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  1. Article: New precise measurement of the pion weak form factors in pi+-->e+ nugamma decay.

    Bychkov, M / Pocanić, D / Vandevender, B A / Baranov, V A / Bertl, W / Bystritsky, Yu M / Frlez, E / Kalinnikov, V A / Khomutov, N V / Korenchenko, A S / Korenchenko, S M / Korolija, M / Kozlowski, T / Kravchuk, N P / Kuchinsky, N A / Li, W / Mekterović, D / Mzhavia, D / Ritt, S /
    Robmann, P / Rondon-Aramayo, O A / Rozhdestvensky, A M / Sakhelashvili, T / Scheu, S / Straumann, U / Supek, I / Tsamalaidze, Z / van der Schaaf, A / Velicheva, E P / Volnykh, V P / Wang, Y / Wirtz, H-P

    Physical review letters

    2009  Volume 103, Issue 5, Page(s) 51802

    Abstract: We have measured the pi+-->e+ nugamma branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-chi2 fits to the measured (E(e+), E(gamma) energy distributions result in the weak form ...

    Abstract We have measured the pi+-->e+ nugamma branching ratio over a wide region of phase space, based on a total of 65 460 events acquired using the PIBETA detector. Minimum-chi2 fits to the measured (E(e+), E(gamma) energy distributions result in the weak form factor value of F(A)=0.0119(1) with a fixed value of F(V)=0.0259. An unconstrained fit yields F(V)=0.0258(17) and F(A)=0.0117(17). In addition, we have measured a=0.10(6) for the dependence of F(V) on q2, the e+ nu pair invariant mass squared, parametrized as F(V)(q2)=F(V)(0)(1+aq(2)). The branching ratio for the kinematic region E(gamma)>10 MeV and theta(e(+)gamma)>40 degrees is measured to be B(expt)=73.86(54)x10(-8). Earlier deviations we reported in the high-E(gamma)-low-E(e+) kinematic region are resolved without a tensor term. We also derive new values for the pion polarizability alpha(E)=2.78(10)x10(-4) fm3 and neutral pion lifetime tau(pi0)=(8.5+/-1.1)x10(-17) s.
    Language English
    Publishing date 2009-07-31
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.103.051802
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  2. Book ; Online: New Precise Measurement of the Pion Weak Form Factors in the Pi+ -> e+ nu gamma Decay

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

    2008  

    Abstract: We have measured the $\pi^+\to {\rm e}^+\nu\gamma$ branching ratio over a wide region of phase space, based on a total of 65,460 events acquired using the PIBETA detector. Minimum-$\chi^2$ fits to the measured $(E_{e^+},E_\gamma)$ energy distributions ... ...

    Abstract We have measured the $\pi^+\to {\rm e}^+\nu\gamma$ branching ratio over a wide region of phase space, based on a total of 65,460 events acquired using the PIBETA detector. Minimum-$\chi^2$ fits to the measured $(E_{e^+},E_\gamma)$ energy distributions result in the weak form factor value of $F_A=0.0119(1)$ with a fixed value of $F_V=0.0259$. An unconstrained fit yields $F_V=0.0258(17)$ and $F_A=0.0117(17)$. In addition, we have measured $a=0.10(6)$ for the dependence of $F_V$ on $q^2$, the ${\rm e}^{+}\nu$ pair invariant mass squared, parametrized as $F_V(q^2)=F_V(0)(1+a\cdot q^2)$. The branching ratio for the kinematic region $E_\gamma > 10 $MeV and $\theta_{{\rm e^+}\gamma} > 40^\circ $ is measured to be $B^{\rm exp}=73.86(54) \times 10^{-8}$. Earlier deviations we reported in the high-$E_\gamma$/low-$E_{{\rm e}^+}$ kinematic region are resolved, and we find full compatibility with CVC and standard $V$$-$$A$ calculations without a tensor term. We also derive new values for the pion polarizability, $\alpha_E = \rm 2.78(10) \times 10^{-4} fm^3$, and neutral pion lifetime, $\tau_{\pi 0} = (8.5 \pm 1.1) \times 10^{-17} $s.

    Comment: 4 pages, 2 PDF figures
    Keywords High Energy Physics - Experiment ; High Energy Physics - Phenomenology ; Nuclear Experiment
    Subject code 612
    Publishing date 2008-04-11
    Publishing country us
    Document type Book ; Online
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