<div dir="ltr"><div><br></div><div>Hi all,</div><div><br></div><div>Below please find a draft response to the readers. I'd appreciate any/all feedback.</div><div><br></div><div>Thanks to Oscar and Dustin for sending comments already. I hope I have incorporated them satisfactorily, but let me know if not.</div>
<div><br></div><div>Dustin : any ETA for the updates to the technote? Ideally we can send them this short email and then provide your note for the full details. </div><div>Most important would be to clarify the overall drift numbers, as I had the same confusion that Ellie raised.</div>
<div><br></div><div>I'll have time to work on this tomorrow morning and early afternoon, but have to leave for DC mid afternoon. I'd love to get a response to Ewa before then if possible.</div><div>
<br></div><div>thanks much,</div><div><br></div><div>
-Karl</div><div><br></div><div><br></div>-----------------------------<br><div class="gmail_quote"><br>
The measurement is very sensitive to the systematic effects and good control of them is the<br>
key point. Therefor I would like to know if there are any estimates of expected size of effects from:</div><div class="gmail_quote"><br></div><div class="gmail_quote">RESPONSE: We agree with the TAC assessment that systematic errors from drifts must be mitigated, but</div>
<div class="gmail_quote"> that they are manageable with a combination of hardware upgrades and a dedicated collaboration </div><div class="gmail_quote"> effort. We note that the recent g2p experiment involved a similar situation where a significant</div>
<div class="gmail_quote"> commitment was made to install and run this polarized target, but separate groups were tasked</div><div class="gmail_quote"> with substantial tasks of beamline, DAQ and detector upgrades. We are grateful to the TAC for</div>
<div class="gmail_quote"> pointing out several effects which were not explicitly discussed in our submitted proposal. We </div><div class="gmail_quote"> have written a short note discussing each of these and conclude that the overall systematic</div>
<div class="gmail_quote"> uncertainty is still of the same order as estimated in the proposal.</div><div class="gmail_quote"><br>
1. beam - one aspect is the stability in terms of position and divergency<br>
this can change acceptance and produce false asymmetries<br><br></div><div class="gmail_quote">RESPONSE: (The TAC report pointed out that the false asymmetries from beam position drifts are easily</div><div class="gmail_quote">
removed by "regression". Can someone fill in the details? I assume that this just means</div><div class="gmail_quote"> that the parity feedback on position is very good, but we need some numbers/examples to</div>
<div class="gmail_quote"> back this up. This is dealt with in section 1.1.4 of the note, but there are few details.)</div><div class="gmail_quote"><br></div><div class="gmail_quote">
2 beam polarization - how the unpolarized beam will be obtained what kind of effects are<br>
expected from beam polarization (ie. to which level exact averaging of opposite beam polarity<br>
is needed and how the phase space of the beam is polarization dependent)</div><div class="gmail_quote"><br></div><div class="gmail_quote">RESPONSE: JLab E06-010 (Transversity) spin-averaged a highly polarized (~80%) beam in order to</div>
<div class="gmail_quote"> obtain an "unpolarized" beam. The parity feedback allowed for knowledge of the residual</div><div class="gmail_quote"> beam polarization at the 2.2*10^{-5} level, according to the lumi monitors. Please see attached</div>
<div class="gmail_quote"> plot, which shows the beam asymmetry from that experiment.</div><div><br></div><div class="gmail_quote"><br>
3. temperature effects on the efficiency (and stability of the detectors allignment) - proposed scheme<br>
of polarization reversals will give data with target polarization during the day and unpolarized<br>
at night or vice versa. This can introduce false asymmetry related to any kind of temperature<br>
dependence in efficiency or allignment. Was it estimated ? Are there any studies of this kind of effects<br>
in previous experiments?</div><div class="gmail_quote"><br></div><div class="gmail_quote">RESPONSE: (This could be addressed by the transversity slides, but I'm not sure if the pion yield plot </div><div class="gmail_quote">
addresses this. The main sensitivity to temperature will be the BCMs and Dave has plans</div><div class="gmail_quote"> to isolate them, but I don't have any details of that yet.)</div>
<div class="gmail_quote"><br></div><div class="gmail_quote"><br></div><div class="gmail_quote"><br>
4. for the drift of efficiency and its time dependence (page 25) linear evolution in time is assumed.<br>
for which effects it is justified? It is clear that for example changes in packing factor of dilution factor<br>
can have "step like" characteristics. Are there any ideas to what level such effects can be controlled<br>
during the run?<br>
<br>RESPONSE : (Linear and sinusoidal drifts are the only type that I've seen. Higher orders could theoretically </div><div class="gmail_quote"> be present, but if they were I suppose they would become an issue for all experiments, not just ours.)<br>
"Step-like" changes in the packing factor or dilution factor have only been observed once in 700 hours</div><div class="gmail_quote"> of running the polarized target. It was immediately obvious from the change in polarization. If it</div>
<div class="gmail_quote"> occurs during this experiment, it would impact only a single pol/unpol cycle, which is either a 12 hour or</div><div class="gmail_quote"> 24 hour portion of data. This data would need to be either discarded or handled with care.</div>
<div class="gmail_quote"><br></div><div class="gmail_quote"><br>
In the proposal "consistency checks on measured cross section for each run" is mentioned.<br>
What precisely is meant? At what level it can be done for the proposed measurement? Please give<br>
more detail, especially on the precision of such test.<br>
<br>RESPONSE : Typically we can monitor the unpolarized yields to the better than 1% level. Luminosity monitors</div><div class="gmail_quote"> installed around the beamline can be monitored to the ?? level (J.P.?)<br>
<br><br>The other test mentioned in the proposal, where I would like to have some more comments on is "the<br>
measurements of dilution and packing factor - with carbon target "- what exactly is planed and which<br>
precision can be obtained? is it included in the beam time estimate?</div><div class="gmail_quote"><br></div><div class="gmail_quote">RESPONSE: The polarized target material is deuterated ammonia (ND_3). </div><div class="gmail_quote">
We determine the dilution factor by the ratio of simulated radiated rates on D to total</div>
<div class="gmail_quote"> rates. The pf is calculated by interpolating the ND3 measured rates between simulated </div>
<div class="gmail_quote"> rates for different packing factors, with the simulation calibrated by the measured rates</div>
<div class="gmail_quote"> on a carbon target of known thickness. The systematic uncertainty of this process</div>
<div class="gmail_quote"> is at the 4% level. It is important to note that the dilution factor is a scale factor so the </div><div class="gmail_quote"> uncertainty is an overall scale factor. We have 6 hours assigned to this task in our overhead table 4. </div>
<div class="gmail_quote"> This is a relatively short time since all that is needed is to measure the unpolarized cross section </div><div class="gmail_quote"> from a carbon disk, and the rate is usually quite high. </div>
<div class="gmail_quote"><br></div><div class="gmail_quote">
<br>
It would be interesting to see comparison of expected statistical errors in each bin with expected false<br>
asymmetries from time variation of beam and efficiency/acceptance.<br>
<br>RESPONSE: We now have plots graphically showing the full systematic uncertainty, both from the normalization</div><div class="gmail_quote"> dependent factors and the possible drifts. The plots are shown in the technote.<br>
<br><br>
What are the arguments for proposed binning in x?<br>
the last bean is clear, as much data in this configuration as possible, but splitting of SHMS data taking<br>
in 3 intervals is not discussed from the optimalization point of view, it would be good to have it in the<br>
presentation.</div><div class="gmail_quote"><br></div><div class="gmail_quote">RESPONSE : (Hmm. Not sure how to answer this. Simple answer is that the points represent the largest</div><div class="gmail_quote">
spread in x that allows a reasonable overlap with HERMES in a reasonable amount of beam-time.</div><div class="gmail_quote"> Ellie has optimized to avoid large systematics from F1, and suppression of rates. )</div>
<div class="gmail_quote"><br></div><div class="gmail_quote"><br>
<br>
In general, also the authors call the measurement "ratio method" it is the cross section difference method<br>
as the two data sets are taken at different time. Advantage of "ratio method" can be fully used when two<br>
target cels are exposed at the same time and next order is reversed. Such configuration allows several<br>
additional cross checks, but requires two cell target.<br>
<br>RESPONSE : We have examined a two cell configuration, and while it is attractive for the reason you point</div><div class="gmail_quote"> out, it was not clear at the time of the proposal submission that it significantly reduced the </div>
<div class="gmail_quote"> overall systematic uncertainty. We will continue to examine this option and are open to using </div><div class="gmail_quote"> it if we are convinced the systematic improvement is significant. </div>
<div class="gmail_quote"> </div><div class="gmail_quote"><br><br>
test of Close-Kumano sum rule - it is very hard to do such test with limited coverage in x, may be some<br>
estimates of contribution measured/extrapolated can be done for specific models. For the models mentioned<br>
on page 17 - can one get some idea what would be the contribution in measured range?<br>
</div><br><div>RESPONSE : Yes, this in an excellent suggestion. G. Miller and M. Sargian have provided us their curves. </div><div> We need to integrate to see the contributions for x<0.15 and x>0.5. (Ellie, I think you have these </div>
<div> now. Can you look into this?)</div><div> </div><div><br></div><div><br></div></div>