arXiv subjects
Publications and source records attributed to P. Rabinowitz.
High-precision measurements of the proton radius from laser spectroscopy of muonic hydrogen demonstrated up to six standard deviations smaller values than obtained from electron-proton scattering and hydrogen spectroscopy. The status of this discrepancy, which is known as the proton radius puzzle will be discussed in this paper, complemented with the new insights obtained from spectroscopy of muonic deuterium.
Metastable ${2S}$ muonic-hydrogen atoms undergo collisional ${2S}$-quenching, with rates which depend strongly on whether the $μp$ kinetic energy is above or below the ${2S}\to {2P}$ energy threshold. Above threshold, collisional ${2S} \to {2P}$ excitation followed by fast radiative ${2P} \to {1S}$ deexcitation is allowed. The corresponding short-lived $μp ({2S})$ component was measured at 0.6 hPa $\mathrm{H}_2$ room temperature gas pressure, with lifetime $τ_{2S}^\mathrm{short} = 165 ^{+38}_{-29}$ ns (i.e., $λ_{2S}^\mathrm{quench} = 7.9 ^{+1.8}_{-1.6} \times 10^{12} \mathrm{s}^{-1}$ at liquid-hydrogen density) and population $ε_{2S}^\mathrm{short} = 1.70^{+0.80}_{-0.56}$ % (per $μp$ atom). In addition, a value of the $μp$ cascade time, $T_\mathrm{cas}^{μp} = (37\pm5)$ ns, was found.
An experiment measuring the 2S Lamb shift in muonic hydrogen mup is being performed at the Paul Scherrer Institute, Switzerland. It requires small and compact detectors for 1.9 keV x rays (2P-1S transition) with an energy resolution around 25% at 2 keV, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We have chosen Large Area Avalanche Photodiodes (LAAPDs) from Radiation Monitoring Devices as x-ray detectors, and they were used during the last data taking period in 2003. For x-ray spectroscopy applications, these LAAPDs have to be cooled in order to suppress the dark current noise, hence, a series of tests were performed to choose the optimal operation temperature. Specifically, the temperature dependence of gain, energy resolution, dark current, excess noise factor, and detector response linearity was studied. Finally, details of the LAAPDs application in the muonic hydrogen experiment as well as their response to alpha particles are presented.