proton photon spectrum

Dear Murat,

please let us know what did you try?
Did you try to evaluate process with two photons in the initial state,
choosing the in state for the photon to be a proton?

Regards
Alexander

On Tue, 31 Jul 2018, 14:47 Murat, <email address hidden>
wrote:

> New question #671251 on CalcHEP:
> https://answers.launchpad.net/calchep/+question/671251
>
> Hello,
>
> I could not find the proton photon spectrum in Calchep? What is the open
> state of the spectrum?
>
> Sincerly Yours,
>
> Murat
>
> --
> You received this question notification because your team CalcHEP is an
> answer contact for CalcHEP.
>
--

___________________________
Prof. Alexander S Belyaev (<email address hidden>)
https://www.hep.phys.soton.ac.uk/content/alexander-belyaev
School of Physics & Astronomy, University of Southampton, Office: 5047
SO17 1BJ, TEL.: +44 (0)23 8059 8509

Dear Belyaev,

First, thank you for your response. I will examine photon-photon processes in ep collisions. The first photon will be emitted from the electron. I know this photon spectrum. Second, The first photon will be emitted from the proton, and I dont find this spectrum.

Sincerly Yours,

Murat

Just compile any process with incoming photon.

In numerical menu you will see

                    IN state

Go here and find S.F.1 / S.F.2   menu items,

They allow to set  distribution for first/second  incoming particles.

Among them there is Proton.Photon   distribution.

Best

     Alexander Pukhov

On 07/31/2018 03:13 PM, Murat wrote:
> Question #671251 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/671251
>
> Status: Answered => Open
>
> Murat is still having a problem:
> Dear Belyaev,
>
> First, thank you for your response. I will examine photon-photon
> processes in ep collisions. The first photon will be emitted from the
> electron. I know this photon spectrum. Second, The first photon will be
> emitted from the proton, and I dont find this spectrum.
>
> Sincerly Yours,
>
> Murat
>

Hi again,

That was not exactly the case. I apologize for asking the wrong question.

In CalcHEP manaul, it gives a possibility to reduce the process of
electro-production to the photo-production one with an appropriate photon
spectrum:

f(x) = (q^2 alf/(2pi))(log((1 − x)/(x^2 del))(1 + (1 − x)2)/x − 2(1 − x −del x2)/x),

This spectrum applies to a photon emitted from the electron. Does the same spectrum apply to the photon emitted from the proton? Is the photon open equation emitted from the proton also valid for the above equation? Or is the photon spectrum emitted by the proton different? If it is different, what is the open state of this equation?

I want to write the spectrum of the photon emitted from the proton as an equation

Sincerly Yours,

Murat

Codes for proton and electron are different. But now I don't remember
what is a reason of this difference.

Code disposed in c_source/strfun/sf_epp.c   See comments in the file:

// * *********************************************************
// *  Equivalent photon approximation structure function.    *
// *     Improved Weizsaecker-Williams formula               *
// *   V.M.Budnev et al., Phys.Rep. 15C (1975) 181           *
// *      see  details on page 273                           *
// * The code was written by Muriel Vander Donckt *
// * *********************************************************

   f+=(1-b)*y/(4*qq*qq1*qq1*qq1);  // here  sign  is differnt with
Budnev et al
       // realization by Muriel Vander Donckt. Investigation by Richard
Ruiz rev
       // Budnev et al have mistake in this place.

====================

Code for  photons emitted by electron  is stored in epa.c file. Here

/* ********************************************************* */
/*  Equivalent photon approximation structure function.   * */
/*     Improved Weizsaecker-Williams formula              * */
/*      C.F.Weizsaecker, Z.Phys. 88 (1934) 612            * */
/*      E.J.Williams,    Phys.Rev. 45 (1934) 729          * */
/*                                                        * */
/*   V.M.Budnev et al., Phys.Rep. 15C (1975) 181          * */

But I do not remember what is the difference.

*But may be  you need something else?  Do you need  photon pdf structure
function  from parton density?
*

Then  use PDT: or LHA menu items.

PDT contains 2 MRST2004 and 2 NNPDF  distributions.

Via LHA menu item you have approach to all LHA structure functions.
LHAPDF  package should be installed and path to LHA library has to be
defined via LHAPDFPATH.

Best

    Alexander Pukhov

*
*

**

On 07/31/2018 04:08 PM, Murat wrote:
> Question #671251 on CalcHEP changed:
> https://answers.launchpad.net/calchep/+question/671251
>
> Status: Answered => Open
>
> Murat is still having a problem:
> Hi again,
>
> That was not exactly the case. I apologize for asking the wrong
> question.
>
> In CalcHEP manaul, it gives a possibility to reduce the process of
> electro-production to the photo-production one with an appropriate photon
> spectrum:
>
> f(x) = (q^2 alf/(2pi))(log((1 − x)/(x^2 del))(1 + (1 − x)2)/x − 2(1 − x
> −del x2)/x),
>
> This spectrum applies to a photon emitted from the electron. Does the
> same spectrum apply to the photon emitted from the proton? Is the photon
> open equation emitted from the proton also valid for the above equation?
> Or is the photon spectrum emitted by the proton different? If it is
> different, what is the open state of this equation?
>
>
> I want to write the spectrum of the photon emitted from the proton as an equation
>
> Sincerly Yours,
>
> Murat
>

Thanks Alexander Pukhov, that solved my question.