Prospects for the observation of quarkonia in heavy ion

VHM07, 17-19 September 2007, Dubna, Russia

Prospects for the observation of quarkonia in heavy ion

collisions with CMS detector at LHC

Olga Kodolova, SINP MSU

(for CMS Collaboration)

CMS HI groups: Adana, Athens, Basel, Budapest, CERN, Demokritos, Dubna, Ioannina, Kiev, Krakow, Los Alamos, Lyon, MIT, Moscow, Mumbai, N. Zealand, Protvino, PSI, Rice, Sofia, Strasbourg, U Kansas, Tbilisi, UC Davis, UI Chicago, U. Iowa, U. Minnesota, Yerevan, Vanderbilt, Warsaw, Zagreb

+-, Pb-Pb, dNch/d = 3500


LHCRHIC

Vogt, hep-ph/0205330

PbPb @ √sNN=5.5 TeV, pPb @ √sNN=8.8 TeV

Quarkonia: from SPS and RHIC to LHC

✔ Factor 30-45 increase in energy compared to AuAu, dAu @RHIC

30-45 times lower Bjorken x=2 mT / sqrt(s)

✔ Larger cross-section✔ Larger luminosity

Heavy-ion physics at LHC:

Plasma hotter, longer-lived than @ RHIC

Access to lower x, higher Q2

Unprecedented gluon densities

Availability of new probes (Y,Y',Y'')

J/

Vogt,hep-ph/0205330

RHIC

LHC


}Muon system:

Drift Tubes (DT) in central barrel region

Cathode Strip Chambers (CSC) in endcap region

Resistive Plate Chambers (RPC) in barrel and endcap

Excellent coverage:~5 units of rapidity and 2 Strongest magnetic field:

4 T, 2 T (return yoke)

Tag from muon stations,

momentum resolution from

Silicon tracker:

~2% of momentum

resolution for tracks with

pT <100 GeV

Ecal+Hcal+Coil – absorbs

hadrons

HCAL

ECAL

Tracker

Coil

Tracker system:

Silicon pixel layers (3 in barrel, 2 in endcap)

Silicon strips layers (10 in barrel, 12 in endcap)

CMS detector

precise measurement of

position (momentum)

fast info for LVL-1 trigger


Signal and background simulation

Resonance cross-section (b):

J/' Y Y' Y”

Bprod 48930 879 304 78.8 44.4

Yellow Report, CERN-2004-009, hep-ph/0311048:

CEM, NLO-pp, shadowing effect (CTEQ5M+EKS98 PDF)

no additional absorption effects

Values are averaged over impact parameter.

Pb-Pb cross-section – 7.8 barn

Main background sources:

uncorrelated muon pairs from /K decays

muons from b- c- quark production

4 orders of magnitude between Y and Pb-Pb cross-section→ need accurate fast Monte-Carlo


We have considered two scenarios for the multiplicity of charged

particles in the most central collisions (5% of total cross-

section):

dNch

/d = 2500 at =0

dNch

/d = 5000 at =0

In fast Monte-Carlo, only pions and kaons are considered,

which represent 90% of charged particles multiplicity.

Kaon/pion = 11% (HIJING)

pT and distributions of pions and kaons according to HIJING

I. Muon background sources: pions and kaons


b=0 5% c.c. min.bias.

N(cc) w/o shadowing 226 206 51

w/ shadowing 150 135 33

b=0 5% c.c. min.bias.

N(bb) w/o shadowing 6 5.5 1.4

w/ shadowing 5 4.7 1.2

The number of pairs produced in PbPb as a function of

impact parameter N(QQ) = (QQ) x TAA

(b),

where nuclear overlap TAA

(b) = 30.4/b

o 1 > 1

cc 0.82 0.17 0.01

bb 0.63 0.31 0.6

Probability of n-muons in c and b quark decays

The number of ccbar and bbbar pairs per event

II. Muon background sources:heavy quark production


L1 Trigger: single muon trigger with no momentum cuts

optimized for HI run conditions

L2 and L3: run on online farm

L2 trigger condition:

either opposite(like) sign dimuon candidate at L1 trigger or

opposite(like) sign dimuon candidate at L2 trigger

L3 includes regional track finder starting from the muon stations,

primary vertex finder with pixel detectors and dimuon vertex

constraints

J/ and Y trigger strategy


➢ Total J/trigger efficiency: 0.97% (OL1-L2 chain)

0.44% (L1-L2 chain)

Comparison of pp and HI HLT trigger performance for J/ and Y (detailed

simulation)

➢J/

➢J/

➢ Total Pb-Pb events trigger efficiency: 1.6% HIJING with ccbar and bbar, OL1-L2 chain

✔L1 : optimized for high luminosity pp

✔OL1 : low quality muon candidate (used in HI)

➢Y

➢Y

➢ Total Ytrigger efficiency:21% (OL1-L2 chain)

16.5% (L1-L2 chain)


Si layers

Si pixels

Z = 190m

-track

-stations

Dimuon reconstruction algorithm for J/ and Y

Primary vertex determination

select pairs of pixel hits

with giving 0.5<pT<5 GeV/c

extrapolate each pair in RZ

to the beam line

Track finding

start from the track candidate

in muon stations

extrapolate inwards from

plane to plane using vertex

constraints

Track selection by cuts:

fit quality (2)

vertex constraint


“realistic” LHC multiplicity range

Dimuon reconstruction efficiency & purity vs dNch/dy

(detailed simulation)

Y is embedded in PbPb events

Efficiency:

Eff = Efftrk-1

x Efftrk-2

x Effvtx

> 80% for all multiplicity (barrel)

> 65% for all multiplicity

(barrel+endcap)

Purity = [true Y reco]/[all vtx reco]

> 90% (all multiplicities)

➢Total Pb-Pb events reconstruction efficiency: 31% HIJING with ccbar and bbar, 0.5% of Pb-Pb events survive after OL1/L2/tracker reconstruction chain.


Dimuon mass resolution (detailed simulation)

➢J/

➢Y

➢Y

J/ = 35 MeV/c2 in (barrel+endcap)

Y = 54 MeV/c2 in (barrel).

Both muons with ||<0.8

90 MeV/c2 in (barrel+endcap)

Both muons with ||<2.4Both muons with ||<0.8

Both muons with ||<2.4Both muons with ||<2.4


Fast Monte-Carlo method

L1 and L2 trigger efficiency tables were generated for single pions, kaons,

muons, b- and c- hadrons in (, pT) bins with detailed CMS simulation

dimuon reconstruction efficiency and purity dependence on the multiplicity

was generated in (, pT) bins with detailed CMS simulation

dimuon mass resolution was obtained with detailed CMS simulation

Each “dimuon” with p>2.8 and ||<2.6

is summed with weight:

W12

= Worigin12

x W12

trig x W12

reco;

Worigin12

= Worigin

1 x

Worigin

2;

Worigin1 =1 (for bg) or

= (quarkonium)/(PbPb)

(for signal)

Worigin2 = the same

Comparison of the

detailed simulation

with fast MC with

the same generator

input: HIJING

500 Kevents

Each Pb Pb event is characterized

by its impact parameter;

5 resonances states are mixed

with the pions+kaons and muons

coming from heavy-quark pairs

Black squares – fast MC

open circles – detailed CMS simulation


J/ and Y L1/L2 trigger acceptance with fast MC

J/'s are accepted above pT ~ 2 GeV/c. High p

T acceptance is ~15%

Y's are accepted (~35%) down to pT=0 GeV/c. High p

T acceptance is ~15%

Single muons acceptance is ~90%

starting from p=4 GeV/c in ||<2.4

Muon pair: ~80%

Single kaons acceptance is ~1%


Kaon pair: 0.01%

Single pions acceptance is ~0.5%


Pion pair: 0.0025%


1 from /K + 1 from J/ 1 from b/c + 1 from /K

Dimuon mass spectra (signal+ background) with fast MC

PbPb, dNch/d = 5000, L=0.5 nb-1

Background: /K (90% of Nch)->X (probability to decay 99.98% / 63%)

Background: c-,b- hadrons->+X

(probability to have at least 1 in ccbar/bbar decays ~18% / 38% )

Combinatorial background: mixed sources

J/, ' peaks seen (S/B~0.6) All 3 Y peaks seen (S/B=0.07)

Fast MC gives systematical error of 20%-25% in mass spectra


1 from /K + 1 from J/ 1 from b/c + 1 from /K

J/, ' peaks seen (S/B~1.2) All 3 Y peaks seen (S/B=0.12)

Dimuon mass spectra (signal+ background) with fast MC

PbPb, dNch/d = 2500, L=0.5 nb-1

Background: /K (90% of Nch)->X (probability to decay 99.98% / 63%)

Background: c-,b- hadrons->+X

(probability to have at least 1 in ccbar/bbar decays ~18% / 38% )

Combinatorial background: mixed sources


“high” multiplicity

dNch

/dη|η=0 = 5000

“low” multiplicity

dNch

/d|η=0

= 2500

J/ mass spectra (like-sign background subtraction) with fast MC

J/ = 35 MeV/c2 in (barrel+endcap). Both muons with ||<2.4


“high” multiplicity

dNch

/dη|η=0

= 5000

Y = 54 MeV/c2 in (barrel). Both muons with ||<0.8

90 MeV/c2 in (barrel+endcap) Both muons with ||<2.4

Barrel:

Both muons

with ||<0.8

Barrel+endcap:

Both muons

with ||<2.4

Y mass spectra (like-sign background subtraction) with fast MC


QQbar rates at CMS (1 nominal PbPb run)

dNch/d|=0 S/B N(J/) S/B N(Y) N(Y') N(Y'')

2500,| |<2.4 1.2 180000 0.12 25000 7300 4400

2500,| |<0.8 4.5 11600 0.97 6400

5000,| |<2.4 0.6 140000 0.07 20000 5900 3500

5000,| |<0.8 2.75 12600 0.52 6000

Signal-to-background ratio and expected quarkonia yields in one

month of PbPb running (0.5 nb-1 integrated luminosity) for two

multiplicity scenarios and two windows

dNch/d | =0 centrality S/B N(J/) S/B N(Y)

2500, 0-10% (central) 0.9 72000 0.1 9200

2500, 15-50% (semicentral) 1.5 100000 0.2 15000

2500, 60-100% (peripheral) 6.7 10400 0.9 1600

5000, 0-10% (central) 0.5 50000 0.04 6200

5000, 15-50% (semicentral) 0.6 85000 0.08 12000

5000, 60-100% (peripheral) 2.5 11000 0.4 1600


Differential QQbar spectra (1 nominal PbPb run)


Summary

J/ and Y are excellent probes of QCD media in A+A:

Step-wise “melting” pattern is the QGP thermometer

Production via gg fusion allows probing of low-x QCD

structure and evolution

Simulation studies of J/ and Y -> in CMS (PbPb @ √s=5.5 TeV/nn)

Geometrical acceptance ~15% (at high pT)

Dimuon efficiency ~80% and purity above 90% for all multiplicities

Y=~1% M

QQ (barrel+endcap),

J/=35 MeV/c2 (barrel+endcap)

Y=54 MeV/c2 (barrel alone)

Full separation of Y family is possible

Signal/Background: ~5(1), 1(0.1) for J/ and Y in barrel(+endcaps)

High rate expected (per year):

J/~ 180 kevents, Y ~ 25 kevents, Y’ ~ 7 kevents,Y’’ ~ 4 kevents

Detailed differential studies of QCD matter are possible


J/

J/

Y

Y

Quarkonia production: kinematical spectra

pT and according to Yellow Report, CERN-2004-009, hep-ph/0311048


ccbar bbbar

Heavy quark pairs production: kinematical spectra

pT and according to Yellow Report, CERN-2004-009, hep-ph/0311048

Documents

Prospects for the observation of quarkonia in heavy ion