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Outline: The CMS detector and its capabilities for hard probes detection

Hard Probes of High Density QCD Physics with CMS. Outline: The CMS detector and its capabilities for hard probes detection Expected performances for jet quenching and quarkonia studies. CERN / LHCC 2007 – 009 5 March 2007 Editor: David d’Enterria to be pub. in J. Phys. G.

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Outline: The CMS detector and its capabilities for hard probes detection

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  1. Hard Probes of High Density QCD Physics with CMS • Outline: • The CMS detector and its capabilities for hard probes detection • Expected performances for jet quenching and quarkonia studies CERN / LHCC 2007–009 5 March 2007Editor: David d’Enterria to be pub. in J. Phys. G Carlos Lourenço, on behalf of CMS SQM 2007, Levoča, Slovakia, June 28, 2007

  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 T1/T2 CASTOR ZDC RP RP  For more details, see the slides of Ferenc Sikler Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  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) Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  4. Probing the QCD matter produced in HI collisions We study the produced matter by studying 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  5. vacuum hadronicmatter QGP Challenge: find good probes of QCD matter The good 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... Jets and heavyquarkonia (J/y, y’, cc, , ’, etc) are particularly good probes! Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  6. 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 (the QGP):  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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  7. “Tomography” of the produced QCD matter Tomography: Uses a calibrated probe, and a well understood interaction, to derive the3-D density profile of the mediumfrom the absorption profile of the probe. In heavy-ion collisions: The suppression of the jets or of the quarkonia states gives the density profile and the state (hadronic or partonic) of the matter they cross Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  8. Why are the jets quenched? In pp, expect twoback-to-back jets In the QGP...expect mono jets The away-side jetgets “absorbed” bythe dense QCDmedium Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  9. Why is jet quenching interesting? • The produced hard partons lose energy by multiple gluon radiation while traversing the dense medium • Observe parton energy loss → derive medium properties • Flavor-dependent energy loss: DEloss(g) > DEloss(q) > DEloss(Q) (color factor) (mass effect) Suppression of high pT leading hadrons → seen at RHIC Disappearance of “away-side” jets → indirectly seen at RHIC Modified energy / particle flow within jet (fragmentation function) → not yet seen Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  10. RHIC pp d-Au centralAu-Au Jet suppression in heavy-ion collisions at RHIC reference process reference data photons The photons are not affected by the dense medium they cross Two-particle azimuthal correlations showback-to-back jets in pp and d-Au collisions;the jet opposite to the high-pT trigger particle “disappears” in central Au-Au collisions Interpretation: the produced hard partons (our probe) are “anomalously absorbed”by the dense colored medium created in central Au+Au collisions at RHIC energies Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  11. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  12. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  13. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  14. 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... Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  15. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  16. The High Level Trigger • CMS High Level Trigger: 12 000 CPUs of 1.8 GHz ~ 50 Tflops ! • Executes offline-like algorithms • pp design luminosity L1 trigger rate: 100 kHz • Pb-Pb collision rate: 3 kHz (peak = 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  17. Impact of the HLT on the pT reach of 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  18. Jet reconstruction and spatial resolution • Iterative cone method plus background subtraction: • Subtract average pile-up • Find jets with iterative cone algorithm • Recalculate pile-up outside the cone • Recalculate jet energy 100 GeV jet ona Pb-Pb event,after Bg subtr. ○ without background ■central Pb-Pb Dh Df New developments (fast-kT algo.) under study  I. Vardanyan et al., CMS note 2006/050 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  19. Jet rec. efficiency, purity and ET resolution The full simulation (OSCAR) is well reproduced by the fast simulation (HIROOT) after smearing  I. Vardanyan et al., CMS note 2006/050 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  20. Jet ET reach and fragmentation functions Jet spectra up to ET ~ 500 GeV (Pb-Pb, 0.5 nb-1, HLT-triggered)  Detailed studies of medium-modified (quenched) jet fragmentation functions min. bias Gluon radiation: large angle (out-of-cone) vs. small angle emission HLT  C. Roland et al., CMS note AN-2006/109  I. Lokhtin et al., PLB567 (2003) 39 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  21. dimuon trigger g* g away side associated hadrons g, g* and Z tagging of jet production Unique possibility to calibrate jet energy loss (and FF) with back-to-back gauge bosons (large cross sections and excellent detection capabilities). Heavy quark dimuon (dominant) background can be rejected by a secondary vertex cut.Resolutions: 50 mm in radius and 20 mm in f Z0+jet  C. Mironov et al., CMS note 2007/xxx Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  22. 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. Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  23. Pb-Pb → + X event in CMS dNch/dh = 3500 - Pb-Pb event simulated using the official CMS software framework (developed for pp) Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  24. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  25. 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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  26. pT reach of quarkonia measurements (for 0.5 nb-1) Expected rec. quarkonia yields: J/y : ~ 180 000  : ~ 26 000 ’ : ~ 7300; ’’ : ~ 4400 ● produced in 0.5 nb-1 ■ rec. if dN/dh ~ 2500 ○ rec. if dN/dh ~ 5000 J/y Statistical accuracy (with HLT) of expected’ /  ratio versus pT model killer...   O. Kodolova, M. Bedjidian, CMS note 2006/089 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  27.  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 Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  28. 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) • However, the fantastic potential of CMS as a heavy-ion detector is presently limited by the lack of human resources; this is a golden opportunity for new collaborators: some of the most exciting physics topics (e.g., open charm and open beauty) are not yet under study within the CMS-HI team... Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

  29. An example of compressed baryonic matter Carlos Lourenço, CMS, SQM 2007, Levoča, Slovakia, June 2007

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