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J/  suppression in p-A and In-In collisions at 158 GeV/nucleon

J/  suppression in p-A and In-In collisions at 158 GeV/nucleon. R. Arnaldi – INFN Torino (Italy) for the NA60 Collaboration. Introduction J/  suppression in In-In collisions New results from p-A collisions at 158 GeV  study of the p T distributions and

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J/  suppression in p-A and In-In collisions at 158 GeV/nucleon

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  1. J/ suppression in p-A and In-In collisions at 158 GeV/nucleon R. Arnaldi – INFN Torino (Italy) for the NA60 Collaboration • Introduction • J/ suppression in In-In collisions • New results from p-A collisions • at 158 GeV •  study of the pT distributions and • comparison with In-In • v2 of the J/ in In-In • Conclusions

  2. In-In Pb-Pb J/ suppression at SPS energy • Nuclear collisions results: Pb-Pb (NA50) and In-In (NA60) • p-A reference results: from p-A collisions at 400/450 GeV (NA50) R. Arnaldi et al. (NA60), PRL99, 132302 (2007) • Observed suppression exceeds nuclear absorption • Onset of the suppression at Npart 80 • Comparison between different systems  Npartscaling • At RHIC (s  10 sSPS) a very similar suppression pattern is observed

  3. (J/)/DY = 29.2  2.3 L = 3.4 fm Nuclear absorption reference • MeasuringJ//DYin p-A collisions at400/450 GeV, NA50 extracts • (Glauber analysis)absJ/ = 4.2±0.5mb, and (J//DY)pp =57.5±0.8 • The expected J/ yield for In-In and Pb-Pb collisions is calculated • assumingabsJ/ (158 GeV) = absJ/ (400/450 GeV) • rescaling (J//DY)pp to 158 GeV with a semi-theoretical procedure • Preliminary pA results from NA60 at 158GeV • (averaged over nuclear targets) seem to • validate the nuclear absorption normalization • extracted from 400/450 GeV data • Results on absJ/ will appear soon (HP08) •  crucial to confirm (or modify) the anomalous suppression pattern Preliminary!

  4. J/transverse momentum At SPS energy, previous results by NA50 seem to indicate that the shape of the pT distributions of the J/ are dominated by initial state effects (multiple scattering of the incoming gluons, i.e. Cronin effect) • Main features: • pT2 (and T) linearly increase with L (mean thickness of nuclear matter) • Phenomenological description with • the expression with an energy dependent pT2ppand a common slope: gN= 0.081±0.002 (GeV/c)2/fm pT distributions for pA and AA never studied in the same energy/kinematical range

  5. W p-In Pb Cu In U Be Al p-A collisions at 158 GeV • A target system including 7 different nuclei (Be, Al, Cu, In, W, Pb, U) has been used • Accurate target ID thanks to the NA60 vertex spectrometer (pixel) pCu • Mass resolution: 100 MeV at the J/, 40 MeV at the  • Under the J/ • Combinatorial background is zero • Drell-Yan contribution is small (<2%)  A simple event counting technique can be used to extract NJ/

  6. Al In Pb Study of pT distributions in pA at 158 GeV • The pT distributions of the J/ have been obtained using a 1D acceptance • correction method • The input distributions for the other kinematical variables (y, cosCS)have been obtained starting from a 3D correction algorithm and then adjusted iteratively on the data • y distribution  gaussian with y=0.52 • cosCS distribution  flat • (no J/ polarization) • Rapidity coverage 0<yCM <1 • Same as in NA50(Pb)/NA60(In) •  extrapolation needed for • upstream targets

  7. pT distributions for 158 GeV pA Distributions fitted with the function 0<ycm<1 |cos|<0.5 in order to obtain the inverse slope Teff values Teff valuesslightly increase with A

  8. mT distributions for 158 GeV pA In the explored mT-M range, no deviations from the exponential behaviour can be appreciated

  9. <pT2>pp=1.13 ± 0.04 (GeV/c)2 gN=0.029 ± 0.011 (GeV/c)2/fm Pb W U Cu In Al Be Dependence of pT2 on L • Systematic errors are mainly • due to the choice of the • generated y and cos • distributions in the • acceptance calculations smaller than statistical errors • Applying more severe event • selection cuts there is no • effect on the results We observe a linear increase of <pT2> with L, consistent with gluon scattering in the initial state

  10. Comparison p-A vs In-In (Pb-Pb) For the first time we compare the transverse momentum distributions of the J/ in p-A and A-A, in the same energy/kinematical range p-A <pT2>pp=1.13 ± 0.04 (GeV/c)2 gN=0.029 ± 0.011 (GeV/c)2 /fm In-In <pT2>pp=1.27 ± 0.09 (GeV/c)2 gN=0.058 ± 0.014 (GeV/c)2 /fm Pb-Pb <pT2>pp=1.19 ± 0.04 (GeV/c)2 gN=0.072 ± 0.005(GeV/c)2 /fm • pT2 increases linearly with L in both p-A, In-In and Pb-Pb • However, the scaling of pT2 with L is broken moving from p-A to A-A • On one hand comparing p-A and peripheral In-In the suppression scales with L • On the other hand the J/ pT distributions do not scale with L ! • gNAA~ 2 gNpA does one simply add up projectile and target broadening ?

  11. Comparison p-A In-In vs. Npart We find an approximate scaling of pT2 with the logarithm of the number of participant nucleons

  12. Comparison pA 158 GeV vs pA 400 GeV • NA60 has also taken p-A data at 400 GeV, i.e. in the same energy and kinematical • domain covered by p-A data previously collected by NA50 • Compare (as a check) the results of the two experiments • The slope of the p-A points at 400 GeV • is compatible between NA50 and NA60 • (1.2 ) NA50 p-A 400 GeV gN=0.087 ± 0.004 NA60 p-A 400 GeV gN=0.104 ± 0.013 New 158 GeV data show that at SPS gN depends on the energy of the collision

  13. RAA 0-1.5% 1.5-5 % 5-10% 10-16% 16-23% 23-33% 33-47% 47-57% pT (GeV/c) RAA for In-In at 158 AGeV • We have not measured reference p-p collisions at 158 GeV • Build a J/ pT distribution using the functional form with T obtained from the value of pT2 pp coming from the fit of the p-A data

  14. RAA for In-In at 158 AGeV (2) • Clear rise at high pT consistent • with the Cronin effect • RAA much lower than 1 at low pT • Effect seen dominated bynuclear absorption • A systematic error (11%) due to • the data normalization is common • to all points

  15. 1.5-5% 5-10% 10-16% 0-1.5% RCP 23-33% 16-23% 33-47% pT (GeV/c) RCPfor In-In at 158 A GeV Normalize pT distributions to the most peripheral In-In bin, corresponding to Npart50 We see that moving towards central collisions there is an increasingly large suppression at low pT (already seen in Pb-Pb)

  16. Comparison with PHENIX RAA similar at SPS and RHIC at low transverse momentum (pT < 1.5 GeV/c)

  17. v2 h± v2 measurements at NA60 • NA60 acceptance: ~ 0 < ycm < 1 • Use elliptic flow v2 to estimate the reaction plane (v1 = 0 at midrapidity)‏ • Determination from charged particle tracks as measured in the vertex tracker v2 for charged particles

  18. central peripheral J/ azimuthal anisotropy (1) • Limited statistics (<30000 J/ events) prevents a fine binning in centrality/pT • Define 2 broad centrality classes v2 consistent with zero for central events, v2 > 0 (2.3) for peripheral

  19. J/ azimuthal anisotropy (2) • Introduce a rough pT binning • In spite of the relatively low statistics, we see an anisotropy for peripheral events, • concentrated at high pT • Hardly a signal of elliptic flow (charm collective motion), since at SPS • Ncc is low (no recombination) • Difficult to have charm thermalisation • Effect likely to be connected with anisotropic absorption in QGP/nuclear matter

  20. Conclusions • First results on the J/ transverse momentum distributions in pA at 158 GeV • We observe a linear increase of <pT2> with L, consistent with gluon scattering • in the initial state • However • The slope is smaller than in In-In and Pb-Pb at the same energy • Peripheral In-In and p-A collisions with approximately the same L • have <pT2> different by ~ 200 MeV • The J/suppression scales with L in p-A and peripheral In-In and Pb-Pb • The L scaling is broken when looking at the pT distributions • First results on the v2 of the J/ at SPS energy • v2 significantly larger than zero for non central events at pT >1 GeV/c • Effect likely to be connected with anisotropic absorption • in QGP/nuclear matter • One key ingredient in the overall J/ suppression picture still missing •  absJ/ (158 GeV) • Results are coming…. stay tuned!

  21. CERN Heidelberg Bern Palaiseau BNL Riken Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon The NA60 Collaboration http://cern.ch/na60 ~ 60 people 13 institutes8 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

  22. Backup

  23. prompt or ! displaced Iron wall magnetic field 2.5 T dipole magnet beam tracker vertex tracker targets hadron absorber ZDC Muon Other Matching in coordinate and momentum space Origin of muons can be accurately determined Improved dimuon mass resolution:  ~20 MeV/c2 (vs. 80 MeV/c2) J/ ~70 MeV/c2 (vs. 105 MeV/c2) The experimental apparatus Muon trigger and tracking (NA10/NA38/NA50 spectrometer)

  24. DY a) DY subtracted DY not subtracted b) Influence of Drell-Yan contamination • The Drell-Yan contribution under the J/ is ~ 2% • and its pT distribution is not known p-Pb • Describe the Drell-Yan pT shape with the • same function used to fit the J/ distributions • Assume the usual dependence of pT2 on L, • <pT2> = <pT2>pp + qN * L, with qN = 4/9 gN • Use pT2pp = 1.25 (GeV/c)2, as given by PYTHIA • 2 assumptions for qN: • a) qN = 0 (no dependence on L) • b) qN = 4/9  0.081(GeV/c)2/fm (dependence on L as measured by NA50 in PbPb) Teff changes by less than 0.4 MeV pT2 changes by less than 0.01 (GeV/c)2

  25. <pT2> vs NPart

  26. Comparison p-A and In-In Comparison peripheral In-In vs p-Pb

  27. <pT2> vs L – different y ranges p-A <pT2>pp=1.13 ± 0.04 (GeV/c)2 gN=0.029 ± 0.011 (GeV/c)2 /fm p-A <pT2>pp=1.14 ± 0.04 (GeV/c)2 gN=0.015 ± 0.012 (GeV/c)2 /fm

  28. RAA*(pT) for In-In at 158 AGeV • In p-A we find a good correlation between pT2 (and therefore T) and L • Effects connected with Cronin and nuclear absorption should scale with L • Extrapolate T to the L values reached in In-In and build the corresponding pT • distribution, which is then used to normalize the measured In-In distributions But we still observe an enhancement at high pT (is the L extrapolation from p-A to A-A a good one?) The suppression effect is mainly present at low pT

  29. RAA

  30. Systematic errors

  31. Comparison with theoretical predictions A. Capella, E. Ferreiro EPJ C42(2005) 419 R.Rapp, EPJ C43(2005) 91 S. Digal, S. Fortunato, H. Satz, EPJ C32(2004) 547 centrality dependent t0 fixed termalization time t0 Dissociation and regeneration in QGP and hadron gas Percolation, with onset of suppression at Npart~140 Suppression by hadronic comovers (co = 0.65 mb, tuned for Pb-Pb collisions) • Size of the anomalous suppression reasonably reproduced • Quantitative description not satisfactory

  32. Maximum hadronic absorption • Compare J/ yield to • calculations assuming • Nuclear absorption • Maximum possible • absorption in a • hadron gas • (T = 180 MeV) L. Maiani et al., Nucl.Phys. A748(2005) 209 F. Becattini et al.,Phys. Lett. B632(2006) 233 • Both Pb-Pb and (to a lesser extent) In-In show extra-suppression

  33. J/ suppression in In-In collisions

  34. ’ in In-In collisions • Use matching of muon spectrometer tracks • Study limited by statistics (N’~ 300) • Normalized to Drell-Yan yields 450, 400 and 200 GeV points rescaled to 158 GeV • Most peripheral point • (Npart ~ 60) does not show • an anomalous suppression • Good agreement with • Pb-Pb results Preliminary

  35. Preliminary! ’ in p-A collisions 450, 400 and 200 GeV points rescaled to 158 GeV ’/DY = 0.51  0.07 L = 3.4 fm Also the ’ value measured by NA60 at 158 GeV is in good agreement with the normal absorption pattern, calculated from 450 (400) GeV data

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