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Register a new userOn the possibility of search for $L_mu - L_tau$ gauge boson at Belle-II and neutrino beam experiments
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We study the possibilities on the search of the light and weakly interacting gauge boson in the gauged $L_mu - L_tau$ model. Introducing the kinetic mixing at the tree-level, the allowed parameter regions for the gauge coupling and kinetic mixing parameter are presented. Then, we analyze one photon plus missing event within the allowed region and show that search for the light gauge boson will be possible at Belle-II experiment. We also analyze neutrino trident production process in neutrino beam experiments.
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We study a model with $U(1)_{L_mu - L_tau}$ gauge symmetry and discuss collider searches for a scalar boson, which breaks $U(1)_{L_mu - L_tau}$ symmetry spontaneously, decaying into light $Z$ gauge boson. In this model, the new gauge boson, $Z$, with a mass lighter than $mathcal{O}(100)$ MeV, plays a role in explaining the anomalous magnetic moment of muon via one-loop contribution. For the gauge boson to have such a low mass, the scalar boson, $phi$ with $mathcal{O}(100)$ GeV mass appears associated with the symmetry breaking. We investigate experimental constraints on $U(1)_{L_mu - L_tau}$ gauge coupling, kinetic mixing, and mixing between the SM Higgs and $phi$. Then collider search is discussed considering $phi$ production followed by decay process $phi to Z Z$ at the large hadron collider and the international linear collider. We also estimate discovery significance at the linear collider taking into account relevant kinematical cut effects.
We discuss the feasibility of detecting the gauge boson of the $U(1)_{L_{mu}-L_{tau}}$ symmetry, which possesses a mass in the range between MeV and GeV, at the Belle-II experiment. The kinetic mixing between the new gauge boson $Z$ and photon is forbidden at the tree level and is radiatively induced. The leptonic force mediated by such a light boson is motivated by the discrepancy in muon anomalous magnetic moment and also the gap in the energy spectrum of cosmic neutrino. Defining the process $e^{+} e^{-} rightarrow gamma Z rightarrow gamma u bar{ u}~(missing~energy)$ to be the signal, we estimate the numbers of the signal and the background events and show the parameter region to which the Belle-II experiment will be sensitive. The signal process in the $L_{mu}-L_{tau}$ model is enhanced with a light $Z$, which is a characteristic feature differing from the dark photon models with a constant kinetic mixing. We find that the Belle-II experiment with the design luminosity will be sensitive to the $Z$ with the mass $M_{Z} lesssim 1 $ GeV and the new gauge coupling $g_{Z} gtrsim 8cdot 10^{-4}$, which covers a half of the unconstrained parameter region that explains the discrepancy in muon anomalous magnetic moment. The possibilities to improve the significance of the detection are also discussed.
Extending the Standard Model (SM) by a $U(1)_{L_mu-L_tau}$ group gives potentially significant new contributions to $g_mu-2$, allows the construction of realistic neutrino mass matrices, incorporates violation of lepton universality violation, and offers an anomaly-free mediator for a Dark Matter (DM) sector. In a recent analysis we showed that published LHC searches are not very sensitive to this model. Here we apply several Machine Learning (ML) algorithms in order to distinguish this model from the SM using simulated LHC data. In particular, we optimize the $3mu$-signal, which has a considerably larger cross section than the $4mu$-signal. Furthermore, since the $2$-muon plus missing $E_T$ final state gets contributions from diagrams involving DM particles, we optimize it as well. We find greatly improved sensitivity, which already for $36$ fb$^{-1}$ of data exceeds the combination of published LHC and non-LHC results. We also emphasize the usefulness of Boosted Decision Trees which, unlike Neural Networks, easily allow to extract additional information from the data which directly connect to the theoretical model. The same scheme could be used to analyze other models.
In this paper, we study the phenomenology of a Dirac dark matter in the $L_mu-L_tau$ model and investigate the neutrino oscillation in the dark halo. Since dark matter couples to the muon neutrino and the tau neutrino with opposite sign couplings, it contributes effective potentials, $pm A_chi$, to the evolution equation of the neutrino flavor transition amplitude, which can be significant for high energy neutrino oscillations in a dense dark matter environment. We discuss neutrino masses, lepton mixing angles, Dirac CP phase, and neutrino oscillation probabilities in the dark halo using full numerical calculations. Results show that neutrinos can endure very different matter effects. When the potential $A_chi$ becomes ultra-large, three neutrino flavors decouple from each other.
We investigate features of the sterile neutrinos in the presence of a light gauge boson $X^mu$ that couples to the neutrino sector. The novel bounds on the active-sterile neutrino mixings $| U_{ell 4} |^2$, especially for tau flavor ($l = tau$), from various collider and fixed target experiments are explored. Also, taking into account the additional decay channel of the sterile neutrino into a light gauge boson ($ u_4 to u_ell e^+ e^-$), we explore and constrain a parameter space for low energy excess in neutrino oscillation experiments.
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