Flavor tagged time-dependent angular analysis of the $B_s^0\to J/\psi \varphi$ decay and extraction of $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ and the weak phase ${\varphi }_s$ in ATLAS

A measurement of the $B_s^0\to J/\psi \varphi$ decay parameters, updated to include flavor tagging is reported using $4.9{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the ATLAS detector from $\sqrt{s}=7\mathrm{TeV}$ $pp$ collisions recorded in 2011 at the LHC. The values measured for the physical parameters are $$\begin{gathered} {\varphi }_s=0.12\pm 0.25(\text{stat})\pm 0.05(\text{syst})\text{rad} \\ \mathrm{\Delta }{\mathrm{\Gamma }}_s=0.053\pm 0.021(\text{stat})\pm 0.010(\text{syst}){\mathrm{ps}}^{-1} \\ {\mathrm{\Gamma }}_s=0.677\pm 0.007(\text{stat})\pm 0.004(\text{syst}){\mathrm{ps}}^{-1} \\ |A_{\parallel }(0){|}^2=0.220\pm 0.008(\text{stat})\pm 0.009(\text{syst}) \\ |A_0(0){|}^2=0.529\pm 0.006(\text{stat})\pm 0.012(\text{syst}) \\ {\delta }_{\perp }=3.89\pm 0.47(\text{stat})\pm 0.11(\text{syst})\text{rad} \end{gathered}$$where the parameter $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ is constrained to be positive. The $S$-wave contribution was measured and found to be compatible with zero. Results for ${\varphi }_s$ and $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ are also presented as 68% and 95% likelihood contours, which show agreement with the Standard Model expectations.

Figure 1

The invariant mass distribution for $B^{\pm }\to J/\psi K^{\pm }$ candidates. Included in this plot are all events passing the selection criteria. The data are shown by points, and the overall result of the fit is given by the blue curve. The combinatorial background component is given by the red dotted line, partially reconstructed $B$ decays by the green shaded area, and decays of $B^{\pm }\to J/\psi {\pi }^{\pm }$, where the pion is misassigned a kaon mass by a purple dashed line.

Figure 2

The opposite-side muon cone charge distribution for $B^{\pm }$ signal candidates for segment tagged (top) and combined (bottom) muons.

Figure 3

Jet-charge distribution for $B^{\pm }$ signal candidates.

Figure 4

The $B_s^0$-tag probability distribution for the events tagged with combined muons (top), segment tagged muons (middle) and jet charge (bottom). Black dots are data after removing spikes, blue is the fit to the sidebands, green is to the signal, and red is a sum of both fits.

Figure 5

(Top) Mass fit projection for the $B_s^0\to J/\psi \varphi$. The red line shows the total fit, the dashed green line shows the signal component while the dotted blue line shows the contribution from $B^0\to J/\psi K^{0*}$ events. (Bottom) Proper decay time fit projection for the $B_s^0\to J/\psi \varphi$. The red line shows the total fit while the green dashed line shows the total signal. The light and heavy components of the signal are shown in green as a dotted and a dash-dotted line, respectively. The total background is shown as a blue dashed line with a grey dotted line showing the prompt $J/\psi$ background. The pull distributions at the bottom show the difference between data and fit value normalized to the data statistical uncertainty.

Figure 6

Fit projections for transversity angles. (Top) ${\varphi }_T$, (middle) $\cos {\theta }_T$, (bottom) $\cos {\psi }_T$. In all three plots, the red line shows the total fit, the dashed green line shows the signal component, and the dotted blue line shows the background contribution.

Figure 7

One-dimensional likelihood scans for ${\varphi }_s$ (left) and $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ (right).

Figure 8

Likelihood contours in the ${\varphi }_s-\mathrm{\Delta }{\mathrm{\Gamma }}_s$ plane. The blue line shows the 68% likelihood contour, the dashed pink line shows the 90% likelihood contour, and the red dotted line shows the 95% likelihood contour (statistical errors only). The green band is the theoretical prediction of mixing-induced $CP$ violation.

Figure 9

One-dimensional likelihood scans for ${\delta }_{||}$ (top left), ${\delta }_{\perp }$ (top right) and ${\delta }_{\perp }-{\delta }_S$ (bottom).