# Design of the Magnet System of the Neutron Decay Facility PERC

## TL;DR

The paper details the design of a superconducting magnet system for the PERC neutron decay facility, aiming to improve precision in fundamental physics measurements and search for new physics beyond the Standard Model.

## Contribution

It presents the innovative design of a 12m superconducting magnet system with specialized regions to optimize neutron decay experiments and reduce systematic uncertainties.

## Key findings

- Design achieves a uniform decay region magnetic field.
- High-field region effectively selects phase space for decay particles.
- Magnet system enhances measurement precision for fundamental physics.

## Abstract

The PERC (Proton and Electron Radiation Channel) facility is currently under construction at the research reactor FRM II, Garching. It will serve as an intense and clean source of electrons and protons from neutron beta decay for precision studies. It aims to contribute to the determination of the Cabibbo-Kobayashi-Maskawa quark-mixing element $V_{ud}$ from neutron decay data and to search for new physics via new effective couplings. PERC's central component is a 12m long superconducting magnet system. It hosts an 8m long decay region in a uniform field. An additional high-field region selects the phase space of electrons and protons which can reach the detectors and largely improves systematic uncertainties. We discuss the design of the magnet system and the resulting properties of the magnetic field.