Probing the Standard Model via rare pion and muon decays

The PIBETA collaboration has used a non-magnetic pure CsI calorimeter operating at the Paul Scherrer Institute to collect the world's largest sample of rare pion and muon decays. We have extracted the absolute pi+ -> pi0 e+ nu decay branching ratio with the 0.55 % total uncertainty. The pi+ -> e + nu gamma data set was used to extract weak axial and vector form factors F_A and F_V, yielding a significant improvement in the precision of F_A and F_V. The mu+ -> e+ nu nu gamma distributions were well described with the two-parameter (rho_SM,eta_bar=0) solution. These results bring major improvements in accuracy over the current Particle Data Group listings and agree well with the predictions of the Standard Model.Comment: 5 pages, 5 postscript figures, 2 tables, LaTeX, presented at the International Workshop e+e- Collisions from phi to psi, February 27 - March 2, 2006, Budker Institute of Nuclear Physics, Novosibirsk, Russia (http://www.inp.nsk.su/conf/phipsi06), to appear in Nuclear Physics B (Proceedings Supplement

Data acquisition system for the MuLan muon lifetime experiment

We describe the data acquisition system for the MuLan muon lifetime experiment at Paul Scherrer Institute. The system was designed to record muon decays at rates up to 1 MHz and acquire data at rates up to 60 MB/sec. The system employed a parallel network of dual-processor machines and repeating acquisition cycles of deadtime-free time segments in order to reach the design goals. The system incorporated a versatile scheme for control and diagnostics and a custom web interface for monitoring experimental conditions.Comment: 19 pages, 8 figures, submitted to Nuclear Instruments and Methods

The WITCH experiment: Acquiring the first recoil ion spectrum

The standard model of the electroweak interaction describes beta-decay in the well-known V-A form. Nevertheless, the most general Hamiltonian of a beta-decay includes also other possible interaction types, e.g. scalar (S) and tensor (T) contributions, which are not fully ruled out yet experimentally. The WITCH experiment aims to study a possible admixture of these exotic interaction types in nuclear beta-decay by a precise measurement of the shape of the recoil ion energy spectrum. The experimental set-up couples a double Penning trap system and a retardation spectrometer. The set-up is installed in ISOLDE/CERN and was recently shown to be fully operational. The current status of the experiment is presented together with the data acquired during the 2006 campaign, showing the first recoil ion energy spectrum obtained. The data taking procedure and corresponding data acquisition system are described in more detail. Several further technical improvements are briefly reviewed.Comment: 11 pages, 6 figures, conference proceedings EMIS 2007 (http://emis2007.ganil.fr), published also in NIM B: doi:10.1016/j.nimb.2008.05.15