<div dir="ltr">Dear Viktor,<div><br></div><div>I agre with everything, but ... " Therefore, for all our needs we may forget on atomic ff putting it equal to unity." the atomic ff is zero not one.</div><div><br></div><div>Cheers, Ralf</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Jul 3, 2015 at 12:28 PM, Viktor Mokeev <span dir="ltr"><<a href="mailto:mokeev@jlab.org" target="_blank">mokeev@jlab.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Dear Annalisa and Lucilla,<br>
<br>
There is no any trick. At Q^2=0 you should not use l.h.s. of Eq. (12), since you have no cross section with virtual photons at Q^2=0. Instead, you should use r.h.s. of Eq.(12) for virtual photon cross section at Q^2=0, which gives you the real photon cross section. You may see this from Eq.(19). At Q^2--->0 eps_{L}--->0. You need to put eps_{T}=0. for the real photon cross sections with unpolarized real photons. The expression (12) is defined by the requirement that at Q^2--->0, cross section for the processes with virtual photons get transformed to the processes with real photons.<br>
<br>
Now, if you have infinitely small Q^2, than QED gives you a very large number for the virtual photon cross section because of the virtual photon propagator ~1/Q^2. Of course, in reality such huge cross sections were never observed. The point is: at small Q^2 that correspond to distances above the atom size >10^-8 cm, you need to incorporate atomic ff, which screens the photon field reducing measurable cross sections (see the famous Mo and Tsai paper). All processes under studies by us correspond to the distances five order if magnitude smaller than then the atom size. Therefore, for all our needs we may forget on atomic ff putting it equal to unity.<br>
<br>
<br>
Considering the aforementioned questions, may be the paper under completion by Iu. Skorodumina for Bull of Mosc State Univ. should be provided also in English when she will come to USC as some publication for the CLAS Collaboration?<br>
<br>
I use CERN lib d-Wigner function. You may easily find manual on CERNlib in web and use it in any code for your own purposes.<br>
<br>
Please let me know, iof you have any further questions.<br>
<br>
Tanti Cordiali Saluti,<br>
Victor<br>
<br>
<br>
<br>
----- Original Message -----<br>
From: "annalisa dangelo" <<a href="mailto:annalisa.dangelo@roma2.infn.it">annalisa.dangelo@roma2.infn.it</a>><br>
To: "Viktor Mokeev" <<a href="mailto:mokeev@jlab.org">mokeev@jlab.org</a>>, "Lucilla Lanza" <<a href="mailto:lucilla.lanza@roma2.infn.it">lucilla.lanza@roma2.infn.it</a>><br>
Sent: Friday, July 3, 2015 11:28:57 AM<br>
Subject: a few questions about the implementation of the hybrid baryons contributions in the event generator<br>
<br>
Dear Victor,<br>
Lucilla and I spent some time to fully understand the model you propose in<br>
chapter IX of the LOI. We think we understand most of it and we are<br>
thinking<br>
about how to implement it using the AmpTool framework.<br>
<br>
Next step would be to extensively write down all the terms in equation<br>
(7) of the LoI, including all the<br>
reduced Wigner rotation matrixes d^(Jr)_mu_nu(cos theta_k).<br>
<br>
Before starting the work we were wondering if you already have written<br>
them down in a form simply accessible<br>
by e-mail.<br>
<br>
We also have a question regarding the behavior of the virtual photon<br>
flux (eq 13 or 15 of the LoI) at Q^2 ->0 limit.<br>
It looks like this flux diverges since Q^2 appears at the denominator.<br>
Where is the trick?<br>
<br>
Thank you in advance<br>
All the best<br>
Lucilla & Annalisa<br>
<br>
--<br>
================================================<br>
Prof. Annalisa D'Angelo<br>
Dip. Fisica, Universita' di Roma "Tor Vergata"<br>
INFN Sezione di Roma Tor Vergata, Rome Italy<br>
<a href="mailto:email%3Aannalisa.dangelo@roma2.infn.it">email:annalisa.dangelo@roma2.infn.it</a><br>
Jefferson Laboratory, Newport News, VA USA<br>
Email: <a href="mailto:annalisa@jlab.org">annalisa@jlab.org</a><br>
Tel: <a href="tel:%2B%2039%2006%2072594562" value="+390672594562">+ 39 06 72594562</a><br>
Fax: <a href="tel:%2B%2039%2006%202040309" value="+39062040309">+ 39 06 2040309</a><br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div>Prof. Ralf W. Gothe</div>
<div>Department of Physics and Astronomy</div>
<div>University of South Carolina</div>
<div>Columbia, SC 29208</div>
<div> </div>
<div>Phone: 803 777 9025</div>
<div>Fax: 803 777 3065</div></div>
</div>