339 Search Results

The radiative effect of aerosol on cloud albedo via altering cloud droplet effective radius (r_e) is a major uncertainty in the Earth's climate system. Remote sensing studies have reported either negative or positive relationships between re and aerosol number concentration (N_a) or other aerosol proxies. However, there are much fewer in situ observational evidences and physical explanation remains elusive for the contrasting N_a-r_e relationships. Here we quantify the N_a-r_e relationship by using in situ aircraft measurements, together with a re decomposition method. Our analysis reveals that the cloud-planetary boundary layer (PBL) coupling plays a pivotal role on the N_a-r_e relationship.more » Quantitative r_e decomposition indicates that the contrasting N_a-r_e relationships in two cloud-PBL coupling regimes result from different balances of four distinct aspects. The widely recognized number effect may be outweighed by the joint effects of the remaining three that have been rarely investigated and largely ignored in N_a-r_e parameterizations.« less

Based on 12.0 fb⁻¹ of 𝑒⁺⁢𝑒⁻ collision data samples collected by the BESIII detector at center-of-mass energies from 4.1271 to 4.3583 GeV, a partial wave analysis is performed for the process 𝑒⁺⁢𝑒⁻ → 𝜋⁺⁢𝜋⁻⁢𝐽/𝜓. The cross sections for the subprocesses 𝑒⁺⁢𝑒⁻ → 𝜋⁺⁢𝑍_𝑐⁢(3900)⁻ + c.c. → 𝜋⁺⁢𝜋⁻⁢𝐽/𝜓, 𝑓₀⁡(980)⁢(→ 𝜋⁺⁢𝜋⁻)⁢𝐽/𝜓, and (𝜋⁺⁢𝜋⁻)_S−wave⁢𝐽/𝜓 are measured for the first time. The mass and width of the 𝑍_𝑐⁢(3900)^± are determined to be 3884.6 ± 0.7 ± 3.3 MeV/𝑐² and 37.2 ± 1.3 ± 6.6 MeV, respectively. The first errors are statistical and the second systematic. The final state (𝜋⁺⁢𝜋⁻)_S−wave⁢𝐽/𝜓 dominates the process 𝑒⁺⁢𝑒⁻ →more » 𝜋⁺⁢𝜋⁻⁢𝐽/𝜓. By analyzing the cross sections of 𝜋^±⁢𝑍_𝑐⁢(3900)^∓ and 𝑓₀⁡(980)⁢𝐽/𝜓, 𝑌⁡(4220) has been observed. Its mass and width are determined to be 4225.7 ± 4.1 ± 3.4 MeV/𝑐² and 57.5 ± 9.4 ± 12.1 MeV, respectively.« less

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a J/ψ decaying into a vector-pseudoscalar final state is performed using 26 energy points of e⁺e⁻ annihilation data between 3.00 GeV and 3.12 GeV. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb⁻¹. By investigating the interference pattern in the cross section lineshape of e⁺e⁻ → ϕη, the relative phase between the strong and electromagnetic amplitudes of J/ψ decay is determined to be within [133°, 228°] at 68% confidence level.

The structural evolution of molecular hydrogen H₂ under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H₂, has been previously confirmed in experiments. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H₂ to a post-hcp structure with a six-fold larger supercell at pressures above 212 GPa, indicating the change of spherical H₂ to various ordered configurations. Theoretical calculations based on our XRDmore » results found a time-averaged structure model in the space group $$P\bar{6}2c$$ with alternating layers of spherically disordered H₂ and new graphene-like layers consisting of H₂ trimers (H₆) formed by the association of three H₂ molecules. Here, this supercell has not been reported by any previous theoretical study for the post-hcp phase, but is close to a number of theoretical models with mixed-layer structures. The evidence of a structural transition beyond hcp establishes the trend of H₂ molecular association towards polymerization at extreme pressures, giving clues about the nature of the molecular-to-atomic transition of metallic hydrogen. Considering the spectroscopic behaviours that show strong vibrational and bending peaks of H₂ up to 400 GPa, it would be prudent to speculate the continuation of hydrogen molecular polymerization up to its metallization.« less

We present the first amplitude analysis and branching fraction measurement of the decay $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0{\pi }^0$ , using $e^{+}{e}^{-}$ collision data collected with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV corresponding to an integrated luminosity of $7.33{\mathrm{fb}}^{-1}$ , and report the first observation of the pure $W$ -annihilation decay $more »$ D s + → ω ρ + with a branching fraction of $(0.99\pm 0.08_{\mathrm{stat}}{{}_{-0.07}^{+0.05}}_{\mathrm{syst}})\%$ . In comparison to the low significance of the $\mathcal{D}$ wave in the decay $D_s^{+}\to \varphi {\rho }^{+}$ , the dominance of the $\mathcal{D}$ wave over the $\mathcal{S}$ and $\mathcal{P}$ waves, with a fraction of $(51.85\pm 7.28_{\mathrm{stat}}{{}_{-7.90}^{+4.83}}_{\mathrm{syst}})\%$ observed in the decay $D_s^{+}\to \omega {\rho }^{+}$ , provides crucial information for the “polarization puzzle,” as well as for the understanding of charm meson decays. The branching fraction of $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0{\pi }^0$ is measured to be $(4.41\pm 0.15_{\mathrm{stat}}\pm 0.13_{\mathrm{syst}})\%$ . Moreover, the branching fraction of $D_s^{+}\to \varphi {\rho }^{+}$ is measured to be $(3.98\pm 0.33_{\mathrm{stat}}{{}_{-0.19}^{+0.21}}_{\mathrm{syst}})\%$ , and the $R_{\varphi }=\mathcal{B}(\varphi \to {\pi }^{+}{\pi }^{-}{\pi }^0)/\mathcal{B}(\varphi \to K^{+}{K}^{-})$ is determined to be ( $0.222\pm 0.019_{\mathrm{stat}}{{}_{-0.016}^{+0.016}}_{\mathrm{syst}}$ ), which is consistent with the previous measurement based on charm meson decays, but deviates from the results from $e^{+}{e}^{-}$ annihilation and $K-N$ scattering experiments by more than $3\sigma$ . Published by the American Physical Society 2025« less

Using $(2712.4\pm 14.3)\times {10}^6$ $\psi \left(3686\right)$ events collected with the BESIII detector at BEPCII, a partial wave analysis of the decay $\psi \left(3686\right)\to \varphi \eta {\eta }^{\prime }$ is performed with the covariant tensor approach. In addition to the established states $h_1(1900$ ) and $\varphi \left(2170\right)$ , an axial-vector state with a mass near $more »$ 2.3     GeV / c 2 is observed for the first time. Its mass and width are measured to be $2316\pm 9_{\mathrm{stat}}\pm 30_{\mathrm{syst}}\mathrm{MeV}/c^2$ and $89\pm 15_{\mathrm{stat}}\pm 26_{\mathrm{syst}}\mathrm{MeV}$ , respectively. The product branching fractions of $\mathcal{B}\left[\psi \right(3686)\to X(2300\left){\eta }^{\prime }\right]\mathcal{B}\left[X\right(2300)\to \varphi \eta ]$ and $\mathcal{B}\left[\psi \right(3686)\to X(2300\left)\eta \right]\mathcal{B}\left[X\right(2300)\to \varphi {\eta }^{\prime }]$ are determined to be $(4.8\pm {1.3}_{\mathrm{stat}}\pm {0.7}_{\mathrm{syst}})\times {10}^{-6}$ and $(2.2\pm {0.7}_{\mathrm{stat}}\pm {0.7}_{\mathrm{syst}})\times {10}^{-6}$ , respectively. The branching fraction $\mathcal{B}\left[\psi \right(3686)\to \varphi \eta {\eta }^{\prime }]$ is measured for the first time to be ( $3.14\pm 0.17_{\mathrm{stat}}\pm 0.24_{\mathrm{syst}})\times {10}^{-5}$ . The first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2025« less

Using $20.3{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector operating at the BEPCII collider, the branching fractions of three hadronic charm meson decays, $D^{+}\to \varphi {\pi }^{+}{\pi }^{+}{\pi }^{-}$ , $D^{+}\to K_S^0{K}^{+more »}$ π + π − π 0 , and $D^{+}\to K_S^0{K}^{+}\omega$ , are measured for the first time to be $(0.54\pm 0.19\pm 0.02)\times {10}^{-4}$ , $(2.51\pm 0.34\pm 0.14)\times {10}^{-4}$ , and $(2.02\pm 0.35\pm 0.10)\times {10}^{-4}$ , respectively. Futhermore, the branching fractions of $D^{+}\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{+}{\pi }^{-}$ and $D^{+}\to K_S^0{K}^{+}\eta$ are measured with improved precision, yielding values of $(0.66\pm 0.11\pm 0.03)\times {10}^{-4}$ and $(2.27\pm 0.22\pm 0.05)\times {10}^{-4}$ , respectively. Published by the American Physical Society 2025« less

Using a dataset of $(27.12\pm 0.14)\times {10}^8\psi \left(3686\right)$ events collected by the BESIII detector operating at the BEPCII collider, we report the first observation of the decay $\psi \left(3686\right)\to {\mathrm{\Sigma }}^0{\overline{\mathrm{\Sigma }}}^0\omega$ with a statistical significance of $8.9\sigma$ . The measured branching fraction is $(1.24\pm 0.16_{\mathrm{stat}}\pm 0.11_{\mathrm{sys}})\times {10}^{more »}$ − 5 , where the first uncertainty is statistical and the second is systematic. Additionally, we investigate potential intermediate states in the invariant mass distributions of ${\mathrm{\Sigma }}^0\omega$ , ${\overline{\mathrm{\Sigma }}}^0\omega$ and ${\mathrm{\Sigma }}^0{\overline{\mathrm{\Sigma }}}^0$ . A hint of a resonance is observed in the invariant mass distribution of $M_{{\mathrm{\Sigma }}^0\left({\overline{\mathrm{\Sigma }}}^0\right)\omega }$ , located around $2.06\mathrm{GeV}/c^2$ , with a significance of $2.5\sigma$ . Published by the American Physical Society 2025« less

Using $7.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we present an analysis of the decay $D^0\to \eta {\pi }^{-}{e}^{+}{\nu }_e$ . The branching fraction of the decay $D^{more »}$ 0 → a 0 ( 980 ) − e + ν e with $a_0(980{)}^{-}\to \eta {\pi }^{-}$ is measured to be $(0.86\pm 0.17_{\mathrm{stat}}\pm 0.05_{\mathrm{syst}})\times {10}^{-4}$ . The decay dynamics of this process is studied with a single-pole parametrization of the hadronic form factor and the Flatté formula describing the $a_0\left(980\right)$ line shape in the differential decay rate. The product of the form factor $f_{+}^{a_0}\left(0\right)$ and the Cabibbo-Kobayashi-Maskawa matrix element $\left|V_{cd}\right|$ is determined for the first time with the result $f_{+}^{a_0}\left(0\right)\left|V_{cd}\right|=0.126\pm 0.013_{\mathrm{stat}}\pm 0.003_{\mathrm{syst}}$ . Published by the American Physical Society 2025« less

Using $(2712.4\pm 14.3)\times {10}^6\psi \left(3686\right)$ events collected with the BESIII detector at the BEPCII collider, the decay ${\eta }_c\to \gamma \gamma$ in $J/\psi \to \gamma {\eta }_c$ is observed. We determine the product branching fraction $\mathcal{B}(J/\psi \to \gamma {\eta }_c)\times \mathcal{B}more »$ ( η c → γ γ ) = ( 5.23 ± 0.2 6 stat ± 0.3 0 syst ) × 10 − 6 . This result is consistent with the lattice QCD calculation $(5.34\pm 0.16)\times {10}^{-6}$ from HPQCD in 2023. By using the world-average values of $\mathcal{B}(J/\psi \to \gamma {\eta }_c)$ and the total decay width of ${\eta }_c$ , the partial decay width $\mathrm{\Gamma }({\eta }_c\to \gamma \gamma )$ is determined to be $(11.30\pm 0.56_{\mathrm{stat}}\pm 0.66_{\mathrm{syst}}\pm 1.14_{\mathrm{ref}})\mathrm{keV}$ , which deviates from the corresponding world-average value by $3.4\sigma$ . Published by the American Physical Society 2025« less