Heavy Ion Physics with the CMS detector

IPM, 1st meeting on LHC Physics, Isphagan,Iran 20 April-24 April 2009

Heavy Ion Physics with the CMS detector

Olga Kodolova, INP MSU

for Collaboration


The temperature and energy density in A-A interactions may be high enough to get the super-dense QCD state in the quasi-macroscopic volumes - QGP (in comparing with hadrons scale)

«Soft» tests (pT~ΛQCD=200 МэВ) Low pt particle spectra and particles correlations Flow effects Thermal photons and dileptons Strangeness flow

«Hard» tests (pT, M>>ΛQCD=200 МэВ) High-pt particle spactra and its angular correlations Jets Onia Heavy quarks flow

Initial state

Pre-equilibrium state

Heating and density increase:QGP formation

hadronization

Freeze-out and hadronic state

Quark-Gluon Plasma (QGP)


Overview

From RHIC to LHC

CMS detector

QCD matter in the soft sector dNch/d

low pT /K/p spectra

Eliptic flow

QCD matter in the hard sector

high-pT hadrons, jets, photon-jet

Qqbar suppression

Y-l+l- photoproduction

Note: For most of measurements in AA we will need the reference measurementsin pp (see talk of Klaus Rabbertz “QCD Physics potential in CMS)

High and low pt tracking

Muon reconstruction

Jet reconstruction

Photon reconstruction

Event plane

Event centrality


Some evidences from RHIC

Calor Glass Condensate?

Local equilibrium in Freeze-out stage?

Deflection from Hydro – Viscosity?

Same J/ suppressionat SPS and RHICMore suppression inforward

Strong interaction ofDense matter with High pt hadronssQGP at RHIC?LHC-? LHC--?

Suppressionvs regeneration?

And manyother questions to LHC


LHC

RHIC

SPS

Initial state fully in the saturated CGC regime Initial energy density ~5 times higher Lifetime of a quark-gluon plasma much longer Large rates of hard probes over a broad kinematical range Plenty of heavy quarks (b,c) Weakly interacting probes become available (Z0, W)

Lo

w x

Hig

h p

TFrom RHIC (200 GeV/n-n) to LHC (5500

GeV/n-n)


TOTEM

5.3 << 6.7

CASTOR

5.2 << 6.6

ZDC

8.3 <

Large Range of Hermetic Coverage:Tracker, muonsTracker, muons ECAL ECAL ++ HCALHCAL Forward HCALForward HCAL CASTORCASTOR ZDC 8.3<ZDC 8.3<

CMS detector


Strongest magnetic field: 4 T, 2 T (return yoke)

Silicon tracker:

Momentum resolution is ~2% for tracks with p

T <100 GeV

Good efficiency and low fake rate for p

T>1 GeV/c

low occupancy of pixel detectors – 1-2% with PbPb central events

Good separation of Onia families

High level trigger capable of full reconstruction of most of HI events in real time

Excellent possibility for hardprobes triggering

HCALECAL

Tracker

Coil

Fine grained high resolution calorimeter with hermetic coverage up to ||<5 (||<7 proposed with CASTOR) ZDC accepted ||>8.3 Jet finder coverage up to ||<5 and photons coverage up to | |<3 Muon stations with:

precise measurement of position (momentum) fast response at LVL1 trigger

CMS detector for heavy ion physics


Bulk (“hydro”) measurements in AA collisions


Simple measurements via hits count in pixels accomplished with dE/dx cutor tracklets with vertex constraints

Charged particle multiplicity ~ gluon density

CGCprediction

HIJING default settings

Pixels hits count

First measurement at LHC

Final AA multiplicity ~ gluon density

Barrel pixels

Endcap pixels

Beam

11 cm


Soft hadron spectra (CMS) ~ medium equation of state

||<1

Single hadron (+-, K+-, p ) pT spectrain pT~0.2-2 GeV/c

PID via dE/dx (Gaussian unfolding)

Collectiveradial flow,hadron ratios,thermalizationtime, mediumequation ofstate constraints


Eliptic flow: medium viscosity

x

yInitial spatial anisotropy

px

py

Final momentum anisotropy

Reaction plane

x

z

y

dN/d( - R ) = N0 (1 + 2v1cos (- R) + 2v2cos (2(- R)) + ... )

Elliptic Flow: v2

2

T

y2

T

xR2 p

p

p

p)(2cosv

- defines R,

(direction of the impact parameter)

LHC


Eliptic flow

Two methods: 1. Using reaction plane determination with Calorimeters and tracker 2. Cumulant analysis: using two and multi particle correlations cos(2(1-2)) = v2

2

Azimuthal ET distribution in different calorimeter layers

Event plane resolutionwith ECAL: 0.37 radian

V2 with tracker


Hard probes of QCD matter:

Qaurkonia and heavy quarksJets and high-pT hadrons


Hard probes triggering for HI in CMS

CMS trigger system is designed for 1034 (pp events) with 40 MHz bunch crossingrate.Two levels system: Level 1 and High Level Trigger

pp40

MHz

DAQ/HLT100 KHz

Offline150 Hz

Level 1 1/400

100 KHz, 1MB

DAQ/HLT 1/600

150 Hz, 1.5 MB

PbPb:

Luminosity(cm-2s-1): 1027

Event rate (KHz): 8 Event size after L1(MB): 2.5 (Minbias) 10 (Central)

Pb-Pb8

KHz

DAQ/HLT8 KHz

Offline10—100

Hz1/1 1/80-1/800


Jet finder in CMS for HI

ETrec vs ET

gen

CMS

Iterative cone (R>=0.5) with

background subtraction

dNch/d = 5000

Iterative cone (R>=0.5) with background

subtraction:

mean value is determined on an

event-by-event basis: calculate average energy and dispersion in

tower (in eta rings) for each event subtract average energy and dispersion

from each tower find jets with a jet finder algorithm (any)

using the new tower energies recalculate average energy and dispersion

using towers free of jets recalculate jet energies

Done, but can do more iterations

Space resolution is less then the size of calorimeter tower


High-pt tracking

Efficiency ~ 70 %, fake rate ~ 1%

Resolution:barrel – 1%

endcap 2-2.5%

3 pixel layers in barrel, 2 pixel layers in endcapSilicon layers: 10 in barrel 11 in endcap


High-pt hadron spectra

different centrality binsfor 0.5 nb-1

jet trigger data

Jet energy loss model in HYDJET

Nuclear modification functionreach for 0.5 nb-1


Photon reconstruction

Photon reconstruction with Island AlgorithmPhoton ID using Multi-Variate Analysis with 21 variables grouped into 3 sets: ECAL cluster shapeand ECAL/HCAL/Tracker isolation cuts

Performance:Efficiency = 60%Fake = 3.5%S/B=4.5


Fragmentation function measurements

FF(z) FF()

RFF()

+jet events are used

UE background subtracted using R=0.5 cone transverse to jet direction

Functions are relative to photon energy

Integrated luminosity

0.5 nb-1


Dissociation of quarkonia: hot QCD thermometer

c

Suppression: RHIC comparable to SPS

Regeneration compensate screening

J/ not screened at RHIC (TD~2Tc)

LHC: recombination or suppression

Suppression of B’onium States

Large Cross-section: 20×RHIC

melts only at LHC: TD~4 TC

Less amount of bb(bar) pairs: less regeneration

Much cleaner probe than J/

Suppression of C'onium states Suppression of B'onium states

• Quarkonia: J/ (BR:5.9%), Y (BR:2.5%)

• Background: combinatorial due- to decays from /K, b-,c- production

'

J/


J/ measurements

both muons

with |<2.4

Expected rate

(per month,106

s, 0.5 nb-1

):

J/ ~ 180 kevents

CMS

“high” multiplicity

dNch

/dη|=0 = 5000

“low” multiplicity

dNch

/dη|=0 = 2500

Excellent mass resolution:

J/ = 35 MeV/c2, both muons

with ||<2.4

Signal/Background:

~5(1) for J/ in ||<0.8 (||<2.4)

Expected rate (per month, 106s, 0.5 nb-1):

J/~ 180 kevents


Upsilon measurements

mass resolution, 54 MeV

“high” multiplicity

dNch

/dη|=0 = 5000

Luminosity

0.5 nb-1

||<2.4

mass resolution, 90 MeV

||<2.4

Y ~ 25 kevents,

Y' ~ 7 kevents,

Y'' ~ 4 kevents

CMS

CMS

CMS

Excellent mass resolution:

Y = 54 MeV/c2 ||<0.8,

Y = 90 MeV/c2 ||<2.4

Signal/Background:

1 (0.1) for Y in ||<0.8 (||<2.4)


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 GeV

Pb: 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

Ultra-peripheral collisions


Summary

The excellent capabilities of CMS give the unique possibility of measuring both soft and hard probes of the dense medium state:

Multiplicity soft and hard spectra of charged particles photons Jets Quarkonia some other probes that are not covered by presentation: Dihadron and dijet correlations HBT

Heavy Ion Physics program at LHC

starts with the FIRST pp data

Post-Summary – next Slide


Post-Summary

Heavy ion physics starts with pp runs !Taking into account the first AA run first pp dataare extremely important for success in first AA run

200 pb-1

B-PAG

QCD-PAG

EWK-PAG

Take pp measurements as reference to AA run

Crucial quarkonia measurements pt-eta spectra primary and secondary J/ production Multiplicity, charged particle spectra (low and high), important input for MC heavy ion models. Jet fragmentation, jet shape, jet spectra as input for RAA measurements.

Z-production: important input for MC heavy ion models


First Pb-Pb data – NEXT YEAR!

First AA runnext year

Note from Chamonix meeting:Early Pb Beam will have lower energy. 10TeV pp corresponds to 4 TeV in Pb+Pb

First Heavy Ion run is scheduled for 2010 Running at nominal PbPb conditions expected in 2012Main tasks for the next half an year is to prepare HLT/DAQand to identify the first AA run papers.

->2


First A-A run

The low interaction rate in year-1 should allow us to write all min bias events to mass storage Deploy full HI HLT to tag events and to test

efficiencies and functionality Fully functional HLT needed at nominal

luminosity We need to estimate carefully what

analyses can be done with statistics of 8-80 mlns of events: 1-10 μb–1 Note: nominal run is 0.5 nb-1

~3kHz

~100Hz

Ave. Coll. rate

1

1

Pile up

~2s~8kHz5.5 TeV Nominal

~60s~150Hz~ 4 TeVYear-1

CPU/EventMax.Coll. RateColl. EnergyPb+Pb


Backup slides


CMS detector for heavy ions

Silicon Tracker (Pixels and Strip) Electromagnetic Calorimeter (PbWO4) Central hadron Calorimeter

(plastic + brass absorber) Forward calorimeter (Quartz-fiber and ferum) Muon Chambers (Drift tubes in barrel,

Cathod strip chambers in endcap, RPC) CASTOR Zero-degree calorimeter

+ TOTEM

4 T magnetic field (solenoid), 2 T return yokemomentum resolution < 2% for pT<100 GeVFast DAQ allows to take almost all eventsto HLT farm


CMS acceptance

ECAL, PbWO40.0174x0.0174

Inner detector

HCAL (sampling)0.087x0.087 (HB)0.087->0.17 (HE)

HFHF

Muon Spectrometer

Castor

Castor

CMS:

Inner detector (||<2.5)ECAL (||<3)HCAL (||<3)HF (3<||<5)Muon (||<2.4)Castor (5<||<6.7)ZDC (||>8)

Heavy Ion Physics with the CMS detector

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