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Register a new userSearch for a light $Z^prime$ at LHC in a neutrinophilic $U(1)$ model
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We consider a neutrinophilic $U(1)$ extension of the standard model (SM) which couples only to SM isosinglet neutral fermions, charged under the new group. The neutral fermions couple to the SM matter fields through Yukawa interactions. The neutrinos in the model get their masses from a standard inverse-seesaw mechanism while an added scalar sector is responsible for the breaking of the gauged $U(1)$ leading to a light neutral gauge boson ($Z$) which has minimal interaction with the SM sector. We study the phenomenology of having such a light $Z$ in the context of neutrinophilic interactions as well as the role of allowing kinetic mixing between the new $U(1)$ group with the SM hypercharge group. We show that current experimental searches allow for a very light $Z$ if it does not couple to SM fields directly and highlight the search strategies at the LHC. We observe that multi-lepton final states in the form of $(4ell + mET)$ and $(3ell + 2j + mET)$ could be crucial in discovering such a neutrinophilic gauge boson lying in a mass range of $200$--$500$ GeV.
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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.
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We study $Z$ phenomenology at hadron colliders in an $U(1)$ extended MSSM. We choose a $U(1)$ model with a secluded sector, where the tension between the electroweak scale and developing a large enough mass for $Z$ is resolved by incorporating three additional singlet superfields into the model. We perform a detailed analysis of the production, followed by decays, including into supersymmetric particles, of a $Z$ boson with mass between 4 and 5.2 TeV, with particular emphasis on its possible discovery. We select three different scenarios consistent with the latest available experimental data and relic density constraints, and concentrate on final signals with two leptons, four leptons and six leptons. Including the SM background from processes with two, three or four vector bosons, we show the likelihood of observing a $Z^prime$ boson is not promising for the HL-LHC at 14 TeV. While at 27 and 100 TeV, the situation is more optimistic, and we devise specific benchmark scenarios which could be observed.
We investigate the potential of LHC resonance searches in leptonic final states to probe the $Z$ in the minimal $U(1)_{B-L}$ model. Considering the current constraints on the $Z$ in terms of its mass $m_{Z}$ and the associated gauge coupling $g_{B-L}$ as well as constraints in the Higgs sector, we analyse the potential of dilepton and four lepton final states for $Z$ production. This includes Drell-Yan production, Higgs mediated decays and final state radiation processes concentrating only on the ATLAS and CMS detectors at the LHC. We show that the four-lepton final state is sensitive to $m_{Z}$ as low as 0.25 GeV. Furthermore, setting the Higgs mixing to $sinalpha = 0.3$, this final state has a strong sensitivity and it probes regions of parameter space where the $Z$ is long-lived. We demonstrate the sensitivity at the High Luminosity LHC and comment on the potential of probing displaced vertices due to long-lived $Z$. Finally, we also comment on the strength of $Z$ and Higgs mediated heavy neutrino processes by taking into account the constraints derived.
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.
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