1. LHC Heavy-Ion Program a CMS Perspective Edwin Norbeck University of Iowa for the CMS Collaboration 20 th Winter Workshop on Nuclear Dynamics CMS HI groups: Athens, Auckland, Demokritos, Dubna, Lyon, MIT, Moscow, Rice, Tbilisi, U Ioannina, U Iowa, U Kansas, UC Davis, UI Chicago, UC Riverside,

2. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa2 The experiments ATLAS: pp experiment, HI proposal in progress ALICE: dedicated HI experiment CMS: pp experiment with HI program

3. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa3 The Physics Landscape: Pb+Pb Collisions SPS->RHIC->LHC dd Extrapolation of RHIC results favors low values

4. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa4 Heavy Ion Physics at the LHC      J/ψ n Medium modification at high p T l Copious production of high p T particles n Different “melting” for members of  family l Large cross section for J/ψ and  family production n Correlations, scattering in medium l Large jet cross section, jets directly identifiable

5. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa5 CMS as a Detector for Heavy Ion Physics n DAQ and Trigger l High rate capability for AA, pA, pp l High Level Trigger capable of full reconstruction of most HI events in real time Solenoid with Si Tracker, ECAL and most of HCAL inside  chambers n Fine Grained High Resolution Calorimeter Hermetic coverage up to |  |<5 (|  |<7 proposed using CASTOR) l Zero Degree Calorimeter (proposed) Tracking  from Z 0, J/ ,  Wide rapidity range |  |<2.4 l σ m ~50 MeV at  n Silicon Tracker n Good efficiency and low fake rate for p T >1 GeV Excellent momentum resolution  p/p~1% for p T <25 GeV and higher Fully functional at highest expected multiplicities Detailed studies at ~3000-5000 and cross-checks at 7000-8000 HF

6. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa6 CMS under construction Hadron Calorimeter Electromagnetic Calorimeter Si tracker & Pixels Magnet & Muon Absorber

7. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa7    CMS Detector in the Heavy Ion Environment High Multiplicity of Low p T Hadrons Occupancies still Reasonable Large Event Size but Lower Event Rate

8. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa8 CMS as a Heavy Ion Experiment n Excellent detector for high p T probes: l High rates and large cross sections  quarkonia (J/ ,  ) and heavy quarks (bb) u high p T jets u high energy photons u Z 0 l Correlations  jet-  u jet-Z 0 u multijets n Global event characterization l Energy flow to very forward region l Charged particle multiplicity l Centrality l Azimuthal asymmetry n CMS can use highest luminosities available at LHC both in AA and pA modes -

9. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa9 Global Measurements: dN ch /d  (single event) a la Phobos n Use high granularity pixel detectors n Use pulse height measurement of pixel clusters to reduce background n Very low p T reach, p T >26 MeV ! (inner pixel layer at R~45 mm) E cluster Preliminary

10. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa10 Azimuthal asymmetry, calorimeters n Use highly segmented calorimeters to determine event plane n Simulations of Pb+Pb with b=6 fm  =0.1 rad Event plane determination

11. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa11 Quarkonia in CMS J/   family Yield/month (k events, 50% eff) Nominal luminosity for each ion species Pb+Pb, 1 month at L=10 27 Pb+PbKr+KrAr+Ar L 10 27 7×10 28 10 30 J/  294702200 ´´ 0.81257  233201400 ´´ 12180770  ´´ 7100440

12. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa12 High Mass Dimuon, Z 0 Production Z 0 ->  can be reconstructed with high efficiency l A probe to study nuclear shadowing l Z 0 also proposed as reference for  production. n Dimuon continuum dominated by b decays l Heavy quark energy loss n High statistics (1 month): Channel (M  > 10 GeV)Barrel + Endcap Events Z+-Z+- 1.1 10 4 BB  +  -, P  T >5 GeV 1.2 10 5 B  J/ψ  +  -, P  T >5 GeV 1.3 10 5

13. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa13 Outside-In Vertex Reconstruction  z =190  m

14. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa14 Jet Reconstruction in CMS using Calorimeters

15. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa15 Charged Particle Jet Studies in CMS n Detailed study of phenomena which are already apparent at RHIC n Study the centrality dependence of: l Charged particle spectra starting at p T ~1 GeV u Possibly lower p T cutoff with reduced B field l Back-to-back correlations a la STAR l Azimuthal asymmetry vs. p T

16. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa16 Performance of the Track Reconstruction: Inside-Out n Match Reconstructed tracks to MC input on a hit by hit basis l (Event sample: dN/dy ~3000 + one 100 GeV Jet/Event)  p T /p T < 1% |  | < 0.7 l The increased local track density in a jet-cone leads to a decrease in reconstruction efficiency of ~5-10% l Can be corrected for since jets will be reconstructed by the calorimetry Tracking efficiency Fake tracks Efficiency Fakes

17. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa17 Jet fragmentation Fragmentation function for 100 GeV Jets embedded in dN/dy ~5000 events. Longitudinal momentum fraction z along the thrust axis of a jet: p T relative to thrust axis: High precision tracking out to high momenta will allow for detailed jet shape analysis to study the energy loss mechanism

18. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa18 L1 HLT Heavy Ion Trigger n Main types of trigger as required by physics: l multiplicity/centrality: “ min- bias”, “central-only” l high pT probes: muons, jets, photons, quarkonia etc. n High occupancy but low luminosity ! l many low level trigger objects may be present, but less isolated than in p+p, Level 1 might be difficult for high pT particles l but we can read most of the events up to High Level Trigger and do partial reconstruction n HLT for HI needs significant software/simulation effort.

19. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa19 CMS Forward Calorimeter 3 < η < 5 36 x 2 = 72 Wedges with a total of 500,000 fibers

20. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa20 CMS Very Forward Region CASTOR, TOTEM and ZDC CASTOR Coverage CASTOR n Multiplicity and hermetic coverage to |η|<7 n Zero Degree Energy n Physics: l Centrality l Limiting Fragmentation l Peripheral and ultra-peripheral collisions l Low-x, Color-Glass Condensate l DCC, Centauros, Strangelets

21. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa21 CMS Very Forward Region CASTOR, TOTEM and ZDC ZDC TOTEM: Roman Pots

22. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa22 PPAC Test at ANL PPAC under beam line to beam dump

23. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa23 Energy Resolution Data of PPAC Test at ANL Ratio E front to E back is constant to within ± 2%

24. March 15, 200420th Winter Workshop Jamaica E. Norbeck U. of Iowa24 Conclusions n LHC will extend energy range and in particular high p T reach of heavy ion physics n CMS is preparing to take advantage of its capabilities l Excellent coverage and resolution u Quarkonia u Jets l Centrality, Multiplicity, Energy Flow reaching very low p T l Essentially no modification to the existing detector hardware l New High Level Trigger algorithms l Zero Degree Calorimeter, CASTOR and TOTEM as important additions extending forward coverage l Heavy Ion program is well integrated into overall CMS Physics Program n The knowledge gained at RHIC will be extended to the new energy domain