Measurement Of E~+e~-→π~0π~0ψ(3686) And E~+e~-→π~0π~0K~+K~- Cross Section And Search For Tetraquark States

Heavy quarkonium physics provides an important approach to understand the prop-erties of perturbative and non-perturbative QCD and the interaction in transition region.Due to the heavy quark c, charmonium could be treated as the cc bound state in non-relativistic theory. These spectrum of states can be described surprisingly well using a simple cc potential model. Evidently there is reasonably good agreement between the current experimental spectrum and the potential model predictions. Except the conven-tional meson (consists of one quark and one anti-quark) and baryon (consists of three quarks), QCD also predicts the existence of glueball (gg), hybrids (qqg) and multiquark states. Charmonium physics provides an excellent laboratory for studying these new hadrons.In past years, a series of charmonium-like states, Y(4260), Y(4360), ZC(3900),ZC(4200), have been observed. Many theoretical interpretations have been proposed to understand the underlying structure of charmonium-like states, searching for new de-cay modes and more precise measurements on line shape experimentally are necessary to give a decisive conclusion. Based on the data collected by the BESIII detector at the BEPCII collider with an integrated luminosity of 5.2 fb-1 at c.m. energies ((?))from 4.009 to 4.600 GeV, the process e+e-→π0π0φ[3686) is studied for the first time. The Born cross sections are measured and found to be half of those of the reaction e+e-→π+π-φ(3686). This is consistent with the expectation from isospin symme-try. Furthermore, their distributions in Dalitz plots of π0π0φ(3686) are accordant with those of π+π-φ(3686) of e+e-→π+π-φ(3686) at all energy points, and a structure around 4040 MeV/c2 observed in π±φ(3686) at (?)=4.416 GeV is confirmed in the isospin neutral mode at the same energy point.In the low energy region((?)=2.0 - 3.0 GeV), BaBar collaboration measured the cross section of e+e-→γISRφπ+π-, and observed a structure around 2.175 GeV with a JPC=1-- in the line shape of φf0(980). The properties of the particle Y(2175)are similar to that of Y(4260), Y(4360). BESIII detector collected data samples with c.m. energies from 2.0 to 3.08 GeV, and the the process e+e-→K+K-π0π0 is studied by the partial wave analysis method.It is widely considered that rare decays of J/φ can offer an ideal opportunity to study non-perturbative QCD effects and the underlying dynamics. On other aspect,compared with the extensive studies of strong and electromagnetic decays of J/φ, both experimental and theoretical investigations of weak decays of J/φ are much behind due to their small fractions. Using data samples of (1310.6 ± 7.2) x 106 J/φ) events and(447.9 ± 2.9) × 106 φ(3686) events collected with the BESⅢ detector, we search for the rare decays J/φ→ D0e+e-+c.c. and φ(3686) → D0e+e-+c.c.. No significant signals are observed and the corresponding upper limits on the branching fractions at 90% confidence level are determined to be B(J/φ→D0e＋e-+c.c.) < 8.5 × 10-8 and B(φ(3686) → D0e+e-+ c.c.) < 1.4 × 10-7, respectively. Here,B(J/φ→D0e＋e-+c.c.) are more stringent by two orders in magnitude than the previous results,and the B(φ(3686) →D0e＋e-+c.c.) are measured for the first time.