Radiative distortion of kinematic edges in cascade decays

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.

Comments: 15 pages, 5 figures