Observation of e+e−→pppˉnˉπ−+c.c.e^+e^- \to p p \bar{p} \bar{n} \pi^{-} + c.c.

Using data taken at 29 center-of-mass energies between 4.16 and 4.70 GeV with the BESIII detector at the Beijing Electron Positron Collider corresponding to a total integrated luminosity of approximately 18.8 $\rm fb^{-1}$, the process $e^+e^- \to p p \bar{p} \bar{n} \pi^{-} + c.c.$ is observed for the first time with a statistical significance of $11.5\sigma$. The average Born cross sections in the energy ranges of (4.160, 4.380) GeV, (4.400, 4.600) GeV and (4.610, 4.700) GeV are measured to be $(21.5\pm5.7\pm1.2)$ fb, $(46.3\pm10.6\pm2.5)$ fb and $(59.0\pm9.4\pm3.2)$ fb, respectively, where the first uncertainties are statistical and the second are systematic. The line shapes of the $\bar{p}\bar{n}$ and $pp\pi^-$ invariant mass spectra are consistent with phase space distributions, indicating that no hexaquark or di-baryon state is observed.Comment: 10 pages, 4 figures. Submitted to Chinese Physics

Study of the process e+e- →φη at center-of-mass energies between 2.00 and 3.08 GeV

The process e+e-→φη is studied at 22 center-of-mass energy points (s) between 2.00 and 3.08 GeV using 715 pb-1 of data collected with the BESIII detector. The measured Born cross section of e+e-→φη is found to be consistent with BABAR measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9σ with mass (2163.5±6.2±3.0) MeV/c2 and width (31.1-11.6+21.1±1.1) MeV, where the first uncertainties are statistical and the second are systematic

Search for the charged lepton flavor violating decay J /ψ →eτ

A search for the charged lepton flavor violating decay J/ψ→e±τ with τ →π π0ντ is performed with about 10×109 J/ψ events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction B(J/ψ→e±τ)<7.5×10-8 at the 90% confidence level. This improves the previously published limit by two orders of magnitude

Measurement of the absolute branching fractions for purely leptonic Ds+ decays

We report new measurements of the branching fraction B(Ds+→ℓ+ν), where is either μ+ or τ+(→π+ν¯τ), based on 6.32 fb-1 of electron-positron annihilation data collected by the BESIII experiment at six center-of-mass energy points between 4.178 and 4.226 GeV. Simultaneously floating the Ds+→μ+νμ and Ds+→τ+ντ components yields B(Ds+→τ+ντ)=(5.21±0.25±0.17)×10-2, B(Ds+→μ+νμ)=(5.35±0.13±0.16)×10-3, and the ratio of decay widths R=Γ(Ds+→τ+ντ)Γ(Ds+→μ+νμ)=9.73-0.58+0.61±0.36, where the first uncertainties are statistical and the second systematic. No evidence of CP asymmetry is observed in the decay rates Ds±→μ±νμ and Ds±→τ±ντ: ACP(μ±ν)=(-1.2±2.5±1.0)% and ACP(τ±ν)=(+2.9±4.8±1.0)%. Constraining our measurement to the Standard Model expectation of lepton universality (R=9.75), we find the more precise results B(Ds+→τ+ντ)=(5.22±0.10±0.14)×10-2 and ACP(τ±ντ)=(-0.1±1.9±1.0)%. Combining our results with inputs external to our analysis, we determine the c→s¯ quark mixing matrix element, Ds+ decay constant, and ratio of the decay constants to be |Vcs|=0.973±0.009±0.014, fDs+=249.9±2.4±3.5 MeV, and fDs+/fD+=1.232±0.035, respectively

Amplitude analysis and branching-fraction measurement of Ds+ → KS0 K-π+π+

Using 6.32 fb-1 of e+e- collision data collected by the BESIII detector at the center-of-mass energies between 4.178 and 4.226 GeV, an amplitude analysis of the Ds+→KS0K-π+π+ decays is performed for the first time to determine the intermediate-resonant contributions. The dominant component is the Ds+→K∗(892)+K̄∗(892)0 decay with a fraction of (40.6±2.9stat±4.9sys)%. Our results of the amplitude analysis are used to obtain a more precise measurement of the branching fraction of the Ds+→KS0K-π+π+ decay, which is determined to be (1.46±0.05stat±0.05sys)%

Study of the Decay D+s → π+π+π−η and Observation of the W-annihilation Decay D+s → a0(980)+ρ0

The decay D+s → π+π+π−η is observed for the first time, using e+e− collision data corresponding to an integrated luminosity of 6.32 fb−1, collected by the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV. The absolute branching fraction for this decay is measured to be B(D+s → π+pi+π−η) = (3.12 ± 0.13stat. ± 0.09syst.)%. The first amplitude analysis of this decay reveals the sub-structures in D+s → π+π+π−η and determines the relative fractions and the phases among these sub-structures. The dominant intermediate process is D+s → a1(1260)+η, a1(1260)+ →ρ(770)0π+ with a branching fraction of (1.73 ± 0.14stat. ± 0.08syst.)%. We also observe the W-annihilation process D+s → a0(980)+ρ(770)0, a0(980)+ → π+η with a branching fraction of (0.21 ±0.08stat. ± 0.05syst.)%, which is larger than the branching fractions of other measured pure Wannihilation decays by one order of magnitude

A Search for Photons with Energies Above 2X10(17) eV Using Hybrid Data from the Low-Energy Extensions of the Pierre Auger Observatory

Ultra-high-energy photons with energies exceeding 10(17) eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent observations of photons with energies in the 10(15) eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 x 10(17) eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 10(17) and 10(18) eV