Log entry time 10:29:11 on November 15, 2008

Entry number 248963

3032 2 1600 10.7694 11.9759 10.4412 0.125956 0.00327211

3033 2 1650 11.2533 12.3594 10.5966 0.120375 0.00325045

3034 2 1700 13.5542 14.4007 12.3047 0.118745 0.00341487

3035 1 1700 8.63673 9.21834 7.84049 0.11292 0.00261163

3036 1 1650 7.09258 7.73918 6.72118 0.116418 0.00278525

3037 1 1600 5.01764 5.50203 4.8951 0.115765 0.00270588

3038 1 1550 4.21197 4.63894 4.0807 0.0863267 0.00153403

other than 1550 V, basically no change in efficiency, thus I think 1600 V is quite safe

2. Will background be a problem?

run# current BG BG BG tracking eff multi-eff

3018 2 3.5 9.91737 11.0025 9.59492 0.124412 0.00296476

3019 4 3.5 17.9016 19.9361 17.4383 0.135158 0.00414776

3020 6 3.5 27.4004 30.5393 26.763 0.149156 0.00569247

3021 8 3.5 37.3478 41.7707 36.3085 0.167662 0.00778043

3022 10 3.5 45.1256 50.2546 44.0906 0.180836 0.0104083

3023 12 3.5 45.2333 50.6488 44.2054 0.181254 0.0104449

Clearly see an increase of "tracking effciency" I think this is due to the trigger, see attached figure.

After adding a cut at 800 channels for BB.ts.ps.e rather than 350. We have

run# current BG BG BG tracking eff

3018 2 3.5 9.91737 11.0025 9.59492 0.113697 0.00248078

3019 4 3.5 17.9016 19.9361 17.4383 0.11646 0.00341339

3020 6 3.5 27.4004 30.5393 26.763 0.124101 0.00447531

3021 8 3.5 37.3478 41.7707 36.3085 0.134892 0.005858

3022 10 3.5 45.1256 50.2546 44.0906 0.143038 0.00799182

3023 12 3.5 45.2333 50.6488 44.2054 0.144841 0.00835857

Again, we see some increasement, but much smaller than the previous case. This again demonstrate that the trigger content changed with beam current. One simple explaination is that the pions are shift to a larger value of the BB.ts.ps.e, due to low energy background. This will mimic a electron, and pions are usually have higher "tracking effieciency". With the shower cut, we can clean the background further. I think that we are quite safe to run 12uA. If the background level is acceptable, I would like to run 1650, rather than 1600 V.

3. Coincidence peak tracking effieicny, cut at 350,

The tracking efficiency under coincidence peak is about 0,224, while the random coincidence gives 0.18, close to the value that we had 0.17 for the previous test run. This means that the tracking is fine, and we do see a huge increase in the tracking effiency for the coincidence events.

4. The background problem that we observed will have effect on the shower counter PID. since pions are moving to the higher channel of BB.ts.ps.e because of the background. This may potential lead to a PID problem, but I guess we may not have much choice anyway.

In conclusion, I think that we should be able to run 12 uA, and I will adjust the HV to 1650, with some careful study.

In principle, we should have an improvment in reducing the background with the additional shielding, we will see!!!

A copy of this log entry has been emailed to: jiang@jlab.org,jpchen@jlab.org,brads@jlab.org,camsonne@jlab.org

Figure 1