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Single-variable asymmetries for measuring the `Higgs' boson spin and CP properties

Radja Boughezal, Thomas J. LeCompte, Frank Petriello

TL;DR

The paper proposes a high-low invariant-mass asymmetry in the four-lepton final state as a simple, robust probe of the new boson's spin and CP properties. By deriving explicit differential decay widths for several spin-0 and spin-2 hypotheses, it links the beta-dependent behavior of the M_{34} distribution to coupling structures and demonstrates how the asymmetry can distinguish hypotheses with early LHC data. Using these asymmetries with current ATLAS/CMS results, it shows partial discrimination among spin-2 couplings (and limited sensitivity to CP-odd spin-0) and outlines a practical program for experimental analyses, including varying M_{cut} and incorporating all M_{12} regions. The approach provides a data-efficient path to characterizing the observed state and sets the stage for deeper measurements as more data become available, complementing multivariate approaches and angular analyses.

Abstract

We introduce a class of asymmetries sensitive to the spin and CP properties of the new boson discovered by the ATLAS and CMS experiments. These asymmetries can be measured in the four-lepton final state, and are defined by integrating the invariant masses of the lepton pairs over specified ranges. We outline a program of measurements using initial LHC data to determine the quantum numbers and coupling structure, provide analytic expressions for decay widths in several representative models, and discuss what can be determined using the available data. As examples, we show how the combination of ATLAS and CMS data already disfavor certain spin-2 couplings, and discuss how further data will allow for discrimination of a pure CP-odd scalar from a CP-even hypothesis.

Single-variable asymmetries for measuring the `Higgs' boson spin and CP properties

TL;DR

The paper proposes a high-low invariant-mass asymmetry in the four-lepton final state as a simple, robust probe of the new boson's spin and CP properties. By deriving explicit differential decay widths for several spin-0 and spin-2 hypotheses, it links the beta-dependent behavior of the M_{34} distribution to coupling structures and demonstrates how the asymmetry can distinguish hypotheses with early LHC data. Using these asymmetries with current ATLAS/CMS results, it shows partial discrimination among spin-2 couplings (and limited sensitivity to CP-odd spin-0) and outlines a practical program for experimental analyses, including varying M_{cut} and incorporating all M_{12} regions. The approach provides a data-efficient path to characterizing the observed state and sets the stage for deeper measurements as more data become available, complementing multivariate approaches and angular analyses.

Abstract

We introduce a class of asymmetries sensitive to the spin and CP properties of the new boson discovered by the ATLAS and CMS experiments. These asymmetries can be measured in the four-lepton final state, and are defined by integrating the invariant masses of the lepton pairs over specified ranges. We outline a program of measurements using initial LHC data to determine the quantum numbers and coupling structure, provide analytic expressions for decay widths in several representative models, and discuss what can be determined using the available data. As examples, we show how the combination of ATLAS and CMS data already disfavor certain spin-2 couplings, and discuss how further data will allow for discrimination of a pure CP-odd scalar from a CP-even hypothesis.

Paper Structure

This paper contains 4 sections, 18 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Derivation of the decay widths
  3. Analysis
  4. Discussion and conclusions

Figures (1)

  • Figure 1: The normalized decay width $1/\Gamma_{tot} \times d^2 \Gamma /(dM_{12}^2 dM_{34}^2)$ as a function of $M_{34}$ for the spin-0 CP-even and CP-odd states $0^{++}$ and $0^{-+}$, the spin-2 graviton $2^{G}$, and the alternate spin-two state $2^A$. The parameter choices are described in the text.