246 Search Results

Abstract A systematic numerical investigation is carried out to understand magnetohydrodynamic stability of the ideal infernal-kink instability in tokamak plasmas with both negative triangularity (neg-D) shaping and negative central shear for the equilibrium safety factor profile. The latter is motivated by the desire to form the internal transport barrier in the neg-D configuration, which is known to have difficulty in forming the edge transport barrier. The infernal-kink mode is generally found to be more unstable in neg-D plasmas as compared to their positive D-shaped (pos-D) counterpart. This is mainly due to less favorable (or even unfavorable) average magnetic curvature near the radial location of the minimum safety factor ( $q_{\text{min}}$ ) as compared to the pos-D configuration. The larger Shafranov shift associated with the neg-D shape helps the mode stabilization but is not sufficient to overcome the destabilizing effect due to bad curvature. Strong poloidal mode coupling due to plasma shaping (toroidicity, elongation, triangularity, etc.) helps explain the slight shift with respect to that predicted by the analytic theory of the peak location of the computed mode growth versus $q_{\text{min}}$ .

Using $\left(2712\pm 14\right)\times {10}^6$ $\psi \left(2S\right)$ events collected with the BESIII detector at the BEPCII collider, we search for the decays ${\eta }_c\left(2S\right)\to \omega \omega$ and ${\eta }_c\left(2S\right)\to \omega \varphi$ via the process $\psi \left(2S\right)\to \gamma {\eta }_c\left(2S\right)$ . No statistically significant signals are observed. The upper limits of their product branching fractions at the 90% confidence level are determined to be $\mathcal{B}\left(\psi \right(2S)\to \gamma {\eta }_c(2S),{\eta }_c(2S)\to \omega \omega )<1.04\times {10}^{-6}$ and $\mathcal{B}\left(\psi \right(2S)\to \gamma {\eta }_c(2S),{\eta }_c(2S)\to \omega \varphi )<1.85\times {10}^{-7}$ , respectively. We also update the branching fractions of ${\chi }_{cJ}\to \omega \omega$ and ${\chi }_{cJ}\to \omega \varphi$ via the $\psi \left(2S\right)\to \gamma {\chi }_{cJ}$ transition. Their branching fractions are determined to be $\mathcal{B}({\chi }_{c0}\to \omega \omega )=(10.66\pm 0.11\pm 0.57)\times {10}^{-4}$ , $\mathcal{B}({\chi }_{c1}\to \omega \omega )=(6.43\pm 0.07\pm 0.31)\times {10}^{-4}$ , $\mathcal{B}({\chi }_{c2}\to \omega \omega )=(8.75\pm 0.08\pm 0.42)\times {10}^{-4}$ , $\mathcal{B}({\chi }_{c0}\to \omega \varphi )=(1.18\pm 0.03\pm 0.07)\times {10}^{-4}$ , $\mathcal{B}({\chi }_{c1}\to \omega \varphi )=(2.04\pm 0.15\pm 0.11)\times {10}^{-5}$ , and $\mathcal{B}({\chi }_{c2}\to \omega \varphi )=(9.58\pm 1.07\pm 0.76)\times {10}^{-6}$ , where the first uncertainties are statistical and the second are systematic. Published by the American Physical Society 2025

Utilizing a dataset of $6.7{\mathrm{fb}}^{-1}$ from electron-positron collisions recorded by the BESIII detector at the BEPCII storage ring, a search is conducted for the processes $e^{+}{e}^{-}\to \varphi {\chi }_{c0}$ and $\varphi {\eta }_{c2}\left(1D\right)$ across center-of-mass energies from 4.47 to 4.95 GeV. In the absence of any significant signals, upper limits are set. These include limits on the dressed cross sections for $e^{+}{e}^{-}\to \varphi {\chi }_{c0}$ , as well as the product of the dressed cross section for $e^{+}{e}^{-}\to \varphi {\eta }_{c2}\left(1D\right)$ and a sum of five branching fractions. Furthermore, the product of the electronic width of $Y\left(4660\right)$ and the branching fraction of the $Y\left(4660\right)\to \varphi {\chi }_{c0}$ , denoted as ${\mathrm{\Gamma }}_{e^{+}{e}^{-}}^{Y\left(4660\right)}{\mathcal{B}}_{Y\left(4660\right)\to \varphi {\chi }_{c0}}$ , is determined to be $<0.35\mathrm{eV}$ at the 90% confidence level. Published by the American Physical Society 2025

Studies are performed of the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{K}^{+}$ and the singly Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{\pi }^{+}$ , based on a sample of $e^{+}{e}^{-}$ collision data, corresponding to an integrated luminosity of $4.5{\mathrm{fb}}^{-1}$ , accumulated at center-of-mass energies between 4599.53 MeV and 4698.82 MeV with the BESIII detector. The decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{\pi }^{+}$ is observed for the first time. The branching fractions of ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{K}^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{\pi }^{+}$ are measured to be $(3.04\pm 0.30\pm 0.16)\times {10}^{-3}$ and $(1.73\pm 0.27\pm 0.10)\times {10}^{-3}$ , respectively, where the first uncertainties are statistical and the second are systematic. These results correspond to the most precise measurement of these quantities for both decays. Evidence of a $K^{*+}$ contribution in the ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}_S^0{\pi }^{+}$ decay is found with a statistical significance of $4.71\sigma$ . The branching fraction of ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}^{*+}$ is calculated under three possible interference scenarios, with the significance increasing to $5.03\sigma$ when interference is taken into account. Published by the American Physical Society 2025

Using $7.9\mathrm{f}{\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector at the BEPCII collider, we search for the massless dark photon with the flavor-changing neutral current processes $D^0\to \omega {\gamma }^{\prime }$ and $D^0\to \gamma {\gamma }^{\prime }$ for the first time. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be $1.1\times {10}^{-5}$ and $2.0\times {10}^{-6}$ for $D^0\to \omega {\gamma }^{\prime }$ and $D^0\to \gamma {\gamma }^{\prime }$ , respectively. These results provide the most stringent constraint on the new physics energy scale associated with $cu{\gamma }^{\prime }$ coupling in the world, with the new physics energy scale related parameter $|\mathbb{C}{|}^2+|{\mathbb{C}}_5{|}^2<8.2\times {10}^{-17}{\mathrm{GeV}}^{-2}$ at the 90% confidence level. Published by the American Physical Society 2025

Using $(27.12\pm 0.14)\times {10}^8$ $\psi \left(2S\right)$ events collected by the BESIII detector operating at BEPCII, we search for the decay ${\eta }_c\left(2S\right)\to p\overline{p}$ via the process $\psi \left(2S\right)\to \gamma {\eta }_c\left(2S\right)$ and only find a signal with a significance of $1.7\sigma$ . The upper limit of the product branching fraction at the 90% confidence level is determined to be $\mathcal{B}\left(\psi \right(2S)\to \gamma {\eta }_c(2S\left)\right)\times \mathcal{B}\left({\eta }_c\right(2S)\to p\overline{p})<2.4\times {10}^{-7}$ . The branching fractions of ${\chi }_{cJ}\to p\overline{p}(J=0,1,2)$ are also measured to be $\mathcal{B}({\chi }_{c0}\to p\overline{p})=(2.51\pm 0.02\pm 0.08)\times {10}^{-4}$ , $\mathcal{B}({\chi }_{c1}\to p\overline{p})=(8.16\pm 0.09\pm 0.25)\times {10}^{-4}$ , and $\mathcal{B}({\chi }_{c2}\to p\overline{p})=(8.33\pm 0.09\pm 0.22)\times {10}^{-4}$ , where the first uncertainty is statistical and the second systematic. Published by the American Physical Society 2025

We perform the first amplitude analysis of $D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ decays based on data samples of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, corresponding to an integrated luminosity of $7.33{\mathrm{fb}}^{-1}$ . We report the observation of $D_s^{+}\to f_0\left(980\right)\rho (770{)}^{+}$ with a statistical significance greater than $10\sigma$ and determine the branching fractions $\mathcal{B}(D_s^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0{|}_{\mathrm{non}-\eta })=(2.04\pm 0.08_{\mathrm{stat}}\pm 0.05_{\mathrm{syst}})\%$ and $\mathcal{B}(D_s^{+}\to \eta {\pi }^{+})=(1.56\pm 0.09_{\mathrm{stat}}\pm 0.04_{\mathrm{syst}})\%$ . Moreover, we measure the relative branching fraction between $\varphi \to {\pi }^{+}{\pi }^{-}{\pi }^0$ and $\varphi \to K^{+}{K}^{-}$ to be $\left[\mathcal{B}\right(\varphi \left(1020\right)\to {\pi }^{+}{\pi }^{-}{\pi }^0)/\mathcal{B}(\varphi \left(1020\right)\to K^{+}{K}^{-}\left)\right]=0.230\pm 0.014_{\mathrm{stat}}\pm 0.010_{\mathrm{syst}}$ ., which deviates from the world average value by more than $4\sigma$ . Published by the American Physical Society 2025

We present a study of the semileptonic decay $D^0\to {\pi }^{-}{\pi }^0{e}^{+}{\nu }_e$ using an $e^{+}{e}^{-}$ annihilation data sample of $7.93{\mathrm{fb}}^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector. The branching fraction of $D^0\to \rho (770{)}^{-}{e}^{+}{\nu }_e$ is measured to be $(1.439\pm 0.033(\mathrm{stat})\pm 0.027(\mathrm{syst}\left)\right)\times {10}^{-3}$ , which is a factor 1.6 more precise than previous measurements. By performing an amplitude analysis, we measure the hadronic form-factor ratios of $D^0\to \rho (770{)}^{-}{e}^{+}{\nu }_e$ at $q^2=0$ assuming the single-pole-dominance parametrization: $r_V=V\left(0\right)/A_1\left(0\right)=1.548\pm 0.079\left(\mathrm{stat}\right)\pm 0.041\left(\mathrm{syst}\right)$ and $r_2=A_2\left(0\right)/A_1\left(0\right)=0.823\pm 0.056\left(\mathrm{stat}\right)\pm 0.026\left(\mathrm{syst}\right)$ . Published by the American Physical Society 2024

We report the first amplitude analyses of the decays $D^0\to {\pi }^{+}{\pi }^{-}\eta$ and $D^{+}\to {\pi }^{+}{\pi }^0\eta$ using a data sample taken with the BESIII detector at the center-of-mass energy of 3773 MeV, corresponding to an integrated luminosity of $7.9{\mathrm{fb}}^{-1}$ . The contribution from the process $D^{0(+)}\to a_0(980{)}^{+}{\pi }^{-\left(0\right)}$ is significantly larger than the $D^{0(+)}\to a_0(980{)}^{-\left(0\right)}{\pi }^{+}$ contribution. The ratios $\mathcal{B}(D^0\to a_0(980{)}^{+}{\pi }^{-})/\mathcal{B}(D^0\to a_0\left(980{)}^{-}{\pi }^{+}\right)$ and $\mathcal{B}(D^{+}\to a_0(980{)}^{+}{\pi }^0)/\mathcal{B}(D^{+}\to a_0\left(980{)}^0{\pi }^{+}\right)$ are measured to be ${7.5}_{-0.8\mathrm{stat}}^{+2.5}\pm {1.7}_{\mathrm{syst}}$ and $2.6\pm {0.6}_{\mathrm{stat}}\pm {0.3}_{\mathrm{syst}}$ , respectively. The measured $D^0$ ratio disagrees with the theoretical predictions by orders of magnitudes, thus implying a substantial contribution from final-state interactions. Published by the American Physical Society 2024

Using the $e^{+}{e}^{-}$ collision data collected with the BESIII detector operating at the BEPCII collider, at center-of-mass energies from the threshold to 4.95 GeV, we present precise measurements of the cross section for the process $e^{+}{e}^{-}\to D_s^{+}{D}_s^{-}$ using a single-tag method. The resulting cross section line shape exhibits several new structures, thereby offering an input for a future coupled-channel analysis and model tests, which are critical to understand vector charmonium-like states with masses between 4 and 5 GeV. Published by the American Physical Society 2024