New precise measurement of the pion weak form factors in pi+-->e+ nugamma decay.
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.
Bychkov
M
M
Department of Physics, University of Virginia, Charlottesville, Virginia 22904-4714, USA. mab3ed@virginia.edu
Pocanić
D
D
Vandevender
B A
BA
Baranov
V A
VA
Bertl
W
W
Bystritsky
Yu M
YM
Frlez
E
E
Kalinnikov
V A
VA
Khomutov
N V
NV
Korenchenko
A S
AS
Korenchenko
S M
SM
Korolija
M
M
Kozlowski
T
T
Kravchuk
N P
NP
Kuchinsky
N A
NA
Li
W
W
Mekterović
D
D
Mzhavia
D
D
Ritt
S
S
Robmann
P
P
Rondon-Aramayo
O A
OA
Rozhdestvensky
A M
AM
Sakhelashvili
T
T
Scheu
S
S
Straumann
U
U
Supek
I
I
Tsamalaidze
Z
Z
van der Schaaf
A
A
Velicheva
E P
EP
Volnykh
V P
VP
Wang
Y
Y
Wirtz
H-P
HP