ABSTRACT
We report an improved measurement of the free neutron lifetime τ_{n} using the UCNτ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38×10^{6} surviving ultracold neutrons (UCNs) after storing in UCNτ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τ_{n} from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τ_{n} measurements and by performing a global likelihood fit to all data while self-consistently incorporating the ß-decay lifetime. Both techniques achieve consistent results and find a value τ_{n}=877.75±0.28_{stat}+0.22/-0.16_{syst} s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
ABSTRACT
The precise value of the mean neutron lifetime, τn, 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.
ABSTRACT
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.
ABSTRACT
With the introduction of continuous-energy heavy charged particle transport in MCNP5, the need for tracking charged particles in a magnetic field becomes increasingly important. Two methods for including magnetic field effects on charged particles are included in the proton transport version of the code. The first technique utilises transfer maps produced by the beam dynamics simulation and analysis code COSY INFINITY. This method is fast and accurate; however, its use is limited to void cells only and to ensembles of particles with a fairly small energy spread. The second technique, particle ray tracing, is based on an algorithm adopted from the MARS transport code. This method can be applied to both void and material cells and is valid over a very large range of particle energies. Results from tracking particles in a quadrupole 'identity lens' using the two techniques are compared.
Subject(s)
Electromagnetic Fields , Heavy Ions , Linear Energy Transfer , Models, Statistical , Monte Carlo Method , Radiometry/methods , Software , Computer Simulation , Radiation Dosage , Radiation Protection/methodsABSTRACT
A moving-coil linear variable differential transformer with no ferromagnetic components is described. The device is essentially interchangeable with a conventional moving-core linear variable differential transformer, but is virtually unaffected by ambient magnetic fields up to 8 T. The transducer is connected to a standard commercially available carrier amplifier for signal conditioning.
