Searching For η_c(2S)→K~+K~-η Process On BESⅢ And Measure Branching Fraction

The discovery of particles J/ψopened the prologue of charmonium physics research in1974.The study of charmonium is one of the major area in the BESⅢ experimental research.The study of charmonium is beneficial to the understanding of non-perturbative strong interactions because in the energy scale of charmonium,the contributions of perturbative and non-perturbative interactions are comparable.BESⅢ takes full advantage of the highly-developed detection technology and the largeψ（2S）samples provided by BEPCII.Theψ（2S）samples provide a very good platform and conditions for the study of charmonium-related experiments,and promote many significant scientific research results.ψ（2S）can transition to the lower energy charmonium state by emitting photons or light hadrons,which also provides basic guarantee for the introduction of a large number of charmonium related scientific research achievements.Using theψ（2S）data samples collected in BESⅢ detector from 2009,2012,and 2021,we search for the processη_c（2S）→K⁺K^-η.After signal reconstruction and event selection,η_c（2S）→K⁺K^-ηchannel is observed in BESⅢ for the first time a statistical with signifi-cance of 6.2σafter considering systematic uncertianties.The product of the branching frac-tion ofψ（2S）→γη_c（2S）andη_c（2S）→K⁺K^-ηis determined to be Br（ψ（2S）→γη_c（2S））·Br（η_c（2S）→K⁺K^-η）=（2.43±0.33±1.28）×10^-6.The branching fraction ofη_c（2S）→K⁺K^-ηis calculated to be Br（η_c（2S）→K⁺K^-η）=（3.49±0.47±0.50±1.76）×10^-3,where the first uncertainty is statistical uncertainty,the second one is the systematic uncertainties without considering the uncertainty from the branching fraction ofψ（2S）→γη_c（2S）,while the third one is the systematic uncertainty of considering the uncertainty from the branching fraction ofψ（2S）→γη_c（2S）.After considering the isospin symmetry of K⁺K^-and K⁰（?）⁰system,the branching fraction ofη_c（2S）→（?）Kηwe get is（6.98±0.66±0.71±2.49）×10^-3.Compared with the PDG result（5±4）×10^-3[16],the uncertainty is reduced and the re-sult is more accurate.At the same time,this paper measures the branching fractions ofχ_c1,c2→K⁺K^-η.The results are（2.43±0.03）×10^-4and（1.87±0.04）×10^-4,respec-tively,with only statistical uncertainty taken into consideration.It is consistent with the results in the PDG.Based on the branching fraction ofη_c（2S）→（?）Kη,we measure the (Br（η_c（2S）→（?）Kη）/（Br（η_c（1S）→（?）Kη））=0.51±0.20 with Br（η_c（1S）→（?）Kη）=（1.36±0.15）%cited by PDG.This work enriches the experimental understanding ofη_c（2S）decay,it also provides an important reference for the relevant theoretical research.