Observation of ${\overline{B}}_s^0\to J/\psi f_2^{\prime }(1525)$ in $J/\psi K^{+}{K}^{-}$ Final States

The decay ${\overline{B}}_s^0\to J/\psi K^{+}{K}^{-}$ is investigated using $0.16{\mathrm{fb}}^{-1}$ of data collected with the LHCb detector using 7 TeV $pp$ collisions. Although the $J/\psi \varphi$ channel is well known, final states at higher $K^{+}{K}^{-}$ masses have not previously been studied. In the $K^{+}{K}^{-}$ mass spectrum we observe a significant signal in the $f_2^{\prime }(1525)$ region as well as a nonresonant component. After subtracting the nonresonant component, we find $\mathcal{B}\mathbf{(}{\overline{B}}_s^0\to J/\psi f_2^{\prime }(1525)\mathbf{)}/\mathcal{B}({\overline{B}}_s^0\to J/\psi \varphi )=(26.4\pm 2.7\pm 2.4)\%$.

Figure 1

Invariant mass of $J/\psi K^{+}{K}^{-}$ combinations. The vertical lines indicate the signal and sideband regions.

Figure 2

Invariant mass of $K^{+}{K}^{-}$ combinations. The histogram shows the data in the signal region while the points (red) show the sidebands.

Figure 3

(a) The $m(K^{+}{K}^{-})$ distribution for simulated ${\overline{B}}^0\to J/\psi {\overline{K}}_2^{*}(1430)$ decays where the ${\pi }^{+}$ from the ${\overline{K}}_2^{*}(1430)$ decay is interpreted as a $K^{+}$. The histogram shows $m(K^{+}{K}^{-})$ in the signal region of ${\overline{B}}_s^0$ mass and the points in the sideband region. The simulation corresponds to approximately $8{\mathrm{fb}}^{-1}$ of data. (b) The $m(J/\psi K^{+}{\pi }^{-})$ distribution for $J/\psi K^{+}{K}^{-}$ data candidates 25–200 MeV above the ${\overline{B}}_s^0$ mass, and with $m(K^{+}{K}^{-})$ within $\pm 300\mathrm{MeV}$ of 1525 MeV, reinterpreted as ${\overline{B}}^0\to J/\psi K^{-}{\pi }^{+}$ events. The fit is to a signal Gaussian whose mass and width are allowed to vary as well as a quadratic background.

Figure 4

Projections of fits to (a) the ${\overline{B}}_s^0$ candidate mass and (b) the dikaon mass. The $f_2^{\prime }$ signal is parametrized by a spin-2 Breit-Wigner function whose width is fixed to 73 MeV (dotted curve). The combinatorial background is shown in the light shaded region, while the darker shaded region shows the nonresonant $J/\psi K^{+}{K}^{-}$ component. The long-dashed (red) line shows the misidentified ${\overline{B}}^0\to J/\psi K^{-}{\pi }^{+}$ decays, and the (blue) line the total.

Figure 5

Distribution of $\cos {\theta }_{J/\psi }$ for ${\overline{B}}_s^0\to J/\psi f_2^{\prime }$ decays. The background and nonresonant $K^{+}{K}^{-}$ components have been subtracted, and the data have been corrected for acceptance. The fit to Eq. (1) is shown by the solid line. Note that for pure $S$ wave the distribution would be ${sin}^2{\theta }_{J/\psi }$ ($p=0$), shown as the dotted curve, while for pure helicity 1 ($p=1$) the data would be described by the dotted-dashed curve.