CMS Heavy Ion Physics

Edwin NorbeckUniversity of Iowa

18th Winter Workshop on Nuclear Dynamics 01/26/02 Edwin Norbeck University of Iowa 2

Energy for Pb + Pb at LHC

• Beam is 7 TeV/charges = 5.5 TeV/nucleon pairor = 1140 TeV total.

• Total energy, mc2, in center of mass is 30 energy at RHIC.

• Energy density ~ 2 900 energy density at RHIC

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Large Hadron Collider at CERN

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What To Expect from LHC

• LHC (Large Heavy ion Collider) is expected to provide pA and AA collisions.

• Energy: 7 TeV/charge• 6 weeks/year• First heavy ion run in

March 2007

Ion Lmax <L>208Pb82 1.0 1027 4.2 1026

120Sn50 1.7 1028 7.6 1027

84Kr36 6.6 1028 3.2 1028

40Ar18 1.0 1030 5.2 1029

16O8 3.1 1031 1.4 1031

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18th Winter Workshop on Nuclear Dynamics 01/26/02 Edwin Norbeck University of Iowa 6

The experimentsCMS: pp experiment with

approved Heavy Ion program, <50 HI physicists (out of 2000)

ALICE: dedicated HI experiment, 900 collaborators

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18th Winter Workshop on Nuclear Dynamics 01/26/02 Edwin Norbeck University of Iowa 8

Pile-up problems

• For CMS• None for Pb + Pb (125 ns between bunches)• None for p + p (25 ns between bunches)• For Ca + Ca should reduce luminosity by 10

(25 ns between bunches)

• For ALICE• None for Pb + Pb• For p + p reduce luminosity by factor of 104

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CMS: High pt edge of HI physics

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Stretching CMS

Pb-Pb

Detector designed for pp. However due to flexible design offers unique capabilities for AA

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Some CMS Assets

• CMS has excellent muon detection capabilities:– ||<1.3 for barrel and ||<2.4 with endcaps.– Good mass resolution: 46 MeV for the Upsilon.– Efficient suppression of background from /K

decays:• Electromagnetic calorimeter at 1.3 m from beam

axis.

• PT threshold at 3.5 GeV/c for a single muon to reach

the -chambers.

• Large calorimeter coverage with good jet reconstruction capabilities.

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Selected Physics Topicsfirst physics studies by CMS

• Event Characterization

• Quarkonium Production: Upsilon and J/in the barrel

• Z detection

• Jet Production:– Single/Double jet ratios, jet quenching

– Z and tagged jets

• Ultra-Peripheral Collisions: and -Pomeron

Muon detector

Calorimetry

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p n

z

partonspartons

plasmaplasmamixedmixed

thermalisation

hadronizationfreeze-out

chiral symmetrythermal equilibriumchemical equilibriumdeconfinement

k

t

hadronshadrons

• mass and width of resonances ()• thermal photons or dileptons (e+e +)• strangeness enhancement (K • energy loss of initial partons (jet quenching)• suppression of heavy-quark bound states (J/ , ’s +)

Particle production in Heavy Ion collision, signs of QGP

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Tracking

• Developed for dNch/dy=8000 and dN0/dy=4000.

• Track only particles with tracks in detector.

• Use -chambers tracks as seeds.

• Use only tracking detector providing 3D space points.

Occ

up

ancy

(%

)

0

10

20

30

40

50

60

60 70 80 90 100 110 120

Detector Pitch m

MSGC 200

MSGC 240

Silicon 147

Radius of tracking layer (cm)

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Pb+Pb Ca+Ca

J /(mb) 58.0 3.6

'(mb) 1.4 0.09

(b) 410 21

' (b) 120 6.4

'' (b) 41 2.1

Quarkonia Cross Sections

A scaling law:

AA= A2pp

pp from CDF @ 1.8

TeV extrapolated to

5.5(7) TeV. (central 2300)

for J/

(Upsilon).

Production Cross Sectionsfor CMS studies

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Most products at small angles

Simulations for pp show average per event of:760 GeV into 3 < < 5 (HF) 0.8° to 5.7°100 GeV into -3 < < +3 (rest of CMS)

In HF most of the 760 GeV is at small angles.

For Pb + Pb ?

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2.5 mm

2.5 mm

TC (30 cm)

HAD (143 cm)

EM (165 cm)

HF Longitudinal SegmentationHF Longitudinal Segmentation

EM HAD

TC

0.6 mm quartz fibers in iron

Half a million quartz fibersviewed with 2400 phototubes

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Shower and jets in HF (forward calorimeter)

• Radius (80%) of e.m. shower 2.5 cm• Radius (80%) of hadron shower 5 cm

– For jet radius || = 0.3 ||(jet) radius in HF 3 (5.7°) 35 cm 4 (2.1°) 14 cm 5 (0.77°) 4.7cm

-ln tan(/2) rapidity for p >> m tanh() = cos ()

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• “Heavy” Higgs 2mZ or 2mW < mH< 1 TeV

• qq (WW, ZZ H)jj• For jets 2 < < 5• But 3 < < 5 seen only in HF

Higgs “tagging” jets

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Response to Electrons and Pions

• HF responds linearly within 1% to electrons in the energy range tested (6 – 200 GeV). The pion (neg) response is highly nonlinear.

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Beam-beam interactions

• Hadronic nuclear interactions • Electromagnetic dissociation

– Ion is excited by a - nucleon interaction (mostly by the giant dipole resonance) and subsequently decays.

• Electron capture to form H-like ion– A two-photon process creates an electron-positron

pair with the electron retained in an atomic orbit (mostly the K-shell).

• Magnetic-monopole production?

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18th Winter Workshop on Nuclear Dynamics 01/26/02 Edwin Norbeck University of Iowa 25

Summary

• LHC will be a natural continuation of the series of Heavy Ion accelerators

• CMS will have unique capabilities at the high transverse momentum frontier , Z0, , high pt jets

• CMS can provide a natural place to do these measurements in the late-RHIC and post-RHIC era

• Complementary to RHIC

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6th Workshop on Heavy Ion Physics with CMS detector at the LHC

Massachusetts Institute of TechnologyFebruary 8-9, 2002

Cambridge, MA

http://bolek.lns.mit.edu or

wyslouch@mit.eduOffice (617) 253-5431

Cell (781 354-5023

High pt heavy ion physics at the LHC