Download Positronium intensity measurement preparation

Positronium intensity
measurement preparation
SNU
Bongho Kim
PbWO4 crystal
02/06/2016
• 1 PMT + 4 PWO Crystal (2x2x3.8cm
for each)
• Yield 0.7~2.6 [p.e./MeV] acheived wi
th 22Na source before cutting.
- Density : 8.3g/cm3
- Radiation length : 0.9cm
- Decay time : 10~30ns
• Good for high intensity beam measu
rement
Already used may experiments like
CMS, Alice, Penda or positronium det
ections..
SNU BongHo
2
PMT
PMT
Attached by normal g
lue
Cover
• H7195 in HAMAMATSU
- Dia : 60mm
- Voltage : >-2700V
- Gain : 3x106
- Transit time spread : 1.1ns
FWHM : 20~30ns
4ns binning
bakelite
PVC
02/06/2016
SNU BongHo
3
Detector shielding
1. Wrapping PWO crystal by Teflon tape.
2. Wrapping this by Black paper. (with
tape)
3. Covering by Bakelite cover with cap.
4. Wrapping all assembly by black tape
and black paper
All done at 2016/06/07
Basic preparation and issue
• Today, I will turn on PMT to check this one’s performance.
- Noise level, Dark count rate without source.
• Na22 source and CsI + PMT detector are usable.
- Adequate high voltage choice.
- Single P.E check and efficiency check(?) for 0.5MeV and 1.2MeV (Do we
need plastic scintillator?)
To measure cross-section, efficiency check is necessary.
For low P.E PWO crystal, effiency for 3 gamma event(E<0.5MeV) will be
lower than 2 gamma event and we need to find the way to measure
each efficiency.
• We can use low intensity positron beam with positronium target.
We can measure 0.5MeV gamma efficiency by install PWO and CsI
back to back
In 3gamma case, we can’t do because this event is not back to back.
So
Because of low Scintillation only 1~2 photon is expected for 511keV
gamma and less photon for o-Ph decay.
-efficiency(1photon)<0.368?(poisson distribution)
If we expect Photo-electron number for 3 gamma event, we can expect
efficiency by poisson distribution. (Does it make sense?)
Eventual result
• We will get gamma yield distribution by time as below
histogtam.
• To measure real yield, we need to fit data and give correction
factor for 2 gamma events and 3 gamma events.
Eventually, we can get l
ike this smooth line
( NIM A 580 (2007) 133
8)
Simulation status
• Yesterday, I got simulation code from Amelia, I will try to
check detail from today.
• Orth-positronium is added as new particle in Geant4.
• There’s some code for decay channel and physics for this
particle and I need to check detail.
Need to added)
Geometry : Positronium target( cavity) and chamber
Physics : reflection of positronium in cavity.
To do list and goal
• PWO detector development and calibration for yield
measurement
• Simulation preparation to expect signal yield and positronium
motion before annihilation.
( there’s some expectation that para-positronium in target
holes has different life time)
• There‘s some discussion for extra-work if I have time and we
will see.