MT2-reconstructed invisible momenta as spin analizers, and an application to top polarization

Abstract

Full event reconstruction is known to be challenging in cases with more than one undetected final-state particle, such as pair production of two states each decaying semi-invisibly. On the other hand, full event reconstruction would allow to access angular distributions sensitive to the spin fractions of the decaying particles, thereby dissecting their production mechanism. We explore this possibility in the case of Standard-Model t-tbar production followed by a leptonic decay of both W bosons, implying two undetected final-state neutrinos. We estimate the t and tbar momentum vectors event by event using information extracted from the kinematic variable MT2. The faithfulness of the estimated momenta to the true momenta is then tested in observables sensitive to top polarization and t-tbar spin correlations. Our method thereby provides a novel approach towards the evaluation of these observables, and towards testing t-tbar production beyond the level of the total cross section. While our discussion is confined to t-tbar production as a benchmark, the method is applicable to any process whose decay topology allows to construct MT2.

28 pages, 14 figures, 3 tables. Changes in v2: new paragraph on ISR (end of sec. 2.2); new sec. 3.3 on the method's comparison with existing ones; typos fixed; reference added. Matches journal version (JHEP)

References in corpus (19)

• FeynRules - Feynman rules made easy
• 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
• MTGEN : Mass scale measurements in pair-production at colliders
• Transverse Observables and Mass Determination at Hadron Colliders
• Mass Determination of New States at Hadron Colliders
• Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization
• Polarized Tops from Stop Decays at the LHC
• On measurement of top polarization as a probe of $t\bar{t}$ production mechanisms at the LHC
• A model independent spin analysis of fundamental particles using azimuthal asymmetries
• A New Twist on Top Quark Spin Correlations
• A Review of Spin Determination at the LHC
• Top Quark Physics at the LHC: A Review of the First Two Years
• Measurement of spin correlation in ttbar production using dilepton final states
• Top Polarization in Stop Production at the LHC
• Measuring Top Quark Polarization in Top Pair plus Missing Energy Events
• Top Polarization and Stop Mixing from Boosted Jet Substructure
• Re-interpreting the Oxbridge stransverse mass variable MT2 in general cases

Cited by in corpus (9)

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• Resolving Combinatorial Ambiguities in Dilepton $t\bar{t}$ Event Topologies with Constrained $M_2$ Variables
• Testing Invisible Momentum Ansatze in Missing Energy Events at the LHC
• Singularity Variables for Missing Energy Event Kinematics
• Kinematic Focus Point Method for Particle Mass Measurements in Missing Energy Events
• Constraining new resonant physics with top spin polarisation information
• Measuring Electroweak Quantum Numbers of Color Sextet Resonances at the LHC
• Could $M_{T2}$ be a singularity variable?