Abstract
We demonstrate the use of the Matrix Element Method (MEM) for the measurement of masses, widths, and couplings in the case of single or pair production of semi-invisibly decaying resonances. For definiteness, we consider the two-body decay of a generic resonance to a visible particle from the Standard Model (SM) and a massive invisible particle. It is well known that the mass difference can be extracted from the endpoint of a transverse kinematic variable like the transverse mass, $M_T$, or the Cambridge $M_{T2}$ variable, but measuring the overall mass scale is a very difficult problem. We show that the MEM can be used to obtain not only the absolute mass scale, but also the width of the resonance and the tensor structure of its couplings. Apart from new physics searches, our results can be readily applied to the case of SM $W$ boson production at the CERN Large Hadron Collider (LHC), where one can repeat the measurements of the $W$ properties in a general and model-independent framework.
Highlights
The dark matter problem is the biggest mystery in particle physics today [1]
This is perhaps due to the practical challenges one usually encounters in the implementation of the matrix element method (MEM), e.g., the presence of instrumental and/or reducible physics backgrounds; the need to account for effects like the finite detector resolution, the underlying event, jet fragmentation; the challenge of integrating peaked integrand structures in phase space; incorporating higher order corrections to the matrix element, etc., [27]
The physical transparency of the MEM greatly motivates expanding its role in Large Hadron Collider (LHC) data analyses
Summary
The dark matter problem is the biggest mystery in particle physics today [1]. It greatly motivates the current experimental efforts to discover new physics beyond the Standard Model (BSM) at the LHC. The MEM has far been underutilized for the purposes of mass spectrum measurements of the sort we describe here This is perhaps due to the practical challenges one usually encounters in the implementation of the MEM, e.g., the presence of instrumental and/or reducible physics backgrounds; the need to account for effects like the finite detector resolution, the underlying event, jet fragmentation; the challenge of integrating peaked integrand structures in phase space; incorporating higher order corrections to the matrix element, etc., [27]. Despite these practical limitations, the physical transparency of the MEM greatly motivates expanding its role in LHC data analyses. We would like to revisit these earlier studies and extend the application of the MEM to the measurement of the remaining properties of the particles involved, namely the width and the chirality of the couplings. (The discrete choices of the spin assignments of the particles in the decay chain were previously investigated in Ref. [40].)
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