Sensitivity of the SHiP experiment to Heavy Neutral Leptons

Abstract: Heavy Neutral Leptons (HNLs) are hypothetical particles predicted by many extensions of the Standard Model. These particles can, among other things, explain the origin of neutrino masses, generate the observed matter-antimatter asymmetry in the Universe and provide a dark matter candidate. The SHiP experiment will be able to search for HNLs produced in decays of heavy mesons and travelling distances ranging between $\mathcal{O}(50\text{ m})$ and tens of kilometers before decaying. We present the sensitivity of the SHiP experiment to a number of HNL's benchmark models and provide a way to calculate the SHiP's sensitivity to HNLs for arbitrary patterns of flavour mixings. The corresponding tools and data files are also made publicly available.

• The paper presents a simulation study quantifying SHiP's capability to detect Heavy Neutral Leptons with up to three orders of magnitude sensitivity improvement.
• The methodology employs advanced Monte Carlo techniques using Pythia and GEANT4 to model particle production and decay processes.
• Findings underscore the experiment's potential impact on understanding neutrino masses, matter-antimatter asymmetry, and dark matter candidates.

Sensitivity of the SHiP Experiment to Heavy Neutral Leptons

The paper "Sensitivity of the SHiP Experiment to Heavy Neutral Leptons" provides a comprehensive evaluation of the SHiP (Search for Hidden Particles) experiment's potential to detect Heavy Neutral Leptons (HNLs). This study is pivotal for extending our understanding of the Standard Model (SM) extensions, as HNLs are hypothesized to elucidate the small neutrino masses, contribute to the matter-antimatter asymmetry, and offer a potential dark matter candidate.

SHiP Experiment Overview

The SHiP experiment, proposed at CERN's SPS accelerator, is designed to discover long-lived, exotic particles within the mass range of hundreds of MeV to several GeV. The initiative aims to optimize the production and detection of charm and beauty mesons, with an ultimate goal to collect $2 \times 10^{20}$ protons on target over five years. A high-density target coupled with a robust detector system, comprising a vacuum tank, spectrometers, and muon shields, ensures minimized background noise from muon interactions and other sources. This configuration is essential to examine the decays of HNLs with precision.

Heavy Neutral Leptons and their Implications

HNLs or right-handed neutrinos have been postulated as plausible mechanisms behind neutrino masses since the late 1970s. Their role has been expanded to potentially explain the Universe's baryon asymmetry, notably through processes like leptogenesis. Current HNL theories suggest their relevance within the GeV mass scale, making them detectable in particle physics laboratories like the SHiP facility. The so-called Neutrino Minimal Standard Model (νMSM) incorporates three HNLs, offering a viable candidate for dark matter and adherence to existing accelerator experiment constraints.

Simulation and Sensitivity Assessment

The paper employs a sophisticated Monte Carlo simulation using FairShip, which incorporates various aspects of SHiP's design and operational parameters. The simulations include primary collision generation using Pythia 8, particle propagation with GEANT4, and heavy flavor production using Pythia 6 alongside cascade enhancements.

Key numerical outputs, such as charm and beauty meson production fractions and the corresponding enhancement factors, underline the SHiP's high sensitivity. The paper meticulously presents simulation results over a wide parameter space, offering a detailed estimation of SHiP's sensitivity to HNLs across various flavour mixings.

Implications and Future Prospects

The SHiP experiment could significantly enhance the detection potential for HNLs, achieving up to three orders of magnitude improvement in sensitivity. This could provide insights into fundamental questions regarding neutrino masses and matter-antimatter imbalance. The research has broader implications for physics beyond the SM, particularly as theories involving HNLs are investigated further. The findings and methods described provide a platform for ongoing and future experimental explorations in particle physics, potentially paving the way for the discovery of new physics phenomena.

In conclusion, the study offers a robust framework and technical resources for probing HNLs, presenting a model-independent approach to assessing the sensitivity of the SHiP experiment. This research represents a significant step towards expanding our understanding of neutrino physics and the potential discovery of new particles related to the dark sector.