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Heavy-Ions in CMS

Richard Hollis University of Illinois at Chicago. Heavy-Ions in CMS. 24 th Winter Workshop on Nuclear Dynamics. Expected energy density at the LHC. CMS Heavy-Ion program. J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455. dE T /d h → ϵ Bj J.D.Bjorken, Phys.Rev.D27(1983) 140.

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Heavy-Ions in CMS

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  1. Richard Hollis University of Illinois at Chicago Heavy-Ionsin CMS 24th Winter Workshop on Nuclear Dynamics

  2. Expected energy density at the LHC CMS Heavy-Ion program J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455 dET/dh→ϵBj J.D.Bjorken, Phys.Rev.D27(1983) 140 Study of QCD matter under extreme conditions Pb+Pb @ √sNN=5.5 TeV • Bulk observables (soft physics) • Hard probes • Ultra peripheral collisions p+p @ √s=14 TeV • First measurements of bulk observables • Analysis exercise “…presents the capabilities of the CMS experiment to explore the rich heavy-ion physics programme offered by the CERN Large Hadron Collider (LHC) .” Richard Hollis University of Illinois at Chicago

  3. The CMS detector Under construction Data! Basic layout: • Tracker • E/M Cal. • Hadronic Cal. • Magnet Iron • Return yoke • Muon Chambers Transverse Slice Cosmic muon in CMS at full magnetic field Richard Hollis University of Illinois at Chicago

  4. Tracker Dh=5 Calorimetry Dh=10 2p Castor Castor 2p Jet 0 f h -8 -6 -4 -2 0 2 4 6 8 Pixel+Strips Ecal ZDC Hcal ZDC Muons The CMS detector CMS h-f coverage • Silicon tracker: |h|<2.5 • Momentum resolution <2% for pT<100GeV and |h|<0.5. • Calorimetry: ECal |h|<3, HB,HE,HF |h|<5, Castor 5<|h|<7, ZDC |h|>8 • Wide energy-space range measure of jets • Muon Chambers: |h|<2.5 • Position/momentum along with a fast L1 response Richard Hollis University of Illinois at Chicago

  5. Soft Physicsin CMS centrality dNch/dh identified low-pT spectra

  6. Soft physics:Global Event Characterization • Centrality: • Forward ET measurements (CASTOR and Had. Cal.) • Multiplicity: • via single-pixel layers (PHOBOS-Style) • Possible as the pixel layer occupancy is <2% for dN/dh~3500 • via integrated Spectra (next slides) Richard Hollis University of Illinois at Chicago

  7. p-p @ 14 TeV (Pythia) Soft physics:Global Event Characterization • Good efficiency and resolution • pT resolution ~1-2% (barrel) • Low-momentum tracking • dE/dx measurement using the inner silicon layers • PID for p±, K± (p<0.8 GeV/c) and protons (p<1.5 GeV/c) K p p Richard Hollis University of Illinois at Chicago

  8. Soft physics:Global Event Characterization • Further PID: • Neutral hadrons from decay topology (L, K0, r, W, …) • Comprehensive Low-pT physics program to study • Freeze-out parameters: • Chemical potential (mB) and temperature • Kinetic freeze-out temperature and radial flow • Baryon transport and strangeness production Richard Hollis University of Illinois at Chicago

  9. Hard Probesin CMS charged hadron spectra full jet reconstruction g-Jet

  10. Full CMS sim reco PbPb background [HYDJET 010 dN/dh~2400] 190 GeV photon [PYTHIA] quenched jet [PYQUEN] minimum bias HLTriggered Hard probes:CMS Capabilities • Large acceptance calorimetry (ECal+HCal) • Fully reconstruct jets in heavy ion collisions • Photon reconstruction in ECal • 4T magnetic field • Momentum resolution <2% • Low fake rates • High-Level Triggering • Online inspection of all events extends pT reach to 250 GeV/c (1 year) PbPb dNch/dh|y=0=3500 Richard Hollis University of Illinois at Chicago

  11. Hard probes:Reconstructing Jets • Jet reconstruction • utilizes Hcal and Ecal • Iterative cone (R=0.5) + Background subtraction • High efficiency and purity for ET>50 GeV jets • Good energy resolution for ET>100 GeV • Jets reconstructed up to ET~ 0.5 TeV • Estimated for one “year” of running PbPb 0.5 nb-1 (or 3.9x109 events,106 sec) Richard Hollis University of Illinois at Chicago

  12. Hard probes:g-Jet • Direct probe for in-medium energy loss Reconstruction • Photon ID: combine Ecal/Hcal/tracker to form g isolation cuts Richard Hollis University of Illinois at Chicago

  13. Hard probes:g-Jet selected working point • Direct probe for in-medium energy loss Reconstruction • Photon ID: combine Ecal/Hcal/tracker to form g isolation cuts • Use of Multivariate analysis • For e = 60%, fake g = 3.5% Richard Hollis University of Illinois at Chicago

  14. Hard probes:g-Jet • Direct probe for in-medium energy loss Reconstruction • Photon ID: combine Ecal/Hcal/tracker to form g isolation cuts • Use of Multivariate analysis • For e = 60%, fake g = 3.5%, S/B=4.5 Richard Hollis University of Illinois at Chicago

  15. Full CMS sim reco PbPb background [HYDJET 010 dN/dh~2400] 190 GeV photon [PYTHIA] quenched jet [PYQUEN] Hard probes:g-Jet • Direct probe for in-medium energy loss Reconstruction • Photon ID: combine Ecal/Hcal/tracker to form g isolation cuts • Use of Multivariate analysis • For e = 60%, fake g = 3.5%, S/B=4.5 • Away-side jet selection • ET > 30 GeV, |h|< 2, Df(g,jet) > 1720 • Calculate dN/dξ • Charged tracks in R=0.5 cone around jet axis Defining Fragmentation Functions: ξ = log(ET/pT) ET usually defined from parton ET of the jet. Here, the g ET is used as we are trying to quantify partonic jet quenching. Richard Hollis University of Illinois at Chicago

  16. Hard probes:g-Jet • Direct probe for in-medium energy loss Final Measurement • Reconstruction using non-quenched and quenched MC • Fragmentation functions differ • Medium modification of fragmentation functions can be discriminated with high significance Significant difference between Non-quenched and Quenched Analysis method has discriminatory power Low-pT High-pT suppressed Richard Hollis University of Illinois at Chicago

  17. Heavy Flavorin CMS J/y and y’ ¡ family

  18. Heavy Flavor:¡ family Reconstructed - in CMS PbPb underlying event: dN/dy ~3500 CMS: precise measurements of muons: tracker + m chambers Richard Hollis University of Illinois at Chicago

  19. Heavy Flavor:¡ family • Direct probe of QGP formation • “Step suppression” of charmonium/bottomonium resonances • Sensitive to QGP temperature Reconstruction performance • Excellent dimuon mass resolution • ~1% of the quarkonium mass for full h • Best Signal/Background at LHC • Clean separation of the states PbPb=2500 Signal/Background~1 Clear separation of states Richard Hollis University of Illinois at Chicago

  20. pT (GeV/c) h Heavy Flavor:¡ family • Direct probe of QGP formation • “Step suppression” of charmonium/bottomonium resonances • Sensitive to QGP temperature Reconstruction performance • Excellent dimuon mass resolution • ~1% of the quarkonium mass for full h • Best Signal/Background at LHC • Clean separation of the states • Broad h-coverage and high-pT reach • Using HLT selection Broad h coverage 1-year statistical reach N¡~2.5 104 Richard Hollis University of Illinois at Chicago

  21. pT (GeV/c) h Heavy Flavor:J/y and y’ PbPb=2500 |h|<2.4 Di-muon mass reconstruction S/B~1.2 sJ/y=35MeV/c2 • Direct probe of QGP formation • “Step suppression” of charmonium/bottomonium resonances • Sensitive to QGP temperature Reconstruction performance • Excellent dimuon mass resolution • ~1% of the quarkonium mass for full h • Best Signal/Background at LHC • Clean separation of the states • Broad h-coverage and high-pT reach • Using HLT selection Broad h coverage NJ/y~1.8×105 1-year statistical reach J/y acceptance Richard Hollis University of Illinois at Chicago

  22. Ultra Peripheralin CMS

  23. Ultra peripheral collisions:¡ photo-production • At LHC the accelerated Pb nucleus can produce strong electromagnetic field • due to the coherent action of the Z = 82 proton charges Equivalent photon flux Egmax ~ 80 GeV g+Pb: cm Emax ≈ 1. TeV/n (~3×e+p HERA) g+g: cm Emax≈160 GeV (~LEP) • Measure the gluon distribution function in the nucleus (gPb) • low background • simpler initial state • gPb→¡ photo-production in CMS • Unexplored (x,Q2) regime: • Pin down amount of low-x suppression in the Pb nuclear PDF (compared to the proton PDF) Richard Hollis University of Illinois at Chicago dAu eA

  24. Summary • CMS has a broad and exciting heavy ion program, including: • Bulk observables (soft physics) Richard Hollis University of Illinois at Chicago

  25. Summary • CMS has a broad and exciting heavy ion program, including: • Jet physics • Quarkonia and heavy-quarks • Ultra peripheral collisions Richard Hollis University of Illinois at Chicago

  26. CMS DATA 2008 GENEVE, SWITZERLAND 2000 PHYSICISTS, (INCL) 50 HEAVY-IONS Produced by CERN, distributed via your local T1 center. GOVERNMENT WARNING: (1) ACCORDING TO THE SURGEON GENERAL, ANALYZING CMS DATA MAY CAUSE SEVERE EUPHORIA. (2) ANALYZING CMS DATA MAY IMPAIR YOUR ABILITY TO DRIVE, PLEASE DON’T ANALYZE DATA WHILST YOU DRIVE Vintage Years Ahead CHF 452m (1995 budget) $12 “Physics World” 1st May 2000 Richard Hollis University of Illinois at Chicago

  27. The CMS detector central detectors transverse slice Global Event Characterization: • Silicon tracker: (p±, K±, p), L, K0 (via displaced vertices) • Infer energy density, freeze-out temperatures and chemical potential... Specific Probes: • Calorimetry: e± , g and hadronic jets • probe of early times and jet-medium interactions, energy loss… • Muon Chambers: μ± (from J/ψ, ¡, Z) • (heavy) quark energy loss and sensitivity to QGP temperature… Richard Hollis University of Illinois at Chicago

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