J/ production in p-A collisions at 158 and 400 GeV: new results from the NA60 experiment Introduction Data analysis Differential distributions (xF,pT) Nuclear effects Polarization Outlook/conclusions E. Scomparin (INFN Torino, Italy) for the NA60 Collaboration

Introduction Study of charmonium production/suppression in pA collisions Production models (CSM, NRQCD, CEM, ....) Initial/final state nuclear effects (shadowing, dissociation,...) Reference for understanding dissociation in a hot medium (Relatively) large amount of fixed-target data (SPS, FNAL, HERA) HERA-B (I. Abt et al., arXiv:0812.0734) p-Cu (p-Ti) p-W, 920 GeV, -0.34<xF<0.14, pT<5 GeV E866 (M.J.Leitch et al., PRL84(2000) 3256) p-Be p-Fe p-W 800 GeV,-0.10<xF<0.93, pT<4 GeV NA50 (B. Alessandro et al., EPJC48(2006) 329) p-Be p-Al p-Cu p-Ag p-W p-Pb, 400/450 GeV, -0.1<xF<0.1, pT<5 GeV NA3 (J. Badier et al., ZPC20 (1983) 101) p-p p-Pt, 200 GeV, 0<xF<0.6, pT<5 GeV pA 158 GeV pA 400 GeV Today: new results from NA60

NA60: pA at 158, 400 GeV Data taking at 158 GeV (3-day long) largely motivated by the need of a reference sample taken in the same conditions of InIn (NA60) and Pb-Pb (NA50) data Data at 400 GeV represent the bulk of the NA60 p-A data taking Results shown here Sub-sample with same experimental set-up used at 158 GeV Useful as a cross-check (same energy/kinematic domain of a large statistics data sample collected by NA50) Kinematical window used in this analysis 0.28 < ycm < 0.78 (158 GeV) 3.2 < ylab < 3.7 -0.17 < ycm < 0.33 (400 GeV) | cos CS | <0.5

pA at 158/400 GeV: analysis Muon Other 3106 dimuon events at 158 GeV y106 dimuon events at 400 GeV Total cumulated statistics: hadron absorber Muon Other and tracking Muon trigger magnetic field Iron wall 2.5 T dipole magnet NA10/38/50 spectrometer beam tracker vertex tracker targets Matching in coordinate and momentum space Two analysis approaches 1) Do not use vertex spectrometer information (PC muons only) Advantages: larger statistics Drawbacks: no target ID possible 2) Use vertex spectrometer: track matching (VT muons) Advantages: accurate target ID Drawbacks: smaller statistics (vertex spectrometer efficiency)

Invariant mass spectra and fits Fit the reconstructed invariant mass spectrum as a superposition of the various expected sources: Drell-Yan, J/, ’, open charm 2/ndf = 1.24 DY J/, ’ DD J/ statistics, after analysis cuts 158 GeV, NJ/PC = yy, NJ/VT= zz 400 GeV, NJ/PC = yy, NJ/VT= zz

Relative cross sections We have When calculating the J/ cross section ratios, the beam luminosity factors Niinc cancel out (apart from a small beam attenuation factor), since all the targets were simultaneously exposed to the beam  no systematic errors The acceptance and reconstruction efficiencies do not cancel out completely because each target sees the vertex spectrometer under a (slightly) different angle Need to compute these quantities, and their time evolution for each target separately

Acceptance/efficiency corrections Based on a Monte-Carlo approach Inject realistic VT efficiencies (following time evolution) Finest granularity (at the pixel level where statistics is enough) Use “matching efficiency” as a check of the goodness of the procedure Efficiency map Matching efficiency

Differential distributions: dN/dy 158 GeV 400 GeV y-distribution wider at 400 GeV, as expected Gaussian fit at 158 GeV gives y=0.05±0.05, y=0.51±0.02 Peak position not well constrained at 400 GeV Imposing y=-0.2 (NA50 at 400 GeV) y=0.81±0.03 (NA50 got 0.85)

Comparison with previous experiments HERA-B observes, at 920 GeV, a displacement of the center of the xF distribution towards negative values, increasing with A (by a small amount, xF< 0.01) HERA-B NA50 observes, at 400 GeV, a strong backward displacement (y=0.2, corresponding to xF= 0.045) Mutually incompatible observations ? NA60 data not precise enough to discriminate between the two scenarioes

Differential distributions: dN/dpT pT broadening (Cronin effect) observed at both 158 and 400 GeV

Comparison with previous experiments <pT2>= <pT2>pp+ gN  L Fit pT2 for various nuclei as <pT2>= <pT2>pp+ (A1/3-1) <pT2>pp shows a roughly linear increase vs s Does  increase with √s ? Disagreement NA60 vs NA3 at low energy Agreement NA60 vs NA50 at 400 GeV

Relative cross sections vs A 6.4±0.5 mb at 158 GeV (exp vs L) A-dependence fitted using the Glauber model Shadowing neglected, as usual (but not correct!) at fixed target abs J/ (158 GeV) = 7.6 ± 0.7 mb abs J/ (400 GeV) = 4.3 ± 0.8 mb We get (158 GeV) = 0.882 ± 0.010 (400 GeV) = 0.927 ± 0.013 Using

Relative cross sections: systematic errors The source of systematic errors investigated are connected with: Uncertainty on target thicknesses Uncertainty on the J/ y distribution Uncertainty in the reconstruction efficiency calculation Work in progress

Comparison with first release (HP08) Less oscillations, slopes (almost) identical between HP08/QM09 No “double slope” required to fit the data, very good 2/ndf

Comparison with other experiments (1) Recent results on  vs xF from HERA-B, together with older data from NA50, E866 (no NA3,  biased by use of p-p) In the region close to xF=0, increase of  with √s NA60 400 GeV: very good agreement with NA50 158 GeV: smaller , hints of a decrease towards high xF ?

Comparison with other experiments (2) Pattern vs x1 at lower energies resembles HERA-B+E866 systematics Shadowing effects scale with x2, clearly other effects are present

Comparison with other experiments (3) absJ/ calculated from cross section ratios for HERA-B,E866,NA3 Increase of absJ/ with √s visible NA3 points deviate from general trend (behavior similar to high energy data)

Shadowing at 400/158 GeV We have evaluated (and corrected for) the (anti)shadowing effect expected for our data points, within the EKS98 and EPS08 scheme 158 GeV, EKS98 400 GeV, EKS98 abs J/,EKS (158 GeV)=9.2±0.8 mb abs J/,EPS (158 GeV)=9.8±0.8 mb abs J/,EKS (400 GeV)=5.4±0.6 mb abs J/,EPS (400 GeV)=6.0±0.6 mb The Glauber fit now gives Significantly higher than the “effective” values

Kinematic dependence of nuclear effects Interpretation of results not easy, many competing effects affect charmonia production/propagation in nuclei Main role believed to be played by anti-shadowing (with large uncertainties on gluon pdf !) and final state absorption Other effects (e.g. parton energy loss) complicate the picture First attempt of a systematic study recently appeared (C. Lourenco, R. Vogt and H.Woehri, JHEP 0902:014,2009) No coherent picture still emerges from the data (no obvious scaling of  or abs with any kinematic variable) Extrapolation to 158 GeV gives abs J/ EKS (158 GeV,0<y<1)=7.2±0.5 mb smaller than our measurement (9.2±0.8 mb)

What about anomalous suppression ? Since abs J/ (158 GeV) is significantly larger than at 400 GeV we expect a smaller anomalous suppression with respect to previous estimates Initial state effects (shadowing) affect also the projectile and not only the target  neglected up to now in the determination of the “normal absorption” reference Study of the influence of shadowing in the determination of “normal absorption” reference has been performed (see poster xxx) In the domain 0<y<1 at 158 GeV, neglecting shadowing, there is a ~10% bias in the determination of the reference  sizeable effect

Anomalous suppression (preliminary) Anomalous suppression still visible in PbPb In In-In almost no effect Careful study of systematics in progress!

Viewed from dimuon rest frae Polarization Interesting variable to investigate the production models and their ingredients Theory still evolving (NLO, contribution of color octet states) Significant amount of studies at collider energy (CDF) Not much guidance at fixed target pprojectile Viewed from dimuon rest frae ptarget z axis x y reaction plane decay plane m+  ϕ Influence of final state (deconfined phase) not really studied up to now Reference frames studied Collins-Soper z axis parallel to the bisector of the angle between beam and target directions in the quarkonium rest frame Helicity z axis coincides with the J/ direction in the target-projectile center of mass frame Study the full angular distribution

NA60: first measurement in nuclear collisions Preliminary results ( only) for In-In already presented (QM06) vs transverse momentum vs centrality Npart Polarization signal is rather small everywhere No significant centrality dependence Hint of  > 0 at moderate pT

Preliminary pA results Large errors for  in the CS frame (acceptance large only at small |cosCS|) Similar pattern for in the two reference systems (slightly >0)

Comparison with HERA-B Results from HERA-B recently published (I. Abt et al., arXiv:0901.1015) Helicity Collins-Soper No large differences between NA60 and HERA-B Feedback from theory urgently needed

Conclusions/outlook New results for pA collisions at 158 and 400 GeV Energy/kinematic domain already investigated (with higher statistics) by NA50  good agreement on differential spectra and nuclear effects 158 GeV Same kinematic domain of NA50/NA60 A-A collisions Nuclear effects more important wrt 400 GeV Anomalous suppression becomes smaller Overall picture of cold nuclear effects on pA still not clear No scaling of  with any investigated variable First results on J/ polarization in A-A and p-A collisions No strong polarization (both  and ) effects Input from theory is necessary

The NA60 collaboration http://cern.ch/na60 Lisbon CERN Bern Torino Yerevan Cagliari Lyon Clermont Riken Stony Brook Palaiseau Heidelberg BNL ~ 60 people 13 institutes 8 countries 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. Damjanović, A. David, A. de Falco, N. de Marco, A. Devaux, A. Drees, L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A.A. Grigoryan, J.Y. Grossiord, N. Guettet, A. Guichard, H. Gulkanyan, 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, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht, R. Tieulent, E. Tveiten, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri

Fit 158 GeV sigma_y=0.60

Shadowing EPS fit

Comparison with other experiments (3) Clearly no scaling with √sN

Kinematic dependence of  NA60 values integrated over xF Kinematical window 3.2<ylab<3.7

Kinematic dependence of abs