Weak phases and CP-symmetry tests in sequential decays of entangled double-strange baryons
Creators: name: Ablikim, M.
name: Achasov, M. N.
name: Adlarson, P.
name: Ahmed, S.
name: Albrecht, M.
name: Aliberti, R.
name: Amoroso, A.
name: An, M. R.
name: An, Q.
name: Bai, X. H.
name: Bai, Y.
name: Bakina, O.
name: Ferroli, R. Baldini
name: Balossino, I.
name: Ban, Y.
name: Begzsuren, K.
name: Berger, N.
name: Bertani, M.
name: Bettoni, D.
name: Bianchi, F.
name: Biernat, J.
name: Bloms, J.
name: Bortone, A.
name: Boyko, I.
name: Briere, R. A.
name: Cai, H.
name: Cai, X.
name: Calcaterra, A.
name: Cao, G. F.
name: Cao, N.
name: Cetin, S. A.
name: Chang, J. F.
name: Chang, W. L.
name: Chelkov, G.
name: Chen, D. Y.
name: Chen, G.
name: Chen, H. S.
name: Chen, M. L.
name: Chen, S. J.
name: Chen, X. R.
name: Chen, Y. B.
name: Chen, Z. J
name: Cheng, W. S.
name: Cibinetto, G.
name: Cossio, F.
name: Cui, X. F.
name: Dai, H. L.
name: Dai, X. C.
name: Dbeyssi, A.
name: de Boer, R. E.
name: Dedovich, D.
name: Deng, Z. Y.
name: Denig, A.
name: Denysenko, I.
name: Destefanis, M.
name: De Mori, F.
name: Ding, Y.
name: Dong, C.
name: Dong, J.
name: Dong, L. Y.
name: Dong, M. Y.
name: Dong, X.
name: Du, S. X.
name: Fan, Y. L.
name: Fang, J.
name: Fang, S. S.
name: Fang, Y.
name: Farinelli, R.
name: Fava, L.
name: Feldbauer, F.
name: Felici, G.
name: Feng, C. Q.
name: Feng, J. H.
name: Fritsch, M.
name: Fu, C. D.
name: Gao, Y.
name: Gao, Y.
name: Gao, Y.
name: Gao, Y. G.
name: Garzia, I.
name: Ge, P. T.
name: Geng, C.
name: Gersabeck, E. M.
name: Gilman, A
name: Goetzen, K.
name: Gong, L.
name: Gong, W. X.
name: Gradl, W.
name: Greco, M.
name: Gu, L. M.
name: Gu, M. H.
name: Gu, S.
name: Gu, Y. T.
name: Guan, C. Y
name: Guo, A. Q.
name: Guo, L. B.
name: Guo, R. P.
name: Guo, Y. P.
name: Guskov, A.
name: Han, T. T.
name: Han, W. Y.
name: Hansson, J.
name: Hao, X. Q.
name: Harris, F. A.
name: Hüsken, N.
name: He, K. L.
name: Heinsius, F. H.
name: Heinz, C. H.
name: Held, T.
name: Heng, Y. K.
name: Herold, C.
name: Himmelreich, M.
name: Holtmann, T.
name: Hou, Y. R.
name: Hou, Z. L.
name: Hu, H. M.
name: Hu, J. F.
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name: Hu, Y.
name: Huang, G. S.
name: Huang, L. Q.
name: Huang, X. T.
name: Huang, Y. P.
name: Huang, Z.
name: Hussain, T.
name: Andersson, W. Ikegami
name: Imoehl, W.
name: Irshad, M.
name: Jaeger, S.
name: Janchiv, S.
name: Ji, Q.
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name: Johansson, T.
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name: Maldaner, S.
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name: Malik, Q. A.
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name: Marcello, S.
name: Meng, Z. X.
name: Messchendorp, J. G.
name: Mezzadri, G.
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name: Mitchell, R. E.
name: Mo, X. H.
name: Mo, Y. J.
name: Muchnoi, N. Yu.
name: Muramatsu, H.
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name: Nefedov, Y.
name: Nerling, F.
name: Nikolaev, I. B.
name: Ning, Z.
name: Nisar, S.
name: Olsen, S. L.
name: Ouyang, Q.
name: Pacetti, S.
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name: Peters, K.
name: Ping, J. L.
name: Ping, R. G.
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Publisher: name: arXiv
Year: 2021
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Using a sample of $1.31\times10^9$ $J/ψ$ events collected with the BESIII detector at the electron-positron collider BEPCII, we analyse the full $J/ψ\to$ $Ξ^-\overlineΞ^+$, $Ξ^-\to Λπ^-$, $Λ\to pπ^-$, $\overlineΞ^+\to\overlineΛπ^+$, $\overlineΛ\to\overline{p}π^+$ decay chain. A new method, exploiting the fact that the $Ξ^-\overlineΞ^+$ pair is entangled and sequentially decaying, and where the complete decay chains are reconstructed, is applied for the first time. This enables precision measurements of the decay parameters for the $Ξ^-\toΛπ^-$ decay ($α_Ξ$, $ϕ_Ξ$) as well as the $\overlineΞ^+\to\overlineΛπ^+$ decay ($\overlineα_Ξ$, $\overlineϕ_Ξ$). From the decay parameters, two independent CP tests were performed, quantified by the observables $A_{\rm CP}^Ξ$ and $Δϕ_Ξ$. Our results, $A_{\rm CP}^Ξ$ = $(6.0\pm13.4\pm5.6)\times10^{-3}$ and $Δϕ_Ξ= (-4.8\pm13.7\pm2.9)\times10^{-3}~{\rm rad}$, are consistent with CP symmetry. Furthermore, our method enables a separation of strong and weak $Ξ\toΛπ$ decay amplitudes. This results in the first direct measurement of the weak phase difference for any baryon decay. The result is found to be $(ξ_{P} - ξ_{S}) = (1.2\pm3.4\pm0.8)\times10^{-2}$ rad and is one of the most precise tests of CP symmetry for strange baryons. The strong phase difference is measured to be $(δ_P - δ_S) = (-4.0\pm3.3\pm1.7)\times10^{-2}$ rad. In addition, we provide an independent measurement of the recently debated $Λ$ decay parameter, $α_Λ = 0.757 \pm 0.011 \pm 0.008 $. The $Λ\overlineΛ$ asymmetry is measured to be $A_{\rm CP}^Λ = (-3.7\pm11.7\pm9.0)\times10^{-3}$.
description: 24 pages, 4 figures and 5 tables