Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi' -> pi+pi-pi0

We study the decays of the J/psi and psi' mesons to pi+pi-pi0 using data samples at both resonances collected with the BES III detector in 2009. We measure the corresponding branching fractions with unprecedented precision and provide mass spectra and Dalitz plots. The branching fraction for J/psi -> pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.) +0.027-0.026 (norm.))*10-2, and the branching fraction for psi' -> pi+pi-pi0 is measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4. The J/psi decay is found to be dominated by an intermediate rho(770) state, whereas the psi' decay is dominated by di-pion masses around 2.2 GeV/c2, leading to strikingly different Dalitz distributions.Comment: 15 pages, 2 figure

Higher-order multipole amplitude measurement in ψ(2S)→γχc2\psi(2S)\to\gamma\chi_{c2}

Using $106\times10^6$ $\psi(2S)$ events collected with the BESIII detector at the BEPCII storage ring, the higher-order multipole amplitudes in the radiative transition $\psi(2S)\to\gamma\chi_{c2}\to\gamma\pi\pi/\gamma KK$ are measured. A fit to the $\chi_{c2}$ production and decay angular distributions yields $M2=0.046\pm0.010\pm0.013$ and $E3=0.015\pm0.008\pm0.018$, where the first errors are statistical and the second systematic. Here $M2$ denotes the normalized magnetic quadrupole amplitude and $E3$ the normalized electric octupole amplitude. This measurement shows evidence for the existence of the $M2$ signal with $4.4\sigma$ statistical significance and is consistent with the charm quark having no anomalous magnetic moment.Comment: 14 pages, 4 figure

First observation of η(1405)\eta(1405) decays into f0(980)π0f_{0}(980)\pi^0

The decays $J/\psi \rightarrow \gamma \pi^+\pi^-\pi^0$ and $J/\psi \rightarrow \gamma \pi^0\pi^0\pi^0$ are analyzed using a sample of 225 million \jpsi events collected with the BESIII detector. The decay of \eta(1405)\ar f_{0}(980)\pi^0 with a large isospin violation is observed for the first time. The width of the $f_{0}(980)$ observed in the dipion mass spectra is anomalously narrower than the world average. Decay rates for three-pion decays of the $\eta'$ are also measured precisely.Comment: Revtex, 6 pages, 4 eps figures, version accepted by Phys. Rev. Letter

Search for ηc′\eta_{c}^{\prime} decays into vector meson pairs

The processes \etacpto \rho^{0}\rho^{0}, $K^{*0}\bar{K}^{*0}$, and $\phi\phi$ are searched for using a sample of $1.06 \times 10^8$ \psip events collected with the BESIII detector at the BEPCII collider. No signals are observed in any of the three final states. The upper limits on the decay branching fractions are determined to be \mathcal{B}(\etacpto\rho^{0}\rho^{0})<3.1\times10^{-3}, \mathcal{B}(\etacpto K^{*0}\bar{K}^{*0})<5.4 \times10^{-3}, and \mathcal{B}(\etacpto\phi\phi)<2.0\times10^{-3} at the 90% confidence level. The upper limits are lower than the existing theoretical predictions.Comment: 7 pages, 9 figures, 2 table

Study of resonant structure around 1.8 GeV/c2c^2 and η(1405)\eta(1405) in J/ψ→ωηπ+π−J/\psi\rightarrow\omega\eta\pi^+\pi^-

We present results of a study of the decay $J/\psi\rightarrow\omega\eta\pi^+\pi^-$ using a sample of $(225.2\pm2.8)\times10^6$ $J/\psi$ events collected by the BESIII detector, and report the observation of a new process of $J/\psi\rightarrow \omega X(1870)$ in which X(1870) decays to $a_0(980)\pi$. The statistical significance of this process is larger than $7.2\sigma$. Signals for $J/\psi\rightarrow \omega f_1(1285)$ and $J/\psi\rightarrow \omega\eta(1405)$ are also observed in $\eta\pi^+\pi^-$ spectrum, with statistical significances much larger than $10\sigma$.Comment: 6 pages, 7 figure

Spin-Parity Analysis of ppbar Mass Threshold Structure in J/psi and psi' Radiative Decays

A partial wave analysis of the $p \bar{p}$ mass-threshold enhancement in the reaction $J/\psi\rightarrow\gamma p\bar{p}$ is used to determine: its $J^{PC}$ quantum numbers to be $0^{-+}$; its peak mass to be below threshold at $M=1832^{+19}_{-5} {\rm(stat.)}^{+18}_{-17} {\rm (syst.)}\pm19 {\rm (model)} {\rm MeV}/c^2$; and its total width to be $\Gamma<76 {\rm MeV}/c^2$ at the 90% C.L. The product branching ratio is measured to be $B(J/\psi\rightarrow\gamma X(p\bar{p}))B(X(p\bar{p})\rightarrow p\bar{p})=(9.0^{+0.4}_{-1.1} {\rm (stat.)}^{+1.5}_{-5.0} {\rm (syst.)}\pm2.3 {\rm (model)})\times10^{-5}$. A similar analysis performed on $\psi^\prime\rightarrow\gamma p\bar{p}$ decays shows, for the first time, the presence of a corresponding enhancement with a production rate relative to that for $J/\psi$ decays of $R=(5.08^{+0.71}_{-0.45} {\rm (stat.)}^{+0.67}_{-3.58} {\rm (syst.)}\pm0.12 {\rm (model)})$.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let

Measurements of the mass and width of the eta_c using psi' -> gamma eta_c

The mass and width of the lowest lying S-wave spin singlet charmonium state, the eta_c, are measured using a data sample of 1.06x10^8 psi' decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates interference between the signal reaction, psi' -> gamma eta_c, and a non-resonant radiative background to successfully describe the line shape of the eta_c. We measure the eta_c mass to be 2984.3 +- 0.6 +- 0.6 MeV/c^2 and the total width to be 32.0 +- 1.2 +- 1.0 MeV, where the first errors are statistical and the second are systematic.Comment: 7 pages, 1 figure, 1 table, matches Phys. Rev. Lett. versio

Growth and passivation of halide perovskite

The all-inorganic halide perovskite (CsPbI$_3$) holds promise for photovoltaic applications but suffers from a detrimental phase transformation to a non-perovskite phase δ-CsPbI$_3$ at low-temperature. The synthesis and stabilization routes to this and other all-inorganic halide perovskites are still not ideal, requiring uneconomical elimination of humidity, toxic solvent or high-temperature quenching. The all-solid-state synthesis method is a kind of green method to avoid the use of expensive and hazardous solvents. We have studied the influence of inorganic element doping and find that, on the one hand, the incorporation of other metal ions such as Bi$^{3+}$ and Mn$^{2+}$ makes little contribution to the stabilization of CsPbI$_3$; on the other hand, these ions seems to aid the formation of yellow phase at lower temperature and accelerate the decomposition of yellow phase into CsI and PbO at high temperature. Br- doping is able to stabilize CsPbI$_3$ in air only for a few minutes to an hour, which lead to some observation of cubic phase in the PXRD pattern. Interestingly, a cubic phase dominant black powder can be obtained by the synergic contribution of Br$^-$ and MA$^+$/FA$^+$ cations. We also studied the synthesis of CsPbI$_3$ in air atmosphere at room temperature by solvent method. Water/moisture is commonly meticulously avoided due the fact that it can accelerate the detrimental degradation of the perovskite. In our work, we used an alternative approach of engineering an in situ degradation process to form a dual-functional PbI(OH) protective covering and succeeded in performing the first room-temperature synthesis of γ-CsPbI$_3$ under ambient humidity. The vastly improved stability benefits from both lattice anchoring and physical coverage of γ-CsPbI$_3$ by an ultra-thin PbI(OH) layer. The resultant γ-CsPbI$_3$ is stable for more than 2 months under ambient conditions (25 °C, RH 30 - 60%). Anti-solvent assistanted crystallization (ASAC) is one the most commonly used methods for the deposition of high-quality perovskite solar cells, where anti-solvents are working to modulate the nucleation process of perovskite films by removing the host solvents, such as N,N-Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO), γ-butyrrolactone (GBL). Their toxicity become a concern during the commercialization process of perovskite solar cells. Various green anti-solvents have appeared in recent years, aiming to reduce the hazardous pollution to human and environment during large-scale industrial production. However, limited green solvents, such acetic ether, anisole and so on, are proven to be efficient to reduce the dependence to the widely used toxic chlorobenzene (CB) and toluene (Tol). One of the most essential reasons is that the green anti-solvent couldn’t satisfy the strict requirement of the self-nuclei process in high-quality perovskite films. To overcome this obstacle and establish more choices for green anti-solvents, we reduce the dependence of perovskite films to self-nuclei process, by adding perovskite CsPbI$_3$ NCs as artificial seeds. When CsPbI$_3$ NCs are added along with the alkane anti-solvents, the NCs could compensate the self-nuclei deficit and result in a high crystalline and dense film for high-efficiency perovskite solar cell

Are Stringent Containment and Closure Policies Associated with a Lower COVID-19 Spread Rate? Global Evidence

Stringent government policies, in general, and strict containment and closure policies in particular including workplace closing, restrictions on gatherings, close of public transport, stay-at-home order, restrictions on internal movement, and international travel control are associated with a lower spread rate of COVID-19 cases. On the other hand, school closures and public event cancellations have not been found to be associated with lower COVID-19 spread. Restrictions on international travel and the closing of public transport are two policies that stand out and have a consistent and slowing effect on the spread of COVID-19. The slowing effect of the containment and closure policies on the spread of COVID-19 becomes stronger one week after the policies have been implemented, consistent with the SARS-CoV-2 transmission pattern and the incubation period evolution. Furthermore, the slowing effect becomes stronger for culturally tight countries and countries with a higher population density. Our findings have important policy implications, implying that governments need to carefully implement containment and closure policies in their own countries&rsquo; social and cultural contexts, with an emphasis on the ideas of the common interest, personal responsibility, and the sense of community