# Nuclear Charge Radii of $^{10,11}$B

## TL;DR

This paper reports the first laser spectroscopy measurement of nuclear charge radii for boron isotopes $^{10,11}$B, combining high-precision calculations and measurements to improve accuracy and provide insights into nuclear structure.

## Contribution

It introduces a novel laser spectroscopy method combined with ab initio calculations to determine charge radii of boron isotopes with unprecedented precision.

## Key findings

- Measured charge radius difference: -0.49(12) fm^2
- Results support a cluster structure in boron nuclei
- Benchmark data for nuclear structure models

## Abstract

The first determination of the nuclear charge radius by laser spectroscopy for a five-electron system is reported. This is achieved by combining high-accuracy ab initio mass-shift calculations and a high-resolution measurement of the isotope shift in the $2s^2 2p\, ^2\mathrm{P}_{1/2} \rightarrow 2s^2 3s\, ^2\mathrm{S}_{1/2}$ ground state transition in boron atoms. Accuracy is increased by orders of magnitude for the stable isotopes $^{10,11}$B and the results are used to extract their difference in the mean-square charge radius $\langle r^2_\mathrm{c}\rangle^{11} - \langle r^2_\mathrm{c}\rangle^{10} = -0.49\,(12)\,\mathrm{fm}^2$. The result is qualitatively explained by a possible cluster structure of the boron nuclei and quantitatively used as a benchmark for new ab initio nuclear structure calculations using the no-core shell model and Green's function Monte Carlo approaches.