Abstract
A measurement of jet substructure observables is presented using tt¯ events in the lepton+jets channel from proton-proton collisions at s=13 TeV recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. Multiple jet substructure observables are measured for jets identified as bottom, light-quark, and gluon jets, as well as for inclusive jets (no flavor information). The results are unfolded to the particle level and compared to next-to-leading-order predictions from powheg interfaced with the parton shower generators pythia 8 and herwig 7, as well as from sherpa 2 and Dire 2. A value of the strong coupling at the Z boson mass, αS(mZ)=0.115−0.013+0.015, is extracted from the substructure data at leading-order plus leading-log accuracy.15 MoreReceived 22 August 2018DOI:https://doi.org/10.1103/PhysRevD.98.092014Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2018 CERN, for the CMS CollaborationPhysics Subject Headings (PhySH)Physical SystemsTop quarkTechniquesHadron collidersParticle decaysParticles & Fields
Highlights
The confinement property of quantum chromodynamics (QCD) renders isolated quarks and gluons unobservable
Within the solenoid volume are a silicon pixel and strip tracker, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two end cap sections
The PYTHIA 8 and SHERPA 2 generators apply a model where the multiparton interactions (MPIs) are interleaved with parton showering [66], while HERWIG 7 models the overlap between the colliding protons through a Fourier transform of the electromagnetic form factor, which plays the role of an effective inverse proton radius [67,68,69,70]
Summary
The confinement property of quantum chromodynamics (QCD) renders isolated quarks and gluons unobservable. Precise measurements of jet properties at the LHC allow improvements in the experimental techniques and theoretical predictions for heavy-quark/light-quark/gluon discrimination, as well as in the identification of merged jets from Lorentz-boosted heavy particle decays [16,17]. They give information about the limits and applicability of the current parton shower and fragmentation models in the gluon-dominated environment of proton-proton (pp).
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