Present: M.D., A.D., S.Š, J.S.
General: Met on Monday 04/20/2020 with committee members for GlueX proposal review, Garth Huber and Frank Nerling. Very productive meeting. It was based on Mark's talk at the APS.
- Overall, it seems that Garth and Frank like very much the physics of the proposal and that they (we believe) will provide a positive recommendation. They said they will provide such recommendation within a week.
- Most of the discussion was on clarifying a number of points, underlying that the proposal needs to be better written. They said that many aspects are probably clear to GDH experts only.
- The only suggestion that may significantly change the proposal is that Garth and Frank suggested that we propose to take more data (especially adding a deuteron run) at half linac energy, without worrying about scheduling/invasiveness issues. Such run could be done e.g. in summer. They suggested also to discuss this with Eugene or someone from the management to confirm that it is not going to hurts the proposal to ask for such beam time. Another thing to clarify here is whether such data is (easily) obtainable from the CLAS 6 GeV runs.
- List of points to clarify re. the proposal:
- Change (M. Dalton):
- "Primary goal" to "Early goal" (meaning what we can learn with an easy analysis)
- "Secondary goal" to "longer term goal" (meaning it involves a more complicated analysis)
- Clarify that the proton GDH running integral has overshot the sum rule predictions and while the missing part is expected to be negative from Regge, the evidence for that from ELSA data is anecdotal. (M. Dalton)
- Add the running integral plot to the proposal (make the running integral for the neutron), with the LEGS data included. Specify that this is all the data available so far. (M. Dalton)
- Clarify that our simulated prediction of the proposed measurement were obtained using the best Regge estimate available. It was unclear to Garth and Frank what was in the simulated data. (M. Dalton)
- Instead, or in addition, to Fig. 1, use the PDG figure that show the pomeron-related increase of the unpolarized cross-section. (M. Dalton)
- The illustration based on Fig. 1 on what we would have missed (the divergence of the unpolarized integral) if unpolarized data stopped at 2.9 GeV seems to not have been clear to Garth and Frank. (M. Dalton)
- Clarify and extend the discussion on the 25% improvement of accuracy for the verification on the proton GDH sum rule. (A. Deur)
- Illustration of what we could learn about quark substructure:
- Make it more prominent in the introduction.
- Mention it in the conclusion
- Instead (or in addition) of assuming that we will find that the sum rule is valid, and computing the compositeness limit within this assumption, discuss what we would learn on quark compositeness if the sum rule is violated by, say, 3σ. (A. Deur)
- Remove in details on HDice. (Just say we are using FROST, unless a bigger program warrant the use of HDice) (A. Deur)
- Clarify that the 3 PS settings are different from the (unique) tagger setting. (M. Dalton)
- Clarify the XEFT part (Garth thought we were directly measuring the Forward Compton reaction). (Simon Širca)
- Change (M. Dalton):
- Will restructure the proposal to make it easier to read.
- Working on the simulation.
- Still struggling with BH event generator but good progress.
- Will write to Reinhard to ask if 6 GeV CLAS data could be easily used to form GDH integrand.
- Will ask Eugene about feasibility of running at lower energy
- Will provide expected results for a 2.5 day (H)+3.5 day(D) run at lower energy (6 GeV or 4 GeV).
- Will revise the quark compositeness part (in particular remove the info on the 7 GeV scale used for the running quark mass, since it may be confusing) and will write to Steven Bass about it.