The BESIII physics programme

Abstract

The standard model of particle physics is a well-tested theoretical framework, but there are still a number of issues that deserve further experimental and theoretical investigation. For quark physics, such questions include: the nature of quark confinement, the mechanism that connects the quarks and gluons of the standard model theory to the strongly interacting particles; and the weak decays of quarks, which may provide insights into new physics mechanisms responsible for the matter-antimatter asymmetry of the Universe. These issues are addressed by the Beijing Spectrometer III (BESIII) experiment at the Beijing Electron-Positron Collider II (BEPCII) storage ring, which for the past decade has been studying particles produced in electron-positron collisions in the tau-charm energy-threshold region, and has by now accumulated the world's largest datasets that enables searches for nonstandard hadrons, weak decays of the charmed particles, and new physics phenomena beyond the standard model. Here, we review the contributions of BESIII to such studies and discuss future prospects for BESIII and other experiments.

Semileptonic decays of heavy mesons with artificial neural networks

“…Starting from the ANN structure (2,1,2,1), we increased the number of hidden nodes per ANN while keeping the number of epochs fixed at 50. Figures 7 and 8 show the ANN fit obtained for (2,1,2,1), (2,3,4,1), (2,6,8,1), (2,15,12,1), (2,20,23,1) and (2,30,37,1).…”

“…Such searches, recently performed in B decays yielded tantalizing results in measurements related by lepton universality requirements, i.e., by the requirement that couplings of leptons to gauge bosons be independent of the lepton flavor. It is interesting to see if similar anomalies exist in semileptonic decays of charmed particles if higher precision data are available [2][3][4][5].…”

Observation of a structure in e+e−→ϕη′ at s from 2.05 to 3.08 GeV

“…Although it has been difficult to unambiguously identify so-called exotic hadrons, such as glueballs, hybrids and multiquarks, remarkable progress has been made in the charm sector during the last decade. Some of those newly observed charmoniumlike or bottomoniumlike states are good candidates for exotics [1][2][3]. The strangeonium family may have states similar to those found in heavier quarkonia, and the more experimental information would be helpful to understand the prediction for the spectrum of strangeonium.…”

“…The process e þ e − → ϕη 0 has been studied for the first time in detail using data sample collected with the BESIII detector at the BEPCII collider at center of mass energies from 2.05 to 3.08 GeV. A resonance with quantum numbers J PC ¼ 1 −− is observed with mass M ¼ ð2177.5 AE 4.8ðstatÞ AE 19.5ðsystÞÞMeV=c 2 and width Γ ¼ ð149.0 AE 15.6ðstatÞ AE 8.9ðsystÞÞ MeV with a statistical significance larger than 10σ, including systematic uncertainties. If the observed structure is identified with the ϕð2170Þ, then the ratio of partial width between the ϕη 0 by BESIII and ϕη by BABAR is (B R ϕη Γ R ee Þ=ðB R ϕη 0 Γ R ee Þ ¼ 0.23 AE 0.10ðstatÞ AE 0.18ðsystÞ, which is smaller than the prediction of the ssg hybrid models by several orders of magnitude.…”

CP symmetry tests in the cascade-anticascade decay of charmonium

“…Vector charmonia J/ψ and ψ can be directly produced in an electronpositron collider with large yields and have relatively large branching fractions into a hyperon-antihyperon pair, see Table I. With the world's largest sample of 10 10 J/ψ collected at BESIII [11,15] detailed studies of the hyperon-antihyperon systems are possible. The potential impact of such measurements was shown in the recent analysis using a data set of 4.2 × 10 5 e + e − → J/ψ → ΛΛ events reconstructed via Λ → pπ − + c.c.…”