Tevatron Run II combination of the effective leptonic electroweak mixing angle

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Tevatron Run II combination of the effective leptonic electroweak mixing angle

T. Aaltonen et al. (CDF Collaboration, D0 Collaboration)

Phys. Rev. D 97, 112007 – Published 28 June 2018

Abstract

Drell-Yan lepton pairs produced in the process $p \bar{p} \to ℓ^{+} ℓ^{-} + X$ through an intermediate $γ^{*} / Z$ boson have an asymmetry in their angular distribution related to the spontaneous symmetry breaking of the electroweak force and the associated mixing of its neutral gauge bosons. The CDF and D0 experiments have measured the effective-leptonic electroweak mixing parameter $\sin^{2} θ_{eff}^{lept}$ using electron and muon pairs selected from the full Tevatron proton-antiproton data sets collected in 2001-2011, corresponding to $9 - 10 {fb}^{- 1}$ of integrated luminosity. The combination of these measurements yields the most precise result from hadron colliders, $\sin^{2} θ_{eff}^{lept} = 0.23148 \pm 0.00033$ . This result is consistent with, and approaches in precision, the best measurements from electron-positron colliders. The standard model inference of the on-shell electroweak mixing parameter $\sin^{2} θ_{W}$ , or equivalently the $W$ -boson mass $M_{W}$ , using the zfitter software package yields $\sin^{2} θ_{W} = 0.22324 \pm 0.00033$ or equivalently, $M_{W} = 80.367 \pm 0.017 GeV / c^{2}$ .

Received 19 January 2018

DOI:https://doi.org/10.1103/PhysRevD.97.112007

Published 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.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Electroweak interaction Leptonic, semileptonic & radiative decays W & Z bosons

Particles & Fields

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Vol. 97, Iss. 11 — 1 June 2018

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Images

Figure 1
Representation of the Collins-Soper coordinate axes $(x, z)$ in the lepton-pair rest frame relative to the laboratory $z$ axis ( $z_{lab}$ ). These three axes are in the plane formed by the proton ( ${\vec{p}}_{A}$ ) and antiproton ( ${\vec{p}}_{B}$ ) momentum vectors in the lepton-pair rest frame. The $z$ axis is the angular bisector of ${\vec{p}}_{A}$ and $- {\vec{p}}_{B}$ . The $y$ axis is along the direction of ${\vec{p}}_{B} \times {\vec{p}}_{A}$ , and the $x$ axis is in the direction opposite to the transverse component of ${\vec{p}}_{A} + {\vec{p}}_{B}$ .
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Figure 2
Typical dependence of $A_{fb}$ as a function of the lepton-pair invariant mass $M$ . The vertical line is at $M = M_{Z}$ . The label $u + d$ denotes the overall asymmetry, and the labels $u$ and $d$ denote the contribution to the overall asymmetry from quarks with charge $2 / 3$ and $- 1 / 3$ , respectively. The asymmetry identified by the $u$ or $d$ label is defined as $(σ_{f}^{q} - σ_{b}^{q}) / σ$ , where $q = u$ or $d$ , $σ_{f (b)}$ is the forward (backward) cross section, and $σ$ is the corresponding cross section from quarks of all charges. Thus, the overall asymmetry is the sum of the asymmetries identified by the $u$ and $d$ labels.
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Figure 3
Comparison of experimental measurements of $\sin^{2} θ_{eff}^{lept}$ in the region of the $Z$ -boson pole mass. The horizontal bars represent total uncertainties. The Tevatron combination (this paper) of CDF and D0 results is denoted as “TeV combined: CDF+D0”. The other measurements are from LEP-1 combination [4], SLD [4], CMS [15], ATLAS [14], LHCb [16], CDF [8, 9], and D0 [12, 13]. The LEP-1 and SLD $Z$ pole result is the combination of their six measurements, and the shaded vertical band shows its uncertainty.
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Figure 4
Comparison of experimental determinations of the $W$ -boson mass at high-energy colliders. The horizontal bars represent total uncertainties. The Tevatron combination (this paper) based on CDF and D0 results is denoted as “TeV combined: $CDF + D 0$ ”. The other indirect measurements are from LEP-1 and SLD [4, 5], CDF [8, 9], and D0 [12, 13]. All indirect measurements use the Tevatron top-quark mass measurement specified in the text [57]. The SM context for the Tevatron inferences is specified in the Appendix, and the SM fit of LEP-1 and SLD is described in Appendix F of Ref. [5]. For the Tevatron inferences of the $W$ -boson mass, the SM Higgs-boson mass parameter is fixed, while in the LEP-1 and SLD SM fit, it is a floating parameter. The direct measurements are from the Tevatron and LEP-2 [58], and the shaded vertical band shows its uncertainty.
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