General Meeting Summary 11/14/13

NPS COLLABORATION MEETING - 14 NOVEMBER 2013

JLAB: BW, CH, CM, RE, SW, BS, DH, AC, HM, PT, RP, AM, SZ, CC, MF, MJ, DG, JB, JZ, NK, KP, MACP, IS, MD

PHONE: NK, JR, DD

RCS theory: Theoretically, the quantity of interest is the WACS differential cross section as a function of s at fixed t, e.g., with a measurement of the t-dependence at two values of s at sufficiently large u. This would provide important information for the soft-spectator contribution and so for the soft overlap mechanism. By universality, the t-dependence of the data could also provide information on other processes, e.g., two-photon exchange contributions to the nucleon FF, comparison with the time-like region. The longitudinal polarization, K_LL, could also be of interest to check the angle and energy dependence at sufficiently large u, s, and t.

RCS experiment: Currently working on updating the kinematics to address the PAC40 comments. To get an optimized set of kinematics, the higher t-points shown on slide #11 will be dropped and the remaining points re-evaluated. The idea is to concentrate on the 90 degree CM settings and have additional points extending the range in t and s to s~20 GeV^2. Initial estimates suggest that the measurement could be done in 20-25 days. A measurement of K_LL would be possible at 58 degrees CM at comparatively small additional cost (~2-3 days). Simulations to optimize the new kinematics and work on improving the background subtraction techniques are ongoing. Updated kinematics and beamtime request should be available soon.

Idea is not to focus on factorization mechanism, e.g., scattering from quarks, but investigate why it works so well.

t-dependence of the cross section could also be interesting since it's to some extent a gauge of the power corrections.

Exclusive photoproduction: currently working on kinematic settings with as much overlap as possible with RCS. Experiment would also need additional 3-pass settings. Work on beam time estimates ongoing. Coordination with RCS important, e.g., with RCS removing the highest t-points (right plot on Dipangkar slide #15), the 120 degree CM settings at 3-pass may not add too much to the measurement. Instead of focusing on factorization would be better to focus on ratio as exploratory measurement to see if the t dependence for neutral to charged pions flattens as seen in pi+/pi-

Hall C: PAC42 - July 28 to August 1, 2014, PAC41: May 19-23 re-prioritization PAC. Hall leaders will send request for information about experiments before Christmas break. Feedback is needed early in 2014.

NPS design: NPS was designed starting from HyCal and scaling it to smallest possible dimensions to fit into Hall C. The NPS design also includes a lifting frame, slides and casters to adjust the detector in z. Angles physically reachable by NPS have been evaluated in the Hall C setup for the desired detector positions. Some positions are difficult due to other equipment in Hall C, e.g., the 3m position where the detector is sandwiched between the beamline and the SHMS, and the 6m position where the NPS angle is limited by the larger beam line diameter (see Mike's slide #8). To move the NPS forward and backward position locators would be used. Need to check the requirements against the values shown on slide #5, in particular for the 6-7m setting. If angle reachable with current design ok, then done, if angle not ok, can explore: i) to move the detector forward to avoid the larger beam pipe, ii) try to find another solution for the base frame of the detector.

Crystal comparison: for experiments need crystals with good energy resolution (high light yield), good coordinate and angular resolution, good timing (fast signals with short tails to minimize pile-up at high rates), radiation hardness (modest damage for integrated doses ~20-30 kRad). Best choices are thus PbWO4 and PbF2. Light yield for PbWO4 depends on temperature - have to optimize the temperature to balance light yield and decay time. PbF2 light yield has no temperature dependence, but is generally lower. Radiation damage to crystals is limiting factor for beam current. Both PbWO4 and PbF2 experience radiation damage. Radiation damage is reversible using different options, e.g., UV curing, thermal recovery. Depending on experiment scheduling even spontaneous recovery may be an option, e.g., if there are a few months between experiments running. Different arrangements of the PbF2 and PbWO4 for the hybrid spectrometer are possible. The quality requirements on PbWO4 crystals for the NPS compared to the CMS requirements can be found on slide #23. In general, NPS requirements are less strict than CMS.

DAQ plans for HC and NPS: SHMS will have fADCs electronics runing in an integrating mode. Fully pipelined operation of the trigger/DAQ will be possible. But, if ~1ns resolution acceptable for NPS experiments then don't need fully pipelined NPS trigger and fADCs can provide all functions needed. Inventory of HC hardware on slides. Data rates of 20 MB/s are fairly straight forward. Important to have online analysis software optimized to keep up with monitoring requirements - coordinate with HC and FE groups. Physics analysis could be done on the farm - may require coordination with HC and other groups well in advance to ensure that enough resources available for NPS. Firmware and trigger development also require coordination with FE and HC groups.

Electronics Status and Upgrade Opportunities: review of pipelined method of signal capture with example of HD level 1 trigger. Inventory and status of testing of production boards on slides #7-8. Note: pre-production boards are not included in the table on slide 8. Adding together the readout hardware that Hall C has and additional hardware available from JLab physics division there should be sufficient digitizing electronics available for NPS. HPS ECAL as an example of fADC based trigger - cluster finding for 3 x 3 square of channels in ECAL. Pipelined DAQ/trigger for NPS using fADC250 and 1116 PMT (R4125) channels. Firmware could be based on that for the HPS. An important point that needs study is how thresholds should be applied, e.g., for each channel and for each cluster. And, if the thresholds should be the same for each channel/cluster. NPS firmware should support wave form readout. The details on reading the wave forms will have to be discussed. Note that signal range of R4125 with active base if used up to its maximum may be larger than front end input range - would get clipped.

Future program and funding discussion: NSF/MRI for funding for hybrid spectrometer (PbWO4 and PbF2) in preparation by CUA, OU, ODU. Includes one magnet, HV active bases, temperature controlled frame, gain monitoring and curing system. Check if HV dividers estimates include circuit cables. Additional details/drawing(s) of magnet and gain monitoring system. Has option to provide active bases for all PbWO4 crystals available from HD/HB, which would also be beneficial for PrimEx. Beyond the items included in MRI: Second magnet - could be funded from European sources, misc. cabling/electronics - available from JLab, lifting frame - can be constructed at JLab.

Future NPS experiments: idea for di-lepton detection using muon detector behind NPS. Would run parasitic with DVCS/pi0. Studies of DVCS with polarized targets ongoing - investigating sensitivity of observables. Studies for polarized WACS with NPS ongoing at, e.g., UVa.