1. Measurement of p0 – induced single leptons in the HADES RICH
T. Eberl, T. Christ, L. Fabbietti, J. Friese, R. Gernhäuser, J. Homolka, H.-J. Körner, M. Münch, B. Sailer, and S. Winkler
for the HADES collaboration
Motivation:
Study of close e+e- - pairs
RICH ring properties
Comb. backgr. in e+e- - spectroscopy
Exp. Setup
HADES with low B-Field
Results
Opening angle distributions of identified close e+e- - pairs
Properties of Cherenkov Rings !!!
T. Eberl, TU München

2. Dilepton Spectroscopy
HADES : Low mass e+e- pairs
from p, p, A + A collisions
Comb. Backgr.
Suppression
Close pair recognition !!!!
&
rejection
2 close rings
in RICH
2 close tracks
in MDC
full scale HGEANT simulation
T. Eberl, TU München

3. Sources of Close Rings & Tracks
Physics processes :
p0 - Dalitz , p gg
g - conversion, compt. scatt.
Possible combinations
P1 P2 RICH MDC
e+ e
e+ e
e+ e
e+ e fake ?
e+ e ??
e+/
p fake !
p+/ fake !
rare cases :
p e+/
p+/- e+/
< Q > ~ 13 0 e+ g e- p0
Dalitz e- g
interesting
pair ??? e+ e-
< Q > ~ 2 0
Conversion in
Target & Radiator
T. Eberl, TU München

4. Experimental Setup @ GSI, Darmstadt
HADES with RICH, MDC 1 / 2 , META , low B – field
optimized for e+/- with low p
full reconstr. of low mass pairs
Deflection in B - field
DQ = QMDC – QMETA ~ 1 / P DQ DQ
standard
T. Eberl, TU München

5. Acceptance for p0-Dalitz leptons
Simulation: p0-Dalitz decay
HADES acceptance
3g-threshold of RICH
T. Eberl, TU München

6. C + C @ E = 1A GeV Experiment @ SIS - GSI Numerical Experiment
Ibeam = 106 / s, Targ: stot = 5%
Trig: MMeta > 3; s/stot ~ 0,7
Nexp = 9 * 106 evts.
Numerical Experiment
(Simulation)
UrQMD + HGEANT
Setup as in exp.
Trig: MMeta > 3; included
Nsim = 7 * 106 evts.
Analysis conditions:
Event selection:
MDC I/II : multiplicity Mtrack > 3
RICH : min. 1 Ring corr. with MDC & META
Hit matching conditions:
before B- field : DQMDC-RICH < 2° ; DFMDC-RICH < 5°
after B- field : DQMDC-META : no ; DFMDC-META < 5°
no TOF cut !!
T. Eberl, TU München

7. e+/e- cand. for C + C @ 1A GeV
Rings in RICH
Defl. angles DQ = QMDC – QMETA
of reconstructed tracks in
RICH & MDC & META
Single ?? e- e+
Double
T. Eberl, TU München

8. p0-Dalitz decay leptons ?!
Measured RICH Rings
C + C
E = 1A GeV
Ring recognition:
Pattern Matrix
Hough-Transf.
p0-Dalitz decay leptons ?!
T. Eberl, TU München

9. e+ e- pairs
Opening angle distr. in MDC (before B – field) Reasonable agreement !!!
C + C
E = 1A GeV
Exp
Sim (total)
Counts [a.u.]
p0 – Dalitz
new spektrum !! Conversion not visible
Conversion
Sim. normalised to Exp.
Opening angle [deg]
T. Eberl, TU München

10. Ring selection for single electrons
e+e- pairs with 1 track / ring
Opening angle distr.
In MDC (before B - field)
Single rings ! e+ e-
2 MDC tracks
2 RICH rings
T. Eberl, TU München

11. e+e- pairs with 2 tracks / ring
Rings for close tracks
Opening angle distr.
in MDC (before B - field)
e+e- pairs with 2 tracks / ring
Double rings ! e+ e-
2 MDC tracks e+ e-
1 MDC track
1 RICH ring
T. Eberl, TU München

12. Ring properties: charge & pads
Charge per ring
Pads per ring
double
double e+ e-
Counts [a.u.]
Counts [a.u.]
C + C
E = 1A GeV
single
single e+ e-
Counts [a.u.]
Counts [a.u.]
Sim
Exp
Charge/ring [a.u.]
Pads/ring
T. Eberl, TU München

13. Ring properties: cluster & quality
Clusters per ring
Pattern Matrix sum
double
double e+ e-
Counts [a.u.]
Counts [a.u.]
Lower right is wrong color
C + C
E = 1A GeV
single
single e+ e-
Counts [a.u.]
Counts [a.u.]
Sim
Exp
clusters/ring
matrix sum [a.u.]
T. Eberl, TU München

14. Lepton recognition p0 e- GEANT Simulation: p0 -Dalitz decay
min 1 lepton required !
META
MDC p0
RICH e+
Momentum [MeV/c]
Polar angle [deg]
RICH
Stat box !!
MDC
META
HADES reconstruction probability for a p0-Dalitz decay lepton
C+C, E=1AGeV, low field setup, cons. param. set
T. Eberl, TU München

15. Pair recognition p0 e- 2 leptons required ! GEANT Simulation:
RICH
MDC
META e+ p0
2 leptons required !
GEANT Simulation:
p0-Dalitz decay
Polar angle [deg]
Momentum [MeV/c]
Explanation: probability to correctly recognize a lep with a certain mom and emission angle
If also the other one was correctly recognized
HADES reconstruction probability for a lepton from an identified p0-Dalitz lepton pair
C+C, E=1AGeV, low field setup
T. Eberl, TU München

16. Summary Dilepton spectroscopy with HADES : Results from prel. analysis
Measurement of close pairs for low momentum e+e-
Good statistics of p0 – Dalitz and conversion leptons
Experimental data for comb. backgr. and eff. studies
Results from prel. analysis
Ident. of rings from fully reconstr. single leptons in RICH
Full scale simulation vs. experiment : ok
Simulation: single lepton reconstr. prob. for p0 – Dalitz
Meas. of key ring prop. for singles and doubles (for each sector)
Outlook:
Quantitative comb. backgr. studies
Efficiencies for single lepton identification
T. Eberl, TU München