Heavy ion physics with the cms detector
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Heavy Ion Physics with the CMS Detector. Lyudmila Sarycheva Scobeltsyn Institute of Nuclear Physics Moscow State University For CMS Collaboration. CMS detector and Heavy Ion program Quarkonia and heavy quarks Jets and jet quenching Global event characterization

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Heavy Ion Physics with the CMS Detector

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Heavy ion physics with the cms detector

Heavy Ion Physics with the CMS Detector

Lyudmila Sarycheva

Scobeltsyn Institute of Nuclear Physics

Moscow State University

For CMS Collaboration

  • CMS detector and Heavy Ion program

  • Quarkonia and heavy quarks

  • Jets and jet quenching

  • Global event characterization

  • Monte-Carlo simulation tools

  • Summary

  • 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

ICHEP'06 Moscow 26.07 - 02.08.2006


1 1 cms detector

1.1 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

TOTEM

CASTOR

ZDC

5.3 <  < 6.7

5.2 < |h| < 6.6

8.3 < ||

ICHEP'06 Moscow 26.07 - 02.08.2006


1 2 forward region layout

1.2 Forward Region Layout

|h| > 3

ZDC

EM

HAD

(8.3 < ||)

Forward HCal

(3 < |h| < 5)

(z =  140 m)

TOTEM

CASTOR (~ 10 λI)

(5.3 <  < 6.7)

(5.2 < h < 6.6)

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

1.3 Overview: CMS Detector Coverage

Kinematics at the LHC

Large Range of Hermetic Coverage:

Tracker, muons || < 2.4

ECAL +HCAL|| < 3

Forward HCAL 3 < || < 5

CASTOR 5.2 < || < 6.6

ZDC

Gluon density

has to saturate

at low x

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

1.4 Heavy Ion program at CMS

  • Excellent detector for high pT probes of quark-gluon plasma:

    - High rates and large cross sections

    - Quarkonia (J/,), heavy quarks ( ) and Z0

    - High acceptance for calorimeters and muon system

    - High pT jets

    - High energy photons

  • Correlations

    - jet-jet

    - jet-, jet-*/Z0

    - multijets

  • Global event characterization

    - Centrality

    - Energy flow to very forward region

    - Charged particle multiplicity

    - Azimuthal anisotropy

  • Forward physics and ultraperipheral interactions

    - Limiting Fragmentation, Saturation, Color Glass Condensate

    - Exotica

  • Monte-Carlo simulation tools:

    - PYTHIA, HIJING, PYQUEN/HYDJET

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

2.1 Quarkonia and heavy quarks from SPS and RHIC to LHC

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

Plasma hotter and longer lived than at RHIC

Unprecedented Gluon densities

Access to lower x, higher Q2

Availability of new probes

LHC

 Quarkonia with high statistics

(J/y, y'; , ', '')

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/

-

-

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

2.2Quarkonia (J/, ): reconstruction

MC simulation/visualization of Pb+Pb event

(dNch/dh|h=0 ~ 3000) using the pp software framework

 →m+m

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

2.3 J/ and  spectra for multiplicity dNch/d = 2500

For Pb-Pb at integrated luminosity 0.5nb-1

p/K decays into mm b,c-hadrons into mm

S/B N

J/y 1.2 180000

 0.12 25000

Combinatorial background:

Mixed sources, i.e.

1 m from p/K + 1 m from J/y

1 mfrom b/c + 1 m from p/K

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

2.4 J/ and  spectra (subtraction of the like sign spectra)

both

muons

|h| < 2.4

both

muons

|h| < 2.4

both

muons

|h| < 0.8

both

muons

|h| < 0.8

See talk of Olga Kodolova for details.

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

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

r is transverse distance between the intersection points

with the beam line belonging two different muon tracks

BB m+m 

BB  J/ym+m

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

ICHEP'06 Moscow 26.07 - 02.08.2006


3 1 jet cross section expected event rate

3.1Jet 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

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

3.2 High pT jets. Jet reconstruction in HI collisions

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 = 5000

BACKGROUND SUBTRACTION ALGORITHM

The algorithm is based on event-by-event-dependent background subtraction:

Efficiency, purity

Measured jet energy

Jet energy resolution

Jet spatial resolution: (rec- gen) = 0.032; (rec- gen) = 0.028

Better, than, size of tower (0.0870.087)

ICHEP'06 Moscow 26.07 - 02.08.2006


3 3 medium induced partonic energy loss

3.3 Medium-induced partonic energy loss

Collisional loss

(incoherent sum over scatterings)

Radiation loss

(coherent LPM interference)

Bjorken; Mrowczynski;

Thoma; Markov; Mustafa et al...

Gulyassy-Wang; BDMPS;

GLV; Zakharov; Wiedemann...

Energy lost by partons in nuclear matter:

ET03 (temperature), g (number degrees of freedom)

EQGP >> EHG

LHC, central Pb+Pb:

T0, QGP ~ 1 GeV >> T0, HGmax ~ 0.2 GeV,

EQGP/EHG (1 GeV / 0.2 GeV)3 ~ 102

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

3.4 Jet quenching in heavy ion collisions

  • 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.

Nuclear geometry and QGP evolution

impact parameter b ≡ |O1O2| -

transverse distance between nucleus centers

j2

B – generation point of jets j1 and j2

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

j1

ICHEP'06 Moscow 26.07 - 02.08.2006


3 5 jet quenching p t distribution and elliptic flow

3.5 Jet quenching: pT-distribution and elliptic flow

30,000 minimum bias Pb+Pb events, √s = 5.5A TeV (ntot= 30000)

v2(pT)

pT-distribution

v2= cos 2 (Elliptic flow): sharp drop due to jets and additional v2 due to jet quenching

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

ICHEP'06 Moscow 26.07 - 02.08.2006


3 6 jet quenching jet fragmentation function d z

3.6 Jet quenching: jet fragmentation functionD(z)

It is probability distribution

for leading hadron in the jet

to carry fraction z = pTh/pTjet

of jet transverse momentum

Pb+Pb (b = 0), √s = 5.5A TeV, ETjet > 100 GeV

(0)

, h

, h

In the jet induced by heavy quark,

the energetic muon can be produced

and detected (“b-tagging”)

DPbPb(z)/Dpp(z) ~ 0.8

(0.4 < z < 0.7)

ICHEP'06 Moscow 26.07 - 02.08.2006


3 7 jet fragmentation function can be reconstructed with cms tracking system

3.7Jet fragmentation function can be reconstructed with CMS tracking system

Transverse momentum relative to thrust jet axis

Longitudinal momentum fraction z

along the thrust jet axis

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

“Spectators”

4.1 Centrality determination

Au+Au @ RHIC

CMS HF acceptance

[email protected]

ZDC

ZDC

“Spectators”

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)

BEAMS

BEAMS

ICHEP'06 Moscow 26.07 - 02.08.2006


4 2 correlation between energy flow and centrality

4.2 Correlation between energy flow and centrality

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

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

1. E/ET  b correlation

2. Impact parameter resolution σb using E/ET, total (a) and

transverse (b) energy responses

in HF-calorimeter and comparison with HIJING predictions.

Average resolution of impact parameter determination for

Ar-Ar collisions is from 0.5 fm

(most central events) up to 1 fm (peripheral events).

ICHEP'06 Moscow 26.07 - 02.08.2006


4 3 azimuthal angle of reaction plane

4.3 Azimuthal angle of reaction plane

  • Non-central heavy-ion collisions (b ≠ 0), elliptic volume of

    interacting nuclear matter, energy flow illustrates

    azimuthally anisotropic elliptic volume.

  • Calorimeters are used to determine event plane.

  • Azimuthal anisotropy can be estimated with CMS calorimeters

    with and without the determination of event plane.

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

Energy flow

ICHEP'06 Moscow 26.07 - 02.08.2006


4 4 charged particle multiplicity dn ch d

4.4 Charged Particle Multiplicity: dNch/d

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

Single layer hit counting

in innermost pixel barrel layer

  • High granularity pixel detectors

  • Pulse height in individual pixels to reduce background

  • Very low pT reach, pT > 26 MeV

    (counting hits!)

On an event-by-event basis,

the reconstructed multiplicity

is within 1-2% of the true value

in the | η | < 2 region.

ICHEP'06 Moscow 26.07 - 02.08.2006


5 1 monte carlo hi simulatons at lhc

5.1Monte-Carlo HI simulatons 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 generated with standard pp generator (PYTHIA,...) and superimposed on background of full heavy ion event

2. Global observables (particle spectra) and multiplicity background for “hard probes” are generated with a heavy ion event generator (HIJING,...)

Problem: In most existing HI event generators such important effects as jet quenching and elliptic flow are not included or implemented poorly

Develop MC tools for adequate, fast simulation of physics phenomena

ICHEP'06 Moscow 26.07 - 02.08.2006


5 2 fast monte carlo tools to simulate jet quenching and flow effects

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

  • PYQUEN- fast code to simulate jet quenching

  • (modify PYTHIA6.4 jet event)

  • http://cern.ch/lokhtin/pyquen

  • HYDRO- fast code to simulate transverse and elliptic flow in central

  • and semi-central AA collisions at LHC,

  • http://cern.ch/lokhtin/hydro

  • HYDJET- merging HYDRO (flow effects), PYTHIA

  • (hard jet production) and PYQUEN (jet quenching)

  • http://cern.ch/lokhtin/hydro/hydjet.html

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

  • It describes RHIC data adequately.

See talk of Igor Lokhtin for details.

ICHEP'06 Moscow 26.07 - 02.08.2006


6 1 summary and outlook

6.1 Summary and outlook

  • At 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

  • much higher than at RHIC, implying stronger partonic energy loss observable

  • in new channels.

  • CMS is an excellent device for the study of quark-gluon plasma by hard probes:

  • - Quarkonia and heavy quarks

  • - Jets, ''jet quenching'' in various physics channels

  • CMS will also study global event characteristics:

  • - Centrality, Multiplicity

  • - Correlation and Energy Flow reaching very low pT

  • CMS is preparing to take advantage of its capabilities

  • - Excellent rapidity and azimuthal coverage, high resolution

    • - Large acceptance, nearly hermetic fine granularity hadronic and

    • electromagnetic calorimetry

      - Excellent muon and tracking systems

      - New High Level Trigger algorithms specific for A+A

  • - Zero Degree Calorimeter, CASTOR and TOTEM will be important

  • additions extending to forward physics

ICHEP'06 Moscow 26.07 - 02.08.2006


6 2 some publications used in report

6.2 Some publications used in report

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

ICHEP'06 Moscow 26.07 - 02.08.2006


6 3 acknowledgement

6.3 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

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

BACKUP SLIDES

(Appendix 7.1 – 7.8)

ICHEP'06 Moscow 26.07 - 02.08.2006


7 1 data acquisition and trigger

7.1 Data Acquisition and Trigger

Level 1 hardware trigger

  • Muon track segments

  • Calorimetric towers

  • No tracker data

  • Output rate (Pb+Pb): 1-2 kHz comparable to collision rate

buffer

High level trigger

  • Full event information available

  • Every event accepted by L1 sent to an online farm of 2000 PCs

  • Output rate (Pb+Pb): ~ 40 Hz

  • Trigger algorithm same or similar to offline reconstruction

switch

Online Farm

ICHEP'06 Moscow 26.07 - 02.08.2006


7 2 measuring muons

7.2 Measuring Muons

30%

10%

20%

10%

2%

Resolution Standalone

Resolution with tracker

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

<ΔE>=0 GeV

< ΔE>=4 GeV

< ΔE>=8 GeV

Background

# Events/4 GeV

Isol. 0+jet

ET/0-ETJet (GeV)

7.3 Balancing  or Z0 vs Jets: Quark Energy Loss

, Z0

1 month at

1027cm-2s-1

Pb+Pb

Jet + Z0

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

7.4 Z0+−detection at CMS

The expected number of

Z0 m+m: ~104/1.3x106 s

of Pb-Pb running at L = 1027cm2s1

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 = 1027cm2s1.

Z0 + jet events with PTZ0

measured from pair + should

allow to study effects of jet

quenching using energy balance

ETjet = PTZ0

AA = A2αpp with =1

spp was taken from PYTHIA, correction

k = 2 for cc and bb and

k = 1.3-1.5 for Z, W, tt

HIJING was used for AA event

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

7.5 Invariant mass spectrum of μ+μ−-pairs from */Z+jet production

New potentially important channel for CMS

Background is insignificant.

Interference between γ*

and Z is important.

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

ICHEP'06 Moscow 26.07 - 02.08.2006


7 6 medium induced partonic energy loss

7.6 Medium-induced partonic energy loss

Collisional loss

(incoherent sum over scatterings)

Radiation loss

(coherent LPM interference)

Gulyassy-Wang; BDMPS; GLV;

Zakharov; Wiedemann...

Bjorken; Mrowczynski;

Thoma; Markov; Mustafa et al...

General kinetic integral equation:

1. Collisional loss and elastic scattering cross section:

2. Radiative loss (BDMS):

“dead cone” approximation for massive quarks:

ICHEP'06 Moscow 26.07 - 02.08.2006


7 7 energy energy correlation function definition

7.7 Energy-energy correlation function (definition)

New potentially important channel for CMS

  • 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

ICHEP'06 Moscow 26.07 - 02.08.2006


Heavy ion physics with the cms detector

7.8 Energy-energy correlation function dT/d

For non-central collisions with a clearly

visible elliptic flow of the transverse energy

minimumbias events

  azimuthal angle.

Correlator dT/d is independent of the

reaction plane angle Rand is calculated

explicitly:

The transverse energy-energy correlator dT/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.)

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

ICHEP'06 Moscow 26.07 - 02.08.2006


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