Transcript RICH rings Dec. 01

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
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
Sources of Close Rings & Tracks
Physics processes :
p0 - Dalitz , p0
gg
g - conversion, compt. scatt.
e+
g
< Q > ~ 13 0
ep0
eg
Possible combinations
P1 P2 RICH MDC
e + e1
1
e + e1
2
e + e2
2
e + e2
1
e + e2
3
fake ?
??
e+/p
p+/-
fake !
fake !
...........
Dalitz
e+
e-
Conversion
in
Target & Radiator
interesting
pair ???
<Q>~20
...........
1
1
1
rare cases :
p e+/1
p+/- e+/- 1
...........
1
1
1
2
2
T. Eberl, TU München
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
standard
DQ
T. Eberl, TU München
Acceptance for p0-Dalitz leptons
Simulation: p0-Dalitz decay
HADES acceptance
3g-threshold of RICH
T. Eberl, TU München
C + C @ E = 1A GeV
Experiment @ SIS - GSI
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
e+/e- cand. for C + C @ 1A GeV
Rings in RICH
Defl. angles DQ = QMDC – QMETA
of reconstructed tracks in
RICH & MDC & META
Single ??
2200
SIM
1800
EXP
N = 89205
1400
1000
600
Double
e-
200
-10 -8
-6
-4
-2
e+
02
46
81
0
Q MDC - Q META [°]
T. Eberl, TU München
Measured RICH Rings
Ring recognition:
 Pattern Matrix
 Hough-Transf.
C+C
E = 1A GeV
p0-Dalitz decay
leptons ?!
T. Eberl, TU München
e+ e- pairs
Opening angle distr. in MDC (before B – field)
Reasonable agreement !!!
C+C
E = 1A GeV
Exp
Sim (total)
p0 – Dalitz
Conversion
Sim. normalised to Exp.
Opening angle [deg]
T. Eberl, TU München
Ring selection for single electrons
Opening angle distr.
In MDC (before B - field)
e+e- pairs with 1 track / ring
Single rings !
180
e+
EXP
160
e-
SIM
140
2 MDC tracks
120
100
80
60
40
20
0
0
2
4
6
8
10
2 RICH rings
opening angle [°]
T. Eberl, TU München
Rings for close tracks
Opening angle distr.
in MDC (before B - field)
e+e- pairs with 2 tracks / ring
Double rings !
400
350
EXP
300
SIM
2 MDC
tracks
250
200
e+ e-
e+ e1 MDC
track
150
100
50
0
0
2
4
6
opening angle [°]
8
10
1 RICH
ring
T. Eberl, TU München
Ring properties: charge & pads
Charge per ring
Pads per ring
double
double
e+ e-
C+C
E = 1A GeV
single
single
e+
Charge/ring [a.u.]
Sim
Exp
e-
Pads/ring
T. Eberl, TU München
Ring properties: cluster & quality
Clusters per ring
Pattern Matrix sum
double
double
e+ e-
C+C
E = 1A GeV
single
single
e+
clusters/ring
Sim
Exp
e-
matrix sum [a.u.]
T. Eberl, TU München
Lepton recognition
GEANT Simulation:
p0 -Dalitz decay
e-
min 1 lepton
required !
META
p0
RICH
MDC
HADES reconstruction
probability for a p0-Dalitz
decay lepton
Momentum [MeV/c]
C+C, E=1AGeV, low field
setup, cons. param. set
T. Eberl, TU München
Pair recognition
eGEANT Simulation:
p0-Dalitz decay
2 leptons
required !
META
p0
RICH
MDC
HADES reconstruction
probability for a lepton
from an identified p0Dalitz lepton pair
Momentum [MeV/c]
C+C, E=1AGeV, low field
setup
T. Eberl, TU München
Summary
Dilepton spectroscopy with HADES :
• 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