Halo structure of $^8$B determined from intermediate energy proton elastic scattering in inverse kinematics

TL;DR

This study measures the elastic scattering of protons on the proton-rich nucleus $^8$B at high energy, revealing a halo structure with an extended matter distribution, using inverse kinematics and Glauber theory analysis.

Contribution

First measurement of small-angle proton elastic scattering on $^8$B in inverse kinematics, providing detailed density distribution and halo structure analysis.

Findings

$^8$B has a halo structure with a large halo radius of 4.24 fm.

The matter radius of $^8$B is determined to be 2.58 fm.

Results are consistent with previous data and theoretical models.

Abstract

The absolute differential cross section for small-angle proton elastic scattering on the proton-rich $^8$B nucleus has been measured in inverse kinematics for the first time. The experiment was performed using a secondary radioactive beam with an energy of 0.7 GeV/u at GSI, Darmstadt. The active target, namely hydrogen-filled time projection ionization chamber IKAR, was used to measure the energy, angle and vertex point of the recoil protons. The scattering angle of the projectiles was simultaneously determined by the tracking detectors. The measured differential cross section is analyzed on the basis of the Glauber multiple scattering theory using phenomenological nuclear-density distributions with two free parameters. The radial density distribution deduced for $^8$B exhibits a halo structure with the root-mean-square (rms) matter radius $R_{\rm m} = 2.58 (6)$ fm and the rms halo radius $R_{\rm h} = 4.24 (25)$ fm. The results on $^8$B are compared to those on the mirror nucleus $^8$Li investigated earlier by the same method. A comparison is also made with previous experimental results and theoretical predictions for both nuclei.