Hunting for neutral leptons with ultrahigh energy neutrinos

Topic

natural sciences

Frequently Asked Questions (FAQ)

What are ultra-high-energy cosmic rays (UHECRs) and why are they important for particle physics? UHECRs are particles from space with extremely high energies, exceeding those achievable in human-made particle accelerators. Studying them can potentially reveal new particles and physics beyond the Standard Model. Neutrinos are particularly interesting UHECR candidates because they interact weakly and can travel long distances through space and Earth.
How does the Standard Model predict UHE neutrinos should behave when traveling through Earth? Standard Model neutrinos interact with matter through charged-current (CC) and neutral-current (NC) interactions. In CC interactions, the neutrino converts into a charged lepton of the same flavor. In NC interactions, the neutrino remains a neutrino but loses energy. The Earth becomes opaque to SM neutrinos above certain energies and chord lengths, making UHE neutrinos observable only when they skim the Earth’s surface at very small angles.
What is tau regeneration and how does it affect the detection of UHE neutrinos? Tau regeneration occurs when a tau neutrino interacts via CC to become a tau lepton, which then decays back into a tau neutrino. This process allows some tau neutrinos to travel further through the Earth than expected based on interaction cross-sections. Tau regeneration is the dominant source of UHE tau neutrino signals at emergence angles greater than ~10 degrees.
How could new physics affect the propagation of UHECRs through Earth? New physics, such as right-handed neutrinos (RHNs), could modify how UHECRs interact with matter. An RHN could mix with SM neutrinos, leading to additional interaction channels and allowing UHECRs to propagate through the Earth more easily at larger emergence angles.
What is the minimal model being considered in this study and how does it affect neutrino propagation? The study introduces a right-handed neutrino (RHN) that mixes with the tau neutrino. This opens a new interaction pathway where a tau neutrino can interact via NC to become an RHN, which could travel a significant distance before decaying back into a tau neutrino or tau lepton. This process could enhance the flux of UHECRs observed at large emergence angles.
How were the simulations performed and what were the key findings? A modified version of the TauRunner program simulated the propagation of UHE tau neutrinos through the Earth, incorporating the new interactions introduced by the RHN model. The simulations calculated the probability of tau leptons and RHNs exiting the Earth for various emergence angles, RHN masses, and mixing angles. The key finding was that, for certain parameter combinations, the RHN model significantly increases the probability of UHECR detection at large emergence angles compared to SM predictions.
What are the differences between GRAND and POEMMA and why is one more suitable for this study? GRAND is a ground-based array of radio antennas designed to detect UHECRs by observing radio signals from extensive air showers. POEMMA is a space-based observatory using optical and ultraviolet fluorescence techniques. GRAND primarily observes UHECRs at shallow emergence angles where the RHN signal is negligible. POEMMA’s high altitude and wider field of view allow it to probe large emergence angles where BSM effects are more prominent.
How could POEMMA be used to search for right-handed neutrinos and what are the potential implications of such a discovery? By observing transient events like gamma-ray bursts at large emergence angles, POEMMA could detect an excess of UHECR events compared to SM predictions. This excess could indicate new physics, possibly the existence of RHNs. Discovering RHNs would have profound implications for particle physics and cosmology, requiring an extension of the SM and offering insights into neutrino masses and dark matter.

Significance

Understanding these findings helps advance our knowledge and inform better decisions. This research represents an important contribution to the field. For the full details, watch the video above and explore the linked resources.

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hunting for neutral leptons with ultrahigh energy neutrinos

ResearchLounge

https://researchlounge.org/natural-sciences/physics/hunting-for-neutral-leptons-with-ultrahigh-energy-neutrinos/