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Heavy-Ion Physics with CMS

Heavy-Ion Physics with CMS. Aneta Iordanova University of Illinois at Chicago. Expected energy density at the LHC. CMS Heavy-Ion program. J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455. Study of QCD matter under extreme conditions Pb+Pb @ √s NN = 5.5 TeV Bulk observables

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Heavy-Ion Physics with CMS

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  1. Heavy-Ion Physics with CMS Aneta Iordanova University of Illinois at Chicago

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

  3. 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… Aneta Iordanova University of Illinois at Chicago

  4. The CMS detector detector 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 and MET • Muon Chambers: |h|<2.5 • Precise measure of position/momentum and fast L1 response Aneta Iordanova University of Illinois at Chicago

  5. Soft physics:Global Event Characterization • 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) • Good efficiency and resolution • Central PbPb collisions occupancy of pixel layers ~2% p-p @ 14 TeV (Pythia) Aneta Iordanova University of Illinois at Chicago

  6. K p p Soft physics:Global Event Characterization Particle identification • Particle identification • Charged hadrons from dE/dx • Neutral hadrons from decay topology (L, K0) • Multistrange baryons (X−,W−) Freeze-out parameters: • Chemical potential (mB) and temperature • From identified particles • Kinetic freeze-out temperature and radial flow • From particle spectra Baryon transport and strangeness production p-p @ 14 TeV (Pythia) Aneta Iordanova University of Illinois at Chicago

  7. Hard probes:energy loss in the medium Motivation • RHIC Physics Results • High-pT suppression → medium induced parton energy loss • Initial gluon medium density dNg/dy • Medium diffusion properties (transport coefficient q) • Disappearance of back-to-back jets • RHIC → LHC: Increased hard scattering cross section and luminosity • CMS detector and triggering capabilities provide extended pT reach for charged hadrons and for fully reconstructed jets Aneta Iordanova University of Illinois at Chicago

  8. 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 provides 20 to 300 times statistical reach PbPb dNch/dh|y=0=3500 Aneta Iordanova University of Illinois at Chicago

  9. Hard probes:Reconstructing Jets • Inclusive jet spectra • 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 • Jet spectra reconstructed up to ET~ 0.5 TeV • Estimated for one “year” of running PbPb 0.5 nb-1 (or 3.9x109 events,106 sec) Aneta Iordanova University of Illinois at Chicago

  10. Hard probes:g-Jet • Direct probe for in-medium energy loss, DE=Eg-Ehjet 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 Aneta Iordanova University of Illinois at Chicago

  11. Hard probes:g-Jet • Direct probe for in-medium energy loss, DE=Eg-Ehjet 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 Aneta Iordanova University of Illinois at Chicago

  12. Heavy Flavor:J/y and y’ PbPb=2500 |h|<2.4 Di-muon mass reconstruction S/B~1.2 • 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 sJ/y=35MeV/c2 pT (GeV/c) Broad h coverage h NJ/y~1.8×105 1-year statistical reach J/y acceptance Aneta Iordanova University of Illinois at Chicago

  13. Heavy Flavor:¡ family Di-muon mass reconstruction • 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 S/B~1 PbPb=2500 pT (GeV/c) Broad h coverage h 1-year statistical reach N¡~2.5 104 Aneta Iordanova University of Illinois at Chicago

  14. 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) Aneta Iordanova University of Illinois at Chicago dAu eA

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

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

  17. Backup slides Aneta Iordanova University of Illinois at Chicago

  18. Soft Physics Charged particle tracking Pixel triplets+vertex+strips • reconstructing down to pT=0.075 GeV/c with high efficiency (~80-90%) and acceptance • The pT resolution is about 1-2% in the barrel region • Fake track rate • around per mille level in p+p, below 10% in central Pb+Pb for pT > 0.4 GeV/c • Steps at 1 and 2 GeV/c are due to stricter requirements (points on track) • Close to flat and smooth in the mid-rapidity region Aneta Iordanova University of Illinois at Chicago

  19. Jet quenching • At RHIC, suppression of leading particles • Interpretated by “parton energy loss” models in the medium • Loose energy by gluon –strahlung • transport coefficient hˆqi, characterizing the scattering power of the medium • GLV: Gyulassy M, Levai P and Vitev I nucl-th/0006010,hep-ph/0209161 • BDMPS:Baier R, Dokshitzer Y L, Mueller A H, Peigne S and Schiff hep-ph/9608322, hep-ph/0002198, hep-ph/0005129, hep-ph/0302184 Aneta Iordanova University of Illinois at Chicago

  20. g+Jet:In medium modified fragmentation function Aneta Iordanova University of Illinois at Chicago

  21. Generated events Aneta Iordanova University of Illinois at Chicago

  22. Reconstruction/Photon ID Aneta Iordanova University of Illinois at Chicago

  23. Jet finding bias Jet finding (away side) Setting working point Main contribution to systematic uncertainty Biased to parton with high ET (high pt particles) Aneta Iordanova University of Illinois at Chicago

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