Heavy-Ions in CMS

Richard HollisUniversity of Illinois at Chicago

Heavy-Ions

in CMS

24th Winter Workshop on Nuclear Dynamics

25th-12th April 2008


24th Winter Workshopon Nuclear Dynamics

C M S

Expected energy densityat the LHC

CMS Heavy-Ion program

Study of QCD matter under extreme conditions

Pb+Pb @ √sNN=5.5 TeV Bulk observables

(soft physics) Hard probes Ultra peripheral

collisions

p+p @ √s=14 TeV First measurements of

bulk observables Analysis exercise

“…presents the capabilities of the CMS experiment to explore the rich heavy-ion physics programme offered by

the CERN Large Hadron Collider (LHC) .”

dET/d → ϵBj J.D.Bjorken, Phys.Rev.D27(1983) 140

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455




C M S The CMS detector

Under construction

Data!

Basic layout: Tracker E/M Cal.E/M Cal. Hadronic Cal.Hadronic Cal. Magnet Iron Return yoke Muon Chambers

Transverse SliceCosmic muon in CMSat full magnetic field




C M S The CMS detectorC

MS

co

vera

ge

Silicon tracker: ||<2.5 Momentum resolution <2% for

pT<100GeV and ||<0.5.

Calorimetry: ECal ||<3, HB,HE,HF ||<5, Castor 5<||<7, ZDC ||>8

Wide energy-space range measure of jets Muon Chambers: ||<2.5

Position/momentum along with a fast L1 response

Casto

r

Casto

r

Jet

0

2

2

-8 -6 -4 -2 0 8642

Pixel+Strips

Ecal

Hcal

Muons

ZDCZDC

Calorimetry

Tracker

Soft Physicsin CMS

centrality

dNch/didentified low-pT spectra




C M S

Soft physics:

Global Event Characterization

Centrality: Forward ET measurements

(CASTOR and Had. Cal.)

Multiplicity: via single-pixel layers

(PHOBOS-Style)• Possible as the pixel layer

occupancy is <2% for dN/d~3500

via integrated Spectra

(next slides)




C M S

Soft physics:


Good efficiency and resolution pT resolution ~1-2% (barrel)

K p

Low-momentum tracking

dE/dx measurement using the inner silicon layers

PID for ±, K± (p<0.8 GeV/c) and protons (p<1.5 GeV/c)

p-p @ 14 TeV (Pythia)




C M S

Soft physics:


Further PID: Neutral hadrons from decay

topology (, K0, , , …)

Comprehensive Low-pT physics program to study Freeze-out parameters:

• Chemical potential (B) and temperature

• Kinetic freeze-out temperature and radial flow

Baryon transport and strangeness production

Hard Probesin CMS

charged hadron spectrafull jet reconstruction-Jet




C M S

PbPb background[HYDJET 010 dN/d~2400]

190 GeV photon [PYTHIA]

quenched jet [PYQUEN]

Full CMS sim reco

Large acceptance calorimetry (ECal+HCal) Fully reconstruct jets in

heavy ion collisions Photon reconstruction in

ECal

4T magnetic field Momentum resolution

<2% Low fake rates

High-Level Triggering Online inspection of all

events extends pT reach to 250 GeV/c (1 year)

minimum bias HLTriggeredPbPb dNch/d|y=0=3500

Hard probes:

CMS Capabilities




C M S

Jet reconstruction utilizes Hcal and Ecal

Iterative cone (R=0.5) + Background subtraction High efficiency and purity for

ET>50 GeV jets Good energy resolution for

ET>100 GeV Jets reconstructed up to ET~ 0.5

TeV• Estimated for one “year” of

running PbPb 0.5 nb-1

(or 3.9x109 events,106 sec)

Hard probes:

Reconstructing Jets




C M S

Hard probes:

-Jet

Direct probe for in-medium energy loss

Reconstruction Photon ID: combine

Ecal/Hcal/tracker to form isolation cuts




C M S

Hard probes:

-Jet




Use of Multivariate analysis For = 60%, fake = 3.5%

selectedworking point




C M S

Hard probes:

-Jet




Use of Multivariate analysis For = 60%, fake = 3.5%,

S/B=4.5




C M S

Hard probes:

-Jet




Use of Multivariate analysis For = 60%, fake = 3.5%,

S/B=4.5 Away-side jet selection

ET > 30 GeV, ||< 2, ,jet > 1720

Calculate dN/dξ Charged tracks in R=0.5 cone

around jet axis

PbPb background[HYDJET 010 dN/d~2400]

190 GeV photon [PYTHIA]

quenched jet [PYQUEN]

Full CMS sim reco

Defining Fragmentation Functions:

ξ = log(ET/pT)

ET usually defined from parton ET of the jet. Here, the ET is used as we are trying to quantify partonic jet quenching.




C M S

Hard probes:

-Jet Direct probe for in-medium

energy loss

Final Measurement Reconstruction using non-

quenched and quenched MC Fragmentation functions differ

Medium modification of fragmentation functions can be discriminated with high significance

Significant difference between

Non-quenched and QuenchedAnalysis method has discriminatory power

Low-pT

High-pT

suppressed

Heavy Flavorin CMS

J/ and ’

family




C M S

Heavy Flavor:

family

Reconstructed

-

in CMS

PbPb underlying event:

dN/dy ~3500

CMS: precise measurements of muons: tracker + chambers




C M S

Heavy Flavor:

family

PbPb=2500

Signal/Background~1Clear separation of states

Direct probe of QGP formation “Step suppression” of

charmonium/bottomonium resonances

• Sensitive to QGP temperature

Reconstruction performance Excellent dimuon mass resolution

~1% of the quarkonium mass for full

Best Signal/Background at LHC• Clean separation of the states




C M S

Heavy Flavor:

family

N~2.5 104

1-yearstatistical

reach

Broad coveragep T

(G

eV/c

)







Broad -coverage and high-pT reach Using HLT selection




C M S

Heavy Flavor:

J/ and ’







Broad -coverage and high-pT reach Using HLT selection

NJ/~1.8×105

Di-m

uon

mas

s re

cons

truc

tion

1-ye

arst

atis

tical

rea

ch

Broad coverage

PbPb=2500

J/y=35MeV/c2

||<2.4

S/B~1.2

J/ acceptance

p T (

GeV

/c)

Ultra Peripheral

in CMS




C M S

Ultra peripheral collisions:

photo-production

At LHC the accelerated Pb nucleus can produce strong electromagnetic field

due to the coherent action of the Z = 82 proton charges

Equivalent photon flux Emax ~ 80 GeVPb: cm Emax ≈ 1. TeV/n (~3×e+p HERA): cm Emax ≈ 160 GeV (~LEP)

Measure the gluon distribution function in the nucleus (Pb)

low background simpler initial state

Pb→ photo-production in CMS Unexplored (x,Q2) regime: Pin down amount of low-x suppression in

the Pb nuclear PDF (compared to the proton PDF)

dAu eA




C M S Summary

CMS has a broad and exciting heavy ion program, including: Bulk observables (soft physics)




C M S Summary

CMS has a broad and exciting heavy ion program, including: Jet physics Quarkonia and heavy-quarks Ultra peripheral collisions




C M S Vintage Years Ahead

CMS DATA 2008GENEVE, SWITZERLAND

2000 PHYSICISTS, (INCL) 50 HEAVY-IONS

Produced by CERN, distributed via your local T1 center.

GOVERNMENT WARNING: (1) ACCORDING TO THE SURGEON GENERAL, ANALYZING CMS DATA MAY CAUSE SEVERE EUPHORIA. (2) ANALYZING CMS DATA MAY IMPAIR YOUR ABILITY TO DRIVE, PLEASE DON’T ANALYZE DATA WHILST YOU DRIVE

$12 CHF 452m(1995 budget)

“Physics World” 1st May 2000




C M S The CMS detectorce

ntra

l det

ecto

rstr

ansv

erse

slic

e

Global Event Characterization: Silicon tracker: (±, K±, p), , K0 (via

displaced vertices) Infer energy density, freeze-out

temperatures and chemical potential...

Specific Probes: Calorimetry: e± , and hadronic jets

probe of early times and jet-medium interactions, energy loss…

Muon Chambers: μ± (from J/ψ, ) (heavy) quark energy loss and

sensitivity to QGP temperature…

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Heavy-Ions in CMS

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