Two-photon radiative decay process $J/\psi \to 2\gamma+hadrons$ is studied, and the main contribution processes $J/\psi \to 2\gamma + g g g$ and $J/\psi \to 2\gamma + q \bar{q}$ are calculated. With the specific condition at the BESIII, this rare decay process and the main background process $e^{+} e^{-} \to \gamma \gamma + hadrons (q \bar{q})$ are investigated. The results show that the ratio of signal to background can reach 1.24 with the optimized selection criteria at the BESIII. In addition, a few distributions of the signal and background are presented. All the results show that the signal is large enough to be measured in the experiment. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.
An effort to search for Kolar-like events within the data set of the L3+C experiment is reported. From a total of 0.89 × 1010 triggered events there are no reliable two-prong Kolar-like events observed. The corresponding event flux upper limit 7.1 × 10−13 cm−2 · s−1 · sr−1 at 90% confidence level is deduced based on some reasonable assumptions.
A new approach for tree-level amplitudes with multiple fermion lines is presented. It primarily focuses on the simplification of fermion lines. By calculating two vectors recursively without any matrix multiplications, the result of a fermion line is reduced to a very compact form depending only on the two vectors. Comparisons with other packages are presented, and the results show that our package FDC provides a very good performance in the processes of multiple fermion lines with this new approach and some other improvements. A further comparison with WHIZARD shows that this new approach has a competitive efficiency in computing pure amplitude squares without phase space integration.
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