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Measurement of the $\bar{B}^0-B^0$ and $\bar{B}^0_s-B^0_s$ production asymmetries in $pp$ collisions at $\sqrt{s}=7$ TeV

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Abstract

The B0bar-B0 and Bsbar-Bs production asymmetries, AP(B0) and AP(Bs), are measured by means of a time-dependent analysis of B0 -> J/\psi K*0, B0 -> D- pi+ and Bs -> Ds- pi+ decays, using a data sample corresponding to an integrated luminosity of 1.0 fb^{-1}, collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the B0 and Bs mesons within the LHCb acceptance. The production asymmetries, integrated over pT and eta in the range 4 < pT< 30 GeV/c and 2.5<eta<4.5, are determined to be AP(B0) = (-0.35 +/- 0.76 +/- 0.28)% and AP(Bs) = (1.09 +/- 2.61 +/- 0.66)%, where the first uncertainties are statistical and the second systematic.

Figures and captions

Distributions of (left) invariant mass and (right) decay time for (top) $ B ^0 \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $, (middle) $ B ^0 \rightarrow D ^- \pi ^+ $ and (bottom) $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ decays, with the results of the fit overlaid. The contributions of the various background sources are also shown.

massBd[..].pdf [149 KiB]
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massBd2JpsiKstar_plain.pdf
timeBd[..].pdf [155 KiB]
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timeBd2JpsiKstar_plain.pdf
massBd[..].pdf [173 KiB]
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massBd2Dpi_plain.pdf
timeBd[..].pdf [160 KiB]
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timeBd2Dpi_plain.pdf
massBs[..].pdf [163 KiB]
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massBs2Dspi_plain.pdf
timeBs[..].pdf [173 KiB]
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timeBs2Dspi_plain.pdf

Time-dependent raw asymmetries for candidates in the (a) $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ , (b) $ B ^0 \rightarrow D ^- \pi ^+ $ and (c) $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ signal mass regions with the results of the global fits overlaid. In (c) the asymmetry is obtained by folding the $\overline{ B }{} {}^0_ s $ and $ B ^0_ s $ decay time distributions into one oscillation period, and the offset $t_0 = 0.2$ $ {\rm \,ps}$ corresponds to the selection requirement on the decay time.

asymBd[..].pdf [99 KiB]
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asymBd2JpsiKstar.pdf
asymBd2Dpi.pdf [96 KiB]
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asymBd2Dpi.pdf
asymBs[..].pdf [123 KiB]
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asymBs2Dspi.pdf

Distributions of $p_\mathrm{T}$ and $\eta$, where the background components are subtracted using the sPlot technique [23], for (a) $ B ^0 \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^{*0} $ , (b) $ B ^0 \rightarrow D ^- \pi ^+ $ and (c) $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ decays. The definition of the various kinematic bins is superimposed.

Bd2Jps[..].pdf [238 KiB]
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Bd2JpsiKstar_bins_paper.pdf
Bd2Dpi[..].pdf [210 KiB]
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Bd2Dpi_bins_paper.pdf
Bs2Dsp[..].pdf [194 KiB]
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Bs2Dspi_bins_paper.pdf

Dependence of (top) $A_\mathrm{P}(B^0)$ and (bottom) $A_\mathrm{P}(B^0_s)$ on (left) $p_{\rm T}$ and (right) $\eta$. The error bars include both statistical and systematic uncertainties.

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ApB0_pt.pdf
ApB0_eta.pdf [103 KiB]
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ApB0_eta.pdf
ApBs_pt.pdf [100 KiB]
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ApBs_pt.pdf
ApBs_eta.pdf [103 KiB]
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ApBs_eta.pdf

Animated gif made out of all figures.

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Tables and captions

Values of the various physical inputs used in the fits.

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Table_1.pdf

Values of signal yields, $A_{\rm P}$, $A_{f}$ and of the correlations $\rho(A_{\rm P},\,A_f)$ obtained from global fits. The smaller value of the correlation in the $ B ^0_ s $ case is due to the much larger mixing frequency of $ B ^0_ s $ mesons.

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Combined values of $A_\mathrm{P}( B ^0 )$ from $B^0\rightarrow J/\psi K^{*0}$ and $ B ^0 \rightarrow D ^- \pi ^+ $ decays, corresponding to the various kinematic bins. The first uncertainties are statistical and the second systematic. For completeness, the values obtained either from $B^0\rightarrow J/\psi K^{*0}$ or $ B ^0 \rightarrow D ^- \pi ^+ $ decays are also reported in the last two columns, with statistical uncertainties only. The values of the last two bins are obtained from $B^0\rightarrow J/\psi K^{*0}$ decays alone.

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Values of $A_\mathrm{P}( B ^0_ s )$ from $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ decays, corresponding to the various kinematic bins. The first uncertainties are statistical and the second systematic.

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Values of $\omega_i$ determined from simulation and $\omega_i^{\rm data}$ extracted from data using $B^0\rightarrow J/\psi K^{*0}$ decays in two different binning schemes. The $\omega_i$ values and the difference between $\omega_i$ and $\omega_i^{\rm data}$ values are used to determine the integrated results and to evaluate the related systematic uncertainties, respectively.

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Absolute values of systematic uncertainties. The total systematic uncertainties are obtained by summing the individual contributions in quadrature.

Table_6.pdf [47 KiB]
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Table_6.pdf

Values of the production asymmetry $A_\mathrm{P}(B^0)$ in bins of $p_{\rm T}$ and $\eta$ from $ B ^0 \rightarrow J/\psi K ^{*0} $ and $ B ^0 \rightarrow D ^- \pi ^+ $ decays. The first uncertainties are statistical and the second systematic.

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Table_7.pdf

Values of the production asymmetry $A_\mathrm{P}(B^0_s)$ in bins of $p_{\rm T}$ and $\eta$ from $ B ^0_ s \rightarrow D ^-_ s \pi ^+ $ decays. The first uncertainties are statistical and the second systematic.

Table_8.pdf [44 KiB]
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Table_8.pdf

Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.