Observation of overlapping spin-1 and spin-3 D0K- resonances at mass 2.86 GeV/c2

An updated review of the new hadron states

The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark statesX(2900) andTcc+(3875)as well as the hidden heavy flavor multiquark statesX(6900),Pcs(4459)0,Zcs(3985)-,Zcs(4000)+, andZcs(4220)+. We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-AbelianSU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.

Spectroscopy of the excited Ds mesons

The discoveries of the Ds0*(2317)+ and Ds1(2460)+ mesons challenge our understanding of quantum chromodynamics. After almost 20 years, the nature of these hadrons is still subject of debate and many models have been proposed to explain their unexpected masses: standard charmed-strange mesons, DK molecules and tetraquarks. The LHCb experiment has studied the production of excited Ds+ meson in prompt proton-proton collisions and from b-hadron decays. Precise measurement of their properties and observation of new Ds+ states have been reported. The latest results on the spectroscopy of the charmed-strange mesons and the prospect to investigate their nature will be presented.

Observation of a New Excited D_{s}^{+} Meson in B^{0}→D^{-}D^{+}K^{+}π^{-} Decays

Using pp collision data corresponding to an integrated luminosity of 5.4  fb^{-1} collected with the LHCb detector at a center-of-mass energy of 13 TeV, the B^{0}→D^{-}D^{+}K^{+}π^{-} decay is studied. A new excited D_{s}^{+} meson is observed decaying into the D^{+}K^{+}π^{-} final state with large statistical significance. The pole mass and width, and the spin parity of the new state are measured with an amplitude analysis to be m_{R}=2591±6±7  MeV, Γ_{R}=89±16±12  MeV, and J^{P}=0^{-}, where the first uncertainty is statistical and the second systematic. Fit fractions for all components in the amplitude analysis are also reported. The new resonance, denoted as D_{s0}(2590)^{+}, is a strong candidate to be the D_{s}(2^{1}S_{0})^{+} state, the radial excitation of the pseudoscalar ground-state D_{s}^{+} meson.

Exploring Possible Triangle Singularities in the Ξ b − → K − J / ψ Λ Decay

We analyze possible singularities in the J/ψΛ invariant mass distribution of the Ξb−→K−J/ψΛ process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with Ξ*-charmonium-Λ intermediate states, the one from the χc1Ξ(2120)Λ loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs S- and P-waves in χc1Λ and J/ψΛ systems, respectively, when the quantum numbers of these systems are 1/2+ or 3/2+. When the quantum numbers of the Ξ(2120) are JP=1/2+, 1/2− or 3/2+, the peak structure should be sharper than the other JP choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the Ξ*-charmonium-Λ triangle diagram if structures are observed in the J/ψΛ invariant mass spectrum experimentally. In addition, a few triangle diagrams with the Ds1*(2700) as one of the intermediate particles can also produce singularities in the J/ψΛ distribution, but at higher energies above 4.9 GeV.

Observation of a Narrow Pentaquark State, P_{c}(4312)^{+}, and of the Two-Peak Structure of the P_{c}(4450)^{+}

A narrow pentaquark state, P_{c}(4312)^{+}, decaying to J/ψp, is discovered with a statistical significance of 7.3σ in a data sample of Λ_{b}^{0}→J/ψpK^{-} decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The P_{c}(4450)^{+} pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, P_{c}(4440)^{+} and P_{c}(4457)^{+}, where the statistical significance of this two-peak interpretation is 5.4σ. The proximity of the Σ_{c}^{+}D[over ¯]^{0} and Σ_{c}^{+}D[over ¯]^{*0} thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.

A review of the open charm and open bottom systems

Since the discovery of the first charmed meson in 1976, many open-charm and open-bottom hadrons were observed. In 2003 two narrow charm-strange states [Formula: see text] and D _s1(2460) were discovered by the BaBar and CLEO Collaborations, respectively. After that, more excited heavy hadrons were reported. In this work, we review the experimental and theoretical progress in this field.

Observation of J/ψp Resonances Consistent with Pentaquark States in Λ_{b}^{0}→J/ψK^{-}p Decays

Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark states, in Λ_{b}^{0}→J/ψK^{-}p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb^{-1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.