Some explanations
=================

The Higgs->gamma gamma signal and QCD background at the Tevatron and LHC 
can be evaluated using the ResBos_P code, 
available at http://hep.pa.msu.edu/resum/index.html#AA . 
Other versions of the ResBos program may not have all relevant 
implementations in them.

The above link contains all files needed to compute Higgs signal 
and diphoton background cross sections sufficient shown in our 2007 papers. 
These files include all input cross section grids, resbos.in configuration files, and
shell scripts for matching the _background_ resummed cross section 
at small transverse momentum Q_T to the perturbative cross section at large Q_T.

With this code, you don't need to separately compute the resummed, perturbative, 
and asymptotic cross sections and match them by hand.  Here is how it works. 
To make the calculation efficient, the cross sections are supplied to ResBos in two ways:

a) in the form of an input grid to be interpolated during Monte-Carlo integration; 
this is done in the case of all resummed and asymptotic cross sections, 
and in the case of the Higgs signal Y=PERT-ASYMPTOTIC cross section;

b) in the form of an explicit matrix element evaluated directly 
during the Monte-Carlo integration; this is done in the case 
of the background perturbative cross section.

In the case of the Higgs signal, both resummed and Y=PERT-ASYMPTOTIC cross sections 
are supplied by input grids. For this process, run ResBos 
using the input file resbos_h130.in and W and Y grids for Higgs production posted 
on the website. ResBos will produce an NTUPLE containing the resummed cross section 
matched to the perturbative cross section at large Q_T. 

For the background, the RESUMMED-ASYMPTOTIC cross section is supplied by the grid, 
while the perturbative cross section is calculated by the matrix element.
In this case, ResBos runs one time to compute the RESUMMED-ASYMPTOTIC 
cross sections (obtained by interpolation), and another time 
to compute the perturbative cross section (obtained from the exact matrix element). 
It produces two NTUPLES that must be added together in the very end.

book_ntuple_lhc_public.bat is a shell script that automatically does all this work 
for you. It computes and matches all cross sections for q+qbar->gamma+gamma ("AA") 
and g+g->gamma gamma ("AG") channels. The output is given in the form of three 
NTUPLES for matched cross sections in the q+qbar, g+g, and all channels. 
Use this shell script to reduce possibilities for numerical mistakes.