Neutron lifetime measurements using gravitationally trapped ultracold neutrons

Abstract

Our experiment using gravitationally trapped ultracold neutrons (UCN) to measure the neutron lifetime is reviewed. Ultracold neutrons were trapped in a material bottle covered with perfluoropolyether. The neutron lifetime was deduced from comparison of UCN losses in the traps with different surface-to-volume ratios. The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. In this experiment, the UCN storage time is brought closer to the neutron lifetime than in any experiments before: the probability of UCN losses from the trap was only 1% of that for neutron β decay. The neutron lifetime obtained, 878.5 ± 0.7 stat ± 0.3 sys s, is the most accurate experimental measurement to date.A. P. SEREBROV et al. PHYSICAL REVIEW C 78, 035505 (2008) 035505-3 A. P. SEREBROV et al. PHYSICAL REVIEW C 78, 035505 (2008)

Surface roughness effect on ultracold neutron interaction with a wall and implications for computer simulations

“…It shows that the loss enhancement strongly depends on the trap geometry and UCN energy and is significant for very low energy UCN "hopping" in small jumps on an essentially flat horizontal surface, for instance the rim of a cylinder with horizontal axis, as in Ref. [3].…”

“…The critical value k c0 is for the LTF oil in its glass state at ∼110 K used in Ref. [3]. The agreement is excellent, indicating that for these parameters the Born approximation for the DWF is adequate.…”

“…We investigate especially the relation between a realistic account of roughness in computer simulations of UCN storage and a reliable data interpretation with respect to the neutron lifetime. The issue has gained added importance since a new UCN storage-based lifetime value 6 standard deviation away from the world average value [2] was published in 2005 [3].…”

Experimental limits on neutron disappearance into another braneworld

“…If the neutron oscillation between branes is detected and presents an annual dependence through ∆p, since we can estimate ∆η we can therefore expect specifying the value of η. [35] 780 9 17 ± 4 Serebrov et al [36] 873 2.6 6 ± 1 Pichlmaier et al [37] 771 13 13 ± 1 Table 1: Summary of UCN storage experiments, with measured UCN storage time and wall collision rate taken from the original literature. The maximum loss probability at wall collision is derived for each experiment.…”

Ultracold neutron accumulation in a superfluid-helium converter with magnetic multipole reflector

“…Long standing are efforts to improve the accuracy of the weak axial-vector and vector coupling constants of the nucleon derived from precise values of the neutron lifetime [21,22,23,24,25] and the beta-asymmetry [26,27,28,29]. Among other applications these values are crucial input for calculations of weak reaction rates in big-bang nucleo-synthesis and stellar fusion [30,31], and of the efficiency of neutrino detectors [32].…”