Abstract
We propose a kinematic method based on a factorization formula for precisely measuring the top quark mass $m_t$ in $pp$ collisions using boosted top jets with light soft drop grooming. By using light grooming, which is an order of magnitude less aggressive than typical grooming, we retain a universal description of the top mass scheme and decay effects, while still effectively removing soft contamination from the top jet. We give field theory results for the hadronization corrections for jets induced by a heavy top quark, showing they are described by a universal hadronic parameter that also appears for groomed light quark jets. An important phenomenological application of our results is that one can obtain $m_t$ in a short distance scheme by fitting the hadron level jet mass distributions, predicted by our factorization formula, to data or by Monte-Carlo calibration. The peaked distributions for $pp$ and $e^+e^-$ collisions are similar, up to sensitivity to underlying event which is significantly reduced by soft drop. Since soft drop implies that the $t$ and $\bar t$ jet masses each can be independently measured, the analysis enables the use of lepton+jet samples.
Highlights
The top quark mass mt is one of the most important Standard Model (SM) parameters
MMt C 1⁄4 172.44ð49Þ GeV ðCMSÞ; mMt C 1⁄4 172.84ð70Þ GeV ðATLASÞ; mMt C 1⁄4 174.34ð64Þ GeV ðTevatronÞ: ð1Þ. These measurements are based on Monte Carlo (MC) simulations and determine the mass parameter mMt C of the MC generator, which depends on the parton shower dynamics and its interface with hadronization
We propose a factorization approach to remove this uncertainty in pp → tt by constructing an observable that has high kinematic sensitivity to mt and at the same time allows for hadron level predictions from QCD, employing a short distance top mass
Summary
The top quark mass mt is one of the most important Standard Model (SM) parameters. It significantly affects studies of the SM vacuum stability [1] and the electroweak precision observables [2]. The measurement of MJ is performed on a hadronically decaying top quark and can be applied to both all the jets and lepton þ jets tt samples This grooming retains strong kinematic sensitivity to mt as in direct reconstruction methods, removes contamination from other parts of the collision, and allows for a factorization based description as demonstrated for massless jets [14]. In the factorization theorem discussed below, the constraint of Eq (10) on the grooming parameters allows for a clear interpretation of the top-mass scheme, determined by the heavy quark jet function [9] which describes the inclusive dynamics of the ultracollinear radiation and the evolution and decay of the top quark in the peak region. We give a more detailed analysis of both the factorization and Monte Carlo results in Ref. [19]
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