the gas Č erenkov detector for the crystal-barrel experiment at elsa
DESCRIPTION
Hemholtz-Institut für Strahlen- und Kernphysik der Uni Bonn. supported by SFB/TR 16. The Gas Č erenkov Detector for the Crystal-Barrel Experiment at ELSA. D. Kaiser. Nucleon Resonances. Breit-Wigner parametrisation. photoproduction reactions with nucleon resonances at the CB experiment: - PowerPoint PPT PresentationTRANSCRIPT
The Gas Čerenkov Detector for the Crystal-
Barrel Experiment at ELSAD. Kaiser
Hemholtz-Institut für Strahlen- undKernphysik der Uni Bonn supported by SFB/TR 16
Bosen 2007D. Kaiser2
Nucleon Resonances
• photoproduction reactions with nucleon
resonances at the CB experiment:
N N* ...
• problem: overlapping resonances
partial wave analysis
polarisation observables
)2cos(1[d
d
d
d
0
ΣlinP
))2sin(( FH circlin PPPx
))2cos(( TP lin
y PP )])2sin(( EG circlinz PPP
Breit-Wigner parametrisation
Bosen 2007D. Kaiser3
Double Polarisation
• polarised target
• polarised photonbeam- linear polarised photon beam by use of
unpolarised electron beam and diamond radiator
50% @ 3.2 GeV
- circular polarised photon beam by use of longitudinally polarised electron beam and amorphous radiator
55% @ 2.4 GeV
Bonn Frozen Spin Target - longitudinally polarised protons
in a butanol target
@ 30-50 mK in frozen-spin mode- polarisation 70 – 90%- repolarisation every ~ 60 h- total relaxation time ~ 360 h
time [hours]
polarisation
Bosen 2007D. Kaiser4
Electron Accelerator ELSA
Bosen 2007D. Kaiser5
Crystal-Barrel Experiment
Crystal-Barrel detector
tagger
MiniTAPS
polarised target
GIM
camera
e- beam dump
goniometer
Gas Čerenkov detector
e- beam
Bosen 2007D. Kaiser6
Electromagnetic Background
for butanol target under forward angles: ~100.000 e± 1 hadr.
due to:
• pair production
• Compton scattering
for hydrogen target in full angular acceptance: ~1.000 e± 1 hadr.
need for supression already on trigger level
Bosen 2007D. Kaiser7
Čerenkov Effect• discovered 1934 by P.A. Čerenkov (and S.I. Vavilov)• Nobelprice 1958, together with I.E. Tamm and I.M. Frank• charged particles with high velocity generate
electromagnetic radiation in dielectric media
cv
cvn
oc
Bosen 2007D. Kaiser8
Čerenkov Effect
22 11
11
ns
s 2mcE ss
nc 1cos
observable radiation for a particular angle c:
cv
threshold for Čerenkov radiation:
with 1noc
v
Bosen 2007D. Kaiser9
Čerenkov Effect
• threshold energy “adjustable“ by use of different Č media
• useful for particle discrimination and determination
• simple set-up with Č medium and photon detector
Čerenkov threshold detector
• other set-ups possible (e.g. RICH)
Bosen 2007D. Kaiser10
Čerenkov Effect
dLN cphotons 2
2 1sin2
approx.1700 photons/cm in water approx. 2 photons/cm in CO2
range of normal PM
Used photomultiplier: Hamamatsu R1584-03SEL
Bosen 2007D. Kaiser11
Gas Čerenkov Detector- drawing and picture
Bosen 2007D. Kaiser12
Gas Čerenkov Detector
forward crystals Gas Čerenkov detector MiniTAPS
- positioning and angular space coverage
Bosen 2007D. Kaiser13
Gas Čerenkov Detector• periodic repolarisation of the target
easy in- and output of the detector is required
Bosen 2007D. Kaiser14
Modifications
• gas system • partial pressure sensor
• scale
Bosen 2007D. Kaiser15
Simulation of the Efficiency• verification of the efficiency of the detector
maximum efficiency of 99.97 %
Bosen 2007D. Kaiser16
Determination of the Efficiency
• done at the old CB area
• e± from pair production / Compton scattering on a carbon target
efficiency of 99.72 % ± 0.45 %
Bosen 2007D. Kaiser17
Installation in the CB Set-up
more adaptions needed:
• electronic• trigger logic• DAQ• analysis software ExPlORA
Bosen 2007D. Kaiser18
Use as Veto Detector
Start of readout if two tagged hits in the Crystal-Barrel-, Forward- or
MiniTAPS detector were found
Start of readout if two tagged hits in the Crystal-Barrel-, Forward- or MiniTAPS detector were found,
with applied Čerenkov veto
Bosen 2007D. Kaiser19
Use as Veto Detector
number of suppressed events in the subdetectors
cut on events correlated in time
Bosen 2007D. Kaiser20
Čerenkov Detector as Time Reference
Bosen 2007D. Kaiser21
Čerenkov Detector as Time Reference
Bosen 2007D. Kaiser22
Summary
• Gas Čerenkov detector modified for use in the Crystal-Barrel experiment
• tests and determination of the efficiency
• detector integrated and in use– as veto detector– as time reference
• data taking has already started