1 / 20

Study of the J/ y production and suppression in Indium-Indium collisions at the CERN SPS

m. m. Study of the J/ y production and suppression in Indium-Indium collisions at the CERN SPS. Outline of the presentation: Physics motivation of NA60 Overview of the detector concept First results from the 2003 Indium run. Alberto Colla - INFN Torino, Italy for the NA60 Collaboration.

xanthe
Download Presentation

Study of the J/ y production and suppression in Indium-Indium collisions at the CERN SPS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. m m Study of the J/y production and suppression in Indium-Indium collisions at the CERN SPS • Outline of the presentation: • Physics motivation of NA60 • Overview of the detector concept • First results from the 2003 Indium run Alberto Colla - INFN Torino, Italy for the NA60 Collaboration Hot Quarks 2004 July 18 - 24, Taos Valley, NM, USA

  2. 1) 2) 3) NA50Pb-Pb 158 GeV CERESPb-Au 158 GeV _ DY DD DY charm central collisions M(GeV) M(GeV) The low mass dielectron data collected in heavy-ion collisions (S-Au, Pb-Au) exceeds the expected sum of light meson decays, which describes the proton data The yield of intermediate mass dimuons seen in heavy-ion collisions (S-U, Pb-Pb) exceeds the sum of Drell-Yan and D meson decays, which describes the proton data Heavy ion collisions and dilepton probes (a) • Dileptons produced in heavy-ion collisions are very useful probes for the study of the QCD phase transition from hadron to quark-gluon matter • Since 1986 a systematic measurement of dilepton spectra from high energy collisions has been carried out at the CERN SPS by various experiments (NA38, NA50, CERES …). • Many interesting results were found:

  3. 3) sabs L. Ramello (NA50 Coll.), QM 2002 sabs Pb-Pb data: J/y anomalously suppressed in central collisions Heavy ion collisions and dilepton probes (b) The J/y production is suppressed in heavy-ion collisions (Pb-Pb) with respect to the yields extrapolated from proton-nucleus data NA50 p-A and S-U data: J/y absorption in “normal” nuclear matter, with (*) (*)G. Borges (NA50 Coll.), QM 2004

  4. Specific questions that remain open What is the origin of the low mass dilepton excess? need much more statistics, better signal to background ratio and mass resolution  resolve the w peak  study the signal versus pT and collision centrality Is the intermediate mass excess due to thermal dimuons from a quark-gluon plasma? What is the open charm yield in nucleus-nucleus collisions?  measure secondary vertices with ~ 50 µm precision  separate prompt dimuons from D meson decays What is the physics variable driving the J/y suppression? L, Npart, energy density? Are the charmonium states broken by deconfined quarks and gluons?  measure the J/y pattern in Indium-Indium and compare it with Pb-Pb Which fraction of J/ comes from c decays(cc → J/y + g) ? What is the impact of the cc feed-down on the observed J/y suppression pattern? study the nuclear dependence ofcc production in p-A collisions NA60 New and accurate measurements are needed

  5. CERN Heidelberg Bern Palaiseau BNL Riken Yerevan Stony Brook Torino Lisbon Cagliari Clermont Lyon The NA60 Experiment http://cern.ch/na60 Idea: place a high granularity and radiation-hardsilicon tracking telescope in the vertex regionto measure the muons before they suffer multiple scattering and energy loss in the absorber ~ 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. 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

  6. ~ 1m Muon Spectrometer Iron wall Hadron absorber Toroidal Magnet MWPC’s Target area m beam m Trigger Hodoscopes ZDC Dipole field2.5 T • Matching in coordinate • and momentum space • Origin of muons can be accurately determined • Improved dimuon mass resolution TARGET BOX MUON FILTER  BEAM BEAMTRACKER VERTEX TELESCOPE IC muon pair fromdisplaced vertices prompt dimuon not on scale ZDC dimuon studies vs. collision centrality  or NA60’s detector concept

  7. The NA60 target region: reality 2.5 T dipole magnet Pixel detectors Beam Tracker Two stations of 50 mm pitch micro-strip detectors Operated at 130 K  increased radiation hardness ~ 100 pixel detectors (radiation tolerant)in 11 tracking points; cells = 50 × 425 µm2

  8. Indium beam 158 A GeV A first look at the Indium data Broad centrality coveragemeasured by the ZDC and by the number of clustersseen in the Vertex Telescope Before event selection • 5-week long run in Oct.–Nov. 2003 • Indium beam of 158 GeV/nucleon • ~ 4 ×1012 ions delivered in total • ~ 230 million dimuon triggers on tape N. Clusters in VT EZDC After event selection • Opposite-sign dimuon • mass distributions • Before quality cuts • No muon matching • Two spectrometer settings N. Clusters in VT (~47% statistics left) dN/dMmm (Events/50 MeV) EZDC Transverse vertexingwith 20 µm accuracy(and < 200 µm in Z) 7 In targets (80% of collected statistics) target boxwindows 4000 A Beam tracker station (100% of collected statistics) 6500 A Mmm (GeV) z-vertex (cm)

  9. all events after rejecting beam pile-up& non-interacting beam ions all events after rejecting beam pile-up after muon quality cuts & in dimuon phase space window & non-interacting Indium ions EZDC distributions and data selection for high mass dimuon analysis Minimum bias (ZDC) trigger Dimuon trigger • Beam pile-up is rejected using Beam Tracker timing information • Non-interacting beam ions are rejected using Interaction Counter • Severe quality cuts have been used in this preliminary analysis (statistics will increase in the future, especially for peripheral collisions) • Dimuon data analysis performed for events with EZDC < 15 TeV • and in the phase space window: 0 < ycms < 1 ; |cos CS| < 0.5

  10. DY yield = 162± 131302 ± 104in range 2.9–4.5 GeV J/y yield = 23532 ± 298 Understanding the opposite-sign dimuon mass distribution Dimuon data from the 6500 A event sample No muon track matching used in this analysis Mass resolution at the J/y : ~100 MeV Combinatorial background from  & K decays estimated from the measured like-sign pairs Signal mass shapes from Monte Carlo:PYTHIA with MRS A (Low Q2) parton densitiesGEANT 3.21 for detector simulation reconstructed as the measured data Acceptances from Monte Carlo simulation:  for J/y : 12.4 %  for DY: 13.4 % (in window 2.9–4.5 GeV) Background J/y Charm y’ DY A multi-step (max likelihood) fit is performed:a) M > 4.2 GeV : normalise the DY b) 2.2<M<2.5 GeV: normalise the charm (with DY fixed) c) 2.9<M<4.2 GeV: get the J/y yield (with DY & charm fixed)

  11. Projectile J/y L Target J/y / Drell-Yan in Indium-Indium collisions preliminary B s(J/y) / s(DY) = 19.5 ± 1.6  0.87 ± 0.07 w.r.t. the absorption curve In-In collisions of EZDC < 15 TeV L = 7.0 fm(from Glauber fit to the minimum bias EZDC distribution) and Npart = 133 all data rescaled to 158 GeV • Stability checks: • Background increase by 10% : less than 3% change • Different event selection or fitting procedure : less than 8% change • Using GRV parton densities instead of MRS :0.87 ± 0.07  0.93 ± 0.08

  12. After event selection Beam Tracker Trigger Dimuon trigger Comments and on-going analysis - 1 study of the centrality dependence of the J/y suppression in several binscannot use the measured Drell-Yan events, due to the low statistics alternative analysis in progress, with the Drell-Yan yield estimated from a Glauber analysis of the Minimum Bias EZDC distribution 2 independent Minimum Bias triggers in NA60:  minimum amount of signal in the ZDC  Indium ion crossing the Beam Tracker EZDC spectra of Beam Trackerand Dimuon triggers The J/y and “DY” EZDC distributions will be obtained withtwo different triggers it is crucial to verify: • the time stability of the dimuon and MB triggers • the influence of any possible trigger timing bias on the ZDC signal acquisition. An analysis of the ZDC signals in the three NA60 triggers was performed: • Stability of the trigger timing confirmed • Small (~5%) timing biases found and corrected. After the corrections, we see the same trend inboth EZDC spectra, for central events EZDC (GeV)

  13. First plots of high mass dimuon spectra after muon track matchingbetween the Vertex Telescope and the Muon Spectrometer With event selection Without event selection Before track matching After track matching Before track matching After track matching dN/dMmm (Events/50 MeV) dN/dMmm (Events/50 MeV) Mmm (GeV) Mmm (GeV) Comments and on-going analysis - 2 • dimuon matching efficiency: ~ 70% at the J/y • mass resolution at the J/yimproves from ~100 MeV to ~70 MeV • track matching useful to get rid of combinatorial background and out-of-target events cleaner spectrum

  14. Low mass dimuon production in Indium-Indium collisions from a preliminary analysis of a very small event sample … mass resolution :20–25 MeV at M ~ 1 GeV less than 1 % of total statistics f w no centrality selection S/B ~ 1/4 opposite-sign signal combinatorial background • With respect to the Pb-Au CERES data: • factor ~ 700higher effective statistics • Mass resolution ~2%, better by a factor 2 • Full information on associated track multiplicity • Completely different systematic uncertainties • The 2.5 T dipole field allows for good pT coverage down to very low dimuon masses • Combinatorial background resulting from p and K decays estimated through a mixed-event technique, using like-sign muon pairs. • The normalization is still preliminary.

  15. Summary and outlook • Harvest from the 5-week long Indium run in Oct.–Nov. 2003: • ~ 1 million signal low mass dimuons (after track matching) • mass resolution~ 20–25 MeV at the w and f masses • more than 100 000 reconstructed J/y events (before track matching) • first results on the analysis of the J/y suppression in In-In and comparison with NA50 • analysis of the centrality dependence of the J/y on the way; results soon available • To understand the heavy-ion results we need a solid reference baseline from p-A data • NA60 is about to take ~ 70 days of 400 GeV protons, for an expected integrated luminosity of ~ 5•104 nb-1, with 7 different nuclear targets, to study: • the impact of cc production on the J/y suppression • the nuclear dependence of open charm production • the intermediate mass prompt dimuons • the low mass dimuons with unprecedented accuracy • (*) latest news: 1 week with a 158 GeV proton beam, to compare p-A, In-In and Pb-Pb data without introducing model-dependent rescaling factors • Together with the proton run of 2004, NA60 should be able to : • study the production of low mass dimuons, including the r, w and f resonances • clarify the cause of the excess of intermediate mass dimuons in heavy-ion collisions • improve the understanding of the production and suppression of charmonium states

  16. Backup slides

  17. Standard analysis of J/y/DY : event selection Dimuon trigger event selection: 2.9<M<3.3 GeV % diff + Beamscope Pixel Pl.7 -27% % diff + Beamscope + Int. Counter -13% + Glob.Cut 10% % diff + Int. Counter -23% % diff + Glob.Cut 10% + Y, CosCS 47% of initial ev. -4% EZDC

  18. p-A Impact ofccproduction on the study of J/ysuppression • A big fraction (~30 %) of the measured J/yyield results fromccdecays: cc→ J/y + g → J/y + e+e- is the observed J/ysuppression due to thecc disappearance? • What is the “normal nuclear absorption” of thecc? • E866, NA50 : They’ is more absorbed • NRQCD : thecc should be less absorbed NA60 will track the converted photons and will measurea(cc)and thecc to J/yratio with ~ 2% accuracy

  19. A A (%) (%) In-In collisions : low mass phase space coverage The dipole field in the target region leads to much better pT coverage than previous dimuon measurementsDimuons now competitive with respect to dielectrons Monte-Carlo without field Acceptance improvesin all M and pT windows by a factor 50 forM ~ 500 MeV andpT ~ 500 MeV/c with 2.5 T field after muontrack matching

More Related