Hi,
During the last week I have been investigating the rate difference between
2004/2005 data. I have discussed this privately with several people but I
want to bring this to the list because I think we may have narrowed the
problem down to a TOF inefficiency. For those I haven't spoken with let me
start at the beginning.
1) In the 2005 e(e',p)n analysis the left sector e-p coincidence rate is
15% less than the right sector, and the right sector rate is about 3-4%
less than the 2004 rate. I decided to plot the scattered electron momentum
vs electron theta for e(e,p') coincidence events for 2004 and 2005 (please
look at attachment c18.eps). The 1st(2nd) column is sector L(R). What you
should see is a kinematic "hole" in the left sector for 2005 in momentum
range < 0.6 and theta = 40-50. In order to quantify this difference I
integrated the # events in theta slices and compared L/R for 2004/2005
*********2004****************
L R R-L/L theta
1982 1987 0.252270 20-30
2755 2305 -16.3339 30-40
1197 1230 2.756892 40-50
664 720 8.433735 50-60
215 244 13.48837 60-70
***********2005*******************
L R R-L/L
3236 3967 22.589617
4064 4612 13.484252
1068 2107 97.284645 <- Big difference!
1056 941 -10.890152
470 404 -14.042553
2) Next, to see if this could be caused by one of the cuts - I repeated
the plots - removing one cut at a time. I did not attach these plots but
the results are the same for all set of cuts, making it appear that it is
not a cut which is removing these events.
3) This morning, Karen took a look at the plot and suggested that this
could be a TOF inefficiency in the region of TOFs #6-8. So I plotted the
TOF# of the TOF hit for progressively tighter cuts (BLUE= electron right,
RED= electron left). If you look at c19.eps you will see that there is a
hole in TOF 6-8 efficiency in the Left sector compared to the right. From
Left to Right panels the cuts are:
1) negative charge track L(R)
2) coin = negative charge track L(R) + postive charged track R(L)
3) coin + CC required for negative track + CC veto for positive track
4) coin + CC + TOF matching CC
5) coin + CC + TOF + Cut on Beta of coin events
Conclusion: The difference in L/R rate for 2005 is due to a trigger
inefficieny which shows up in the TOF. If I make the correpsonding plot
c19.eps for protons I also see a slight inefficiency in the same TOF
region but because this is on the tail of the proton scattering kinematic
region the effect is not as big. BUT it is big enough to account for the
3-4% difference in rate I see in the right sector (electron right - proton
left) from 2004 to 2005.
Questions: Is this trigger inefficiency really due to a TOF inefficiency?
Trigger 1 also required 3 hits in the WC so perhaps, as Chi said, a WC
inefficiency could result in the reduction of TOF#6-8 rate? I need to
investigate more ... but any ideas/suggestions/comments are welcome.
Best,
Renee
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