Dielectron production in C+C collisions at 2AGeV with HADES Jochen Markert For the HADES...

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


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


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-


Spectra before efficiency correction

~ 2300023000 signal pairs for full Mee range

~ 20002000 signal pairs for full Mee > 150 MeV/c2


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


• 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


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


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)



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)


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 !!


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


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)


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


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


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


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


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


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


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


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


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


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


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


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


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]


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


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


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 %


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


Self-consistency check of efficiency correction

SIMULATION SIMULATION

THEORY THEORY

Pluto data through HADES acceptance filter

Pluto data through reconstruction chain and efficiency correction



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


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


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

Dielectron production in C+C collisions at 2AGeV with HADES Jochen Markert For the HADES...

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