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Register a new userObservation of a structure at 1.84 GeV/c$^2$ in the $3(pi^+pi^-)$ mass spectrum in $J/psirightarrow gamma 3(pi^+pi^-)$ decays
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With a sample of 225.3 million $J/psi$ events taken with the BESIII detector, the decay $J/psirightarrow gamma 3(pi^+pi^-)$ is analyzed. A structure at 1.84 GeV/c$^2$ is observed in the $3(pi^+pi^-)$ invariant mass spectrum with a statistical significance of 7.6$sigma$ . The mass and width are measured to be $M=1842.2pm 4.2^{+7.1}_{-2.6}$ MeV/c$^2$ and $Gamma=83pm 14 pm 11$ MeV. The product branching fraction is determined to be $B(J/psirightarrowgamma X(1840))times B(X(1840)rightarrow 3(pi^+pi^-))=(2.44pm0.36^{+0.60}_{-0.74})times 10^{-5}$. No $eta^prime$ signals are observed in the $3(pi^+pi^-)$ invariant mass spectrum, and the upper limit of the branching fraction for the decay $eta^primerightarrow 3(pi^+pi^-)$ is set to be $3.1times10^{-5}$ at a 90% confidence level.
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We have performed the most comprehensive resonance-model fit of $pi^-pi^-pi^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $pi^- + p to pi^-pi^-pi^+ + p_text{recoil}$ with a 190 GeV/$c$ pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, $0.5 < m_{3pi} < 2.5$ GeV/$c^2$, and simultaneously in 11 bins of the reduced four-momentum transfer squared, $0.1 < t < 1.0$ $($GeV$/c)^2$, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{++}$, $2^{-+}$, $4^{++}$, and spin-exotic $1^{-+}$ quantum numbers. The model contains the well-known resonances $pi(1800)$, $a_1(1260)$, $a_2(1320)$, $pi_2(1670)$, $pi_2(1880)$, and $a_4(2040)$. In addition, it includes the disputed $pi_1(1600)$, the excited states $a_1(1640)$, $a_2(1700)$, and $pi_2(2005)$, as well as the resonancelike $a_1(1420)$. We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 $t$ bins. We extract the relative branching fractions of the $rho(770) pi$ and $f_2(1270) pi$ decays of $a_2(1320)$ and $a_4(2040)$, where the former one is measured for the first time. In a novel approach, we extract the $t$ dependence of the intensity of the resonances and of their phases. The $t$ dependence of the intensities of most resonances differs distinctly from the $t$ dependence of the nonresonant components. For the first time, we determine the $t$ dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances.
We present a numerical computation of matrix elements of DI=3/2 K-->pi pi decays by using Wilson fermions. In order to extrapolate to the physical point we work at unphysical kinematics and we resort to Chiral Perturbation Theory at the next-to-leading order. In particular we explain the case of the electroweak penguins O_{7,8} which can contribute significantly in the theoretical prediction of epsilon/epsilon. The study is done at beta=6.0 on a 24^3x64 lattice.
Using $1.09times10^{9}$ $J/psi$ events collected by the BESIII experiment in 2012, we study the $J/psirightarrowgammaeta^{prime}pi^{+}pi^{-}$ process and observe a significant abrupt change in the slope of the $eta^{prime}pi^{+}pi^{-}$ invariant mass distribution at the proton-antiproton ($pbar{p}$) mass threshold. We use two models to characterize the $eta^{prime}pi^{+}pi^{-}$ line shape around $1.85~text{GeV}/c^{2}$: one which explicitly incorporates the opening of a decay threshold in the mass spectrum (Flatt{e} formula), and another which is the coherent sum of two resonant amplitudes. Both fits show almost equally good agreement with data, and suggest the existence of either a broad state around $1.85~text{GeV}/c^{2}$ with strong couplings to $pbar{p}$ final states or a narrow state just below the $pbar{p}$ mass threshold. Although we cannot distinguish between the fits, either one supports the existence of a $pbar{p}$ molecule-like state or bound state with greater than $7sigma$ significance.
We present new results on the related rare KL decay modes KL -> pi+ pi- gamma and KL -> pi+ pi- e+ e-. KTeV has performed the first direct measurement of the form factor for the direct emission component of KL -> pi+ pi- gamma decays, a quantity with ramifications for particular chiral models. In addition, the form factor and direct emission/inner bremsstrahlung branching ratio - also presented here - are important input parameters for the understanding of the planar-angle distribution of KL -> pi+ pi- e+ e- decays. Preliminary results indicating the presence of a T-violating asymmetry in the KL -> pi+ pi- e+ e- angular distribution are presented.
We study the process e+e- to pi+pi-J/psi at a center-of-mass energy of 4.260 GeV using a 525 pb^{-1} data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9pm 1.9pm 3.7) pb, consistent with the production of the Y(4260). We observe a structure at around 3.9 GeV/c^2 in the pi^pm J/psi mass spectrum, which we refer to as the Z_c(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the pi^pm J/psi invariant mass spectrum, neglecting interference, results in a mass of (3899.0pm 3.6pm 4.9) MeV/c^2 and a width of (46pm 10pm 20) MeV. Its production ratio is measured to be R=frac{sigma(e+e- to pi^pm Z_c(3900)^mp to pi+pi-J/psi))} {sigma(e+e- to pi+pi-J/psi)}=(21.5pm 3.3pm 7.5)%. In all measurements the first errors are statistical and the second are systematic.
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