Pinning down the Invisible Sneutrino

TL;DR

This paper explores methods to determine the sneutrino mass at the ILC when it decays invisibly, using chargino decay measurements and detailed simulations including backgrounds and radiation effects.

Contribution

It presents a comprehensive simulation study for measuring sneutrino properties via chargino decays at the ILC, accounting for realistic experimental conditions and backgrounds.

Findings

Sneutrino mass can be inferred from chargino decay spectra.

Radiation effects and backgrounds significantly affect mass measurement accuracy.

Optimal strategies for sneutrino mass determination are discussed.

Abstract

For points in SUSY parameter space where the sneutrino is lighter than the lightest chargino and next-to-lightest neutralino, its direct mass determination from sneutrino pair production process at e+e- collider is impossible since it decays invisibly. In such a scenario the sneutrino can be discovered and its mass determined from measurements of two-body decays of charginos produced in pairs at the ILC. Using the event generator WHIZARD we study the prospects of measuring sneutrino properties in a realistic ILC environment. In our analysis we include beamstrahlung, initial state radiation, a complete account of reducible backgrounds from SM and SUSY processes, and a complete matrix-element calculation of the SUSY signal which encompasses all irreducible background and interference contributions. We also simulate photon induced background processes using exact matrix elements. Radiation effects and the cuts to reduce background strongly modify the edges of the lepton energy spectra from which the sneutrino and chargino mass are determined. We discuss possible approaches to measure the sneutrino mass with optimal precision.