Notes

2013

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 talkign 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.