Two-Nucleon Momentum Distributions Measured in ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }pp)n$

We have measured the ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }pp)n$ reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for “fast” nucleons ($p>250\mathrm{M}\mathrm{e}\mathrm{V}/c$) peaks where two nucleons each have 20% or less, and the third nucleon has most of the transferred energy. These fast $pp$ and $pn$ pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.

Figure 1

(a) $Q^2$ vs $\omega$ for ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }pp)n$ events. The line shows the quasielastic condition $\omega =Q^2/2m_p$. Note the large acceptance. (b) Missing mass for ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }pp)X$. The vertical lines indicate the neutron missing mass cuts. The dashed histogram shows the result of a GEANT simulation of the CLAS.

Figure 2

(a) ${}^3\mathrm{H}\mathrm{e}(e,e^{\prime }pp)n$ lab frame Dalitz plot. $T_{p1}/\omega$ versus $T_{p2}/\omega$ for events with $p_N>0.25\mathrm{G}\mathrm{e}\mathrm{V}/c$; (b) the cosine of the $pp$ lab frame opening angle for events with a leading $n$ and a $pp$ pair: $T_{p1},T_{p2}<0.2*\omega$. Filled points show the data, open points show the data cut on $p_n^{\perp }<300\mathrm{M}\mathrm{e}\mathrm{V}/c$, and the histogram shows the phase space (normalized to the data).

Figure 3

(a) Lab frame cross section vs $pn$ pair relative momentum. Points show the data, solid histogram shows the PWIA calculation times $\frac{1}{5}$ [17], dashed histogram shows Laget’s one-body calculation [18, 19, 20], dotted histogram shows Laget’s full calculation; (b) the same for total momentum; (c),(d) the same for $pp$ pairs.

Figure 4

Feynman diagrams for (a) plane wave impulse approximation and (b) pair distortion.