2,941 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

We measure the time-integrated $CP$ asymmetry in $D^0\to K_S^0{K}_S^0$ decays reconstructed in $e^{+}{e}^{-}\to c\overline{c}$ events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and $428{\mathrm{fb}}^{-1}$ , respectively. The $D^0$ decays are required to originate from the $D^{*+}\to D^0{\pi }^{+}$ decay, which determines the charm flavor at production time. A control sample of $D^0\to K^{+}{K}^{-}$ decays is used to correct for production and detection asymmetries. The result, $(-1.4\pm 1.3\left(\mathrm{stat}\right)\pm 0.1\left(\mathrm{syst}\right))\%$ , is consistent with previous determinations and with $CP$ symmetry. Published by the American Physical Society 2025

We present a measurement of the branching fraction and time-dependent charge-parity ( $CP$ ) decay-rate asymmetries in $B^0\to J/\psi {\pi }^0$ decays. The data sample was collected with the Belle II detector at the SuperKEKB asymmetric $e^{+}{e}^{-}$ collider in 2019–2022 and contains $(387\pm 6)\times {10}^{6}B\overline{B}$ meson pairs from $\mathrm{\Upsilon }\left(4S\right)$ decays. We reconstruct $392\pm 24$ signal decays and fit the $CP$ parameters from the distribution of the proper-decay-time difference of the two $B$ mesons. We measure the branching fraction to be $\left({\mathcal{B}}^0\to J/\psi {\pi }^0\right)=(2.00\pm 0.12\pm 0.09)\times {10}^{-5}$ and the direct and mixing-induced $CP$ asymmetries to be $C_{CP}=0.13\pm 0.12\pm 0.03$ and $S_{CP}=-0.88\pm 0.17\pm 0.03$ , respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced $CP$ violation with a significance of 5.0 standard deviations for the first time in this mode. Published by the American Physical Society 2025

In the bottomonium sector, the hindered magnetic dipole transitions between P-wave states $h_b\left(2P\right)\to {\chi }_{bJ}\left(1P\right)\gamma$ , $J=0$ , 1, 2, are expected to be severely suppressed according to the relativized quark model, due to the spin flip of the $b$ quark. Nevertheless, a recent model following the coupled-channel approach predicts the corresponding branching fractions to be enhanced by orders of magnitude. In this Letter, we report the first search for such transitions. We find no significant signals and set upper limits at 90% confidence level on the corresponding branching fractions: $\mathcal{B}\left[h_b\right(2P)\to \gamma {\chi }_{b0}(1P\left)\right]<2.7\times {10}^{-1}$ , $\mathcal{B}\left[h_b\right(2P)\to \gamma {\chi }_{b1}(1P\left)\right]<5.4\times {10}^{-3}$ and $\mathcal{B}\left[h_b\right(2P)\to \gamma {\chi }_{b2}(1P\left)\right]<1.3\times {10}^{-2}$ . These values help to constrain the parameters of the coupled-channel models. The results are obtained using a $121.4{\mathrm{fb}}^{-1}$ data sample taken around $\sqrt{s}=10.860\mathrm{GeV}$ with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. Published by the American Physical Society 2025

The first study of $J/\psi \varphi$ production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5{\mathrm{fb}}^{-1}$ . The data disfavor a nonresonant $J/\psi \varphi$ production but are consistent with a resonant model including several resonant states observed previously only in $B^{+}\to J/\psi \varphi K^{+}$ decays. The ${\chi }_{c0}\left(4500\right)$ state is observed with a significance over $6\sigma$ and the ${\chi }_{c1}\left(4274\right)$ is confirmed with a significance of more than $4\sigma$ . © 2025 CERN, for the LHCb Collaboration 2025 CERN

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