Mixing It Up With MT2: Unbiased Mass Measurements at Hadron Colliders

Abstract

Recently, much progress has been made on techniques to measure the masses of new particles with partially-invisible decays at a hadron collider. We examine for the first time the realistic application of MT2-based measurement methods to a fully hadronic final state from a symmetric two-step decay chain with maximal combinatorial uncertainty. Several problems arise in such an analysis: the MT2 variables are powerful but fragile, with shallow edges that are easily washed out or faked by ubiquitous combinatorics background. Traditional methods of both cleaning up the distribution and determining edge position can fail badly. To perform successful mass measurements we introduce several new techniques: the Edge-to-Bump method of extracting an edge from a distribution by analyzing a distribution of fits rather than a single fit; a very simple yet high-yield method for determining decay-chain assignments event-by-event; and a systematic procedure to obtain MT2 edge measurements in the presence of heavy combinatorics background, they key element being the parallel use of at least two independent methods of reducing combinatorics background to avoid fake measurements. All of these techniques are developed in a Monte Carlo study of the decay gluino gluino -> 2 sbottom + 2 b -> 4 b + 2 chi_0^1 and verified in a second blind study with a different spectrum. In both cases, the gluino and sbottom masses are measured to a precision of ~ 10% with O(100 fb^{-1}) at the LHC14 (assuming pessimistic b-tag efficiencies).

35 pages, 12 figures

References in corpus (21)

• PYTHIA 6.4 Physics and Manual
• Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions
• Search for Supersymmetry at the LHC in Events with Jets and Missing Transverse Energy
• Gluino Stransverse Mass
• Measuring superparticle masses at hadron collider using the transverse mass kink
• Using Subsystem MT2 for Complete Mass Determinations in Decay Chains with Missing Energy at Hadron Colliders
• Minimal Kinematic Constraints and MT2
• On measuring the masses of pair-produced semi-invisibly decaying particles at hadron colliders
• Accurate Mass Determinations in Decay Chains with Missing Energy
• A Review of the Mass Measurement Techniques proposed for the Large Hadron Collider
• MTGEN : Mass scale measurements in pair-production at colliders
• Transverse Observables and Mass Determination at Hadron Colliders
• Inclusive transverse mass analysis for squark and gluino mass determination
• Handling jets + missing E_T channel using inclusive mT2
• Novel reconstruction technique for New Physics processes with initial state radiation
• Revisiting Combinatorial Ambiguities at Hadron Colliders with MT2
• A New Method for Resolving Combinatorial Ambiguities at Hadron Colliders
• Reducing combinatorial uncertainties: A new technique based on MT2 variables
• Controlling ISR in sparticle mass reconstruction
• Extracting the Dark Matter Mass from Single Stage Cascade Decays at the LHC
• On the Feasibility and Utility of ISR Tagging

Cited by in corpus (18)

• Measurement of masses in the t t-bar system by kinematic endpoints in pp collisions at sqrt(s) = 7 TeV
• Using Energy Peaks to Measure New Particle Masses
• Using Energy Peaks to Count Dark Matter Particles in Decays
• Determination of the CMSSM Parameters using Neural Networks
• Leptonic Scalars and Collider Signatures in a UV-complete Model
• Improved mass measurement using the boundary of many-body phase space
• Non-Simplified SUSY: Stau-Coannihilation at LHC and ILC
• Multi-Dimensional Phase Space Methods for Mass Measurements and Decay Topology Determination
• Extracting gluino endpoints with event topology patterns
• Mitigation of the LHC Inverse Problem
• Dreaming Awake: Disentangling the Underlying Physics in Case of a SUSY-like Discovery at the LHC
• Identifying the production process of new physics at colliders; symmetric or asymmetric?
• SUSY-Yukawa Sum Rule at the LHC and the ILC
• Discovering New Physics with Voronoi Tessellations
• Mass Measurement Using Energy Spectra in Three-body Decays
• The Lightest Massive Invisible Particles at the LHC
• Testing LHT at the LHC Run-II
• Resolving Histogram Binning Dilemmas with Binless and Binfull Algorithms