Welcome to the AlCap Experiment

PSI Experiment R-13-03, spokespersons P. Kammel and Y. Kuno


Set-up Run 2013

Charged particle spectra after muon capture

Work packages

  • WP1: Charged Particle Emission after Muon Capture.
    Protons emitted after nuclear muon capture in the stopping target dominate the single-hit rates in the tracking chambers for both the Mu2e and COMET Phase-I experiments. We plan to measure both the total rate and the energy spectrum to a precision of 5% down to proton energies of 2.5 MeV.
  • WP2: Gamma and X-ray Emission after Muon Capture.
    A Ge detector will be used to measure X-rays from the muonic atomic cascade, in order to provide the muon-capture normalization for WP1, and is essential for very thin stopping targets. It is also the primary method proposed for calibrating the number of muon stops in the Mu2e and COMET experiments. Two additional calibration techniques will also be explored; (1) detection of delayed gamma rays from nuclei activated during nuclear muon capture, and (2) measurement of the rate of photons produced in radiative muon decay.
  • WP3: Neutron Emission after Muon Capture.
    Neutron rates and spectra after capture in Al and Ti are not well known. In particular, the low energy region below 10 MeV is important for determining backgrounds in the Mu2e/COMET detectors and veto counters as well as evaluating the radiation damage to electronic components. Carefully calibrated liquid scintillation detectors, employing neutron-gamma discrimination and spectrum unfolding techniques, will measure these spectra. The measurement will attempt to obtain spectra as low or lower than 1 MeV up to 10 MeV.


Argonne National Laboratory Boston University Brookhaven National Laboratory
Fermilab National Accelerator Laboratory Imperial College London INFN Lecce INFN Pisa
Institute of High Energy Physics, China Laboratori Nazionali di Frascati, INFN Nanjing University
Osaka University University College London University of Houston University of Washington, Seattle

Photo during 2013 experiment.


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