Precise Extraction of the Induced Polarization in the ${}^4\mathrm{He}(e,e^{\prime }\overrightarrow{p}){}^3\mathrm{H}$ Reaction

We measured with unprecedented precision the induced polarization $P_y$ in ${}^4\mathrm{He}(e,e^{\prime }\overrightarrow{p}){}^3\mathrm{H}$ at $Q^2=0.8$ and $1.3(\mathrm{GeV}/c{)}^2$. The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation.

Figure 1

The acceptance-averaged induced polarization $P_y$ in ${}^4\mathrm{He}(e,e^{\prime }\overrightarrow{p}){}^3\mathrm{H}$ as a function of $Q^2$ from E03-104 (upper panel) and E93-049 (lower panel) [1]. The inner and outer error bars represent the statistical and total uncertainties, respectively. The green band displays the Madrid calculation [2] when using MRW as optical potential and $cc1$ or $cc2$ for the form of the nuclear current operator. For the solid and dashed curves RLF was used with $cc1$ (solid) and $cc2$ (dashed). The dash-dotted and dotted curves were obtained from the dashed and solid ones, respectively, by including medium-modified form factors via the QMC model [6]. Lines connect the acceptance-averaged theory calculations.

Figure 2

$P_y$ in ${}^4\mathrm{He}(e,e^{\prime }\overrightarrow{p}){}^3\mathrm{H}$ as a function of missing momentum $p_m$ from E03-104 (solid circles). Also shown are calculations from the Madrid group [2] (notations as in Fig. 1).

Figure 3

The induced polarization $P_y$ in ${}^4\mathrm{He}(e,e^{\prime }\overrightarrow{p}){}^3\mathrm{H}$ as a function of $Q^2$ extrapolated at missing momentum $p_m\approx 0$ from E03-104 (solid circles) and E93-049 (empty circles) [1]. The inner and outer error bars represent the statistical and total uncertainties, respectively. Calculations from the Madrid group [2] (continuous and dashed curves) and from Schiavilla et al. [3, 14] (bands) are also shown.