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Heavy Ion Physics with the CMS Detector

Heavy Ion Physics with the CMS Detector. Lyudmila Sarycheva Scobeltsyn Institute of Nuclear Physics Moscow State University For CMS Collaboration. CMS detector and Heavy Ion program Quarkonia and heavy quarks Jets and jet quenching Global event characterization

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Heavy Ion Physics with the CMS Detector

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  1. Heavy Ion Physics with the CMS Detector Lyudmila Sarycheva Scobeltsyn Institute of Nuclear Physics Moscow State University For CMS Collaboration • CMS detector and Heavy Ion program • Quarkonia and heavy quarks • Jets and jet quenching • Global event characterization • Monte-Carlo simulation tools • Summary • Appendix CMS Heavy-Ion Groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, Minnesota, MIT, Moscow, Mumbai, N.Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas, Tbilisi, UC Davis,UI Chicago, U. Iowa, Yerevan, Warsaw, Zagreb ICHEP'06 Moscow 26.07 - 02.08.2006

  2. 1.1 CMS detector  Si tracker with pixels | | < 2.4 good efficiency and low fake rates for pt > 1 GeV, excellent momentum resolution, p: pt/pt < 2% Muon chambers || < 2.4 Fine grained high resolution calorimetry (HCAL, ECAL, HF) with hermetic coverage up to || < 5 TOTEM (5.3  η 6.7) CASTOR (5.2 < || < 6.6) ZDC (z = ±140 m, 8.3 ||) B = 4 T Fully functional at highest multiplicities; high rate capability for (pp, pA, AA), DAQ and HLT capable of selecting HI events in real time TOTEM CASTOR ZDC 5.3 <  < 6.7 5.2 < |h| < 6.6 8.3 < || ICHEP'06 Moscow 26.07 - 02.08.2006

  3. 1.2 Forward Region Layout |h| > 3 ZDC EM HAD (8.3 < ||) Forward HCal (3 < |h| < 5) (z =  140 m) TOTEM CASTOR (~ 10 λI) (5.3 <  < 6.7) (5.2 < h < 6.6) ICHEP'06 Moscow 26.07 - 02.08.2006

  4. 1.3 Overview: CMS Detector Coverage Kinematics at the LHC Large Range of Hermetic Coverage: Tracker, muons || < 2.4 ECAL +HCAL|| < 3 Forward HCAL 3 < || < 5 CASTOR 5.2 < || < 6.6 ZDC Gluon density has to saturate at low x ICHEP'06 Moscow 26.07 - 02.08.2006

  5. 1.4 Heavy Ion program at CMS • Excellent detector for high pT probes of quark-gluon plasma: - High rates and large cross sections - Quarkonia (J/,), heavy quarks ( ) and Z0 - High acceptance for calorimeters and muon system - High pT jets - High energy photons • Correlations - jet-jet - jet-, jet-*/Z0 - multijets • Global event characterization - Centrality - Energy flow to very forward region - Charged particle multiplicity - Azimuthal anisotropy • Forward physics and ultraperipheral interactions - Limiting Fragmentation, Saturation, Color Glass Condensate - Exotica • Monte-Carlo simulation tools: - PYTHIA, HIJING, PYQUEN/HYDJET ICHEP'06 Moscow 26.07 - 02.08.2006

  6. 2.1 Quarkonia and heavy quarks from SPS and RHIC to LHC Increase energy √S=17-200 GeV/n-n  5500 GeV/n-n Plasma hotter and longer lived than at RHIC Unprecedented Gluon densities Access to lower x, higher Q2 Availability of new probes LHC  Quarkonia with high statistics (J/y, y'; , ', '') Large cross-section for J/ and  families Different melting for , ', '‘ Z0 with high statistics. The possibility to use ET balance of Z0(*)+jet to observe medium induced energy loss. Large cross-section for heavy-quarks (b, c): observation of medium induced energy loss in high mass dimuon spectrum and secondary J/ - - ICHEP'06 Moscow 26.07 - 02.08.2006

  7. 2.2Quarkonia (J/, ): reconstruction MC simulation/visualization of Pb+Pb event (dNch/dh|h=0 ~ 3000) using the pp software framework  →m+m ICHEP'06 Moscow 26.07 - 02.08.2006

  8. 2.3 J/ and  spectra for multiplicity dNch/d = 2500 For Pb-Pb at integrated luminosity 0.5nb-1 p/K decays into mm b,c-hadrons into mm S/B N J/y 1.2 180000  0.12 25000 Combinatorial background: Mixed sources, i.e. 1 m from p/K + 1 m from J/y 1 mfrom b/c + 1 m from p/K ICHEP'06 Moscow 26.07 - 02.08.2006

  9. 2.4 J/ and  spectra (subtraction of the like sign spectra)  both muons |h| < 2.4 both muons |h| < 2.4 both muons |h| < 0.8 both muons |h| < 0.8 See talk of Olga Kodolova for details. ICHEP'06 Moscow 26.07 - 02.08.2006

  10. 2.5 Heavy quarks b, c  / J/ +X. Secondary vertex finding and correlated background rejection r is transverse distance between the intersection points with the beam line belonging two different muon tracks BB m+m  BB  J/ym+m b-quark energy loss affects B-jet fragmentation and modification dimuon spectra depending on mechanism of heavy-quark production (for BB → + ) and intensity of jet quenching ICHEP'06 Moscow 26.07 - 02.08.2006

  11. 3.1Jet cross section & expected event rate Expected statistics for CMS acceptance (no trigger and reconstruction efficiency) jet,| < 3, |h,| < 2.4 CERN Yellow Report, hep-ph/0310274 ICHEP'06 Moscow 26.07 - 02.08.2006

  12. 3.2 High pT jets. Jet reconstruction in HI collisions 1. Subtract average pileup 2. Find jets with iterative cone algorithm 3. Recalculate pileup outside the cone 4. Recalculate jet energy Full jet reconstruction in central Pb-Pb collision HIJING, dNch/dy = 5000 BACKGROUND SUBTRACTION ALGORITHM The algorithm is based on event-by-event-dependent background subtraction: Efficiency, purity Measured jet energy Jet energy resolution Jet spatial resolution: (rec- gen) = 0.032; (rec- gen) = 0.028 Better, than, size of tower (0.0870.087) ICHEP'06 Moscow 26.07 - 02.08.2006

  13. 3.3 Medium-induced partonic energy loss Collisional loss (incoherent sum over scatterings) Radiation loss (coherent LPM interference) Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al... Gulyassy-Wang; BDMPS; GLV; Zakharov; Wiedemann... Energy lost by partons in nuclear matter: ET03 (temperature), g (number degrees of freedom) EQGP >> EHG LHC, central Pb+Pb: T0, QGP ~ 1 GeV >> T0, HGmax ~ 0.2 GeV, EQGP/EHG (1 GeV / 0.2 GeV)3 ~ 102 ICHEP'06 Moscow 26.07 - 02.08.2006

  14. 3.4 Jet quenching in heavy ion collisions • One of the important tools to study QGP properties in ultrarelativistic heavy ion collisions is a QCD jet production: medium-induced energy loss of energetic partons (jet quenching) is very different in cold nuclear matter and in QGP, resulting in many observable phenomena. Nuclear geometry and QGP evolution impact parameter b ≡ |O1O2| - transverse distance between nucleus centers j2 B – generation point of jets j1 and j2 Space-time evolution of dense matter, created in region of initial overlaping of colliding nuclei, is described by Lorenz-invariant Bjorken's hydrodynamics J.D. Bjorken, PRD 27 (1983) 140 j1 ICHEP'06 Moscow 26.07 - 02.08.2006

  15. 3.5 Jet quenching: pT-distribution and elliptic flow 30,000 minimum bias Pb+Pb events, √s = 5.5A TeV (ntot= 30000) v2(pT) pT-distribution v2= cos 2 (Elliptic flow): sharp drop due to jets and additional v2 due to jet quenching v2(pT): ~30%-reduction due to jets and small influence due to jet quenching ICHEP'06 Moscow 26.07 - 02.08.2006

  16. 3.6 Jet quenching: jet fragmentation functionD(z) It is probability distribution for leading hadron in the jet to carry fraction z = pTh/pTjet of jet transverse momentum Pb+Pb (b = 0), √s = 5.5A TeV, ETjet > 100 GeV (0) , h , h In the jet induced by heavy quark, the energetic muon can be produced and detected (“b-tagging”) DPbPb(z)/Dpp(z) ~ 0.8 (0.4 < z < 0.7) ICHEP'06 Moscow 26.07 - 02.08.2006

  17. 3.7Jet fragmentation function can be reconstructed with CMS tracking system Transverse momentum relative to thrust jet axis Longitudinal momentum fraction z along the thrust jet axis ICHEP'06 Moscow 26.07 - 02.08.2006

  18. “Spectators” 4.1 Centrality determination Au+Au @ RHIC CMS HF acceptance Phobos@RHIC ZDC ZDC “Spectators” CMS HF and CASTOR will provide best correlation between energy flow and event centrality (maximal energy deposition and minimal energy relative fluctuations) ZDC improves resolution at large b (like RHIC) BEAMS BEAMS ICHEP'06 Moscow 26.07 - 02.08.2006

  19. 4.2 Correlation between energy flow and centrality We use energy response of the HF-calorimeter (3 < | h |< 5.2) where the bulk of reaction energy is deposited for Ar+Ar collisions. 1. E/ET  b correlation 2. Impact parameter resolution σb using E/ET, total (a) and transverse (b) energy responses in HF-calorimeter and comparison with HIJING predictions. Average resolution of impact parameter determination for Ar-Ar collisions is from 0.5 fm (most central events) up to 1 fm (peripheral events). ICHEP'06 Moscow 26.07 - 02.08.2006

  20. 4.3 Azimuthal angle of reaction plane • Non-central heavy-ion collisions (b ≠ 0), elliptic volume of interacting nuclear matter, energy flow illustrates azimuthally anisotropic elliptic volume. • Calorimeters are used to determine event plane. • Azimuthal anisotropy can be estimated with CMS calorimeters with and without the determination of event plane. HYDRO, Pb+Pb collisions, b = 6 fm. GEANT-based simulation Energy flow ICHEP'06 Moscow 26.07 - 02.08.2006

  21. 4.4 Charged Particle Multiplicity: dNch/d Determination of the primary charged-particle multiplicity is based on the relation between the pseudorapidity distribution of reconstructed clusters in the innermost layer of the CMS pixel tracker and that of charged-particle tracks originating from the primary vertex. Single layer hit counting in innermost pixel barrel layer • High granularity pixel detectors • Pulse height in individual pixels to reduce background • Very low pT reach, pT > 26 MeV (counting hits!) On an event-by-event basis, the reconstructed multiplicity is within 1-2% of the true value in the | η | < 2 region. ICHEP'06 Moscow 26.07 - 02.08.2006

  22. 5.1Monte-Carlo HI simulatons at LHC There are two kind of MC HI simulations in HIC at LHC: 1. “Hard probes” signal event (jets, quarkonia, heavy quarks, Z) is generated with standard pp generator (PYTHIA,...) and superimposed on background of full heavy ion event 2. Global observables (particle spectra) and multiplicity background for “hard probes” are generated with a heavy ion event generator (HIJING,...) Problem: In most existing HI event generators such important effects as jet quenching and elliptic flow are not included or implemented poorly Develop MC tools for adequate, fast simulation of physics phenomena ICHEP'06 Moscow 26.07 - 02.08.2006

  23. 5.2 Fast Monte-Carlo tools to simulate jet quenching and flow effects • PYQUEN- fast code to simulate jet quenching • (modify PYTHIA6.4 jet event) • http://cern.ch/lokhtin/pyquen • HYDRO- fast code to simulate transverse and elliptic flow in central • and semi-central AA collisions at LHC, • http://cern.ch/lokhtin/hydro • HYDJET- merging HYDRO (flow effects), PYTHIA • (hard jet production) and PYQUEN (jet quenching) • http://cern.ch/lokhtin/hydro/hydjet.html • Significant progress in development of Monte-Carlo models for simulation of jet quenching is achieved (PYQUEN, HIDJET). • It describes RHIC data adequately. See talk of Igor Lokhtin for details. ICHEP'06 Moscow 26.07 - 02.08.2006

  24. 6.1 Summary and outlook • At LHC a new regime of heavy ion physics will be reached where hard particle • production can dominate over soft events, while the initial gluon densities are • much higher than at RHIC, implying stronger partonic energy loss observable • in new channels. • CMS is an excellent device for the study of quark-gluon plasma by hard probes: • - Quarkonia and heavy quarks • - Jets, ''jet quenching'' in various physics channels • CMS will also study global event characteristics: • - Centrality, Multiplicity • - Correlation and Energy Flow reaching very low pT • CMS is preparing to take advantage of its capabilities • - Excellent rapidity and azimuthal coverage, high resolution • - Large acceptance, nearly hermetic fine granularity hadronic and • electromagnetic calorimetry - Excellent muon and tracking systems - New High Level Trigger algorithms specific for A+A • - Zero Degree Calorimeter, CASTOR and TOTEM will be important • additions extending to forward physics ICHEP'06 Moscow 26.07 - 02.08.2006

  25. 6.2 Some publications used in report CMS HCAL Technical Design Report 1997 CERN/LHCC 97-31 CMS MUON Technical Design Report 1997 CERN/LHCC 97-32 CMS ECAL Technical Design Report 1997 CERN/LHCC 97-33 CMS Technical Tracker Design Report 1998 CERN/LHCC 98-6 Quarkonia. M.Bedjidian, O.Kodolova, pTDR, v.2, CMS-NOTE-2006/089 M.Bedjidian, V.Kartvelishvili and R.Kvatadze, CMS-NOTE-1999/017(1999) Jets reconstruction algorithm . I.Vardanyan, pTDR, v.2, CMS-NOTE-2006/050 Jet fragmentation with tracker. C.Roland, CMS-NOTE-2006/031, CMS-RN-2003/003 R.Vogt, Phys. Rep., v.310, p.197, 1999 I.Lokhtin, S.Petrushanko, L.Sarycheva, A.Snigirev, CMS-NOTE-2003/019 I.Damgov, V.Genchev, V.Kolosov, I.Lokhtin, S.Petrushanko, L.Sarycheva, C.Teplov, S.Shmatov, P.Zarubin, CMS-NOTE-2001/055 I.Lokhtin, A.Snigirev, Eur. Phys. J., C45, p.211-217, 2006 ICHEP'06 Moscow 26.07 - 02.08.2006

  26. 6.3 Acknowledgement This report includes the remarks of I.P.Lokhtin, A.M.Snigirev, O.L.Kodolova, M.Bedjidian, B.Wyslouch, D.Denegri, M.Murrey, C.Roland, C.Mironov, I.N.Vardanyan, K.Yu.Teplov, S.V.Petrushanko and other CMS HI collaborators ICHEP'06 Moscow 26.07 - 02.08.2006

  27. BACKUP SLIDES (Appendix 7.1 – 7.8) ICHEP'06 Moscow 26.07 - 02.08.2006

  28. 7.1 Data Acquisition and Trigger Level 1 hardware trigger • Muon track segments • Calorimetric towers • No tracker data • Output rate (Pb+Pb): 1-2 kHz comparable to collision rate buffer High level trigger • Full event information available • Every event accepted by L1 sent to an online farm of 2000 PCs • Output rate (Pb+Pb): ~ 40 Hz • Trigger algorithm same or similar to offline reconstruction switch Online Farm ICHEP'06 Moscow 26.07 - 02.08.2006

  29. 7.2 Measuring Muons 30% 10% 20% 10% 2% Resolution Standalone Resolution with tracker ICHEP'06 Moscow 26.07 - 02.08.2006

  30. <ΔE>=0 GeV < ΔE>=4 GeV < ΔE>=8 GeV Background # Events/4 GeV Isol. 0+jet ET/0-ETJet (GeV) 7.3 Balancing  or Z0 vs Jets: Quark Energy Loss , Z0 1 month at 1027cm-2s-1 Pb+Pb Jet + Z0 ICHEP'06 Moscow 26.07 - 02.08.2006

  31. 7.4 Z0+−detection at CMS The expected number of Z0 m+m: ~104/1.3x106 s of Pb-Pb running at L = 1027cm2s1 Z0 can be measured with muon system alone and with muon+tracker systems. Z0+jet events The expected number of Z0+jet for jet ET > 50 GeV and |hjet| < 1.5: 900/1.3x106 s of Pb-Pb run at L = 1027cm2s1. Z0 + jet events with PTZ0 measured from pair + should allow to study effects of jet quenching using energy balance ETjet = PTZ0 AA = A2αpp with =1 spp was taken from PYTHIA, correction k = 2 for cc and bb and k = 1.3-1.5 for Z, W, tt HIJING was used for AA event ICHEP'06 Moscow 26.07 - 02.08.2006

  32. 7.5 Invariant mass spectrum of μ+μ−-pairs from */Z+jet production New potentially important channel for CMS Background is insignificant. Interference between γ* and Z is important. I.Lokhtin, A.Snigirev, A.Sherstnev, Phys. Lett. B599, p.260-268, 2004 ICHEP'06 Moscow 26.07 - 02.08.2006

  33. 7.6 Medium-induced partonic energy loss Collisional loss (incoherent sum over scatterings) Radiation loss (coherent LPM interference) Gulyassy-Wang; BDMPS; GLV; Zakharov; Wiedemann... Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al... General kinetic integral equation: 1. Collisional loss and elastic scattering cross section: 2. Radiative loss (BDMS): “dead cone” approximation for massive quarks: ICHEP'06 Moscow 26.07 - 02.08.2006

  34. 7.7 Energy-energy correlation function (definition) New potentially important channel for CMS • ET() – transverse energy flow in , •  – azimuthal size of a calorimeter sector •  – azimuthal angle of a calorimeter sector • – relative azimuthal angle between two azimuthal sectors In the continuous limit  → 0 ICHEP'06 Moscow 26.07 - 02.08.2006

  35. 7.8 Energy-energy correlation function dT/d For non-central collisions with a clearly visible elliptic flow of the transverse energy minimumbias events   azimuthal angle. Correlator dT/d is independent of the reaction plane angle Rand is calculated explicitly: The transverse energy-energy correlator dT/d as a function of relative azimuthal angle  without (blue histogram) and with partonic energy loss for the “small-angular” (red histogram) and the “broad-angular” (magenta histogram) parameterizations of emitted gluon spectrum in central Pb-Pb collisions. (Histograms calculated without effects of installation.) I.Lokhtin, L.Sarycheva, A.Snigirev, Eur. Phys. J., C36, p.375-379, 2004 ICHEP'06 Moscow 26.07 - 02.08.2006

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