Measurement of the branching fraction of and search for a CP-violating asymmetry in η′ → π+ π- e+ e- at BESIII

作者：Ablikim, M.; Achasov, M. N.; Adlarson, P.; Ahmed, S.; Albrecht, M.; Amoroso, A.; An, Q.; Bai, X. H.; Bai, Y.; Bakina, O.; Ferroli, R. Baldini; Balossino, I; Ban, Y.; Begzsuren, K.; Bennett, J., V; Berger, N.; Bertani, M.; Bettoni, D.; Bianchi, F.; Biernat, J.; Bloms, J.; Bortone, A.; Boyko, I; Briere, R. A.; Cai, H.; Cai, X.; Calcaterra, A.; Cao, G. F.; Cao, N.; Cetin, S. A.; Chang, J. F.; Chang, W. L.; Chelkov, G.; Chen, D. Y.; Chen, G.; Chen, H. S.; Chen, M. L.; Chen, S. J.; Chen, X. R.

来源：Physical Review D, 2021, 103(9): 092005.

DOI：10.1103/PhysRevD.103.092005

• EVENT GENERATORS

Therare decay eta' -> pi(+) pi(-) e(+) e(-) is studied using a sample of1.3 x 10(9) J/Psi events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be (2.42 +/- 0.05(stat) +/- 0.08(syst)) x 10(-3). Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the CP-violating asymmetry in the angle between the decay planes of the pi(+)pi(-)-pair and the e(+)e(-)-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is A(CP) = (2.9 +/- 3.7(stat) +/- 1.1(syst))%, which is consistent with the standard model expectation of no CP-violation. The precision is comparable to the asymmetry measurement in the K-L(0) -> pi(+) pi(-) e(+) e(-) decay where the observed (14 +/- 2)% effect is driven by a standard model mechanism.