Session Y10: Invited Session: Hadron Spectroscopy with Heavy Quarks

New Hadronic States at LHCb

The LHCb experiment has enabled an unprecedentedly large sample of $b$-hadron decays to be collected and studied in great detail. These samples are being used not only to search for the presence of new physics in the decays of $b$-hadrons, but to probe the very nature of QCD. In particular, these samples provide a unique laboratory in which to study scalar mesons, such as the $f_0(980)$ and the $\sigma$, as well as more exotic states, such as the $Z(4430)^-$. In addition, these samples have enabled searches for, and discoveries of, additional excited $b$-hadron states, such as the $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. The speaker will review recent results on new hadronic states studied at LHCb.   

New Hadronic States at BESIII

Recent discoveries of charged charmonium-like states have generated a great deal of interest in the particle physics community. The simplest interpretation of the quark model of charmonium, in which states consist of bound charm-anticharm quark pairs, is remarkably successful in describing the experimental results for states below $D\bar{D}$ threshold. Within the last decade, however, many new and unexpected states, collectively called XYZ states, have been discovered in the higher mass charmonium spectrum. Several of these states do not appear to be consistent with the simple quark-antiquark interpretation of charmonium. In addition to its world leading samples of $J/\psi$ and $\psi$' decays, the BESIII collaboration has collected a significant amount of data for the study of XYZ states. In this talk, I will review some of the recent experimental results in hadron spectrocopy from the BESIII collaboration, with a particular emphasis on XYZ studies.   

Lattice Results for New Hadronic States

Recent results related to the new hadronic states from ab-initio lattice QCD calculations will be presented. I will focus on the charmonium and charmonium-like states as well as the interesting positive parity $D_s$ and $B_s$ mesons. Charmonia below open charm threshold are rather well understood, and their theoretical treatment is precise and reliable. I will consider charmonium(like) states near or above open charm threshold. These are very interesting, not only because of the experimental discoveries during the past decade, but also due to the theoretical challenges in their understanding. I will present one of the first studies that take into account the effects of thresholds for near-threshold states, and also the effect of strong decays for resonances above thresholds. New results on the extoic states $X(3872)$ and $Z_c^+$, as well as on the more conventional charmonium resonances will be presented. The meson spectrum contains a few interesting states that are located slightly below strong decay threshold. Observed positive parity $D_s$ mesons represent one such example and I will discuss the first simulation that takes into account the effect of the nearby $D^{(*)}K$ threshold. The positive parity partners $B_s$ are still missing experimentally, and mass prediction for those will be presented.