\(Z^\prime\) Models for Neutral Current B−Anomalies

Ben Allanach, Jon Butterworth, Tyler Corbett

See reference [81]. This paper describes the implications (as of Jan 2020) of LHC searches, and the measurements then in Contur, on three models which describe the neutral current B-anomalies (\(R_{K^*}\) and the angular distributions, mainly from LHCb. See the paper for references of their status at the time). Three models are considered in which a \(Z^\prime\) couples to muons and to some combination of the quarks. In the “Mixed Up” and “Mixed Down” Muon models (MUM, MDM) this new boson is added to the SM Lagrangian ad hoc. In the “Third Family Hypercharge Model” (TFHM) [82], it arises from the spontaneous symmetry breaking of a new U(1) symmetry under which third generation fermions are charged.

The Contur limits for these three simple models were shown in Fig.5 of the paper (as well as in the Fig.4 summary for the TFHM). These are updated below for the TFHM with the data in Contur 2.0.2, Rivet 3.1.4, and also making use of the correlation information in the measurement uncertainties where available (something Contur could not do at the time of the publication).

Third family hypercharge model exclusion for measurements in Rivet 2.7

Third family hypercharge model exclusion for measurements in Contur 2.0.2, Rivet 3.1.4.

In the plot below on the left, the colours indicate which final states are dominantly providing the sensitivity. The main relevant addition since the paper is the CMS 13 TeV dilepton measurement [174], which provides additional exclusion even though it uses only 3.2/fb of Run 2 data. (Note that the interpolation settings in Contur were changed, meaning that the sensitivity around 300 GeV mass and high \(\theta_{sb}\) seems significantly less, although the heatmap itself shows very little difference in this region.)

Contur now also has a small number of searches available, exploiting the detector-smearing machinery now added to Rivet [108]. Amongst these searches is the ATLAS full run 2 dilepton search [64] used in [81]. The righthand plot above shows the impact of adding this. The combined exclusion goes up to \(Z^\prime\) masses of around 2 TeV, somewhat higher than the exclusion from this search alone based on the fit in [81].

MUM model exclusion for measurements in Rivet 2.7.

MUM model exclusion for measurements in Rivet 2.7.

Summary including searches from [81]

The model files are available in the Zprime_TFHM_Mix_UFO, Zprime_MUM_UFO and Zprime_MDM_UFO directories here