Investigation of Rare Pion Decays with the PIBETA Spectrometer |
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Authors: | 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 |
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Institution: | 1.Institute of Nuclear and Particle Physics,University of Virginia,Charlottesville,USA;2.Joint Institute for Nuclear Research,Dubna, Moscow oblast,Russia;3.Paul Scherrer Institut,Villigen PSI,Switzerland;4.NCBJ National Centre for Nuclear Research,Otwock,Poland;5.Institute Rudjer Bo?kovi?,Zagreb,Croatia;6.Physik-Institut,University of Zurich,Zurich,Switzerland |
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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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