The precise value of the mean neutron lifetime, τ, plays an important role in nuclear and particle physics and cosmology. It is used to predict the ratio of protons to helium atoms in the primordial universe and to search for physics beyond the Standard Model of particle physics. We eliminated loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls. As a result of this approach and the use of an in situ neutron detector, the lifetime reported here [877.7 ± 0.7 (stat) +0.4/-0.2 (sys) seconds] does not require corrections larger than the quoted uncertainties.
Using the BNL Accelerator Test Facility we have shown that a tightly focused laser on a vacuum can accelerate an electron beam in free space. The electron beam had energy of 20 MeV and the CO2 laser had energy of about 3 Joule. In the readout of the experiment we detect a clear effect for the laser beam off and on. The size of the effect is about 20% and is reproducible over many laser and beam shots. This is a proof of principle and the data are fully consistent with the CAS theory. The results of this experiment may have an impact on the LASER fusion method.
In this paper, we describe a new method for measuring surviving neutrons in neutron lifetime measurements
using bottled ultracold neutrons (UCN), which provides better characterization of systematic
uncertainties
and enables higher precision than previous measurement techniques. An active detector
that can be lowered into the trap has been used to measure the
neutron
distribution as a function of height and measure the influence of marginally trapped
UCN on the neutron
lifetime measurement. In addition, measurements have demonstrated phase-space
evolution and its effect on the lifetime measurement.
A multilayer surface detector for ultracold neutrons (UCNs) is described.
The top10 B layer is exposed to vacuum and directly captures UCNs. The ZnS:Ag layer beneath the 10 B layer is a few microns thick, which is sufficient to detect the charged particles from the 10 B(n,α)
The neutron is the simplest nuclear system that can be used to probe the structure of the weak interaction and search for physics beyond the standard model. Measurements of neutron lifetime and β-decay correlation coefficients with precisions of 0.02% and 0.1%, respectively, would allow for stringent constraints on new physics. The UCNτ experiment uses an asymmetric magneto-gravitational UCN trap with in situ counting of surviving neutrons to measure the neutron lifetime, τn = 877.7s (0.7s)stat (+0.4/−0.2s)sys. We discuss the recent result from UCNτ, the status of ongoing data collection and analysis, and the path toward a 0.25 s measurement of the neutron lifetime with UCNτ.
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