Abstract
We study the inclusive production of bottom-flavored hadrons from semileptonic decays of polarized top quarks at next-to-leading order in QCD using fragmentation functions recently determined from a global fit to $e^+e^-$ data. We provide the relevant differential decay widths at parton level in analytic form. These results fill an important gap in the theoretical interpretation of recent measurements of the top-quark polarization and the $t\bar{t}$ spin correlations using dilepton final states in proton-proton collisions at the CERN Large Hadron Collider. As an illustration, we study the distributions in the scaled bottom-hadron energy of the polarized-top-quark decay widths for different $W$-boson helicities.
Highlights
The top quark t of the standard model (SM) is the heaviest known elementary particle
The top-quark lifetime τt 1⁄4 ħ=Γt ≈ 5 × 10−25 s [1] is shorter than the typical time scale of quantum chromodynamics (QCD) ħ=ΛQCD ≈ 10−24 s and much shorter than the spin correlation time scale ħmt=Λ2QCD ≈ 10−21 s, where ΛQCD is the asymptotic scale parameter of QCD
We work at next-to-leading order (NLO) in the ZM-VFNS, implemented in the modified minimal-subtraction (MS) scheme, and consider the decay process tðpt; sÞ → bðpbÞ þ WþðpW; λÞðþgðpgÞÞ → BðpBÞ þ lþðplÞ þ νlðpνÞ þ X; ð1Þ
Summary
The top quark t of the standard model (SM) is the heaviest known elementary particle. The precise determination of its properties, including its mass mt and total decay width Γt, and its process-dependent features, like its polarization or the correlation of its spin with that of a co-produced antitop quark, is of prime importance. ATLAS found a deviation of 3.8 standard deviations (σ) from the SM prediction of the asymmetry AjΔφllj of the distribution in the azimuthal angular difference Δφll of the decay leptons This deviation was confirmed by CMS, albeit with a smaller significance of about 2σ. [8], by a comparative analysis of the partial width of the decay t → B þ Wþ in the GM-VFNS and the zero-mass variable-flavor-number scheme (ZMVFNS), where bottom is included among the massless quark flavors.
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