Experimental study of the $$e^+e^-\rightarrow n{\bar{n}}$$ process at the VEPP-2000 $$e^+e^-$$ collider with the SND detector
М. Н. Ачасов, A. Barnyakov, K. Beloborodov, A. V. Berdyugin, D. E. Berkaev, A. G. Bogdanchikov, A. A. Botov, G. S. Chizhik, T. Dimova, V. P. Druzhinin, L. Kardapoltsev, A. G. Kharlamov, V. A. Kladov, I. A. Koop, A. A. Korol, D. P. Kovrizhin, A. Kupich, А. П. Лысенко, N. A. Melnikova, N. Yu. Muchnoi, A. E. Obrazovsky, Е. В. Пахтусова, E. A. Perevedentsev, К. В. Пугачев, S. I. Serednyakov, З. К. Силагадзе, P. Yu. Shatunov, Yu. M. Shatunov, D. Shtol, D. B. Shwartz, I. K. Surin, Y. Usov, I. M. Zemlyansky, V. N. Zhabin, V. Zhulanov
Abstract
Abstract The process $$e^+e^-\rightarrow n{\bar{n}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mo>→</mml:mo> <mml:mi>n</mml:mi> <mml:mover> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> </mml:math> is studied in the experiment at the VEPP-2000 $$e^+e^-$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> collider with the SND detector. The technique of the time measurements in the multichannel NaI(Tl) electromagnetic calorimeter is used to select $$n{\bar{n}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>n</mml:mi> <mml:mover> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> </mml:math> events. The value of the measured cross section in the center-of-mass energy range from 1.894 to 2 GeV varies from 0.5 to 0.35 nb. The effective neutron timelike form factor is derived from the measured cross section and compared with the proton form factor. The ratio of the neutron electric and magnetic form factors is obtained from the analysis of the antineutron polar angle distribution and found to be consistent with unity.