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Register a new userProbing the nature of Z_c states via the eta_c rho decay
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The nature of the so-called XYZ states is a long-standing problem. It has been suggested that such particles may be described as compact four-quark states or loosely bound meson molecules. In the present work we analyze the Z_c() -> eta_c rho decay using both approaches. Such channel might provide useful insights on the nature of the Z_c(), helping discriminating between the two different models.
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Employing the relativized quark model and the quark-interchange model, we investigate the decay of the charged heavy quarkonium-like states $Z_c(3900)$, $Z_c(4020)$, $Z_c(4430)$, $Z_b(10610)$ and $Z_b(10650)$ into the ground and radially excited heavy quarkonia via emitting a pion meson. The $Z_c$ and $Z_b$ states are assumed to be hadronic molecules composed of open-flavor heavy mesons. The calculated decay ratios can be compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding $Z_c$ or $Z_b$ state is reasonable or not. The theoretical framework constructed in this work will be helpful in revealing the underlying structures of some exotic hadrons.
The production of the $eta_c (1S)$ state in proton-proton collisions is probed via its decay to the $p bar{p}$ final state with the LHCb detector, in the rapidity range $2.0 < y < 4.5$ and in the meson transverse-momentum range $p_T > 6.5$ GeV/c. The cross-section for prompt production of $eta_c (1S)$ mesons relative to the prompt $J/psi$ cross-section is measured, for the first time, to be $sigma_{eta_c (1S)}/sigma_{J/psi} = 1.74 pm 0.29 pm 0.28 pm 0.18 _{B}$ at a centre-of-mass energy $sqrt{s} = 7$ TeV using data corresponding to an integrated luminosity of 0.7 fb$^{-1}$, and $sigma_{eta_c (1S)}/sigma_{J/psi} = 1.60 pm 0.29 pm 0.25 pm 0.17 _{B}$ at $sqrt{s} = 8$ TeV using 2.0 fb$^{-1}$. The uncertainties quoted are, in order, statistical, systematic, and that on the ratio of branching fractions of the $eta_c (1S)$ and $J/psi$ decays to the $p bar{p}$ final state. In addition, the inclusive branching fraction of $b$-hadron decays into $eta_c (1S)$ mesons is measured, for the first time, to be $B ( b rightarrow eta_c X ) = (4.88 pm 0.64 pm 0.29 pm 0.67 _{B}) times 10^{-3}$, where the third uncertainty includes also the uncertainty on the $J/psi$ inclusive branching fraction from $b$-hadron decays. The difference between the $J/psi$ and $eta_c (1S)$ meson masses is determined to be $114.7 pm 1.5 pm 0.1$ MeV/c$^2$.
We identify the recently observed charmonium-like structure $Z_c^pm(3900)$ as the charged partner of the X(3872) state. Using standard techniques of QCD sum rules, we evaluate the three-point function and extract the coupling constants of the $Z_c , J/psi , pi^+$ and $Z_c , eta_c , rho^+$ vertices and the corresponding decay widths in these channels. The good agreement with the experimental data gives support to the tetraquark picture of this state.
While the masses of light hadrons have been extensively studied in lattice QCD simulations, there exist only a few exploratory calculations of the strong decay widths of hadronic resonances. We will present preliminary results of a computation of the rho meson width obtained using $N_f=2+1$ flavor simulations. The work is based on Luschers formalism and its extension to moving frames.
We present preliminary results on the $rho$ meson decay width estimated from the scattering phase shift of the I=1 two-pion system. The phase shift is calculated by the finite size formula for non-zero total momentum frame (the moving frame) derived by Rummukainen and Gottlieb, using the $N_f=2$ improved Wilson fermion action at $m_pi/m_rho=0.41$ and $L=2.53 {rm fm}$.
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