Minutes of the CALCOM meeting, November 21, 1997: ================================================= Agenda: L.C. Smith - Trigger/event type identification problems in level 1/trigger supervisor S. Barrow - Efficiency studies of forward calorimeter level 1 trigger E. Wolin - Problems with using the F.Cup in the live time measurement R. Thompson - Electron selectivity of EC and EC.CC triggers D. Cords - Status of the DAQ/Online/Run control systems R. Minehart - Angle and sector dependence of the elastic ep peak E. Anciant - Time structure of Hall B beam during photon run in August/Septembet ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ The meeting focussed largely on trigger issues presented by Cole Smith, Steve Barrow, and Richard Thompson. Kyungseon Joo who was scheduled to talk about trigger uniformity was not able to attend the meeting. Also Bogdan Niczyporuk was not able to attend and his contribution on tracking efficiency vs luminosity was not presented. Both of these issues are important enough to warrant another CALCOM meeting on these two issues. I will schedule the next CALCOM meeting for Monday December 1. Meeting time and room will be announced shortly. Eric Anciant ----------- Eric presented the SACLAY study on the beam-time structure during the photon commissioning run. Using the difference between the T-counters and the beam rf signal from the injector one can clearly identify 2nsec structure of the beam. The disturbing news is that in addition to the Hall B bunches, other bunches with +/- 2/3nsec distance are observed, likely belonging to the Hall A and Hall C lines. The frequency of this occurence appears to depend on the beam current, increasing with current. The effect is quite dramatic, and needs to be understood and fixed before we can run physics experiments in Hall B. There is speculation, that the "wings" we saw on the beam profile during the September run have the same origin. However, the effect then was much smaller, of the order of <10^-3, though still worrysome. Volker Burkert =========================================================================== Individual reports: C.L. Smith --------- The contribution by Cole Smith will be included in the next minutes. S. Barrow: Efficiency studies of forward calorimeter level 1 trigger. ---------- Two studies of the EC level 1 trigger efficiency were performed. Both took advantage of the fact the EC uses CAEN C207 discriminators, and therefore it is possible to pulse these discriminators with the CAMAC "test" command. During these studies the EC high voltages were set to zero. 1) The first study tested the communication between the EC trigger discriminators and the trigger supervisor. For every output channel of the C207 discriminators the efficiency of information transfer to the trigger supervisor was measured to be exactly 100%. 2) The second study checked if level 1 triggers that have the same functionality but different internal representations are in fact identical in performance. This was verified to be the case. Similar studies for other detector systems are pending. E. Wolin: -------- I briefly described how the current delivered to the hall is measured using the Faraday cup, an EG&G current integrator, and a scaler. Due to the integration time of the EG&G module, there are problems measuring the livetime-gated Faraday cup charge. The consensus was that simply correcting the total (ungated) Faraday cup charge with the well-measured livetime (using clocks) is adequate, as there is no reason to expect correlations between the livetime and the beam current at the accuracy level we need. Also, evidence that the scalers modules occasionally count backwards is being investigated. R. Thompson: ----------- An analysis of electron selectivity for several different triggers was presented. The approach was to use a very basic particle identification to get a measure of the fraction of total triggers that appear to be electron triggers. The electron id used is: o Drift chamber track reconstructed negative particle at the hit based level. o EC hit geometrical match within 60cm o EC inner layer energy > 198 MeV o EC outer layer energy > 0.0 o EC summed energy above the trigger threshold. o |E - p*c*c| < 690 MeV where E = EC summed energy, p = track momentum Based on this, the electron selectivities measured is: run 6498: EC*CC trigger, 2.4 GeV beam, 1/2 field, 433 MeV EC thresh., -39 mV CC thresh 34% electron triggers. run 6500: EC*TOF triger, 2.4 GeV beam, 1/2 field, 433 MeV EC thresh 4% electron triggers run 6095: EC trigger, 1.6 GeV beam, 1/4 field, 433 MeV EC thresh 12% electron triggers Since the electron id cuts were all quite loose, these should be considered upper limits. An examination of the W spectra indicated that the contamination from pi- was not large: probably less that 15 percent of the measured electron trigger fraction. A study of the EC*CC trigger was also presented. Runs 6498(EC*CC) and 6500(EC*TOF) were used. For electron id, negative particle tracks with EC geometrical match within 60cm and CC geometrical match within 4 degrees were used. The W spectra for the particles passing this electron id cut were compared for the two runs. The ratio of W spectra reveals what appears to be a depletion of approximately 75% in the EC*CC trigger for events above 1.9 GeV. Future directions: Simulate CC threshold in EC*TOF. Apply an EC fiducial cut. Normalize W spectra by Faraday cup and livetime. richardt@cebaf.gov 757-269-7475 \ R. Minehart: ----------- I showed some early results of a study to check the combination of torus field, wire-chamber survey, and whatever else enters into the determination of track momentum. I used a set of 1.6 GeV negative track momenta that had been calculated with Bogdan's SDA program. I calculated the missing mass associated with these tracks and studied the width and location of the elastic peak. It was found that the peak position varied from one sector to another over a range of about 35 MeV. I also found a theta dependence within a single sector. I will look at this in more detail to try to find the source of the variation, or a correction factor for it. D. Cords: -------- During the commissioning period of September we ran at a trigger rate up to 600 Hz and at data rates up to 2 MB/s. With the fast ethernet switch for the read-out controllers in place and several improvements of CODA, we saw the data rate go up to 3.8 MB/s (which corresponds to 7 to 8 MB/s peak rates). The dead time is expected to be between 10% and 25% depending on trigger rate. The pipeline mode is not yet im- plemented. For the next run it is planned to provide DC statistics banks. The run control and start-up procedure will provide better visual control of run conditioned. Run sheets are presented in a GUI. Physics Runs will only start after the operator made some entries and submitted the information.