Mass and width of the lowest resonance in QCD.
We demonstrate that near the threshold, the pi pi scattering amplitude contains a pole with the quantum numbers of the vacuum--commonly referred to as the sigma--and determine its mass and width within small uncertainties. Our derivation does not involve models or parametrizations but relies on a straightforward calculation based on the Roy equation for the isoscalar S wave.
Caprini
I
I
National Institute of Physics and Nuclear Engineering, Bucharest, R-077125 Romania.
Colangelo
G
G
Leutwyler
H
H