11

Lepton identification in CBMLepton identification in CBM

Tetyana Galatyuk for the CBM CollaborationGoethe-Universität, Frankfurt

Outline: Dileptons as a probe for extreme matter Efficiency, purity and background rejection Performance studies Résumé

22

D

Searching for the landmarks of the Searching for the landmarks of the phase diagram of matterphase diagram of matter

SHM: P. Braun-Munzinger, K. Redlich,J. Stachel, nucl-th/0304013 J. Cleymans, K. Redlich, PRC 60 054908lQCD: Z. Fodor et al., hep-lat/0402006, F. Karsch, QM04 : Schäfer, Wambach (priv. communication) qq

Quark-Gluon Plasma

Hadron gas

Critical point? (Lattice QCD)Cross overLHC

RHIC

Earl

y U

niv

ers

e

Nuclei

SIS

AGS

FAIR

SPS

00

Β

Β

,μΤ

Τ,μ

qq

qq

Neutron Stars

What do we know experimentally?✗ chemical „freeze-out“ points

obtained from a fit of the SHM to data.

What does theory says?✗ LQCD explores unknown regions

along the temperature axis.

✗ QCD inspired effective models predict rich structure of phase diagram at finite B:o Substantial depletion of the chiral

over almost the full lifetime of the fireball.

o Separation of the chiral from the deconfinement phase transition.

o 1st-order transition with a critical end point

Intr

oduct

ion

33

D

The SIS100/300 heavy-ion energy regimeThe SIS100/300 heavy-ion energy regime

✗ Probing nuclear matter at:o densities: max/0 10

o moderate temperature

✗ System stays above ground state density for ~5 fm/c

What are the best probes?

I prefer penetrating probes.

Evolution of net baryon density ( system)

Energy density (net baryon density)

[CB

M P

hysi

cs B

ook

(200

9)]

[CB

M P

hysi

cs B

ook

(200

9)]

Intr

oduct

ion

44

Electromagnetic structure of dense/hot matterElectromagnetic structure of dense/hot matter

✗ Lepton pairs couple to hadrons through time-like virtual photons. ✗ The reconstruction of virtual photons via dileptons gives access to the

electromagnetic properties of nuclear matter under extreme conditions.

l+

l-

Decays of (long-lived)neutral mesons ()

Resonance decay

Bremsstrahlung

*

*

l+

l-

*

l+l -

π+

π-

e-

e+

JP = 1- for both * and VM Strong coupling of * to VM (VMD model)

Intr

oduct

ion

55

The experimental challenge…The experimental challenge…

✗ Rare probes (BR < 10-4)✗ Large physical background in

o e+e- from:- Dalitz decays (0)- Conversion pairs

from:- Weak , K decays

SIS

RHIC/LHC SPS

© BNL

Intr

oduct

ion

66

D

e+e- pair yield after subtraction of the "hadronic cocktail“, Pb+Au, 158 AGeV

Dilepton pair excess at SPSDilepton pair excess at SPS

[D. A

dam

ova

et a

l. nu

cl-e

x/06

1102

2][R

app,

Wam

bach

EP

JA 6

(19

99)

415]

Main source: e+e-

Strength of dilepton yield at low masses is due to coupling to baryons!

π

N-1

Δ

>

>

N*

N-1

l

l

pair yield after subtraction of the "hadronic cocktail“, In+In, 158 AGeV

R. R

app,

CP

OD

’09,

to b

e pu

blis

hed

on P

oS

Intr

oduct

ion

77

D

Dalitz decays of baryonic resonances - dominant source at low beam energies.

Medium effects at moderate energies are closely linked to the effects at high beam energies through VMD.

Understanding these contributions is important for low-mass lepton pair program at FAIR.

Will be investigated with HADES. Theoretical treatment:

o Off-shell transport approach (HSD)o Hybrid approaches (?)

Dilepton pair excess: from SPS to SIS…Dilepton pair excess: from SPS to SIS…

N*

N

*

l+

l-

e+e- from transport

e+e- pair yield, Ar+KCl, 1.76 AGeV

Preliminary

Intr

oduct

ion

88

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Searching for the landmarks of the Searching for the landmarks of the phase diagram of matterphase diagram of matter

00

Β

Β

,μΤ

Τ,μ

qq

qq

Highly interesting results from RHIC to SIS importance of baryons!

No measurement for beam energies of 2-40 AGeV

Experimental focus on rare diagnostic probes:

o Charm: how are the produced charm

quarks propagating in the dense phase (J/ψ, ψ‘, D, J/ψ, ψ‘, D, cc

for a complete picture)for a complete picture)

o Low-mass lepton pairs: electromagnetic structure of

hadrons, emissivity of dense matter, thermal radiation?

Intr

oduct

ion

99

Excitation function of excess yield from 8 to 45 GeV/u

✗ Accuracy✗ Significance✗ Systematic

The CBM mission:The CBM mission:D

1010

DD

Strategy of CBMStrategy of CBM

✗ Fastest HI detector ever: more than one million reactions / second

✗ Fast high resolution tracking in a compact dipol field directly after the target

✗ High speed DAQ and trigger✗ Excellent particle identification✗ Flexible arrangement of PID detectors

and calorimeters:

o Aim:Aim: optimize setup to include optimize setup to include both, electron and muon IDboth, electron and muon ID

muonsmuons

electronselectrons

The C

BM

mis

sion

1111

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Di-eletron reconstruction in CBM: the challengeDi-eletron reconstruction in CBM: the challengeEle

ctro

n o

pti

on

Ele

ctro

n o

pti

on

Without hadron-blind detector before the tracknig

Background due to material budget of the STS

Sufficient discrimination (misidentification <10-4)

~350 0 98.8%

e+ e-

1.2%

~3 target e+e-

~700 +/- could be identified asan electron

UrQMD: Au+Au collision at beam energy 25AGeV, zero zero

impact parameterimpact parameter

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Electron identificationElectron identificationEle

ctro

n o

pti

on

Ele

ctro

n o

pti

on

RICHRICH

TRDTRD TOFTOF

1313

DD

Electron identification in RICHElectron identification in RICH

✗ RICH: strategy and R&Do Conventional design based on

commercial productso Float glass mirror (carbon as

backup)o Multi-anode PMT photodetector

e+/-

Ring radius vs. momentum photophotodetectordetector

mirrormirror

Ele

ctro

n o

pti

on

Ele

ctro

n o

pti

on

1414

D

Electron identification using Time-Of-Flight informationElectron identification using Time-Of-Flight information

σT=80 ps, σx=5 mm

RICH identified electrons in TOF

Ele

ctro

n o

pti

on

Ele

ctro

n o

pti

on

ToF nicely works for p > 1 GeV/c!

m2 vs momentum distribution

All tracks

supression factor

1515

D TRD: strategy and R&D

o Thin gap design based on ALICE TRD

3 TRD detectors, each consist of 4 layers

Electron identification using TRDElectron identification using TRD

Use statistical analysis of the Use statistical analysis of the energy loss spectra to further energy loss spectra to further

discriminate discriminate

Ele

ctro

n o

pti

on

Ele

ctro

n o

pti

on

Fsupr. = 9500

~ 50%

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The muon optionThe muon option

✗ Goal:o Clean dilepton signal for charm

measurement and low-mass pairs

✗ Challenge: at low energies!at low energies!

- Large energy loss and substantial multiple scattering of muons in the absorber

o High areal particle rates in first detector.- smallest pad 2.8 2.8 mm2

- 0.7 hit/cm2 0.4 A/cm2 (full intensity)

✗ Strategy:o Identification after hadron absorber with

intermediate tracking layerso Detector technology still under discussion,

probably combination of several depending on rates

o Triple GEM detectors with pad read-out

20 20 20 30 35 100 cm20 20 20 30 35 100 cm

FeFe

n suppressio 105.55.7 4 l

n suppressio 104.15.13 6 l

Muon o

pti

on

Muon o

pti

on

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Detector performance: efficiency and purityDetector performance: efficiency and purity

Production vertex in z-direction of secondary muons reconstructed in the STS

STS statistic:o 0.4% of all reconstructed tracks – from weak decays (94% - ,6% - K weak decay)

Muon o

pti

on

Muon o

pti

on

✗ Reconstruction efficiency for tracks passing the absorber (225 cm Fe, “hard ”) ~90%

✗ Only tracks with p > 3 GeV/c can be reconstructed!

Track reconstruction efficiency as a function of momentum

p ~ 3 GeV/c

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The Charm of CBMThe Charm of CBM

D

1919

D

J/ m = 38 MeV/c2

electronselectrons

Au+Au, 25 AGeV

Reconstruction of J/Reconstruction of J/Invariant Mass Spectra Invariant Mass Spectra

✗ Signal efficiency ~10%✗ Signal-to-background ratio > 10

… andcan be further improved if time-of-flightcan be further improved if time-of-flight

information is obtained for each trackinformation is obtained for each track

■ with mass cut

■ no mass cut

Au+Au, 35 AGeV

muonsmuons

Invariant mass spectra of tracks ID as electrons in RICH and TRD, pt>1.2 GeV/c

Invariant mass spectra of tracks ID as muons in MuCh

The C

harm

of

CB

MThe C

harm

of

CB

M

2020

D

ReconstructionReconstruction of J/ of J/Phase space coveragePhase space coverage

Full phase space very well covered!Full phase space very well covered!

yCMyCM

muonsmuonselectronselectrons

The C

harm

of

CB

MThe C

harm

of

CB

M

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D

The low-mass Signal in CBMThe low-mass Signal in CBM

Meson N/event Decay mode BR

36 e+ e- 5.×10-3

23 e+ e- 4.7×10-5

38 e+ e- 0

e+ e-

7.7×10-4

7.18×10-5

1.28 e+ e- 2.97×10-4

0 mass distribution generated including:o Breit – Wigner shape around the pole

mass;o 1/M3, to account for vector dominance in

the decay to l+l-;o Thermal phase space factor;o Ansatz: is governed by the phase

space.

Invariant mass spectrum in 25 AGeV Au+Au collisions (full phase space, b=0)

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

2222

D

Reconstruction of the Low-mass Signal : eReconstruction of the Low-mass Signal : e++ee- -

✗ Reduction of physical background byreconstructing pairs from -conversion(~3/event) and -Dalitz decays (~8/event) by means of their track topology

✗ Transverse momentum cut of single electron – powerful, but has to be taken with special care!

✗ Pair cuts, i.e. opening angle cut

mediume+e-

ee

Track Segment

Identified e+/-

Track Fragment

Fakepair

ππ0 0 γγee++ee--

ππ00ee++ee--

ηη γγee++ee--

ρρ ee++ee--

ee++ee--

φφ ee++ee--

All eAll e++ee--

CBCB

Invariant mass spectra

Before cutsBefore cuts

After cutsAfter cuts

Central Au+Au@25AGeV

Ele

ctro

n o

pti

on

Ele

ctro

n o

pti

on

2323

D

Efficiency of cuts, S/B ratio : eEfficiency of cuts, S/B ratio : e++ee--

0 Dalitz region Enhancement region / region

ε

S/Bratio

S/B ratio [%] M [MeV]

0.4 6.7 13

0.32 9.4 13

- 4.7

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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D

Reconstruction of the Low-mass Signal : Reconstruction of the Low-mass Signal :

signals ρ ω φ η ηDalitz

background

S/B ratio [%] M [MeV]

0.08 3.7 10

0.03 6 12

0.001 2.7

Major background from: , decays into punch through of hadrons track mismatches

Can performance be improve?Can performance be improve?

Use TOF!Use TOF!

Muon o

pti

on

Muon o

pti

on

2525

Background rejection using TOF informationBackground rejection using TOF information

MuChMuCh

TOFTOF

layer Nr.12 ToF RPC

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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D

Muon identification using TOF informationMuon identification using TOF information

p

S/B ratio [%]

0.17 (0.08*) 1.5 (3.7*)

0.06 (0.03*) 3. (6*)

* - TOF information not used

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

Work in progress

Work in progress

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Reconstruction of Low-mass SigalReconstruction of Low-mass SigalPhase space Phase space coveragecoverage

0 e+ e–

yCMyCM

Muons: use so called "hard*-hard„ and "soft**-hard" pairs: the latter improve the acceptance towards midrapidity, however on account of a much higher background

* - “hard ” – after 125 cm Fe** - “soft ” – after 90 cm Fe

Electrons: no phase space limitationElectrons: no phase space limitation

The “sweet spot” is at midrapidity and low pt!The “sweet spot” is at midrapidity and low pt!

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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D

Pair detection , with pPair detection , with ptt cut on single e cut on single e+/-+/-

Self-consistent avarage spectral function of the meson for

N =

N = 2

N =

5

Coverage in pair pt-minv plane

no pno p tt-cut-cut

M2

muonsmuons

electronselectrons

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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Overview of existing dilepton experiments (summary)Overview of existing dilepton experiments (summary)

ExperimentExperiment SystemSystem √√ss dNdNchch/d/dηη EE S/BS/B Sys error (%)Sys error (%)

CERES Pb+Au 8.86 216 5.9 1/6 20

CERES (σ/σtot = 28%) Pb+Au 17.2 245 2.31 1/13 24

CERES (σ/σtot = 7%) Pb+Au 17.2 350 2.58 1/21 16

NA60(central) In+In 17.2 193 3 1/11 25

NA60(semi-central) In+In 17.2 133 2 1/8 25

NA60(semi-peripheral) In+In 17.2 63 2 1/3 12

NA60(peripheral) In+In 17.2 17 1.5 2 3

CERES S+Au 19.5 125 5 1/4.3 25

PHENIX(0-10% centrality) Au+Au 200 650 ?= 3 1/500 ?= 50

SIMULATIONSIMULATION

CBM (real) (b=0fm) Au+Au 8 300 ? 1/16* -

* - free cocktail only (without medium contribution)ree cocktail only (without medium contribution)

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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Signal-to-Background ratio, EnhancementSignal-to-Background ratio, Enhancement

NA60 In+In @ 158 AGeVNA60 In+In @ 158 AGeVCERES Pb+Au @ 40 AGeVCERES Pb+Au @ 40 AGeVCERES Pb+Au @ 158 AGeV (CERES Pb+Au @ 158 AGeV (σσ//σσtottot = 28%) = 28%)CERES Pb+Au @ 158 AGeV (CERES Pb+Au @ 158 AGeV (σσ//σσtottot = 7%) = 7%)CERES Pb+Au @ 158 AGeV CERES Pb+Au @ 158 AGeV PHENIX Au+Au @ √s = 200 AGeVPHENIX Au+Au @ √s = 200 AGeV

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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Signal-to-Background ratio for CBMSignal-to-Background ratio for CBM

safety factorsafety factor

;);)

The L

ow

-mass

sig

nal

The L

ow

-mass

sig

nal

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RésuméRésumé

✗ Both electron and muon option give access to low-mass vector mesons and charmonium✗ Feasibility studies are based on full event reconstruction and electron/muon identification.

They are still subject to further optimization!They are still subject to further optimization!✗ Performance on low-mass vector mesons (at Ekin = 25 GeV/u) is comparable, mid-rapidity

coverage is more difficult for muons✗ Performance on charmonium is similar for electrons and muons✗ If we could achieve such results in reality – would be nice !

✗ Electron measurements rely on established detector technology (RICH, TRD)✗ Detector issues for muon measurements not yet solved

✗ CBM will not be limited by statistics, systematic uncertainties might be limiting in the end

A measurement of both, muons and electronsA measurement of both, muons and electronswill be the best systematic study we can ever do!will be the best systematic study we can ever do!

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China:Tsinghua Univ., BeijingUSTC, HefeiCCNU, WuhanCroatia: University of SplitRBI, Zagreb Czech Republic:Techn. Univ., PragueCAS, RezFrance:IPHC StrasbourgGermany: GSI, DarmstadtFZ Dresden-RossendorfUniv. Heidelberg, Phys. Inst.Univ. HD, Kirchhoff Inst. Univ. Heidelberg, ZITI

The CBM CollaborationThe CBM Collaboration

Univ. of Kashmir, SrinagarBanaras Hindu Univ., VaranasiKorea:Korea Univ. SeoulPusan National Univ.Norway:University of BergenPoland:Silesia Univ. KatowiceAGH Univ. KrakowJagiellonian Univ., KrakowWarsaw Univ.Portugal: LIP CoimbraRomania: NIPNE, BucharestBucharest University

Univ. Frankfurt, IKFUniv. Frankfurt, Inst.Comp.Sc.Univ. MünsterUniv. WuppertalHungaria:KFKI, BudapestEötvös Univ. BudapestIndia:Aligarh Muslim Univ., AligarhIOP, BhubaneswarPanjab Univ., ChandigarhGauhati Univ., GuwahatiUniv. of Rajasthan, JaipurUniv. of Jammu, JammuIIT, KharagpurSAHA, KolkataUniv. of Calcutta, KolkataVECC, Kolkata

Russia:VBLHE, JINR, DubnaLIT, JINR, DubnaLPP, JINR, DubnaPNPI, GatchinaITEP, MoscowMEPhI, MoscowKurchatov Inst. MoscowSINP, Moscow State Univ. Obninsk State Univ.IHEP, ProtvinoKRI, St. PetersburgSt. Petersburg Polytec. U.INR TroitzkUkraine: INR, KievShevchenko Univ. , Kiev

Split, 2009 56 institutions> 400 members

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Thank youThank you

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