Spin before mass at the LHC

TL;DR

This paper introduces two new variables, $ heta_{V}$ and $A_{V}$, that enable spin determination of new particles at the LHC without prior mass measurements, improving early discovery analysis.

Contribution

The paper proposes mass-independent variables for early spin analysis of new particles, enhancing initial discovery capabilities at the LHC.

Findings

$ heta_{V}$ approximates the polar production angle of $Y$.

$ heta_{V}$ has greater statistical power than previous variables.

$A_{V}$ provides information about the couplings of spin-half particles.

Abstract

What can be said about the spin of new particles without knowing their mass during an initial discovery phase at CERN? We consider this question in a topology where mass measurement is particularly difficult, $pp\to Y\bar{Y}\to lX\bar{l}\,\bar{X}$, and introduce two new variables $\ctv$ and $\Av$ which we prove are both independent of the mass of $X$. The variable $\ctv$ approximates the polar production angle of $Y$, and we find that it possesses greater statistical power in determining the spin of this particle than a previous, related variable, $\ctll$ \cite{Barr:2005dz}. $\Av$ is an asymmetry which can provide information about the couplings of a spin half $Y$. Because these variables can be used from the outset, without any knowledge of the masses of the new particles, we find here that it is possible to reverse the usual `mass before spin' determination timeline.