(\Sigma^{+}\) and \(\bar{\Sigma}^-\) polarization in the \(J/\psi\) and \(\psi(3686)\) decays

• Published in: arXiv.org 2020-04
• Main Authors: Ablikim, M, Anita, Bettoni, D, Bloms, J, Cetin, S A, Chang, W L, Chen, G, Chen, M L, Chen, X R, Dong, M Y, Gao, Y, Garzia, I, S Gu, Gu, Y T, Guo, Y P, Guskov, A, Heinsius, F H, Huang, Z, Jiang, X Y, Khoukaz, A, Kuessner, M, Kühn, W, Lange, J S, Lavezzi, L, Lenz, T, C Li, Li, H J, Li, Lei, Li, S Y, Li, X H, Li, Z B, Liang, Y F, Liu, B J, Liu, D, Liu, D Y, Liu, H B, Liu, J B, Liu, K, Liu, X, Lu, H J, Lusso, S, Ma, H L, Ma, L L, Ma, X N, Ma, X X, Maas, F E, Maldaner, S, Mao, Y J, Mao, Z P, Mitchell, R E, Mo, X H, Mo, Y J, Nakhoul, S, Nefedov, Y, Nikolaev, I B, Nisar, S, Pacetti, S, Qian, S, Qin, L Q, Qin, X S, Qiu, J F, Shan, X Y, Shen, C P, Song, J J, Sun, S S, Sun, Y K, Sun, Z T, Wang, X L, Wang, Y, Wang, Ziyi, Wei, D H, Wilkinson, G, Wolke, M, Wu, L H, Xiong, X A, Xu, J J, Xu, Q J, Yan, W B, Yang, H X, Yang, Y H, Yang, Y X, Yin, J H, You, Z Y, Yu, B X, G Yu, Yu, J S, Yuan, X Q, Yuan, Y, Yuncu, A, Zeng, Y, Zhang, Guangyi, Zhang, Y H, Zhang, Yao, Zhao, J, Zhao, M G, Zhemchugov, A, Zhou, L P, Zhou, Q, Zhu, J, Zhu, X L
• Format: Article
• Language: English
• Subjects: Alpha decay; Asymmetry; Form factors; Mathematical analysis; Polarization (spin alignment)
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2004.07701

From \(1310.6\times10^{6}\) \(J/\psi\) and \(448.1\times10^{6}\) \(\psi(3686)\) events collected with the BESIII experiment, we report the first observation of \(\Sigma^{+}\) and \(\bar{\Sigma}^{-}\) spin polarization in \(e^+e^-\rightarrow J/\psi (\psi(3686)) \rightarrow \Sigma^{+} \bar{\Sigma}^{-}\) decays. The relative phases of the form factors \(\Delta\Phi\) have been measured to be \((-15.5\pm0.7\pm0.5)^{\circ}\) and \((21.7\pm4.0\pm0.8)^{\circ}\) with \(J/\psi\) and \(\psi(3686)\) data, respectively. The non-zero value of \(\Delta\Phi\) allows for a direct and simultaneous measurement of the decay asymmetry parameters of \(\Sigma^{+}\rightarrow p \pi^{0}~(\alpha_0 = -0.998\pm0.037\pm0.009)\) and \(\bar{\Sigma}^{-}\rightarrow \bar{p} \pi^{0}~(\bar{\alpha}_0 = 0.990\pm0.037\pm0.011)\), the latter value being determined for the first time. The average decay asymmetry, \((\alpha_{0} - \bar{\alpha}_{0})/2\), is calculated to be \(-0.994\pm0.004\pm0.002\). The CP asymmetry \(A_{\rm CP,\Sigma} = (\alpha_0 + \bar{\alpha}_0)/(\alpha_0 - \bar{\alpha}_0) = -0.004\pm0.037\pm0.010\) is extracted for the first time, and is found to be consistent with CP conservation.