From or@virginia.edu Tue Nov 25 15:02:05 2003 Date: Tue, 25 Nov 2003 01:22:51 -0500 From: O. Rondon To: Xiaochao Zheng Subject: Re: proposal, presentation etc.. Hi Xiaochao, General comment: The experimental technique that we are proposing to use has already been used several times for both proton and deuteron single arm asymmetry measurements in Hall C and even in Hall B. So we really don't need to worry much about this aspect. Of course, you and everybody need to become familiarized with the polarized target method, but the PAC is aware that the technique works. What I think the PAC will look in more detail is whether the experiment has been optimized for the greatest sensitivity to the ratio, which you have done very well. So it should be OK to emphasize that we are proposing to use a well tested method that has been used successfully, and not be too concerned about explaining things like dilution factor, target operation, etc. in great detail. Detailed comments: - p. 4, end of next to last line, paragraph 3: "...\mu_p = 2.791..." => "...\mu_p = 2.793..." - p. 5, end of 3rd. line: " ...invoked" => "...provoked" - p. 6, 2nd. parag. 4th. line from end: "...polarization transfer fit" is ambiguous. Do you mean that the true ratio is 20% below the Rosenbluth separation analyzed with the PT fit? - p. 7, 2nd. para: line 3 "... the recoiled.." => "... the recoil.." line 4: "..data sets were.." => "..data sets was.." (One set was considered) ".. and were .." => ".. and was .." (here "was" would refer to the one set that was considered as dibaryon evidence, otherwise, "were" would refer to the two sets). - p. 8, sec. 3.2, parag. 2: ". In addition...beam dump." => ". A He bag will be used for transporting the beam downstream of the target to the beam dump". "GEn experiment E93-026 [35, 37]..." => "GEn experiment E93-026 [35] and the Resonances Spin Structure E01-006 [37]..." - p. 9, last parag.: "Using the same method as previous experiment E93-026,.." => "Using the same Secondary Emission Beam Position Monitor - SEM as in previous experiments E93-026 and E01-006 [SEM ref].." \bibitem{SEMref} M. Steinacher, I. Sick, NIM A455 (2000) 759. ..achieved and the beam ..." => "...achieved. An upgrade of the SEM electronics to operate in updating mode at the 30 Hz beam helicity flip rate is desirable, but not required. The beam ..." - p. 10, end of 1st. parag.: "..because of the beam depolarization effect. " => "..because of beam induced radiation damage." 2nd. parag., line 1: "...superconducting dipole magnet.." => "...superconducting Helmholtz coils pair.." next to last line: "5 mm clearance...the coil." => "about 5 mm clearance...the coils." - p. 11, line 2: "..and will serve to dilute.." => "..and will dilute.." - p. 12, Table 1, first row: "4He | 0.37" => "4He (50% packing fraction) | 2.5". There are 0.5 cm upstream + 0.5 cm downstream of LHe outside the 3 cm long target cell plus 3*(1 -pf) cm of LHe in the cell, or 2.5 cm total for the usual 50% p.f. By the way, all this LHe contributes to the d.f. 5th. row: "Titanium.." => "Aluminum.." I see that you are using an outdated table, based on E155 cells. The actual RSS cell materials are at http://www.jlab.org/~jones/rss/rsstgt.htm Only the materials seen by the HMS enter into the dilution factor (NH3, LHe, cell windows, tailpiece windows and 4K Shield windows - all Al). Of course, for radiative corrections and energy loss, the target chamber, beam line and HMS windows need to be included, but that is a separate issue. Fig. 7 label: "Cu-plated Al cell" => "Kel-F plastic cell" 1st. line of text: "opportunistally" => "opportunistically" - p. 13, section 3.5, line 3: "..Table 2 Figure 8..." => "..Table 2. Figure 8..." - p. 15, section 4.4, line 3: "..pf/M = +/- 10%" I don't understand what you mean. Fig. 9 x axis: units (MeV?) Also, are the plots integrated over the HMS horizontal angle acceptance, or just for the central angle? This is related to my suggestion about using cuts in W, rather than in E': W is independent of horizontal angle, while delta depends on theta, so the elastic peak is broader in E' (E'_el changes across the acceptance) than in W. It may be cleaner (and more consistent across Q^2) to cut in W. - p. 16, second parag. last 3 lines: "During a previous experiment [37].." => "In E01-006 [37].." "..dilution factor was determined .." => " dilution factor is expected to be determined.." "..(2.5-3)%." => "..(2.5-3)% over the final state invariant mass range 0.8 GeV <= W <= 2 GeV." " a 2.5% uncertainty." => " a 2.5% uncertainty at the elastic peak." - p. 17, line 2: " ..mirror nuclei ^15 O..." => " ..mirror nucleus ^15 O..." Equations (5) and (6): In the analysis of the nitrogen asymmetry, a factor of 1/3 multiplying A_p15N is missing: there are three free protons in ammonia (three hydrogen atoms), but only one unpaired proton in 15N. So the correction is 0.4%, with 0.1% error (for f = 0.5) section 4.7: Are we sure the Mo and Tsai corrections are identically zero? I would think that the radiative corrections for the cross section difference aren't identical for sigma_unpol*(1+A) and sigma_unpol*(1-A) and therefore, the correction for the difference of cross sections does not entirely cancel with the corrections for the sum. At least this is the case for inelastic, but there maybe exact cancellation for the elastic case, as the draft says. - p. 19, bullet list, line 1: "E_p" => see comments on Appendix: inconsistent use of E and E_b for the beam energy. We should use the conventional notation: E. - p. 20, table 2, total rate row: The total rate quoted is only for the elastic peak. The HMS will count events in a +/- 10% momentum bite, so the total rate in the HMS acceptance will be higher. We need to make sure that this total rate is < ~ 1 KHz, for DAQ reasons. - p. 21, last parag. (continues to p. 22): The HMS will see all q.e. protons from all materials (N, He, Al, etc.), so I think the dilution factor is identical to single arm electron. So single arm proton is even less favorable (no dilution advantage) than stated in the draft. - p. 22, section 6.2: "..as can be seen from Eq. (16) and (17)..". The indicated eqs. aren't clearly related to A_L, A_T. - p. 23, eq. (7): "d\sigma" => "d^2\sigma" 1st. line after eq. (7): "where Q^2 = 4EE'.." Here the standard symbol E for the beam energy is used, but not defined. It should be used everywhere in the proposal, rather than E_b. eq. (8): "d^2\sigma" => "d\sigma" - p. 24, figure 14: Try to put "*" symbols on axes labels (x*, etc.) Appendix B, line 2 and elsewhere: "E_b" => "E" Cheers, Oscar