Radiative distortion of kinematic edges in cascade decays

TL;DR

This paper analyzes how radiative effects distort the kinematic edges in cascade decays of new particles, providing a detailed next-to-leading order calculation to improve mass measurements in high-energy collisions.

Contribution

It introduces a systematic expansion approach for calculating radiative distortions of kinematic edges in cascade decays at NLO in QCD, including universal and process-dependent features.

Findings

Next-to-leading order calculation of invariant mass distribution near kinematic edges.

Separation of contributions into hard, collinear, and soft components.

Identification of universal and process-specific features in the edge region.

Abstract

Kinematic edges of cascade decays of new particles produced in high-energy collisions may provide important constraints on the involved particles' masses. For the exemplary case of gluino decay $\tilde{g}\to q\bar q \tilde{\chi}$ into a pair of quarks and a neutralino through a squark resonance, we study the hadronic invariant mass distribution in the vicinity of the kinematic edge. We perform a next-to-leading order calculation in the strong coupling $\alpha_s$ and the ratio of squark width and squark mass $\Gamma_\tilde{q}/m_\tilde{q}$, based on a systematic expansion in $\Gamma_\tilde{q}/m_\tilde{q}$. The separation into hard, collinear and soft contributions elucidates the process dependent and universal features of distributions in the edge region, represented by on-shell decay matrix elements, universal jet functions and a soft function that depends on the resonance propagator and soft Wilson lines.