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First measurement of the $CP$-violating phase in $B_s^0 \to \phi \phi$ decays

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Abstract

A first flavour-tagged measurement of the time-dependent CP-violating asymmetry in $B_s^0 \to \phi\phi$ decays is presented. In this decay channel, the CP-violating weak phase arises due to CP violation in the interference between $B_s^0$-$\bar{B}_s^0$ mixing and the $b \to s \bar{s} s $ gluonic penguin decay amplitude. Using a sample of $pp$ collision data corresponding to an integrated luminosity of $1.0\; fb^{-1}$ and collected at a centre-of-mass energy of $7 \rm TeV$ with the LHCb detector, $880\ \B_s^0 \to \phi\phi$ signal decays are obtained. The CP-violating phase is measured to be in the interval [-2.46, -0.76] \rm rad$ at 68% confidence level. The p-value of the Standard Model prediction is 16%.

Figures and captions

Invariant $K^+K^-K^+K^-$ mass distribution for selected $ B ^0_ s \rightarrow \phi \phi$ candidates. The total fit (solid line) consists of a double Gaussian signal component together with an exponential background (dotted line).

phiphi[..].pdf [24 KiB]
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phiphi_1fb-1_pub.pdf

One-dimensional projections of the $ B ^0_ s \rightarrow \phi\phi$ fit for (a) decay time, (b) helicity angle $\Phi$ and the cosine of the helicity angles (c) $\theta_1$ and (d) $\theta_2$. The data are marked as points, while the solid lines represent the projections of the best fit. The $ C\!P$ -even $P$-wave, the $ C\!P$ -odd $P$-wave and $S$-wave components are shown by the long dashed, short dashed and dotted lines, respectively.

time_p[..].pdf [30 KiB]
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time_pub_highres.pdf
phi_pu[..].pdf [19 KiB]
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phi_pub_components.pdf
ctheta[..].pdf [19 KiB]
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ctheta_1_pub_components.pdf
ctheta[..].pdf [19 KiB]
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ctheta_2_pub_components.pdf

Negative $\Delta$ln likelihood scan of $\phi_s$. Only the statistical uncertainty is included.

RapidL[..].pdf [13 KiB]
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*.C file
RapidLL_Phi_s_nopoints_pub.pdf

Animated gif made out of all figures.

PAPER-2013-007.gif
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thumbnail_PAPER-2013-007.gif

Tables and captions

Coefficients of the time-dependent terms and angular functions defined in Eqs. 1 and 2. Amplitudes are defined at $t=0$.

Table_1.pdf [54 KiB]
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tex code
Table_1.pdf

Fit results with statistical and systematic uncertainties. A 68% statistical confidence interval is quoted for $\phi_{ s }$ . Amplitudes are defined at $t = 0$.

Table_2.pdf [53 KiB]
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Table_2.pdf

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.