<div dir="ltr"><div><br></div><div>sorry, meant to reply to everybody on this....</div><div><br></div><div>-Karl</div><br clear="all"><div><br></div>
<br><br><div class="gmail_quote">---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Karl Slifer</b> <<a href="mailto:karl.slifer@unh.edu">karl.slifer@unh.edu</a>><br>
Date: Fri, Apr 19, 2013 at 10:01 AM<br>Subject: Re: [b1_ana] b1 higher twist<br>To: Dustin Keller <<a href="mailto:dustin@jlab.org">dustin@jlab.org</a>><br><br><br><div dir="ltr"><br><div>Hi Dustin,</div><div><br></div>
<div>Yes, considering your careful systematic study, I think the best place to focus may be the x>1 region. Patricia previously showed some predictions (from Misak?) for a quite large tensor asymmetry and some strong interest from several theorists. We put that on the back burner at the last PAC, but it seems very promising and is very closely related to the inclusive DIS measurement we had been considering. We would have to step down the incident energy a bit, and Ellie will need to tweak the rates code a bit. Focusing on this region also makes it easier (in principle) to simultaneously measure P_zz via the elastic asymmetry. </div>
<div><br></div><div>Simonetta, I am *definitely* interested in your proposal, although I believe realistically that it will need to be for next year's PAC. I'm happy to start working on this also, but I believe our focus has to be on proposing a 'simple' inclusive experiment for this PAC.</div>
<div><br></div><div><br></div><div>-Karl</div></div><div class="gmail_extra"><br clear="all"><div><div><div><div>---<br><div>Karl J. Slifer<div>Assistant Professor</div><div>University of New Hampshire<br>
<div>Telephone : <a>603-722-0695</a></div></div></div></div></div></div></div><div><div class="h5">
<br><br><div class="gmail_quote">On Fri, Apr 19, 2013 at 9:46 AM, Dustin Keller <<a href="mailto:dustin@jlab.org">dustin@jlab.org</a>> wrote:<br><blockquote class="gmail_quote">
Hi b1,<br>
Axx is the very best possible tensor polarized observable that we can<br>
extract being it is available without negative polarization. But just a<br>
reminder about the uncertainty, the range of systematic uncertainty in Axx<br>
would be around the green point (middle point) in the plot I showed. The<br>
uncertainty in the observable we are discussing now would be a combination<br>
of the uncertainty in Axx and the unpolarized cross section. This is true<br>
for both statistical and systematic. So if we are able to find additional<br>
points of interest at say elastic or something else then we may as well<br>
use b1 as additional motivation. Otherwise the overall concern has not<br>
changed.<br>
<font color="#888888"><br>
dustin<br>
</font><div><div><br>
<br>
<br>
<br>
On Fri, 19 Apr 2013, Oscar Rondon-Aramayo wrote:<br>
<br>
> Hi Simonetta,<br>
><br>
> Thank you for checking that Jaffe's formulas refer to the electron beam. It<br>
> would be more difficult to measure things with the field along the q vector.<br>
><br>
> We don't need to do two separate measurements (in the sense of measuring<br>
> first one cross section and then the other). We can have two target cells in<br>
> the beam at the same time, one polarized, the other unpolarized. They would<br>
> essentially have the same acceptance. Corrections for the residual<br>
> difference in acceptances can be investigated following the method used 25<br>
> years ago by the EMC experiment that found the proton spin crisis.<br>
><br>
> The EMC had to take data on two targets of opposite polarizations, because<br>
> they could not flip the helicity of their muon beam. Nevertheless, they<br>
> managed to control the systematic effects of their acceptances, etc. A<br>
> discussion of their method is posted on my b1 page<br>
> <a href="http://twist.phys.virginia.edu/~or/b1/EMC-piegaia_thesis.pdf">http://twist.phys.virginia.edu/~or/b1/EMC-piegaia_thesis.pdf</a><br>
><br>
> The method I suggested is based on the EMC approach,<br>
> <a href="http://twist.phys.virginia.edu/~or/b1/b1_method.pdf">http://twist.phys.virginia.edu/~or/b1/b1_method.pdf</a><br>
><br>
> with the difference being one cup polarized, the other not, and alternating<br>
> them during the run, just like the EMC did. Narbe has already done<br>
> simulations that show we can cleanly separate the events from each cup, see<br>
> <a href="http://twist.phys.virginia.edu/~or/b1/zbeam2.eps">http://twist.phys.virginia.edu/~or/b1/zbeam2.eps</a><br>
> (He has many more examples, I'll send links to his plots folder later)<br>
><br>
> So, my view is that I think the method can achieve the necessary statistical<br>
> precision, and I'm not yet convinced that the systematics cannot be<br>
> controlled to the corresponding precision.<br>
><br>
> For example, in the outline of the method I proposed, the \delta pf that is<br>
> introduced before eq. (10) is a relative fraction, should really be dpf/pf.<br>
> So in eq. (11), the contribution of the dilution factor is suppressed by the<br>
> relative error on the packing fraction, which is about 4% for current<br>
> experiments (SANE, RSS) and can be made smaller by using targets shaped as<br>
> disks, instead of irregular fragments, etc. For an error in f itself ~<br>
> 0.05*f (RSS achieved 0.047*f), and f=0.3, we have a systematic error on b1<br>
> due to f and pf of 0.05*0.3*0.04 = 6E-4. Remember that f and pf are proxies<br>
> for the target thickness and unpolarized contributions.<br>
><br>
> The same kind of relative errors are involved in the propagation of the<br>
> differences in charge and acceptance. We need to estimate them<br>
> conservatively, following the EMC approach, before reaching conclusions.<br>
><br>
> Finally, there is the method of taking the ratio sigma_pol/sigma_unpol<br>
> discussed in Anklin's and Boeglin's proposal, which could be an alternative<br>
> to the EMC method, and could be directly applied to the data taken<br>
> simultaneously on polarized+unpolarized cups, as I propose.<br>
><br>
> Cheers,<br>
><br>
> Oscar<br>
><br>
> On Thu, 18 Apr 2013 18:21:54 -0400<br>
> "Simonetta Liuti" <<a href="mailto:sl4y@cms.mail.virginia.edu">sl4y@cms.mail.virginia.edu</a>> wrote:<br>
>> Hi All,<br>
>><br>
>> even if higher twists are negligible, I am skeptical of the Jaffe et al.<br>
>> formulae for extracting b_1 (Chapter 6).<br>
>><br>
>> In fact, I checked that the observable is OK in the sense that they are<br>
>> referring to the electron beam (and not the virtual photon).<br>
>><br>
>> However, I expect systematic errors to be very big. The "polarized cross<br>
>> sections" observables can be obtained with two separate measurements. A<br>
>> polarized spin 1 target one, and an unpolarized one. The two measurements<br>
>> have to be carried out separately, just to be clear. And this is going to<br>
>> impact the systematics.<br>
>> This is exactly why Hermes came up with A_zz which only involves target<br>
>> polarization.<br>
>> I do not see the advantage of going back to Section 6 of Jaffe et al.,<br>
>> while one could do something new and exciting measuring deuteron DVCS<br>
>> asymmetries.<br>
>><br>
>> However...please let me know what you think.<br>
>> Simonetta<br>
>><br>
>> On Thu, 18 Apr 2013 16:06:07 -0400<br>
>> "O. A. Rondon" <<a href="mailto:or@virginia.edu">or@virginia.edu</a>> wrote:<br>
>>> Hi,<br>
>>><br>
>>> There is a paper by Hoodbhoy, Jaffe and Sather, which says that higher<br>
>>> twist (twist-4) effects on b1 at Q^2 = 1 GeV^2 are only 5%. So they<br>
>>> would seem negligible at the kinematics of our proposal or HERMES. See<br>
>>><br>
>>> <a href="http://dx.doi.org/10.1103/PhysRevD.43.3071">http://dx.doi.org/10.1103/PhysRevD.43.3071</a><br>
>>><br>
>>> Cheers,<br>
>>><br>
>>> Oscar<br>
>>> _______________________________________________<br>
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>><br>
>> **************************************************************<br>
>> **************************************************************<br>
>> Prof. Simonetta Liuti telephone <a href="tel:%28434%29%20982-2087">(434) 982-2087</a><br>
>> Department of Physics FAX <a href="tel:%28434%29%20924-4576">(434) 924-4576</a><br>
>> University of Virginia home <a href="tel:%28434%29%20973%209593">(434) 973 9593</a><br>
>> 382 McCormick Rd.<br>
>> PO Box 400714<br>
>> Charlottesville, VA 22904-4714<br>
>><br>
><br>
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