Private:Analysis of JETSET data: A Search for XYZ Meson Analogs

Review of XYZ Mesons Spectroscopy
Based on the 2008 review by Stephen Godfrey, Stephen L. Olsen: "The Exotic XYZ Charmonium-Like Mesons", the following is a summary of experimentally observed states:


 * $$X(3872): \{M,\Gamma\}(\pi^+\pi^-J/\psi)=\{3871.4\pm0.6, 2.3\}~\mbox{in}~B^- \rightarrow K^-X $$. Decay analysis indicates $$\gamma \rightarrow \rho$$ origins of the $$\pi^+\pi^-$$. PWA suggests $$J^{PC}=1^{++}$$ and $$J^{PC}=2^{-+}$$. These findings imply that the charmonium states corresponding to these quantum numbers: $$\chi_{c1}$$ and $$\eta_{c2}$$ would be poor choices due to isospin violation necessary for decay to $$\rho J/\psi$$. Evidence of a competing decay to $$\pi^+\pi^-\pi^0 J/\psi$$, likely via a virtual $$\omega$$ may confirm isostate mixing. Speculations:
 * $$X(3872)$$ is a $$D^0 D^{*0}$$ molecule! The mass is nearly equal to the sum of $$D^0$$ and $$D^{*0}$$ masses.
 * Tetraquark explanation also proposed with the prediction of strong X production from $$B^0$$ decays to $$K^0\pi^+\pi^-J/\psi$$


 * $$Z(3930): \{M,\Gamma \}(D\bar{D})=\{3929 \pm 6, 29 \pm 10\}~\mbox{in}~\gamma\gamma \rightarrow Z $$. The 2&gamma; production allows $$0^{++}$$ and $$2^{++}$$ states, but the PWA favors the latter. The result is consistent with the predicted $$\{M,\Gamma\}(\chi_{c2}(2P))=\{3972,28.6\}$$. The production rate is also thought consistent.


 * $$X(3940): \{M,\Gamma \}=\{3943 \pm 8, 52\}~\mbox{in}~e^+e^- \rightarrow J/\psi~X$$. Given the expected $$J=0$$ characteristic of this production mechanism, absence of substantial $$D\bar{D}$$ suggests the $$0^{-+}~\eta_c(1S)$$ state. This is reasonably consistent with the predicted $$\{M,\Gamma\}=\{3943,50\}$$. However, it is in competition with another found state, $$X(4160): \{M,\Gamma \}(D^*\bar{D^*})=\{4156 \pm 29, 139\}~\mbox{in}~e^+e^- \rightarrow J/\psi~X$$, for the assignment, according to the quantum numbers. However, the mass is between that predicted for compatible orbital states. Also, the X(3940) is below the potential model estimates.


 * $$Y(3940): \{M,\Gamma \}(\omega J/\psi)=\{3943 \pm 17, 87 \pm 34\}~\mbox{in}~B \rightarrow KX $$. Based on the confidence levels of branching fraction measurements, it is not yet clear whether this state is distinct from X(3940). The large branching fraction for $$Y \rightarrow \omega J/\psi$$ thwarts attempts to label this state as P-wave charmonium. However, this may still be a plausible assuming Y decays via a $$D\bar{D^*}$$ pair or if there is mixing with the X(3872) molecular state.


 * $$Y(4260): \{M,\Gamma \}(\pi^+\pi^-J/\psi)=\{4259 \pm 10, 88 \pm 24\}~\mbox{in ISR events}$$. These values do not match those of established charmonium states. There is no evidence of the expected D meson pair decay channels. Charmonium hybrid is a candidate, given the broad hadronic transitions found in bottomonium hybrids by LQCD.


 * broad resonances in ISR production of $$\pi^+\pi^- \psi'$$ inconsistent with the established charmonium states:
 * $$Y(4360): \{M,\Gamma \}=\{4361 \pm 13, 74 \pm 18\}$$
 * $$Y(4360): \{M,\Gamma \}=\{4664 \pm 12, 48 \pm 15\}$$


 * $$Z^+(4430): \{M,\Gamma \}(\pi^+ \psi')=\{4433 \pm 5, 45^{+35}_{-18} \}~\mbox{in}~B \rightarrow KZ^+ $$. Non-zero charge suggests that this may be a molecule or tetraquark.

Possible Analogs in the $$s\bar{s}$$ Sector
$$f_0(980)$$ and $$a_0(980)$$ are thought to be molecular states of K mesons.

$$Y(2175)$$
Events of the form $$e^+e^- \rightarrow \gamma_{ISR} \phi f_0(980), \phi \rightarrow K^+K^-, f_0(980) \rightarrow \pi^+\pi^-$$ yield a resonance in $$\phi f_0(980)$$ with $$\{M,\Gamma \}=\{2175 \pm 18, 58 \pm 26\}$$. With &phi; as an analog of J/&psi;, this is thought to be a counterpart to the Y(4260) state.