Secondly, to check the efficiency for each channel, plot of adc_sum vs. det_xgeom for each channel of gas cherenkov on the left arm is given in Figure . Here a cut in adc_c[i;i]
chan
is used to choose the
mirror, where chan
is the channel number of the upper edge of single photoelectron peak in adc_c spectra. Part of the espace_kumac file is shown as follows:
define/variable 'eadcgas:spec_e.gas.adc_sum_t'
define/variable 'egasxg:spec_e.gas.xdetgeom'
define/variable 'egasyg:spec_e.gas.ydetgeom'
do i=1,10
define/cut/1d spec_e.gas.adc_c[[i];[i]]-1 130. 6000. /* cut #1 */
define/cut/1d spec_e.gas.adc_c[[i];[i]]-2 380. 6000. /* cut #2 */
define/cut/1d spec_e.gas.adc_c[[i];[i]]-3 130. 380. /* cut #3 */
define/logical egc1[i] spec_e.gas.adc_c[[i];[i]]-1
define/logical egc2[i] spec_e.gas.adc_c[[i];[i]]-2
define/logical egc3[i] spec_e.gas.adc_c[[i];[i]]-3
enddo
do i=1,10
set/ntuple on
spectra/save event_type/eadcgas/egasxg/egasyg egc1[i]
spectra/save event_type/eadcgas/egasxg/egasyg egc2[i]
spectra/save event_type/eadcgas/egasxg/egasyg egc3[i]
set/ntuple off
enddo
The plot shows that mirror # 10 has a high single photo-electron peak, which means it probablly have problem in alignment. Figure shows the performance of mirror # 9 and # 10 during E94-010 (GDH) experiment in 1998. Can see that mirror # 9 had alignment problem during E94-010. Obviously when redoing the alignment after E94-010 mirror # 9 was fixed but # 10 was affected. The overall efficiency is probablly not optimized and furthur work needs to be done if high pion rejection efficiency is required.
Figure shows the event distribution for each gas cherenkov mirror on the left arm. For the
mirror, the grey region shows the events which has only one photoelectron in it (cut#3: adc_c[i;i]
chan
). Here the grey region shows the edge of each mirror.
From these plots can see that the outgoing particles are not pointing to the center of the detector, mirror #1 and #2 are not fully covered. The overall efficiency could be improved by moving the whole detector lower by 1/4 of the mirror size (vertical). By doing this the bad performance of mirror #10 can also be partially avoided.