

25. EPS HEP 2007P. Cortese for the NA60 Collaboration Study limited by statistics (N  ’ ~ 300 in both In-In and p-A) Normalized to Drell-Yan yield Most peripheral point (  N part  ~ 60) does not show an anomalous suppression Good agreement with Pb-Pb results Preliminary! 450, 400 and 200 GeV points rescaled to 158 GeV Also the  ’ value measured by NA60 in p-A at 158 GeV is in good agreement with the normal absorption pattern, calculated from 450 (400) GeV data ’ suppression in In-In and p-A collisions

26. EPS HEP 2007P. Cortese for the NA60 Collaboration Transverse momentum distributions Kinematical region Distributions fitted with 1/p T dN/dp T = e –m T /T Study evolution of T and  p T 2  with centrality If p T broadening is due to gluon scattering in the initial state, then  p T 2  =  p T 2  pp +  gN · L 0.1 < y CM < 0.9 -0.4 < cos  H < 0.4 We get T J/  = 231  2 MeV (integrated over centrality)  seen in the data

27. EPS HEP 2007P. Cortese for the NA60 Collaboration Polarization vs p T, y, centrality Helicity reference system (good coverage in NA60, -0.8<cos  H <0.8) No significant polarization effects as a function of Centrality Kinematical region 0.1<y CM <0.8 0.5<p T <5 0.1<y CM <0.6 0.2<p T <5 Quarkonium polarization  test of production models Deconfinement should lead to a higher degree of polarization (Ioffe, Kharzeev PRC 68(2003) 094013)

28. EPS HEP 2007P. Cortese for the NA60 Collaboration J/ rapidity distributions  y = 0.68  0.02  2 /ndf = 0.60 0<p T <5, -0.4 < cos H < 0.4 Data are consistent with a gaussian rapidity distribution Centrality independent Slightly narrower at high p T ?

29. EPS HEP 2007P. Cortese for the NA60 Collaboration Pion annihilation through an intermediate  is the most important source for the dilepton excess at m< 1 GeV In-medium  spectral function identified; no significant mass shift of the intermediate , only broadening First observation of radial flow of thermal dileptons Open charm production compatible with extrapolations from pA collisions Intermediate mass excess is prompt, concentrated at low p T, and increasing with the number of participants Mass dependence of the m T spectra of the low-intermediate mass excess may be used as a tool to identify the nature of the emitting source; mostly partonic radiation for M>1 GeV? Conclusions (1)

30. EPS HEP 2007P. Cortese for the NA60 Collaboration The anomalous J/  suppression, seen in Pb-Pb collisions by NA50, is confirmed for a lighter system (onset at  Bj ~ 1.5 GeV/fm 3 ) Preliminary results from p-A collisions at 158 GeV show that the normalization of the absorption curve is correct peripheral In-In and Pb-Pb results are compatible with p-A No J/  polarization p T distributions sensitive to initial state effects Conclusions (2)

31. EPS HEP 2007P. Cortese for the NA60 Collaboration The NA60 Collaboration Lisbon CERN Bern Torino Yerevan Cagliari Lyon Clermont BNL Riken Stony Brook Palaiseau Heidelberg BNL 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 ~ 60 people 13 institutes 8 countries