User name C.F. Perdrisat
Log entry time 23:17:21 on September 25,1999
Entry number 27184
Curiosity often can gets you into trouble, but here hopefully it will get us closer to the truth.
The matter of the background, a continuation of yesterday's investigation.
Question was: did this background really appear in this run period? To answer we looked at run 1422, (Aug. 24) gammap at 1.7 GeV, pmom=1.787 GeV/c: this h-data is as clean as elastic ep; we see the expected 27% of neutrals in back FPP, no neutrals in VDC or front FPP.
looked at run 1150 (Aug. 16) gammad at 1.7 GeV, pmom=1.46 GeV/c: this h-data
has 50% zeros in VDC, 70% 0's in back FPP; it shows 2 peaks in theta-phi reconstructed from Front FPP, just as in current runs, exactly same position.
(-60 mr PH, -80 mr TH).
The fraction associated with 0's in VDC is much smaller (10%), rather than 40%
in current kinematics, but it is the same effect.
Additional info. on run 1837 is that in the S1-S2 correlation (dhist), S1.1 with S2.1 contains most of the background.
The prime suspect would seem to be the neutron in d. But there are many questions: how do they come in (outside spectro vs. inside spectro). The source appears to be quite small, and should be close to the target to explain the rates. The probability of n-conversion in the S's to form trigger is <1% probably. Yet we have 100 empty VDC events for 1 good gammad,p event approx.
We are closer to believe that this is a neutron problem than yesterday.
Of course at this point the background does not affect the quality of the data.