Abstract
We investigate the sensitivity of the FASERν detector to new physics in the form of non-standard neutrino interactions. FASERν, which will be installed 480 m downstream of the ATLAS interaction point, will for the first time study interactions of multi-TeV neutrinos from a controlled source. Our formalism — which is applicable to any current and future neutrino experiment — is based on the Standard Model Effective Theory (SMEFT) and its counterpart, Weak Effective Field Theory (WEFT), below the electroweak scale. Starting from the WEFT Lagrangian, we compute the coefficients that modify neutrino production in meson decays and detection via deep-inelastic scattering, and we express the new physics effects in terms of modified flavor transition probabilities. For some coupling structures, we find that FASERν will be able to constrain interactions that are two to three orders of magnitude weaker than Standard Model weak interactions, implying that the experiment will be indirectly probing new physics at the multi-TeV scale. In some cases, FASERν constraints will become comparable to existing limits — some of them derived for the first time in this paper — already with 150 fb−1 of data.
Highlights
We investigate the sensitivity of the FASERν detector to new physics in the form of non-standard neutrino interactions
We have highlighted the significant potential of the FASERν detector at CERN to constrain new physics affecting neutrino interactions with matter
Weak Effective Field Theory, we have identified the charged-current dimension-6 operators that modify the observable neutrino rates in FASERν
Summary
Let us present the Effective Field Theory (EFT) formalism that we will use and that was introduced in refs. [8, 9]. Up-quark and charged lepton fields are denoted by dk, uj and α, respectively. The interaction strengths of the new operators in eq (2.1) are parameterized in terms of the dimensionless Wilson coefficients [ jXk]αβ, where j, k specify the quark generations and α, β the lepton generations involved in the corresponding dimension-6 operator. From a UV point of view, the Wilson coefficients [ jXk]αβ encode new interactions between quarks and leptons mediated by heavy (above ∼ 2 GeV) nonstandard fields. This might seem problematic, given that FASERν will only be sensitive at quadratic order to some of the dimension-6 operators It is not at odds with WEFT power counting.
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