Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006 1 Heavy Ion Physics with the CMS Experiment at the LHC Gábor Veres Eötvös Loránd University,

Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006

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Heavy Ion Physics with the CMS Experiment at the LHC

Gábor VeresEötvös Loránd University, Budapest, Hungary

Massachusetts Institute of Technology, Cambridge, USAfor the CMS Collaboration

Strangeness in Quark Matter ’06UCLA, California, March 26, 2006

CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, New Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas,

Tbilisi, UC Davis, UC Riverside, UI Chicago, U Iowa, Yerevan, Warsaw, Zagreb


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Physics opportunities at the LHC LHC: a large increase in collision energy compared to

existing accelerators:• Extended kinematical reach (y, pT) for p+p, p+A, A+A collisions

• New properties of initial state, saturation even at mid-rapidity

• A hotter and longer lived partonic phase

• Increased cross sections of hard probes, heavy quarks

• Last but not least: unknown territory/surprises?

New energy regime will open a new window on hot and dense matter physics: another large energy jump!

AGS SPS RHIC LHC (Pb+Pb)

sNN [GeV] 5 17 200 5500

increase in sNN 3-4 12 28

y range 1.6 2.9 5.4 8.7


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Heavy Ion Physics Topics at the LHC

High pT: modification by the medium

Copious production of high pT particles

Large jet production cross section

RHIC

LHCRHICLHC

J/ψ Different “melting” for the family

members, depending on binding energyLarge production cross section for the J/ψ and family

Correlations, scattering in mediumjets clearly identifiable, for the first time in heavy ion collisions


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CMS, as a heavy ion experiment

Calorimeters: high resolution and segmentation

Hermetic coverage up to ||<5 (||<7 with the proposed CASTOR)Zero Degree Calorimeter (approved)

Muon tracking: from Z0, J/, Wide rapidity coverage: ||<2.4 σm 50 MeV at the mass in the barrel

Silicon Tracker Good efficiency and purity for pT>1 GeV Pixel occupancy: <2% at dNch/d 3500 p/p 2% for pT<70 GeV

Functional at the highest expected multiplicities: studied in detail at dNch/d 3000-5000 and cross-checked at 7000-8000

DAQ and TriggerHigh rate capability for A+A, p+A, p+p

High Level Trigger: real time HI event reconstruction

CASTORCASTOR(5.32 < η < 6.86)

ZDCZDC(z = 140 m)


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HLT

Lvl-1

Data Acquisition and Trigger

Level 1 hardware trigger Muon track segmentsCalorimetric towersNo tracker dataOutput rate (Pb+Pb): 1-2 kHz comparable to collision rate

High level trigger Full event information available Every event accepted by L1 sent to an online farm of 2000 PCsOutput rate (Pb+Pb): 40 HzTrigger algorithm: similar to offline reconstruction

- Every event must pass the whole chain- Selectivity depends on available CPU power

switchswitch


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Centrality and forward detectors

Energy in the forward hadronic calorimeter

Zero Degree Calorimeter

Tungsten-quartz fibre structure electromagnetic section: 19X

0

hadronic section 5.6λ0

Rad. hard to 20 Grad (AA, pp low lum.) Energy resolution: 10% at 2.75 TeV Position resolution: 2 mm (EM sect.)

Centrality (impact parameter) determination is needed for physics analysis

impact parameter [fm]

ET [

GeV

]

Pb+Pb


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Charged particle multiplicityWill be one of the first results, important for initial energy density, saturation, detector performance etc.

ch

Muon detection, tracking, jet finding performance checked up to dNch/d5000

high granularity pixel detectors pulse height measurement in each pixel

reduces background Very low pT reach, pT>26 MeV (counting hits)

W. Busza, CMS Workshop, June 2004

Simple extrapolation from RHIC data


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Track reconstruction

MomentumResolution [%]

Transverse Impact Parameter Resolution

[cm]

(Event sample: dn/dy3000 + one 100GeV jet/event)

Excellent performance, even at the highest particle densities

Efficiency and fake rate [%]

-0.5<<0.5

2.0<<2.5

-0.5<<0.5

2.0<<2.5

-0.5<<0.5

efficiency

fake rate

%


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Quarkonia in CMS Heavy Ions

J/ acceptance

J/ familyM+- spectrum, family

Y=50 MeV

in the barrel

Expected: 24000 J/and ~ 18000/5000/3000 /’/’’

After one month of Pb+Pb running at L=1027cm-2s-

1

with 50% efficiencyOnline HLT farm improves acceptanceby 2.5 at high and low pT


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Jets – a new observable at LHC

Hard, perturbative scale: Q>>QCD. Hard parton production unaffected by medium

Parton shower development affected by the medium At LHC in Pb+Pb collisions:

– wider pT range for suppression, quenching studies

– jet structure will likely be modified, compared to jets produced in p+p– comparison to p+p and p+A is essential

Observables:High pT particles and particle correlations (similar to RHIC analyses)

Jet rates: single and multi-jets (quenching studies)Jet fragmentation and shape:

Distance R to leading particle (in - space) forward-backward correlation: (particle, jet axis)– Fragmentation function: F(z)=1/NjdNch/dz where z=pt/pjet

correlations with non-hadronic particles: jets+, jets+ZJets originating from heavy quarks (b, c)

c

d

ab

Extensive theoretical and experimental preparatory workpresently in progress


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Jet reconstruction in the calorimeters

||<0.3

1.6<||<1.9||<0.3

1.6<||<1.9

resolution resolution

efficiency efficiency


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Jet studies using the tracking

Centrality dependence of pT specra can be studied:Azimuthal correlations (as studied at RHIC):

Fragmentation functions: pT with respect to jet axis:

Tracking is a very important capability for jet physics

dN/d

p T1/

Nje

tsdN

ch/d

z

1/N

jetsdN

ch/d

p Tje

tdN

/d(

)


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Advantages of CMS over other HI experiments

CASTORCASTOR TOTEMTOTEM

ZDCZDC

(5.32 < η < 6.86)

(z = 140 m)

Hermeticity, Resolution, GranularityCentral region: tracker, electromagnetic and hadronic calorimeters and muon detector

Forward coverage calorimeters extend to 10 Proposed CASTOR calorimeter to 14

High data taking speed and trigger versatility

Two-level triggerAbility to “inspect” every heavy ion event on the High Level Trigger computer farm


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CMS under construction…

Hadron Calorimeter

Electromagnetic Calorimeter

Si tracker &Pixels

Muon Absorber

DAQ

Solenoid

superconducting, already at 4K

Documents

Gábor Veres Strangeness in Quark Matter ‘06, UCLA, March 26, 2006 1 Heavy Ion Physics with the CMS Experiment at the LHC Gábor Veres Eötvös Loránd University,