Higgs look-alikes at the LHC

TL;DR

This paper assesses how well the LHC can distinguish a Standard Model Higgs boson from similar particles with different properties using decay distributions, achieving significant discrimination with limited events.

Contribution

It introduces a detailed method utilizing full decay information and phase space acceptance effects to differentiate Higgs look-alikes at the LHC.

Findings

Discrimination significance of 3 sigma with 19 events at 200 GeV/c^2

Enhanced discrimination using off-shell decays at 145 GeV/c^2

Full angular decay analysis improves identification accuracy

Abstract

The discovery of a Higgs particle is possible in a variety of search channels at the LHC. However the true identity of any putative Higgs boson will at first remain ambiguous, until one has experimentally excluded other possible assignments of quantum numbers and couplings. We quantify to what degree one can discriminate a Standard Model Higgs boson from "look-alikes" at, or close to, the moment of discovery at the LHC. We focus on the fully-reconstructible "golden" decay mode to a pair of Z bosons and a four-lepton final state, simulating sPlot-weighted samples of signal and background events. Considering both on-shell and off-shell Z's, we show how to utilize the full decay information from the events, including the distributions and correlations of the five relevant angular variables. We demonstrate how the finite phase space acceptance of any LHC detector sculpts the decay distributions, a feature neglected in previous studies. We use likelihood ratios to discriminate a Standard Model Higgs from look-alikes with other spins or nonstandard parity, CP, or form factors. For a benchmark resonance mass of 200 GeV/c^2, we achieve a median expected discrimination significance of 3 sigma with as few as 19 events, and even better discrimination for the off-shell decays of a 145 GeV/c^2 resonance.