Naslov
New precise measurement of the pion weak form factors in pi+ --> e+ nu gamma decay

Autori
Bychkov, M. ; Počanić, Dinko ; VanDevender, V.A. ; Baranov, V.A. ; Bertl, W. ; Bystritsky, Yu.M. ; Frlez, E. ; Kalinnikov, V.A. ; Khomutov, N.V. ; Korenchenko, A.S. ; Korenchenko, S.M. ; Korolija, Milorad ; Kozlowski, T. ; Kravchuk, N.P. ; Kuchinsky, N.A. ; Li, W. ; Mekterović, Darko ; Mzhavia, D. ; Ritt, S. ; Robmann, P. ; Rondon-Aramayo, O.A. ; Rozhdestvensky, A.M. ; Sakhelashvili, T. ; Scheu, S. ; Straumann, U. ; Supek, Ivan ; Tsamalaidze, Z. ; van der Schaaf, A. ; Velicheva, E.P. ; Volnykh, V.P. ; Wang, Y. ; Wirtz, H.-P.

Izvornik
Physical review letters (0031-9007) 103 (2009), 5; 051802, 4

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
pion ; gamma decay

Sažetak
We have measured the π+→e+νγ branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-χ2 fits to the measured (Ee+, Eγ) energy distributions result in the weak form factor value of FA=0.0119(1) with a fixed value of FV=0.0259. An unconstrained fit yields FV=0.0258(17) and FA=0.0117(17). In addition, we have measured a=0.10(6) for the dependence of FV on q2, the e+ν pair invariant mass squared, parametrized as FV(q2)=FV(0)(1+aq2). The branching ratio for the kinematic region Eγ>10 MeV and θe+γ>40° is measured to be Bexpt=73.86(54)×10-8. Earlier deviations we reported in the high-Eγ–low-Ee+ kinematic region are resolved without a tensor term. We also derive new values for the pion polarizability αE=2.78(10)×10-4 fm3 and neutral pion lifetime τπ0=(8.5±1.1)×10-17 s.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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