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.

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Heavy quarkonium: progress, puzzles, and opportunities

To solve the discrepancy between the experimental data on the partial widths and lineshapes of the dipion emission of $\Upsilon(4S)$ and the theoretical predictions, we suggest that there is an additional contribution which was not taken into account in previous calculations. Noticing that the mass of $\Upsilon(4S)$ is above the production threshold of $B\bar B$, the contribution of the sequential process $\Upsilon(4S)\to B\bar B\to \Upsilon(nS)+S\to \Upsilon(nS)+\pi^+\pi^-$ ($n=1,2$) may be sizable, and its interference with that from the direct production would be important. The goal of this work is to investigate if a sum of the two contributions with a relative phase indeed reproduces the data. Our numerical results on the partial widths and the lineshapes $d\Gamma(\Upsilon(4S)\to \Upsilon(2S,1S)\pi^+\pi^-)/d(m_{\pi^+\pi^-})$ are satisfactorily consistent with the measurements, thus the role of this mechanism is confirmed. Moreover, with the parameters obtained by fitting the data of the Belle and Babar collaborations, we predict the distributions $d\Gamma(\Upsilon(4S)\to \Upsilon(2S,1S)\pi^+\pi^-)/d\cos\theta$ which have not been measured yet.

Anomalous dipion invariant mass distribution of the $\Upsilon(4S)$ decays into $\Upsilon(1S) \pi^{+} \pi^{-}$ and $\Upsilon(2S) \pi^{+} \pi^{-}$

Very recently a new enhancement around 4.05 GeV was observed by Belle experiment. In this short note, we discuss some possible assignments for this enhancement, i.e. $\psi(3S)$ and $D^*\bar{D}^*$ molecular state. In these two assignments, Y(4008) can decay into $J/\psi\pi^0\pi^0$ with comparable branching ratio with that of $Y(4008)\to J/\psi\pi^+\pi^-$. Thus one suggests high energy experimentalists to look for Y(4008) in $J/\psi\pi^0\pi^0$ channel. Furthermore one proposes further experiments to search missing channel $D\bar{D}$, $D\bar{D}^*+h.c.$ and especially $\chi_{cJ}\pi^+\pi^-\pi^0$ and $\eta_c\pi^+\pi^-\pi^0$, which will be helpful to distinguish $\psi(3S)$ and $D^*\bar{D}^*$ molecular state assignments for this new enhancement.

Understanding the newly observed Y(4008) by Belle

Very recently, the Belle and BESIII experiments observed a new charmonium-like state X(3823), which is a good candidate for the D-wave charmonium ψ(13
 D
 2). Because the X(3823) is just near the D
 $$\bar D*$$
 threshold, the decay X(3823)→ J/ψπ
 +
 π
 − can be a golden channel to test the significance of coupled-channel effects. In this work, this decay is considered including both the hidden-charm dipion and the usual quantum chromodynamics multipole expansion (QCDME) contributions. The partial decay width, the dipion invariant mass spectrum distribution dΓ[X(3823) → J/ψπ
 +
 π
 −]/dm
 π+π−, and the corresponding dΓ[X(3823) → J/ψπ
 +
 π
 −]/dcosθ distribution are computed. Many parameters are determined from existing experimental data, so the results depend mainly only on one unknown phase between the QCDME and hidden-charm dipion amplitudes.

Using X (3823)→ J / ψπ + π − to identify coupled-channel effects

The $Y(4220)$ production in the process of $p\overline{p}\ensuremath{\rightarrow}Y(4220){\ensuremath{\pi}}^{0}$ is studied within the effective Lagrangian approach. We first study the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}Y(4220)\ensuremath{\rightarrow}p\overline{p}{\ensuremath{\pi}}^{0}$ reaction at center-of-mass energy 4.258 GeV with the assumption that the $Y(4220)$ is a $\ensuremath{\psi}(4S)$ state. We show that the inclusion of nucleon and nucleon resonance leads to a quite good description of the experimental data of ${\ensuremath{\pi}}^{0}p$ and ${\ensuremath{\pi}}^{0}\overline{p}$ invariant mass distributions. Then, the total and angular distributions of the $p\overline{p}\ensuremath{\rightarrow}Y(4220){\ensuremath{\pi}}^{0}$ reaction are investigated. It is shown that the nucleon pole is dominant but the contributions from excited nucleon resonances are non-negligible. The $p\overline{p}\ensuremath{\rightarrow}Y(4220){\ensuremath{\pi}}^{0}$ reaction is useful for studying the property of $Y(4220)$ and our calculated results may be tested at the forthcoming $\overline{\mathrm{P}}\mathrm{ANDA}$ experiments.

Production of the charmoniumlike state Y ( 4220 ) through the p p ¯ → Y ( 4220 ) π 0 reaction

In this work, we carry out the study of heavy flavor pentaquarks with four heavy quarks, which have typical $QQQQ\overline{q}$ configuration. Within the chromomagnetic interaction model, the mass spectrum of these discussed $QQQQ\overline{q}$ pentaquarks is given. In addition to the mass spectrum analysis, we also illustrate their two-body strong decay behavior by estimating some ratios of decay channels. By these efforts, we suggest that a future experiment should pay attention to this kind of pentaquark.

Xiang Liu

Papers

Anomalous dipion invariant mass distribution of the $\Upsilon(4S)$ decays into $\Upsilon(1S) \pi^{+} \pi^{-}$ and $\Upsilon(2S) \pi^{+} \pi^{-}$

Understanding the newly observed Y(4008) by Belle

Using X (3823)→ J / ψπ + π − to identify coupled-channel effects

Production of the charmoniumlike state Y ( 4220 ) through the p p ¯ → Y ( 4220 ) π 0 reaction

Heavy flavor pentaquarks with four heavy quarks