E. García 1 Heavy Ion Physics with CMS E. García University of Illinois at Chicago for the CMS Collaboration Noviembre 2006 Puerto Vallarta, México CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas, Tbilisi, UC Davis, UI Chicago, U. Iowa, U. Maryland, U. Minnesota, Yerevan, Vanderbilt, Warsaw, Zagreb VI Latin American Symposium on High Energy Physics

E. García 2 Outline 1. Introduction 2. Soft physics and global event characterization l Charged particle multiplicity l Centrality determination l Azimuthal asymmetry (Flow) l p T spectra - tracking 3. High p T Probes l High p T Jets jet- , jet-Z 0  reconstruction: Z 0 l Quarkonia (J/ ,  ) 4. Forward Physics l Gluon Saturation, Limiting Fragmentation l Ultra Peripheral Collisions

E. García 3 The reference: RHIC Elliptic Flow Jet Suppression High energy density Applicability of thermodynamics BRAHMS, Nucl. Phys. A757 (2005) 1-27 STAR, PRL 91, PHOBOS, Nucl. Phys. A757 (2005) 28

E. García 4 From RHIC to LHC Factor 28 increase in energy to √s NN =5.5 TeV High Luminosity Large Cross sections – High p T particles – Jets, which are now directly identifiable – J/ψ, Z 0 and  -family production Baier,hep-ph/ RHIC Vogt, hep-ph/ LHC  Accardi, hep-ph/

E. García 5 LHC kinematics LHC provides access to the widest range of Q 2 and x, including regions where Z 0 and  will be accessible, and low x where gluon saturation is expected J/  Z0Z0  Q2Q2 Q = M gluon saturation Stirling, Eur. Phys. J. C 14, 133 (2000)

E. García 6 CMS detector - |  |<2.4 Silicon Microstrips and Pixels Si TRACKER CALORIMETERS ECAL Scintillating PbWO 4 crystals HCAL Plastic scintillator/brass sandwich MUON BARREL Drift Tube Chambers (DT) Resistive Plate Chambers (RPC)

E. García 7 Forward Region (5.2 <  < 6.7) TOTEM Forward HCal (3 <  < 5.2) CASTOR (5.2 <  < 6.6) ZDC HAD EM (z =  140 m) (8.3 <  )

E. García 8 CMS coverage HCAL (Barrel+Endcap+Forward) Sub detectorCoverage Tracker, muons |  | < 2.4 ECAL + HCAL |  | < 3.0 Forward HCAL 3.0< |  | < 5.2 Totem/Castor 5.2 < |  | < 6.6 ZDC 8.3 < |  | Q2Q2

E. García 9 Charged particle multiplicity Pixels Inner Strips Outer Strips Simulated central Pb+Pb event: dN ch /d  |  =0 ~ 3000 Tracker : Pixel layers and the silicon strip counters. – Pixel detector: 3 pixel barrel layers and 2 endcap disks in forward and backward directions. Barrel layers cover up to |η| < 2.1. –T he barrel layers contain ~ 9.6, 16, and 22.4 million pixels, respectively.

E. García 10 Charged particle multiplicity cont. High granularity pixel detectors Pulse height in individual pixels to reduce background Very low p T reach, p T > 26 MeV On the left – Single layer hit counting in innermost pixel barrel layer – cosh  dependence of dE in adc units

E. García 11 Event Characterization: Centrality E T [GeV] impact parameter [fm] LHC RHIC Energy in Forward HCal PHOBOS ZDC Peripheral Central (Forward HCal or Castor signal for CMS ) Forward HCal will provide correlation between E T and event centrality In addition ZDC and Castor will improve the centrality determination and increase various physics triggers at large b. CMS Note

E. García 12 Centrality cont. Simulations of the calorimeter collisions indicate that over 80% of E T will be detected. Shown on the left –500 min bias Ar-Ar Hijing collisions (3 <  < 5) – Upper plot is the relationship between the simulation and reconstructed (HF) transverse energy vs. the impact parameter. –The lower plot is the accuracy (  E / ) of the impact parameter measurement. CMS Note

E. García 13 Flow  x Reaction plane (  R ) x z y x (defines  R ) y z PHOBOS Initial spatial azymuthal asymmetry Azimuthal (momentum) asymmetry preserved when measured in the detectors  Highly interactive medium

E. García 14 Flow measurements in CMS CMS Note  =0.19 rad CMS Note Left: difference between generated and reconstructed reaction plane angle for Pb+ Pb collisions b = 6 fm Right: reconstructed energy deposition in the barrel and endcap regions for electromagnetic and hadronic calorimeters as function of as function of the azimuthal angle for b = 6 fm

E. García 15 Nuclear modification factor RHIC to LHC – p T spectra Yield suppression  partonic energy loss in medium generated in collision STAR-Jana Bielcikova Hard Probes 2006

E. García 16 CMS Tracking Performance Top: charged particle spectra Bottom: track reconstruction efficiency as function of p T. –Pb+Pb collisions dN ch /dy ~ 3000 –Left : track quality cuts optimized for low fake track rate –Right: cuts optimized for high efficiency Reconstructed Tracks Fake Tracks Reconstructed Tracks Fake Tracks dN/dp T Central Pb+Pb dN ch /d  |  =0 ~ 5000 p T (GeV/c)

E. García 17 Tracking resolution Momentum Resolution Track-pointing Resolution Transverse (  t ~20  m) Longitudinal (  l ~50  m) With current studies: good tracking purity and efficiency down to p T ~ 1 GeV/c. -

E. García 18 Jets at LHC Using reconstructed jets we will be able to study directly – Fragmentation functions – Azimuthal correlations – Energy loss in dense medium STAR PRL (2004) Jet tomography

E. García 19 Jet Reconstruction Use calorimeters for jet reconstruction Jet E T ~100 GeV, background dN ch /dy ~ 5000 Event-by-Event  -dependent background subtraction+ iterative jet cone-finder algorithm Jet resolution :  (  rec -  gen ) = 0.032;  (  rec -  gen ) =  (   rec -   gen )  16 % Jet in pp after pileup subtraction Jet superimposed on Pb + Pb background Jet in Pb + Pb after pileup subtraction CMS NOTE 2006/050

E. García 20 Efficiency, Purity vs. Jet Energy Reconstruction of GeV Jets in Pb-Pb background Efficiency: number of events with true reco. Jets/Number of all generated events Purity : number of events with true reco. QCD Jets/ Number of all reco. Jet events (true+fake). Threshold of jet reco. E T >30 GeV. CMS NOTE 2006/050

E. García 21 Jet studies using calorimeter + tracking Azimuthal correlations Jet Fragmentation: z distribution Jet Fragmentation: p T with respect to jet axis 1/N jets dN ch /dz 1/N jets dN ch /dp T jet dN/d(  ) p T jet (GeV/c) dN ch /d  |  =0 ~ one 30 GeV jet/event Pb+Pb dN ch /d  |  =0 ~ GeV jets  (rad) Some example Jets observables using calorimetry –Jet cross sections –Jet - Jet correlations –Jet-  /Z correlations Calorimetry and tracking –Jet fragmentation –Jet shape –Tagged heavy quark jets –Inclusive p T spectra –Back-to-back particle correlations

E. García 22 Measuring muons

E. García 23 Z 0 production Z 0 -  can be reconstructed with high efficiency Z 0 production will probe nuclear shadowing and parton energy loss M z 0 > M  –Z 0 not as sensitive to nuclear effects –Z 0 may be used as reference to  production. CMS Note

E. García 24 jet-  and jet-Z 0 Study of jet quenching with “calibrated” energy: – On average Z 0 (or  and jet E T should balance – Z 0 (or  can be reconstructed with very good E T resolution  - jet: Larger background from leading  0 in QCD dijets Z – jet: Cleaner but lower rates Simulation dN/dy ~7000 E Tjet,  > 120GeV in Barrel E T    o - E T Jet (GeV) isolated  0 +jet # Events /4 GeV E T  -  0 -E T Jet (GeV) = 8 GeV = 4 GeV = 0 GeV  0 +jet 1 month at cm -2 s -1 Pb+Pb Simulation dN/dy ~7000 E Tjet,  > 120GeV in Barrel for different values of jet energy loss ( ΔE) CMS Note

E. García 25 Quarkonia: probe of high-density QCD media H.Satz, hep-ph/ J/  at LHC will clarify SPS/RHIC suppression (  ~ 30 GeV/fm 3 ) Dissociation = hot QCD matter thermometer Charmonium spectral suppression as function vs. T deconfinement

E. García 26 Simulation studies Signals (J/ ,  ): CEM, NLO-pp, CTEQ5M+EKS98 PDF, T AA -scaled Light-q background ( ,K): HIJING normalized to dN ch /dη=2500, 5000 Heavy-Q background (c,b): NLO-pp, CTEQ5M+EKS98 PDF, T AA -scaled σ J/ψ = 35 MeV/c 2 in barrel+endcap (i.e. both muons |η| < 2.4) Kodolova, Bedjidian CMS Note-2006/089 Signal+Background Estimate background using same sign di-muons Subtracted background

E. García 27  production in AA at the LHC Large cross-sections: d  /dy ~ 20 x RHIC  melts only at LHC: T D ~ 4 Tc  unaffected by final-state interactions –Small hadronic absorption –Small # bbar pairs  small  regeneration  suppression will be a “cleaner” probe than J/   spectroscopy: T D (  ’) ~ T D (J/  ) -  ’/  vs p T very sensitive to system temperature & size minijet model parton gas model Gunion, Vogt, NPB 492 (1997) 301

E. García 28  mass spectra simulations Multiplicity dN ch /d  ~ 5000 σ  = 54 MeV/c 2 (barrel), and σ  = 90 MeV/c 2 (barrel+endcap) Barrel+ Endcap: (bothmuons |η| < 2.4) Barrel: (both muons |η| < 0.8) Kodolova, Bedjidian CMS Note-2006/089

E. García 29 Forward Physics: Gluon saturation region Sub detectorCoverage Forward HCAL 3.0< |  | < 5.2 CASTOR 5.2 < |  | < 6.6 ZDC 8.3 < |  | McLerran, hep-ph/ ZEUS data for gluon distribution In partons Q2Q2 New regime of QCD is expected to reveal at small x due to effects of large gluon density Forward measurements will be a good test ground for this physics CGC

E. García 30 Limiting Fragmentation At RHIC limited fragmentation can be explained by gluon saturation (Colour Glass Condensate) model. –Data PHOBOS 200, 130 and 62 GeV AuAu –Model McLerran-Venugopalan This can be measured also at LHC for larger gluon density region Phys. Rev. D 49, 2233 (1994 ) Castor Coverage

E. García 31 Ultra-peripheral collisions photo production ZDC to trigger of A* fragments + two muons in the central detector Meson or lepton/quark pair A* A A  

E. García 32 Soft physics and global event characterization Centrality and good event selection Charged particle multiplicity Azimuthal asymmetry (Flow) Spectra + Correlations High p T Probes High p T Jets - detailed studies of jet fragmentation, centrality dependence, azimuthal asymmetry, flavour dependence, leading particle studies High energy photons, Z 0 jet- , jet-Z 0, multi-jet events Quarkonia (J/ ,  ) and heavy quarks Forward Physics Limiting Fragmentation, Saturation, Colour Glass Condensate Ultra Peripheral Collisions Exotica Heavy Ion Physics Program in CMS

E. García 33 Backup Transparencies

E. García 34 Results At RHIC Energies Phys Lett. B. 518, 41 (2001); J. Phys G28, 1745 (2002) Can fit each energy with a common chemical “freeze-out” temperature, T ch, and baryon chemical potential  B. Suggests a high degree of chemical equilibrium (and thermalization) at the point where particles are “frozen-out” (created).

E. García 35 Background Subtraction Algorithm Event-by-event background subtraction: Calculate and D Tower (h) for each h ring Recalculate all E T Tower tower energies: E T Tower = E T Tower – E t pile-up E t pile-up = + D Tower (h) Negative tower energies are replaced by zero Find Jets with E T jet > E t cut using standard iterative cone algorithm using new tower energies Recalculate pile-up energy with towers outside of the jet cone Recalculate tower energy with new pile up energy Final jets are found with the same iterative cone algorithm E T Jet = E T cone – E t pile-up new

E. García 36 Jet Definitions Parton jet –This is what we can calculate Final state particle jet –Fragmentation/hdronization –Non-pertubative –MC generators rely on parametrizations of experimental data Calorimeter Jet –This is what we measure in the detector Need to associate final state particles with initial parton –No unique way of doing this! –Jet algorithms –=> Jet Calibration

E. García 37   Jet Resolutions  better than size of calorimeter tower (0.087x0.087) E T resolution ~16% at 100GeV Further improvement can be achieved by adding tracker information –p T measurement of tracks is more precise than the response of the calorimeter –Recover charged tracks that are bent out of the jet cone by the magnetic field ETET

E. García 38 J/ ,  acceptances J/Ψ accepted above p T ~2 GeV/c (low-p T muons absorbed in material at y=0, but punchthrough at y~2). High-p T acceptance ~15%  accepted (~35%) down to p T =0 GeV/c. High-p T acceptance ~15% acceptance Improved low p T J/ Ψ acceptance at forward rapidities  JΨJΨ JΨJΨ η pTpT p T (GeV/c)

E. García 39 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 Onli ne Far m switch 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 buffer

E. García 40 EECAL BECAL Electromagnetic Calorimeter PbWO4 crystals –Granularity in  x  : – x (Barrel) and – x to 0.05x0.05 (Endcap) Endcap with preshower for  /p0 separation Details in CMS Technical Design Reports |  |< 3 (1.5 barrel)

E. García 41 HCAL Barrel (HB) and Endcap (HE): Cu/Scintillator Forward (HF): Fe/Cerenkov(fiber) High granularity:  x  x (barrel) x (endcap) x (HF) 5.15 interaction lengths at  =0 Dynamic range: 5 MeV-3 TeV HF: 3<|  |<5 HB, HE: |  |<3  Energy Resolution

E. García 42 Granularity

E. García 43 Zero Degree Calorimeter Tungsten-quartz fibre structure electromagnetic section: 19X 0 hadronic section 5.6λ 0 Rad. hard to  20 Grad (AA, pp low lum.) Energy resolution:  10% at 2.75 TeV Position resolution:  2 mm (EM sect.)

E. García 44 CASTOR

E. García 45 TOTEM (T2)

E. García 46 +-+- +-+- +-+- e+e-e+e- J/  acceptances LHC experiments Andrea Dainese Hard Probes 2006

E. García 47 ALICE  +  - ALICE e + e - CMS  +  - ATLAS  +  - acc.  -4 <  < -2.5|  | < 0.9|  | < 2.5|  | < 2 M res.65 MeV35 MeV37 MeV70 MeV J/ ,  ’ 150, 7245, --313, --60, -- perf. , ?  ’ , ??  ’ , ?  ’ p t J/  0-20 GeV0-10 GeVfew-20 GeV-- LHC experiments Charmonia Performance Bkg input: dN ch /dy~ in central Pb-Pb. for 1 month central min. bias Andrea Dainese Hard Probes 2006

E. García 48  Physics Cont. Light quark pairs –Difficult to measure at CMS because of low p T (~ 50 MeV) and low rate, challenge for triggering –Use ZDC + multiplicity trigger as in STAR Phys. Rev. Lett. 89 (2002) STAR

E. García 49 Ultra peripheral collisions photo production