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HK: Fachverband Physik der Hadronen und Kerne

HK 42: Fundamental Symmetries II

HK 42.2: Group Report

Thursday, March 19, 2026, 16:45–17:15, AM 00.021

Status report of the free neutron lifetime experiment τSPECT — •Martin Fertl for the tauSPECT collaboration — Institute of Physics, Johannes Gutenberg University Mainz, 55099 Mainz, Germany

The accurate determination of the free neutron lifetime τ_n is of particular interest in low-energy precision particle physics. The Standard Model relates the neutron lifetime τ_n to the CKM matrix element V_ud and the ratio λ=g_V/g_A through precisely calculated radiative corrections. A neutron-based determination of V_ud provides a nuclear-structure free input to the test of the CKM matrix unitarity. The τSPECT experiment pursues the approach of suspending ultracold neutrons in a three-dimensional fully-magnetic trap with the goal to determine τ_n with an uncertainty of <0.3 s. Magnetic storage minimizes experimental systematic uncertainties related to neutron losses on material walls. We present the status of τSPECT currently operated at the Paul Scherrer Institute (PSI) in Switzerland. We address the optimization of UCN loading, systematic studies, and comparisons with simulations. Ideas for experimental developments for future improvements below will <0.3 s be presented.

Keywords: Neutron lifetime; Ultracold Neutrons; CKM matrix