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

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Abstract

The $B_s^0\pi^\pm$ invariant mass distribution is investigated in order to search for possible exotic meson states. 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 $8$ TeV. No significant excess is found, and upper limits are set on the production rate of the claimed $X(5568)$ state within the LHCb acceptance. Upper limits are also set as a function of the mass and width of a possible exotic meson decaying to the $B_s^0\pi^\pm$ final state. The same limits also apply to a possible exotic meson decaying through the chain $B_s^{*0}\pi^\pm$, $B_s^{*0} \to B_s^0 \gamma$ where the photon is excluded from the reconstructed decays.

Figures and captions

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, with $ p_{\mathrm{ T}} ( B ^0_ s ) > 5 \mathrm{ Ge V} $, where the $ B ^0_ s $ signal window requirements of $|m( D ^-_ s \pi ^+ ) - 5367 \mathrm{ Me V} | < 30 \mathrm{ Me V} $ and $|m( { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \phi) - 5367 \mathrm{ Me V} | < 13 \mathrm{ Me V} $ are indicated by dotted lines. Results of the fits described in the text are superimposed with the total fit result shown as a red line, the signal component as an unfilled area, the combinatorial background component as a dark blue area and additional background contributions as a light green area.

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Results of the fit to the $ B ^0_ s \pi ^\pm $ mass distribution for candidates (both $ B ^0_ s $ modes combined) with minimum $ p_{\mathrm{ T}} ( B ^0_ s )$ of (top) $5 \mathrm{ Ge V} $, (middle) $10 \mathrm{ Ge V} $ and (bottom) $15 \mathrm{ Ge V} $. The component for the claimed $X(5568)$ state is included in the fit but is not significant. The distributions of the normalised residuals, or "pulls", displayed underneath the main figures show good agreement between the fit functions and the data.

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Upper limits (ULs) at 90 % confidence level (CL) as functions of the mass and width of a purported exotic state $X$ decaying to $ B ^0_ s \pi ^\pm $ with minimum $ p_{\mathrm{ T}} ( B ^0_ s )$ of (top) $5 \mathrm{ Ge V} $, (middle) $10 \mathrm{ Ge V} $ and (bottom) $15 \mathrm{ Ge V} $. The same limits also apply to a possible exotic meson decaying through the chain $ B ^{*0}_ s \pi ^\pm $, $ B ^{*0}_ s \rightarrow B ^0_ s \gamma$ where the photon is excluded from the reconstructed decays. In the latter case the nominal mass difference $m( B ^{*0}_ s ) - m( B ^0_ s ) = 48.6^{+1.8}_{-1.6} \mathrm{ Me V} $ [16] has to be added to the values on the x-axis to get the mass of the exotic meson under investigation.

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Tables and captions

Yields, $N$, of $ B ^0_ s $ and $X(5568)$ candidates obtained from the fits to the $ B ^0_ s $ and $ B ^0_ s \pi ^\pm $ candidate mass distributions, with statistical uncertainties only. The values reported for $N( B ^0_ s )$ are those inside the $ B ^0_ s $ signal window. The reported values for $X(5568)$ are obtained from fits with signal mass and width parameters fixed to those determined by the D0 collaboration. Relative efficiencies $\epsilon^{\rm rel}(X)$ of the $ B ^0_ s $ and $X(5568)$ candidate selection criteria are also given. The reported uncertainties on the relative efficiencies are only statistical, due to the finite size of the simulated samples.

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2016-029. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats

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Created on 21 October 2019.