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arXiv · 1710.00150

Precision measurement of the $e^{+}e^{-}~\rightarrow~\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ cross section near threshold

M. Ablikim·M. N. Achasov·S. Ahmed·M. Albrecht·M. Alekseev·A. Amoroso·F. F. An·Q. An·J. Z. Bai·Y. Bai·O. Bakina·R. Baldini Ferroli·Y. Ban·K. Begzsuren·D. W. Bennett·J. V. Bennett·N. Berger·M. Bertani·D. Bettoni·F. Bianchi·E. Boger·I. Boyko·R. A. Briere·H. Cai·X. Cai·O. Cakir·A. Calcaterra·G. F. Cao·S. A. Cetin·J. Chai·J. F. Chang·G. Chelkov·G. Chen·H. S. Chen·J. C. Chen·M. L. Chen·P. L. Chen·S. J. Chen·X. R. Chen·Y. B. Chen·X. K. Chu·G. Cibinetto·F. Cossio·H. L. Dai·J. P. Dai·A. Dbeyssi·D. Dedovich·Z. Y. Deng·A. Denig·I. Denysenko·M. Destefanis·F. DeMori·Y. Ding·C. Dong·J. Dong·L. Y. Dong·M. Y. Dong·Z. L. Dou·S. X. Du·P. F. Duan·J. Fang·S. S. Fang·Y. Fang·R. Farinelli·L. Fava·S. Fegan·F. Feldbauer·G. Felici·C. Q. Feng·E. Fioravanti·M. Fritsch·C. D. Fu·Q. Gao·X. L. Gao·Y. Gao·Y. G. Gao·Z. Gao·B. Garillon·I. Garzia·A. Gilman·K. Goetzen·L. Gong·W. X. Gong·W. Gradl·M. Greco·M. H. Gu·Y. T. Gu·A. Q. Guo·R. P. Guo·Y. P. Guo·A. Guskov·Z. Haddadi·S. Han·X. Q. Hao·F. A. Harris·K. L. He·X. Q. He·F. H. Heinsius·T. Held·Y. K. Heng
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Abstract

The Born cross section of the $e^{+}e^{-}~\rightarrow~\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ process is measured with unprecedented precision using data collected with the BESIII detector at $\sqrt{s}=4574.5$, $45580.0$, $4590.0$ and $4599.5$ $\mathrm{MeV}$. The non-zero cross section near the $\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ production threshold is discerned. At center-of-mass energies $\sqrt{s}=4574.5$ and $4599.5 $ $\mathrm{MeV}$, the higher statistics data enable us to measure the $\Lambda_{c}$ polar angle distributions. From these, the ratio between the $\Lambda_{c}$ electric and magnetic form factors ($|G_{E}/G_{M}|$) is measured for the first time. They are found to be $1.14\pm0.14\pm0.07$ and $1.23\pm0.05\pm0.03$ respectively, where the first uncertainties are statistical and the second are systematic.

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M. Ablikim, M. N. Achasov, S. Ahmed, M. Albrecht, M. Alekseev, A. Amoroso, F. F. An, Q. An, J. Z. Bai, Y. Bai, O. Bakina, R. Baldini Ferroli, Y. Ban, K. Begzsuren, D. W. Bennett, J. V. Bennett, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, E. Boger, I. Boyko, R. A. Briere, H. Cai, X. Cai, O. Cakir, A. Calcaterra, G. F. Cao, S. A. Cetin, J. Chai, J. F. Chang, G. Chelkov, G. Chen, H. S. Chen, J. C. Chen, M. L. Chen, P. L. Chen, S. J. Chen, X. R. Chen, Y. B. Chen, X. K. Chu, G. Cibinetto, F. Cossio, H. L. Dai, J. P. Dai, A. Dbeyssi, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. DeMori, Y. Ding, C. Dong, J. Dong, L. Y. Dong, M. Y. Dong, Z. L. Dou, S. X. Du, P. F. Duan, J. Fang, S. S. Fang, Y. Fang, R. Farinelli, L. Fava, S. Fegan, F. Feldbauer, G. Felici, C. Q. Feng, E. Fioravanti, M. Fritsch, C. D. Fu, Q. Gao, X. L. Gao, Y. Gao, Y. G. Gao, Z. Gao, B. Garillon, I. Garzia, A. Gilman, K. Goetzen, L. Gong, W. X. Gong, W. Gradl, M. Greco, M. H. Gu, Y. T. Gu, A. Q. Guo, R. P. Guo, Y. P. Guo, A. Guskov, Z. Haddadi, S. Han, X. Q. Hao, F. A. Harris, K. L. He, X. Q. He, F. H. Heinsius, T. Held, Y. K. Heng. 2017-09-30. Precision measurement of the $e^{+}e^{-}~\rightarrow~\Lambda_{c}^{+} \bar{\Lambda}_{c}^{-}$ cross section near threshold. https://doi.org/10.1103/physrevlett.120.132001

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