CMS 2008:2014 Michael Murray Kansas, Athens,Basel, CERN, Demokritos, Dubna, Ioannina, Kent State, Kiev, Lyon, MIT, Moscow, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, Kansas, Tbilisi, UC Davis, UC Riverside, UI Chicago, U. Iowa, Yerevan, Warsaw

Are our projections reliable? “There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things we know we don't know. But, there are also unknown unknowns. These are things we don't know we don't know.” Donald Rumsfeld Washington 2002 “These theories (this talk) ain’t worth a bucket of worm piss” Bill Willis CERN Council 1982 It’s the unexpected stuff that is fun.

Muons Hadron Calorimeter Cyrostat EM Tracker A Generic Detector 17 pp collisions each 25ns = 20% of a PbPb collision

What do we want to run? The first pp collisions should be April 2007 and PbPb expected one year later. Each year expect several weeks of ion beams (10 6 s effective). The CERN HI community wants a short exploratory run in 2007 Future includes other ion species and pA. Start off with surveys of such as flow, J/  etc. We will then move onto statistics limited measurements such as, , high p T, jets, and correlations of jets with  and Z.

It is vital to understand pp well At RHIC we had some idea what to expect but still had to learn pp. At LHC pp √S is 7 times greater than FNAL.

Measure leptons, hadrons & neutrals

Abundant hard probes      J/ 

Balancing  or Z 0 vs Jets: Quark Energy Loss

Suppression (or enhancement) of quarkonia can tell us about the medium. J/   AA pp  Di-muon mass J/  Energy Density (GeV/fm 3 )  m = 50MeV for the .

Jets in the calorimeters: |  |<5 100 GeV Jet PbPb dN/d  =5000

Jet E T (GeV)  E % Eff % 1. Subtract average pileup 2. Find jets with sliding window 3. Build a cone around Etmax 4. Recalculate pileup outside the cone 5. Recalculate jet energy Spatial resolution:   =   = Jet Reconstruction

Use calorimeters and tracking to measure V 2  =0.1 rad Event plane determination CMS

Fragmentation & hydrodynamics dN d  N partD Calos cover 14 units of 

Event by Event Multiplicity (and E T ) PHOBOS: Single Layer ~15000 channels CMS: Three Layers ~60 Million channels  dN/d  Min p T =26 MeV

Measure multiplicity on day 1 LHC? Extrapolated to LHC: dN/d  ~1400

Evidence for Saturation NdAu N pp

Kinematics at the LHC J/  Z0Z0 Saturation Gluon density has to saturate at low x  Access to widest range of Q 2 and x

Where do the protons go? At RHIC the protons lose about two units of rapidity. Rapidity Loss Beam Rapidity CASTOR covers 5<  <7. This should cover the maximum baryon density

Beam pipe splits 140m from IR ZDC LOCATION BEAMS b 2R ~ 15fm Spectators Participant Region At zero degrees study energy flow and trigger on ultraperipheral  ~7*10 7 J/  and  can be made

Fragmentation of jets A jet covers ~ 9000 crystals p T jet dN d p T jet dN dZ

Physics Goals of CMS 2008:2014 Observe the weakly interacting QGP. This state may be characterized by a collapse of directed flow, thermalization of charm and stronger energy loss. Use jets,  resonances Z 0 and photons to measure its properties. Pin down the color glass condensate by measuring the saturation scale as a function of rapidity (x) and system size. Be ready for unknown unknowns.

Backups

Si Tracker Performance with Heavy Ions 6 layers Outer Barrel 4 layers Inner Barrel 3 disks 9 disks in the End Cap 1 Single Detector 2 Detectors Back to Back Pixel Layers Crucial for Heavy Ions

p T Inside a Jet 100 GeV

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

Tracking works well for p T > 1GeV

Refinement of RHIC results at the LHC: What lies beyond ? Many phenomena measured at RHIC have surprisingly simple energy dependence, will this continue at the LHC ? Hydrodynamic limit, will it hold? dN ch /d  / /2 Flow Charged particle multiplicity, scaling, limited fragmentation

CASTOR 5.32 < η < 6.86 T2 Tracker 5.32 < η < 6.71 CASTOR and Totem T2 Forward coverage: 1.Access to region of relatively high baryon density in HI collisions 2.Study diffractive & low-x (<10 6 ) Physics in p-p interactions

ZDC integration with TAN

Level-1 Trigger Fast algorithms: 3  s with coarse local data Only Calorimetry and Muon Detectors Special purpose hardware (ASICS) Centrality with ECAL, HCAL (including HF) ZDC for minbias. Trigger on e, , jets, Missing E T. Rates steep function of p T thresholds AA higher backgrounds

High Level Trigger (HLT) All event data available: –Fine data for Calorimetry and Muon Detectors –Tracker Refine triggered object Allows to go lower in p T Processing time O(s) Filtering Farms of commodity processors (Linux) L1 in AA has larger backgrounds than in pp due to underlying event. Efficiency trigger requires more careful analysis. HLT can do a better job than L1. HLT to play a greater role in AA

Illustration Of Online Farm Power: Low p T J/ψ Only a small fraction of produced J/ψ are seen in LHC detectors –E.g. CMS J/ψ→  acceptance %, ~O(10 4 ) per LHC run 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

PILE UP SUBTRACTION ALGORITHM 1. Subtract average pileup 2. Find jets with iterative cone algorithm 3. Recalculate pileup outside the cone 4. Recalculate jet energy Jet spatial resolution:  (  rec -  gen ) = 0.032;  (  rec -  gen ) = It is better, than ,  size of tower (0.087 x0.087) Measured jet energy Efficiency, purity Jet energy resolution Calorimetric Jet reconstruction

CMS coverage

Finding charged tracks Occupancy in central Pb+Pb Event: 1-3% in Pixel Layers Up to 70% in Strip dNdy 7000 Efficiency and fake rates

Jet fragmentation Longitudinal momentum fraction z along the thrust axis of a jet: p T relative to thrust axis: Using ECAL clusters~  0 in CMS Fragmentation function for 100GeV Jets embedded in dN/dy ~5000 events. Use charged particles and electromagnetic clusters