There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The hidden-charm pentaquark and tetraquark states

A large number of experimental discoveries especially in the heavy quarkonium sector that did not at all fit to the expectations of the until then very successful quark model led to a renaissance of hadron spectroscopy Among various explanations of the internal structure of these excitations, hadronic molecules, being analogues of light nuclei, play a unique role since for those predictions can be made with controlled uncertainty We review experimental evidences of various candidates of hadronic molecules, and methods of identifying such structures Nonrelativistic effective field theories are the suitable framework for studying hadronic molecules, and are discussed in both the continuum and finite volumes Also pertinent lattice QCD results are presented Further, we discuss the production mechanisms and decays of hadronic molecules, and comment on the reliability of certain assertions often made in the literature

Hadronic molecules

Heavy-light diquarks can be the building blocks of a rich spectrum of states which can accommodate some of the newly observed charmoniumlike resonances not fitting a pure $c\overline{c}$ assignment. We examine this possibility for hidden and open charm diquark-antidiquark states deducing spectra from constituent quark masses and spin-spin interactions. Taking the $X(3872)$ as input we predict the existence of a ${2}^{++}$ state that can be associated to the $X(3940)$ observed by Belle and reexamine the state claimed by SELEX, $X(2632)$. The possible assignment of the previously discovered states ${D}_{s}(2317)$ and ${D}_{s}(2457)$ is discussed. We predict $X(3872)$ to be made of two components with a mass difference related to ${m}_{u}\ensuremath{-}{m}_{d}$ and discuss the production of $X(3872)$ and of its charged partner ${X}^{\ifmmode\pm\else\textpm\fi{}}$ in the weak decays of ${B}^{+,0}$.

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Diquark-antidiquark states with hidden or open charm and the nature of X(3872)

The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states P_{c}(4380) and P_{c}(4450). These two hidden-charm states are interpreted as the loosely bound Σ_{c}(2455)D^{*} and Σ_{c}^{*}(2520)D^{*} molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of P_{c}(4450) is much narrower than that of P_{c}(4380). The discovery of the new resonances P_{c}(4380) and P_{c}(4450), indeed, opens a new page for hadron physics. The partners of P_{c}(4380) and P_{c}(4450) should be pursued in future experiments.

Identifying exotic hidden-charm pentaquarks

The recently observed new member of the charm-strange family D-s(2632), which has a surprisingly narrow width, is challenging our theory. D-s(2317) and D-s(2457), which were observed earlier, have similar behaviors and receive various theoretical explanations. Some authors use the heavy hadron chiral effective theory to evaluate heavy-light quark systems and obtain a reasonable evaluation on the masses of D-s(2317) and D-s(2457). An alternative picture is to interpret them as four-quark or molecular states. In this work, we are following the latter and propose a unitive description for all three new members, D-s(2632), D-s(2317), and D-s(2457), and, at least, so far our picture is consistent with the data.

Comprehensive Four-Quark Interpretation of D s ( 2317 ) , D s ( 2457 ) , and D s ( 2632 )

The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states $P_c(4380)$ and $P_c(4450)$. These two hidden-charm states are interpreted as the loosely bound $\Sigma_c(2455)D^*$ and $\Sigma_c^*(2520)D^*$ molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of $P_c(4450)$ is much narrower than that of $P_c(4380)$. The discovery of the new resonances $P_c(4380)$ and $P_c(4450)$, indeed, opens a new page for hadron physics. The partners of $P_c(4380)$ and $P_c(4450)$ should be pursued in future experiments.

Xue-Qian Li

Papers

Identifying exotic hidden-charm pentaquarks

Comprehensive Four-Quark Interpretation of D s ( 2317 ) , D s ( 2457 ) , and D s ( 2632 )

A new page for hadron physics: Identifying exotic hidden-charm pentaquarks