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DVCS related cross-sections

Executables downloadable here provide cross-sections for

, as resulting from global fits to DVCS measurements of CLAS, Hall A, HERMES, H1 and ZEUS collaborations. Five different models are presently available: two (KM09a and KM09b) are described in K. Kumerički and D. Müller, Nucl. Phys. B841 (2010) 1-58, arXiv:0904.0458, while the remaining three are preliminary fits, where KM10a and KM10b are similar to the first two, but they include the LO evolution of the parton sea. KM10 is similar to KM10b, but also normalization of Hall A data is used in fits, and not only ratios. Only last three models are appropriate for xB smaller than 10^(-3) or Q2 larger than 5 GeV^2.

Download

xs-Win.exe (MS Windows, 8 MB)
xs-Lin64.exe (Linux, x86_64, 64 bit, 12 MB)
xs-Lin32.exe (Linux, i686, 32 bit, 8 MB)

These executables are completely self-contained. Because of that they are not very fast. If they are too slow for you contact the authors - we can in principle provide also a much faster library linkable into your software, or even numerical grids for some specific kinematical points. If you need executable for another architecture (e.g. MacOS), contact the authors and be prepared to do some work. Also, if you have quite old Linux machine (more than few years), executables above may not work. Please, contact the authors in this case.

Documentation

Executables are simply invoked like this:

  xs.exe  ModelID  Charge  Polarization  Ee  Ep  xB  Q2  t  phi

This returns cross section (in nb) for scattering of lepton of energy Ee 
on unpolarized proton of energy Ep. Charge=-1 is for electron. Polarization
of lepton is +1 or -1.

ModelID is one of  
   0 debug, always returns 42, 
   1 KM09a - arXiv:0904.0458 fit without Hall A,
   2 KM09b - arXiv:0904.0458 fit with Hall A, 
   3 KM10  - preliminary hybrid fit with LO sea evolution, from Trento presentation,
   4 KM10a - preliminary hybrid fit with LO sea evolution, without Hall A data
   5 KM10b - preliminary hybrid fit with LO sea evolution, with Hall A data


xB Q2 t phi  -- usual kinematics (phi is in Trento convention)

For convenience, if last argument (phi=n) is larger than 2pi, you get grid 
of n equidistant points with phi=0..2pi.

Example:
    ./xs.exe 1 -1 1 27.6 0.938  0.111 3. -0.3 8

0.000  0.18584386497251
0.898  0.09704361389598
1.795  0.03732297043480
2.693  0.02109202422949
3.590  0.01759508608912
4.488  0.02343728118610
5.386  0.06334833619861
6.283  0.18584386497251

Note

If the phase space bounds, given by the minimal values of the Bjorken scaling variable xB and negative momentum transfer squared -t, are exceeded, the cross section is set to zero. Also, because of DVCS kinematics, the upper bound on -t is set by max(Q^2/4, 1) GeV^2, and the lower bound for the photon virtuality by 1.5 GeV^2 = Q^2. Moreover, the cut xB <= 0.5 is implemented for all models and, in addition, models 1 and 2 (which rely on the scaling hypothesis) are restricted to the region Q^2 <= 5 GeV^2 and max(10^-3, xBmin) <= xB. Violating the kinematical cuts will return error. Also note that for convenience each positive value for Ep that is smaller than the proton mass is internally interpreted as the proton mass itself. Finally, the electron mass is set to zero in the the theoretical description.

Authors

Krešimir Kumerički [email] and Dieter Müller [email]

Last update: 2011-05-10