Revealing the origin of neutrino masses through the Type II Seesaw mechanism at high-energy muon colliders

We discuss sensitivities to lepton flavor violating (and conserving) interactions at future muon colliders, especially at μ+μ+ colliders. Compared with the searches for rare decays of μ and τ, we find that the TeV-scale future colliders have better sensitivities depending on the pattern of hierarchy in the flavor mixings. As an example, we study the case with the type-II seesaw model, where the flavor mixing parameters have direct relation to the neutrino mass matrix. At a μ+μ+ collider, the number of events of the μ+μ+ → μ+τ+ process can be larger than $$ \mathcal{O}(100) $$ O 100 with the center of mass energy $$ \sqrt{s} $$ s = 2 TeV, and with an integrated luminosity $$ \mathcal{L} $$ L = 1 ab−1, while satisfying bounds from rare decays of μ and τ. We discuss impacts of the overall mass scale of neutrinos as well as CP violating phases to the number of expected events.

“…The type-II seesaw was studied in refs. [21][22][23][24][25][26] for opposite sign lepton colliders and in ref. [27] for a same sign electron collider.…”

Section: Jhep06(2023)086mentioning

confidence: 94%

Lepton flavor physics at μ+μ+ colliders

Fridell

Kitano

Takai

2023

The new physics case for beam-dump experiments with accelerated muon beams

Cesarotti,

Gambhir

2024

As the field examines a future muon collider as a possible successor to the LHC, we must consider how to fully utilize not only the high-energy particle collisions, but also any lower-energy staging facilities necessary in the R&D process. An economical and efficient possibility is to use the accelerated muon beam from either the full experiment or from cooling and acceleration tests in beam-dump experiments. Beam-dump experiments are complementary to the main collider as they achieve sensitivity to very small couplings with minimal instrumentation. We demonstrate the utility of muon beam-dump experiments for new physics searches at energies from 10 GeV to 5 TeV. We find that, even at low energies like those accessible at staging or demonstrator facilities, it is possible to probe new regions of parameter space for a variety of generic BSM models, including muonphilic, leptophilic, Lμ − Lτ, and dark photon scenarios. Such experiments could therefore provide opportunities for discovery of new physics well before the completion of the full multi-TeV collider.

Searching for heavy neutral lepton and lepton number violation through VBS at high-energy muon colliders

Li,

Yao,

Yuan

2023

High-energy muon collider can play as an emitter of electroweak gauge bosons and thus leads to substantial vector boson scattering (VBS) processes. In this work, we investigate the production of heavy neutral lepton (HNL) N and lepton number violation (LNV) signature through VBS at high-energy muon colliders. VBS induces LNV processes W±Z/γ → ℓ±N → ℓ±ℓ±W∓ → ℓ±ℓ±$$ q\overline{q} $$ q q ¯ ′ with an on-shell HNL N at μ+μ− colliders. In analogy to neutrinoless double-beta decay with the HNL in t-channel, the LNV signature W+W+ → ℓ+ℓ+ can also happen via VBS at same-sign muon collider. They provide clean and robust LNV signatures to tell the nature of Majorana HNLs and thus have more advantageous benefits than direct μμ annihilation. We analyze the potential of searching for Majorana HNL and obtain the exclusion limits on mixing VℓN. Based on this same-sign lepton signature, we also obtain the sensitivity of muon collider to the Weinberg operator.