Abstract
A Dalitz plot analysis of {{B} ^0} !rightarrow eta _c(1S) {{K} ^+} {{pi } ^-} decays is performed using data samples of pp collisions collected with the text{ LHCb } detector at centre-of-mass energies of {sqrt{s}} =7,~8 and 13{,mathrm {Te}mathrm {V}} , corresponding to a total integrated luminosity of 4.7 ,text{ fb }^{-1} . A satisfactory description of the data is obtained when including a contribution representing an exotic eta _c(1S) pi ^- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096 pm 20~^{+18}_{-22} ,mathrm {Me}mathrm {V} and 152 pm 58~^{+60}_{-35} ,mathrm {Me}mathrm {V} , respectively. The spin-parity assignments J^P=0^+ and J^{P}=1^- are both consistent with the data. In addition, the first measurement of the {{B} ^0} !rightarrow eta _c(1S) {{K} ^+} {{pi } ^-} branching fraction is performed and gives B(B0→ηc(1S)K+π-)=(5.73±0.24±0.13±0.66)×10-4,\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$\\begin{aligned} \\displaystyle \\mathcal {B}({{B} ^0} \\!\\rightarrow \\eta _c(1S) {{K} ^+} {{\\pi } ^-} ) = (5.73 \\pm 0.24 \\pm 0.13 \\pm 0.66) \\times 10^{-4}, \\end{aligned}$$\\end{document}where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.
Highlights
Since the discovery of the X (3872) state in 2003 [1], several exotic hadron candidates have been observed, as reported in recent reviews [2,3,4,5,6,7].1 The decay modes of these states indicate that they must contain a heavy quark–antiquark pair in their internal structure; they cannot be accommodated as an unassigned charmonium or bottomonium state due to either their mass, decay properties or electric charge, which are inconsistent with those of pure charmonium or bottomonium states
1 excitation of the gluon and light-quark fields [13]. This interpretation, which is based on lattice QCD, predicts different multiplets of charmonium tetraquarks, comprising states with quantum numbers allowing the decay into the ηcπ − system
The Zc(4430)− resonance, discovered by the Belle collaboration [16] and confirmed by LHCb [17,18], could fit into this scenario. Another prediction of a possible exotic candidate decaying to the ηcπ − system is provided by the diquark model [19], where quarks and diquarks are the fundamental units to build a rich spectrum of hadrons, including the exotic states observed far
Summary
Since the discovery of the X (3872) state in 2003 [1], several exotic hadron candidates have been observed, as reported in recent reviews [2,3,4,5,6,7].1 The decay modes of these states indicate that they must contain a heavy quark–antiquark pair in their internal structure; they cannot be accommodated as an unassigned charmonium or bottomonium state due to either their mass, decay properties or electric charge, which are inconsistent with those of pure charmonium or bottomonium states. 1 excitation of the gluon and light-quark fields [13] This interpretation, which is based on lattice QCD, predicts different multiplets of charmonium tetraquarks, comprising states with quantum numbers allowing the decay into the ηcπ − system. The Zc(4430)− resonance, discovered by the Belle collaboration [16] and confirmed by LHCb [17,18], could fit into this scenario Another prediction of a possible exotic candidate decaying to the ηcπ − system is provided by the diquark model [19], where quarks and diquarks are the fundamental units to build a rich spectrum of hadrons, including the exotic states observed far.
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