Notes

2013

30 May

Joining: OR, PS, EL, JC, KS, DK, NK

Elena made progress on the systematic error-bands. This includes systematic drift. It seems preferable to show the total error-bars (stat & syst) on the plots, for now. She also did a tech-note on the diluting asymmetries for A_zz.

Karl has been thoroughly looking at the TAC report and poitned out that they recommended a developmentof P_zz ~ 30%. The seemed to have an issue with the target material rearranging during data-taking. Oscar has been arguing and showing that this manageable, based also partly on experience.

JP has been thinking about the luminosity monitor. and mentioned the idea of what was used for QWeak, called "lumi".

Dustin has been working on a write-up, which addresses the PAC/TAC concerns and questions over A_zz. This is still very much in progress.

The effort is in place for drafting a response to the TAC (iTAC) report(s). JP is working on charge-acceptanc. Oscar is working on target-length. Dustin's writeup is being ustilized as the basis for this.

16 May

Joining: OR, PS, EL, JC, KS, NK

Elena made updated in the rates tech-note, incorporating and expanding on the method that is in recently submitted proposal to PAC 40. Still applying some finishing touches.

Oscar has been following up on Steve Wood's suggestion to look at the systematics table for the R proposal (PR12-13-001) that was also recently submitted. Dustin will work with him to sort out what is relevant for this measurement.

Karl has been talking with Dave Mack, going over the TAC review. One of his suggestions is to have something like a (local) beam-dump and/or Farady cup, down-stream, to help monitor the luminosity.

One other thing Dave pointed out is to look in to whether any of the PV asymmetries could contribute to A_zz. Narbe is talking with Wally Melnitchouk about this.

Dave is actually interested in becoming a collaborator on the experiment, heloing with the beam diagnostics, which would indeed be a bonus.

Pertaining to the target the recommendations were to have a graduatue student working on the polarization read-out/analysis and to utilize some (physics) process to also account for the polarization. These are consistent with the proposal.

25 April

Joining: OR, PS, EL, JC, KS, DK, NK

Elena made further progress in the rates study, adding in the Bosted/Christy fit for higher x and also total rates. The rates seem high, becuase the angles are really forward. Will put in limits of HMS and SHMS.

Dustin looked further at observables, with focus on A_xx as outlined in the Boeglin/Anklin proposal. He pointed out that this method could cirumvent the need for negative tensor polarization and could be done with vecotr-optimized. He also made a point that A_xx and A_zz could be similar things, with the axis notation being more a matter of semantics.

Patricia has been talking with Mark Strikmann and Misak Sargisian, both of whom are working on calculations for the higher x region.

18 April

Joining: OR, PS, EL, SL, KS, DK, NK

Simonetta and Dustin have done some work on figurng out what observables would be relevant. In the case of vector-optimized target it seems that DVCS with a deuteron (A_UT). This would result on a combination of g_1 and b_1 without P_zz. They are in the process of working out the details. The issue with this is that that by requiring a tagged deuteron the rates would be very limited.

Dustin has been working on systematics, looking at what each polarized target scenario would result in for an uncertainty on A_zz.

Oscar pointed out an earlier proposal, by Boeglin and Anklin, for measuring A_xx. The method they proposed is similar to that mentioned in the Jaffe, Manohar, Hoodbhoy paper. Simonetta is taking a closer look at this, to see if it would be valid in the desired kinematic region.

Elena made some more progress on the rates study for higher x -> 1. It was difficult to get beyond x > 0.98. Will use the Bosted/Christy fit for this and also get out total rates (total target sample)

11 April

Joining: OR, PS, EL, KS, DK, NK

Elena made some further progress on the (physics) rates studies. The plots can be seen here. These are assuming 100% efficiency and 50% uncertainty (relative projection). For SHMS/HMS, the physics DAQ rate limit is 1 KHZ, subject to upgrade. These are failry consistent with what was obtained for the previous proposal that was submitted to PAC 37; ~30 PAC days.

The higher x_Bj point might require a lower beam energy and also lower Q^2. Patricia menioned that the rates code uses nucleon pdf's, which is limited to x_Bj < 1. To look at anything for x_Bj > 1 would require a calculation from Misak Sargisian. Oscar also mentioned the F1F209 cross-section model being a possible input.

Dustin has continued looking at the sytematics related to the polarized target, and prepared a follow-up to his previous write-up. This has been focusing on getting tensor polarization through the convential method and via the relation of vector polarization. He presented a concern that the error propagation for tensor polarization goes something along the line of being 2 x's the error for vector polarization.

Oscar is going to revisit his calcuation on this, as well as what is the possible effect of any polarized beam, which is on his tech-note.

4 April

Joining: OR, PS, EL, KS, DK, NK

Oscar is going through the formalism and making sure things are done correctly. Dustin is working with him on this. he is also trying to better understand the mechanism(s) behind tensor polarization sign flips. Suggested to look at x = 0.1,0.5,1.0 for the calculations to see how well we can overlap with HERMES, for some type of standard.

Simonetta couldn't join, but had sent an email out, on April 3rd, suggesting some thought/consideration about semi-inclusive or exclusive scenarios. Her argument is that through the Bethe-Heitler terms, there would be some enhancement of the various contributing helicity amplitudes.

Dustin prepared a write-up detailing the exercise he did in working through the formalism of the Hoodbhoy,Jaffe,Manohar paper. His finding is that the asymmetry method seems a lot more plausible than the cross-section difference. He is working on relating the statistical and systematic aspects.

Elena has been using the rates code from Patricia and looking at many scenarios, using different detectors/spectrometers. This is assuming 11 GeV beam at 90 nA and a packing fraction of 0.60. The plots can be seen here. Looking at dependencies for Q^2, W, theta(scattering), and minimizing error bars.

19 March

Joining: OR, PS, SL, EL, KS, JP, NK

Oscar has produced a kinematics table suitable for JLab. After going through the relevant literature, he looked into coherence length, which seems to be related to mutliple scattering. Lower x_Bj may be more sensitive to b1, higher x_Bj more sensitive to exotic spin-1 effects. Simonetta mentioned that coherence isn't exclusive to multiple scattering and that higher x_Bj could be a segue-way to nuclear effects.

Simonetta, her student Kunal, and Dustin are working on understanding the formalism in the Jaffe-Hoodbhoy-Manohar paper. This is to clarify the observables of interest for this measurement. They will report next meeting.

Patricia has been looking at the rates/kinematics requirements, for the asymmetry method. She has seen that lower x_Bj is considerably more difficult to access. After an exhcnage of emails between her, JP, and Oscar, it was realized that a particular dilution term N_D is already folded into the calculations. This was giving a suppression factor of about 400. With this being (possibly) resolved, the measurement seems realistic and encouraging. A lower scattering angle is needed (~8 degrees), and it seems that HMS/SHMS are suitable for this. Ellie will be helping with this effort.

Karl mentioned that it is realistic to expect 20-22% tensor polarization, using conventional methods. This is for ND_3. After talking with Don and Chris (Keith), it seems that it is feasible to get a negative tensor polarization. Using deuterated lithium, it is possible to expect about 40% tensor polarization, but there is the trade-off of having less beam current, needing a dilution fridge.

Karl has also looked into the idea of having a measurement of T20 (elastic), for an independent measurement of the poarization. The physics measurement involves coincidence, tagging a recoil deuteron. However, JP pointed out that for the purpose of polarization measurement, this can be done with single arm and the T20 (world) data can be used for reference. This makes it seems more doable.

5 March

Joining: OR, PS, EL, KS, JP, NK

For the asymmetry method, it seems that the target polarization needs to be parallel with the q-vector (virtual gamma). This would probably entail the use of spectrometers, because the setting would rotate some for each kinematic setting and the detectors would need to adjust accordingly. The quantities of interest are A_zz & b_1.

The issue with this is understanding/mitigating the contamination from the various spin observables; g_1,2, A_1,2, b_2,4. These need to be cancelled to a level at/below the b_1 errors (~10^-4). g_2 ~10*b_1 in the higher x_Bj region, which is of interest. One other lever arm for this is to ensure there is minimal beam polarization.

Patricia is going to be looking at the rates for this. She is also going to start with assuming there being no beam polarization and try to include it later.

Regarding magnets, based on Oscar's calculations, a suitable magnet would need an aperture of ± 15 degrees (at least) to accommodate the ~30 degree range of the q-vector. Also, the magnet would need to be able to space for a target length of 3-4 cm.

Please let me know if I missed anything. I know there was also some talk of the Jaffe + friends method, which was in the previously submitted proposal, expect to adjust using asymmetries.