cern.ch

Measurement of the $CP$-violating phase $\phi_s$ from $B_{s}^{0}\to J/\psi\pi^+\pi^-$ decays in 13 TeV $pp$ collisions

[to restricted-access page]

Information

Tools

Contact

Abstract

Decays of $B_{s}^{0}$ and $\overline{B}{}_{s}^{0}$ mesons into $J/\psi\pi^+\pi^-$ final states are studied in a data sample corresponding to 1.9 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in 13 TeV $pp$ collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the $CP$-violating phase $\phi_s=-0.057\pm 0.060\pm 0.011$ rad, the decay-width difference between the heavier mass $B_{s}^{0}$ eigenstate and the $B^{0}$ meson of $-0.050\pm 0.004\pm 0.004$ ps$^{-1}$, and the $CP$-violating parameter $|\lambda|=1.01_{-0.06}^{+0.08}\pm0.03$, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV $pp$ collisions obtaining $\phi_s =0.002\pm0.044\pm0.012$ rad, and $|\lambda| =0.949\pm0.036\pm0.019$.

Figures and captions

Results of the simultaneous fit to the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi\pi$ mass distributions RS (black points) and WS (light-brown points) samples. The solid (blue) curve shows the fit to the RS sample, the long dashed (red) curve shows the signal, the dot-dashed (magenta) curve shows $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- $ decays, the dot-long-dashed (brown) curve shows the combinatorial background, the dotted (black) curve shows the sum of $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta^\prime$ and $\Lambda ^0_ b $ background, while the dot-dot-dashed (green) curve shows the fit to WS sample.

Fig1.pdf [28 KiB]
HiDef png [399 KiB]
Thumbnail [102 KiB]
*.C file
Fig1.pdf

Overall efficiency normalized to unity for (a) $m_{\pi\pi}$ , (b) $\cos \theta_{\pi\pi}$ , (c) $\cos \theta_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} }$ and (d) $\chi$ observables. The points with error bars are from the $ B ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- $ simulation, while the curves show the projection of the efficiency function.

Fig2a.pdf [19 KiB]
HiDef png [149 KiB]
Thumbnail [58 KiB]
*.C file
Fig2a.pdf
Fig2b.pdf [16 KiB]
HiDef png [140 KiB]
Thumbnail [54 KiB]
*.C file
Fig2b.pdf
Fig2c.pdf [17 KiB]
HiDef png [130 KiB]
Thumbnail [51 KiB]
*.C file
Fig2c.pdf
Fig2d.pdf [17 KiB]
HiDef png [126 KiB]
Thumbnail [48 KiB]
*.C file
Fig2d.pdf

Overall efficiency for (a) $m_{\pi\pi}$ vs $\cos \theta_{\pi\pi}$ and (b) $m^2_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ }$ vs $m^2_{\pi\pi}$. The inefficiency is at the kinematic boundary of $m^2_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+}$ where the pion is almost at rest in the $ B ^0_ s $ frame.

Fig3a.pdf [226 KiB]
HiDef png [1 MiB]
Thumbnail [181 KiB]
*.C file
Fig3a.pdf
Fig3b.pdf [312 KiB]
HiDef png [1 MiB]
Thumbnail [136 KiB]
*.C file
Fig3b.pdf

Projections of the angular and decay-time variables with the fit result overlaid. The points (black) show the data and the curves (blue) the fits.

Fig4a.pdf [20 KiB]
HiDef png [133 KiB]
Thumbnail [52 KiB]
*.C file
Fig4a.pdf
Fig4b.pdf [18 KiB]
HiDef png [145 KiB]
Thumbnail [54 KiB]
*.C file
Fig4b.pdf
Fig4c.pdf [20 KiB]
HiDef png [122 KiB]
Thumbnail [48 KiB]
*.C file
Fig4c.pdf
Fig4d.pdf [20 KiB]
HiDef png [132 KiB]
Thumbnail [51 KiB]
*.C file
Fig4d.pdf

Data distribution of $m_{\pi\pi}$ with the projection of the Solution I fit result overlaid. The data are described by the points (black) with error bars. The solid (blue) curve shows the overall fit.

Fig5.pdf [29 KiB]
HiDef png [324 KiB]
Thumbnail [97 KiB]
*.C file
Fig5.pdf

Animated gif made out of all figures.

PAPER-2019-003.gif
Thumbnail
thumbnail_PAPER-2019-003.gif

Tables and captions

Tagging efficiency, $\varepsilon_{\rm tag}$, and tagging power given as the efficiency times dilution squared, $\varepsilon_{\rm tag}D^2$, where $D=(1-2\omega)$ for each category and the total. The uncertainties on $\varepsilon_{\rm tag}$ are statistical only, and those for $\varepsilon_{\rm tag}D^2$ contain both statistical and systematic components.

Table_1.pdf [38 KiB]
HiDef png [103 KiB]
Thumbnail [16 KiB]
tex code
Table_1.pdf

Resonance parameters.

Table_2.pdf [63 KiB]
HiDef png [111 KiB]
Thumbnail [18 KiB]
tex code
Table_2.pdf

Likelihoods of various resonance model fits. Positive or negative interferences (Int) among the contributing resonances are indicated. The Solutions are indicated by \#.

Table_3.pdf [43 KiB]
HiDef png [81 KiB]
Thumbnail [13 KiB]
tex code
Table_3.pdf

Fit results for the $ C P$ -violating parameters for Solution I. The first uncertainties are statistical, and the second systematic. The last three columns show the statistical correlation coefficients for the three parameters.

Table_4.pdf [59 KiB]
HiDef png [45 KiB]
Thumbnail [8 KiB]
tex code
Table_4.pdf

Fit results of the resonant structure for both Solutions I and II. These results do not supersede those in Ref. \cite{LHCb-PAPER-2013-069} for the resonant fractions because no systematic uncertainties are quoted. The sum of fit fraction is not necessary 100% due to possible interferences between resonances with the same spin.

Table_5.pdf [46 KiB]
HiDef png [142 KiB]
Thumbnail [24 KiB]
tex code
Table_5.pdf

Absolute systematic uncertainties for the physics parameters.

Table_6.pdf [65 KiB]
HiDef png [137 KiB]
Thumbnail [22 KiB]
tex code
Table_6.pdf

Created on 15 June 2019.Citation count from INSPIRE on 15 June 2019.