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Register a new userBottom-quark Fusion Processes at the LHC for Probing $Z^{prime}$ Models and B-meson Decay Anomalies
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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.
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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.
Combining the $bto smu^+mu^-$ anomaly and dark matter observables, we study the capability of LHC to test dark matter, $Z^{prime}$, and vector-like quark. We focus on a local $U(1)_{L_mu-L_tau}$ model with a vector-like $SU(2)_L$ doublet quark $Q$ and a complex singlet scalar whose lightest component $X_I$ is a candidate of dark matter. After imposing relevant constraints, we find that the $bto smu^+mu^-$ anomaly and the relic abundance of dark matter favor $m_{X_I}< 350$ GeV and $m_{Z^{prime}}< 450$ GeV for $m_Q<$ 2 TeV and $m_{X_R}<$ 2 TeV (the heavy partner of $m_{X_I}$). The current searches for jets and missing transverse momentum at the LHC sizably reduce the mass ranges of the vector-like quark, and $m_Q$ is required to be larger than 1.7 TeV. Finally, we discuss the possibility of probing these new particles at the high luminosity LHC via the QCD process $pp to Dbar{D}$ or $pp to Ubar{U}$ followed by the decay $Dto s (b) ZX_I$ or $U to u (c) Z X_I$ and then $Ztomu^+mu^-$. Taking a benchmark point of $m_Q$=1.93 TeV, $m_{Z^prime}=170$ GeV, and $m_{X_I}=$ 145 GeV, we perform a detailed Monte Carlo simulation, and find that such benchmark point can be accessible at the 14 TeV LHC with an integrated luminosity 3000 fb$^{-1}$.
There are lots of new physics models which predict an extra neutral gauge boson, referred as Z-boson. In a certain class of these new physics models, the Z-boson has flavor-dependent couplings with the fermions in the Standard Model (SM). Based on a simple model in which couplings of the SM fermions in the third generation with the Z-boson are different from those of the corresponding fermions in the first two generations, we study the signatures of Z-boson at the Large Hadron Collider (LHC) and the International Linear Collider (ILC). We show that at the LHC, the Z-boson with mass around 1 TeV can be produced through the Drell-Yan processes and its dilepton decay modes provide us clean signatures not only for the resonant production of Z-boson but also for flavor-dependences of the production cross sections. We also study fermion pair productions at the ILC involving the virtual Z-boson exchange. Even though the center-of-energy of the ILC is much lower than a Z-boson mass, the angular distributions and the forward-backward asymmetries of fermion pair productions show not only sizable deviations from the SM predictions but also significant flavor-dependences.
We study the effect of new physics on the Z-decay into b anti-b pairs in the framework of 331 models. The decay Z -> b anti-b is computed at one loop level and, using previous results, we evaluate this branching fraction in the framework of 331 models. A wide range of the space parameter of the model is considered and possible deviations from the standard model predictions are explored. From precision measurements at the Z-pole we find the allowed region for MJ3, MX at 95 % CL.
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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