Minutes of E97-111 Meeting, 24 July 2000 present: Joe Mitchell, Xiadong, Nilanga Liyange, Jeff Templon, Mark Jones, Eric Voutier, Kevin Fissum, Arun Saha, Larry Weinstein Jeff gave his standard physics motivation talk. Also an update of the simulations with AEEXB was presented. This has to do with the actual beam energies we received, plus our expectation that we will receive 70 uA of beam rather than 100 uA, plus our expectation that the target density will be lower than that assumed in the proposal. The bottom line answer: we have enough time for PY-I, and we are short about 1 day (out of 4.4) for PY-II the allocated times for CQW-I and CQW-II appear to agree with the readjusted numbers from the proposal, but the rates are substantially lower than what we'd like. For CQW-I this is not a large problem since we don't expect to see the minimum there, but for CQW-II we have a better chance, and the sensitivity is low. So any extra time we have should probably go here (in case things go better than hoped). Joe's MCEEP simulations agree perfectly with AEEXB for PY kinematics, but disagree up to a factor of 3 for some CQW kinematics. To be investigated Other points brought up by attendees during JT's talk: * Arun noted that the PY kinematics contain lots of angle and momentum changes. Need to be careful that linking is done properly to preserve link to 4He elastic measurement. Also, question was raised how well do we know luminosity without linking? N-Delta and 89-044 people should be able to tell us this. * Was pointed out that we can't do serious optics commissioning before experiment since one- and two-pass beam are unavailable (used by other halls). Nilanga has developed a 3-pass check program; full optics data to be taken with 1-pass data during facility time after expt. * Sabine Jeschonnek pointed out that Sargsian's calcs (displayed during the talk) were factorized, and for our CQW kinematics this was likely not going to be a big plus. ============= Nilanga gave a short summary of the optics programs for the experiment. It would be very advantageous to have the carbon stack ready for this expt. We can get a rough momentum calibration using quasielastic on carbon. Somebody recommended a y-target scan be done too Also was recommended that we look into doing 1H(e,ep) at not just one setting, but several settings per beam energy ... this helps pin down both beam energy and detector angle offsets. ARC and ep beam energy measurements still do not agree. ================= There was some discussion at this point about how well we needed to know kinematical quantities. We hope to get Paul Ulmer to tell us the answer since he apparently has some program which is good at doing this quickly. At the moment we don't have a quantitative answer, although the simulations indicate that CQW kinematics are much more sensitive than are PY kinematics. ==================== Joe gave a summary of singles rates calculations with QFS. All looks good although rates and backgrounds are relatively high (several to one) for some of PY kinematics. Will want PID in both arms in order to kill randoms, since we are trying to measure small cross sections. Gas Cerenkov will be installed in arm with FPP since we use it to detect electrons. In other arm, the mirror aerogel will be installed. Joe also pointed out that we need to reduce trigger coinc window for PY kinematics, otherwise we may be DAQ-limited by randoms rate. Larry pointed out that we need to worry about real coincidences with pions; Joe will calculate what the cross sections are at our kinematics. =================== Mark Jones presented the latest on the deadtime saga. We will definitely want this measurement!! Also we discussed various improvements: * having the measurement not only in the "1" paddles but in others as well where rates are higher * implementing it with scalers instead of TDC. This requires a "pulser-gated scaler" or else lots of channels of AND to gate the individual signals * also would like same set of scalers, ungated. * would like to have separate measurements in H and E arms * would like pulser triggered by some beam-driven rate, not uniform * need to worry about change in pulser trigger time with hadron/electron momenta since coinc time window changes. ========================= Xiaodong presented a scheme to measure luminosity. However this requires constructing a new detector, installing, and testing. Given limited time before the experiment this is almost certainly not feasible. ============================= Doug Higinbotham gave JT a table of 4He elastic cross sections at the energies and angles we plan to run, but JT was forgetful enough that it did not get brought to the meeting. ========================= stuff still to do on the TODO list: * make commissioning plan for gas cerenkov detector * figure out discrepancy between MCEEP and AEEXB (JT, JHM) * compare pinhole aperture, reconstruction-off versions of the two codes ... * compute derivatives of cross section with various kinematic quantities; this determines how well we must measure them! * make target commissioning plan * optics plans before and after run (Nilanga) * need to know what will happen with VDCs during swap; stay mounted on spectrometer, or follow detector package? JT has contacted Segal, waiting for reply. If VDCs move, need to survey them. * decide whether we want to do full 1H(e,ep) measurement or only one point per energy * decide collimator issue; waiting for info from N-Delta and 89-044. JT seems to be only one really convinced that we need to run with collimators?? * investigate VDC efficiencies. Mark Jones will look into this. he suggests that we run with FPP front chambers on; then we can play games by tracking between two of three chambers, and looking at efficiency of the odd man out. * Arun Saha will take care of making sure energy measurements, surveys of beamline, etc. are done properly * Doug Higinbotham, Konrad Aniol, and someone else (who volunteered?) will take care of making a normalization plan including 4He elastics (also at 1-pass beam at end of expt) and linking. Also suggested was to do a current scan on 12C target as well as on 4He target, to check that 12C target gives null effect. * I think Dmitri volunteered to be our shift czar * Joe will make a COO/ESAD/RSAD document set ================================== Other things happened since the meeting: * reaction losses in scintillators seems to be a non-issue. Correction is on order of 0.6%. We can probably calculate it to 20% so no special measurement will be needed (thanks Riad S.) * detector packages in two arms are finalized. Here they are (VDCs are not mentioned). Complain loudly and often if you do not agree. Left Spectrometer (let's call her Lisa for short): S1 plane S0 plane First straw chamber short Gas Cerenkov Second straw chamber S2 other FPP stuff Lisa will be used in our experiment to detect ELECTRONS Right Spectrometer (let's call her Risa for short): S1 plane Mirror Aerogel Counter (n = 1.025, 9 cm thick) S0 plane long Gas Cerenkov S2 plane preshower counter total shower counter Risa will be used in our experiment to detect PROTONS =============================== That's all I can remember. Let me know if I left anything out. Respectfully submitted 7/25/00 JAT