Using subsystem MT2 for complete mass determinations in decay chains with missing energy at hadron colliders

By Michael E. Burns, Kyoungchul Kong, Konstantin T. Matchev, Myeonghun Park. 2008

186 citations recorded by the source corpus.

We propose to use the MT2 concept to measure the masses of all particles in SUSY-like events with two unobservable, identical particles. To this end we generalize the usual notion of MT2 and define a new MT2(n,p,c) variable, which can be applied to various subsystem topologies, as well as the full event topology. We derive analytic formulas for its endpoint MT2,max(n,p,c) as a function of the unknown test mass c of the final particle in the subchain and the transverse momentum pT due to radiation from the initial state. We show that the endpoint functions MT2,max(n,p,c)(c,pT) may exhibit three different types of kinks and discuss the origin of each type. We prove that the subsystem MT2(n,p,c) variables by themselves already yield a sufficient number of measurements for a complete determination of the mass spectrum (including the overall mass scale). As an illustration, we consider the simple case of a decay chain with up to three heavy particles, X2 → X1 → X0, which is rather problematic for all other mass measurement methods. We propose three different MT2-based methods, each of which allows a complete determination of the masses of particles X0, X1 and X2. The first method only uses MT2(n,p,c) endpoint measurements at a single fixed value of the test mass c. In the second method the unknown mass spectrum is fitted to one or more endpoint functions MT2,max(n,p,c)(c,pT) exhibiting a kink. The third method is hybrid, combining MT2 endpoints with measurements of kinematic edges in invariant mass distributions. As a practical application of our methods, we show that the dilepton W+W− and t samples at the Tevatron can be used for an independent determination of the masses of the top quark, the W boson and the neutrino, without any prior assumptions.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/af7b0b13624771ed02197317ac0bd043eeafc5d2

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In Nuclear and High Energy Physics

Citations in the corpus

Supersymmetric particle mass measurement with the boost-corrected contransverse mass (2009, methodology): “This approach has been used previously to study alternative SUSY particle mass measurement techniques [ 14 , 18].”
Higgs Physics at the HL-LHC and HE-LHC (2019, methodology): “The method also utilises two less commonly used variables, the subsystem MT2 (or subsystem M2) [298, 299, 300] for tt̄ and the subsystem p ŝmin (or subsystem M1) [301, 302, 300] for hh production.”
A review of the mass measurement techniques proposed for the Large Hadron Collider (2010, background): “Formulae for Mmax T2 with mB 6= 0 are given in [137] for PUT = 0, and in [142] for arbitrary PUT .”
Search for direct top-squark pair production in final states with two leptons in pp collisions at root s=8 TeV with the ATLAS detector (2014, background): “For tt̄ or WW decays, if the transverse momenta of the two leptons in each event are taken as pT,1 and pT,2, and E miss T as qT, mT2(`, `, E miss T ) is bounded sharply from above by the mass of the W boson [84, 85].”