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Register a new userProduction of the X(3872) in charmonia radiative decays
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We discuss the possibilities of producing the X(3872), which is assumed to be a D bar D^* bound state, in radiative decays of charmonia. We argue that the ideal energy regions to observe the X(3872) associated with a photon in e^+e^- annihilations are around the Y(4260) mass and around 4.45 GeV, due to the presence of the S-wave D bar D_1(2420) and D^* bar D_1(2420) threshold, respectively. Especially, if the Y(4260) is dominantly a D bar D_1 molecule and the X(3872) a D bar D^* molecule, the radiative transition strength will be quite large.
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In this work, we revisit the isospin violating decays of $X(3872)$ in a coupled-channel effective field theory. In the molecular scheme, the $X(3872)$ is interpreted as the bound state of $bar{D}^{*0}D^0/bar{D}^0D^{*0}$ and $D^{*-}D^+/D^-D^{*+}$ channels. In a cutoff-independent formalism, we relate the coupling constants of $X(3872)$ with the two channels to the molecular wave function. The isospin violating decays of $X(3872)$ are obtained by two equivalent approaches, which amend some deficiencies about this issue in literature. In the quantum field theory approach, the isospin violating decays arise from the coupling constants of $X(3872)$ to two di-meson channels. In the quantum mechanics approach, the isospin violating is attributed to wave functions at the origin. We illustrate that how to cure the insufficient results in literature. Within the comprehensive analysis, we bridge the isospin violating decays of $X(3872)$ to its inner structure. Our results show that the proportion of the neutral channel in $X(3872)$ is over $80%$. As a by-product, we calculate the strong decay width of $X(3872)to bar{D}^0 D^0pi^0$ and radiative one $X(3872)to bar{D}^0 D^0gamma$. The strong decay width and radiative decay width are about 30 keV and 10 keV, respectively, for the binding energy from $-300$ keV to $-50$ keV.
The processes $X(3872)to D^{*0}bar{D^{0}}+c.c.,~gamma J/psi,~gamma psi(2S),$ and $gamma D^{+}D^{-}$ are searched for in a $9.0~rm fb^{-1}$ data sample collected at center-of-mass energies between $4.178$ and $4.278$ GeV with the BESIII detector. We observe $X(3872)to D^{*0}bar{D^{0}}+c.c.$ and find evidence for $X(3872)togamma J/psi$ with statistical significances of $7.4sigma$ and $3.5sigma$, respectively. No evident signals for $X(3872)togammapsi(2S)$ and $gamma D^{+}D^{-}$ are found, and upper limit on the relative branching ratio $R_{gamma psi} equivfrac{mathcal{B}(X(3872)togammapsi(2S))}{mathcal{B}(X(3872)togamma J/psi)}<0.59$ is set at 90$%$ confidence level. Measurements of branching ratios relative to decay $X(3872)topi^+pi^- J/psi$ are also reported for decays $X(3872)to D^{*0}bar{D^{0}}+c.c., ~gammapsi(2S),~gamma J/psi$, $gamma D^{+}D^{-}$, as well as the non-$D^{*0}bar{D}^{0}$ three-body decays $pi^0 D^{0}bar{D}^{0}$ and $gamma D^{0}bar{D}^{0}$.
Based on the hypothesis that the $X(3872)$ exotic hadron is a mixture of $chi_{c1}(2P)$ and other states and that its prompt hadroproduction predominately proceeds via its $chi_{c1}(2P)$ component, we calculate the prompt-$X(3872)$ polarization at the CERN LHC through next-to-leading order in $alpha_s$ within the factorization formalism of nonrelativistic QCD, including both the color-singlet $^3!P_1^{[1]}$ and color-octet $^3!S_1^{[8]}$ $cbar c$ Fock states. We also consider the polarization of the $J/psi$ produced by the subsequent $X(3872)$ decay. We predict that, under ATLAS, CMS, and LHCb experimental conditions, the $X(3872)$ is largely longitudinally polarized, while the $J/psi$ is largely transversely polarized. We propose that the LHC experiments perform such polarization measurements to pin down the nature of the $X(3872)$ and other $X$, $Y$, $Z$ exotic states with non-zero spin.
We study strong decays of the possible fully-charm tetraquarks recently observed by LHCb, and calculate their relative branching ratios through the Fierz rearrangement. Together with our previous QCD sum rule study [Phys. Lett. B 773, 247 (2017)], our results suggest that the broad structure around $6.2$-$6.8$ GeV can be interpreted as an $S$-wave $ccbar c bar c$ tetraquark state with $J^{PC} = 0^{++}$ or $2^{++}$, and the narrow structure around 6.9 GeV can be interpreted as a $P$-wave one with $J^{PC} = 0^{-+}$ or $1^{-+}$. These structures were observed in the di-$J/psi$ invariant mass spectrum, and we propose to confirm them in the di-$eta_c$, $J/psi h_c$, $eta_c chi_{c0}$, and $eta_c chi_{c1}$ channels. We also propose to search for their partner states having the negative charge-conjugation parity in the $J/psi eta_c$, $J/psi chi_{c0}$, $J/psi chi_{c1}$, and $eta_c h_c$ channels.
We report the first observation of $B^0 to X(3872) (K^{+}pi^{-})$ and evidence for $B^+ to X(3872) (K^{0}pi^{+})$. We measure the product of branching fractions for the former to be ${cal B}(B^0 to X(3872) (K^+ pi^-)) times {cal B}(X(3872) to J/psi pi^+ pi^-) = (7.9 pm 1.3(mbox{stat.})pm 0.4(mbox{syst.})) times 10^{-6}$ and find that $B^{0}to X(3872) K^{*}(892)^{0}$ does not dominate the $B^{0}to X(3872)K^{+}pi^{-}$ decay mode. We also measure ${cal B}(B^+ to X(3872) (K^0 pi^+)) times {cal B}(X(3872) to J/psi pi^+ pi^-) = (10.6 pm 3.0(mbox{stat.}) pm 0.9(mbox{syst.})) times 10^{-6}$. This study is based on the full data sample of 711~fb$^{-1}$ ($772times 10^6 Bbar B$ pairs) collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB collider.
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