nlodisfit

BK evolved dipole amplitude fitted to HERA data at NLO

This library provides easy access to the dipole-target scattering amplitude obtained by fitting the HERA reduced cross section data at NLO accuracy.

This is the dataset version 1.0 dated on 2020-11-03.

Reference

When using this code, please cite [1] G. Beuf, H. Hänninen, T. Lappi, H. Mäntysaari, Color Glass Condensate at next-to-leading order meets HERA data. Phys. Rev. D102 (2020) 074028, e-Print: 2007.01645 [hep-ph]

Questions and comments to heikki.mantysaari@jyu.fi and henri.j.hanninen@jyu.fi

Building

Requires

Cmake
GSL

How to compile:

 mkdir build
 cd build
 cmake ..
 make

This generates a library build/lib/libamplitude.a that you can link in your own program. The necessary header files can be found from the src directory. For example, see how src/dipole_amplitude.cpp is complied (see src/CMakeLists.txt).

Usage

See example src/dipole_amplitude.cpp

Add ```#include "amplitudelib.hpp"
Read datafile: AmplitudeLib N(datafile);
Initialize interpolation, BK evolution over Y units of rapidity (optional, but makes evaluation of the dipole amplitude faster): N.InitializeInterpolation(Y);
Evaluate dipole: N.DipoleAmplitude(r,Y);

Note that r has units [1/GeV].

Datafiles

The different datafiles can be found as data/dipole-BKTYPE-FITDATA-COUPLING-Y0.dip

The different BK equations (BKTYPE) are

resumbk
kcbk
tbk

The coupling constants (COUPLING) are

parent: Parent dipole
Bal+SD: Balitsky+smallest

The initial rapidity where the BK evolution is started is Y0 (in case of TBK, the number refers to the target rapidity eta_0).

These abbreviations are the same as used in the article referred above.

Evolution rapidity

The initial condition is parametrized at Y=Y0 in case of resumbk and kcbk, and at eta=eta0 in case of tbk. Consequently, the dipole in the rapidity region [0,Y0] (or [0,eta0]) is constant.

When using tbk solution, the rapidity argument in the code refers to the evolution rapidity eta. In case of resumbk and kcbk, it refers to evolution rapidity Y. They are defined in Ref. [1] in Eqs. (16) and (26).