Probing the muon g − 2 with future beam dump experiments

Abstract

We consider the light Z′ explanation of the muon g − 2 anomaly. Even if such a Z′ has no tree-level coupling to electrons, in general one will be induced at loop-level. We show that future beam dump experiments are powerful enough to place stringent constraints on—or discover—a Z′ with loop-suppressed couplings to electrons. Such bounds are avoided only if the Z′ has a large interaction with neutrinos, in which case the scenario will be bounded by ongoing neutrino scattering experiments. The complementarity between beam dump and neutrino scattering experiments therefore indicates that there are good prospects of probing a large part of the Z′ parameter space in the near future.

Dark matter produced from neutrinos

“…Given the small coupling values in figure 3 and the issue of gauge invariance, we would like to comment on the implication for the anomalous magnetic moment of the muon (g−2) µ , which has shown a 4.2σ tension between the SM value and the recent measurement [55]. If the vector boson is coupled to the muon via a coupling y µ , its contribution to (g − 2) µ in the low-mass limit is ∆a µ = y 2 µ /(8π 2 ) [56,57]. Hence, the recent measurement ∆a µ ≈ (25.1 ± 5.9) × 10 −10 indicates that y µ needs to be > 4.5 × 10 −4 in order to address this anomaly.…”

Probing the $ν_{R}$-philic $Z'$ at DUNE near detectors

“…6, being labelled as (g − 2) µ and (g − 2) e , respectively. These curves are obtained by setting ∆α µ ≤ 5.5 × 10 −9 (5σ) [45] and ∆α e ≤ 13.8 × 10 −13 (3σ) [46] where ∆α ( = µ, e) is computed by [27,47]…”

“…A number of studies have shown that beam dump experiments in general have great capabilities to constrain Z with very weak couplings, provided that its visible decay width is not too small [23][24][25][26][27]. For the ν R -philic Z , the comparatively large couplings to neutrinos would suppress the visible decay width but enhance the production rate.…”

Neutrino forces and the Sommerfeld enhancement

“…The Z of a gauged L µ − L τ is permitted by experiments to have order-one couplings as long as its mass is m Z 200 GeV, around which it is mainly constrained by the muon g − 2 and CCFR -see e.g. [79]. One can then introduce a vector-like fermion (thereby avoiding gauge anomalies), χ, which is charged under the L µ − L τ , as the DM candidate.…”