Pion charge radius from pion plus electron elastic scattering data

With the aim of extracting the pion charge radius, we analyse extant precise pion+electron elastic scattering data on Q(2) is an element of [0.015, 0.144] GeV2 using a method based on interpolation via continued fractions augmented by statistical sampling. The scheme avoids any assumptions on the form of function used for the representation of data and subsequent extrapolation onto Q(2) similar or equal to 0. Combining results obtained from the two available data sets, we obtain r(pi) = 0.640(7) fm, a value 2.4 sigma below today's commonly quoted average. The tension may be relieved by collection and similar analysis of new precise data that densely cover a domain which reaches well below Q(2) = 0.015 GeV2. Considering available kaon+electron elastic scattering data sets, our analysis reveals that they contain insufficient information to extract an objective result for the charged-kaon radius, r(K). New data with much improved precision, low-Q(2) reach and coverage are necessary before a sound result for r(K) can be recorded. (C) 2021 The Author(s). Published by Elsevier B.V.