[Paper Review] Testing heavy neutral leptons produced in the supernovae explosions with future neutrino detectors

Vsevolod Syvolap|arXiv (Cornell University)|Jan 17, 2023

Neutrino Physics Research4 citations

TL;DR

This paper proposes using future neutrino detectors like Hyper-Kamiokande to detect secondary high-energy neutrinos produced by the decay of heavy neutral leptons (HNLs) generated in supernova cores. It demonstrates that Hyper-K could probe HNL masses from 160–700 MeV and lifetimes >0.02 seconds, closing a critical gap between current Big Bang nucleosynthesis constraints and the future SHiP experiment's sensitivity.

ABSTRACT

Hypothetical particles called heavy neutral leptons (HNLs) can be produced in large quantities in the cores of supernovae during the first seconds of the explosion. These particles then decay, producing secondary energetic neutrinos that can be detected by neutrino detectors. In this paper, I identify a region of the HNL parameter space that could be tested using this method, assuming a supernova explosion at distances from 0.2 to 10 kpc. The range of HNLs masses $m_N \sim 160-700$ MeV and lifetimes of $τ_N \gtrsim 0.02$ seconds can be probed using the Hyper-Kamiokande neutrino detector. This region of the parameter space is complementary to existing bounds from primordial nucleosynthesis and to the expected sensitivity of the future SHiP experiment, thus covering a gap in our current knowledge of HNLs up to masses of $m_N \simeq 400$ MeV.

Motivation & Objective

• To identify a previously untested region of the heavy neutral lepton (HNL) parameter space using secondary neutrinos from supernova-produced HNL decays.
• To demonstrate that future neutrino detectors like Hyper-Kamiokande can probe HNL masses and lifetimes inaccessible to current energy-loss constraints or upcoming experiments like SHiP.
• To extend prior work by systematically analyzing HNL production, decay, and detection across different flavor mixings and detector configurations.
• To quantify the sensitivity of Hyper-Kamiokande to HNLs produced in supernovae at distances from 0.2 to 10 kpc, particularly for tau-flavored HNLs.
• To assess the complementarity of this method with existing bounds from Big Bang nucleosynthesis and future SHiP sensitivity, especially in the 160–450 MeV mass range.

Proposed method

• Uses a snapshot-based supernova model to simulate HNL production in the core, assuming thermal equilibrium and known neutrino and lepton densities.
• Calculates HNL production cross-sections via weak interactions involving tau, muon, and electron neutrinos, using matrix elements normalized to Fermi coupling and mixing parameters.
• Models HNL decays into secondary neutrinos via 2- and 3-body processes, including kinematical constraints and branching ratios dependent on HNL mass and lifetime.
• Incorporates neutrino oscillations and the MSW effect to compute the final flavor composition of secondary neutrinos at Earth, focusing on anti-electron neutrinos.
• Applies detector response functions to estimate detectable event rates in Hyper-Kamiokande and Super-Kamiokande, assuming a 10 kpc supernova distance.
• Compares detection sensitivity across different HNL mixing scenarios (tau, muon, electron flavors), with emphasis on the dominant tau-flavor channel.

Experimental results

Research questions

• RQ1 Can secondary neutrinos from decaying heavy neutral leptons in supernovae be detected by future neutrino telescopes like Hyper-Kamiokande?
• RQ2 What range of HNL masses and lifetimes can be probed using this method, particularly in the context of a nearby supernova (0.2–10 kpc)?
• RQ3 How does this detection method complement existing constraints from Big Bang nucleosynthesis and the future SHiP experiment?
• RQ4 What is the impact of different HNL flavor mixings (tau, muon, electron) on the detectable secondary neutrino flux and event rates?
• RQ5 How does detector size and sensitivity affect the feasibility of detecting these secondary neutrino signals?

Key findings

• Hyper-Kamiokande can detect secondary neutrinos from HNL decays with masses between 160 MeV and 700 MeV, provided their lifetimes exceed approximately 0.02 seconds.
• For a supernova at 10 kpc, Hyper-Kamiokande would detect more than 100 events for HNLs with masses in the 160–450 MeV range and mixing parameters consistent with the model.
• The method closes a critical gap in HNL parameter space between current Big Bang nucleosynthesis bounds and the expected sensitivity of the SHiP experiment, particularly for HNLs with masses up to 400 MeV.
• The sensitivity is significantly reduced for Super-Kamiokande due to its smaller size, requiring a factor of ~10 larger mixing angles to achieve comparable detection thresholds.
• For a nearby supernova like Betelgeuse (200 pc), event rates could increase by several orders of magnitude, potentially enabling detection even with existing detectors.
• HNLs mixed with the muon flavor would produce similar secondary neutrino fluxes as those mixed with the tau flavor, but with faster decay rates due to additional decay channels, though the detectable parameter space remains largely comparable.