1 Report on analysis of PoGO Beam Test at Spring-8 Tsunefumi Mizuno July 15, 2003 July 21, 2003 revised

2 Detector/Beam configuration (1) Beam goes from +x to –x Polarization vector of incident beam: along x-axis Beam size (for detector): a circle of 2.68cm diameter Expected beam energy (for detector):83.6 keV (incident beam of 100keV is scattered at 90 degree; this direction picks up the minor component of incident beam whose polarization vector is along z-axis) Expected polarization vector (for detector): along z-axis We decreased the beam rate by a factor of ~100 (from ~10^13Hz down to ~10^11Hz) to prevent pile-up (<=5kHz at the center scintillator). We used an Al block instead of a foil to get an appropriate S/N ratio. Typical trigger rate was ~160Hz and that of background was ~80Hz (Pb block was put in front of the collimator hole). Beam(100keV) polarization vector Collimator (Pb with smaller hole) Collimator (Pb with bigger hole) x y Scatterer (Al block) (Pb sheet)

3 Detector/Beam configuration (2) y z Id: Expected polarization vector 26.8mm 49mm hexagonal scintillators 20cm long Beam direction Beam goes from +x to –x Beam size: a circle of 2.68cm diameter Expected polarization vector: along z-axis Expected beam energy:83.6 keV (incident beam of 100keV is scattered at 90 degree) Right figure corresponds to the rotation angle of 0 degree. We rotated the detector. rotation angle

4 Run summary Data are stored in calibration with 241Am for PMT1 (before beam test): run16_p.txt. Shaper gains (for all PMTs) were adjusted to give ~3V for 60keV. 0 degree run/bg: run17_p.txt and run18_p.txt 30 degree run/bg: run19_p.txt and run20_p.txt 15 degree run/bg: run21_p.txt and run22_p.txt 180 degree run/bg: run23_p.txt and run24_p.txt bg without beam: run25_p.txt calibration with 241Am (after beam test): run26_p.txt Data files with _p are peak data and without are waveform data (binary).

5 Calibration run (1) PMT/scint 1 PMT/scint 2 PMT/scint 3 PMT/scint 4 A gain of PMT1 might be shifted during the test. (from ~3V to ~2.7V)

6 Calibration run (2) PMT/scint 5 PMT/scint 6 PMT/scint 7 PMT/scint 4 PMT/scintillator of #4 is taken by ch4(upper card) and ch8(lower card) and gives consistent spectra -> DAQ itself works well.

7 Energy spectrum of each scint. 0 degree 180 degree Event selection: 2 scintillators are with hit (detection threshold is set at 3keV) Total deposit energy above 45 keV is selected. Energy scale of ch1 might have been shifted during the test and not appropriate for 0 degree run (see page 5). For other PMT/scintillators, no significant difference (modulation) is observed. ch1 ch2 ch3 ch1 ch2 ch3 ch5 ch6 ch7 ch5 ch6 ch7

8 Total energy deposition Event selection:2 scintillators are with hit (detection threshold is set at 3keV) Beam energy was expected to be 83.6 keV (100keV is scattered at 90 degree), but is ~70 keV. -> main component is double scattered photons? might be unpolarized? run17: 0 degreerun23: 180 degree

9 Summary Gain of PMT/scint. #1 seemed to have changed during the test; We have adjusted shaper gain so that 60keV peak comes to 3V, but it was 2.7V in the calibration run (run26). For other PMT/scintillators, no significant difference (modulation) is observed in spectra. This might be due to that beam (after 90degree scattering) was not what we expected. Mean energy(70keV) is lower than calculation (100keV->83.6keV). ->Double scattered beam is the main component? unpolarized?