Received 5 July 2016, Revised 26 August 2016 * Supported by National Key Basic Research Program of China (2015CB856700), National Natural Science Foundation of China (NSFC) (10805053, 11125525, 11175188, 11235011, 11322544, 11335008, 11425524) Abstract: A measurement of the number of J/ψ events collected with the BESIII detector in 2009 and 2012 is performed using inclusive decays of the J/ψ. The number of J/ψ events taken in 2009 is recalculated to be (223.7 ± 1.4) × 10 6 , which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESIII software. The number of J/ψ events taken in 2012 is determined to be (1086.9 ± 6.0) × 10 6 . In total, the number of J/ψ events collected with the BESIII detector is measured to be (1310.6 ± 7.0) × 10 6 , where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.
BES data on J/ψ → γ(K + K − π + π − ) are presented. The K * K * contribution peaks strongly near threshold. It is fitted with a broad 0 −+ resonance with mass M = 1800 ± 100 MeV, width Γ = 500 ± 200 MeV. A broad 2 ++ resonance peaking at 2020 MeV is also required with width ∼ 500 MeV. There is further evidence for a 2 −+ component peaking at 2.55 GeV. The non-K * K * contribution is close to phase space; it peaks at 2.6 GeV and is very different from K * K * .PACS numbers: 14.40. Cs, 12.39.Mk, 13.25.Jx, 13.40.Hq Typeset using REVT E X [4]. There, we also find a broad 2 The analysis in this paper uses 7.8 × 10 6 J/ψ triggers collected by the Beijing Spectrometer(BES). This detector has been described in detail in Ref [12]. Here we describe briefly those detector elements crucial to this measurement. Tracking is provided by a 10 superlayer main drift chamber (MDC). Each superlayer contains four layers of sense wires measuring both the position and the ionization energy loss (dE/dx) of charged particles.The momentum resolution is σ P /P = 1.7% A positive identification of at least one K ± and one π ± is required using time of flight and/or dE/dx. If two tracks are ambiguous, both alternative identifications are tried. Events are fitted kinematically to the 4C hypothesis J/ψ → γ(, requiring a confidence level > 5%. If there is more than one photon, the fit is repeated using all permutations.Events with two or more photons are also fitted to J/ψ → γγKThose giving a better fit than to γ(K + K − π + π − ) are rejected, as are events fitting the final stateNext, we require | U miss |=| E miss − P miss |< 0.12 GeV/c 2 , so as to reject the events with multi-photons or more or less than two charged kaons; here, E miss and P miss are, respectively, the missing energy and missing momentum of all charged particles; they are calculated by assuming the charged particles are(GeV/c) 2 is required in order to remove the background J/ψ → π 0
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.