Heavy Ion Physics with CMS

Heavy Ion Physics with CMS

Pablo Yepes, Rice Universityfor the CMS CollaborationQuark Matter Jan 16, 2001

Pablo Yepes, Rice U.

Heavy Ion Physics with CMS, Jan 16, 2001 2

What To Expect from LHC

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

Energy: 7 TeV/charge

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

Luminosity



What to Expect From CMS



Stretching CMS

A minimum bias Pb-Pb event in CMS

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



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.



Physics Topics

Event Characterization

Quarkonium Production: Upsilon and J/ Z Jet Production:

Single/Double jet ratios.

Z and tagged jets

Ultra-Peripheral Collisions: and -Pomeron



Event Characterization

In spite of very strong magnetic field(4 Tesla) there is a good correlation between centrality and transverse energy.



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.

for J/

(Upsilon).

Production Cross Sectionsfor our studies



Quarkonia Acceptance in Chambers

10%

20%

Acc

epta

nce

J/

UpsilonPt(GeV)

Full Detector

Full Detector

Barrel

Barrel

•J/ with pT>5 GeVin Barrel

•Upsilon down to low transverse momentum



Quarkonia Reconstruction

Essential sub-detectors:Tracking devices Muon system

Pessimistic assumptions for background estimates:dNch/dy=8000

(most generators < 5500)<pt>GeV/c (HIJING

0.39 GeV/c)<pt>k=0.67 GeV/c

Special Heavy Ion Tracking AlgorithmSignificant Muon background from and K decays



J/ Signal

1 month running at top Luminosity: J/’s detected and reconstructed in the Barrel:

Ca-Ca Pb-Pb

# J/ 2.2 105 104

S/B 9.7 1.0

103

104

2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5

Min bias collisions - 1 month run - barrel onlymuons with P > 3.5 GeV/c

Pb-Pb

/cont.= 1.0

# ev

ents

/25

MeV

/c2

104

105

2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5

Ca-Ca

/cont.= 9.7

Opposite-sign di-muon invariant mass (GeV/c2)

L= 2.5 1029 cm2 s-1

# ev

ents

/25

MeV

/c2

L= 1027 cm2 s-1



1 month: 22000 and 7500

’ detected in the barrel

Upsilon in Pb-Pb

Opposite-sign di-muon Invariant Mass (GeV/c2)Background contributions

1022

1033

104

8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11

L= 1027 cm-2 s-1

Total

Decay-Decay Decay-b

Decay-c

b-b

c-c

Upsilon/cont.= 1.6

# E

ven

ts/2

5 M

eV/c

2

0

1000

2000

3000

4000

5000

6000

7000

8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11

Di-muon Invariant Mass (GeV/c2)

# E

ven

ts/2

5 M

eV/c

2

Combinatorial background subtracted after reconstruction



Upsilon in Ca-Ca

103

104

105

8.5 8.75 9 9.25 9.5 9.75 10 10.25 10.5 10.75 11

Opposite-sign di-muon invariant mass (GeV/c2)

L= 2.5 1029 cm-2s-1

Total

Decay-Decay

Decay-b

Decay-c

b-b

Upsilon/cont.= 9.4

# E

ven

ts/2

5 M

eV/c

2

• 1 month:

• 340000 • 115000 ’

• Only barrel used.



Quarkonia Reference At SPS, J/ is compared to

Drell-Yan. At LHC Drell-Yan

contribution is negligible. Z0 proposed as reference to

production.MZ>M

Different production mechanisms: Z0: antiquark-quark, quark-gluon and

antiquark-gluon. : gluon-gluon.

Cross check di-muon reconstruction algorithm



Jets are Easy

monojet/dijet enhancement jet-Z0or jet-

dNch/dy=8000

Tot

al C

alor

imet

er E

nerg

y

Jet Finding100 GeV ET

-~100%- (ET)/ET=11.6%.

Jet quenching



Balancing Photons and Jets

Etjet,

120GeV in the barrel

1 month:900 events

for Pb-Pb104 events

for Ca-Ca

# E

ven

ts/4

GeV

ET//0-ET

Jet (GeV)

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

Background

2 weeks at L=1027 cm-2s-

1



10-14

10-12

10-10

10

10-6

10-4

10-2

100

10-1 100 10 10210-12

10-10

10-8

10-6

10-4

10-2

10

102

AA

(bar

n)

even

ts/s

ec

M (GeV)

p0f2

a2

f2'ccc0c2

b

0bb

HSM

H'

10-5

10-3

10-1

10

103

105

107

even

ts/y

ear

1 10 102M (GeV)

10-14

10-12

10-10

10-8

10-6

10-4

10-2

1

10 -12

10-10

10-8

10-6

10-4

10-2

1

102

AA

(M)

(bar

n/G

eV)

even

ts/s

ec/G

eVhadrons

e+e-

-

cc

bb

10-5

10-3

10-1

10

103

105

107

even

ts/y

ear/

GeV

Ultra-Peripheral Collisions

A

A

Meson orlepton/quark pair

orPA

A

orP



Conclusions

CMS is provides unique tools to study Heavy Ion Collisions at LHC.

Physics considered:Event characterization with large rapidity coverage.Quarkonium production: and J/ families.Jet quenching. Ultra-Peripheral collisions.



Addendum: 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 MSGC layer (cm)



LHC Parameters (Addendum)

Bunches 7.5 cm long every 125 ns.



Addendum: Upsilon Acceptance

1 2 3 4 5 6 7 8 9 10

y

Tp (GeV/c)

-8 -6 -4 -2 0 2 4 6 8 10

hdN

/d

dN /

dydN

/dpT

¡¡

¡

-8 -6 -4 -2 0 2 4 6 8 10

0

1000

2000

3000

0

0

2000

4000

6000

-10

0

2000

4000

-10

69



STAR First Ultra-Peripheral Collisions

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Heavy Ion Physics with CMS

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