Measurement of p0 induced single leptons in the HADES RICH

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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 ee- - pairs
• RICH ring properties
• Comb. backgr. in ee- - spectroscopy
• Exp. Setup
• HADES with low B-Field
• Results
• Opening angle distributions of identified
  close ee- - pairs
• Properties of Cherenkov Rings !!!

T. Eberl, TU München
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Dilepton Spectroscopy
HADES Low mass ee- 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
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Sources of Close Rings Tracks
Physics processes p0 - Dalitz , p0
gg g - conversion, compt. scatt.
Possible combinations P1 P2 RICH MDC e
e- 1 1 e e- 1
2 e e- 2 2 e e-
2 1 fake ? e e- 2
3 ?? ........... e/- 1 1 p
1 1 fake ! p/- 1 1
fake ! ........... rare cases p e/-
1 2 p/- e/- 1
2 ...........
lt Q gt 13 0
e
g
e-
p0
Dalitz
e-
g
interesting pair ???
e
e-
lt Q gt 2 0
Conversion in Target Radiator
T. Eberl, TU München
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Properties of p0-Dalitz decay
GEANT Simulation p0-Dalitz decay
Reconstr. p0 mass
p0 -gt e e- g, BR 1.2
ee- pair opening angle
Inv. Mass ee- pair
T. Eberl, TU München
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Experimental Setup _at_ 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
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Acceptance for p0-Dalitz leptons
Simulation p0-Dalitz decay
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C C _at_ E 1A GeV
Experiment _at_ SIS - GSI Ibeam 106 / s, Targ
stot 5 Trig MMeta gt 3 s/stot
0,7 Nexp 9 106 evts.
Numerical Experiment (Simulation) UrQMD
HGEANT Setup as in exp. Trig MMeta gt 3
included Nsim 7 106 evts.

• Analysis conditions
• Event selection
• MDC I/II multiplicity Mtrack gt 3
• RICH min. 1 Ring corr. with MDC META
• Hit matching conditions
• before B- field DQMDC-RICH lt 2 DFMDC-RICH
  lt 5
• after B- field DQMDC-META no
  DFMDC-META lt 5
• no TOF cut !!

T. Eberl, TU München
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e/e- cand. for C C _at_ 1A GeV
Rings in RICH Defl. angles DQ QMDC
QMETA of reconstructed tracks in RICH MDC
META
Single ??
e
e-
Double
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Measured RICH Rings
C C E 1A GeV

• Ring recognition
• Pattern Matrix
• Hough-Transf.

p0-Dalitz decay leptons ?!
T. Eberl, TU München
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Simulated RICH Rings
Full scale GEANT simulation of the HADES RICH
based on measured material and optical properties
Rings for p0-Dalitz leptons
C C E 1A GeV
T. Eberl, TU München
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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
Conversion
Sim. normalised to Exp.
Opening angle deg
T. Eberl, TU München
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Ring selection for single electrons
ee- pairs with 1 track / ring
Opening angle distr. In MDC (before B - field)
Single rings !
e
e-
2 MDC tracks
2 RICH rings
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Rings for close tracks
Opening angle distr. in MDC (before B - field)
ee- pairs with 2 tracks / ring
Double rings !
e
e-
2 MDC tracks
1 MDC track
1 RICH ring
T. Eberl, TU München
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Ring properties charge pads
Charge per ring
Pads per ring
double
double
Counts a.u.
Counts a.u.
C C E 1A GeV
single
single
Counts a.u.
Counts a.u.
Charge/ring a.u.
Pads/ring
T. Eberl, TU München
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Ring properties cluster quality
Clusters per ring
Pattern Matrix sum
double
double
Counts a.u.
Counts a.u.
C C E 1A GeV
single
single
Counts a.u.
Counts a.u.
clusters/ring
matrix sum a.u.
T. Eberl, TU München
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Ring properties all sectors
Double rings
Single rings
pol angle deg
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Ring properties all sectors
Pat. rec. qual.
4-clusters/ring
quality a.u.
clusters/ring
Double rings
Single rings
quality a.u.
clusters/ring
pol angle deg
pol angle deg
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Ring properties var. sectors
Pads per ring
Double rings
Pads/ring
Pads/ring
Pads/ring
Sector 1,3
Sector 4,6
Sector 2,5
pol angle deg
pol angle deg
pol angle deg
Single rings
Pads/ring
Pads/ring
Pads/ring
Sector 1,3
Sector 2,5
Sector 4,6
pol angle deg
pol angle deg
pol angle deg
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Ring properties var. sectors
Charge per ring
Double rings
Charge/ring a.u.
Charge/ring a.u.
Charge/ring a.u.
Sector 1,3
Sector 4,6
Sector 2,5
pol angle deg
pol angle deg
pol angle deg
Single rings
Charge/ring a.u.
Charge/ring a.u.
Charge/ring a.u.
Sector 1,3
Sector 2,5
Sector 4,6
pol angle deg
pol angle deg
pol angle deg
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Ring properties var. sectors
4-clusters per ring
Double rings
Clusters/ring
Clusters/ring
Clusters/ring
Sector 1,3
Sector 4,6
Sector 2,5
pol angle deg
pol angle deg
pol angle deg
Single rings
Clusters/ring
Clusters/ring
Clusters/ring
Sector 1,3
Sector 2,5
Sector 4,6
pol angle deg
pol angle deg
pol angle deg
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Ring properties var. sectors
Hough-quality for ring
Double rings
quality a.u.
quality a.u.
quality a.u.
Sector 1,3
Sector 4,6
Sector 2,5
pol angle deg
pol angle deg
pol angle deg
Single rings
quality a.u.
quality a.u.
quality a.u.
Sector 1,3
Sector 2,5
Sector 4,6
pol angle deg
pol angle deg
pol angle deg
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Ring properties var. sectors
Matrix-quality for ring
Double rings
quality a.u.
quality a.u.
quality a.u.
Sector 1,3
Sector 4,6
Sector 2,5
pol angle deg
pol angle deg
pol angle deg
Single rings
quality a.u.
quality a.u.
quality a.u.
Sector 1,3
Sector 2,5
Sector 4,6
pol angle deg
pol angle deg
pol angle deg
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Lepton recognition
e-
GEANT Simulation p0 -Dalitz decay
min 1 lepton required !
META
MDC
RICH
p0
e
RICH
MDC
META
HADES reconstruction probability for a p0-Dalitz
decay lepton CC, E1AGeV, low field setup, cons.
param. set
T. Eberl, TU München
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Pair recognition
2 leptons required !
GEANT Simulation p0-Dalitz decay
HADES reconstruction probability for a lepton
from an identified p0-Dalitz lepton pair CC,
E1AGeV, low field setup
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Summary

• Dilepton spectroscopy with HADES
• Measurement of close pairs for low momentum
  ee-
• 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
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e e- pairs
Opening angle distr. in MDC (before B
field)for lepton momenta gt 50 MeV/c
C C E 1A GeV
Exp
Sim (total)
Counts a.u.
p0 Dalitz
Sim. normalised to Exp.
Conversion
Opening angle deg
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e e- pairs
Pairs detected in META 1 / defl. angle
(momentum) vs. opening angle in
META
low p cut off (Acc., RICH, ...)
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Commiss.- Res. PID CC _at_ 1.5A GeV
all ch.p.
e/e-
q lt 45
velocity v/c
q gt 45
velocity v/c
momentum MeV/c
momentum MeV/c
T. Eberl, TU München
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PID e/e- candidates
all ch.p.
C C E 1A GeV Analysis for N 2 106
evts
velocity v/c
e/e- only
velocity v/c
Cut on RICH
momentum MeV/c
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Dileptons from C C _at_ 1 A GeV
Simulation comb. backgr. a) close pair rej.
by RICH b) close pair rej. by ideal
track
350
2
Signal (no comb.)25000 ee-
needs 2 109 events
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