Inclusive Production of the X(4140) State in pp[over ¯] Collisions at D0

Coupling Hadron-Hadron Thresholds within a Chiral Quark Model Approach

Heavy hadron spectroscopy was well understood within the naive quark model until the end of the past century. However, in 2003, the X(3872) was discovered, with puzzling properties difficult to understand in the simple naive quark model picture. This state made clear that excited states of heavy mesons should be coupled to two-meson states in order to understand not only the masses but, in some cases, unexpected decay properties. In this work, we will give an overview of a way in which the naive quark model can be complemented with the coupling to two hadron thresholds. This program has been already applied to the heavy meson spectrum with the chiral quark model, and we show some examples where thresholds are of special relevance.

Threshold effects in hadron spectrum: a new spectroscopy?

The exploration of energies above the open-flavor threshold in the meson spectra has led to the appearance of unexpected states difficult to accommodate in the naive picture of a bound state of a quark and an antiquark. Many of such states are located close to meson-meson thresholds, which suggests that molecular structures may be a relevant component in the total wave function of such resonances. In this work, the state of meson-meson molecules calculations is reviewed, using a nonrelativistic constituent quark model that has been applied to a wide range of hadronic observables, and therefore all model parameters are completely constrained. The model has been able to reproduce, among others, the properties of the X(3872), described as a mixture of cc and DD* states, or the spectrum of the P-wave charm-strange mesons, which are well reproduced only if DK and D*K structures are taken into account. We show that such constituent quark model, which is able to describe the ordinary heavy meson spectra, is also capable of providing a good description of many new states recently reported.

Observation of J/ψϕ Structures Consistent with Exotic States from Amplitude Analysis of B^{+}→J/ψϕK^{+} Decays

The first full amplitude analysis of B^{+}→J/ψϕK^{+} with J/ψ→μ^{+}μ^{-}, ϕ→K^{+}K^{-} decays is performed with a data sample of 3  fb^{-1} of pp collision data collected at sqrt[s]=7 and 8 TeV with the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ϕK^{+}, and four J/ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state.

Evidence for a B_{s}^{0}π^{±} State

We report evidence for a narrow structure, X(5568), in the decay sequence X(5568)→B_{s}^{0}π^{±}, B_{s}^{0}→J/ψϕ, J/ψ→μ^{+}μ^{-}, ϕ→K^{+}K^{-}. This is evidence for the first instance of a hadronic state with valence quarks of four different flavors. The mass and natural width of this state are measured to be m=5567.8±2.9(stat)_{-1.9}^{+0.9}(syst)  MeV/c^{2} and Γ=21.9±6.4(stat)_{-2.5}^{+5.0}(syst)  MeV/c^{2}. If the decay is X(5568)→B_{s}^{*}π^{±}→B_{s}^{0}γπ^{±} with an unseen γ, m(X(5568)) will be shifted up by m(B_{s}^{*})-m(B_{s}^{0})∼49  MeV/c^{2}. This measurement is based on 10.4  fb^{-1} of pp[over ¯] collision data at sqrt[s]=1.96  TeV collected by the D0 experiment at the Fermilab Tevatron collider.