1. March 13, 2006CMS Heavy Ions Bolek Wyslouch1 Bolek Wyslouch Massachusetts Institute of Technology for the CMS Collaboration 22 nd Winter Workshop on Nuclear Dynamics Heavy-Ion Physics with the CMS Experiment at the Large Hadron Collider CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas, Tbilisi, UC Davis, UI Chicago, U. Iowa, Yerevan, Warsaw, Zagreb La Jolla, March 13, 2006

2. March 13, 2006CMS Heavy Ions Bolek Wyslouch2 Summary of physics opportunities n LHC will accelerate and collide heavy ions at energies far exceeding the range of existing accelerators l The increase of beam energy will result in: u Extended kinematic reach for pp, pA, AA u New properties of initial state, saturation at mid-rapidity u A hotter and longer lived partonic phase u Increased cross sections of hard probes u New experimentally accessible hard probes n New energy regime will open a new window on hot and dense matter physics: another large energy jump! AGSSPSRHICLHC (Pb+Pb)  s NN [GeV] 5202005500 E increasex4x10x28 y range  1.6  3.0  5.3  8.6

3. March 13, 2006CMS Heavy Ions Bolek Wyslouch3 Heavy-Ion Physics at the LHC J/ψ n Medium modification at high p T l Copious production of high p T particles l Large jet cross section, n Different “melting” for members of  family depending on binding energy l Large cross section for J/ψ and  family production n Correlations, scattering in medium l jets directly identifiable 

4. March 13, 2006CMS Heavy Ions Bolek Wyslouch4 Kinematics at the LHC J/  Z0Z0 Saturation Gluon density has to saturate at low x  Access to widest range of Q 2 and x

5. March 13, 2006CMS Heavy Ions Bolek Wyslouch5 CMS as a Detector for Heavy-Ion Physics Si Tracker including Pixels n DAQ and Trigger l High rate capability for A+A, p+A, p+p l High Level Trigger capable of full reconstruction of most HI events in real time ECAL HCAL  chambers n Fine Grained High Resolution Calorimeter Hermetic coverage up to |  |<5 (|  |<7 proposed using CASTOR) l Zero Degree Calorimeter (approved) 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 n Pixel occupancy at 1-2% level even in Pb+Pb Excellent momentum resolution  p/p~2% for p T <70 GeV and higher Fully functional at highest expected multiplicities Detailed studies at ~dN ch /d  ~3000-5000 and cross-checks at 7000-8000

6. March 13, 2006CMS Heavy Ions Bolek Wyslouch6 CMS under construction Hadron Calorimeter Electromagnetic Calorimeter Si tracker & Pixels Muon Absorber DAQ Swiveling coil

7. March 13, 2006CMS Heavy Ions Bolek Wyslouch7 CMS getting ready for beam Latest News from CERN: CMS Magnet is cold and superconducting ! Field is about to be mapped at 4T, 3.5T, 2T, 1T, 0-field Cosmic Muons

8. March 13, 2006CMS Heavy Ions Bolek Wyslouch8 Measuring Muons Resolution Standalone Resolution with tracker 10% 20% 30% 2% 10%

9. March 13, 2006CMS Heavy Ions Bolek Wyslouch9 5.4 m Outer Barrel –TOB- Inner Barrel –TIB- Pixel 2,4 m volume 24.4 m 3 running temperature – 10 0 C Inner Disks –TID- End cap –TEC- ~ 60 Million electronics channels The CMS all Silicon Tracker The Tracking Device

10. March 13, 2006CMS Heavy Ions Bolek Wyslouch10 Tracker Layout 6 layers Outer Barrel 9 Disks in the End Cap 1 Single detector 2 detectors back to back 4 layers Inner Barrel 3 layers Pixel Barrel 3 Disks2 Pixel Disks

11. March 13, 2006CMS Heavy Ions Bolek Wyslouch11 CMS tracker is a powerful tool n Multiple layers of Si pixel and Si strip detectors will give us plenty of information about charged tracks Pixel wafer with “hit” channels Particles traverse Multiple channels Forming small “tracklets” Pulseheight available for each pixel Direction and dE/dx

12. March 13, 2006CMS Heavy Ions Bolek Wyslouch12 Detectors near beamline: forward physics in p+A and A+A ZDC @ 140 m CASTOR Lumi monitor Hermetic coverage up to |  |<7 Zero degree neutral energy Physics: Centrality, Low-x, Limiting fragmentation, strangelets, DCC

13. March 13, 2006CMS Heavy Ions Bolek Wyslouch13 Data Acquisition and Trigger Level 1 hardware trigger l Muon track segments l Calorimetric towers l No tracker data l Output rate (Pb+Pb): 1-2 kHz comparable to collision rate Onli ne Far m switch High level trigger l Full event information available l Every event accepted by L1 sent to an online farm of 2000 PCs l Output rate (Pb+Pb): ~ 40 Hz l Trigger algorithm same or similar to offline reconstruction Every event must pass the whole chain Selectivity depends on available CPU buffer

14. March 13, 2006CMS Heavy Ions Bolek Wyslouch14 Expectation based on RHIC results: Charged particle multiplicity Wit Busza, (MIT) @ CMS Workshop, June 2004 Determines Physics Landscape Influences Detector Performance CMS Physics studies conducted for multiplicity densities up or larger than dN ch /d  =5000 Muon detection, tracking, jet finding ch

15. March 13, 2006CMS Heavy Ions Bolek Wyslouch15 Global Measurements: dN ch /d  (single event) n Use high granularity pixel detectors n Use pulse height measurement in individual pixels to reduce background n Very low p T reach, p T >26 MeV (counting hits!)

16. March 13, 2006CMS Heavy Ions Bolek Wyslouch16 (Event sample: dn/dy ~3000 + one 100GeV Jet/Event) l Excellent resolution event at the highest particle densities Performance of the Track Reconstruction Momentum Resolution Transverse Impact Parameter Resolution CDF

17. March 13, 2006CMS Heavy Ions Bolek Wyslouch17 Good efficiency and low fake rate in large acceptance tracker

18. March 13, 2006CMS Heavy Ions Bolek Wyslouch18 Centrality and collision trigger: forward detectors Energy in forward hadronic calorimeter x (Follows closely RHIC experience). EM section: x33 2mm-W cells (~19X 0 ) HAD sect: x24 15mm-W cells (~5.6λ 0 ) PMTs: R7525 (CMS HF) Rad hard to ~20 Grad (AA, pp low lum.) Energy resolution (n,  ):  E ~E·10% Position resolution: ~2 mm (EM sect.) Zero Degree Calorimeter

19. March 13, 2006CMS Heavy Ions Bolek Wyslouch19 Quarkonia in CMS J/   family Expect ~24k J/  and ~ 18/5/3 k ,  ’,  ’’ After one month of Pb+Pb running at L =10 27 cm -2 s -1 with 50% efficiency  Family region M  +  -   Y =50 MeV J/  acceptance Coverage in central rapidity region

20. March 13, 2006CMS Heavy Ions Bolek Wyslouch20 Illustration Of Online Farm Power: Low p T J/ψ n Only a small fraction of produced J/ψ are seen in LHC detectors E.g. CMS J/ψ→  acceptance 0.1-0.2%, ~O(10 4 ) per LHC run n Detection of low p T J/ψ requires efficient selection of low momentum, forward going muons. Simple hardware L1 dimuon trigger is not sufficient L1 trigger Two  60 Hz L2 triggerNone60 Hz L3 triggerNone60 Hz J/ψ p T >3 GeV/c L1 trigger Single  ~2 kHz L2 trigger Re-fit  70 Hz L3 trigger Match tracker <40 Hz J/ψ p T >1 GeV/c Without online farm (HLT) With online farm (HLT)  Online farm pTpT Improvement Acceptance x2.5

21. March 13, 2006CMS Heavy Ions Bolek Wyslouch21 Jets in heavy ion collisions, role of LHC Production of high p T partons involves hard, perturbative scale Q>>  QCD. n Q is much larger than any momentum scale characterizing the medium (production unaffected by the medium) n Initial “luminosity” modified by nuclear effects n Parton shower development affected by the medium n At LHC in A+A collisions: l wider p T range for suppression studies l partons will appear as jets for E T > 20-30 GeV, their structure will likely be modified compared to jets produced in p+p c d a b

22. March 13, 2006CMS Heavy Ions Bolek Wyslouch22 Jets as probes: the observables n High p T particles and particle correlations n Jet rates: single jets, multi-jets n Jet fragmentation and shape l distance R to leading particle l p T of particles for R < R max l Multiplicity of particles for R < R max Heating: k T = p  sin(  (particle, jet axis)) Forward backward correlation  (particle, jet axis) l Fragmentation function: F(z)=1/N j  dN ch /dz z=p t / p jet Rates and shape aided by correlations Jets+ , Jets+Z n Jets originating from heavy quarks (b, c) Extensive theoretical and experimental preparatory work presently in progress Note: comparison to p+p and p+A is essential

23. March 13, 2006CMS Heavy Ions Bolek Wyslouch23 Jet Reconstruction in CMS using Calorimeters

24. March 13, 2006CMS Heavy Ions Bolek Wyslouch24 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 particle correlations l Azimuthal asymmetry vs. p T

25. March 13, 2006CMS Heavy Ions Bolek Wyslouch25 Jet fragmentation Fragmentation function for 100 GeV Jets embedded in dN ch /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

26. March 13, 2006CMS Heavy Ions Bolek Wyslouch26 Balancing  or Z 0 vs Jets: study of jet with known energy Jet+Z 0 E Tjet,  >120 GeV in Barrel 1 month at 10 27 cm -2 s -1 Pb+Pb , Z 0

27. March 13, 2006CMS Heavy Ions Bolek Wyslouch27 Future jet studies: new generators n Need better jet modeling at LHC: HYDJET l Soft particle production using Hydrodynamic model, includes flow l Jets produced using PYQUEN (PYTHIA with medium-induced quenching) l Full control of soft and hard physics assumptions n Improvement compared to available generators l Centrality/geometry dependence l Energy loss modeling l Consistency with RHIC results n New CMS simulations in progress: l Physics “Technical Design Report” in preparation

28. March 13, 2006CMS Heavy Ions Bolek Wyslouch28 HYDJET tuned to RHIC data Charged Multiplicity  0 p T distribution Leading particle quenching Jet-jet correlations (I.P. Lokhtin and A.M. Snigirev, hep-ph/0506189) HYDJET is being used in CMS Physics TDR preparations

29. March 13, 2006CMS Heavy Ions Bolek Wyslouch29 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 rapidity and azimuthal coverage and high resolution u Quarkonia u Jets l Centrality, Multiplicity, Energy Flow reaching very low p T l Essentially no modification to the detector hardware l New High Level Trigger algorithms specific for A+A l Zero Degree Calorimeter, CASTOR and TOTEM will be important additions extending forward coverage l Heavy-Ion program is well integrated into the overall CMS Physics Program n The knowledge gained at RHIC will be extended to the new energy domain

30. March 13, 2006CMS Heavy Ions Bolek Wyslouch30 CMS advantages compared to other HI experiments n Hermeticity, Resolution, Granularity Central region  ~5 equipped with tracker, electromagnetic and hadronic calorimeters and muon detector n Forward coverage Base-line calorimeters extend the coverage to  ~10 Proposed additional calorimeter CASTOR extends the coverage to  ~14 n High data taking speed and trigger versatility l Unique two-level trigger system l Potential ability of “inspecting” every fully built heavy ion event on the High Level trigger farm processors CASTOR TOTEM ZDC (5.32 < η < 6.86) (z =  140 m)