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Search for weakly decaying $b$-flavored pentaquarks

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Abstract

Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states J/$\psi K^+\pi^- p$, J/$\psi K^- \pi^- p$, J/$\psi K^- \pi^+ p$, and $J/\psi \phi (1020) p$ are reported. The data sample corresponds to an integrated luminosity of 3.0/fb in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the $\Lambda_b$.

Figures and captions

Leading-order diagrams for pentaquark decay modes into (a) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+ \pi^- p$ or (b) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi p$ final states.

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Invariant mass distributions above the decay mass thresholds for the indicated modes.

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For the ${P_{ B ^0 p}^+\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+\pi^- p}$ decay search (mode I), the invariant mass of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+ \pi^-$ combinations in the (a) region above threshold and in the (b) signal region. The peak in the sideband region results from $ B ^0$ decays.

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(a) Outputs of the BDT classifier for the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+\pi^- p$ final state. The circles (blue) show the signal training sample, and the triangles (red) show the background training sample, while the shaded (blue) histogram shows the signal test sample, and the diagonal (red) line-shaded histogram the background test sample. (b) Efficiencies of signal, solid (blue) curve, and background, dotted (red) curve, and the value of the $S/(\sqrt{B}+1.5)$, dashed (green) curve, called "significance," as a function of the BDT output.

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Reconstructed mass distributions after the BDT selection for the (a) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+\pi^- p$, (b) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^- \pi^- p,$ (c) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^-\pi^+ p$, and (d) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi p$ final states.

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Upper limits on $R$ at 90% {\rm CL} for (a) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+\pi^- p$, (b) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^-\pi^- p$, (c) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^-\pi^+ p$, and (d) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi p$ final states.

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Animated gif made out of all figures.

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Tables and captions

Quark content of the $b$-flavored pentaquarks and their weak decay modes explored here. We consider only the quark decay process $b \rightarrow c\overline{c}s$. The lower and upper bounds of the mass region searched are also given. (In this paper we use natural units where $\hbar=c=1$.)

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Decay modes that are vetoed for each pentaquark candidate mode and the specific particle misidentification that causes the reflection.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.