We report measurement of the cross section of $e^+e^-to pi^+pi^-psi(2S)$ between 4.0 and $5.5 {rm GeV}$, based on an analysis of initial state radiation events in a $980 rm fb^{-1}$ data sample recorded with the Belle detector. The properties of the
$Y(4360)$ and $Y(4660)$ states are determined. Fitting the mass spectrum of $pi^+pi^-psi(2S)$ with two coherent Breit-Wigner functions, we find two solutions with identical mass and width but different couplings to electron-positron pairs: $M_{Y(4360)} = (4347pm 6pm 3) {rm MeV}/c^2$, $Gamma_{Y(4360)} = (103pm 9pm 5) {rm MeV}$, $M_{Y(4660)} = (4652pm10pm 8) {rm MeV}/c^2$, $Gamma_{Y(4660)} = (68pm 11pm 1) rm MeV$; and ${cal{B}}[Y(4360)to pi^+pi^-psi(2S)]cdot Gamma_{Y(4360)}^{e^+e^-} = (10.9pm 0.6pm 0.7) rm eV$ and ${cal{B}}[Y(4660)to pi^+pi^-psi(2S)]cdot Gamma_{Y(4660)}^{e^+e^-} = (8.1pm 1.1pm 0.5) rm eV$ for one solution; or ${cal{B}}[Y(4360)to pi^+pi^-psi(2S)]cdot Gamma_{Y(4360)}^{e^+e^-} = (9.2pm 0.6pm 0.6) rm eV$ and ${cal{B}}[Y(4660)to pi^+pi^-psi(2S)]cdot Gamma_{Y(4660)}^{e^+e^-} = (2.0pm 0.3pm 0.2) rm eV$ for the other. Here, the first errors are statistical and the second systematic. Evidence for a charged charmoniumlike structure at $4.05 {rm GeV}/c^2$ is observed in the $pi^{pm}psi(2S)$ intermediate state in the $Y(4360)$ decays.
Using data samples of $102times10^6$ $Upsilon(1S)$ and $158times10^6$ $Upsilon(2S)$ events collected with the Belle detector, a first experimental search has been made for double-charmonium production in the exclusive decays $Upsilon(1S,2S)rightarrow
J/psi(psi)+X$, where $X=eta_c$, $chi_{cJ} (J=~0,~1,~2)$, $eta_c(2S)$, $X(3940)$, and $X(4160)$. No significant signal is observed in the spectra of the mass recoiling against the reconstructed $J/psi$ or $psi$ except for the evidence of $chi_{c1}$ production with a significance of $4.6sigma$ for $Upsilon(1S)rightarrow J/psi+chi_{c1}$. The measured branching fraction $BR(Upsilon(1S)rightarrow J/psi+chi_{c1})$ is $(3.90pm1.21(rm stat.)pm0.23 (rm syst.))times10^{-6}$. The $90%$ confidence level upper limits on the branching fractions of the other modes having a significance of less than $3sigma$ are determined. These results are consistent with theoretical calculations using the nonrelativistic QCD factorization approach.
The $e^+e^- to pi^+ pi^- pi^0 chi_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $Upsilon(10860)$ energy range, with the Belle detector. The $pi^+ pi^- pi^0 chi_{
b1}$, $pi^+pi^-pi^0chi_{b2}$, $omegachi_{b1}$ signals and the evidence of $omegachi_{b2}$ are observed for the first time and the cross sections are measured. No significant $pi^+pi^-pi^0chi_{b0}$ or $omegachi_{b0}$ signal is observed and 90% confidence level upper limits on the cross sections for these two processes are obtained. In the $pi^+pi^-pi^0$ invariant mass spectrum, significant non-$omega$ signals are also observed. We search for the $X(3872)$-like state with a hidden $bbar{b}$ component (named $X_b$) decaying into $omega Upsilon(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.
The cross sections of the processes $e^+ e^- to K^+ K^- J/psi$ and $K_S^0K_S^0J/psi$ are measured via initial state radiation at center-of-mass energies between the threshold and 6.0~GeV using a data sample of 980~fb$^{-1}$ collected with the Belle d
etector on or near the $Upsilon(nS)$ resonances, where $n=$1, 2, ..., 5. The cross sections for $e^+ e^- to K^+ K^- J/psi$ are at a few pb level and the average cross section for $e^+ e^- to K_S^0K_S^0J/psi$ is $1.8pm 0.6 (rm stat.)pm 0.3 (rm syst.)$~pb between 4.4 and 5.2~GeV. All of them are consistent with previously published results with improved precision. A search for resonant structures and associated intermediate states in the cross section of the process $e^+ e^- to K^+ K^- J/psi$ is performed.
Single-layer FeSe films with extremely expanded in-plane lattice constant of 3.99A are fabricated by epitaxially growing FeSe/Nb:SrTiO3/KTaO3 heterostructures, and studied by in situ angle-resolved photoemission spectroscopy. Two elliptical electron
pockets at the Brillion zone corner are resolved with negligible hybridization between them, indicating the symmetry of the low energy electronic structure remains intact as a free-standing single-layer FeSe, although it is on a substrate. The superconducting gap closes at a record high temperature of 70K for the iron based superconductors. Intriguingly, the superconducting gap distribution is anisotropic but nodeless around the electron pockets, with minima at the crossings of the two pockets. Our results put strong constraints on the current theories, and support the coexistence of both even and odd parity spin-singlet pairing channels as classified by the lattice symmetry.
Using data samples of 89 fb$^{-1}$, 703 fb$^{-1}$, and 121 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at center-of-mass energies 10.52 GeV, 10.58 GeV, and 10.876 GeV, respectively, we study the exclusi
ve reactions $e^+e^- to omegapi^0$, $K^{ast}(892)bar{K}$, and $K_2^{ast}(1430)bar{K}$ (Charge-conjugate modes are included implicitly). Significant signals of $omegapi^0$, $K^{ast}(892)^0bar{K}^0$, and $K_2^{ast}(1430)^-K^+$ are observed for the first time at these energies, and the energy dependencies of the cross sections are presented. On the other hand, no significant excesses for $K^{ast}(892)^-K^+$ and $K_2^{ast}(1430)^0 bar{K}^0$ are found, and we set limits on the cross section ratios $R_{rm VP} = frac{sigma_B(e^+e^-to K^{ast}(892)^0bar K^0)} {sigma_B(e^+e^-to K^{ast}(892)^-K^+)}>$ 4.3, 20.0, and 5.4, and $R_{rm TP} = frac{sigma_B(e^+e^-to K_2^{ast}(1430)^0bar K^0)} {sigma_B(e^+e^-to K_2^{ast}(1430)^-K^+)}<$ 1.1, 0.4, and 0.6, for center-of-mass energies of 10.52 GeV, 10.58 GeV, and 10.876 GeV, respectively, at the 90% C.L.
Using samples of 102 million $Upsilon(1S)$ and 158 million $Upsilon(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to $ks K^+ pi^-$ and charge-conjugate (c.c.) states, $pi^+ pi^-
pi^0 pi^0$, and $pi^+ pi^- pi^0$, and to the two-body Vector-Pseudoscalar ($K^{ast}(892)^0bar{K}^0+ {rm c.c.}$, $K^{ast}(892)^-K^+ + {rm c.c.}$, $omegapi^0$, and $rhopi$) final states. For the first time, signals are observed in the modes $Upsilon(1S) to ks K^+ pi^- + {rm c.c.}$, $pi^+ pi^- pi^0 pi^0$, and $Upsilon(2S) to pi^+ pi^- pi^0 pi^0$, and evidence is found for the modes $Upsilon(1S)to pi^+ pi^- pi^0$, $K^{ast}(892)^0 bar{K}^0+ {rm c.c.}$, and $Upsilon(2S) to ks K^+ pi^- + {rm c.c.}$ Branching fractions are measured for all the processes, while 90% confidence level upper limits on the branching fractions are also set for the modes with a statistical significance of less than $3sigma$. The ratios of the branching fractions of $Upsilon(2S)$ and $Upsilon(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI-suppressed bottomonium decays.
The electronic structure of a quantum spin liquid compound, EtMe3Sb[Pd(dmit)2]2, has been studied with angle-resolved photoemission spectroscopy, together with two other Pd(dmit)2 salts in the valence bond solid or antiferromagnetic state. We have re
solved several bands that have negligible dispersions and fit well to the calculated energy levels of an isolated [Pd(dmit)2]2 dimer. EtMe3Sb[Pd(dmit)2]2 being a Mott insulator, its lower Hubbard band is identified, and there is a small gap of ~ 50 meV between this band and the chemical potential. Moreover, the spectral features exhibit polaronic behavior with anomalously broad linewidth. Compared with existing theories, our results suggest that strong electron-boson interactions, together with smaller hopping and on-site Coulomb interaction terms have to be considered for a realistic modeling of the organic quantum spin liquid systems like the Pd(dmit)2 salt.
The cross section for $e^+ e^- to pi^+ pi^- J/psi$ between 3.8 GeV and 5.5 GeV is measured with a 967 fb$^{-1}$ data sample collected by the Belle detector at or near the $Upsilon(nS)$ ($n = 1, 2, ..., 5$) resonances. The Y(4260) state is observed, a
nd its resonance parameters are determined. In addition, an excess of $pi^+ pi^- J/psi$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parameterization with properties that are consistent with the Y(4008) state that was previously reported by Belle. In a study of $Y(4260) to pi^+ pi^- J/psi$ decays, a structure is observed in the $M(pi^pmjpsi)$ mass spectrum with $5.2sigma$ significance, with mass $M=(3894.5pm 6.6pm 4.5) {rm MeV}/c^2$ and width $Gamma=(63pm 24pm 26)$ MeV/$c^{2}$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmonium-like state.
Using samples of 102 million $Upsilon(1S)$ and 158 million $Upsilon(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to the three-body final states $phi K^+ K^-$, $omega pi^+ pi^-$
and $K^{ast 0}(892) K^- pi^+ $, and to the two-body Vector-Tensor ($phi f_2(1525)$, $omega f_2(1270)$, $rho a_2(1320)$ and $K^{ast 0}(892) bar{K}_2^{ast 0}(1430) $) and Axial-vector-Pseudoscalar ($K_1(1270)^+ K^-$, $K_1(1400)^+ K^- $ and $b_1(1235)^+ pi^- $) pairs. Signals are observed for the first time in the $Upsilon(1S) to phi K^+ K^-$, $omega pi^+ pi^-$, $K^{ast 0} K^- pi^+$, $K^{ast0} K_2^{ast 0}$ and $Upsilon(2S) to phi K^+ K^-$, $K^{ast 0} K^- pi^+$ decay modes. Branching fractions are determined for all the processes, while 90% confidence level upper limits are established on the branching fractions for the modes with a statistical significance less than $3sigma$. The ratios of the branching fractions of $Upsilon(2S)$ and $Upsilon(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.
