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Search for structure in the $B_s^0\pi^\pm$ invariant mass spectrum

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Abstract

The claim by the D0 collaboration of the observation of a tetraquark state, dubbed the $X(5568)$, in the $ B ^0_ s \pi ^\pm $ invariant mass distribution is investigated. The analysis is based on a data sample recorded with the LHCb detector corresponding to $3\,fb^{-1} $ of $pp$ collision data at $\sqrt{s} = 7$ and $8 \mathrm{\,Te\kern -0.1em V} $. No significant excess is found, and upper limits are set on the production rate of the claimed $X(5568)$ state.

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Selected candidates for (left) $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ and (right) $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi$ decays. Results of the fits described in the text are superimposed with the total fit result shown as a dashed black line, and signal and background components as red and blue solid lines.

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Results of the fit to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^\pm $ invariant mass, for $ B ^0_ s \pi ^\pm $ candidates (both $ B ^0_ s $ modes combined) with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of (top) $5 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ and (bottom) $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $. The pull distributions, shown underneath the main figures, show good agreement between the fit functions and the data.

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Results of the fit to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass, for $ B ^0_ s \pi$ candidates (both $ B ^0_ s $ modes combined) with the signal yield fixed to zero. The fits are shown for minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of (left) $5 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ and (right) $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $. The pull distributions, shown underneath the main figures, show good agreement between the fit functions and the data.

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Results of the fit to the $Q$ value distribution for $ B ^0 \pi$ candidates.

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Results of the fit to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass, for $ B ^0_ s \pi$, $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ candidates with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of (left) $5 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ and (right) $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $. The pull distributions, shown underneath the main figures, show good agreement between the fit functions and the data.

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Results of the fit to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass, for $ B ^0_ s \pi$, $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi$ candidates with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of (left) $5 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ and (right) $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $. The pull distributions, shown underneath the main figures, show good agreement between the fit functions and the data.

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Results of fits to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass, for $ B ^0_ s \pi$ candidates (both $ B ^0_ s $ modes combined) with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of $5 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ in different rapidity bins. From left to right, top to bottom: $y\in [1.8,2.6]$, $y\in [2.6,3.0]$, $y\in [3.0,3.4]$, $y\in [3.4,5.0]$.

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Results of fits to the $Q$ value distribution, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass, for $ B ^0_ s \pi$ candidates (both $ B ^0_ s $ modes combined) with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $ in different rapidity bins. From left to right, top to bottom: $y\in [1.8,2.6]$, $y\in [2.6,3.0]$, $y\in [3.0,3.4]$, $y\in [3.4,5.0]$.

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Distribution of $Q$ value, shifted to display the $ B ^0_ s \pi ^+ $ invariant mass (both $ B ^0_ s $ modes combined), for candidates with minimum $ B ^0_ s $ $p_{\mathrm{ T}}$ of $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $, with a signal component superimposed that corresponds to $\rho_X^{\rm LHCb} = 8.6\,\%$. The shape and yield of the combinatorial background component is obtained from the fit with the signal yield fixed to zero, shown in Fig. 3 (right).

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Tables and captions

Yields $N( B ^0_ s )$ and $N(X)$ obtained from the fits to the $ B ^0_ s $ candidate mass distributions and the $ B ^0_ s \pi ^\pm $ Q-value distributions, respectively, with statistical uncertainties only. The values reported for $N( B ^0_ s )$ are those inside the $ B ^0_ s $ signal window. Relative efficiencies $\epsilon^{\rm rel}(X)$ are also given. Results are given for the baseline selection and for the case where the $ B ^0_ s $ minimum $p_{\mathrm{ T}}$ requirement is increased to $10 {\mathrm{\,Ge\kern -0.1em V\!/}c} $.

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Created on 04 March 2017.Citation count from INSPIRE on 04 March 2017.