Search for a Structure in the $B_s^0{\pi }^{\pm }$ Invariant Mass Spectrum with the ATLAS Experiment

A search for the narrow structure, $X(5568)$, reported by the D0 Collaboration in the decay sequence $X\to B_s^0{\pi }^{\pm }$, $B_s^0\to J/\psi \varphi$, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to $4.9{\mathrm{fb}}^{-1}$ of $pp$ collisions at 7 TeV and $19.5{\mathrm{fb}}^{-1}$ at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the $X$ production rate relative to $B_s^0$ mesons, ${\rho }_X$, were determined at 95% confidence level. The results are $N(X)<382$ and ${\rho }_X<0.015$ for $B_s^0$ mesons with transverse momenta above 10 GeV, and $N(X)<356$ and ${\rho }_X<0.016$ for transverse momenta above 15 GeV. Limits are also set for potential $B_s^0{\pi }^{\pm }$ resonances in the mass range 5550 to 5700 MeV.

Figure 1

The invariant mass distribution for $B_s^0\to J/\psi \varphi$ candidates satisfying the selection criteria. Data are shown as points and results of fits to signal (dashed), background (dotted), and the total fit (solid) are shown as lines. The two outer (red) shaded bands and the central (green) shaded band represent the mass sidebands and the signal region of $B_s^0$ meson candidates, respectively.

Figure 2

Results of the fit to the $B_s^0{\pi }^{\pm }$ mass distribution for candidates with $p_T(B_s^0)>10\mathrm{GeV}$ (left) and $p_T(B_s^0)>15\mathrm{GeV}$ (right). The bottom panels show the difference between each data point and the fit divided by the statistical uncertainty of that point.

Figure 3

Upper limits on ${\rho }_X$ at 95% C.L. (black squares connected by line) at different masses of a hypothetical resonant state $X$ decaying to $B_s^0{\pi }^{\pm }$, for events with $p_T(B_s^0)>10\mathrm{GeV}$. A BW width of $21.9\pm 6.4(\mathrm{stat}{)}_{-2.5}^{+5.0}(\mathrm{syst})\mathrm{MeV}$ is assumed, as reported by D0. The values include systematic uncertainties. The expected 95% C.L. upper limits (central black dot-dashed line) with $\pm 1\sigma$ (green) and $\pm 2\sigma$ (yellow) uncertainty bands on ${\rho }_X$ are shown as a function of the assumed resonance mass.