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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

비만아 부모의 돌봄 경험: q 방법론

A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h(c)(1P), chi(c2)(2P), B-c(+), and eta(b)(1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like "XYZ" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c (c) over bar, b (b) over bar, and b (c) over bar bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

/pdf/heavy-quarkonium-progress-puzzles-and-opportunities-2tru0l8jyp.pdf

Heavy quarkonium: progress, puzzles, and opportunities

In the past decade, more and more charmoniumlike and bottomoniumlike states have been reported in experiments, which have led us to extensive discussions on the underlying structure of these states. In this review paper, we briefly summarize the experimental and theoretical status of these observed states.

An overview of $XYZ$ new particles

We perform a coupled-channel study of the possible deuteron-like molecules with two heavy flavor quarks, including the systems of ${D}^{(*)}{D}^{(*)}$ with double charm, ${\overline{B}}^{(*)}{\overline{B}}^{(*)}$ with double bottom, and ${D}^{(*)}{\overline{B}}^{(*)}$ with both charm and bottom, within the one-boson-exchange potential model In our study, we take into account the $S\mathrm{\text{\ensuremath{-}}}D$ mixing which plays an important role in the formation of the loosely bound deuteron, and particularly, the coupled-channel effect in the flavor space According to our results, the state ${D}^{(*)}{D}^{(*)}[I({J}^{P})=0({1}^{+})]$ with double charm, the states ${\overline{B}}^{(*)}{\overline{B}}^{(*)}[I({J}^{P})=0({1}^{+}),1({1}^{+})]$, $({\overline{B}}^{(*)}{\overline{B}}^{(*)}{)}_{s}[{J}^{P}={1}^{+},{2}^{+}]$ and $({\overline{B}}^{(*)}{\overline{B}}^{(*)}{)}_{ss}[{J}^{P}={1}^{+},{2}^{+}]$ with double bottom, and the states ${D}^{(*)}{\overline{B}}^{(*)}[I({J}^{P})=0({1}^{+}),0({2}^{+})]$ with both charm and bottom might be good molecule candidates However, the states ${D}^{(*)}{D}^{(*)}[I({J}^{P})=0({2}^{+}),1({0}^{+}),1({1}^{+}),1({2}^{+})]$, $({D}^{(*)}{D}^{(*)}{)}_{s}[{J}^{P}={0}^{+},{2}^{+}]$ and $({D}^{(*)}{D}^{(*)}{)}_{ss}[{J}^{P}={0}^{+},{1}^{+},{2}^{+}]$ with double charm and the state ${D}^{(*)}{\overline{B}}^{(*)}[I({J}^{P})=1({1}^{+})]$ with both charm and bottom are not supported to be molecules

Coupled-channel analysis of the possible D (*) D (*) , B̄ (*) B̄ (*) and D (*) B̄ (*) molecular states

We propose a unique mechanism called initial single pion emission existing in the $\ensuremath{\Upsilon}(5S)$ decays, and further study the line shapes of $d\ensuremath{\Gamma}(\ensuremath{\Upsilon}(5S\ensuremath{\rightarrow}\ensuremath{\Upsilon}(nS){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}))/d{m}_{\ensuremath{\Upsilon}(nS){\ensuremath{\pi}}^{+}}$ ($n=1,2,3$) and $d\ensuremath{\Gamma}(\ensuremath{\Upsilon}(5S\ensuremath{\rightarrow}{h}_{b}(mP){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}))/d{m}_{{h}_{b}(mP){\ensuremath{\pi}}^{+}}$ ($m=1,2$). We find sharp structures around 10 610 MeV and 10 650 MeV in the obtained theoretical line shapes of $d\ensuremath{\Gamma}(\ensuremath{\Upsilon}(5S\ensuremath{\rightarrow}\ensuremath{\Upsilon}(nS){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}))/d{m}_{\ensuremath{\Upsilon}(nS){\ensuremath{\pi}}^{+}}$ and $d\ensuremath{\Gamma}(\ensuremath{\Upsilon}(5S\ensuremath{\rightarrow}{h}_{b}(mP){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}))/d{m}_{{h}_{b}(mP){\ensuremath{\pi}}^{+}}$ distributions, which could naturally correspond to the ${Z}_{b}(10\text{ }610)$ and ${Z}_{b}(10\text{ }650)$ structures newly observed by Belle.

Z b ( 10 610 ) and Z b ( 10 650 ) structures produced by the initial single pion emission in the Υ ( 5 S ) decays

We study the $D$-wave charmed baryons of $SU(3)$ flavor ${\overline{\mathbf{3}}}_{F}$ using the method of QCD sum rules in the framework of heavy quark effective theory. We find that the ${\mathrm{\ensuremath{\Lambda}}}_{c}(2880)$, ${\mathrm{\ensuremath{\Xi}}}_{c}(3055)$, and ${\mathrm{\ensuremath{\Xi}}}_{c}(3080)$ can be well described by the $D$-wave $SU(3)$ ${\overline{\mathbf{3}}}_{F}$ charmed baryon multiplets of ${J}^{P}=3/{2}^{+}$ and $5/{2}^{+}$, which contain two $\ensuremath{\lambda}$-mode orbital excitations; i.e., the ${\mathrm{\ensuremath{\Lambda}}}_{c}(2880)$ has ${J}^{P}=5/{2}^{+}$, and the ${\mathrm{\ensuremath{\Xi}}}_{c}(3055)$ and ${\mathrm{\ensuremath{\Xi}}}_{c}(3080)$ have ${J}^{P}=3/{2}^{+}$ and $5/{2}^{+}$, respectively. Our results also suggest that the ${\mathrm{\ensuremath{\Lambda}}}_{c}(2880)$ has a partner state, the ${\mathrm{\ensuremath{\Lambda}}}_{c}(3/{2}^{+})$ of ${J}^{P}=3/{2}^{+}$. Its mass is around $2.8{1}_{\ensuremath{-}0.18}^{+0.33}\text{ }\text{ }\mathrm{GeV}$, and the mass difference between it and the ${\mathrm{\ensuremath{\Lambda}}}_{c}(2880)$ is $2{8}_{\ensuremath{-}24}^{+45}\text{ }\text{ }\mathrm{MeV}$. We also evaluate the masses of their bottom partners.

D -wave charmed and bottomed baryons from QCD sum rules

In this work, we systematically study the mass spectra and strong decays of 1P and 2S charmed and charmed-strange baryons in the framework of non-relativistic constituent quark models. With the light quark cluster–heavy quark picture, the masses are simply calculated by a potential model. The strong decays are studied by the Eichten–Hill–Quigg decay formula. Masses and decay properties of the well-established 1S and 1P states can be reproduced by our method. $$\Sigma _c(2800)^{0,+,++}$$
 can be assigned as a $$\Sigma _{c2}(3/2^-)$$
 or $$\Sigma _{c2}(5/2^-)$$
 state. We prefer to interpret the signal $$\Sigma _c(2850)^0$$
 as a $$2S(1/2^+)$$
 state although at present we cannot thoroughly exclude the possibility that this is the same state as $$\Sigma _c(2800)^0$$
 . $$\Lambda _c(2765)^+$$
 or $$\Sigma _c(2765)^+$$
 could be explained as the $$\Lambda _c^+(2S)$$
 state or $$\Sigma ^+_{c1}(1/2^-)$$
 state, respectively. We propose to measure the branching ratio of $$\mathcal {B}(\Sigma _c(2455)\pi )/\mathcal {B}(\Sigma _c(2520)\pi )$$
 in the future, which may disentangle the puzzle of this state. Our results support $$\Xi _c(2980)^{0,+}$$
 as the first radial excited state of $$\Xi _c(2470)^{0,+}$$
 with $$J^P=1/2^+$$
 . The assignment of $$\Xi _c(2930)^0$$
 is analogous to $$\Sigma _c(2800)^{0,+,++}$$
 , i.e., a $$\Xi ^\prime _{c2}(3/2^-)$$
 or $$\Xi ^\prime _{c2}(5/2^-)$$
 state. In addition, we predict some typical ratios among partial decay widths, which are valuable for experimental search for these missing charmed and charmed-strange baryons.

/pdf/low-lying-charmed-and-charmed-strange-baryon-states-55ijyr1yac.pdf

Xiang Liu

Papers

An overview of $XYZ$ new particles

Coupled-channel analysis of the possible D () D () , B̄ () B̄ () and D () B̄ () molecular states

Z b ( 10 610 ) and Z b ( 10 650 ) structures produced by the initial single pion emission in the Υ ( 5 S ) decays

D -wave charmed and bottomed baryons from QCD sum rules

Low-lying charmed and charmed-strange baryon states