Reconstructing masses for semi-invisibly decaying particles pair-produced at lepton colliders

TL;DR

This paper introduces Lorentz-invariant kinematic variables for reconstructing masses of semi-invisible particles at lepton colliders, improving detection sensitivity and precision in new physics searches and W-boson mass measurements.

Contribution

The paper develops analytical formulas for new kinematic variables that bound the mass of semi-invisible particles, enhancing collider analysis capabilities.

Findings

Increases detection limits for smuon pair production.

Sets new exclusion and discovery bounds above half the collider energy.

Improves W-boson mass measurement precision to 2-3 MeV.

Abstract

We present a set of Lorentz invariant kinematic variables for reconstructing mass of semi-invisible decaying particles pair-produced at lepton colliders, $m_{\rm RC}^{\rm min}$, $m_{\rm RC}^{\rm max}$ and $m_{\rm LSP}^{\rm max}$, with analytical formulas. They give the minimal and maximum bounds of the decaying particle mass and upper bound of the invisible particle mass. In the search of new physics, these variables can greatly enhance the statistical significance of signal. For the process of smuon pair production at $\sqrt{s}=240~{\rm GeV}$ lepton collider of 5 ab$^{-1}$, the cross section detection limit is pushed by one order, and the expected exclusion and discovery limits are set above $\sqrt{s}\big/2$ and go into the off-shell region. Moreover, these variables can also be used to improve the precision of $W$-boson mass measurement in full leptonic decayed channel. At future lepton collider, the precision can reach to $2\sim 3$ MeV level.