Hawaiian Vrap

This program is an extension of Vrap-v0.9. Vrap is a program that computes rapidity distributions for production of lepton-pairs via virtual photons, W or Z bosons at hadron colliders at NNLO in QCD. The program was originally developed by Frank Petriello and Lance Dixon. The original version of Vrap can be obtained in Lance Dixon's website.

The code in this repository modifies version 0.9 of Vrap and it is redistributed with permission of the authors.

Citation policy

The original implementation of the numerical program "Vrap" is based on the paper Phys.Rev.D69:094008,2004 [hep-ph/0312266] by C. Anastasiou, L. Dixon, K. Melnikov and F. Petriello.

The extension of "Vrap" with PineAPPL is described in the paper: hep-ph/2302.12124

Please cite both these papers whenever the "Hawaiian Vrap" program is used.

Changes with respect to Vrap

Isoscalar targets

The code in this repository adds and option to use isoscalar targets as a hadron type (piso) in addition to the original pp and ppbar options.

PineAPPL interface

It also interfaces the code with PineAPPL, a library that produces fast-interpolation grids for fitting parton distribution functions.

Apfel-jacobian factors

The calculations used in NNPDF need to match the format of the experimental data. For this a jacobian factor of $\sqrt{2s}$ is applied with respect to the vanilla vrap implementation.

In addition, the data from DYE886 and DYE605 differ by a factor of $\left(\frac{\sqrt{s}}{M}\right)$, which is added as an option to the runcard: jacobian886: True.

See issue #10 for more information.

⚠️ The goal of these modifications is to generate PineAPPL grids for fixed-target Drell-Yan. These grids are used by the NNPDF Collaboration to determine parton distribution functions. As such, this use-case is the only one that has been tested and benchmarked (see regression tests).

How to run

In order to run the code, clone the repository and run the following commands:

git clone https://github.com/NNPDF/Hawaiian_vrap.git
cd Hawaiian_vrap
cd src && autoreconf -fiv && cd ..
mkdir -p build && cd build
../src/configure --prefix=$PWD
make -j4
./Vrap ../regression_test/inputE605nlo.dat 7 0.2 # needs to have NNPDF40_nnlo_as_01180 installed

Disclaimer

As warned in Lance Dixon's webpage, for fixed-target kinematics the results might be slightly off due to an integration problem at high $\tau=\frac{M^2}{s}$.

For large values of M^2/s, as typically encountered in fixed-target production, the version of the program given here is a bit off, due to an integration issue.

A cut on $\tau$ is typically enforced on the data to avoid this issue.