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To solve the ``neutron lifetime puzzle,'' where measured neutron lifetimesdiffer depending on the measurement methods, an experiment with pulsed neutronbeam at J-PARC is in progress. In this experiment, neutrons are bunched into40-cm lengths using a spin flip chopper (SFC), where the statisticalsensitivity was limited by the aperture size of the SFC. The SFC comprisesthree sets of magnetic supermirrors and two resonant spin flippers. In thispaper, we discuss an upgrade to enlarge the apertures of the SFC. The improvedSFC achieved a signal-to-noise ratio of 250--400, which is comparable to theprevious one. The statistics per unit time of the neutron lifetime experimentincreased 2.8 times with the upgrade. Consequently, the time required to reachan accuracy of 1~s in the neutron lifetime experiment was reduced from 590 to170~days, which is a significant reduction in time. This improvement instatistical accuracy will also contribute to the reduction of systematicuncertainties, such as background evaluation, fostering further advancements inthe neutron lifetime experiments at J-PARC.

Performance of the Full-equipped Spin Flip Chopper For Neutron Lifetime Experiment at J-PARC