User name A. Puckett
Log entry time 19:25:40 on October24,2006
Entry number 188219
keyword=Online Spectra are coincidence (T5) events onlyThere was some confusion and considerable alarm this evening about the online spectra because it looked as if the left arm collimator controls were actually telling us one thing and doing another. Below is a comparison of the left arm spectra for runs 1735 and 1737, respectively. 1735 is with the left arm collimator in the SIEVE position, while 1737 has the left arm collimator in the OPEN position. However, IF we were under the impression that these were singles spectra, that is, T3 events, then it looks more as if the sieve is in on 1737, and out on 1735, or the opposite of what we thought and what the control GUIs told us. However, we checked the cut definition file for the online replay, and found that only T5s (two-arm coincidence triggers) are plotted, so the spikes in the target theta distribution evident in run 1737 are evidence of the strong absorption of electrons by the sieve collimator on the RIGHT arm. The fact that no spikes are evident in the run 1735 left arm spectrum is due to the poor stopping power of the sieve collimator for protons at this energy scale. We were nervous because at first glance the spectra DO look like something is wrong/backwards, and since the collimator motion controls were worked on today, we were not entirely without reason to be suspicious of their reliability. However, after clearing up the confusion, we were able to verify using holecheck.C that the sieve was where we thought it was, and we are not in trouble. The fact that its downward motion appears to still want to hang up around .6 m or so makes it all the more relieving that we have accumulated plenty of left arm SIEVE data, because it may not be easy to go back at this point.
FIGURE 1
FIGURE 2
