Search for a bound di-neutron by comparing ${}^3$He(e,e'p)d and ${}^3$H(e,e'p)X measurements

Abstract

We report on a search for a bound di-neutron by comparing electron-induced proton-knockout $(e,e^{\prime }p)$ measurements from Helium-3 (${}^3$He) and Tritium (${}^3$H). The measurements were performed at Jefferson Lab Hall A with a 4.326 GeV electron beam, and kinematics of large momentum transfer $Q^2\approx 1.9$ (GeV/$c$)${}^2$ and $x_B>1$, to minimize contributions from non quasi-elastic (QE) reaction mechanisms. Analyzing the measured ${}^3$He missing mass ($M_{miss}$) and missing energy ($E_{miss}$) distributions, we can distinguish the two-body break-up reaction, in which the residual proton-neutron system remains bound as a deuteron. In the ${}^3$H mirror case, under the exact same kinematic conditions, we do not identify a signature for a bound di-neutron with similar binding energy to that of the deuteron. We calculate exclusion limits as a function of the di-neutron binding energy and find that, for binding equivalent to the deuteron, the two-body break-up cross section on ${}^3$H is less than 0.9% of that on ${}^3$He in the measured kinematics at the 95% confidence level.

6 pages, 3 figures