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Highlights from NA60 and other SPS experiments

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Presentation on theme: "Highlights from NA60 and other SPS experiments"— Presentation transcript:

1 Highlights from NA60 and other SPS experiments
Gianluca Usai – INFN and University of Cagliari (Italy) QM06 Shanghai - 14/11/2006

2 Outline of this talk Highlights of results from SPS experiments shown at this conference (in several parallel talks and posters) CERES (high pT correlations) WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y)

3 CERES (high pT correlations)
WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y)

4 High pT azimuthal correlations and QGP effects
Data: 2000 run, pions identified in TPC  higher pT coverage Select 2.5<pTtrig<4 GeV/c and 1.0<pTassoc<2.5 GeV/c (same as Phenix) At higher pT distinct change in shape of away-side peak Correlation function between 2 high pT particles Contains elliptic flow plus jet-like correlation

5 Comparing CERES and RHIC
PHENIX features very similar at RHIC and SPS 3-particle correlations to distinguish different physics interpretations of shape – study in progress nucl-ex/

6 3-particle correlations – raw: one trigger particle 2-4 GeV/c, two more between 1-2.5 GeV/c
all charge combinations ti tj  like-sign unlike-sign these raw correlations need to be corrected for elliptic flow effects

7 3-particle correlations: yields of non jet-jet contribution corrected by Monte Carlo simulations of flow induced correlations Yield of away side pairs per trigger correlation function a.u. Df(rad) Indication of cone structure on the away side  needs further investigation S. Kniege, Parallel 1.3

8 CERES (high pT correlations)
WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y)

9 RAA in Pb+Pb at sNN = 17.3 GeV with Measured Reference Data
p+Pb reference measured at same energy: Pb+Pb, % most central p+Pb reference p0 nuclear overlap function preliminary p+Pb reference partially takes out Cronin effect expected in Pb+Pb Suppression in central Pb+Pb possibly due to parton energy loss p+Pb reference RAA (2 < pT < 2.5 GeV/c) preliminary

10 CERES (high pT correlations)
WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y)

11 Nuclear Suppression Factors at the SPS
RpA and RAA with p+p Baseline RAA with p+A Baseline -0.3 < y < 0.7 (+ + -)/2 (+ + -)/2 NA49 preliminary -0.3 < y < 0.7 SPS RpA RAA NA49 preliminary RHIC Suppression factors for p+Pb and Pb+Pb reach hard scattering expectation at pt = 2GeV/c Limited p+p statistics prevents measurement at higher pt Cronin effect removed by p+A baseline Only small suppression at SPS observed C. Blume, Parallel 3.1

12 Energy dependence of fluctuations in central Pb-Pb collisions
strangeness multiplicity transverse momentum NA49 data: Roland Lungwitz Grebieszkow -a significant increase of strangenss fluctuations at low SPS energies is observed, it may be related to the onset of deconfinement -the energy dependence is smooth for multiplicity and transverse momentum fluctuations R. Lacey, Parallel 3.4 G. Stefanek - poster

13 Net-Baryon Distributions and Rapidity Shifts in Central A+A Collisons at the SPS
NA49 preliminary Rapidity shift NA49 preliminary Clear evolution of shape of dn/dy distributions at SPS  Rapid decrease of net-baryon density at mid-rapidity Rapidity shift of participant nucleons is a constant fraction of beam rapidity at AGS+SPS BRAHMS Phys. Rev. Lett. 93 (2004), Net-baryons n(B-B) 158A GeV Phys. Rev. Lett. 82 (1999), 2471 E802 Phys. Rev. C 60 (1999), Scaling factors SX taken from statistical model fits (F. Becattini et al., Phys. Rev. C 73 (2006), ) C. Blume, QM06 Parallel 3.1

14 CERES (high pT correlations)
WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y)

15 NA50: J/ elliptic anisotropy in Pb-Pb collisions at 158 AGeV/c
J/ azimuthal anisotropy with respect to the reaction plane Estimate of the event-plane resolution is still under study F. Prino, poster Not corrected for event plane resol. More J/’s exiting “in plane” than “out of plane”  positive J/ v2 Observed anisotropy: probably not due to elliptic flow (i.e. collective motion) Because charm thermalization and J/ formation from recombination are not likely at SPS energies Could originate from anisotropic cc absorption in the medium due to: cc dissociation by hard gluons in the QGP or J/ breakup by comoving hadrons _ _

16 CERES (high pT correlations)
WA98 (high pT nuclear suppression factors) NA49 (high pT nuclear suppression factors, baryon stopping, fluctuations) NA50 (J/Y elliptic anysotropy) NA60 (low and intermediate mass dimuons, J/Y, Y’)

17 Low dimuon masses – NA60 In-In data
Search for in-medium modifications of vector mesons Isolating the excess by subtracting the cocktail Phys. Rev. Lett. 96 (2006) f  and : fix yields such as to get, after subtraction, a smooth underlying continuum :  set upper limit, defined by saturating the measured yield in the mass region close to 0.2 GeV (lower limit for excess).  use yield measured for pT > 1.4 GeV/c

18 Excess spectra from difference
Fine analysis in 12 centrality bins data – cocktail (all pT) No cocktail r and no DD subtracted Clear excess above the cocktail , centered at the nominal r pole and rising with centrality Excess even more pronounced at low pT cocktail / =1.2

19 Evolution of the excess shape as a function of centrality
Quantify the peak and the broad symmetric continuum with a mass interval C around the peak (0.64 <M<0.84 GeV) and two equal side bins L, U “continuum” = 3/2(L+U) “peak” = C-1/2(L+U) Fine analysis in 12 centrality bins continuum/r Peak/cocktail r drops by a factor 2 from peripheral to central: the peak seen is not the cocktail r peak/r nontrivial changes of all three variables at dNch/dy>100? peak/continuum

20 Description of the mass region below 1 GeV
dropping r mass ruled out by data hadronic models predicting strong broadening/no mass shift in fair agreement with data Calculations for In-In by Rapp et al. (11/2005) for <dNch/d> = 140 Improved model: Fireball dynamics 4 p processes spectrum described in absolute terms Baryons important in the low mass tail

21 Hadron-parton duality?
Description of the mass region above 1 GeV Rapp/Hees hep-ph/ (2006) Ruppert / Renk, Phys.Rev.C (2005) Mass region above 1 GeV described in terms of hadronic processes, 4 p …, sensitive to vector-axialvector mixing and therefore to chiral symmetry restoration! Mass region above 1 GeV described in terms of partonic processes, dominated by qqbar annihilation Hadron-parton duality?

22 Acceptance corrected excess pT spectra
2-dimensional acceptance correction in M-pT (use measured y distribution as an input) hardly any centrality dependence significant mass dependence 0.4<M<0.6 GeV 0.6<M<0.9 GeV 1.0<M<1.4 GeV

23 Trend at small mT opposite to what expected from radial flow
High mass interval shows steepest slope  smaller T slope differential fits with gliding windows of pT=0.8 GeV  local slope Teff Teff dynamic range not compatible with flow alone (assuming one component only) At high pT, r-like region hardest, high mass region softest! J. Seixas, QM06 Parallel 3.3

24 No theoretical model able to account completely for all of the features of the pT spectra at present!

25 Intermediate dimuon masses (IMR – 1.1<mmm<2.5 GeV)
Observed IMR excess in In-In over expected Charm and Drell-Yan yields. What is it? NA60 measures the muon offsets Dm: distance between interaction vertex and track impact point Dimuon offset Fix prompt contribution to the expected DY – leave open charm free Leave both DY and open charm yields free Good Fit Bad Fit The excess is a prompt source 1.6 times higher than the expected DY yield

26 Centrality dependence of the excess
Slight increase as a function of number of participant with respect to Drell-Yan preliminary

27 Mass spectrum (1.16<M<2.56 GeV/c2)
Contributions to IMR corrected for the acceptance in < cos  < < ylab < 3.92 (both 4000 and 6500 A data sample used) preliminary

28 pT dependence of the excess (1.16<M<2.56 GeV/c2)
No acceptance correction 6500 A High pT tail strongly depends on the correctness of Drell-Yan description by Pythia  Teff fits are performed in 0< PT <2.5 GeV/c preliminary Corrected for acceptance Corrected for acceptance

29 Towards a “unification” of low and intermediate dimuon mass regions: evolution of excess Teff vs Mmm
preliminary R. Shahoyan, QM06 Parallel 3.3

30 Direct J/ sample – NA60 InIn data
The measured J/ EZDC distribution is compared to the distribution expected in case of pure nuclear absorption Normalization of the nuclear absorption curve Ratio measured/expected, integrated over centrality, fixed to the one of J//DY analysis (0.87 ± 0.05) E. Scomparin, QM06 Plenary 12

31 pT2 vs centrality If pT broadening is due to gluon scattering in the initial state  pT2 = pT2pp + gN · L NA60 In-In points are in fair agreement with Pb-Pb results We get gNInIn =  (GeV/c)2/fm pT2ppInIn = 1.15  0.07 (GeV/c)2 2/ndf = 0.62 to be compared with gNPbPb96 =  (GeV/c)2/fm pT2ppPbPb96 = 1.10  0.03 (GeV/c)2 2/ndf = 1.38 gNPbPb =  (GeV/c)2/fm pT2ppPbPb = 1.19  0.04 (GeV/c)2 2/ndf = 1.22 (NA event sample)

32 J/ polarization Quarkonium polarization  test of production models
CSM: transverse polarization CEM: no polarization NRQCD: transverse polarization at high pT Deconfinement should lead to a higher degree of polarization (Ioffe,Kharzeev PRC 68(2003) ) 0.5 < pT < 5 GeV 0.1 < yCM < 0.6 0 < pT < 5 GeV 0.4 < yCM < 0.75 H = 0.03  0.06 CS =  0.17 2/ndf =1.01 2/ndf =1.42

33 (J/)/DY at 158 GeV (J/)/DY = 29.2  2.3 L = 3.4 fm Preliminary! Preliminary NA60 result shows that the rescaling of the J/ production cross section from 450(400) GeV to 158 GeV is correct ! Next step: obtain absJ/ at 158 GeV

34 ’ suppression in In-In and pA collisions
Study limited by statistics in In-In (N’ ~ 300) Normalized to Drell-Yan yields In-In: Preliminary! Most peripheral point (Npart ~ 60) does not show an anomalous suppression Good agreement with Pb-Pb results pA: Also the ’ value measured by NA60 at 158 GeV is in good agreement with the normal absorption pattern, calculated from 450 (400) GeV data

35 Correlation between J/ and low mass excess?
RMS of total low mass excess Low mass excess Step position Meas/Exp 1 A1 A2 Npart Step at Npart = 86 ± 8 ( Bj ~ 1.6 GeV/fm3 ) A1= 0.98 ± 0.02 A2= 0.84 ± 0.01 Non trivial changes of J/ pattern and low mass excess both at ~ 100 Npart

36 Conclusions SPS data are still being analyzed and new results produced
S. Kniege, CERES 1.3 C. Blume NA49 3.1 K. Reygers, WA98 2.2 Nuclear suppression factors and high pT correlations Hadron physics, fluctuations C. Blume, NA49 3.1 R. Lacey, NA49 3.4 G. Stefanek, NA49 poster J/Y azimuthal anysotropy F. Prino, NA50 poster Dilepton physics: in medium modifications of the r meson excess in intermediate dimuon mass J/, ’ suppression J. Seixas, NA60 3.3 R. Shahoyan, NA60 3.3 E. Scomparin, NA60 plenary 12

37 A word on future perspectives
Besides still ongoing analyses ... NA49 has submitted a proposal for a new experiment to look for the onset of deconfinement studying hadron production, in particular fluctuations and long range correlations as a function of energy and collision system (SPSC-P-330) Also NA60 would have interest to complete its program with Pb ions

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