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Heavy-Ion Physics with Compact Muon Solenoid at Large Hadron Collider

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  1. Heavy-Ion Physics with Compact Muon Solenoidat Large Hadron Collider Bolek Wyslouch Massachusetts Institute of Technology Los Alamos 25 October 2007 CMS

  2. Quark Gluon Plasma • Data from SPS & RHIC show new and unexpected properties of hot nuclear matter • Jet quenching, strong elliptical flow, d+Au- control data indicate that we have produced strongly interacting color liquid • LHC will significantly increase energy density • New properties of the plasma • Continuation of strong coupling regime? • Weakly interacting Plasma? • New tools to study to hot and dense state • Hard probes • Access to very low-x Los Alamos Bolek Wyslouch

  3. Summary of physics opportunities • LHC will accelerate and collide heavy ions at energies far exceeding the range of existing accelerators • The increase of beam energy will result in: • Extended kinematic reach for pp, pA, AA • New properties of initial state, saturation at mid-rapidity • A hotter and longer lived partonic phase • Increased cross sections and availability of new hard probes • New energy regime will open a new window on hot and dense matter physics: another large energy jump! Los Alamos Bolek Wyslouch

  4. Large Hadron Collider • LHC is about to start operations: • 2008: • proton-proton collisions at ~14 TeV • 2008: • p+p at 14 TeV • Pb+Pb at 5.5 TeV per nucleon pair • Heavy Ions • Expect ~1 month of heavy ion collisions each year Beam Energy Los Alamos Bolek Wyslouch

  5. PHOBOS Central Au+Au (200 GeV) 600 1200 Compilation by K. Eskola Rapidity Density First RHIC Surprise: Multiplicities Are “Low” • Low, that is, compared to pre-data predictions of “cascading partons” • Consistent with predictions based on gluon saturation : Kharzeev & Levin, Phys. Lett. B523 (2001) 79 Color Glass Data: PHOBOS, Phys. Rev. Lett. 87, 102303 (2001) From Eskola, QM 2000 Los Alamos Bolek Wyslouch

  6. LHC multiplicity is likely to be low ? Extrapolated to LHC: dN/dh~1000-2000 Is it saturation that makes it so low? Will it increase at higher energies? LHC? Note: this is an important experimental issue! Los Alamos Bolek Wyslouch

  7. RHIC’s Two Major Discoveries • Discovery of strong “elliptic” flow: • Elliptic flow in Au + Au collisions at √sNN= 130 GeV, STAR Collaboration, (K.H. Ackermann et al.). Phys.Rev.Lett.86:402-407,2001 • 307 citations • Discovery of “jet quenching” • Suppression of hadrons with large transverse momentum in central Au+Au collisions at √sNN = 130 GeV, PHENIX Collaboration (K. Adcox et al.), Phys.Rev.Lett.88:022301,2002 • 357 citations Flow strength Suppresion Factor Strongly interacting liquid with very low viscosity Los Alamos Bolek Wyslouch

  8. Flow Elliptic Flow at RHIC HYDRODYNAMICS STAR Flow (asymmetry in pT) is near to hydrodynamic limit, LHC: can it grow even more ? Los Alamos Bolek Wyslouch

  9. p+p Au+Au “Jet Quenching” at high pT: will it continue at LHC ? • Energy loss of partons in hot and dense matter • E.g. charged particle RAA for multi-100 GeV/c pT Parton Energy loss Los Alamos Bolek Wyslouch

  10. Regeneration ? SPS RHIC LHC Suppression ? Energy Density Quarkonia in Heavy Ions • J/ suppression in heavy ion collisions has been heralded as a discovery of Quark Gluon Plasma at CERN SPS circa 2000: there are fewer J/’s produced as energy density is increasing • There is a lot of detailed experimental data from SPS. RHIC is now releasing new information, it is consistent with SPS • Theoretical interpretation is difficult: we possibly need to look towards LHC:  family can provide important hints, there are three states with differing binding energy Los Alamos Bolek Wyslouch

  11. CMS Post-RHIC Dream heavy-ion detector • Large acceptance for charged and neutral hadrons, muons, photons, electrons covering wide pT range hermeticity • Good resolution for high pT probes (jets, J/,  family) resolution • Good trigger to allow selection of rare events speed • Good particle identification p0, b-, c-quarks, muons, electrons, photons, L, Ks, p, K , p particle ID • Most likely it does NOT have to handle extreme multiplicities • Relatively low luminosity of LHC as a heavy-ion accelerator     Los Alamos Bolek Wyslouch

  12. “High density QCD with heavy-ions” 170 pages 10 chapters ~90 figures, ~20 tables ~20 CMS-AN-Notes ~25 CMS-HI institutions ~100 collaborators Athens, Auckland, Budapest, CERN, Chongbuk, Colorado, Cukurova, Ioannina, Iowa, Kansas, Korea, Lisbon, Los Alamos, Lyon, Maryland, Minnesota, MIT, Moscow, Mumbai, Seoul, Vanderbilt, UC Davis, UI Chicago, Vilnius, Zagreb D.d'E (ed.) CERN-LHCC-2007-009; J.Phys.G. to appear. Los Alamos Bolek Wyslouch

  13. Calorimeters: high resolution and segmentation • Hermetic coverage up to ||<5 • (||<6.6 with the proposed CASTOR) • Zero Degree Calorimeter • Muon tracking:  from Z0, J/,  • Wide rapidity coverage: ||<2.4 • σm 50 MeV at the  mass in the barrel • Silicon Tracker • Good efficiency and purity for pT~>0.3 GeV • Pixel occupancy: <2% at dNch/d 3500 • p/p  1-2% for 1<pT <100 GeV • Good low pT reach using pixels • DAQ and Trigger • High rate capability for A+A, p+A, p+p • High Level Trigger: real time HI event reconstruction CMS, as a heavy ion experiment CASTOR (5.2 < |η| < 6.6) ZDC (z = 140 m, |η| > 8.2 neutrals) Functional at the highest expected multiplicities: studied in detail at dNch/d3000-5000 and cross-checked at 7000-8000 Los Alamos Bolek Wyslouch

  14. Q2 Sub detector Coverage Tracker, muons |  | < 2.4 ECAL + HCAL |  | < 3.0 Forward HCAL 3 .0< |  | < 5.2 CASTOR 5.2 < |  | < 6.6 ZDC (neutrals) 8.2 < || CMS coverage HCAL (Barrel+Endcap+Forward) Los Alamos Bolek Wyslouch

  15. CMS under construction Silicon Tracker Hadron Calorimeter Electromagnetic Calorimeter Muon Absorber DAQ Si tracker & Pixels Los Alamos Bolek Wyslouch

  16. Centrality and forward detectors Centrality (impact parameter) determination is needed for most physics analyses Zero Degree Calorimeter Energy in the forward hadronic calorimeter Tungsten-quartz fibre structure electromagnetic section: 19X0 hadronic section 5.6λ0 Rad. hard to ~20 Grad (AA, pp low lum.) Energy resolution (n,g): E~E·10% Position resolution: ~2 mm (EM sect.) ~140 meters from CMS IP Los Alamos Bolek Wyslouch

  17. Zero Degree Calorimeter Los Alamos Bolek Wyslouch

  18. CASTOR T2 Tracker TOTEM 5.2< η < 6.6 CASTOR: Tungsten-Quartz 5.2< η < 6.6 Los Alamos Bolek Wyslouch

  19. ch Charged particle multiplicity • high granularity pixel detectors • pulse height measurement in each pixel reduces background • Very low pT reach, pT>26 MeV (counting hits) Will be one of the first results, important for initial energy density, saturation, detector performance etc. Simple extrapolation from RHIC data W. Busza, CMS Workshop, June 2004 Muon detection, tracking, jet finding performance checked up or larger than dNch/dh=5000 Los Alamos Bolek Wyslouch

  20. Elliptic Flow measurements in CMS • Use calorimeters and tracker • Event plane reconstruction • v2 measurements • Very large acceptance v2(h) tracker Los Alamos Bolek Wyslouch

  21. jet parton nucleon nucleon Jets at RHIC Find this……….in this Los Alamos Bolek Wyslouch

  22. c c a a b b d d Production of QCD jets Proton-proton Ion-ion “Clean” Jet Quenched, absorbed, modified jet “Soft QCD” “Hard QCD” 2008-> 2009-> Los Alamos Bolek Wyslouch

  23. nhit > 12 pchi2 > 0.01 dca <3 High-pT (leading) charged hadrons C.Roland, CMS-AN06-001 • Excellent tracking performances (PbPb, dNch/dh = 3500): • Efficiency • Fake Rate Momentum resolution Expected dN/dpT reach pT~300 GeV/c (high ET HLT) Impact parameter resolution Displaced vertexes from heavy-Q decays measurable Los Alamos Bolek Wyslouch

  24. Pixel tracking All tracker fitting Pixel Tracking, low pT reach of CMS 800 MeV Los Alamos Bolek Wyslouch

  25. F. Sikler Pixel tracking Track finding efficiency vs pT and for p+p and central Pb+Pb Fakes are controlled using pixel hit shape Los Alamos Bolek Wyslouch

  26. High-pT (leading) charged hadrons C.Roland et al., CMS-AN06-110 Nuclear modification factor (= AA-yield / pp-yield) at the LHC: PbPb (PYQUEN) 0.5 nb-1 extended reach ~300 GeV/c w/ high-ET (jet)trigger ×5 suppr. Strong discriminationpower for parton energy loss models: - Initial parton medium density: dNg/dy~O(2-4·103) - Medium transport coefficient: <q>~O(10-100) GeV2/fm Los Alamos Bolek Wyslouch

  27. 1. Subtract average soft background 2. Find jets: iterative cone algorithm 3. Recalculate pileup outside cone 4. Recalculate jet energy jet energy: reco vs. MC energy resolution efficiency, purity Pb-Pb full jet reconstruction I. Vardanyan et al. CMS-Note-2006-50 • Iterative-cone + backgd subtraction. [New developments (fast-KT) under study] Los Alamos Bolek Wyslouch

  28. Pb-Pb full jet reconstruction C.Roland et al., CMS-AN06-110 • Jet spectra up to ET~ 0.5 TeV (PbPb, 0.5 nb-1, HLT-triggered). • Detailed studies of medium-modified (quenched) jet FF possible. min.bias Gluon radiation: large-angle (out-of-cone) vs. small-angle emission HLT Njets~6·106 I. Lokhtin et al., PLB567 (03)39 Los Alamos Bolek Wyslouch

  29. g- , g*- , Z- jet tagging (CMS) • Possibility to calibrate jet-energy loss (and Fragmentation Functions) with back-to-back gauge boson (large cross-sections, good detection capabilities): • Dominant (heavy-Q) dimuon backgd. “removable” via secondary-vtx. cut C.Mironov et al. Dimuon trigger NZ-jet~103 Z0/g* q/g Away side Associated Hadrons pT >25 GeV/c sr=50 mm sj=20 mm 3s vtx. cut Los Alamos Bolek Wyslouch

  30. g, Z0 Jet Events/ 5 GeV ETo - ETJet (GeV) Balancing  or Z0/g* vs Jets • Jet quenching with calibrated energy • On average Z/ ET and jet ET should balance (unquenched jets) • Z ->  and  can be reconstructed with very good ET resolution • Dominated by quark jets q + g -> q + Z0/ • -Jet: • Need to control the background from leading 0 in QCD dijets • Reject 0 by cluster isolation cuts in the calorimeters • Quenching will help • Lower Thresholds • Z0 - Jet • Cleaner but lower rates ETjet, g > 120GeV in Barrel, 1 month at 1027 cm-2s-1 Pb+Pb new studies to appear shortly dN/dy ~7000, unquenched Jets Los Alamos Bolek Wyslouch

  31. Quarkonia: probe of high-density QCD media • Dissociation (color screening) = hot QCD matter thermometer • Probe of low-x gluon structure/evolution: _ [H.Satz, hep-ph/0512217] Spectral function vs T: Lattice QQ free energy vs T: Suppression pattern vs e :   gluon saturation, non-linear QCD production via gg fusion: x~10-3 (10-5) Q2~10 GeV2 Los Alamos Bolek Wyslouch

  32. Heavy Ion MC Event in CMS Pb+Pb event (dN/dy = 3500) with  -> - Pb+Pb event display: Produced in CMS software framework (simulation, data structures, visualization) Los Alamos Bolek Wyslouch

  33. regeneration ? SPS RHIC LHC suppression ? Energy Density J/ψ suppression O.Kodolova, M. Bedjidian, CMS-AN06-116 J/ acceptance Best mass resolution @ LHC J/,' S/B = 35 MeV/c2 |y|<1 pT reach (0.5 nb-1) NJ/Y~1.8·105 Los Alamos Bolek Wyslouch

  34. ’ ’’ ¡suppression O.Kodolova, M. Bedjidian, CMS-AN06-116  family S/B  acceptance Best mass resolution @ LHC = 54 MeV/c2  spectroscopy (seq. suppr.) pT reach (0.5 nb-1) ’/  stat. reach (HLT) Strong models constraint N~2.5·104 Gunion&R.Vogt Los Alamos Bolek Wyslouch

  35. Ultra-Peripheral collisions g Pb • Quarkonia photoproduction • Probes nuclear PDF in unexplored (x,M2) range • Uses ZDC to trigger on forward emitted neutrons • Measurement --> m+m-, e+e- in the central detector Los Alamos Bolek Wyslouch Bolek Wyslouch

  36. CMS Trigger and DAQ in p+p Level 1 trigger - Uses custom hardware - Muon tracks + calorimeter information - Decision after ~ 3μsec High level Trigger - ~1500 Linux servers (~10k CPU cores) - Full event information available - Runs “offline” algorithms Los Alamos Bolek Wyslouch

  37. CMS Trigger+DAQ in Pb+Pb vs p+p Level 1 trigger - Uses custom hardware - Muon tracks + calorimeter information - Decision after ~ 3μsec High level Trigger - ~1500 Linux servers (~10k CPU cores) - Full event information available - Runs “offline” algorithms Los Alamos Bolek Wyslouch

  38. Trigger/DAQ Architecture Standard rack servers Dual CPU - dual core 2008/09: quad/8 core 8 “DAQ slices” modular ~1500 “Filter Unit” servers ~12000 1.8GHz Opteron equivalent Los Alamos Bolek Wyslouch

  39. Acceptance, BR Efficiency d2/dydpT Production rate Acc(y,pT) Eff(y,pT) Acceptance, efficiency, backgrounds measured and parametrized from full offline simulation + algorithms Luminosity Ncoll Trigger Table x DAQ rate Rate to tape Trigger rate (signal + bkg) 1 + Bkg/Sig(y,pT) Signal rate Output Rates to tape Timing of offline algorithms and event size bias measured on full simulations High Level Trigger Simulations Production X-sections Los Alamos Bolek Wyslouch

  40. Minimum bias vs HLT HLT CPU time Budget ~ 8 CPUsec per event (1.8GHz Opteron) Strawman trigger table for design lumi with HLT with HLT Significance (106 sec @ design lumi) Rates to tape Min bias Min bias Los Alamos Bolek Wyslouch

  41. Activities of HI physicists • Exploration of the capabilities of CMS as a heavy ion detector and preparations for data taking • Development of analysis tools and reconstruction algorithms • Development of generators • Reconstruction algorithms • Development of trigger algorithms • HLT Farm operations • Trigger algorithms • Simulation studies • Studies of detector behavior in HI collisions • Design and construction of “HI motivated” detectors • Zero Degree Calorimeter • CASTOR Los Alamos Bolek Wyslouch

  42. Heavy Ion Physicists within CMS Collaboration • Overall CMS Collaboration • 38 Countries, 181 Institutions, ~2500 Scientists • Heavy Ion Institutions • Athens, Auckland, Budapest, CERN, Chongbuk, Colorado, Cukurova, Ioannina, Iowa, Kansas, Korea, Lisbon, Los Alamos, Lyon, Maryland, Minnesota, MIT, Moscow, Mumbai, Seoul, Vanderbilt, UC Davis, UI Chicago, Vilnius, Zagreb • Total of about 65 PhDs, 35 Students, 50% from the US Los Alamos Bolek Wyslouch

  43. Calendar Year Physics (known physics) Total on tape 2008 Preparations: HLT, Reconstruction, first p+p physics at low energy 0 2009 Reference p+p, global observables, jets ET<200 GeV, charged particle spectra, first dimuon events, 0.3 k 2010 Centrality and event plane dependence of global obs., charged particle spectra to 200 GeV, multi-100 GeV jets, open b,c, first quarkonia 3k 2011 Detailed jet fragmentation studies, multi-jets, quarkonia physics, first tagged jet studies, detailed open b,c studies 15k 2012 Extensive studies of rare channels, centrality, event plane dependence of quarkonia, tagged jets, heavy quarks 35k 2013 Detailed studies of rare channels 55k Physics Plan • Comprehensive heavy ion physics program with emphasis on hard probes • Program follows increasing luminosity • Continuously extend pT range • New probes • Increase level of precision and detail • Tighten and optimize trigger • Pb+Pb for the first few years, expect other ions and p+Pb later, in close coordination with ALICE Los Alamos Bolek Wyslouch

  44. Conclusions • LHC will extend energy range and in particular high pT reach of heavy-ion physics • CMS is preparing to take advantage of its capabilities • Excellent rapidity and azimuthal coverage and high resolution • Quarkonia • Jets • Centrality, Multiplicity, Energy Flow reaching very low pT • Essentially no modification to the detector hardware • New High Level Trigger algorithms specific for A+A • Zero Degree Calorimeter, CASTOR and TOTEM will be important additions extending forward coverage • Heavy-Ion program is well integrated into the overall CMS Physics Program • The knowledge gained at RHIC will be extended to the new energy domain Los Alamos Bolek Wyslouch