Ashwani Rajan | Searcharxiv

arXiv2019

A meta-analysis of neutron lifetime measurements

We calculated the median as well as weighted mean central estimates for the neutron lifetime, from a subset of measurements compiled in the 2019 update of the Particle Data Group (PDG). We then reconstruct the error distributions for the residuals using three different central estimates and then check for consistency with a Gaussian distribution. We find that although the error distributions using the weighted mean as well as median estimate are consistent with a Gaussian distribution, the Student's $t$ and Cauchy distribution provide a better fit. This median statistic estimate of the neutron lifetime from these measurements is given by $881.5 \pm 0.47$ seconds. This can be used as an alternate estimate of the neutron lifetime. We also note that the discrepancy between beam and bottle-based measurements using median statistics of the neutron lifetime persists with a significance between 4-8$σ$, depending on which combination of measurements is used.

hep-ph↗

arXiv2018

Non-Gaussian Error Distributions of Galactic Rotation Speed Measurements

We construct the error distributions for the galactic rotation speed ($Θ_0$) using 137 data points from measurements compiled in De Grijs et al. (arXiv:1709.02501), with all observations normalized to the galactocentric distance of 8.3 kpc. We then checked (using the same procedures as in works by Ratra et al) if the errors constructed using the weighted mean and the median as the estimate, obey Gaussian statistics. We find using both these estimates that they have much wider tails than a Gaussian distribution. We also tried to fit the data to three other distributions: Cauchy, double-exponential, and Students-t. The best fit is obtained using the Students-$t$ distribution for $n=2$ using the median value as the central estimate, corresponding to a $p$-value of 0.1. We also calculate the median value of $Θ_0$ using all the data as well as using the median of each set of measurements based on the tracer population used. Because of the non-gaussianity of the residuals, we point out that the subgroup median value, given by $Θ_{med}=219.65$ km/sec should be used as the central estimate for $Θ_0$.

astro-ph.IM↗