Measurements of the reaction $\bar{p}p \to \phi \eta$ of antiproton annihilation at rest at three hydrogen target densities

TL;DR

This study measures the proton-antiproton annihilation into phi eta at rest across three hydrogen target densities, revealing differences in reaction yields and branching ratios linked to target density and initial states.

Contribution

It provides new measurements of the $ar{p}p o \phi ext{eta}$ reaction at different target densities and analyzes the dependence of branching ratios on initial protonium states.

Findings

Yield of reaction varies with target density.

Branching ratio from $^3S_1$ state is ten times smaller than from $^1P_1$ state.

Reaction characteristics depend on initial protonium state.

Abstract

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.