Dielectron production in C+C collisions at 2AGeV with
HADES
Jochen MarkertFor the
HADES Collaboration
Jochen Markert - QM 2006 219 - November - 2006
Reconstruction of the electron signal
Results from C+C collisions at 2AGeV
Comparison with models
Comparison with DLS
Dielectron production in C+C collisions at 2AGeV with HADES
Jochen Markert - QM 2006 319 - November - 2006
Introduction
C+C at 2AGeV Large pair acceptance ~35% Trigger
1st level : charged particle mult. > 4 (60% reaction )
2nd level: RICH+TOF/PreSHOWER → enhancement ~10
9% dM/M resolution at 0.8 GeV/c2 Mee
Total statistic: 650 M 1st level events
Opening angle > 9o
Averaged over 0 < Y < 2
Jochen Markert - QM 2006 419 - November - 2006
Selection criteria
Hit matching RICH rings ↔ MDC tracks MDC tracks ↔ TOF and PreShower hits
PID : e+, e- β vs momentum correlation PreShower condition
Background rejection cuts Opening angle > 9°
DATA
Single e+,e-
Jochen Markert - QM 2006 519 - November - 2006
Spectra before efficiency correction
~ 2300023000 signal pairs for full Mee range
~ 20002000 signal pairs for full Mee > 150 MeV/c2
Jochen Markert - QM 2006 619 - November - 2006
Event generator PLUTO : • thermal source (T=80MeV) polar angle distribution from
charged analysis• η (TAPS data) • ρ, ω : m -scaling• Δ scales with
Comparison of the data with cocktail
18 %18 % 21 %21 %
systematic errors:systematic errors:15 % - efficiency correction 10 % - combinatorial background11 % - 0 normalization
• Cocktail A: 0 + η + ω “long lived components“
• Cocktail B: Cocktail A + Δ + ρ
Jochen Markert - QM 2006 719 - November - 2006
• Yield over Cocktail A
• Cocktail B/ Cocktail A
• factor 2 below data in 200< Mee <500 MeV/c2
• factor 4 below data in 500<Mee<650 MeV/c2
Comparison of the data with models• RQMD: M. D. Cozma, C. Fuchs, E. Santini, A. Faessler,
Phys. Lett. B 640, 150 (2006)
• UrQMD: D. Schumacher, S. Vogel, M. Bleicher,
nucl-th/06080401.• HSD (v2.5): W. Cassing and E. L. Bratkovskaya,
Phys. Rep. 308, 65 (1999).
“free” spectral function
• Closer to data than cocktail B
• But model calculations
• Undershoot between 200<Mee<500 MeV/c2
• Overshoot for Mee> 700 MeV/c2
C+C at 2AGeV
Jochen Markert - QM 2006 819 - November - 2006
P┴ and Y distributionscomparison data vs. cocktail
ωη
MMeeee < 150 MeV/c < 150 MeV/c2 :2 : Data well described (Data well described (00-Dalitz region)-Dalitz region) 150 < M150 < Meeee < 550 MeV/c < 550 MeV/c2 :2 : Underestimation over whole pUnderestimation over whole p range range (factor 2) (factor 2)..
preliminary
Jochen Markert - QM 2006 919 - November - 2006
Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV)
F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys)
HADES
DLS
η
Enhancement factor F over η for 150<Mee<500 MeV/c2 :
R. J. Porter et al., Phys. Rev. Lett. 79 1229 (1997)
Jochen Markert - QM 2006 1019 - November - 2006
Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV)
F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys)
F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys)
Yexc(2.0)/Yexc(1.04) = 2.5 ± 0.5(stat) ± 1.5(sys)
η
η
(2.0)13 3 (stat)
(1.04)
Y
Y
DLS
HADES
η
DLS
exc η
Excess Yield:
( 1)Y F Y
• R. Averbeck et al., TAPS coll., Z. Phys. A 359, 65 (1997)
• R. Holzmann et al., TAPS coll., Phys. Rev. C 56, R2920 (1997)
Jochen Markert - QM 2006 1119 - November - 2006
A closer look to the excess yield
π
π
(2.0)2.3 0.3 (stat)
(1.04)YY
TAPS, KaoS measurements:
exc
exc
(2.0)2.5 0.5 (stat) 1.5 (sys)
(1.04)YY
Excess yield :
Excess yield scales like Excess yield scales like 0 0 !!
Jochen Markert - QM 2006 1219 - November - 2006
C+C at 1 AGeV (HADES)
before efficiency correction
HADES
preliminary
• Spectrum before efficiency correction
• Enhancement factor F(1.0) ≈ 5.8 (in 150<Mee<500 MeV/c2 range)
• Enhancement within errors in agreement with DLS
Jochen Markert - QM 2006 1319 - November - 2006
Summary & outlookSummary
2 AGeV C+C dielectron spectra
excess yield established
no specific p dependence for enhancement
Comparison to models ongoing
Comparison to DLS:
Preliminary 1 AGeV spectra shows no contradiction to DLS data
Excess of yield for 150<Mee<500 MeV/c2 measured at 1.04 and 2 AGeV scales like 0 multiplicity
OutLook
Ongoing analysis of
p+p at 2.2 GeV (Jan. 04) exp. check of η reconstruction eff.
C+C at 1 AGeV (Aug. 04) direct comparison with DLS
Ar+KCl at 1.757 AGeV (Sep. 05)
p+p at 1.25 GeV (Jan. 06) Δ production
Next physics runs
p/d+p, at 3.5/1.25 AGeV (Spring. 07) ω production/isospin dependence
p+A (2007+)
Heavy systems, pion beam (2008/9)
Jochen Markert - QM 2006 1419 - November - 2006
The HADES collaboration Bratislava (SAS, PI), Slovakia Catania (INFN - LNS), Italy Cracow (Univ.), Poland Darmstadt (GSI), Germany Dresden (FZD), Germany Dubna (JINR), Russia Frankfurt (Univ.), Germany Giessen (Univ.), Germany Milano (INFN, Univ.), Italy Munich (TUM), Germany Moscow (ITEP,MEPhI,RAS), Russia Nicosia (Univ.), Cyprus Orsay (IPN), France Rez (CAS, NPI), Czech Rep. Sant. de Compostela (Univ.), Spain Valencia (Univ.), Spain Coimbra (Univ.), Portugal
The END
Thank you for your attention
Jochen Markert - QM 2006 1619 - November - 2006
Hades@GSI and DLS@LBL
design
π0, η acceptance
C+C @ 1AGeV Comparison with
Pluto cocktail
preliminary
Pluto vs Hades data
ππ00→e+e–γHadesHades DLSDLS
mid-rapidity
η→e+e–γ
HadesHades DLSDLS
mid-rapidity
Jochen Markert - QM 2006 1719 - November - 2006
Phase space coverage: HADES vs DLS
• A direct Comparison between HADES and DLS dielectron results not feasible
ππ00→e+e–γ η→e+e–γ
Jochen Markert - QM 2006 1819 - November - 2006
Efficiency correctionsEfficiency matrix is created for single leptons (e+, e-) in p (0 – 2 GeV/c), Θ (0o – 90o), Φ (0o – 360o)
averaged over momentumaveraged over all sectors
rectrue
acc
( , , )P
Eff pP
Jochen Markert - QM 2006 1919 - November - 2006
Acceptance matrix
Acceptance matrix is created inp (0 – 2 GeV/c), Φ (0o – 60o), Θ (0o – 90o) for the single leptons.
Integrating over internal dilepton angle → Pair acceptance matrix: Mee, PT and Y
( , , ) acc
all
PAcc p
P
Jochen Markert - QM 2006 2019 - November - 2006
Acceptance matrix
Opening angle > 9o
• Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0o – 60o) and Θ (0o – 90o) for the single leptons.
( , , ) acc
all
PAcc p
P
• Integrating over internal dilepton angle one can create pair acceptance matrix in 3D: Mee, PT and Y
acc
all
( , , )T
PAcc M P Y
P
Jochen Markert - QM 2006 2119 - November - 2006
ExperimentExperiment
RawRaw DataData
HADESHADES
AnalysisAnalysis
PhysicsPhysics
PairPair SpectraSpectra
SimulationSimulation
Monte-Carlo DataMonte-Carlo Data
Detector SimulationDetector Simulation
AnalysisAnalysis
Event GeneratorEvent Generator
Pair SpectraPair Spectra
EfficiencyEfficiency CorrectionCorrection
dN/dMdN/dM
AcceptanceAcceptance FilterFilter
TheoryTheory
Analysis flow
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0 5 10 15 200
2000000
4000000
6000000
8000000
10000000
12000000
14000000
16000000
18000000
Y A
xis
Titl
e
X Axis Title
B
Days of data taking
Even
ts
• all filesall files• all good filesall good files• only M4 eventsonly M4 events• only events with >=1 trackonly events with >=1 track
Evaluation of the statisticsEvaluation of the statistics
242 M - recorded events242 M - recorded events217 M – trigger M4 events217 M – trigger M4 events
6 % of LVL1 events are also LVL2
46% - LVL246% - LVL260% - LVL160% - LVL1
Jochen Markert - QM 2006 2319 - November - 2006
0
1000
2000
3000
4000
5000
6000
7000
8000
UrQMD
impact parameter [fm]4 62
σtot
σreac
σtrigger
LVL1 trigger - centrality selection
σgeom - Π b2max
* in agreement with Kox et all.* in agreement with Kox et all. 864 ± 45 mbarn 864 ± 45 mbarn
tot geom
reac reactot
tot geom
LVL1 triggertot
tot
LVL1tot
reac
947 mbarn
570
6
b rn
%
m
0
a
Jochen Markert - QM 2006 2419 - November - 2006
Normalization factor
NOV02
Yield/event 0.79 HADES acceptance – LVL1 trigger
Correction to 4Π 1.44
Yield corr to 4Π 1.15
Corr. to trigger 0.71 4Π – LVL1 trigger
Min. bias yield 0.81 4Π min. bias
• respective number of LVL1 events * DS factor : 6.5 ● 106.5 ● 1088
0 multiplicity extrapolated into 4Π : 1.151.15• efficiency of the LVL2 trigger : 0.920.92
Jochen Markert - QM 2006 2519 - November - 2006
The spectrometer conceptGeometry Full azimuth, polar angles 18o - 85o
Pair acceptance 0.35 About 80.000 detector channels
Particle identification
RICH: CsI solid photo cathode, C4F10 radiator,
No 80, pion suppression 104
TOF: 384 scintillator rods TOFino: 24 scintillator paddles
temporary solution, RPC in future Pre-Shower: 18 pad chambers & lead
converters)
Momentum measurement Magnet: superconducting Toroid with B = 0.36
Tm MDC: 24 multi-wire drift chambers,
single-cell resolution 140 m
1 m
During run in November 2002
• RICH, inner MDC’s, TOF and SHOWER ready
• outer MDC’s only partly installed
• In analysis presented here only inner MDC’s are used
Jochen Markert - QM 2006 2619 - November - 2006
Lepton multiplicity per event• ~7% of the events
contain 2 opposite sign leptons
• ~7% of the events contain 2 like sign leptons
• ~83% of the events contain only 1 lepton
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rec true
all true
rec true
rec all
Efficiency
Purity
NNNN
Efficiency: 80%Purity: 85%
Contamination: lepton fakes 15% (mainly close pairs) hadrons < 3%
Single leptons: Efficiency and Purity
Simulation
p*q [MeV/c]
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Background rejection
C1C1 – the only pair cut
C2C2, C3C3 – lepton cuts
TOF/ShowerTOF/Shower<9o
RICHRICH
MDC I-IIMDC I-II
C1 C2 C3C1 C2 C3
<90
Close Close pairpair
Shared Shared detector detector
hithit
close close conversioconversio
n n candidatecandidate
Rel
ativ
e su
ppre
ssio
n
C1 C2 C3
Jochen Markert - QM 2006 2919 - November - 2006
combinatorial background:
M < 150 MeV/c2 - sLSM > 150 MeV/c2 - mOS
MMeeee > 150MeV/c > 150MeV/c22
MMeeee > 150MeV/c > 150MeV/c22
Combinatorial background same event Like-Sign (sLS) vs. mixed event Opposite-Sign (mOS)
• Normalization done between 150-550 MeV/c2 Mee
• sLS and mOS background show same behavior for Mee > 150 MeV/c2
Jochen Markert - QM 2006 3019 - November - 2006
Summary of the eff corrections, normalization and systematic errors
Components for the efficiency corrections:Components for the efficiency corrections:
• efficiency correction
• opening angle correlation
• tracking efficiency – 92% for each singles
Components for the normalization:Components for the normalization:
• number of LVL1 * DS events
• second level trigger (LVL2) efficiency – 92%
• 0 multiplicity into 4 - 1.15
Components for the systematic errors:Components for the systematic errors:
• 15 % - efficiency correction (self-consistence check)
• 10 % - combinatorial background
• 11 % - 0 normalization
18 %18 % 21 %21 %
Jochen Markert - QM 2006 3119 - November - 2006
Estimation of the systematic errors
efficiency correctionsefficiency corrections
at maximum 15%at maximum 15%
combinatorial backgroundcombinatorial background
at maximum 10%at maximum 10%
Normalization to Normalization to 00 multiplicity multiplicity
11 % systematic error comes from:11 % systematic error comes from:• efficiency/purity corrections• extrapolation to 4, full momenta
Jochen Markert - QM 2006 3219 - November - 2006
Self-consistency check of efficiency correction
SIMULATION SIMULATION
THEORY THEORY
Pluto data through HADES acceptance filter
Pluto data through reconstruction chain and efficiency correction
Jochen Markert - QM 2006 3319 - November - 2006
Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV)
F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys)
F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys)
exc ηtot exc
η η η
exc η
ηexc
exc η
1
( 1)*
(2.0)(2.0) (2.0) 1*
(1.04) (1.04) 1 (1.04)
Y YY YF
Y Y Y
Y F Y
YY F
Y F Y
Yexc(2.0)/Yexc(1.04) = 2.5 ± 0.5(stat) ± 1.5(sys)
η
η
(2.0)13 3
(1.04)
Y
Y
Jochen Markert - QM 2006 3419 - November - 2006
P┴ and Y distributionscomparison Data vs. PLUTO
Good agreement for the low masses !Good agreement for the low masses !No strong PNo strong P┴ ┴ dependence for enhancement !dependence for enhancement !
ω
η
Jochen Markert - QM 2006 3519 - November - 2006
Comparison of the data with models• RQMD Tübingen C.Fuchs, D. Cozma• HSD Gießen (v2.5) E. Bratkovskaya, W.
Cassing
In-medium calculation
• Undershoot between 200<Mee<500 MeV/c2 (HSD)
• Overshoot between 450<Mee<600 MeV/c2 (RQMD)
in-medium
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