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Investigation of Rare Pion Decays with the PIBETA Spectrometer

  • Physics of Elementary Particles and Atomic Nuclei. Experiment
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Abstract

Experimental results on pion decays obtained with the PIBETA spectrometer at the Paul Scherrer Institute (PSI) are reviewed. For pion beta decay π+ → π0е+ν (πβ), a precision measurement of relative probability yields Г(πβ) = [1.036 ± 0.004(stat) ± 0.004(syst) ± 0.003(π+→е+ν)] × 10–8, which implies Vud = 0.9728(30) for the corresponding element of the Cabibbo–Kobayashi–Maskawa mixing matrix. Using a sample of 65 × 103 events, relative probability of the π+→е+νγ radiative pion decay (RPD) in the kinematic region of Eγ > 10 MeV and θeγ > 40° is measured as Bexp = 73.86(54) × 10–8. A statistical analysis of measured Ee+ and Eγ distributions for this decay yield the values FV = 0.0258(17) and FA = 0.0117(17) for the pion weak formfactors. Assuming that FV linearly depends on the е+ν invariant mass q2 as FV(q2) = FV(0)(1 + aq2), the slope parameter is extracted as а = 0.10(6). The pion polarizability and neutral-pion lifetime are estimated as αE = 2.78(10) × 10–4 fm3 and τ(π0) = (8.5 ± 1.1) × 10–17 s, respectively. The data for decays π+→ е+ ν and \({\mu ^ + } \to {e^ + }v\bar v\gamma \) have been collected and are being processed. The follow-up PEN experiment aims at reducing the uncertainty on the π+ → е+ ν relative probability by almost an order of magnitude (to 5 × 10–4).

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Authors and Affiliations

  1. Institute of Nuclear and Particle Physics, University of Virginia, Charlottesville, VA, 22904, USA

    D. Počanić, L. P. Alonzi, M. A. Bychkov, M. Lehman, A. Palladino, O. A. Rondon-Aramayo & E. Frlež

  2. Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980, Russia

    V. A. Baranov, Yu. M. Bystritsky, E. P. Velicheva, V. P. Vol’nykh, V. A. Kalinnikov, A. S. Korenchenko, S. M. Korenchenko, N. P. Kravchuk, N. A. Kuchinsky, D. A. Mzhavia, A. M. Rozhdestvensky, N. V. Khomutov & Z. Tsamalaidze

  3. Paul Scherrer Institut, Villigen PSI, CH-5232, Switzerland

    W. Bertl

  4. NCBJ National Centre for Nuclear Research, Otwock, Poland

    T. Kozlowski

  5. Institute Rudjer Bošković, Zagreb, HR-10000, Croatia

    M. Korolija & I. Supek

  6. Physik-Institut, University of Zurich, Zurich, CH-8057, Switzerland

    P. Robmann, P. Truöl & A. van der Schaaf

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  1. D. Počanić
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  2. L. P. Alonzi
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Correspondence to A. M. Rozhdestvensky.

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Original Russian Text © D. Počanić, L.P. Alonzi, V.A. Baranov, W. Bertl, Yu.M. Bystritsky, M.A. Bychkov, E.P. Velicheva, V.P. Vol’nykh, V.A. Kalinnikov, T. Kozlowski, A.S. Korenchenko, S.M. Korenchenko, M. Korolija, N.P. Kravchuk, N.A. Kuchinsky, M. Lehman, D.A. Mzhavia, A. Palladino, P. Robmann, A.M. Rozhdestvensky, O.A. Rondon-Aramayo, I. Supek, P. Truöl, E. Frlež, N.V. Khomutov, Z. Tsamalaidze, A. van der Schaaf, 2018, published in Pis’ma v Zhurnal Fizika Elementarnykh Chastits i Atomnogo Yadra, 2018.

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Počanić, D., Alonzi, L.P., Baranov, V.A. et al. Investigation of Rare Pion Decays with the PIBETA Spectrometer. Phys. Part. Nuclei Lett. 15, 610–620 (2018). https://doi.org/10.1134/S1547477118060158

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