Tensor Correlations Measured in ${}^3\mathrm{He}(e,e^{\prime }pp)n$

We have measured the ${}^3\mathrm{He}(e,e^{\prime }pp)n$ reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated $pp$ and $pn$ nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of $pp$ to $pn$ pairs as a function of pair total momentum $p_{\mathrm{tot}}$. For pair relative momenta between 0.3 and $0.5\mathrm{GeV}/c$, the ratio is very small at low $p_{\mathrm{tot}}$ and rises to approximately 0.5 at large $p_{\mathrm{tot}}$. This shows the dominance of tensor over central correlations at this relative momentum.

Figure 1

(a) $Q^2$ vs $\omega$ for ${}^3\mathrm{He}(e,e^{\prime }pp)n$ events. The line shows the quasielastic condition $\omega =Q^2/2m_p$. Note the large acceptance. (b) Missing mass for ${}^3\mathrm{He}(e,e^{\prime }pp)X$. The vertical line indicates the neutron missing mass cut.

Figure 2

(a) ${}^3\mathrm{He}(e,e^{\prime }pp)n$ lab frame “Dalitz plot.” $T_{p1}/\omega$ vs $T_{p2}/\omega$ for events with $p_N>0.25\mathrm{GeV}/c$. The solid lines indicate the “leading $n$ plus $pp$ pair,” and the dashed lines indicate the “leading $p$ plus $pn$ pair” selection cuts. (b) The cosine of the $pn$ lab frame opening angle for events with a leading $p$ and a $pn$ pair. The thick solid line shows the uncut data, the dashed line shows the data cut on $p_{\mathrm{leading}}^{\perp }<0.3\mathrm{GeV}/c$, and the thin solid line (color online) shows the uncut three-body absorption simulation (with arbitrary normalization).

Figure 3

(a) Cross section vs $pn$ pair $p_{\mathrm{rel}}$. Solid points show these data ($Q^2\sim 1.5{\mathrm{GeV}}^2$), open squares (blue online) show $Q^2\sim 0.7{\mathrm{GeV}}^2$ data [15], the dashed histogram shows the Golak one-body calculation [23], the thin solid line shows the Laget one-body calculation, and the thick solid line (red online) shows the Laget full calculation [18, 24, 25]; (b) the same for $p_{\mathrm{tot}}$; (c),(d) the same for $pp$ pairs. All quantities are in the lab frame. The $Q^2\sim 0.7{\mathrm{GeV}}^2$ data have been reduced by a factor of 5.3 (the ratio of the cross sections) for comparison.

Figure 4

Ratio of $pp$ to $pn$ spectator pair cross sections at fixed $p_{\mathrm{rel}}$. For $0.3<p_{\mathrm{rel}}<0.5\mathrm{GeV}/c$, the solid points show the data, the solid histogram shows the Golak one-body calculation [23], and the dashed histogram (color online) shows the ratio of the Golak $pp$ and $pn$ bound state momentum distributions. For $0.4<p_{\mathrm{rel}}<0.6\mathrm{GeV}/c$, the star points show the data. The dotted line at 0.5 shows the simple-minded pair counting result. The data and the one-body calculation have been multiplied by 1.5 to approximately account for the ratio of the average $ep$ and $en$ elementary cross sections.