Bremsstrahlung simulation in K to pi l^pm nu_l (gamma) decays

TL;DR

This paper evaluates the precision of the PHOTOS Monte Carlo program in simulating bremsstrahlung effects in K to pi l nu decays, achieving a 0.2% relative accuracy by implementing the exact matrix element.

Contribution

The paper introduces an exact matrix element implementation for the PHOTOS program specific to K to pi l nu decays, improving simulation accuracy.

Findings

Achieved 0.2% relative precision in bremsstrahlung simulation.

Validated the implementation against exact matrix elements.

Enhanced the reliability of QED effects modeling in decay simulations.

Abstract

In physics simulation chains, the PHOTOS Monte Carlo program is often used to simulate QED effects in decays of intermediate particles and resonances. The program is based on an exact multiphoton phase space. In general, the matrix element is obtained from iterations of a universal kernel and approximations are involved. To evaluate the program precision, it is necessary to formulate and implement within the generator the exact matrix element, which depends on the decay channel. Then, all terms necessary for non-leading logarithms are taken into account. In the present letter we focus on the decay K to pi l^pm nu_l and tests of the PHOTOS Monte Carlo program. We conclude a 0.2% relative precision in the implementation of the hard photon matrix element into the emission kernel, including the case where approximations are used.