Intermediate Charmed Meson Loops Research Articles

Heavy quark spin partners of the Y(4260) in coupled-channel formalism

The charmoniumlike state $Y(4260)$ is described as predominantly a $D_1 \bar{D}$ molecule in a coupled-channel quark model [Phys.\,Rev.\,D\,\textbf{96},\,114022\,(2017)]. The heavy quark spin symmetry (HQSS) thus implies the possible emergence of its heavy quark spin partners with molecular configuration as $D_1 \bar{D}^*$ and $D_2^* \bar{D}^*$ below these charmed mesons' thresholds. We analyze the probabilities of various intermediate charmed meson loops for $J^{PC}=1^{--}$ exotic state $Y(4360)$ and find that the channel $D_1 \bar{D}^*$ couples more strongly around its mass regime, and the coupling behavior remains the same even if the mass of $Y(4360)$ is pushed closer to $D_1 \bar{D}^*$ threshold. This enlightens that the most favorable molecular scenario for the $Y(4360)$ could be $D_1 \bar{D}^*$, and hence it can be interpreted as HQSS partner of the $Y(4260)$. We also find the strong coupling behavior of $D_2^* \bar{D}^*$ channel with the $\psi(4415)$, which makes it a good candidate for a dominant $D_2^* \bar{D}^*$ molecule. We discuss the important decay patterns of these resonances to disentangle their long- and short-distance structures.

Evasion of HSR in the charmless decays of excited P-wave charmonia

We investigate the charmless decays of excited P-wave charmonia chi _{c1}^prime rightarrow VV and chi _{c2}^prime rightarrow VP via intermediate charmed meson loops, where V and P denote the light vector and pseudoscalar mesons, respectively. Within the model parameters, the charmed meson loop contributions are evaluated by using the effective Lagrangian approach. For chi _{c1}^prime rightarrow VV, the partial widths of the rho rho , omega omega , and K^*{bar{K}}^* channels can reach to the order of MeV, while the partial width of the phi phi channel is very small and in the order of keV. For chi _{c2}^prime rightarrow V P, the partial widths of chi _{c2}^{prime } rightarrow K^*bar{K}+c.c turns out to be sizeable, while the partial widths of chi _{c2}^{prime } rightarrow rho ^+pi ^- +c.c is found to be much smaller than the K^*bar{K}+c.c channel. Our calculations may be examined by the future BESIII experiments.

Study on the radiative decays of h_c via intermediate meson loops model

Recently, the BESIII Collaboration reported two new decay processes: h_c(1P)rightarrow gamma eta and gamma eta ^prime . Inspired by this measurement, we propose to study the radiative decays of h_c via intermediate charmed meson loops in an effective Lagrangian approach. With the acceptable cutoff parameter range, the calculated branching ratios of h_c(1P)rightarrow gamma eta and gamma eta ^prime are of the orders of 10^{-4} to 10^{-3} and 10^{-3} to 10^{-2}, respectively. The ratio R_{h_c}= mathcal {B}( h_crightarrow gamma eta )/mathcal {B}( h_crightarrow gamma eta ^prime ) can reproduce the experimental measurements with the commonly acceptable alpha range. This ratio provide us with some information on the eta –eta ^prime mixing, which may be helpful for us to test the SU(3)-flavor symmetries in QCD.

Evasion of HSR in S-wave charmonium decaying to P-wave light hadrons

The S-wave charmonium decaying to a P-wave and S-wave light hadron pairs are supposed to be suppressed by the helicity selection rule in the perturbative QCD framework. With an effective Lagrangian method, we show that the intermediate charmed meson loops can provide a possible mechanism for the evasion of the helicity selection rule, and result in sizeable decay branching ratios in some of those channels. The theoretical predictions can be examined by the forthcoming BES-III data in the near future.

Further understanding of the non-DD¯decays ofψ(3770)

We provide details of the study of $\ensuremath{\psi}(3770)$ non-$D\overline{D}$ decays into $VP$, where $V$ and $P$ denote light vector meson and pseudoscalar meson, respectively. We find that the electromagnetic interaction plays little role in these processes, while the strong interaction dominates. The strong interaction can be separated into two parts, i.e., the short-distance part probing the wave function at origin and the long-distance part reflecting the soft gluon exchanged dynamics. The long-distance part is thus described by the intermediate charmed meson loops. We show that the transition of $\ensuremath{\psi}(3770)\ensuremath{\rightarrow}VP$ can be related to $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}VP$ such that the parameters in our model can be constrained by comparing the different parts in $\ensuremath{\psi}(3770)\ensuremath{\rightarrow}VP$ to those in $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}VP$. Our quantitative results confirm the findings of Zhang et al. [Phys. Rev. Lett. 102, 172001 (2009)] that the OZI-rule-evading long-distance strong interaction via the intermediate meson loops plays an important role in $\ensuremath{\psi}(3770)$ decays and could be a key towards a full understanding of the mysterious $\ensuremath{\psi}(3770)$ non-$D\overline{D}$ decay mechanism.

The role of charmed meson loops in charmonium decays

We investigate the effect of intermediate charmed meson loops on the M1 radiative decays $J/\psi \to \eta_c \gamma$ and $\psi'\rightarrow\eta^{(\prime)}_c\gamma$ as well as the isospin violating hadronic decays $\psi'\rightarrow J/\psi \,\pi^0(\eta)$ using heavy hadron chiral perturbation theory (HH$\chi$PT). The calculations include tree level as well as one loop diagrams and are compared to the latest data from CLEO and BES-III. Our fit constrains the couplings of 1S and 2S charmonium multiplets to charmed mesons, denoted $g_2$ and $g_2^\prime$, respectively. We find that there are two sets of solutions for $g_2$ and $g_2^\prime$. One set, which agrees with previous values of the product $g_2 g_2^\prime$ extracted from analyses that consider only loop contributions to $\psi'\rightarrow J/\psi \,\pi^0(\eta)$, can only fit data on radiative decays with fine-tuned cancellations between tree level diagrams and loops in that process. The other solution for $g_2$ and $g_2^\prime$ leads to couplings that are smaller by a factor of 2.3. In this case tree level and loop contributions are of comparable size and the numerical values of the tree level contributions to radiative decays are consistent with estimates based on the quark model as well as non-relativistic QCD (NRQCD). This result shows that tree level HH$\chi$PT couplings are as important as the one loop graphs with charmed mesons in these charmonium decays. The couplings $g_2$ and $g_2^\prime$ are also important for the calculations of the decays of charmed meson bound states, such as the X(3872), to conventional charmonia.

Evasion of helicity selection rule inχc1→VVandχc2→VPvia intermediate charmed meson loops

The hadronic decays of $\chi_{c1}\to VV$ and $\chi_{c2}\to VP$ are supposed to be suppressed by the helicity selection rule in the pQCD framework. With an effective Lagrangian method, we show that the intermediate charmed meson loops can provide a mechanism for the evasion of the helicity selection rule, and result in sizeable decay branching ratios in some of those channels. The theoretical predictions can be examined by the forthcoming BES-III data in the near future.

Extraction of the Light Quark Mass Ratio from the Decaysψ′→J/ψπ0(η)

Light quark masses are important fundamental parameters of the Standard Model. The decays psi'-->J/psi pi^0 (eta) were widely used in determining the light quark mass ratio m_u/m_d. However, there is a large discrepancy between the resulting value of m_u/m_d and the one determined from the light pseudoscalar meson masses. Using the technique of non-relativistic effective field theory, we show that intermediate charmed meson loops lead to a sizeable contribution to the decays and hence make the psi'-->J/psi pi^0 (eta) decays not suitable for a precise extraction of the light quark mass ratio.