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The CMS Heavy Ion Program

Michael Murray Kansas

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CMS is a running experiment

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Overview

The detector Soft Physics

Multiplicity ,k,p at low pt Flow

Hard Physics Jets Photons Quarkonia Photon nucleus

Z Jet Event

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Rapidity Range

A new telescope for new probes

Hig

h R

ate

, Tri

gg

er

Y=4

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LHC

RHIC

SPS

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Hard probes are rare

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The Central Detector

Pixels

Strips

EM Cal

HCal

Coil

Muons

Iron

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A transverse slice through CMS

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HCAL

ECAL

Tracker

Coil

A slice along Z

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Castor 5.2<<6.6

ZDC >8.3

Forward Detectors

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HIJING default settings

Pixels hits count

Multiplicity/event

Pseudo rapidity

Find hits in pixels, using an energy cut. We also have a tracklet analysis.

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||<1

Low pT hadrons

Find tracks in pixels and use energy loss vs momentum for particle ID

pT (GeV/c)pT (GeV/c)

pT (GeV/c)

pT

Effi

cie

ncy

dNdpT

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1. Find the reaction plane calorimeters and tracker 2. Use 2, 4 particle correlations or Lee Yang Zeros

Ecal 0.37

V2 with tracker

Elliptic Flow Reaction plane

x

z

y

rad pT (GeV/c)

V2

d dE

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Triggering

L /cm2

/s

Bunch cross

Interaction rate

Level 1 Event size

HLT rate

offline

pp 1034 25ns 40MHz 1/400 1MB 100 KHz

150Hz

PbPb 1027 125ns 8KHz 1/1 2.5-10MB

8 Khz

10-100 Hz

Trigger increases pT range by > 2 for many probes

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dNch/d = 5000

Iterative cone (R>=0.5) with background

subtraction: calculate average energy and dispersion in

tower (in eta rings) for each event subtract average energy and dispersion

from each tower find jets with a jet finder algorithm (any)

using the new tower energies recalculate average energy and dispersion

using towers free of jets recalculate jet energies

Done, but can do more iterations

Space resolution is less then the tower size

Finding Jets

MC Jet ET (GeV)

Rec ET

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1.0

Efficiency ~ 70 %, fake rate ~ 1%

pT (GeV/c)

<0.5

Single stripsDouble stripsPixels

Z (m)

Y (m)

Effi

cie

ncy %

Fakes %

1.00.5

0.5

pT %

z cm

2.0<<2.5

<0.5Pointing useful for heavy quarks

pT (GeV/c)

Tracking

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jet trigger

data

High Pt Assume luminosity = 0.5 nb-1

10% Central

Energy loss from HYDJET

No trigger

RAA

RAA

pT (GeV/c)

Charged particles ||<2.5

pT (GeV/c)

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Efficiency = 60%Fake = 3.5%S/B=4.5

Photons

Photon ID based only on cluster shape and isolation cuts using a multi-variate analysis. We reconstruct photon energy with Island algorithm

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I =0..5 nb-1

Jet fragmention from jet events

Require photon ET > 70GeV

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c

Suppression: RHIC similar to SPS

Regeneration compensate screening

J/ not screened at RHIC (TD~2Tc)

LHC: recombination or suppression

Suppression of B’onium states

Large Cross-section: 20 x RHIC

melts only at LHC: TD~4 TC

Fewer of bb pairs: less regeneration

Much cleaner probe than J/

'

J/

Quarkonia

Branching ration is 5.9% for J/ , 2.5%Y (BR:2.5%)

Background is from decays from /K, b-,c-mesons

Suppression of charmonion

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J/ +-

dNch

/d = 5000

dNch

/d = 2500

For 0.5 nb-1 we reconstruct 180K J/

Signal/Background:

~5 for ||<0.8, 1 for ||<2.4

= 35 MeV

||<2.4

Produced

Reconstructed 2500

Reconstructed 5000

pT (GeV/c) M (GeV)

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||<2.4, = 90MeV

mass resolution, 90 MeV

||<2.4

Y ~ 25 000,

Y' ~ 7 000,

Y'' ~ 4 000Signal/Background: 1 ||<0.8, 0.1 for ||<2.4)

Y +-

M (GeV)

Produced

Reconstructed 2500

Reconstructed 5000

pT (GeV/c)

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Photon nucleus

Max photon energy ~ 80 GeVPb: S ≈ 1. TeV/n S ≈ 160 GeV

M (GeV)

Mee (GeV)

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Summary

CMS has an excellent opportunity to study partonic matter at both soft and hard scales, via

• Multiplicity

• Soft spectra

• Flow

• Forward Physics

• Quarkonia

• Hard spectra

• Photons

• Jets

• Z

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Backup slides

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CMS acceptance

ECAL, PbWO40.0174x0.0174

Inner detector

HCAL (sampling)0.087x0.087 (HB)0.087->0.17 (HE)

HFHF

Muon Spectrometer

Castor

Castor

CMS:

Inner detector (||<2.5)ECAL (||<3)HCAL (||<3)HF (3<||<5)Muon (||<2.4)Castor (5<||<6.7)ZDC (||>8)