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In this work, the $S$- and $P$-wave $bar{D}^ast K^ast$ interactions are studied in a coupled-channel formalism to understand the recently observed $X_0(2900)$ and $X_1(2900)$ at LHCb. The experimental event distributions can be well described, and two states with $I(J^P)=0(0^+)$ and $0(1^-)$ are yielded in an unified framework with the same set of parameters. Their masses and widths are determined to be $[m,Gamma]_{0^+}=[2873.2^{+10.8}_{-12.2},72.2^{+9.6}_{-8.3}]$ MeV and $[m,Gamma]_{1^-}=[2905.6^{+14.6}_{-10.7},52.5_{-1.3}^{+9.5}]$ MeV from the pole analyses, respectively. The masses of the $0^+$ and $1^-$ states are consistent with the experimental data, but the width of the $0^+$ state is larger than that of the $1^-$ one. The $X_1(2900)$ can be interpreted as the $P$-wave excitation of the ground-state $X_0(2900)$ in the hadronic molecular picture. The $S$- and $P$-wave multiplets in the $bar{D}^ast K^ast$ system have many members, so the present peak in the $D^-K^+$ invariant mass distributions might contain multi subpeaks. In order to probe the fine structures behind the single whole peak now, more refined measurements in the $B^+to D^+D^-K^+$ decay channel are necessary.
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We investigate the possible rescattering effects which may contribute to the process $B^+to J/psiphi K^+$. It is shown that the $D_{s}^{*+}D_{s}^-$ rescattering via the open-charmed meson loops, and $psi^prime phi$ rescattering via the $psi^prime K_1$ loops may simulate the structures of $X(4140)$ and $X(4700)$, respectively. However, if the quantum numbers of $X(4274)$ ($X(4500)$) are $1^{++}$ ($0^{++}$), it is hard to to ascribe the observation of $X(4274)$ and $X(4500)$ to the $P$-wave threshold rescattering effects, which implies that $X(4274)$ and $X(4500)$ could be genuine resonances. We also suggest that $X(4274)$ may be the conventional orbitally excited state $chi_{c1}(3P)$.
I give a brief overview of the science cases of the Electron-Ion Collider (EIC) with a particular emphasis on the connections to the physics of ultrarelativistic heavy-ion collisions.
The LHCb collaboration reported the observation of a narrow peak in the $D^- K^+$ invariant mass distributions from the $B^+to D^+ D^- K^+$ decay. The peak is parameterized in terms of two resonances $X_0(2900)$ and $X_1(2900)$ with the quark contents $bar{c}bar{s}ud$, and their spin-parity quantum numbers are $0^+$ and $1^-$, respectively. We investigate the rescattering processes which may contribute to the $B^+to D^+ D^- K^+$ decays. It is shown that the $D^{*-}K^{*+}$ rescattering via the $chi_{c1}K^{*+}D^{*-}$ loop or the $bar{D}_{1}^{0}K^{0}$ rescattering via the $D_{sJ}^{+}bar{D}_{1}^{0}K^{0}$ loop simulate the $X_0(2900)$ and $X_1(2900)$ structures. Such phenomena are due to the analytical property of the scattering amplitudes with the triangle singularities located to the vicinity of the physical boundary.
Multi-quark states were predicted by Gell-Mann when the quark model was first formulated. Recently, numerous exotic states that are considered to be multi-quark states have been experimentally confirmed (four-quark mesons and five-quark baryons). Theoretical research indicates that the four-quark state might comprise molecular and/or tetraquark structures. We consider that the meson containing four different flavors $subar bbar d$ should exist and decay via the $X(5568)to B_spi$ channel. However, except for the D0 collaboration, all other experimental collaborations have reported negative observations for $X(5568)$ in this golden portal. This contradiction has stimulated the interest of both theorists and experimentalists. To address this discrepancy, we propose that the assumed $X(5568)$ is a mixture of a molecular state and tetraquark, which contributes destructively to $X(5568)to B_spi$. The cancellation may be accidental and it should be incomplete. In this scenario, there should be two physical states with the same flavor ingredients, with spectra of $5344pm307$ and $6318pm315$. $X(5568)$ lies in the error range of the first state. We predict the width of the second state (designated as $S_2$) as $Gamma(X_{S_2}to B_spi)=224pm97$ MeV. We strongly suggest searching for it in future experiments.
The axion, originated from the Peccei-Quinn mechanism proposed to solve the strong-CP problem, is a well motivated and popular dark matter candidate. Experimental searches for this hypothetical particle are starting to reach theoretically interesting sensitivity levels. However, only a small fraction of the allowed parameter space has been explored so far, mostly in the $mu$eV (GHz) region, relying on large volume solenoid magnetic fields and microwave resonators with signals read out by quantum noise limited amplifiers. There have been intensive experimental efforts to widen the search range by devising various techniques as well as to enhance sensitivities by implementing advanced technologies. The developments and improvements in these orthogonal approaches will enable us to explore most of the parameter space of the axion and axion-like particles within the next five to ten years. We review the experimental aspects of axion physics and discuss the past, present and future of the individual search programs.
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