Quarkonia: experimental possibilities

1. Quarkonia: experimental possibilities Denis Jouan Institut de Physique Nucléaire Orsay International Workshop on the Physics of the Quark-Gluon Plasma Ecole Polytechnique, Palaiseau, France September 4-7, 2001 • In the next 10 years two major worldwide facilities, RHIC and LHC, will allow the study of heavy ion collisions at increased energies. • Quarkonia are specific probe of the deconfinement, in this talk I try to summarize the main characteristics of the data that will be produced in the experiment measuring lepton pairs: NA60, PHENIX, CMS and ALICE. • Not all number are official ones. they could be personal extrapolation

2. Some orders of magnitude and scenarii Various detectors of heavy quarkonia Sketch of expectable measurements Some connected aspects Reference ? Open flavour Combinatorial background Plan Hypothesis: energy density thresholds in PbPb at SPS for y, y’ and c (some features of the experiments)

3. dimuon production psi:psi’: uspilon 1000 : 15 : 1 Dimuon upsilon family: 1 : 0.3: 0.15 ~40% feeding for J/y and U • ds/dY: Factor 10 between SPS, RHIC and LHC • min bias collisions rate (Hz): SPS 106 RHIC 103- 105 LHC 103-105 • RHIC period ~10 times SPS/LHC

4. NA60 • Add a pixel silicon tracker (and a beam vertex detector) in a magnetic field upstream the NA50 absorber • Main goal : open charm measurement, low masses studies, cc A dependance • Extension of NA50 J/y measurement to intermediate system In+In possible too • (first threshold) Where are the thresholds in an intermediate system ?

5. PHENIX 2 central spectrometer (2000 and later) 2 forward muon spectrometer (2001 and 2002)

6. PHENIX Phenix muon arms Radialmagnetic field ~7 lI firstabsorber (magnet) trigger: 5 layers steel/iarocci tubes 1.2<h<2.5 flexible trigger for selection of complete events 2arms-> central rapidity for U But p+k decay background (as for CMS)

7. PHENIX e+e- central measurement (W.A.Zajc QM2001)

9. Alice muon arm • High resolution measurement for resolving the U states • Minimize p,K decay background • 11 l absorber, optimized beam shield • Coincidence measurement with other observables (if trigger)

10. ALICE central arm TRD • Add a transition radiation detector to the alice central detector to identify high pt electrons • J/y • U • e-m • separates J/ycomingfrom B decays

11. CMS Highest statistic for U but huge Background from mesons decays High Pt J/y only (Ptm>3.5GeV) Very clean reference from Z0(but different origin: qq ? X domain ? M ?) Jet study possible separation of Drell Yan by vetoing b and c decays. G.Baur et al. CMS 2000/060

12. Mass Resolutions

13. Global comparison between experiments Light ions allow higher statistic: ex: 3 106J/y (SiSi RHIC), 50000 y’ forward measurement at LHC will use low X domain ( down to 10-5)

14. Qualitative Sketch of the future measurements • Try to summarize the main trend of the future measurement (statistical) • This is aiming at order of magnitude and global comparison, from NA50 to LHC, no conclusion can be drawn from precise comparison between experiments

15. conservative, but consistent, rough estimate, following the PHENIX recent paper, PRL 87, 052301 (2001) • t considered fixed ( lower limit at LHC contrarily for upsilon creation time is short (0.2 fm/c) • <Et>, T, <Pt> Saturation ? • threshold energies estimated through binding energy Energy densities cc Energy densities extrapolated following this NA50 plot Y’ Y’

16. More precise estimate through lattice QCD calculations J/y S.Digal, P.petreczky, H.Satz, HEP/ph0106017 U

17. Central Energy densities (at 1fm/c) R=1.18 A1/3 ethNA50 ~2.1GeV/fm3 dN/dY ~ A1.1 Rhic 130200 : +9%

18. Tentative anwer to « what can we hope to get in future » Tentative viewing (preliminary) Significance, Squared (for central collisions) in areas where threshold could be expected [Significance: S/sqrt(S+B)]

19. Quarkonia versus Open flavour Plausible dn/dy LHC ~ 15 (cc) 1.5 (bb) • Same production mechanism (~gluon fusion) The ideal reference ? • But different hadronic or ion effects (energy loss, decays, combinatorial, …) remains • Z0 good reference too, cleanly measured in CMS • relative importance of Drell Yan production (qq fusion) % cc and bb (gg fusion) decays ? • em measures cc and bb decays • ee, mm, me Combinatorial background: more critical with energy (when Psame domain(c) compares with Bc) • B decay: mixing produce correlated like signs • Also indirect production of resonances  need to measure D and B production

20. SPS Background NA50 • open charm replaces the pi, K decays in the combinatorial background, • Combinatorials are more critical than ever, specially for continuum: open flavour are signal and combinatorial background at the same time. • This technical (method, biases) point has to be studied in detail (P.Crochet et al., M.Gadzinsky et al., D.J et al.,… ), already perhaps at SPS: +/- symetry, combinatorial effects, precisions, Event mixing Better suited ? RHIC PHENIX LHC ALICE PBM

21. For instance: combinatorials in open flavour become dominant at LHC (P.Crochet, P.Braun Munzinger 2001) But this effect decreases with mass (D.C. Zhou, D.J. 1997) B mixing, exchanging charges, makes the background subtraction more questionnable (P.Crochet 2000) BD produces correlated low mass pairs (double bump) (Lin,Vogt 1999) Event mixing is effective here

22. Epilogue • A large set of dimuon measurements will give access to complementary observations for Quarkonia production: • y, cc, y’ (SPS, RHIC)’ • U’,(U’’), cb (RHIC, LHC) • Y (LHC) • X domains • Energy density • Statistics , backgrounds, references • in addition to ee, mm, and em measurements, direct measurement of open flavour is needed • Correlations with other observables (central electrons or any observable (strangeness, plane, jets,…) in PHENIX , perhaps ALICE ) • some room for possible upgrades: direct measurement of open charm (phenix), full use of detector capability (L3 trigger for Alice),…open beauty (single leptons) ?... • Combinatorials: to be studied in more details