Search

Motivated by the recent observation of $T_{c\bar{s}0}(2900)^0$ and $T_{c\bar{s}0}(2900)^{++}$ in the $D_s π$ invariant mass distributions, we investigate $D^{\ast}K^{\ast}$ interactions in a coupled-channel approach. We show that the relativistic corrections could be significant for the energy far away from the threshold. Within the hidden local symmetry formalism, a sizable attraction interaction is found in the $J=0$ isospin triplet sector that can form a bound or a virtual state, which is consistent with the experimentally observed $T_{c\bar{s}0}(2900)$. By reproducing a $D_s^*ρ$-$D^*K^*$ bound/virtual state with the pole mass equal to that of the $T_{c\bar{s}0}(2900)$ measured by LHCb in the sector $(I,J)=(1,0)$, we determine the unknown parameter in the loop function, and then search for possible poles in the sectors of $I=1$, $J=1,$ 2 and $I=0$, $J=0$, 1, 2. The predicted resonances provide a useful reference for the future experimental studies of the $(C,S)=(1,1)$ systems and can be also helpful to unravel the nature of the $T_{c\bar{s}0}(2900)$.10, 10 pages, 6 figures, 3 tables

Recently, the LHCb Collaboration reported a near-threshold enhancement, $X(3960)$, in the $D_s^+D_s^-$ invariant mass distribution. We show that the data can be well described by either a bound or a virtual state below the $D_s^+D_s^-$ threshold. The mass given by the pole position is $(3928\pm3)$ MeV. Using this mass and the existing information on the $X(3872)$ and $Z_c(3900)$ resonances, a complete spectrum of the $S$-wave hadronic molecules formed by a pair of ground state charmed and anticharmed mesons is established. Thus, pole positions of the partners of the $X(3872)$, $Z_c(3900)$ and the newly observed $D_s^+D_s^-$ state are predicted. Calculations have been carried out at the leading order of nonrelativistic effective field theory and considering both heavy quark spin and light flavor SU(3) symmetries, though conservative errors from the breaking of these symmetries are provided., Comment: 19 pages, 4 figures and 5 tables. Version to appear in PRD

We use a $\mathcal{O}(Λ_\text{QCD}/m_c)$ heavy quark effective theory scheme, where only $\mathcal{O}(Λ_\text{QCD}/m_b)$ and perturbative QCD short distance corrections are neglected, to study the matrix elements of the scalar, pseudoscalar, vector, axial-vector and tensor currents between the $Λ_b$ ground state and the odd parity charm $Λ_c(2595)^+$ and $Λ_c(2625)^+$ resonances. We show that in the near-zero recoil regime, the scheme describes reasonably well, taking into account uncertainties, the results for the 24 form-factors obtained in lattice QCD (LQCD) just in terms of only 4 Isgur-Wise (IW) functions. We also find some support for the possibility that the $Λ_c(2595)^+$ and $Λ_c(2625)^+$ resonances might form a heavy-quark spin symmetry (HQSS) doublet. However, we argue that the available LQCD description of these two resonances is not accurate enough to disentangle the possible effects of the $Σ_c π$ and $Σ_c^*π$ thresholds, located only a few MeV above their position, and that it cannot be ruled out that these states are not HQSS partners. Finally, we study the ratio $\frac{dΓ[Λ_b\to Λ_{c,1/2^-}^* \ell \barν_\ell]/dq^2}{dΓ[Λ_b\to Λ_{c,3/2^-}^*\ell \barν_\ell]/dq^2}$ of the Standard Model differential semileptonic decay widths, with $q^μ$ the momentum transferred between the initial and final hadrons. We provide a natural explanation for the existence of large deviations, near the zero recoil, of this ratio from 1/2 (value predicted in the infinite heavy quark mass limit, assuming that the $Λ_{c,1/2^-}^*$ and $Λ_{c,3/2^-}^*$ are the two members of a HQSS doublet) based on S-wave contributions to the $Λ_b\to Λ_{c,1/2^-}^*$ decay amplitude driven by a sub-leading IW function., 26 pages, 8 figures

We benefit from a recent lattice determination of the full set of vector, axial and tensor form factors for the $Λ_b\to Λ^*_c(2595)τ\barν_τ$ and $Λ^*_c(2625)τ\barν_τ$ semileptonic decays to study the possible role of these two reactions in lepton flavor universality violation studies. Using an effective theory approach, we analyze different observables that can be accessed through the visible kinematics of the charged particles produced in the tau decay, for which we consider the $π^-ν_τ,ρ^-ν_τ$ and $μ^-\barν_μν_τ$ channels. We compare the results obtained in the Standard Model and other schemes containing new physics (NP) interactions, with either left-handed or right-handed neutrino operators. We find a discriminating power between models similar to the one of the $Λ_b\to Λ_c$ decay, although somewhat hindered in this case by the larger errors of the $Λ_b\toΛ^*_c$ lattice form factors. Notwithstanding this, the analysis of these reactions is already able to discriminate between some of the NP scenarios and its potentiality will certainly improve when more precise form factors are available., 27 latex pages, 6 figures, 1 table. Version accepted for publication in Phys. Rev. D

Recently, the CMS and ATLAS collaborations have reported their $J/ψJ/ψ$ and $J/ψψ^\prime$ invariant mass distributions, respectively, for searching for fully charmed tetraquarks. Both of them reported the existence of a peak structure around $7.2~\gev$. In this article, we exhibit the role of the $η_c(2S)η_c(2S)$ channel, which is close to this peak position, by studying the $J/ψJ/ψ$ and $J/ψψ^\prime$ invariant mass distributions for the potential quantum numbers $J^{PC}=0^{++}$ or $2^{++}$ by considering both the coherence and incoherence with the background contribution. All these frameworks can describe the experimental data very well, however with different pole structures. For instance, in the case of $2^{++}$ description of these structures, there always exists a pole slightly below the $J/ψJ/ψ$ threshold. For the $0^{++}$ case, a similar pole can also be found below the $J/ψJ/ψ$ threshold however with a much lower mass. More importantly, the number of the poles is found to be case-dependent. For the $0^{++}$ ($2^{++}$) case, the peak structure around $7.2~\gev$ can (cannot) be produced due to the presence (absence) of the $η_c(2S)η_c(2S)$ channel. Although the pole positions are case-dependent, the relation between the peak structure in the $J/ψJ/ψ$ invariant mass distribution and the dip structure in the $J/ψψ^\prime$ invariant mass distribution around $7.2~\gev$ is unambiguous. We suggest experimentalists to detailed scan both the $J/ψJ/ψ$ and the $J/ψψ^\prime$ invariant mass distributions, especially around $7.2~\gev$ to probe the nature of the third fully charmed state., 15 pages, 5 figures; accepted by Science Bulletin

We have performed a combined analysis of the BESIII data for both the $Z_c(3900)$ and $Z_{cs}(3985)$ structures, assuming that the latter is an SU(3) flavor partner of the former one. We have improved on the previous analysis of Albaladejo $et$ $al.$ [Phys. Lett. B 755, 337 (2016)] by computing the amplitude for the $D_1\bar{D}D^*$ triangle diagram considering both $D$ and $S$-wave $D_1D^*\pi$ couplings. We have also investigated effects from SU(3) light-flavor violations, which are found to be moderate and of the order of 20%. The successful reproduction of the BESIII spectra, in both the hidden-charm and hidden-charm strange sectors, strongly supports that the $Z_{cs}(3985)$ and $Z_c(3900)$ are SU(3) flavor partners placed in the same octet multiplet. The best results are obtained when an energy-dependent term in the diagonal $D^{(*)}\bar D_{(s)}^{(*)}$ interaction is included, leading to resonances (poles above the thresholds) to describe these exotic states. We have also made predictions for the isovector $Z_{c}^*$ and isodoublet $Z_{cs}^*$, $D^*\bar{D}^*$ and $D^*\bar{D}_{s}^*$ molecules, with $J^{PC}=1^{+-}$ and $J^{P}=1^{+}$, respectively. These states would be heavy-quark spin symmetry partners of the $Z_{c}$ and $Z_{cs}$. Besides the determination of the masses and widths of the $Z_c(3900)$ and $Z_{cs}(3985)$, we also predict those of the $Z_c^*$ and $Z_{cs}^*$ resonances., Comment: 27 pages, 9 figures, and 4 tables, version published in physical review D

We study the nature of the recently observed $P_{cs}(4459)$ by the LHCb collaboration by employing three methods based on the elastic effective-range expansion and the resulting size of the effective-range, the saturation of the compositeness relation and width of the resonance, and a direct fit to data involving the channels $J/\psi\Lambda$, $\Xi'_c\bar{D}$ and $\Xi_c\bar{D}^*$. We have also considered the addition of a CDD pole but this scenario can be discarded. Our different analyses clearly indicate the molecular nature of the $P_{cs}(4459)$ with a clear $\Xi_c\bar{D}^*$ dominant component. In relation with heavy-quark-spin symmetry our results also favor the actual existence of two resonances with $J=1/2$ (the lighter one) and $3/2$ (the heavier one) in the energy region of the $P_{cs}(4459)$. In the scenario of two-resonance for the $P_{cs}(4459)$, the inclusion of the $\Xi_c'\bar{D}$ channel is required for the their mass splitting and it allows one to determine the spin structures of the two resonances., Comment: 23 pages, 1 figure

A coupled-channel approach including the $��_c\bar{D}^{(*)}$ and $��_c p$ channels in addition to the $��_c^{(*)}\bar{D}^{(*)}$ and $J/��p$ channels, as required by unitarity and heavy quark spin symmetry (HQSS), is applied to the hidden-charm pentaquark $P_c$ states, i.e., $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$, discovered by LHCb Collaboration. It is demonstrated that to obtain cutoff independent results, the one-pion exchange potential in the multichannel systems is to be supplemented with next-leading order counter terms responsible for the $S$-wave-to-$D$-wave transitions. We show that the experimental data for the $J/��p$ mass distributions are fully in line with the $��_c\bar{D}$ and $��_c\bar{D}^*$ hadronic molecular interpretation of the $P_c(4312)$ and $P_c(4440)/P_c(4457)$, respectively. A narrow $��_c^*\bar{D}$ molecule around 4.38 GeV is required by the HQSS with the evidence for its existence seen in the $J/��p$ spectrum. Moreover, we predict the line shapes for the elastic and inelastic channels., Contribution to the proceedings of A Virtual Tribute to Quark Confinement and the Hadron Spectrum (vConf21), August 2nd-6th 2021, to be published in EPJ Web of Conferences

A coupled-channel approach is applied to the charged tetraquark state $T_{cc}^+$ recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body $D^0D^0\pi^+$ channel. Special attention is paid to the three-body dynamics in the $T_{cc}^+$ due to the finite life time of the $D^*$. An approach to the $T_{cc}^+$ is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the $D$ and $D^*$ mesons and the finite $D^*$ width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The $D^0D^0$ and $D^0D^+$ invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the $D^*D$ scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the $T_{cc}^+$ is found to be close to unity, which implies that the $T_{cc}^+$ is a hadronic molecule generated by the interactions in the $D^{*+}D^0$ and $D^{*0}D^+$ channels. Employing heavy-quark spin symmetry, an isoscalar $D^*D^*$ molecular partner of the $T_{cc}^+$ with $J^P=1^+$ is predicted under the assumption that the $ DD^*$-$D^*D^*$ coupled-channel effects can be neglected., Comment: 28 pages, 8 figures. Version published in Phys. Rev. D

The photoproduction of the $J/��$ off the proton is believed to deepen our understanding of various physics issues. On the one hand, it is proposed to provide access to the origin of the proton mass, based on the QCD multipole expansion. On the other hand, it can be employed in a study of pentaquark states. The process is usually assumed to proceed through vector-meson dominance, that is the photon couples to a $J/��$ which rescatters with the proton to give the $J/��p$ final state. In this Letter, we provide a compelling hint for and propose measurements necessary to confirm a novel production mechanism via the $��_c \bar D^{(*)}$ intermediate states. In particular, there must be cusp structures at the $��_c \bar D^{(*)}$ thresholds in the energy dependence of the $J/��$ photoproduction cross section. The same mechanism also implies the $J/��$-nucleon scattering lengths of order 1 mfm. Given this, one expects only a minor contribution of charm quarks to the nucleon mass., 6 pages, 5 figures

At low energies, the strong interaction is governed by the Goldstone bosons associated with the spontaneous chiral symmetry breaking, which can be systematically described by chiral perturbation theory. In this paper, we apply this theory to study the $��$-vacuum energy density and hence the QCD axion potential up to next-to-leading order with $N$ non-degenerate quark masses. By setting $N=3$, we then derive the axion mass, self-coupling, topological susceptibility and the normalized fourth cumulant both analytically and numerically, taking the strong isospin breaking effects into account. In addition, the model-independent part of the axion-photon coupling, which is important for axion search experiments, is also extracted from the chiral Lagrangian supplemented with the anomalous terms up to $\mathcal{O}(p^6)$., 22 pages, 1 figure, 2 tables; Version to appear in JHEP

Three hidden-charm pentaquark $P_c$ states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ were revealed in the $\Lambda_b^0\to J/\psi p K^-$ process measured by LHCb using both run I and run II data. Their nature is under lively discussion, and their quantum numbers have not been determined. We analyze the $J/\psi p$ invariant mass distributions under the assumption that the crossed-channel effects provide a smooth background. For the first time, such an analysis is performed employing a coupled-channel formalism with the scattering potential involving both one-pion exchange as well as short-range operators constrained by heavy quark spin symmetry. We find that the data can be well described in the hadronic molecular picture, which predicts seven $\Sigma_c^{(*)}\bar D^{(*)}$ molecular states in two spin multiplets, such that the $P_c(4312)$ is mainly a $\Sigma_c\bar D$ bound state with $J^P=1/2^-$, while $P_c(4440)$ and $P_c(4457)$ are $\Sigma_c\bar D^*$ bound states with quantum numbers $3/2^-$ and $1/2^-$, respectively. We also show that there is evidence for a narrow $\Sigma_c^*\bar D$ bound state in the data which we call $P_c(4380)$, different from the broad one reported by LHCb in 2015. With this state included, all predicted $\Sigma_c \bar D$, $\Sigma_c^* \bar D$, and $\Sigma_c \bar D^*$ hadronic molecules are seen in the data, while the missing three $\Sigma_c^*\bar D^*$ states are expected to be found in future runs of the LHC or in photoproduction experiments., Comment: 13 pages, version for publication

Many hadronic states observed since 2003, especially for the positive-parity charm-strange states $D_{s0}^\ast (2317)$ and $D_{s1}(2460)$, do not conform with the conventional quark model expectations and raise various puzzles in charm meson spectroscopy. We demonstrate that those puzzles find a natural solution thanks to the recent development of chiral effective theory and Lattice simulations. The existence of the $D_{s0}^\ast (2317)$ and $D_{s1}(2460)$ are attributed to the nonperturbative dynamics of Goldstone bosons scattering off $D$ and $D^\ast$ mesons. It indicates that the lowest positive parity nonstrange scalar charm mesons, the $D_0^\ast(2400)$ in the Review of Particel Physics, should be replaced by two states. The well constructed amplitudes are fully in line with the high quality data on the decays $B^-\to D^+\pi^-\pi^-$ and $D_s^0\to \bar{D}^0K^-\pi^+$. This implies that the lowest positve-parity states are dynamically generated rather than conventional quark-antiquark states. This pattern has also been established for the scalar and axial-vector mesons made from light quarks ($u$, $d$ and $s$ quarks)., Comment: Talk presented CIPANP2018. 9 pages, LaTeX, 3 pdf figures