Outline: The CMS detector and its capabilities for heavy quarkonia

1. Heavy quarkonia perspectives with Heavy-Ions in CMS • Outline: • The CMS detector and its capabilities for heavy quarkonia • Expected performances for quarkonia studies CERN / LHCC 2007–009 5 March 2007Editor: David d’Enterria to be pub. in J. Phys. G QWG 2007, DESY, Hamburg, October 19, 2007 Pedro Ramalhete, on behalf of CMS

2. 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

3. 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)

4. Lattice QQbar free energy T Why is quarkonia suppression interesting? In a deconfined phase the QCD binding potential is screened and the heavy quarkonia states are “dissolved”. 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.

5. 1.10 0.74 0.15 2.31 1.13 0.93 0.83 0.74 A “smoking gun” signature of QGP formation The feed-down from higher states leads to “step-wise” J/y and suppression patterns. It is very important to measure the heavy quarkonium yields produced in Pb-Pb collisions at the LHC energies, as a function of pT and of collision centrality. y’ cc

6. reference process J/y normal nuclear absorption curve exp(-r L sabs) Drell-Yan dimuons are not affected by the dense medium they cross J/y suppression in heavy-ion collisions at the SPS 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

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

8. Hard Probes at LHC energies • Experimentally & theoretically controlled probes of the early phase in the collision • Very large cross sections at the LHC • CMS is ideally suited to measure them • 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

9. The High Level Trigger • CMS High Level Trigger: 12 000 CPUs of 1.8 GHz ~ 50 Tflops ! • Executes faster versions of “offline algorithms” (on full events) • pp design luminosity L1 trigger rate: 100 kHz • Pb-Pb collision rate: < 8 kHz •  pp L1 trigger rate >> Pb-Pb collision rate run HLT codes on 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: ~4 s • Using the HLT, 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

10. Impact of the HLT on the pT reach of the RAA Nuclear modification factor = AA-yield / pp-yield = “QCD medium” / “QCD vacuum” Pb-Pb (PYQUEN) 0.5 nb-1 HLT Important measurement to compare with parton energy loss models and derive the initial parton density, dNg/dy, and the medium transport coefficient, 〈q〉 ^  C. Roland et al., CMS note AN-2006/109

11. 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.

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

13. 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 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

14. 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. • 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

15. pT reach of quarkonia measurements (for 0.5 nb-1) ● produced in 0.5 nb-1 ■ rec. if dN/dh ~ 2500 ○ rec. if dN/dh ~ 5000 Expected rec. quarkonia yields: J/y : ~ 180 000  : ~ 26 000 J/y Statistical accuracy (with HLT) of expected’ /  ratio versus pT model killer...  curves from Nucl. Phys. B492 (1997) 301–337  O. Kodolova, M. Bedjidian, CMS note 2006/089

16.  production in Ultra-Peripheral Pb-Pb Collisions • CMS will also study Upsilon photo-production, which occurs when the electromagnetic fields of the 82 protons of each nuclei interact with each other • This measurement (based on neutron tagging in the ZDCs) allows us, in particular, to study the gluon distribution function in the Pb nucleus • Around 500 events are expected after 0.5 nb-1, adding the e+e- and m+m- decay channels    D. d’Enterria, A. Hees, CMS note AN-2006/107

17. Summary • The CMS detector has excellent capabilities to study the dense QCD matter produced in very-high-energy heavy-ion collisions, through the use of hard probes such as high-ET (fully reconstructed) jets and heavy quarkonia • With a high granularity inner tracker (full silicon, analog readout), a state-of-the-art crystal ECAL, large acceptance muon stations, and a powerful DAQ & HLT system, CMS has the means to measure charged hadrons, jets, photons, electron pairs, dimuons, quarkonia, Z0, etc! • This opens the door to high-quality measurements that so far lived only in the realm of dreams (maybe even including the study of cc → J/y + g using the ECAL)