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Register a new userOne way to verify the molecular picture of exotic hadrons --from $DK$ to $DDK/Dbar{D}^{(*)}K$
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Starting from 2003, a large number of the so-called exotic hadrons, such as $X(3872)$ and $D_{s0}^*(2317)$, were discovered experimentally. Since then, understanding the nature of these states has been a central issue both theoretically and experimentally. As many of these states are located close to two hadron thresholds, they are believed to be molecular states or at least contain large molecular components. We argue that if they are indeed molecular states, in the way that the deuteron is a bound state of proton and neutron, then molecular states of three or more hadrons are likely, in the sense that atomic nuclei are bound states of nucleons. Following this conjecture, we study the likely existence of $DDK$, $Dbar{D}K$, and $Dbar{D}^{*}K$ molecular states. We show that within the theoretical uncertainties of the two-body interactions deduced, they most likely exist. Furthermore, we predict their strong decays to help guide future experimental searches. In addition, we show that the same approach can indeed reproduce some of the known three-body systems from the two-body inputs, such as the deuteron-triton and the $Lambda(1405)$-$bar{K}NN$ systems.
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We investigate the exotic $OmegaOmega$ dibaryon states with $J^P=0^+$ and $2^+$ in a molecular picture. We construct the scalar and tensor $Omega$$Omega$ molecular interpolating currents and calculate their masses within the method of QCD sum rules. Our results indicate that the mass of the scalar dibaryon state is $m_{OmegaOmega, , 0^+}=(3.33pm0.22) ,unit$, which is about $15 ,mathrm{MeV}$ below the $2m_Omega$ threshold. This result suggests the existence of a loosely bound molecular state of the $J^P=0^+$ scalar $OmegaOmega$ dibaryon with a small binding energy around 15 MeV. The mass of the tensor dibaryon is predicted to be $m_{OmegaOmega,, 2^+}=(3.24pm0.23), mbox{GeV}$, which may imply a deeper molecular state of the tensor $OmegaOmega$ dibaryon than the scalar channel. These exotic strangeness $S=-6$ and doubly-charged $OmegaOmega$ dibaryon states may be identified in the heavy-ion collision processes.
In two recent reactions by Belle producing $Dbar D$ and $Dbar D^*$ meson pairs, peaks above threshold have been measured in the differential cross sections, possibly indicating new resonances in these channels. We want to study such reactions from the point of view that the $D$ meson pairs are produced from already known or predicted resonances below threshold. Our study shows that the peak in the $Dbar D^*$ production is not likely to be caused by the X(3872) resonance, but the peak seen in $Dbar D$ invariant mass can be well described if the $Dbar D$ pair comes from the already predicted scalar X(3700) resonance.
The exciting discovery by LHCb of the $P_c(4312)^+$ and $P_c(4450)^+$ pentaquarks, or the suggestion of a tetraquark nature for the $Z_c(3900)$ state seen at BESIII and Belle, have triggered a lot of activity in the field of hadron physics, with new experiments planned for searching other exotic mesons and baryons, and many theoretical developments trying to disentangle the true multiquark nature from their possible molecular origin. After a brief review of the present status of these searches, this paper focusses on recently seen or yet to be discovered exotic heavy baryons that may emerge from a conveniently unitarized meson-baryon interaction model in coupled channels. In particular, we will show how interferences between the different coupled-channel amplitudes of the model may reveal the existence of a $N^*$ resonance around 2 GeV having a meson-baryon quasi-bound state nature. We also discuss the possible interpretation of some of the $Omega_c$ states recently discovered at LHCb as being hadron molecules. The model also predicts the existence of doubly-charmed quasibound meson-baryon $Xi_{cc}$ states, which would be excited states of the ground-state $Xi_{cc}(3621)$ MeV, whose mass has only been recently established. Extensions of these results to the bottom sector will also be presented.
The present status of the LHC anomalies found in exclusive semileptonic $bto sell^+ell^-$ decays is discussed with special emphasis on the exclusive 4-body angular distribution $B to K^*(to Kpi)ell^+ell^-$. The treatment of hadronic uncertainties in this mode is briefly reviewed, and some of the analyses in the literature are critically reassessed. The global picture provided by the global fit points to a coherent pattern of deviations with a significance substantially above 4$sigma$ for different New Physics scenarios. Finally, we propose as the next step in the field to focus on the study of optimized observables that compare electron and muon modes, sensitive to lepton-flavour universality violations and free from hadronic uncertainties (including charm) in the SM, the so called $Q_i$ observables.
We analyze two recent reactions of Belle, producing $Dbar D$ and $Dbar D^*$ states that have an enhancement of the invariant $Dbar D$, $Dbar D^*$ mass distribution close to threshold, from the point of view that they might be indicative of the existence of a hidden charm scalar and an axial vector meson states below $Dbar D$ or $Dbar D^*$ thresholds, respectively. We conclude that the data is compatible with the existing prediction of a hidden charm scalar meson with mass around 3700 MeV, though other possibilities cannot be discarded. The peak seen in the $Dbar D^*$ spectrum above threshold is, however, unlikely to be due to a threshold enhancement produced by the presence, below threshold, of the hidden charm axial vector meson X(3872).
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