LHC Heavy-Ion Program a CMS Perspective

Edwin NorbeckUniversity of Iowa

for the CMS Collaboration

20th 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,

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The experiments

ATLAS: pp experiment, HI proposal in progress

ALICE: dedicated HI experiment

CMS: pp experiment with HI program

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The Physics Landscape: Pb+Pb Collisions SPS->RHIC->LHC

d

Extrapolation of RHIC results favors low values

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Heavy Ion Physics at the LHC

J/ψ

Medium modification at high pT Copious production of high pT

particles

Different “melting” for members of family Large cross section for J/ψ and

family production

Correlations, scattering in medium Large jet cross section, jets

directly identifiable

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CMS as a Detector for Heavy Ion Physics

DAQ and Trigger High rate capability for AA,

pA, pp 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

Fine Grained High Resolution Calorimeter

Hermetic coverage up to ||<5 (||<7 proposed using CASTOR) Zero Degree Calorimeter

(proposed)Tracking from Z0, J/,

Wide rapidity range ||<2.4 σm ~50 MeV at

Silicon Tracker Good efficiency and low fake

rate for pT>1 GeV Excellent momentum

resolution p/p~1% for pT<25 GeV and higher

Fully functional at highest expected multiplicitiesDetailed studies at ~3000-5000 and cross-checks at 7000-8000

HF

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CMS under construction

Hadron Calorimeter

Electromagnetic Calorimeter

Si tracker &Pixels

Magnet &Muon Absorber

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CMS Detector in the Heavy Ion Environment

High Multiplicity of Low pT Hadrons

Occupancies still Reasonable

Large Event Size but Lower Event Rate

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CMS as a Heavy Ion Experiment Excellent detector for high pT probes:

High rates and large cross sections quarkonia (J/ ,) and heavy quarks (bb) high pT jets high energy photons Z0

Correlations jet- jet-Z0

multijets Global event characterization

Energy flow to very forward region Charged particle multiplicity Centrality Azimuthal asymmetry

CMS can use highest luminosities available at LHC both in AA and pA modes

-

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Global Measurements: dNch/d (single event) a la Phobos

Use high granularity pixel detectors Use pulse height measurement of pixel clusters to reduce

background Very low pT reach, pT>26 MeV ! (inner pixel layer at R~45 mm)

EclusterPreliminary

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Azimuthal asymmetry, calorimetersUse highly segmented calorimeters to determine event plane

Simulations of Pb+Pb with b=6 fm

=0.1 rad

Event plane determination

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Quarkonia in CMS

J/ family Yield/month (k events, 50% eff)Nominal luminosity for each ion

species

Pb+Pb, 1 month at L=1027

  

Pb+Pb Kr+Kr Ar+Ar

L 1027 7×1028 1030

J/ 29 470 2200

´ 0.8 12 57

23 320 1400

´ 12 180 770

´´ 7 100 440

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High Mass Dimuon, Z0 Production

Z0-> can be reconstructed with high efficiency

A probe to study nuclear shadowing

Z0 also proposed as reference for production.

Dimuon continuum dominated by b decays

Heavy quark energy loss

High statistics (1 month):

Channel (M> 10 GeV) Barrel + EndcapEvents

Z+- 1.1 104

BB+-, PT>5 GeV 1.2 105

BJ/ψ+-, PT>5 GeV 1.3 105

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Outside-In

Vertex Reconstruction

z=190 m

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Jet Reconstruction in CMS using Calorimeters

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Charged Particle Jet Studies in CMS

Detailed study of phenomena which are already apparent at RHIC Study the centrality dependence of:

Charged particle spectra starting at pT~1 GeV Possibly lower pT cutoff with reduced B field

Back-to-back correlations a la STAR Azimuthal asymmetry vs. pT

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Performance of the Track Reconstruction: Inside-Out

Match Reconstructed tracks to MC input on a hit by hit basis

(Event sample: dN/dy ~3000 + one 100 GeV Jet/Event)

pT/pT < 1% || < 0.7

The increased local track density in a jet-cone leads to a decrease in reconstruction efficiency of ~5-10%

Can be corrected for since jets will be reconstructed by the calorimetry

Tracking efficiency

Fake tracks

Efficiency

Fakes

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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: pT relative to thrust axis:

High precision tracking out to high momenta will allow for detailed jet shape analysis to study the energy loss mechanism

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L1

HLT

Heavy Ion TriggerMain 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.

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CMS Forward Calorimeter 3 < η < 5

36 x 2 = 72 Wedges with a total of 500,000 fibers

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CMS Very Forward Region CASTOR, TOTEM and ZDC

CASTOR Coverage

CASTOR

Multiplicity and hermetic coverage to |η|<7

Zero Degree Energy Physics:

Centrality Limiting Fragmentation Peripheral and ultra-peripheral collisions Low-x, Color-Glass Condensate DCC, Centauros, Strangelets

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CMS Very Forward Region CASTOR, TOTEM and ZDC

ZDC

TOTEM: Roman Pots

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PPAC Test at ANL

PPAC under beam line to beam dump

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Energy Resolution Data of PPAC Test at ANL

Ratio Efront to Eback is constant to within ± 2%

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Conclusions

LHC will extend energy range and in particular high pT reach of heavy ion physics

CMS is preparing to take advantage of its capabilities Excellent coverage and resolution

Quarkonia Jets

Centrality, Multiplicity, Energy Flow reaching very low pT

Essentially no modification to the existing detector hardware New High Level Trigger algorithms Zero Degree Calorimeter, CASTOR and TOTEM as important

additions extending forward coverage Heavy Ion program is well integrated into overall CMS Physics

Program The knowledge gained at RHIC will be extended to the

new energy domain