XYZ states at LHCb

Marcin Kucharczyk,A Wrońska,A Magiera,W Przygoda

doi:10.1051/epjconf/201919904001

XYZ states at LHCb

Marcin Kucharczyk, A Wrońska + Show 2 more

Open Access

https://doi.org/10.1051/epjconf/201919904001

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Abstract

The latest years have observed a resurrection of interest in searches for exotic states motivated by precision spectroscopy studies of beauty and charm hadrons providing the observation of several exotic states. The latest results on spectroscopy of exotic hadrons are reviewed, using the proton-proton collision data collected by the LHCb experiment. The document focuses among others on the confirmation of the resonant nature of the Z(4430) mesonic state and observation of $J/\Psi \phi $ structures consistent with exotic states. LHCb has also made significant contributions to the determination of the quantum numbers of the X(3872) state and excluded the existence of the X(5568) tetraquark candidate.

Highlights

Bound states of quarks would be new states of matter beyond the simple quark-model picture, where only two types of quark combinations are required to account for the existing hadrons, i.e. qqcombinations form mesons, while baryons are made up of three quarks
They may coincide with other SU(3) color-neutral combinations of quarks and gluons such as gg glueballs, qqg hybrids, qqqqtetraquarks, qqqqq pentaquarks etc., predicted in the quark model proposed by GellMann and Zweig in 1960s [1]
The LHCb experiment has already collected an impressive set of results on exotic heavy flavour states, with the first unambiguous spin-parity assignments of the X(3872) [3], confirmation of resonant nature of the Z(4430)− [4] or observation of puzzling J/Ψφ structures consistent with exotic states [6, 7]

Summary

Introduction

Bound states of quarks would be new states of matter beyond the simple quark-model picture, where only two types of quark combinations are required to account for the existing hadrons, i.e. qqcombinations form mesons, while baryons are made up of three quarks. The X(3872) state was first discovered by Belle experiment in 2003 [2], being the first charmonium-like exotic state ever observed, and led to a revolution in exotic hadron spectroscopy It was observed as an unexpected structure in the J/ψπ+π− invariant mass while investigating B+ → J/ψK+π+π− decays. LHCb has recently found a 4.4σ evidence of the X(3872) → ψ(2S )γ in B+ → X(3872)K+, and measured its branching fraction relative to X(3872) → J/ψγ, i.e. Rψγ = 2.46 ± 0.64(stat) ± 0.29(syst) [11] This result indicates a presence of charmonium component in the X(3872), it cannot definitively exclude a pure D∗+D− molecule interpretation.

MeV and width

Conclusions