Towards Meson Spectroscopy Instead of Bump Hunting
George Rupp, Susana Coito, Eef van Beveren
备注：
Invited seminar given by G. Rupp at the International School of Nuclear Physics, 33rd course: "From Quarks and Gluons to Hadrons and Nuclei", Erice, Sicily, Italy, 16 - 24 September 2011; 7 pages, 5 figures (9 plots), style of Progress in Particle and Nuclear Physics
Mesonic resonances are generally observed in data as narrow, moderately broad, or wide peaks in scattering or production processes. In the eyes of nearly all experimentalists, any suchlike bump is a true resonance as soon as its statistical significance exceeds certain minimal values. However, this simple point of view ignores possible effects from competing hadronic channels and the opening of the corresponding thresholds. On the other hand, most theoretical hadron-model builders consider mesons merely bound states of a quark and an antiquark, or of more exotic combinations sometimes involving valence gluons as well. Also the latter description is much too naive, since considerable mass shifts or even the dynamical generation of extra states due to unquenching are equally ignored.
In the present paper, a largely empirical yet very successful approach to meson spectroscopy is revisited, in which all the above phenomena can be accounted for non-perturbatively, with concrete examples of some enigmatic mesonic states described in detail. First, the X(4260) charmonium enhancement is argued to be a non-resonant structure resulting from depletion effects due to competing channels and resonances. Then, the X(3872) charmonium-like meson is described as a unitarised $J^{PC}=1^{++}$ $c\bar{c}$ state. Also, the unusual pattern of masses and widths of the open-charm axial-vector mesons $D_1(2420)$, $D_1(2430)$, $D_{s1}(2536)$, and $D_{s1}(2460)$ is shown to follow from highly non-perturbative coupled-channel and mixing effects. Finally, first indications of a very light scalar boson are presented, on the basis of published BABAR data.
Hunting for new physics in $B$ meson $b \to u$ transitions: A fresh look with Belle II data
Istituto Nazionale di Fisica Nucleare, Sezione di Bari（意大利国家核物理研究所巴里分部）；Dipartimento Interateneo di Fisica ”Michelangelo Merlin”, Università degli Studi di Bari（巴里大学米开朗基罗·梅林联合物理系）
The scalar $f_0(500)$ and $f_0(980)$ resonances and vector mesons in the single Cabibbo-suppressed decays $Λ_c \to p K^+K^-$ and $pπ^+π^-$
在手征么正方法中，我们考虑了$s$波介子-介子相互作用以及中间矢量$ϕ$和$ρ^0$的贡献，研究了单个Cabibbo抑制衰变$Λ_c\to pK^+K^-$和$Λ_c \to p π^+π^-$.我们对$Λ_c\to p \bar{K}^{*0}$和$Λ_c\to p ω$的支化分数与$Λ_c\to p ϕ$的支化分数之比的理论计算结果与实验数据一致。在$s$波中赝标-赝标相互作用动态产生标量共振$f_0(500)$、$f_0(980)$和$a_0(980)$的情况下，我们分别计算了衰变$Λ_c\to pK^+K^-$和$Λ_c\to pπ^+π^-$的$K^+K^-$和$π^+π^-$不变质量分布.在衰变$Λ_c\to pπ^+π^-$的$π^+π^-$不变质量分布中，可以发现$f_0(500)$的宽凸起结构和$f_0(980)$的窄峰。对于$K^+K^-$不变质量分布，除了$ϕ$介子的窄峰之外，在$K^+K^-$阈值附近存在主要归因于$f_0(980)$贡献的增强结构。$π^+π^-$和$K^+K^-$不变质量分布都与BESIII测量兼容。我们鼓励我们的实验同事测量这两个衰变，这将有助于理解$f_0(500)$，$f_0(980)$和$a_0(980)$的性质。
On the near-threshold peak structure in the differential cross section of ϕ-meson photoproduction: indication of a missing resonance with non-negligible strangeness content
Mechanisms of $D \bar{D}$ pair production in $e^{+} e^{-} \to e^{+} e^{-} D \bar{D}$ and $AA \to AA D \bar{D}$ reactions and production of exotic charmonia
Institute of Nuclear Physics Polish Academy of Sciences（波兰科学院核物理研究所）；Institute of Physics, Faculty of Exact and Technical Sciences, University of Rzeszów（热舒夫大学精确与技术科学学院物理研究所）
