# Measurement of CP violation in the $B_s^0 \to \phi \phi$ decay and search for the $B^0 \to \phi\phi$ decay

[to restricted-access page]

## Abstract

A measurement of the time-dependent $C P$ -violating asymmetry in $B ^0_ s \rightarrow \phi\phi$ decays is presented, along with measurements of the $T$ -odd triple-product asymmetries. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.0 fb^{-1}$ collected with the LHCb detector, a signal yield of approximately 8500 $B ^0_ s \rightarrow \phi\phi$ decays is obtained. The $C P$ -violating phase is measured to be ${\phi_{ s }^{ s \overline s s } =-0.07\pm0.13\mathrm{ (stat)} \pm0.03\mathrm{ (syst)} }\rm rad$. The triple-product asymmetries are measured to be ${A_U=0.000\pm0.012\mathrm{ (stat)} \pm0.004\mathrm{ (syst)} }$ and ${A_V=-0.003\pm0.012\mathrm{ (stat)} \pm0.004\mathrm{ (syst)} }$. The results obtained are consistent with the hypothesis of $C P$ conservation in $b \rightarrow s \overline s s$ transitions. In addition, an improved limit on the branching fraction of the $B ^0 \rightarrow \phi\phi$ decay is set, $\mathcal{B}( B ^0 \rightarrow \phi\phi)<2.4\times 10^{-8}$ at 90 % confidence level.

## Figures and captions

 A fit to the 2011 (top left), 2012 (top right), 2015 (bottom left) and 2016 (bottom right) data, represented by the black points. Also shown are the results of the total fit (blue solid line), with the $B ^0_ s \rightarrow \phi\phi$ (red dashed), the $\Lambda ^0_ b \rightarrow \phi p K ^-$ (magenta long dashed), and the combinatorial (blue short dashed) fit components. 2011Da[..].pdf [75 KiB] HiDef png [399 KiB] Thumbnail [280 KiB] *.C file 2012Da[..].pdf [73 KiB] HiDef png [379 KiB] Thumbnail [263 KiB] *.C file 2015Da[..].pdf [72 KiB] HiDef png [392 KiB] Thumbnail [280 KiB] *.C file 2016Da[..].pdf [74 KiB] HiDef png [370 KiB] Thumbnail [257 KiB] *.C file Decay angles for the $B ^0_ s \rightarrow \phi \phi$ decay, where $\theta_{1,2}$ is the angle between the $K^+$ track momentum in the $\phi_{1,2}$ meson rest frame and the parent $\phi_{1,2}$ momentum in the $B ^0_ s$ rest frame, $\Phi$ is the angle between the two $\phi$ meson decay planes and $\hat{n}_{V_{1,2}}$ is the unit vector normal to the decay plane of the $\phi_{1,2}$ meson. Fig_2.pdf [56 KiB] HiDef png [66 KiB] Thumbnail [45 KiB] *.C file tex code Angular acceptance found from simulated $B ^0_ s \rightarrow \phi\phi$ decays (top-left) integrated over $\cos\theta_2$ and $\Phi$ as a function of $\cos\theta_1$, (top-right) integrated over $\cos\theta_1$ and $\Phi$ as a function of $\cos\theta_2$, and (bottom) integrated over $\cos\theta_1$ and $\cos\theta_2$ as a function of $\Phi$. accep_[..].pdf [25 KiB] HiDef png [107 KiB] Thumbnail [110 KiB] *.C file accep_[..].pdf [25 KiB] HiDef png [108 KiB] Thumbnail [110 KiB] *.C file accep_[..].pdf [25 KiB] HiDef png [107 KiB] Thumbnail [105 KiB] *.C file Decay-time acceptances calculated from (left) $B ^0_ s \rightarrow D ^-_ s \pi ^+$ and (right) $B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0}$ decays. Superimposed are calculated analytical splines. accep-[..].pdf [15 KiB] HiDef png [157 KiB] Thumbnail [123 KiB] *.C file accep-[..].pdf [15 KiB] HiDef png [154 KiB] Thumbnail [120 KiB] *.C file One-dimensional projections of the $B ^0_ s \rightarrow \phi\phi$ fit for (top-left) decay time with binned acceptance, (top-right) helicity angle $\Phi$ and (bottom-left and bottom-right) cosine of the helicity angles $\theta_1$ and $\theta_2$. The background-subtracted data are marked as black points, while the blue solid lines represent the projections of the best fit. The $C P$ -even $P$-wave, the $C P$ -odd $P$-wave and $S$-wave combined with double $S$-wave components are shown by the red long dashed, green short dashed and purple dot-dashed lines, respectively. Fitted components are plotted taking in to account efficiencies in the time and angular observables. Plots_[..].png [821 KiB] HiDef png [177 KiB] Thumbnail [74 KiB] *.C file Plots_[..].png [864 KiB] HiDef png [195 KiB] Thumbnail [84 KiB] *.C file Plots_[..].png [740 KiB] HiDef png [173 KiB] Thumbnail [75 KiB] *.C file Plots_[..].png [747 KiB] HiDef png [175 KiB] Thumbnail [76 KiB] *.C file Fit to the four-kaon invariant mass. The total PDF as described in the text is shown as a blue solid line, $B ^0_ s \rightarrow \phi\phi$ as a red dashed line, $B ^0 \rightarrow \phi \phi$ as a green dotted line, the $\Lambda ^0_ b \rightarrow \phi p K$ as a magenta long-dashed line and the combinatorial background as a blue short-dashed line. DataFi[..].pdf [68 KiB] HiDef png [388 KiB] Thumbnail [248 KiB] *.C file Results of the ${\rm CL}_s$ scan as a function of $N_{ B ^0 }$. The solid black line shows the observed ${\rm CL}_s$ distribution, while the dotted black line indicates the expected distribution. The green (yellow) band marks the $1\sigma$ ($2\sigma$) confidence region on the expected ${\rm CL}_s$. The $90 (95) \%$ CL limit is indicated as a solid (dashed) red line. CLplot[..].pdf [34 KiB] HiDef png [190 KiB] Thumbnail [136 KiB] *.C file Animated gif made out of all figures. CONF-2018-001.gif Thumbnail

## Tables and captions

 Coefficients of the time-dependent terms and angular functions used in Eq. 2. Amplitudes are defined at $t=0$. Table_1.pdf [54 KiB] HiDef png [158 KiB] Thumbnail [73 KiB] tex code Angular coefficients, written in the same basis as the efficiency parameterisation. Table_2.pdf [60 KiB] HiDef png [136 KiB] Thumbnail [65 KiB] tex code Tagging performance of the opposite side (OS) and same side kaon (SSK) flavour taggers. Table_3.pdf [33 KiB] HiDef png [23 KiB] Thumbnail [10 KiB] tex code Results of the time-dependent fit. Uncertainties shown do not include systematic contributions. Table_4.pdf [50 KiB] HiDef png [152 KiB] Thumbnail [63 KiB] tex code Correlation matrix associated with the result of the time-dependent fit and relate to the statistical uncertainties. Table_5.pdf [48 KiB] HiDef png [71 KiB] Thumbnail [34 KiB] tex code Summary of systematic uncertainties for physics parameters in the time-dependent measurement, where AA denotes angular acceptance, TA denotes time acceptance, and TR time resolution. Table_6.pdf [52 KiB] HiDef png [89 KiB] Thumbnail [40 KiB] tex code Summary of systematic uncertainties on $A_U$ and $A_V$. Table_7.pdf [16 KiB] HiDef png [85 KiB] Thumbnail [39 KiB] tex code

Created on 27 July 2019.Citation count from INSPIRE on 27 July 2019.