Measurement of the $^1S_0$ neutron-neutron effective range in neutron-deuteron breakup

TL;DR

This study precisely measures the neutron-neutron effective range parameter ($r_{nn}$) through neutron-deuteron breakup experiments, using advanced detection and theoretical modeling to achieve results consistent with prior data.

Contribution

The paper presents the most precise measurement of $r_{nn}$ using neutron-deuteron breakup, combining experimental data with Faddeev calculations and chiral interactions for improved accuracy.

Findings

Measured $r_{nn}$ as 2.86 and 2.87 fm with high precision.

Results are consistent with charge symmetry and previous measurements.

Used both CD Bonn and N$^4$LO$^+$ potentials for analysis.

Abstract

We report the most precise determination of the $^{1}S_{0}$ neutron-neutron effective range parameter ($r_{nn}$) from neutron-neutron quasifree scattering in neutron-deuteron breakup. The experiment setup utilized a collimated beam of 15.5 MeV neutrons and an array of eight neutron detectors positioned at angles sensitive to several quasifree scattering kinematic configurations. The two neutrons emitted from the breakup reaction were detected in coincidence and time-of-flight techniques were used to determine their energies. The beam-target luminosity was measured in-situ with the yields from neutron-deuteron elastic scattering. Rigorous Faddeev-type calculations using the CD Bonn nucleon-nucleon potential were fit to our cross-section data to determine the value of $r_{nn}$. The analysis was repeated using a semilocal momentum-space regularized N$^4$LO$^+$ chiral interaction potential. We obtained values of $r_{nn} = 2.86 \pm 0.01 \,(stat) \pm 0.10 \,(sys)$ fm and $r_{nn} = 2.87 \pm 0.01 \,(stat) \pm 0.10 \,(sys)$ fm using the CD Bonn and N$^4$LO$^+$ potentials, respectively. Our results are consistent with charge symmetry and previously reported values of $r_{nn}$.