General Meeting Summary 5/22/14

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  • Since still waiting for irradiation of PbWO4 crystals, an initial performance test of the blue and IR LED prototype curing systems was done with irradiated lead glass (280 rad/hr for 48 hrs with Cs-137/photon source). The lead glass was irradiated from one side and transversely. The LED driving current (intensity) was 50 mA. Note that lead glass is NOT a material considered for NPS.
  • Illumination with 4 IR LED from either longitudinal or transverse direction shows no crystal recovery
  • Illumination with (blue) LEDs at an emission angle of about 10 deg for about 3 hours shows small recovery in transmittance, but far from non-irradiated state
  • Increasing the LED emission angle and curing time to 20 hours further improves the transmission, but it is a very small effect

Though these tests are interesting and one can see a difference between before/after curing with the LED system it seems that thermal annealing is the best method for recovering lead glass.

  • Some discussion about tests of the LED curing system once irradiated PbWO4 crystals are available. The PbWO4 crystals will be irradiated to 40 krad and since the samples are relatively small the whole crystal will be irradiated.
  • Based on previous studies from, e.g., CMS, expect PbWO4 to be more radiation hard than lead glass. Studies have shown that can go up to 50 krad before curing is needed. On the other hand lead glass needs curing at doses of ~10 krad already.
  • If see the same trends with PbWO4 as seen with lead glass then may need to increase the blue LED intensity
  • Discussion about a curing test with the blue lamps used for DVCS/HA, which could be more powerful than the LEDs.


  • NPS update document describing the current status of the project is being finalized. Should be ready next week. Idea is to attach it to one of the proposals as an appendix to show activities on the project. The older version of the document submitted as attachment to PAC40 is available on the Wiki.

  • RCS - major updates from last submission (discussion based on proposal draft from 5/21/14)
  • new section 2.6 to address the PAC40 comments and includes the current status of the theory (an overview of the latter is presented on p.16). Idea is to discuss how each model/theory can be helped by the measurement
  • new section 2.7 to connect to the pi0 photoproduction proposal
  • updated expected raw rates on p.23 (Fig. 14) and projections
  • Figure 24 shows the motivation for the choice of kinematics - it is a compromise between s and t.
  • updated dose rates (p.28/29)
  • updated kinematic settings in Table 2 - lowest t were dropped.
  • Beam time at each setting is show in Table 4 on page 35
  • improved sections 4.2-4.4 with more detailed explanations of rates, backgrounds, optimizations of calorimeter distance, systematic uncertainty, etc. Fig. 21 and pp.38/39 show the background subtraction procedure.
  • RCS comments/discussion
  • To distinguish Fig. 21/22 perhaps clarify in the figure captions what is included in the peak, e.g., WACS including pi0 background
  • Discussion about Fig. 19 clarifications. In general shows very slow scaling with energy
  • Discussion about sharing the draft with N. Kivel and ask for comments
  • HMS drift chambers are not vertical
  • Discussion about adding a paragraph at the beginning emphasizing what has been added/changed since the last submission
  • Discussion about connecting to pi0 photoproduction - data are taken simultaneously and physics described in companion proposal
  • Add the NPS update document as an appendix

  • Pi0 photoproduction (based on draft from 5/21/14)
  • Discussion about adding more kinematics & more theoretical work and postpone proposal to another PAC. Discussion about mutual benefit to submit RCS and pi0 photoproduction together.
  • Discussion about extra beam time beyond RCS. There may be a way to reduce the additional needed beam time significantly and also link to CLAS experiment.
  • Working on trimming physics case
  • Waiting on radiation dose estimations
  • Discussion about including a section on what can be done with the HA (calibration) charged pion data. Since these seem rather low in energy it may not be beneficial to include here

  • To give people the chance to review the proposal and sign up on it it would be good to circulate the proposal drafts to interested members of the HA/HB/HC collaborations early next week.


  • NPS design and prototype
  • Electronics tests