Disentangling Genuine from Matter-Induced CP Violation in Neutrino Oscillations

Area of Science:

• Particle Physics
• Astrophysics
• Cosmology

Background:

• Neutrino oscillations are a key phenomenon in particle physics, demonstrating that neutrinos have mass.
• Understanding CP violation in the neutrino sector is crucial for explaining the matter-antimatter asymmetry in the universe.
• Matter effects in neutrino propagation can influence oscillation patterns, complicating the extraction of fundamental parameters.

Purpose of the Study:

• To disentangle the CPT-odd and T-odd components of CP-violating asymmetries in neutrino oscillations in matter.
• To identify distinct observables for probing the neutrino mass hierarchy and genuine CP violation.
• To explore the potential of specific neutrino channels and energy ranges for these investigations.

Main Methods:

• Theoretical analysis of neutrino flavor transitions in the presence of matter.
• Derivation of distinct L-even and L-odd observables.
• Investigation of the energy and baseline dependence of CP-violating asymmetries.
• Focus on the golden muon neutrino to electron neutrino (ν_{μ}→ν_{e}) channel.

Main Results:

• CP-violating asymmetries in matter are shown to have two disentangled components: a CPT-odd term dependent on matter interactions and a T-odd term dependent on genuine CP violation.
• These components manifest as distinct L-even and L-odd observables, allowing separate tests of the neutrino hierarchy and CP violation.
• A 'magic energy' at 0.91 GeV for a 1300 km baseline is identified, where the CPT-odd component vanishes, leading to maximal CP asymmetry.
• Above 1.5 GeV, the sign of the CP asymmetry can discriminate the neutrino hierarchy.

Conclusions:

• The disentanglement of CPT-odd and T-odd components provides a novel framework for studying neutrino properties.
• Separate measurements of matter effects and CP violation are achievable through distinct observables.
• The identified magic energy and high-energy CP asymmetry signatures offer promising experimental probes for future neutrino experiments.