Combined collider constraints on neutralinos and charginos

Peter Athron,Csaba Balázs,Tomás E Gonzalo,Rose Kudzman-Blais,Gregory D Martinez,A G Buckley ,M Danninger ,A S Sharma ,Julia Harz,Benjamin Farmer ,Are Raklev,P Jackson ,Anders Kvellestad,Pat Scott,Jonathan M Cornell,Andrew Fowlie,A Petridis ,C Rogan ,M J White ,Yang Zhang

doi:10.1140/epjc/s10052-019-6837-x

Abstract

Searches for supersymmetric electroweakinos have entered a crucial phase, as the integrated luminosity of the Large Hadron Collider is now high enough to compensate for their weak production cross-sections. Working in a framework where the neutralinos and charginos are the only light sparticles in the Minimal Supersymmetric Standard Model, we use GAMBIT to perform a detailed likelihood analysis of the electroweakino sector. We focus on the impacts of recent ATLAS and CMS searches with of 13 TeV proton-proton collision data. We also include constraints from LEP and invisible decays of the Z and Higgs bosons. Under the background-only hypothesis, we show that current LHC searches do not robustly exclude any range of neutralino or chargino masses. However, a pattern of excesses in several LHC analyses points towards a possible signal, with neutralino masses of = (8–155, 103–260, 130–473, 219–502) GeV and chargino masses of = (104–259, 224–507) GeV at the 95% confidence level. The lightest neutralino is mostly bino, with a possible modest Higgsino or wino component. We find that this excess has a combined local significance of 3.3sigma , subject to a number of cautions. If one includes LHC searches for charginos and neutralinos conducted with 8 TeV proton-proton collision data, the local significance is lowered to 2.9sigma . We briefly consider the implications for dark matter, finding that the correct relic density can be obtained through the Higgs-funnel and Z-funnel mechanisms, even assuming that all other sparticles are decoupled. All samples, GAMBIT input files and best-fit models from this study are available on Zenodo.

Highlights

Supersymmetry (SUSY) provides well-justified extensions of the Standard Model (SM) of particle physics that can stabilise the electroweak scale against quantum corrections [1–6], radiatively break electroweak symmetry [7,8,9,10] and provide a dark matter (DM) candidate with the right abundance [11,12]
This preference is driven by the small number of coincident excesses in a variety of ATLAS and CMS searches, which we discuss in detail below
We have performed a comprehensive global statistical fit of a 4D minimal supersymmetric standard model (MSSM) model in which M1, M2, μ and tan β are varied, whilst other MSSM parameters are held at fixed values in order to decouple all sparticles except the electroweakinos

Summary

Introduction

Supersymmetry (SUSY) provides well-justified extensions of the Standard Model (SM) of particle physics that can stabilise the electroweak scale against quantum corrections [1–6], radiatively break electroweak symmetry [7,8,9,10] and provide a dark matter (DM) candidate with the right abundance [11,12]. In the minimal supersymmetric standard model (MSSM), the superpartners of the electroweak gauge and Higgs bosons mix to form electroweakinos. These consist of four Majorana fermions (neutralinos χi0, with i = 1, of increasing mass), and two Dirac fermions. SUSY models with electroweakino states significantly lighter than the other SUSY states have been presented as natural SUSY [35,36,37,38,39,40,41,42] and in models where naturalness has been abandoned as a guiding principle [43,44,45,46,47,48,49,50,51] In the latter, other motivations such as DM, where the lightest neutralino may play the role of DM even if the rest of the SUSY spectrum is heavy, are used as the guiding principles.

Objectives

Results

Discussion

Conclusion