New evaluation of neutron lifetime from UCN storage experiments and beam experiments

The analysis of experiments on measuring neutron lifetime has been made. The latest most accurate result of measuring the neutron lifetime [Phys. Lett. B 605, 72 (2005)] 878.5 ± 0.8 s differs from the world average value [Phys. Lett. B 667, 1 (2008)] 885.7 ± 0.8 s by 6.5 standard deviations. In view of this both the analysis and the Monte Carlo simulation of experiments [Phys. Lett. B 483, 15 (2000)] and [Phys. Rev. Lett. 63, 593 (1989)] have been performed. Systematic errors about –6 s have been found in both experiments. The table of results of neutron lifetime measurements is given after corrections and additions have been made. A new world average value of the neutron lifetime of 880.0 ± 0.9 s is given. Here is also presented a separate analysis of experiments on measuring neutron lifetime with UCN and with beam experiments. The average neutron lifetime for experiments with UCN is equal to 879.3(0.6) s, while for beam experiments it is equal to 889.1(2.9) s. The present difference of average values for both groups is 3.3σ and needs consideration. The contribution of beam experiments to the world average is not high, therefore it does not influence our analysis. However, it is an independent problem to be solved. It seems desirable that the precision of beam experiments should be enhanced.