The CCFM Monte Carlo generator CASCADE

TL;DR

The paper introduces CASCADE, a full hadron-level Monte Carlo event generator for e-p, gamma-p, and p-pbar processes that implements the CCFM evolution equation via backward evolution with off-shell matrix elements. It details the unintegrated gluon density, scale choices for $\alpha_s$, and quark masses, and describes how leptoproduction, photoproduction, and hadroproduction are simulated with both initial and final-state showers and Lund string fragmentation. A key contribution is the integration of CCFM-based initial-state radiation with off-shell matrix elements into a complete event generator, including remnant treatment and data-driven unintegrated gluon densities stored in external grids. The work enables efficient, hadron-level predictions in small-x and high-energy regimes, with configurable parameters for kinematics, subprocesses, showers, and structure functions, published with an accompanying example and modular components for broader use and comparison with alternative approaches.

Abstract

CASCADE is a full hadron level Monte Carlo event generator for e-p, gamma-p and p-p_bar processes, which uses the CCFM evolution equation for the initial state cascade in a backward evolution approach supplemented with off-shell matrix elements for the hard scattering. A detailed program description is given, with emphasis on parameters the user wants to change and common block variables which completely specify the generated events.

Figures (1)

• Figure 1: Kinematic variables for multi-gluon emission. The $t$-channel gluon four-vectors are given by $k_i$ and the gluons emitted in the initial state cascade have four-vectors $p_i$. The maximum angle for any emission is obtained from the quark box, as indicated with $\Xi$.