A Stable Dyon of Unit Electric Charge at the LHC: The Acceptance Gap of the Existing Searches and a Tracker Based Search to Close It

Abstract

A stable spin one half particle with unit electric charge and one Dirac unit of magnetic charge is examined at 1.86 TeV, with a 3 TeV monopole as a second benchmark. In the ATLAS barrel it reaches the electromagnetic calorimeter only if its initial velocity exceeds 0.45c at central rapidity and 0.62c at the edge of the barrel. The ATLAS search for highly ionizing particles triggers on a calorimeter deposit, so a slower object leaves no trigger signal at any collision energy. The track based searches fit helices, and a magnetic charge follows a parabola. For Drell-Yan kinematics one third to two fifths of the produced objects fall in a region that no selection of the general purpose detectors has examined. The null result bounds the product of the cross section and the visible fraction to 0.026 fb at 13 TeV. A pointlike Drell-Yan dyon at 1.86 TeV exceeds that bound fifty times and is excluded; a 3 TeV monopole is not. The electric channel alone lies a hundred times below it. A search that starts from the raw tracker hits, fits a trajectory circular in the transverse plane and parabolic in the longitudinal plane, and triggers on the recoil of initial state radiation covers the region the calorimeter selection cannot reach. Its acceptance is computed, with the recoil fraction from a parton shower, and its reach is given as a function of the reconstruction efficiency that only the collaborations can determine.