[Paper Review] Possible exotic neutrino signature in electron muon collisions

Jai Kumar Singhal, Sardar Singh+1 more|ArXiv.org|Mar 13, 2007

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates lepton flavor violation (LFV) in electron-muon collisions via t-channel exchange of exotic neutrinos, including both light and heavy states, within a generalized neutrino mixing framework. Using constraints from μ→eγ decay, it shows that the differential cross section and angular distribution of e⁺μ⁻→W⁺W⁻ processes are sensitive to heavy neutrino mass and center-of-mass energy, offering a detectable signature for exotic neutrino mixings at future e⁻μ colliders.

ABSTRACT

With the strong experimental evidence for standard neutrino mass and mixings, there exists now a possibility of the lepton flavor violating process e\sup + mu \sup - \arrow W \sup + W \sup -, which would occur via t-channel neutrino exchange induced by neutrino mixings. We consider Langackers generalized neutrino mixings including ordinary (canonical SU(2) \sub L x U(1) \sub Y assignments), exotic (non-canonical SU(2) \sub L x U(1) \sub Y assignments) and singlet neutrinos leading to light and heavy mass eigen states. Constraints on lepton flavor violating (LFV) ordinary and heavy neutrino overlap parameters are obtained by using the current experimental bounds on LFV process Mu \arrow e gamma . These constraints are used to analyze the dependence of differential cross section and angular distribution, for the process e\sup + mu \sup - \arrow W \sup + W \sup -, on the mass of heavy (exotic) neutrino and c. m. energy (sqrt(s)). The possibility of obtaining signatures of exotic neutrino mixings at e - Mu collider is discussed.

Motivation & Objective

• To explore the possibility of lepton flavor violation (LFV) in electron-muon collisions due to t-channel exchange of exotic neutrinos.
• To extend standard neutrino mixing to include non-canonical SU(2)_L × U(1)_Y assignments and singlet neutrinos, generating both light and heavy mass eigenstates.
• To constrain overlap parameters of ordinary and heavy neutrinos using experimental bounds from the μ→eγ decay process.
• To analyze the differential cross section and angular distribution of e⁺μ⁻→W⁺W⁻ as a function of heavy neutrino mass and center-of-mass energy.
• To assess the feasibility of detecting exotic neutrino mixings at future e⁻μ colliders through observable signatures in W-boson production.

Proposed method

• The study employs Langacker's generalized neutrino mixing framework, incorporating canonical, non-canonical, and singlet neutrino states to describe light and heavy mass eigenstates.
• It derives constraints on lepton flavor violating overlap parameters using current experimental limits on the μ→eγ decay branching ratio.
• The differential cross section for e⁺μ⁻→W⁺W⁻ is calculated in the t-channel exchange approximation, assuming neutrino mixing mediates the process.
• The angular distribution of the final-state W bosons is analyzed to identify kinematic signatures sensitive to exotic neutrino contributions.
• Numerical simulations are performed across varying center-of-mass energies (√s) and heavy neutrino masses to map observable signal dependence.

Experimental results

Research questions

• RQ1 Can lepton flavor violation in e⁺μ⁻ collisions be mediated by t-channel exchange of exotic neutrinos within a generalized mixing framework?
• RQ2 How do constraints from the μ→eγ decay process affect the allowed overlap parameters of heavy and ordinary neutrinos?
• RQ3 What is the dependence of the differential cross section for e⁺μ⁻→W⁺W⁻ on the mass of the heavy (exotic) neutrino and the center-of-mass energy?
• RQ4 How does the angular distribution of W bosons in the final state reflect the presence of exotic neutrino states?
• RQ5 Can future e⁻μ colliders detect signatures of exotic neutrino mixings through measurable deviations in cross section and angular distributions?

Key findings

• The differential cross section for e⁺μ⁻→W⁺W⁻ shows a significant dependence on the mass of the heavy (exotic) neutrino, with observable enhancements in specific mass and energy regimes.
• The angular distribution of the final-state W bosons exhibits a distinct pattern sensitive to the presence of exotic neutrino states, differing from the standard model prediction.
• Constraints from the μ→eγ decay process limit the overlap parameters of heavy and ordinary neutrinos, reducing the parameter space for observable LFV signals.
• The signal strength increases with center-of-mass energy, suggesting higher sensitivity at higher-energy e⁻μ colliders.
• The study identifies specific kinematic regions where exotic neutrino contributions could produce a measurable deviation from the standard model in e⁺μ⁻→W⁺W⁻ processes.