Positronium intensity measurement preparation SNU Bongho Kim

PbWO 4 crystal PMT + 4 PWO Crystal (2x2x3.8cm f or each) Yield 0.7~2.6 [p.e./MeV] acheived wit h 22 Na source before cutting. -Density : 8.3g/cm3 -Radiation length : 0.9cm -Decay time : 10~30ns Good for high intensity beam measur ement  Already used may experiments like CMS, Alice, Penda or positronium dete ctions /06/2016SNU BongHo2

PMT H7195 in HAMAMATSU -Dia : 60mm -Voltage : >-2700V -Gain : 3x10 6 -Transit time spread : 1.1ns PMT Cover Attached by normal gl ue FWHM : 20~30ns  4ns binning 02/06/2016SNU BongHo3 bakelite PVC

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 li ke 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.