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Abstract

The neutron lifetime is an essential parameter in Big Bang nucleosynthesis, and to determine Vud of the CKM matrix. Currently, a 4σ discrepancy exists between beam and trap lifetime experiments. The PENeLOPE experiment aims to measure the neutron lifetime using ultracold neutrons (UCNs) with a precision of 0.1 s. Two butterfly shutters were tested for PENeLOPE and had average relative leak rates of 2.23 ± 1.10 % and 1.01 ± 0.85 %,which proved them to be inadequate. PENeLOPE simulations showed the precision goal is met with a stainless-steel spin-flip probability (βSS) of 10−5, resulting in a 0.0451 ± 0.0022 s systematic shift created by marginally trapped UCNs. Seven runs yielded a statistical precision of 0.096 ± 0.0012 s, using the neutron yield from the planned UCN source at FRM II. Higher βSS values caused prohibitively large systematic shifts, which could be mitigated by nickel-phosphorous coating to reduce β.