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G á bor I. Veres Eötvös Loránd University , Budapest

Preparation for the first p+p physics with the CMS experiment and the plans of the CMS Heavy Ion Group. Members of our working group in Budapest: Ferenc Sikl é r (KFKI RMKI) Kriszti á n Krajcz á r (ELTE) S á ndor Szeles (ELTE) G á bor I. Veres (ELTE). G á bor I. Veres

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G á bor I. Veres Eötvös Loránd University , Budapest

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  1. Preparation for the first p+p physics with the CMS experiment and the plans of the CMS Heavy Ion Group Members of our working group in Budapest: Ferenc Siklér (KFKI RMKI) Krisztián Krajczár (ELTE) Sándor Szeles (ELTE) Gábor I. Veres (ELTE) Gábor I. Veres Eötvös Loránd University, Budapest Zimányi 2008 Winter School on Heavy Ion Physics Budapest, 25-28 November 2008 Sponsors: OTKA F 49823, NKTH-OTKA H07-C 74248 OTKA T 48898, NKTH-OTKA H07-B 74296

  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 5.3<||<6.6, ZDC ||>8.3) 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 ET>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 pT 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 pT=75 MeV/c • cluster shape must match trajectory direction, very low fake track rate Tracking optimized for all pT 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 pT 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 pT is expected Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

  14. Results - multiplicity The pT distribution gets flatter with increasing Nch After unfolding the detector responsewe 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 (K0s, , also ,  and their antiparticles) • Fundamental measurements (N, dN/d, dN/dpT), 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 • The CMS detector and the Heavy Ion program • Quarkonia and heavy quarks • Jet spectra • Jet quenching in heavy ion collisions • Azimuthal anysotropy • Summary 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 Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

  17. Evolution of the heavy ion collision QGPand hydrodynamic expansion hadronic phase and freeze-out initial state pre-equilibrium hadronization Kineticfreeze out dN/dt Chemical freeze out RHIC side & out radii: 2 fm/c Rlong & radii vs reaction plane: 10 fm/c 1 fm/c 5 fm/c 10 fm/c 50 fm/c time 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: pT/pT < 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 TOTEM Collaboration CASTOR ZDC 5.3 <  < 6.7 5.2 < |h| < 6.6 8.3 < || 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) 2307-2455 Broad and exciting range of observables -Jets and photons - Quarkonia, Z0 and heavy quarks in high-mass dimuon decay modes‏ - High-pT hadrons - Low-pT hadrons - Ultraperipheral collisions, forward physics Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

  20. regeneration ? SPS RHIC LHC suppression ? Energy Density High mass dimuons Dissociation of Quarkonia (Debye-screening): Hot QCD Thermometer • Y: large cross-section: 20×RHIC • Y melts only at LHC: TD~4 TC • few bb(bar) pairs: less regeneration • much cleaner probe than J/ψ • LHC: new probe: Y vs. Y' vs. Y'' • J/ψsuppression: RHIC comparable to SPS • Regeneration compensate screening • J/ψ not screened at RHIC (TD~2Tc)? • LHC: recombination or suppression? • Z0- 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 Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

  21. Dimuon efficiency and purity  is embedded in Pb+Pb events “realistic” LHC multiplicity range Eff = Efftrk-1 x Efftrk-2 x Effvtx > 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 0.5nb-1 background:p/K mm b, c-hadrons mm S/B N J/y 1.2 180000  0.12 25000 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 ET~ 0.5 TeV [PbPb, 0.5 nb-1] Njets~6·106 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. 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 Jet reconstruction in HI events 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) Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

  25. High-pT hadron reconstruction CMS tracking performance for Pb+Pb collisions, HYDJET, dNch/d|y=0 = 3500 • Efficiency • Fake Rate pT resolution<1% 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) Radiation loss (coherent LPM interference) Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al... Gyulassy-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 Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

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

  28. Jet axis Hadrons q,g q,g q,g Photon Photon-tagged jet fragmentation functions Jet axis provides parton direction Multiplicity and flow measurements characterize density, path length Charged hadron tracks used to calculate z = pT/ET Measure jet fragmentation function: dN/dξ with ξ=-log z Photon energy tags parton energy ET Ingredients: • Event/Centrality selection • Reaction plane determination • Vertex finding • Track reconstruction • Jet finding • Photon identification 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 ET >70GeV ET >100GeV Medium modification of fragmentation functions can be measured High significance for 0.2 < ξ < 5 for bothETγ>70GeV andETγ>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 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-pT hadrons, ''jet quenching'' in various physics channels • CMS will also study global event characteristics: • Centrality, Multiplicity • Correlations and energy flow in wide range of pT 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 Gábor I. Veres Zimányi 2008 Winter School on Heavy Ion Physics

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