Problem 2049

Summary:	mu- lifetime correction for binding energy is wrong
Product:	Geant4	Reporter:	Duncan Prindle <prindle>
Component:	processes/decay	Assignee:	Krzysztof Genser <resnegfk>
Status:	RESOLVED FIXED
Severity:	normal	CC:	Gunter.Folger
Priority:	P4
Version:	10.2
Hardware:	All
OS:	All

Description Duncan Prindle 2018-03-30 00:18:28 CEST

In G4MuonMinusBoundDecay::GetMuonDecayRate(G4int Z) there is a factor (1-2.5*x*x) applied to the free mu- decay rate (x = Z_eff/137). The 2.5 accounts for the change in phase space but there are a couple of other corrections that nearly cancel this. A more accurate correction is (1-0.5*x*x).

References:
H. Uberall, Phys. Rev. 119, 365 (1960).
H. C. Von Baeyer and D. Leiter, Phys. Rev. A 19, 1371 (1979).

Comment 1 Krzysztof Genser 2018-04-11 01:41:09 CEST

Hello Duncan,

Thank you for the report.

The current implementation is based on N.C.Mukhopadhyay Phys. Rep. 30 (1977)
and T. Suzuki, D. F. Measday, J.P. Roalsvig Phys. Rev. C35 (1987) 2212.
using Zeff. Although the formula you suggest seems to be better for light nuclei
it is much worse for the very heavy ones. 

We shall try to somehow improve the current one to achieve a better
agreement for all Z.

Krzysztof

Comment 2 Krzysztof Genser 2019-02-25 23:58:27 CET

I modified G4MuonMinusBoundDecay::GetMuonDecayRate to use the Von
Baeyer/Leiter, Phys. Rev. A 19, 1371 (1979) formula up to Al(Z=13),
assuming the mass of the nucleus of the most abundant isotope for a
given Z, and then a formula based on a polynomial fit to the data quoted
in Phys.Rev. C35 (1987) 2212.  It should improve the overall agreement
with the available data for all the nuclei. It is available starting
with Geant4 10.5.