Distinguishing spins in decay chains with photons at the Large Hadron Collider

TL;DR

This paper explores how to distinguish between different new physics models at the LHC by analyzing the invariant mass distributions involving photons, focusing on spin differences of new particles in decay chains.

Contribution

It introduces a method to extract spin information from invariant mass distributions at the LHC, differentiating models like GMSB and universal extra dimensions.

Findings

Analytical derivation of distribution shapes for different spins

Monte Carlo simulations confirm discriminating power at 14 TeV with 10 fb$^{-1}$

High significance discrimination achievable for particles below 1 TeV

Abstract

Several models for physics beyond the Standard Model predict new particles with a decay signature including hard photons and missing energy. Two well-motivated examples are supersymmetry with gauge-mediated breaking (GMSB) and the standard model with two universal extra dimensions. Both models lead to decay chains with similar collider signatures, including hard photon emission. The main discriminating feature are the spins of the new particles. In this paper we discuss how information about the spins of the particles can be extracted from lepton-photon or quark-photon invariant mass distributions at the Large Hadron Collider. The characteristic shapes of the distributions are derived analytically and then studied in a realistic Monte-Carlo simulation. We find that for a typical GMSB mass spectrum with particle masses below 1 TeV, already 10 fb$^{-1}$ integrated luminosity at 14 TeV center-of-mass energy are sufficient to discriminate the two models with high significance.