Pentaquarks and Tetraquarks at LHCb

TL;DR

This paper reports the discovery and analysis of pentaquark and tetraquark states observed in LHCb experiments, providing measurements of their properties and discussing models of their internal structure.

Contribution

It presents the observation of charmonium pentaquarks with specific masses, widths, and quantum numbers, and discusses their possible internal binding models.

Findings

Two pentaquark states with distinct masses and widths identified.

Quantum numbers of the pentaquark states determined as opposite parity, spins 3/2 and 5/2.

Observation of the Z(4430)^- mesonic state with J^P=1^+.

Abstract

Exotic resonant structures found in $\Lambda^0_b$ and $\overline{B}^0$ decays into charmonium in the LHCb experiment are discussed. Examination of the $J/\psi p$ system in $\Lambda^0_b\to J/\psi K^- p$ decays shows two states each of which must be composed of $uudc\overline{c}$ quarks, and thus are called charmonium pentaquarks. Their masses are $4380\pm 8\pm 29$~MeV and $4449.8\pm 1.7\pm 2.5$~MeV, and their corresponding widths ($\Gamma$) are $205\pm 18\pm 86$ MeV, and $39\pm 5\pm 19$ MeV. The preferred $J^P$ assignments are of opposite parity, with one state having spin 3/2 and the other 5/2. Models of internal binding of the pentaquark states are discussed. Finally, another mesonic state is discussed, the $Z(4430)^-$ that decays into $\psi' \pi^-$ and was first observed by the Belle collaboration in $B^0\to \psi' K^+\pi^-$ decays. Using a sample of approximately 25,000 signal events, LHCb determines the $J^{P}$ to be $1^{+}$.