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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
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
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
D
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
1212
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%
1616
D
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
1717
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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
1818
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
2121
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
2424
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
2626
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
2727
D
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
2828
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
2929
D
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
3030
D
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
3131
D
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
3232
D
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!
3333
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
3434
Thank youThank you
D
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