Driven Production of Cold Antihydrogen and the First Measured Distribution of Antihydrogen States

Cold antihydrogen is produced when antiprotons are repeatedly driven into collisions with cold positrons within a nested Penning trap. Efficient antihydrogen production takes place during many cycles of positron cooling of antiprotons. A first measurement of a distribution of antihydrogen states is made using a preionizing electric field between separated production and detection regions. Surviving antihydrogen is stripped in an ionization well that captures and stores the freed antiproton for background-free detection.

Figure 1

Antiprotons are loaded from below (left), into the trap electrodes below the rotatable electrode. Positrons are simultaneously loaded from above (right) into the electrodes above the rotatable electrode. $\overline{\mathrm{H}}$ formation is observed within the region detailed in Fig. 2.

Figure 2

Trap electrodes (a). Two values of the potential (b) and electric field magnitude (c) on axis. In a one-hour trial, $718$ $\overline{p}$ from $\overline{\mathrm{H}}$ are captured in the ionization well (d).

Figure 3

Axial bounce frequency for $\overline{p}$ oscillating along the magnetic field direction in the nested Penning trap depends upon their energy, calculated with respect to their potential energy on axis at the center of the nested well. The chosen drive frequency is indicated.

Figure 4

Antiprotons lost while being driven from one side of the nested Penning trap to the other.

Figure 5

(a) The ratio of ionized $\overline{\mathrm{H}}$ in ionization and normalization wells decreases linearly with state-analysis electric field $F$. (b) Distribution $dR/dF$ is flat up to a cutoff. (c) The distribution $dR/dn\sim n^{-5}$ depends upon the choice of $A$ used in Eq. (1) to relate $F$ and $n$.