CMS 2008:2014 Michael MurrayMichael Murray

Athens,Basel, CERN, Demokritos, Dubna, Ioannina, Kent State, Kiev, Lyon, MIT, Moscow, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, Kansas,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 andPbPb expected one year later. Each year expectseveral weeks of ion beams (106s effective). TheCERN HI community wants a short exploratoryrun in 2007 Future includes other ion species andpA. Start off with surveys of such as flow, J/ etc.We will then move onto statistics limited

measurements such as, , high pT, 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 Z0 vs Jets: Quark Energy Loss

# E

ven

ts/4

GeV

ET/0-ET

Jet (GeV)

<E>=8 GeV<E>=4 GeV<E>=0 GeV

Background

Isol. 0+jet

Suppression (or enhancement) of quarkonia can tell us about the medium.

J/

AA pp

Di-muon mass

J/

Energy Density (GeV/fm3)

m = 50MeV for the .

Jets in the calorimeters: ||<5

100 GeV JetPbPb dN/d =5000

Jet ET (GeV)

E %

Eff %

1. Subtract average pileup2. Find jets with sliding window3. Build a cone around Etmax 4. Recalculate pileup outside the cone5. Recalculate jet energy

Spatial resolution: = 0.045 = 0.051

Jet Reconstruction

Use calorimeters and tracking to measure V2

=0.1 rad

Event plane determination

CMS

Fragmentation & hydrodynamics

dNdNpartD

Calos cover 14 units of

Event by Event Multiplicity (and ET)

PHOBOS: Single Layer ~15000 channels

CMS: Three Layers ~60 Million channels

dN

/d

Min pT=26 MeV

Measure multiplicity on day 1

LHC?

Extrapolated to LHC:dN/d~1400

Evidence for Saturation

NdAuNpp

Kinematics at the LHC

J/

Z0

SaturationGluon density has to saturate at low x

Access to widest range of Q2 and x

Where do the protons go?

At RHIC the protons lose about two units of rapidity.

Rap

idit

y L

oss

Beam Rapidity

CASTOR covers 5< <7. This should cover the maximum baryon density

Beam pipe splits 140m from IR

ZDC LOCATION

BEAMS

b2R ~ 15fm

Spectators

Spectators

Participant Region

At zero degrees study energy flow and trigger on ultraperipheral

~7*107 J/ and can be made

Fragmentation of jets

A jet covers ~ 9000 crystals

pTjet

dN

dpTjet

dNdZ

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 Z0 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 layersOuterBarrel

4 layersInnerBarrel

3 disks 9 disks in the End Cap

1 Single Detector

2 Detectors Back to Back

Pixel Layers Crucial for Heavy Ions

pT Inside a Jet

100 GeV

Heavy Ion Trigger

• Main types of trigger as required by physics:– multiplicity/centrality:”min-bias”, “central-only”

– high pT 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 pT 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 pT > 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?

beamy−≡′

dN

ch/d

′/<

Np

art>

/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

collisions2. Study diffractive & low-x (<106) 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 ET. Rates steep function of pT thresholds

• AA higher backgrounds

Electromagnetic Hadron

High Level Trigger (HLT) • All event data available:– Fine data for Calorimetry

and Muon Detectors

– Tracker

• Refine triggered object

• Allows to go lower in pT

• 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 pT J/ψ

• Only a small fraction of produced J/ψ are seen in LHC detectors– E.g. CMS J/ψ→ acceptance 0.1-0.2%, ~O(104) per LHC run

• Detection of low pT 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 trigger None 60 Hz

L3 trigger None 60 Hz

J/ψ pT >3 GeV/c

L1 trigger Single ~2 kHz

L2 trigger Re-fit 70 Hz

L3 trigger Match tracker

<40 Hz

J/ψ pT >1 GeV/c

Without online farm (HLT) With online farm (HLT)

Online farm

pT

Online farmImprovement

Acceptance x2.5

PILE UP SUBTRACTION PILE UP SUBTRACTION

ALGORITHMALGORITHM1. Subtract average pileup2. Find jets with iterative cone algorithm3. Recalculate pileup outside the cone4. Recalculate jet energy

Jet spatial resolution: (rec

- gen

) = 0.032; (rec

- gen

) = 0.028

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 Layers @

dNdy 7000

Efficiency and fake rates

Jet fragmentationLongitudinal momentum fraction z along the thrust axis of a jet:

pT 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