Evidence of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1770.svg"> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mi mathvariant="normal">Λ</mml:mi> </mml:math> structure and observation of excited <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si176.svg"> <mml:msup> <mml:mi mathvariant="normal">Ξ</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:math> states in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si177.svg"> <mml:msubsup> <mml:mi mathvariant="normal">Ξ</mml:mi> <mml:mi>b</mml:mi> <mml:mo>-</mml:mo> </mml:msubsup> <mml:mo>→</mml:mo> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mi mathvariant="normal">Λ</mml:mi> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:math> decay
LHCb Collaboration
Abstract
First evidence of a structure in the J / ψ Λ invariant mass distribution is obtained from an amplitude analysis of Ξ b - → J / ψ Λ K - decays. The observed structure is consistent with being due to a charmonium pentaquark with strangeness with a significance of 3.1 σ including systematic uncertainties and look-elsewhere effect. Its mass and width are determined to be 4458.8 ± 2.9 - 1.1 + 4.7 MeV and 17.3 ± 6.5 - 5.7 + 8.0 MeV , respectively, where the quoted uncertainties are statistical and systematic. The structure is also consistent with being due to two resonances. In addition, the narrow excited Ξ - states, Ξ 1690 - and Ξ 1820 - , are seen for the first time in a Ξ b - decay, and their masses and widths are measured with improved precision. The analysis is performed using pp collision data corresponding to a total integrated luminosity of 9 fb - 1 , collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV.