Now there isn’t...

1. Heavy Quarkonia as Probes of High Density QCD Physics: from pp to Pb-Pb collisions, from NA38/NA50/NA60 to CMS • Outline: • Heavy quarkonia : a hard probe of dense QCD matter • Reminder of some NA38, NA50 and NA60 results • Quarkonia studies with the CMS detector • Bonus track; previously unreleased: • Is there a “step” in the SPS J/y suppression pattern ? Now there isn’t... Now there is Carlos Lourenço, CERN Early Time Dynamics in HI Collisions, Montréal, July 16-19, 2007

2. Probing the QCD matter produced in HI collisions We study the QCD matter produced in HI collisions by seeing how it affects well understood probes, as a function of the temperature of the system (centrality of the nuclear collisions) Matter under study QGP ? Calibrated “probe meter” Calibrated “probe source” Probe Calibrated heat source

3. Challenge: find good probes of QCD matter vacuum The good QCD matter probes should be: Well understood in “pp collisions” Only slightly affected by the hadronic matter, in a very well understood way, which can be “accounted for” Strongly affected by the deconfined QCD medium... hadronicmatter QGP Heavyquarkonia (J/y, y’, cc, , ’, etc) are particularly good QCD matter probes !

4. Creating and calibrating the probes The “probes” must be produced together with the system they probe ! They must be created very early in the collision evolution, so that they are there before the matter to be probed:  hard probes (jets, quarkonia, ...) We must have “trivial” probes,not affected by the dense QCD matter,to serve as baseline reference:photons, Drell-Yan dimuons We must have “trivial” collision systems,to understand how the probes are affectedin the absence of “new physics”:pp, p-nucleus, d-Au, light ions

5. “Tomography” of the produced QCD matter Tomography in medical imaging: Uses a calibrated probe, and a well understood interaction, to derive the 3-D density profile of the medium from the absorption profile of the probe. “Tomography” in heavy-ion collisions: Jet suppression gives the density profile of the matter Quarkonia suppression gives the state(hadronic or partonic) of the matter

6. Lattice QQbar free energy T Why is quarkonia suppression interesting? In a deconfined phase the QCD binding potential is Debye screened and the heavy quarkonia states are “dissolved”. In other words, the free hard gluons are energetic enough to break the bound QQ states into open charm and beauty mesons. Different heavy quarkonium states have different binding energies and, hence, are dissolved at successive thresholds in energy density or temperature of the medium. Their suppression pattern is a thermometer of the produced QCD matter.  H. Satz, hep-ph/0512217

7. 1.10 0.74 0.15 2.31 1.13 0.93 0.83 0.74 A “smoking gun” signature of QGP formation Feed-down from higher states leads to “step-wise” J/y and suppression patterns. The suppression of bottomonium states is a very important component of the LHC HI physics program. y’ cc  H. Satz, hep-ph/0512217

8. p-Pb @ 400 GeV sJ/y ~ 105 MeV J/y Pb-Pb 158 GeV p-Pb 400 GeV Charmonia studies made by NA50 Studies of J/y and y’ production, in p-nucleus and Pb-Pb collisions, have been published in the last few years by the NA50 collaboration. Charmonia production yields have been presented either in relative terms, with respect to the yield of high-mass Drell-Yan dimuons, or as absolute production cross-sections per target nucleon. With rather good charmonia statistics... real data !

9. c2/ndf = 0.7 c2/ndf = 1.4 The J/y and y’ are absorbed in p-A collisions The lines are the result of Glauber calculations, assuming that the reduction of the production cross section per target nucleon is exclusively due to final state absorption of the charmonia states in the cold nuclear matter it crosses. From a global fit to the 400 and 450 GeV p-A data (16 independent measurements), NA50 determined the following absorption cross-sections: sabs(J/y) = 4.2 ± 0.5 mb ; sabs(y’) = 7.7 ± 0.9 mb

10. reference process J/y normal nuclear absorption curve Drell-Yan dimuons are not affected by the dense medium they cross J/y suppression at the CERN SPS: NA38 / NA50 p-Be p-Pb centralPb-Pb reference data The yield of J/y mesons per DY dimuon is “slightly smaller” in p-Pb collisions than inp-Be collisions; and is strongly suppressedin central Pb-Pb collisions Interpretation:strongly bound ccbar pairs (our probe) are “anomalously dissolved” by the deconfined medium created in central Pb-Pb collisions at SPS energies

11. Rescaled to 158 GeV J/y suppression at the CERN SPS: NA60 Nuclear absorption NA60 In-In 158 A GeV 1) There is a remarkable agreement between the NA60 p-A data point at 158 GeV and the 400–450 GeV points rescaled to 158 GeV... 2) There is a remarkable agreement between the Pb-Pb and In-In suppression patterns when plotted as a function of the Npart variable, determined from the (same) ZDC detector. The statistical accuracy of the In-In points is, however, much better...

12. Digal, Fortunato and Satz EPJ C32 (2004) 547 Grandchamp and Rapp NP A715 (2003) 545PRL 92 (2004) 212301 Capella and Ferreiro hep-ph/0505032 Data vs. theoretical predictions: the model tuning The In-In NA60 data can be compared with theoretical predictions based on models tuned on the J/y suppression pattern defined by the Pb-Pb NA50 data Pb-Pb @ 158 GeV CF: suppression by “comovers” DFS: percolation phase transition GR:dissociation and regeneration in QGP and hadron gas, inc. in-medium properties of open charm and charmonium states

13. Data vs. theoretical predictions: the results S. Digal et al. EPJ C32 (2004) 547 R. Rapp EPJ C43 (2005) 91 centrality dependent t0 None of these predictions describes the measured suppression pattern... Homework exercise: calculate the c2/ndf for eachof these curves (ndf = 8) In-In 158 A GeV R. Rapp EPJ C43 (2005) 91 fixed termalization time t0 A. Capella, E. Ferreiro EPJ C42 (2005) 419 Note: the In data was taken at the same energy as the Pb data to minimise the “freedom” of the theoretical calculations 

14. This figure Data vs. theoretical post-dictions... Nuclear plus hadron gas absorption L. Maiani et al., NP A748 (2005) 209 F. Becattini et al., PL B632 (2006) 233 Nuclear absorption... plus largest possible absorption in a hadron gas (T=180 MeV)

15. 1.2 NA60, In+In, 158 A GeV 1.0 Comover absorption NA50, Pb+Pb, 158 A GeV Comover absorption 0.8 1.2 1.2 Glauber ) NA60, In+In, 158 A GeV (DY) 0.6 1.0 QGP threshold melting s 1.0 / NA50, Pb+Pb, 158 A GeV ) Y QGP threshold melting J/ ( 0.8 s ( 0.8 / ) QGP threshold melting (DY) 0.6 Comover absorption s / 0.6 ) In+In, 158 A GeV Y J/ ( s 0.4 ( 0 50 100 150 200 250 300 350 0.4 0 50 100 150 200 250 300 350 N part HSD Data vs. theoretical post-dictions... (cont.) Charmonium dynamics in heavy ion collisions O. Linnyk et al., SQM 2007, June 28, 2007 and Nucl. Phys. A 786 (2007) 183. HSD It looks really strange that the curve“QGP threshold melting” is very smooth... and the “comover absorption” has a step ! N part

16. Data vs. theoretical post-dictions... (the end) The probability that the measurements should really be on any of these two curves and “statistically fluctuated” to where they were in fact observed is... zero In-In 158 A GeV HSD

17. In-In data vs. a sharp step function in Npart 1 Measured / Expected A1 A2 Npart Step position Step at Npart = 86 ± 8 A1 = 0.98 ± 0.02 A2 = 0.84 ± 0.01 2/ndf = 0.75 (ndf = 5) Taking into account the EZDC resolution, the measured pattern is perfectly compatible with a step function in Npart... The real function can have the step in a different variable (energy density, etc) if the smearing induced when converting that variable to Npart is not larger than the ZDC resolution (around 20 in Npart whatever the centrality)

18. 1 Measured / Expected A1 A2 A3 Npart Step positions What about the Pb-Pb pattern? Another step? Steps: Npart = 90 ± 5 and 247 ± 19 A1 = 0.96 ± 0.02 A2 = 0.84 ± 0.01 A3 = 0.63 ± 0.03 2/ndf = 0.72 (ndf = 11) If we try fitting the In and Pb data with one single step we get c2/ndf = 5 !... The Pb data points rule out the single-step function... and strongly indicate the presence of a second step...

19. y’ suppression in heavy-ion collisions at the SPS The y’ suppression pattern also shows a significantly stronger drop than expected from the “normal extrapolation” of the p-A data y’ y’ sabs ~ 20 mb The “change of slope” at L ~ 4 fm is quite significant and looks very abrupt...

20. Hard Probes at LHC energies • Very large cross sections at the LHC • Pb-Pb instant. luminosity: 1027 cm-2s-1 • ∫ Lumi = 0.5 nb-1 (1 month, 50% run eff.) • Hard cross sections: Pb-Pb = A2 x pp •  pp-equivalent ∫ Lumi = 20 pb-1 •  1 event limit at 0.05 pb (pp equiv.) pp s = 5.5 TeV 1 mb J/y 1 nb  h+/h- jet Z0+jet g*+jet 1 pb gprompt 1 event  M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099

21. Phase space coverage of the CMS detector CMS (with HF, CASTOR, ZDC) + TOTEM: almost full η acceptance at the LHC ! • charged tracks and muons: |η| < 2.5, full φ • electrons and photons: |η| < 3, full φ • jets, energy flow: |η| < 6.7 (plus η > 8.3 for neutrals), full φ • excellent granularity and resolution • very powerful and flexible High-Level-Trigger TOTEM CASTOR 5.2 < |η| < 6.6 HF HF ZDC h = -8 -6 -4 -2 0 2 4 6 8 η > 8.3 neutrals T1/T2 CASTOR ZDC RP RP

22. h±, e±, g, m± measurement in the barrel (|| < 2.5) Si Tracker + ECAL + muon-chambers CalorimetersECAL PbWO4HCAL Plastic Sci/Steel sandwich Si TrackerSilicon micro-stripsand pixels Muon BarrelDrift Tube Chambers (DT)Resistive Plate Chambers (RPC)

23. Quarkonia studies in CMS So far, only the dimuon decay channel has been considered. The physics performance has been evaluated with the 4 T field (2 T in return yoke) and requiring a good track in the muon chambers. The good momentum resolution results from the matching of the muon tracks to the tracks in the silicon tracker.

24. Pb-Pb → + X event in CMS dNch/dh = 3500 - Pb-Pb event simulated using the CMS software framework developed for pp

25. Barrel + endcaps: muons in |h| < 2.4  Barrel: both muons in |h| < 0.8 Acceptance pT (GeV/c) → m+m-: acceptances and mass resolutions CMS has a very good acceptance for dimuons in the Upsilon mass region(21% total acceptance, barrel + endcaps) The dimuon mass resolution allows usto separate the three Upsilon states:~ 54 MeV within the barrel and~ 86 MeV when including the endcaps  O. Kodolova, M. Bedjidian, CMS note 2006/089

26. pT (GeV/c) h J/y→ m+m-: acceptances and mass resolutions • The material between the silicon tracker and the muon chambers (ECAL, HCAL, magnet’s iron) prevents hadrons from giving a muon tag but impose a minimum muon momentum of 3.5–4.0 GeV/c. This is no problem for the Upsilons, given their high mass, but sets a relatively high threshold on the pT of the detected J/y’s. • The low pT J/y acceptance is better at forward rapidities; total acceptance ~1%. • The dimuon mass resolution is 35 MeV, in the full h region. J/y barrel +endcaps Acceptance barrel +endcaps barrel pT (GeV/c)  O. Kodolova, M. Bedjidian, CMS note 2006/089

27. The CMS High Level Trigger • CMS High Level Trigger: 12 000 CPUs of 1.8 GHz ~ 50 Tflops ! • Processes full events with fast versions of the offline algorithms • pp L1 trigger rate (design L): 100 kHz • Pb-Pb collision rate: less than 8 kHz •  pp L1 trigger rate > Pb-Pb collision rate the HLT can process all Pb-Pb events • Pb-Pb event size: ~2.5 MB (up to ~9 MB) • Data storage bandwidth: 225 MB/s 10–100 Pb-Pb events/s • HLT reduction factor: 3000 Hz → 100 Hz • Average HLT time budget per event: ~10 s • The event samples of hard processes are statistically enhanced by very large factors Pb-Pb at 5.5 TeV design luminosity ET reach x2 jets x35 x35  M. Ballitjin, C. Loizides, G. Roland, CMS note AN-2006/099

28. Reach of quarkonia measurements (for 0.5 nb-1) Expected rec. quarkonia yields: J/y : ~ 180 000  : ~ 26 000 ’ : ~ 7 300; ’’ : ~ 4 400 ● produced in 0.5 nb-1 ■ rec. if dN/dh ~ 2500 ○ rec. if dN/dh ~ 5000 J/y Pb-Pb  Good statistical accuracy (with HLT) of the expected ’ /  ratio versus pT Similar low pT yields for J/y and    O. Kodolova, M. Bedjidian, CMS note 2006/089

29. Summary  The J/y is “anomalously” suppressed in Pb-Pb and In-In collisions at the SPS with respect to the “normal nuclear absorption curve” derived from the p-nucleus data  No theoretical model gives a good description of the measured data, until now further work is needed, including studies of pT distributions, y’ yields, etc  The In-In pattern indicates a step-like suppression functionwith a drop of ~ 15% for collisions of Npart higher than around 86 “La science donne du monde des images crédibles, non parce qu’elles sont vraies mais parce qu’elles sont les meilleures que l’on trouve à un moment donné” The existence of step-wise patterns might be an incorrect interpretation of the SPS suppression data, but it is, today, the only good description of the measurements  Next goal: measure the suppression patterns of the  states at LHC energies, as a function of centrality and pT  The CMS experiment is particularly well suited for such studiesfirst physics data taking periods expected in 2008 (protons) and 2009 (Pb-Pb)

30. Bonus slide: a lesson from the SPS to the LHC Before the measurements are made, theorists often tell us that the interpretation of the data will be easy However, theorists are often wrong... especially before the measurements are made... The good news is that nowwe have clear instructions...