Preparation for the first p+p physics with the CMS experiment and the plans of the CMS Heavy Ion Group Gábor I. Veres Eötvös Loránd University, Budapest Zimányi 2008 Winter School on Heavy Ion Physics Budapest, November 2008 Sponsors: OTKA F 49823, NKTH-OTKA H07-C OTKA T 48898, NKTH-OTKA H07-B Members of our working group in Budapest: Ferenc Siklér (KFKI RMKI) Krisztián Krajczár (ELTE) Sándor Szeles (ELTE) Gábor I. Veres (ELTE)

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 2 First physics with hadrons at CMS Contents –The detector –First physics with hadrons –Triggers: L1 and HLT –Charged hadron rapidity density –Charged hadron spectra –Preparations for the heavy ion program –Observables with heavy ions First analyses based on silicon pixel detector and strip tracker Early physics, constrain QCD models of hadron production Also important for MC tuning, backgrounds, pile-up, calibration and understanding of the detector, basis for exclusive physics This talk: preparations, results of analysis exercises

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 3 The CMS detector A single detector combines global characterization and specific probes Silicon tracker: pixels and strips (|  |<2.4) Electromagnetic (|  |<3) and hadronic (|  |<5) calorimeters Muon chambers (|  |<2.4) Extension with forward detectors (CASTOR ) CMS can measure leptons (e,  ), charged ( , K, p), and neutral (n,  ) hadrons

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 4 Minimum bias triggers – zero bias or pixel track Random trigger, Level-1 Zero bias: trigger on crossing of filled bunches Optimal for moderate intensity, heavily prescaled At least one track in the pixel detector, HLT Very low bias, optimal for very low intensity running (e.g. 900 GeV) Efficiency: 88% IN, 99% ND, 69% DD, 59% SD at 14 TeV Can be combined with offline vertex trigger

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 5 Minimum bias triggers – forward calorimeters Forward hadronic calorimeters, Level-1 - Count towers with E T >1 GeV in the forward calorimeters (HF, 3<|  |<5) - Require hits on one side: 89% IN efficiency (900 GeV) - Require hits on both sides: 59% IN efficiency only, but insensitive to beam-gas Usability of triggers depend on bunch pattern and luminosity

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 6 Charged particle rapidity density - Count clusters in the pixel barrel layers, as done in PHOBOS at RHIC - Use pixel cluster size information to:  estimate the z position of the interaction vertex  remove hits at high  from non-primary sources - Correction for loopers, secondaries, expected systematic error below 10% - No need for tracking and alignment, sensitivity down to p T of 30 MeV Important cross check with particle spectra from tracking

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 7 Tracking – pixel detector Pixel detector 3 barrel layers (radii: 4, 7, 10 cm) and 2 endcaps on each side Hit triplets Use pixel hit triplets instead of pairs, lower fake track rate modified triplet finding, reconstruction down to p T =75 MeV/c cluster shape must match trajectory direction, very low fake track rate Tracking optimized for all p T

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 8 Tracking – pixel tracks

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 9 Tracking – global tracks

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 10 Tracking - spectra Comparison of simulated (histogram) and reconstructed (symbols) spectra, 0.4<|  |<0.6 We can also IDENTIFY these particles  see talk by Sándor Szeles

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 11 Results – pions, kaons, protons Empirical (Tsallis) fit: Rapidity dependence can also be studied

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 12 Results – rapidity density The p T spectrum is integrated The acceptance of the tracker limits the accessible  /y range, Total number of produced charged particles cannot be measured

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 13 Results – energy dependence Comparison to lower energy measurements: FNAL, ISR, UA1, UA5, E735, CDF We can verify if dN/d  |  =0 continues its linear increase in log(s) A strong, non-linear increase of  p T  is expected

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 14 Results - multiplicity The p T distribution gets flatter with increasing N ch After unfolding the detector response we can measure multiplicity distribution Interesting physics (multiparton interactions, underlying event)

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 15 Conclusions so far Inclusive hadron physics –Charged hadrons (h ± ) –Identified charged particles via dE/dx (  ±,K ±,p/p) –Identified neutral particles via their decay (K 0 s, , also  ,   and their antiparticles) –Fundamental measurements (N, dN/d , dN/dp T ), tests of models Preparing for 900 GeV (?), 10 TeV and 14 TeV data taking The p+p physics at the LHC starts in a few months!

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 16 The CMS heavy ion physics program CMS Heavy-Ion Groups: Moscow, Lyon, CERN, Budapest, Athens, Ioannina, Demokritos, Lisbon, Adana, MIT, Illinois, Los Alamos, Maryland, Minnesota, Iowa, California Davis, Kansas, Mumbai, Auckland, Seoul, Vanderbilt, Colorado, Zagreb 1.The CMS detector and the Heavy Ion program 2.Quarkonia and heavy quarks 3.Jet spectra 4.Jet quenching in heavy ion collisions 5.Azimuthal anysotropy 6.Summary

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 17 Evolution of the heavy ion collision hadronization initial state pre-equilibrium QGP and hydrodynamic expansion hadronic phase and freeze-out dN/dt 1 fm/c5 fm/c10 fm/c50 fm/c time Kinetic freeze out Chemical freeze out RHIC side & out radii:   2 fm/c R long & radii vs reaction plane:   10 fm/c Correlation Femtoscopy R. Lednický, JINR Dubna & IP ASCR Prague

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 18 Heavy ion physics with CMS  Si tracker with pixels |  | < 2.4 good efficiency and low fake rates excellent momentum resolution,  p:  p T /p T < 2%  Muon chambers |  | < 2.4  Fine grained high resolution calorimetry (ECAL, HCAL, HF) with hermetic coverage up to |  | < 5  B = 4 T  TOTEM (5.3  η  6.7) CASTOR (5.2 < |  | < 6.6) ZDC (z = ±140 m, 8.3  |  |)  Fully functional at highest multiplicities; high rate capability for (pp, pA, AA), DAQ and HLT capable of selecting HI events real time CASTORZDC TOTEM Collaboration 5.2 <  < <  5.3 <  < 6.7

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 19 The CMS Heavy Ion program J. Phys. G: Nucl. Part. Phys. 34 (2007) Broad and exciting range of observables - Jets and photons - Quarkonia, Z 0 and heavy quarks in high-mass dimuon decay modes‏ - High-p T hadrons - Low-p T hadrons - Ultraperipheral collisions, forward physics

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 20 High mass dimuons J/ψ suppression: RHIC comparable to SPS Regeneration compensate screening J/ψ not screened at RHIC (T D ~2Tc)? LHC: recombination or suppression? Dissociation of Quarkonia (Debye-screening): Hot QCD Thermometer SPS suppression ? regeneration ? RHIC LHC Energy Density Z 0 - no final state effect, baseline for quarkonia (LHC: large section section)‏ B → J/ψ, BB → μ + μ - - information about b-quark in-medium rescattering & energy loss Y: large cross-section: 20×RHIC Y melts only at LHC: T D ~4 T C few bb(bar) pairs: less regeneration much cleaner probe than J/ψ LHC: new probe: Y vs. Y' vs. Y''

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 21 Dimuon efficiency and purity “realistic” LHC multiplicity range  is embedded in Pb+Pb events Eff = Eff trk-1 x Eff trk-2 x Eff vtx > 80% for all multiplicity (barrel)‏ > 65% for all multiplicity (barrel+endcap)‏ Purity = [true  reco]/[all vtx reco] > 90% (all multiplicities)‏

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 22 J/ and  spectra at dN/=2500 for Pb+Pb at integrated luminosity 0.5 nb -1 background:   /K   b, c-hadrons   S/B N J/   Combinatorial background: Mixed sources, i.e. 1  from  /K + 1  from J/  1  from b/c + 1  from 

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 23 Jet spectra Jet spectra up to E T ~ 0.5 TeV [PbPb, 0.5 nb -1 ] N jets ~6 · 10 6 HLT Detailed jet-quenching studies: jet fragmentation function, jet shape, jet azimuthal anisotropy,...

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 24 Jet reconstruction in HI events BACKGROUND SUBTRACTION ALGORITHM The algorithm is based on event-by-event  -dependent background subtraction: 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, dN ch /dy = 5000 Efficiency, purityMeasured jet energyJet energy resolution Jet spatial resolution:  (  rec -  gen ) = 0.032;  (  rec -  gen ) = Better than ,  size of tower (0.087  0.087)

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 25 High-p T hadron reconstruction p T resolution<1% Efficiency o Fake Rate CMS tracking performance for Pb+Pb collisions, HYDJET, dN ch /d  | y=0 = 3500 C. Roland et al.: NIM A566 (2006) 123

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 26 Jet quenching Collisional loss (incoherent sum over scatterings) Energy lost by partons in nuclear matter:  E  T 0 3 (temperature), g (number degrees of freedom)  E  QGP >>  E  HG LHC, central Pb+Pb: T 0, QGP ~ 1 GeV >> T 0, HG max ~ 0.2 GeV,  E QGP /  E HG  (1 GeV / 0.2 GeV) 3 ~ 10 2 Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al... Radiation loss (coherent LPM interference) Gyulassy-Wang; BDMPS; GLV; Zakharov; Wiedemann...

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 27 Nuclear modification factor Binary scalingp+p reference  One can measure at CMS:  jets up to E T ≈ 500 GeV  charged hadrons up to p T ≈ 300 GeV/c HYDJET

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 28 Photon-tagged jet fragmentation functions Event/Centrality selection Reaction plane determination Vertex finding Track reconstruction Jet finding Photon identification Ingredients: q,g Hadrons Jet axis q,g Photon Jet axis provides parton direction Photon energy tags parton energy E T Charged hadron tracks used to calculate z = p T /E T Multiplicity and flow measurements characterize density, path length Measure jet fragmentation function: dN/d ξ with ξ=-log z Main advantage Photon unaffected by the medium Avoids measurement of absolute jet energy

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 29 Jet fragmentation function ratio Reco quenched Pb+Pb / MC unquenched p+p E T   70GeV E T   100GeV Medium modification of fragmentation functions can be measured High significance for GeV and E T γ > 100 GeV

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 30 Elliptic flow in HI events with the CMS tracker (b=9 fm) Open circles are simulated and closed squares reconstructed events Method v 2 from fitting

Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics 31 Summary and outlook At LHC a new regime of heavy ion physics will be reached where –hard particle production dominates over soft events –the initial gluon densities are much higher than at RHIC –stronger QCD medium effects will be observable –also in new channels. CMS is an excellent apparatus for the study of quark-gluon plasma with hard probes: –Quarkonia and heavy quarks –Jets and high-p T hadrons, ''jet quenching'' in various physics channels CMS will also study global event characteristics: –Centrality, Multiplicity –Correlations and energy flow in wide range of p T and  CMS is preparing to take advantage of its capabilities –Excellent rapidity and asimuthal 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 extends to forward physics