Heavy Ion Physics with the CMS Detector

ICHEP'06 MoICHEP'06 Moscow 26.07 - 02.08.2006 scow 26.07 - 02.08.2006

11

Heavy Ion Physics Heavy Ion Physics with the CMS Detectorwith the CMS Detector

Lyudmila Sarycheva

Scobeltsyn Institute of Nuclear Physics Moscow State University

For CMS Collaboration

1.1. CMS detector and Heavy Ion program CMS detector and Heavy Ion program 2.2. Quarkonia and heavy quarks Quarkonia and heavy quarks 3.3. Jets and jet quenchingJets and jet quenching4.4. Global event characterization Global event characterization 5.5. Monte-Carlo simulation tools Monte-Carlo simulation tools 6.6. Summary Summary 7.7. Appendix Appendix

CMS Heavy-Ion Groups: Adana, Athens, Basel, Budapest,

CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon,

Minnesota, MIT, Moscow, Mumbai, N.Zealand, Protvino, PSI, Rice, Sofia,

Strasbourg, U Kansas, Tbilisi, UC Davis,UI Chicago, U. Iowa,

Yerevan, Warsaw, Zagreb


22

1.1 CMS detector1.1 CMS detector

Si tracker with pixels | | < 2.4 good efficiency and low fake rates for pt > 1 GeV, excellent momentum resolution, p: pt/pt < 2%

Muon chambers || < 2.4 Fine grained high resolution calorimetry (HCAL, ECAL, HF) with hermetic coverage up to || < 5

TOTEM (5.3 η 6.7) CASTOR (5.2 < || < 6.6) ZDC (z = ±140 m, 8.3 ||)

B = 4 T

Fully functional at highest multiplicities; high rate capability for (pp, pA, AA), DAQ and HLT capable of selecting HI events in real time

CASTOR ZDCTOTEM

5.2 << 6.6 8.3 <5.3 << 6.7


33

1.2 Forward Region Layout1.2 Forward Region Layout

|| > 3

(5.3 << 6.7)

TOTEM

Forward Forward HCalHCal

(3 << 5)

CASTOR (~ 10 λI)

(5.2 << 6.6)

ZDC

HADHADEMEM

(z = 140 m)

(8.3 <)


44

1.3 Overview: CMS Detector Coverage1.3 Overview: CMS Detector Coverage

Large Range of Hermetic Coverage:Tracker, muonsTracker, muons ECAL ECAL ++ HCALHCAL Forward HCALForward HCAL CASTORCASTOR ZDCZDC

Kinematics at the LHC

Gluon density has to saturate at low x


55

Excellent detector for high pExcellent detector for high pTT probes of quark-gluon plasma: probes of quark-gluon plasma: - High rates and large cross sections- High rates and large cross sections - Quarkonia (J/- Quarkonia (J/,,), heavy quarks ( ) and Z), heavy quarks ( ) and Z00

- High acceptance for calorimeters and muon system - High acceptance for calorimeters and muon system - High p- High pTT jets jets - High energy photons- High energy photons

Correlations Correlations - jet-jet- jet-jet - jet-- jet-, jet-, jet-*/Z*/Z00

- multijets- multijets Global event characterizationGlobal event characterization

- Centrality- Centrality - Energy flow to very forward region- Energy flow to very forward region - Charged particle multiplicity- Charged particle multiplicity - Azimuthal anisotropy- Azimuthal anisotropy

Forward physics and ultraperipheral interactionsForward physics and ultraperipheral interactions - Limiting Fragmentation, Saturation, Color Glass CondensateLimiting Fragmentation, Saturation, Color Glass Condensate - Exotica- Exotica

Monte-Carlo simulation tools: Monte-Carlo simulation tools: - PYTHIA, HIJING, PYQUEN/HYDJET- PYTHIA, HIJING, PYQUEN/HYDJET

1.4 Heavy Ion program at CMS1.4 Heavy Ion program at CMS

bb


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LHC Quarkonia with high statistics (J/, '; , ', '')

Large cross-section for J/ and families

Different melting for , ', '‘

Z0 with high statistics. The possibility to use ET balance of Z0(*)+jet to observe medium induced energy loss.

Large cross-section for heavy-quarks (b, c): observation of medium induced energy loss in high mass dimuon spectrum and secondary J/

-

Plasma hotter and longer lived than

at RHIC

Unprecedented Gluon densities

Access to lower x, higher Q2

Availability of new probes

-

Increase energy √S=17-200 GeV/n-n 5500 GeV/n-n

2.1 Quarkonia and heavy quarks 2.1 Quarkonia and heavy quarks

from SPS and RHIC to LHCfrom SPS and RHIC to LHC


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MC simulation/visualization of Pb+Pb event (dNch/d|=0 ~ 3000) using the pp software framework

→ +

2.22.2 Quarkonia (J/Quarkonia (J/, , ): ): reconstruction reconstruction


88

2.3 J/2.3 J/ and and spectra for multiplicity dN spectra for multiplicity dNchch/d/d = 2500 = 2500

For Pb-Pb at integrated luminosity 0.5 nb-1

/K decays into b,c-hadrons into

S/B N

J/ 1.2 180000

0.12 25000

Combinatorial background: Mixed sources, i.e. 1 from /K + 1 from J/ 1 from b/c + 1 from /K


99

2.4 J/2.4 J/ and and spectra spectra

(subtraction of the like sign spectra)(subtraction of the like sign spectra)

both

muons

|| < 2.4

both

muons

|| < 0.8

both

muons

|| < 2.4

both

muons

|| < 0.8

See talk of Olga Kodolova for details.See talk of Olga Kodolova for details.


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2.5 Heavy quarks b, c 2.5 Heavy quarks b, c / J/ / J/ +X. +X. Secondary vertex finding and correlated background rejectionSecondary vertex finding and correlated background rejection

r is transverse distance between the intersection points with the beam line belonging two different muon tracks

b-quark energy loss affects B-jet fragmentation and modification dimuon spectra depending on mechanism of heavy-quark production (for BB → + ) and intensity of jet quenching

BB J/ +BB +


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Channel Time = 1.2 106 s,

AA = A2pp, A = 208 (Pb) (Pythia6.2, CTEQ5M)

jet+jet, ETjet > 100 GeV 4 106

jet tagged by h,0, ET

jet > 100 GeV,

zh,0 > 0.5

2 105

B-jet tagged by ,

ETjet > 100 GeV, z > 0.3

ETjet > 50 GeV, z > 0.3

700

2 104

3.13.1 Jet cross section & expected event rateJet cross section & expected event rate

Expected statistics for CMS acceptance(no trigger and reconstruction efficiency)

jet,| < 3, |h,| < 2.4

CERN Yellow Report, hep-ph/0310274


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3.2 High p3.2 High pTT jets. Jet reconstruction in HI collisions jets. Jet reconstruction in HI collisions

BACKGROUND SUBTRACTION ALGORITHMThe algorithm is based on event-by-event -dependent background subtraction:

1. Subtract average pileup 2. Find jets with iterative cone algorithm 3. Recalculate pileup outside the cone 4. Recalculate jet energy

Full jet reconstruction in central Pb-Pb collision HIJING, dNch/dy = 5000Efficiency, purity Measured jet energy Jet energy resolution

Jet spatial resolution: (rec

- gen

) = 0.032; (rec

- gen

) = 0.028

Better, than , size of tower (0.0870.087)


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3.3 Medium-induced partonic energy loss3.3 Medium-induced partonic energy loss Collisional loss

(incoherent sum over scatterings)

Energy lost by partons in nuclear matter:E T

03 (temperature), g (number degrees of freedom)

EQGP

>> EHG

LHC, central Pb+Pb:T

0, QGP ~ 1 GeV >> T

0, HGmax ~ 0.2 GeV,

EQGP

/ EHG

(1 GeV / 0.2 GeV)3 ~ 102

Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al...

Radiation loss(coherent LPM interference)

Gulyassy-Wang; BDMPS; GLV; Zakharov; Wiedemann...


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Space-time evolution of dense matter, created in region of initial overlaping of colliding nuclei, is described by Lorenz-invariant Bjorken's hydrodynamics

J.D. Bjorken, PRD 27 (1983) 140

One of the important tools to study QGP properties in ultrarelativistic heavy ion collisions is a QCD jet production: medium-induced energy loss of energetic partons (jet quenching) is very different in cold nuclear matter and in QGP, resulting in many observable phenomena.

3.4 Jet quenching in heavy ion collisions3.4 Jet quenching in heavy ion collisions

Nuclear geometry and QGP evolutionimpact parameter b ≡ |O

1O

2| -

transverse distance between nucleus centers

j1

j2

B – generation point of jets j1 and j2


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3.5 Jet quenching: p3.5 Jet quenching: pTT-distribution and elliptic flow -distribution and elliptic flow

v2 = cos 2 (Elliptic flow): sharp drop due to jets and additional v

2 due to jet quenching

30,000 minimum bias Pb+Pb events, √s = 5.5A TeV (ntot

= 30000)

v2(pT): ~30%-reduction due to jets and small influence due to jet quenching

pT-distribution v2(pT)


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3.6 Jet quenching: jet fragmentation function3.6 Jet quenching: jet fragmentation function D(z)D(z)

In the jet induced by heavy quark, the energetic muon can be produced

and detected (“b-tagging”)

It is probability distribution for leading hadron in the jet to carry fraction z = pT

h/pTjet

of jet transverse momentum

Pb+Pb (b = 0), √s = 5.5A TeV, ET

jet > 100 GeV

(0)

DPbPb(z)/Dpp(z) ~ 0.8 (0.4 < z < 0.7)

, h

, h


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3.73.7 Jet fragmentation function can be reconstructed Jet fragmentation function can be reconstructed with CMS tracking systemwith CMS tracking system

Longitudinal momentum fraction z along the thrust jet axis

Transverse momentum relative to thrust jet axis


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Phobos@RHIC

CMS HF

acceptance

CMS HF and CASTOR will provide

best correlation between energy flow

and event centrality (maximal energy

deposition and minimal energy relative

fluctuations)

ZDC improves resolution

at large b (like RHIC)

4.1 Centrality determination4.1 Centrality determination

“Spectators”

ZDCZDC

ZDCZDC

BEAMS

Au+Au @ RHIC

BEAMS

“Spectators”


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4.2 Correlation between energy flow and centrality4.2 Correlation between energy flow and centrality

We use energy response of the HF-calorimeter (3 < | We use energy response of the HF-calorimeter (3 < | < 5.2) < 5.2)

where the bulk of reaction energy is deposited for Ar+Ar collisions.where the bulk of reaction energy is deposited for Ar+Ar collisions.

transverse (b) energy responses transverse (b) energy responses

in HF-calorimeter and comparison in HF-calorimeter and comparison with HIJING predictions.with HIJING predictions.

1. E/E1. E/ET T b correlation b correlation

Average resolution of impact Average resolution of impact parameter determination for parameter determination for Ar-Ar collisions is from 0.5 fm Ar-Ar collisions is from 0.5 fm (most central events) up to 1 fm (most central events) up to 1 fm (peripheral events).(peripheral events).

2. 2. Impact parameter resolution Impact parameter resolution σσb using E/ET, b using E/ET, total (a) andtotal (a) and


2020

4.3 Azimuthal angle of reaction plane4.3 Azimuthal angle of reaction plane Non-central heavy-ion collisions (Non-central heavy-ion collisions (b b ≠≠0), e0), elliptic volume of lliptic volume of interacting nuclear matter, energy flow illustrates interacting nuclear matter, energy flow illustrates azimuthally anisotropic elliptic volume. azimuthally anisotropic elliptic volume.

Calorimeters are used to determine event plane. Calorimeters are used to determine event plane.

Azimuthal anisotropy can be estimated with CMS calorimeters with and without the determination of event plane.

HYDROHYDRO, Pb+Pb collisions, b = 6 fm. GEANT-based simulation, Pb+Pb collisions, b = 6 fm. GEANT-based simulation

Energy flowEnergy flow


2121

4.4 4.4 Charged Particle Multiplicity: dNCharged Particle Multiplicity: dNchch/d/d

Determination of the primary charged-particle multiplicity is based on the Determination of the primary charged-particle multiplicity is based on the relation between the pseudorapidity distribution of reconstructed clusters in the relation between the pseudorapidity distribution of reconstructed clusters in the innermost layer of the CMS pixel tracker and that of charged-particle tracks innermost layer of the CMS pixel tracker and that of charged-particle tracks originating from the primary vertex.originating from the primary vertex.

On an event-by-event basis, On an event-by-event basis, the reconstructed multiplicity the reconstructed multiplicity is within 1-2% of the true value is within 1-2% of the true value in the | in the | ηη | < 2 region. | < 2 region.

Single layer hit counting in innermost pixel barrel layer

High granularity pixel detectorsHigh granularity pixel detectors

Pulse height in individual Pulse height in individual pixels to reduce backgroundpixels to reduce background

Very low pVery low pTT reach, p reach, pT T > 26 MeV > 26 MeV (counting hits!)(counting hits!)


2222

5.15.1 Monte-Carlo HI simulatons at LHCMonte-Carlo HI simulatons at LHC

There are two kind of MC HI simulations in HIC at LHC:There are two kind of MC HI simulations in HIC at LHC:

1. “Hard probes” signal event (jets, quarkonia, heavy quarks, Z) is 1. “Hard probes” signal event (jets, quarkonia, heavy quarks, Z) is

generated with standard pp generator (PYTHIA,...) and superimposed generated with standard pp generator (PYTHIA,...) and superimposed

on background of full heavy ion event on background of full heavy ion event

2. Global observables (particle spectra) and multiplicity background for 2. Global observables (particle spectra) and multiplicity background for

“hard probes” are generated with a heavy ion event generator “hard probes” are generated with a heavy ion event generator

(HIJING,...)(HIJING,...)

Problem:Problem: In most existing HI event generators such important effects as In most existing HI event generators such important effects as

jet quenching and elliptic flow are not included or implemented poorlyjet quenching and elliptic flow are not included or implemented poorly

Develop MC tools for adequate, fast simulation of physics phenomenaDevelop MC tools for adequate, fast simulation of physics phenomena


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5.2 Fast Monte-Carlo tools to simulate jet 5.2 Fast Monte-Carlo tools to simulate jet quenching and flow effectsquenching and flow effects

PYQUENPYQUEN - fast code to simulate jet quenching - fast code to simulate jet quenching (modify PYTHIA6.4 jet event)(modify PYTHIA6.4 jet event) http://cern.ch/lokhtin/pyquenhttp://cern.ch/lokhtin/pyquen

HYDROHYDRO - fast code to simulate transverse and elliptic flow in central- fast code to simulate transverse and elliptic flow in central and semi-central AA collisions at LHC,and semi-central AA collisions at LHC, http://cern.ch/lokhtin/hydro http://cern.ch/lokhtin/hydro

HYDJETHYDJET - merging HYDRO (flow effects), PYTHIA - merging HYDRO (flow effects), PYTHIA (hard jet production) and PYQUEN (jet quenching)(hard jet production) and PYQUEN (jet quenching) http://cern.ch/lokhtin/hydro/hydjet.htmlhttp://cern.ch/lokhtin/hydro/hydjet.html

Significant progress in development of Monte-Carlo models for Significant progress in development of Monte-Carlo models for simulation of jet quenching is achieved (PYQUEN, HIDJET). simulation of jet quenching is achieved (PYQUEN, HIDJET).

It describes RHIC data adequately. It describes RHIC data adequately.

See talk of Igor Lokhtin for details.See talk of Igor Lokhtin for details.


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6.1 Summary and outlook6.1 Summary and outlook

At LHC a new regime of heavy ion physics will be reached where hard particleAt LHC a new regime of heavy ion physics will be reached where hard particle production can dominate over soft events, while the initial gluon densities are production can dominate over soft events, while the initial gluon densities are much higher than at RHIC, implying stronger partonic energy loss observable much higher than at RHIC, implying stronger partonic energy loss observable in new channels. in new channels.

CMS is an excellent device for the study of quark-gluon plasma by hard probes:CMS is an excellent device for the study of quark-gluon plasma by hard probes: - - Quarkonia Quarkonia and heavy quarks and heavy quarks - Jets, - Jets, ''jet quenching'' in various physics channels ''jet quenching'' in various physics channels CMS will also study global event characteristics:CMS will also study global event characteristics: - - Centrality, Multiplicity Centrality, Multiplicity

- - Correlation and Correlation and Energy Flow reaching very low pEnergy Flow reaching very low pT T

CMS CMS is preparing to take advantage of its capabilitiesis preparing to take advantage of its capabilities - - Excellent rapidity and azimuthal coverage, high resolutionExcellent rapidity and azimuthal coverage, high resolution

- Large acceptance, nearly hermetic fine granularity hadronic and - Large acceptance, nearly hermetic fine granularity hadronic and electromagnetic calorimetry electromagnetic calorimetry - Excellent muon and tracking systems - Excellent muon and tracking systems - - New High Level Trigger algorithms specific for A+ANew High Level Trigger algorithms specific for A+A

- - Zero Degree Calorimeter, CASTOR and TOTEM will be important Zero Degree Calorimeter, CASTOR and TOTEM will be important additions extending to forward physics additions extending to forward physics


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CMS HCAL Technical Design Report 1997 CERN/LHCC 97-31

CMS MUON Technical Design Report 1997 CERN/LHCC 97-32

CMS ECAL Technical Design Report 1997 CERN/LHCC 97-33

CMS Technical Tracker Design Report 1998 CERN/LHCC 98-6

Quarkonia. M.Bedjidian, O.Kodolova, pTDR, v.2, CMS-NOTE-2006/089

M.Bedjidian, V.Kartvelishvili and R.Kvatadze, CMS-NOTE-1999/017(1999)

Jets reconstruction algorithm . I.Vardanyan, pTDR, v.2, CMS-NOTE-2006/050

Jet fragmentation with tracker. C.Roland, CMS-NOTE-2006/031, CMS-RN-2003/003

R.Vogt, Phys. Rep., v.310, p.197, 1999

I.Lokhtin, S.Petrushanko, L.Sarycheva, A.Snigirev, CMS-NOTE-2003/019

I.Damgov, V.Genchev, V.Kolosov, I.Lokhtin, S.Petrushanko, L.Sarycheva, C.Teplov, S.Shmatov, P.Zarubin, CMS-NOTE-2001/055

I.Lokhtin, A.Snigirev, Eur. Phys. J., C45, p.211-217, 2006

6.2 Some publications used in report6.2 Some publications used in report


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6.3 Acknowledgement6.3 Acknowledgement

This report includes the remarks of

I.P.Lokhtin, A.M.Snigirev, O.L.Kodolova, M.Bedjidian, B.Wyslouch, D.Denegri,

M.Murrey, C.Roland, C.Mironov, I.N.Vardanyan, K.Yu.Teplov, S.V.Petrushanko

and other CMS HI collaborators


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BACKUP SLIDES BACKUP SLIDES

(Appendix 7.1 – 7.8)(Appendix 7.1 – 7.8)


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7.1 Data Acquisition and Trigger7.1 Data Acquisition and Trigger

Level 1 hardware trigger Level 1 hardware trigger Muon track segmentsMuon track segments Calorimetric towersCalorimetric towers No tracker dataNo tracker data Output rate (Pb+Pb): Output rate (Pb+Pb): 1-2 1-2

kHz comparable to kHz comparable to collision ratecollision rate

Online Farm

switchswitch

High level trigger High level trigger Full event information available Full event information available Every event accepted by L1 sent to an Every event accepted by L1 sent to an

online farm of 2000 PCsonline farm of 2000 PCs Output rate (Pb+Pb): Output rate (Pb+Pb): ~ 40 Hz~ 40 Hz Trigger algorithm same or similar to Trigger algorithm same or similar to

offline reconstructionoffline reconstruction

bufferbuffer


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7.2 Measuring Muons7.2 Measuring Muons

Resolution Standalone Resolution with tracker

10%

20%

30%

2%

10%


3030Jet + Z0

# E

ven

ts/4

GeV

ET/0-ET

Jet (GeV)

< ΔE>=8 GeV < ΔE>=4 GeV <ΔE>=0 GeV

Background

Isol. 0+jet

, Z0

1 month at

1027cm-2s-1

Pb+Pb

7.3 Balancing 7.3 Balancing or Z or Z00 vs Jets: Quark Energy Loss vs Jets: Quark Energy Loss


3131

7.4 Z7.4 Z00 ++−− detection at CMSdetection at CMS

AA = A2α pp with =1

pp was taken from PYTHIA, correction

k = 2 for cc and bb and

k = 1.3-1.5 for Z, W, tt

The expected number of

Z0 +: ~104/1.3x106 s

of Pb-Pb running at L = 1027cm2s1

Z0 can be measured with muon

system alone and with

muon+tracker systems.

Z0+jet events The expected number of Z0+jet for jet ET > 50 GeV and |hjet| < 1.5: 900/1.3x106 s of Pb-Pb run at L = 1027cm2s1.

Z0 + jet events with PTZ0

measured from pair + should allow to study effects of jet quenching using energy balance ETjet = PTZ0

HIJING was used for AA event


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7.5 Invariant mass spectrum of 7.5 Invariant mass spectrum of μμ++μμ−−-pairs -pairs

from from */Z+jet production*/Z+jet production

Background is insignificant.

Interference between γ*

and Z is important.

New potentially important channel for CMS

I.Lokhtin, A.Snigirev, A.Sherstnev, Phys. Lett. B599, p.260-268, 2004


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7.6 Medium-induced partonic energy loss7.6 Medium-induced partonic energy loss

xλxxλ

=xdx

dP,Ex,

dx

dExλx

dx

dPdx=EL,ΔE

L

/exp1

0

Collisional loss

(incoherent sum over scatterings)

Radiation loss

(coherent LPM interference)

qq,gq,gg=C,ΛtN

π=α

,t

tπαC

dt

dσt,

dt

dσtdt

Tλλ=

dx

dE

QCDfS

smax

Dμ

9/414/9/ln233

12

2

4

1

2

2

2

2

3

4

21

16ln

31cosln

21

20 1

22

111

2

2

=C,E

ω=y,

λ

τ=τ,

yω

λμ=k,

kky

C+yi=ω,τω

y+yω

E

μλ~d

πτ

Cα==m

dx

dEF

g

LgDF

DgLPMEL

Fsq

3/43/1

2

22/30

1

10

E

m

μ

λ=l

,=mdx

dE

lω+=m

dx

dE

q

D

qq

“dead cone” approximation for massive quarks:

General kinetic integral equation:

1. Collisional loss and elastic scattering cross section: 2. Radiative loss (BDMS):

Bjorken; Mrowczynski; Thoma; Markov; Mustafa et al...

Gulyassy-Wang; BDMPS; GLV; Zakharov; Wiedemann...


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7.7 Energy-energy correlation function (definition)7.7 Energy-energy correlation function (definition)

d

dE

d

dEd

ENd

d TT

T

T

2

02visevent

event )(

11

ET() – transverse energy flow in , – azimuthal size of a calorimeter sector – azimuthal angle of a calorimeter sector – relative azimuthal angle between two azimuthal sectors

In the continuous limit → 0

2

0

vis

d

dEdE T

T

New potentially important channel for CMS


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,2cos212

)(2 R

visTT vE

d

dE

The transverse energy-energy correlator dT/d as a function of relative azimuthal angle without (blue histogram) and with partonic energy loss for the “small-angular” (red histogram) and the “broad-angular” (magenta histogram) parameterizations of emitted gluon spectrum in central Pb-Pb collisions. (Histograms calculated without effects of installation.)

7.8 Energy-energy correlation function 7.8 Energy-energy correlation function ddTT/d/d

For non-central collisions with a clearly visible elliptic flow of the transverse energy

Correlator dT/d is independent of the reaction plane angle R and is calculated explicitly:

.2cos21

2

1 22

d

dv

d

d TT

azimuthal angle.

minimum bias events

I.Lokhtin, L.Sarycheva, A.Snigirev, Eur. Phys. J., C36, p.375-379, 2004

Heavy Ion Physics with the CMS Detector

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