We report the first measurement of the temperature dependence of muon transfer rate from $mu$p atoms to oxygen between 100 and 300 K. Data were obtained from the X-ray spectra of delayed events in gaseous target H$_2$/O$_2$ exposed to a muon beam. Ba
sed on the data, we determined the muon transfer energy dependence up to 0.1 eV, showing an 8-fold increase in contrast with the predictions of constant rate in the low energy limit. This work set constraints on theoretical models of muon transfer, and is of fundamental importance for the measurement of the hyperfine splitting of $mu$p by the FAMU collaboration.
The main goal of the FAMU experiment is the measurement of the hyperfine splitting (hfs) in the 1S state of muonic hydrogen $Delta E_{hfs}(mu^-p)1S$. The physical process behind this experiment is the following: $mu p$ are formed in a mixture of hydr
ogen and a higher-Z gas. When absorbing a photon at resonance-energy $Delta E_{hfs}approx0.182$~eV, in subsequent collisions with the surrounding $H_2$ molecules, the $mu p$ is quickly de-excited and accelerated by $sim2/3$ of the excitation energy. The observable is the time distribution of the K-lines X-rays emitted from the $mu Z$ formed by muon transfer $(mu p) +Z rightarrow (mu Z)^*+p$, a reaction whose rate depends on the $mu p$ kinetic energy. The maximal response, to the tuned laser wavelength, of the time distribution of X-ray from K-lines of the $(mu Z)^*$ cascade indicate the resonance. During the preparatory phase of the FAMU experiment, several measurements have been performed both to validate the methodology and to prepare the best configuration of target and detectors for the spectroscopic measurement. We present here the crucial study of the energy dependence of the transfer rate from muonic hydrogen to oxygen ($Lambda_{mu p rightarrow mu O}$), precisely measured for the first time.
An imaging calorimeter has been designed and is being built for the PAMELA satellite-borne experiment. The physics goals of the experiment are the measurement of the flux of antiprotons, positrons and light isotopes in the cosmic radiation. The cal
orimeter is designed to perform a precise measurement of the total energy deposited, to reconstruct the spatial development of the showers (both in the longitudinal and in the transverse directions), and to measure the energy distribution along the shower itself. From this information, the calorimeter will identify antiprotons from a electron background and positrons in a background of protons with an efficiency of about 95% and a rejection power better than 10^-4. Furthermore, a self-trigger system has been implemented with the calorimeter that will be employed to measure high-energy (from about 300 GeV to more than 1 TeV) electrons. The instrument is composed of 22 layers of tungsten, each sandwiched between two views of silicon strip detectors (X and Y). The signals are read out by a custom VLSI front-end chip, the CR1.4P, specifically designed for the PAMELA calorimeter, with a dynamic range of 7.14 pC or 1400 mip (minimum ionizing particle). We report on the simulated performance and prototype design.
