First direct measurement of the absolute branching fraction of Σ+ → Λe+υe

Ablikim, M.; Achasov, M. N.; Adlarson, P.; Aliberti, R.; Amoroso, A.; An, M. R.; An, Q.; Bai, Y.; Bakina, O.; Ferroli, R. Baldini; Balossino, I.; Ban, Y.; Batozskaya, V.; Becker, D.; Begzsuren, K.; Berger, N.; Bertani, M.; Bettoni, D.; Bianchi, F.; Bianco, E.; Bloms, J.; Bortone, A.; Boyko, I.; Briere, R. A.; Brueggemann, A.; Cai, H.; Cai, X.; Calcaterra, A.; Cao, G. F.; Cao, N.; Cetin, S. A.; Chang, J. F.; Chang, T. T.; Chang, W. L.; Che, G. R.; Chelkov, G.; Chen, C.; Chen, Chao; Chen, G.

Science Citation Index Expanded

摘要

The first direct measurement of the absolute branching fraction of Sigma(+) -> Lambda e(+)nu(e) is reported based on an e(+) e(-) annihilation sample of (10087 +/- 44) x 10(6) J/psi events collected with the BESIII detector at root s = 3.097 GeV. The branching fraction is determined to be B(Sigma(+)-> Lambda e(+)nu(e))=2.93 +/- 0.74 (stat) +/- 0.13(syst)] x 10(-5), which is the most precise measurement obtained in a single experiment to date and also the first result obtained at a collider experiment. Combining this result with the world average of B(Sigma(-)-> Lambda e(-) (nu) over bar (e). and the lifetimes of Sigma(+/-), the ratio, Gamma (Sigma(-) ->Lambda e(-) (nu) over bar (e) /Sigma(+) -> Lambda e(+) (nu) over bar (e), is determined to be 1.06 +/- 0.28, which is within 1.8 standard deviations of the value expected in the absence of second-class currents.

关键词

BETA-DECAY WEAK MAGNETISM 2ND-CLASS