Measurements in Gauge Mediated SUSY Breaking Models at LHC

TL;DR

This work investigates LHC phenomenology for gauge mediated SUSY breaking (GMSB) with a gravitino LSP and various NLSP lifetimes, using ISAJET-based simulations to illustrate how the collider can fully reconstruct SUSY events from decay chains. A key contribution is a novel, constraint-driven method that reconstructs the two unobserved gravitino momenta, allowing direct measurements of superpartner masses rather than relying solely on kinematic endpoints. The study analyzes four benchmark points (G1a, G1b, G2a, G2b) to show how leptons, photons, and long-lived sleptons enable precise mass determinations, endpoint extractions, and spectrum mapping, and it demonstrates how LHC data can over-constrain the underlying GMSB parameters ($\Lambda$, $M_m$, $N_5$, $\tan\beta$, $\text{sgn}\mu$, $C_{\rm grav}$). It also assesses the capability to distinguish GMSB from SUGRA, highlighting the role of characteristic signatures and over-constrained parameter fits for robust model discrimination and quantitative constraints on the SUSY-breaking scale.

Abstract

Characteristic examples are presented of scenarios of particle production and decay in supersymmetry models in which the supersymmetry breaking is transmitted to the observable world via gauge interactions. The cases are chosen to illustrate the main classes of LHC phenomenology that can arise in these models. A new technique is illustrated that allows the full reconstruction of supersymmetry events despite the presence of two unobserved particles. This technique enables superparticle masses to be measured directly rather than being inferred from kinematic distributions. It is demonstrated that the LHC is capable of making sufficient measurements so as to severely over-constrain the model and determine the parameters with great precision

Figures (35)

• Figure 1: $M_{\ell\ell}$ distribution for $e^+e^- + \mu^+\mu^- - e^\pm\mu^\mp$ events with two photons and two isolated leptons arising at Point G1a. The Standard Model background is negligible.
• Figure 2: $M_{\ell\ell\gamma}$ distribution for $e^+e^- + \mu^+\mu^- - e^\pm\mu^\mp$ events with two photons at Point G1a. A linear fit from 160 to 190 GeV used to determine the position of the 4-body endpoint is also shown as a dashed line.
• Figure 3: $M_{\ell^\pm\gamma}$ distribution for $e^+e^- + \mu^+\mu^- - e^\pm\mu^\mp$ events sample with two photons; a linear fit from 115 to 150 GeV is used to determine the endpoint for the photon and the "wrong" lepton and is shown as a dashed line.
• Figure 4: The distribution in $\left| \Delta p\right|/\left| p\right|$ for reconstructed gravitino momenta. The gravitino momenta are reconstructed using the method described in the text. The difference ($\Delta p$) between the reconstructed ($p$) and generated momentum is then formed for the combination with the lowest $\chi^2$. Events are included where the lowest $\chi^2$ is less than 10 or 1 (dashed line).
• Figure 5: Invariant mass of $\tilde{\chi}_2^0$ and two jets, for events at Point G1a. The peak is due to the decay $\tilde{g} \to q\overline{q} \tilde{\chi}_2^0$. Events are required to have two $\tilde{\chi}_2^0$ momenta reconstructed and at least four jets with $p_T>75$ GeV.