Precise measurement of the pion axial form factor in the pi+-->e+nugamma decay.
We have studied radiative pion decays pi(+)-->e(+)nugamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 41 601 events we have evaluated absolute pi-->enugamma branching ratios in the three regions. Minimum chi(2) fits to the integral and differential (E(e(+)),E(gamma)) distributions result in the axial-to-vector weak form factor ratio of gamma identical with F(A)/F(V)=0.443(15), or F(A)=0.0115(4) with F(V)=0.0259. However, deviations from standard model predictions in the high-E(gamma)-low-E(e(+)) kinematic region indicate the need for further theoretical and experimental work.
Frlez
E
E
Department of Physics, University of Virginia, Charlottesville, VA 22904-4714, USA. frlez@virginia.edu
Pocanić
D
D
Baranov
V A
VA
Bertl
W
W
Bychkov
M
M
Khomutov
N V
NV
Korenchenko
A S
AS
Korenchenko
S M
SM
Kozlowski
T
T
Kravchuk
N P
NP
Kuchinsky
N A
NA
Li
W
W
Minehart
R C
RC
Mzhavia
D
D
Ritchie
B G
BG
Ritt
S
S
Rozhdestvensky
A M
AM
Sidorkin
V V
VV
Smith
L C
LC
Supek
I
I
Tsamalaidze
Z
Z
VanDevender
B A
BA
Velicheva
E P
EP
Wang
Y
Y
Wirtz
H-P
HP
Ziock
K O H
KO