Hi,
First, to complete the story, ed elastic rates were like the following:
2004: 0.58/C at average 97.8mA current
2005: 0.49/C at average 178.6mA (runs with corrected dcct calib)
2005: 0.63/C at average 84.5mA (runs 16383 to 16433, 100mA Imax)
Genya, Nick and I went through this almost as soon as the runs were
completed so it was a surprise that people are surprised by it a few
months after. Rate drop is also seen in unpol runs where comparable
buffer flow produced lower rate in 2005 than in 2004. So it seems ABS is
OK at least before the gas passed into the storage cell.
Secondly, as Genya suggested, I looked at the pure TOF based ed elastic
again. I hereby report the findings. TOF rate is higher for the 100mA
runs than the 180mA runs immediately before those. This excludes the
speculation that the lowering of event rates going to higher current is
due to tracking inefficiencies.
Following is the detail of this study.
1. TOF timing cuts and coplanary cuts are calibrated with the help of wire
chamber information. These cuts select ed elastic events. TOF paddle
combinations (15,0)-(15,2) and (14,1)-(14,3) and the revese, i.e.
(0,15)-(2,15) and (1,14)-(3,14) are used. The cuts are not all that clean
without the help of WC tracking. Likely 10-20% are e'p events but for
purpose of trigger/WC efficiency study, I believe they are not a problem.
2. runs 16383-16433 are used: I_average= 84.5mA, Q=11220.9C
in comparison to runs 16352-16382: I average=180.8mA, Q=10520.2C
3. events in those paddels passing the TOF timing and coplanary cuts are
counted. charges of tracks have to be assigned but the choice is
obvious. for the low current runs, the "TOF ed elastics rate" was
1.32/C while for the high current runs immediately prior to them, the "TOF
ed elastic rate" was 1.02/C. the relative drop in TOF rate is the
same as the drop in rate with tracking. This excludes tracking efficiency
as the cause of the current dependency of event rates. So seems wire
chamber is also fine.
4. checked the ratio between event rates which: a:coming straight out of
2nd level trigger, b:with # of WC hits between 10 and 80, c:with
reconstructed tracks. b/a is more or less constant and most of the time 1
due to the definition of 2nd level trigger. c/a changed slightly from 95%
to 97% when current is lowered from 200mA to 100mA. The 2% difference is
far from enough to account for the more than 20% change in ed elastic
rates, both pure TOF and with tracks.
5. checked the trigger rate in trigger type I. when current is lowered
from 200mA to 100mA, average beam gate scaler rate dropped by a factor of
2 as expected. In the mean time, the number of 2nd level trigger /C
increased by about 7%. but this is not any larger than the
fluctuations in 2nd level trigger rate under constant running
condition. So this quick check could not identify big changes
in trigger rate that corresponds to the change in final event rates.
Chi
On Mon, 5 Sep 2005, Renee H Fatemi wrote:
>
> Hi Vitaliy,
>
> I looked at % of events removed for each cut in the 2004/2005 (e,e'p)n
> analysis. I found that 2.2/2.4% of events survived exactly the same series
> of cuts (no MM or kinematic corrections). Yet the rate of ep_coin/kC for
> each year is 19.36/16.52 -> about a 15% reduction. From this the
> difference seems to be in the charge. We are looking at different channels
> but I would be interested to see if your analysis give the same results,
> ie similar reduction in #events from 2004-2005 but still a different rate.
>
> One other difference is that the rate of ep_coin in 2004 was equal for the
> R/L sector but in 2005 the electron L side had about 20% for events than
> eRight.
>
> Just another clue...
> Renee
>
> P.S. I chose runs 15392-15398 from 2005 which are after the charge
> calibration changed, so this shouldn't be an explaination/issue.
>
>
> On Fri, 2 Sep 2005, vziskin wrote:
>
> > Dear all,
> > I include two graphs similar to the ones in my thesis for the 2005
> > data. The first is the rate per coulomb for each run and the second is
> > the histogram of the rate. The mean rate is about 0.76 \pm 0.1.
> > Compare that to 1.05 \pm 0.11 from 2004. Correspondingly the mean rate
> > in 2005 is about 72 % of 2005. Of course the mean rate is not average.
> > It is if the rate is not current dependent (like in 2004). So I expect
> > the average current to be even lower. One thing to note is in the first
> > plot the rate is higher at the beginning and the end of the run period.
> > These are the times when the injection current was kept lower. So,
> > where is the missing rate.
> >
> > Best regards,
> > Vitaliy
> >
>
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