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Top Quark Mass Calibration for Monte Carlo Event Generators

Mathias Butenschoen, Bahman Dehnadi, André H. Hoang, Vicent Mateu, Moritz Preisser, and Iain W. Stewart
Phys. Rev. Lett. 117, 232001 – Published 29 November 2016
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    Abstract

    The most precise top quark mass measurements use kinematic reconstruction methods, determining the top mass parameter of a Monte Carlo event generator mtMC. Because of hadronization and parton-shower dynamics, relating mtMC to a field theory mass is difficult. We present a calibration procedure to determine this relation using hadron level QCD predictions for observables with kinematic mass sensitivity. Fitting e+e− 2-jettiness calculations at next-to-leading-logarithmic and next-to-next-to-leading-logarithmic order to pythia 8.205, mtMC differs from the pole mass by 900 and 600 MeV, respectively, and agrees with the MSR mass within uncertainties, mtMC≃mt,1  GeVMSR.

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    • Received 19 August 2016

    DOI:https://doi.org/10.1103/PhysRevLett.117.232001

    © 2016 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Heavy quark effective theoryPerturbative QCDQuark & gluon jetsResummation methods
    1. Physical Systems
    Top quark
    1. Properties
    Mass
    Particles & Fields

    Authors & Affiliations

    Mathias Butenschoen1,*, Bahman Dehnadi2,†, André H. Hoang2,3,‡, Vicent Mateu4,§, Moritz Preisser2,∥, and Iain W. Stewart5,¶

    • 1II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, D-22761 Hamburg, Germany
    • 2University of Vienna, Faculty of Physics, Boltzmanngasse 5, A-1090 Wien, Austria
    • 3Erwin Schrödinger International Institute for Mathematical Physics, University of Vienna, Boltzmanngasse 9, A-1090 Wien, Austria
    • 4Departamento de Física Teórica and Instituto de Física Teórica, IFT-UAM/CSIC, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
    • 5Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • *mathias.butenschoen@desy.de
    • †bahman.dehnadi@univie.ac.at
    • ‡andre.hoang@univie.ac.at
    • §vicent.mateu@uam.es
    • ∥moritz.preisser@univie.ac.at
    • iains@mit.edu

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    Vol. 117, Iss. 23 — 2 December 2016

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    Images

    • Figure 1
      Figure 1

      Distribution of best-fit mass values from the scan over parameters describing perturbative uncertainties. Results are shown for cross sections employing the MSR mass mtMSR(1  GeV) (top two panels) and the pole mass mtpole (bottom two panels), both at NNLL and NLL. The pythia data sets use mtMC=173  GeV as an input (vertical red lines).

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    • Figure 2
      Figure 2

      Comparison of pythia samples with 107 events and mtMC=173  GeV (red dots) to the theoretical prediction in the MSR scheme at NNLL for mtMSR(1  GeV)=172.81  GeV and Ω1=0.44  GeV. The blue band shows the perturbative uncertainty from a random scan over 500 profile functions. Vertical error bars on the pythia points are obtained by a global rescaling of pythia statistical uncertainties such that the average χmin2/dof=1 and roughly indicate the incompatibility uncertainties on the cross sections. Horizontal error bars are related to the NLL2 incompatibility uncertainty in the MSR mass shown in Table 1.

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    • Figure 3
      Figure 3

      Dependence of the NNLL fit result for the MSR mass on the input mtMC value in pythia. The error bars show the total calibration uncertainty. The red solid lines correspond to the weighted average of the individual results. The red shaded area shows the average of the individual uncertainties.

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