cern.ch

Measurement of the CP-violating phase $\phi_s$ in $\overline{B}^0_s\rightarrow J/\psi \pi^+\pi^-$ decays

[to restricted-access page]

Information

Tools

Abstract

The mixing-induced CP-violating phase $\phi_s$ in ${B}^0_s$ and $\overline{B}^0_s$ decays is measured using the $J/\psi \pi^+\pi^-$ final state in data, taken from 3 fb$^{-1}$ of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centre-of-mass $pp$ collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct \CP violation, yields a value for the phase $\phi_s=70\pm 68\pm 8$ mrad. This result is consistent with the Standard Model expectation and previous measurements.

Figures and captions

Invariant mass of $J/\psi \pi^+\pi^-$ combinations. The data are fitted with double Crystal Ball signal functions and several background functions. The (red) solid line shows the $\optbar{ B}{} ^0_{ s}$ signal, the (brown) dotted line shows the exponential combinatorial background, the (green) short-dashed line shows the $B^{\mp}$ background, the (magenta) dot-dashed line shows the $\optbar{ B}{} ^0$ signal, the (light blue) dashed line is the sum of $\optbar{ B}{} ^0_{ s}\rightarrow J/\psi\eta'$, $\optbar{ B}{} ^0_{ s}\rightarrow J/\psi\phi$, $\phi\rightarrow \pi^+\pi^-\pi^0$ backgrounds, and the $\Lambda ^0_ b \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^- p$ plus $\ensuremath\overline{{\Lambda ^0_ b }} \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K^+\overline{p}$ reflections, the (black) dot-dashed line is the $\optbar{ B}{} ^0\rightarrow J/\psi K^{\mp} \pi^{\pm}$ reflection and the (blue) solid line is the total.

 fitm-ft.pdf [50 KiB]
HiDef png [300 KiB]
Thumbnail [217 KiB]
*.C file
fitm-ft.pdf

Projections of (a) $m(\pi^+\pi^-)$, (b) $\cos\theta_{\pi\pi}$, (c) $\cos \theta_{J/\psi}$ and (d) $\chi$ [13]. The points with error bars are data, the signal fits are shown with (red) dashed lines, the background with a (black) dotted lines, and the (blue) solid lines represent the total fits. The difference between the data and the fits divided by the uncertainty on the data is shown below.

 mpp6N0.pdf [40 KiB]
HiDef png [391 KiB]
Thumbnail [258 KiB]
*.C file
mpp6N0.pdf
cospp6N0.pdf [39 KiB]
HiDef png [345 KiB]
Thumbnail [231 KiB]
*.C file
cospp6N0.pdf
cosH6N0.pdf [40 KiB]
HiDef png [363 KiB]
Thumbnail [236 KiB]
*.C file
cosH6N0.pdf
chi6N0.pdf [47 KiB]
HiDef png [305 KiB]
Thumbnail [214 KiB]
*.C file
chi6N0.pdf

Estimated fractions of mistag probabilities from (a) the SSK tagger, $\eta^{\rm SSK}$, and (b) the OS tagger, $\eta^{\rm OS}$.

 etaSS_1d.pdf [31 KiB]
HiDef png [154 KiB]
Thumbnail [113 KiB]
*.C file
etaSS_1d.pdf
etaOS_1d.pdf [32 KiB]
HiDef png [170 KiB]
Thumbnail [127 KiB]
*.C file
etaOS_1d.pdf

Distributions of (a) decay time of $\optbar{ B}{} ^0 \rightarrow J/\psi \optbar{ K}{} ^{ *0}$ candidates in data, (b) ratio of time acceptance between $\overline{ B }{} ^0_ s \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+\pi^-$ and $\overline{ B }{} ^0 \rightarrow J/\psi \overline{ K }{} ^{*0} $ decays from simulation.

 fitkst.pdf [35 KiB]
HiDef png [269 KiB]
Thumbnail [166 KiB]
*.C file
fitkst.pdf
eff-ratio.pdf [35 KiB]
HiDef png [288 KiB]
Thumbnail [153 KiB]
*.C file
eff-ratio.pdf

Decay time distribution of $\optbar{ B}{} ^0\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi^+\pi^-$ candidates. The signal PDF is shown with a (red) dashed line, the background with a (black) dotted line, and the (blue) solid line represents the total.

 time6NII5.pdf [39 KiB]
HiDef png [402 KiB]
Thumbnail [256 KiB]
*.C file
time6NII5.pdf

Animated gif made out of all figures.

 PAPER-2014-019.gif
Thumbnail
thumbnail_PAPER-2014-019.gif

Tables and captions

Acceptance function parameter values and their correlations.

 Table_1.pdf [45 KiB]
HiDef png [70 KiB]
Thumbnail [21 KiB]
tex code 		Table_1.pdf

Systematic uncertainties. The total is the sum in quadrature of each entry.

 Table_2.pdf [40 KiB]
HiDef png [96 KiB]
Thumbnail [43 KiB]
tex code 		Table_2.pdf

Created on 27 April 2024.