Neutral exotica at FASERν and SND@LHC.

The (g − 2)μ anomaly indicates that the second generation of leptons should have new interactions beyond the standard model. The high flux of νμ and ν ¯ μ at the forward experiments such as FASERν and SND@LHC makes them suitable setups to search for new interactions of the second generation leptons. In this paper, we build a model in which the second generation left-handed leptons couple to a new right-handed neutrino, N and a new Higgs doublet which also couples to the quarks. The scattering of high energy νμ off nuclei can produce N. We investigate how forward experiments can test this model by looking for the N production vertex followed by the displaced vertex of the N decay. Discovering even a single such event can be a harbinger to look for the spectacular signals of the new Higgs doublet production at the LHC. We discuss the possibility of explaining the (g − 2)μ anomaly by adding more generations of N which will lead to chain decays of N and multiple leptons with distinct signals both at forward experiments and at the CMS and ATLAS detectors. Finally, we show that by adding a new light singlet scalar mixed with the neutral component of the new Higgs doublet (i.e., 2HDM+S model), the statistics of the data sample can be dramatically increased. [ABSTRACT FROM AUTHOR]