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Register a new userCollider Constraints on $Z^prime$ Models for Neutral Current $B-$Anomalies
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We examine current collider constraints on some simple $Z^prime$ models that fit neutral current $B-$anomalies, including constraints coming from measurements of Standard Model (SM) signatures at the LHC. The `MDM simplified model is not constrained by the SM measurements but {em is} strongly constrained by a 139 fb$^{-1}$ 13 TeV ATLAS di-muon search. Constraints upon the `MUM simplified model are much weaker. A combination of the current $B_s$ mixing constraint and ATLAS $Z^prime$ search implies $M_{Z^prime}>1.2$ TeV in the Third Family Hypercharge Model example case. LHC SM measurements rule out a portion of the parameter space of the model for $M_{Z^prime}<1.5$ TeV.
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We investigate a speculative short-distance force, proposed to explain discrepancies observed between measurements of certain neutral current decays of $B$ hadrons and their Standard Model predictions. The force derives from a spontaneously broken, gauged $U(1)_{B_3-L_2}$ extension to the Standard Model, where the extra quantum numbers of Standard Model fields are given by third family baryon number minus second family lepton number. The only fields beyond those of the Standard Model are three right-handed neutrinos, a gauge field associated with $U(1)_{B_3-L_2}$ and a Standard Model singlet complex scalar which breaks $U(1)_{B_3-L_2}$, a `flavon. This simple model, via interactions involving a TeV scale force-carrying $Z^prime$ vector boson, can successfully explain the neutral current $B-$anomalies whilst accommodating other empirical constraints. In an ansatz for fermion mixing, a combination of up-to-date $B-$anomaly fits, LHC direct $Z^prime$ search limits and other bounds rule out the domain 0.15 TeV$< M_{Z^prime} <$ 1.9 TeV at the 95$%$ confidence level. For more massive $Z^prime$s, the model possesses a {em flavonstrahlung} signal, where $pp$ collisions produce a $Z^prime$ and a flavon, which subsequently decays into two Higgs bosons.
While it is known that third family hypercharge models can explain the neutral current $B-$anomalies, it was hitherto unclear whether the $Z-Z^prime$ mixing predicted by such models could simultaneously fit electroweak precision observables. Here, we perform global fits of several third family hypercharge models to a combination of electroweak data and those data pertinent to the neutral current $B-$anomalies. While the Standard Model is in tension with this combined data set with a $p-$value of $.00068$, simp
We investigate models of a heavy neutral gauge boson Z which could explain anomalies in B meson decays reported by the LHCb experiment. In these models, the Z boson couples mostly to third generation fermions. We show that bottom quarks arising from gluon splitting can fuse into Z as an essential production mechanism at the LHC, thereby allowing to probe these models. The study is performed within a generic framework for explaining the B anomalies that can be accommodated in well motivated models. The flavor violating b s coupling associated with Z in such models produces lower bound on the production cross-section which gives rise to a cross-section range for such scenarios for the LHC to probe. Results are presented in Z -> $mu mu$ decays with at least one bottom-tagged jet in its final state. Some parts of the model parameter space become constrained by the existing dimuon-resonance searches by the ATLAS and CMS collaborations. However, the requirement of one or two additional bottom-tagged jets in the final state would allow for probing a larger region of the parameter space of the models at the ongoing LHC program.
We further investigate the case where new physics in the form of a massive $Z^prime$ particle explains apparent measurements of lepton flavour non-universality in $B rightarrow K^{(ast)} l^+ l^-$ decays. Hadron collider sensitivities for direct production of such $Z^prime$s have been previously studied in the narrow width limit for a $mu^+ mu^-$ final state. Here, we extend the analysis to sizeable decay widths and improve the sensitivity estimate for the narrow width case. We estimate the sensitivities of the high luminosity 14 TeV Large Hadron Collider (HL-LHC), a high energy 27 TeV LHC (HE-LHC), as well as a potential 100 TeV future circular collider (FCC). The HL-LHC has sensitivity to narrow $Z^prime$ resonances consistent with the anomalies. In one of our simplified models the FCC could probe 23 TeV $Z^prime$ particles with widths of up to 0.35 of their mass at 95% confidence level (CL). In another model, the HL-LHC and HE-LHC cover sizeable portions of parameter space, but the whole of perturbative parameter space can be covered by the FCC.
We consider right-handed neutrino pair production in generic $Z^prime$ models. We propose a new, model-independent analysis using final states containing a pair of same-sign muons. A key aspect of this analysis is the reconstruction of the RH neutrino mass, which leads to a significantly improved sensitivity. Within the $U(1)_{(B-L)_{3}}$ model, we find that at the HL-LHC it will be possible to probe RH neutrino masses in the range $0.2lesssim M_{N_R} lesssim 1.1,$TeV.
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