The decay Bs > J/\psi K+ K is investigated using 0.16/fb of data collected with the LHCb detector using 7 TeV pp collisions. Although the J/\psi \phi\ 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(1525) region as well as a nonresonant component. After subtracting the nonresonant component, we find B(Bs>J/\psi f'_2(1525))/B(Bs>J/\psi \phi)=(26.4 +/ 2.7 +/ 2.4).
Invariant mass of $J/\psi K^+K^$ combinations. The vertical lines indicate the signal and sideband regions. 
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Invariant mass of $K^+K^$ combinations. The histogram shows the data in the signal region while the points (red) show the sidebands. 
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(a) The $m(K^+K^)$ distribution for simulated $\overline{B}^0\rightarrow J/\psi \overline{K}_2^*(1430)$ 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 fb$^{1}$ of data. (b) The $m(J/\psi K^+\pi^)$ distribution for $J/\psi K^+K^$ data candidates $25200$ MeV above the $\overline{B}_s^0$ mass, and with $m(K^+K^)$ within $\pm$300 MeV of 1525 MeV, reinterpreted as $\overline{B}^0\rightarrow J/\psi K^\pi^+$ events. The fit is to a signal Gaussian whose mass and width are allowed to vary as well as a quadratic background. 
MC_mkk[..].pdf [63 KiB] HiDef png [147 KiB] Thumbnail [110 KiB] *.C file 

Projections of fits to (a) the $\overline{B}_s^0$ candidate mass and (b) the dikaon mass. The $f'_2$ signal is parameterized by a spin2 BreitWigner 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 longdashed (red) line shows the misidentified $\overline{B}^0\rightarrow J/\psi K^\pi^+$ decays, and the (blue) line the total. 
fit_mb[..].pdf [120 KiB] HiDef png [247 KiB] Thumbnail [157 KiB] *.C file 

Distribution of $\cos\theta_{J/\psi}$ for $\overline{B}_s^0\rightarrow J/\psi f'_2$ 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 Swave 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 dotdashed curve. 
hel_f2_new.pdf [57 KiB] HiDef png [134 KiB] Thumbnail [142 KiB] *.C file 

Animated gif made out of all figures. 
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Systematic uncertainties on $R$. 
Table_1.pdf [56 KiB] HiDef png [113 KiB] Thumbnail [51 KiB] tex code 
Created on 06 March 2021.