GRAPE-Dilepton (version1.1), A Generator for Dilepton Production in ep Collisions

TL;DR

GRAPE-Dilepton introduces a Monte Carlo generator for dilepton production in ep collisions based on exact tree-level electroweak amplitudes, including $\gamma\gamma$, $\gamma Z^0$, and $Z^0 Z^0$ processes as well as photon internal conversion. It treats the proton vertex across elastic, quasi-elastic, and DIS regimes using dipole form factors and hadron-tensor parameterizations, with ISR/FSR and radiative corrections included, and excludes certain contributions (Higgs, proton–$Z^0$ coupling, resolved-photon Drell–Yan). The package uses GRACE to generate amplitudes and interfaces with PYTHIA and SOPHIA to produce complete hadronic final states, while BASES/SPRING provide cross-section integration and event generation controlled by flexible input cards. This enables precise background estimations for ep collision analyses and expands prior approaches by incorporating interference effects and on/off-shell $Z^0$ contributions across the full proton-vertex kinematics.

Abstract

GRAPE-Dilepton is a Monte Carlo event generator for dilepton production in ep collisions. The cross-section calculation is based on the exact matrix elements in the electroweak theory at tree level. The dilepton productions via $γγ$, $γZ^0$, $Z^0 Z^0$ collisions and via photon internal conversion are taken into account. In addition, the effects of the $Z^0$ on/off-shell production are also included. The relevant Feynman amplitudes are generated by the automatic calculation system GRACE. The calculation of the proton vertex covers the whole kinematical region. This generator has an interface to PYTHIA and SOPHIA to obtain complete hadronic final states.

Figures (3)

• Figure 1: Feynman diagrams included in the (quasi-)elastic process. $e$=$\left\{ e^+,e^- \right\}$, l$^{\pm}$=$\left\{ e^{\pm}, \mu^{\pm}, \tau^{\pm} \right\}$. N means a (dissociated) proton or a nucleon resonance.
• Figure 2: Feynman diagrams included in the DIS process. $e$=$\left\{ e^+,e^- \right\}$, l$^{\pm}$=$\left\{ e^{\pm}, \mu^{\pm}, \tau^{\pm} \right\}$ and $q$=$\left\{\right.$$u$$^{^{(}}$$^{-}$$^{^{)}}$,$d$$^{^{^{(}}}$$^{^-}$$^{^{^{)}}}$,$s$$^{^{(}}$$^{-}$$^{^{)}}$,$c$$^{^{(}}$$^{-}$$^{^{)}}$,$b$$^{^{^{(}}}$$^{^-}$$^{^{^{)}}}$,$t$$^{^{^{(}}}$$^{^-}$$^{^{^{)}}}$$\left.\right\}$.
• Figure 3: Flowchart for the program structure