= Model of Block et al. =

== References ==

|| ![1] || [[http://link.aps.org/doi/10.1103/PhysRevD.60.054024|BLOCK, M. M., GREGORES, E. M., HALZEN, F. and PANCHERI, G., Phys. Rev. D60 (1999) 054024]] ||
|| ![2] || [[http://dx.doi.org/10.1016/j.physrep.2006.06.003|BLOCK, M. M., Phys. Rept. 436 (2006) 71-215]] ||


== Implementation notes ==

Implemented in class `BHModel` (see in [[http://elegent.hepforge.org/doxygen/classElegent_1_1BHModel.html|Doxygen]]).

There have been two issues discovered when implementing the model.

1. The definition of `N_g` is inconsistent between ![1] and ![2]. As confirmed in private communication with the authors, the correct normalisation is such that the average x carried by the gluons is 1/2 - which is the case of the value published in ![1].
1. Using Eq. (478) from ![2] does not give reasonable dsigma/dt. However, if a factor of 1/2 is applied to the r.h.s. (see `BHModel::chi_without_i`) the results overlap with the published predictions from the original authors (see a [[https://elegent.hepforge.org/comparisons/bh/bh_comparison.pdf|test sheet]] with Elegent calculations in green). It is possible that the 1/2 factor was omitted due to confusion with the other 1/2 factor mentioned in point 1.