MEAN LIFE

We have omitted some results that have been superseded by later experiments. See our earlier editions.

[a] See the Particle Listings below for the pion momentum range used in this measurement.

CONSTRAINED FIT INFORMATION CONSTRAINED FIT INFORMATION CONSTRAINED FIT INFORMATION CONSTRAINED FIT INFORMATION
An overall fit to 3 branching ratios uses 16 measurements and one constraint to determine 4 parameters. The overall fit has a χ 2 = 8.7 for 13 degrees of freedom.
The following off-diagonal array elements are the correlation coefficients δx i δx j /(δx i ·δx j ), in percent, from the fit to the branching fractions, The fit constrains the x i whose labels appear in this array to sum to one.
See the "Note on Baryon Decay Parameters" in the neutron Listings. Older, outdated results have been omitted.
0.237g 2 f 1 . This reduces to g A /g V ≡ g 1 (0) f 1 (0) on making the usual assumption that g 2 = 0. See also the note on HSUEH 88. The sign is, with our conventions, unambiguously positive. The value assumes, as usual, that g 2 = 0. If g 2 is included in the fit, than (with our sign convention) g 2 = −0.56 ± 0.37, with a corresponding reduction of g A /g V to +0.20 ± 0.08. 7 BOURQUIN 83C favors the positive sign by at least 2.6 standard deviations. 8 TANENBAUM 74 gives 0.435 ± 0.035, assuming no q 2 dependence in g A and g V . The listed result allows q 2 dependence, and is taken from HSUEH 88.
The signs have been changed to be in accord with our conventions, given in the "Note on Baryon Decay Parameters" in the neutron Listings.
The coefficient D of the term D P P P P·(p p p p e ×p p p p ν ) in the Σ − → n e − ν decay angular distribution. A nonzero value would indicate a violation of time-reversal invariance.
For the sign convention, see the "Note on Baryon Decay Parameters" in the neutron Listings. The value is predicted to be zero by conserved vector current theory. The values averaged assume CVC-SU (3)  186 9,10 FRANZINI 72 HBC 9 The sign has been changed to agree with our convention. 10 The FRANZINI 72 value includes the events of earlier papers.