From afanas@jlab.org Mon Nov 24 13:22:42 2003 Date: Mon, 24 Nov 2003 13:20:10 -0500 From: Andrei Afanasev To: Xiaochao Zheng Subject: Re: radiative correction Dear Xiaochao, I calculated 2-photon exchange corections for polarization asymmetries for your proposal kinematics. The model is the axial-vector dominance fit of 2-photon exchange, where its couypling strength was used as a free parameter to fit Rosenbluth/polarization discrepancy. The numbers are ratios of corrected to uncorrected physical quantities. Q2 0.56 2.10 3.50 eps 0.973 0.945 0.873 Al_cor 0.817 0.786 0.858 As_cor 0.820 0.792 0.870 R_cor 1.003 1.008 1.014 The last line here means that the correction due to two-photon exchange in this model to Gep/Gmp ratio measured via target asymmetry is 0.3%, 0.8% and 1.4% for your kinematic points. I still need to run the code for a conventional radiative correction for your kinematics. Regards, Andrei Xiaochao Zheng wrote: > Hi Andrei: > > Great! That is good enough for now. Thanks! > > Xiaochao > ------------------------------------------------------- > Physics Division-203, Argonne National Laboratory > 9700 South Cass Avenue, Lemont, IL 60439 > Tel: 630-252-3431 Fax: 630-252-6008 > http://www.jlab.org/~xiaochao/ > ------------------------------------------------------- > > On Fri, 21 Nov 2003, Andrei Afanasev wrote: > > >>"Traditional" radiative corrections based on Tsai's formalism for >>elastic scattering are identically zero. But addition of nonfactorizable >>radiation based on Afanasev et al., Phys.Rev.D64:113009,2001, >>Phys.Lett.B514:269-278,2001, Phys.Rev.D65:013006,2002, >>will produce a nonzero correction. I can run our code for your >>kinematics, but I need to know where you cut the radiative tail. >>Let me assume you do it at a single-pion production threshold, OK? >> >>Andrei >> >> >>Xiaochao Zheng wrote: >> >>>How about the "traditional" radiative corrections (based on Mo and Tsai)? >>> >>>Xiaochao >>> >>>------------------------------------------------------- >>>Physics Division-203, Argonne National Laboratory >>>9700 South Cass Avenue, Lemont, IL 60439 >>>Tel: 630-252-3431 Fax: 630-252-6008 >>>http://www.jlab.org/~xiaochao/ >>>------------------------------------------------------- >>> >>>On Fri, 21 Nov 2003, Andrei Afanasev wrote: >>> >>> >>> >>>>Dear Xiaochao, >>>> >>>>Thanks for the numbers. I will send you an estimate for the two-photon >>>>correction later today. >>>> >>>>Regards, >>>>Andrei >>>> >>>>Xiaochao Zheng wrote: >>>> >>>> >>>>>Dear Andrei: >>>>> >>>>>The latest version of the proposal is posted at >>>>>http://www.jlab.org/~xiaochao/pac25/lastest/ >>>>> >>>>>The kinematics table is on page 21. At the moment we just need to know the >>>>>"traditional" radiative corrections (i.e. without the new two-photon >>>>>calculation) for AL and AT at Q2=2.1 and 3.5 points, the size of the >>>>>correction and the uncertainty. >>>>> >>>>>For the two photon correction, if it takes too much time, then we don't >>>>>need a "well developed" calculation. We just need to know the approximate >>>>>amplitude, and will not apply the two-photon correction to our measured >>>>>asymmetry. >>>>> >>>>>Thank you very much and please let me know when you will finish the >>>>>calculation. >>>>> >>>>>Best regards, >>>>> >>>>>Xiaochao >>>>>------------------------------------------------------- >>>>>Physics Division-203, Argonne National Laboratory >>>>>9700 South Cass Avenue, Lemont, IL 60439 >>>>>Tel: 630-252-3431 Fax: 630-252-6008 >>>>>http://www.jlab.org/~xiaochao/ >>>>>------------------------------------------------------- >>>>> >>>>>On Fri, 14 Nov 2003, Andrei Afanasev wrote: >>>>> >>>>> >>>>> >>>>> >>>>>>Hello Xiaochao, >>>>>> >>>>>>I have been working on a model for the 2-photon effect. I need to verify >>>>>>some formulas and then I will send you the predictions for asymmetries. >>>>>> >>>>>>Please send me the updated kinematics of your proposal. >>>>>> >>>>>>Note that 2-photon exchange effect contributes to target asymmetries and >>>>>>recoil polarization in exactly the same way, as required by >>>>>>T-invariance. It includes both single-spin and double-spin observables. >>>>>> >>>>>>Regards, >>>>>>Andrei >>>>>> >>>>>>Xiaochao Zheng wrote: >>>>>> >>>>>> >>>>>> >>>>>>>Hi Andrei: >>>>>>> >>>>>>>Did you have time to calculate the two-photon exchange correction for AL >>>>>>>and AT for the GEp/GMp proposal kinematics I sent you a while ago? The >>>>>>>kinematics changed a little since then. I also wonder if you have a code >>>>>>>handy to calculate the regular radiative correction to elastic >>>>>>>asymmetries, for the case where only the scattered electrons are detected. >>>>>>> >>>>>>>Thank you very much, >>>>>>> >>>>>>>Xiaochao >>>>>>> >>>>>>>------------------------------------------------------- >>>>>>>Physics Division-203, Argonne National Laboratory >>>>>>>9700 South Cass Avenue, Lemont, IL 60439 >>>>>>>Tel: 630-252-3431 Fax: 630-252-6008 >>>>>>>------------------------------------------------------- >>>>>>> >>>>>> >>>>>> >>>>>>-- >>>>>>Andrei Afanasev >>>>>>Staff Scientist, Jefferson Lab >>>>>>tel: (757)269-7251 >>>>>> >>>>>> >>>>> >>>>> >>>>-- >>>>Andrei Afanasev >>>>Staff Scientist, Jefferson Lab >>>>tel: (757)269-7251 >>>> >>>> >>> >>> >> >>-- >>Andrei Afanasev >>Staff Scientist, Jefferson Lab >>tel: (757)269-7251 >> >> > > -- Andrei Afanasev Staff Scientist, Jefferson Lab tel: (757)269-7251