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Measurement of $B^+$, $B^0$ and $\Lambda_b^0$ production and nuclear modification in $p$Pb collisions at $\sqrt{s_\mathrm{NN}}=8.16 \text {TeV}$

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Abstract

The production of $ B ^+ $, $ B ^0 $ and $\Lambda ^0_ b $ hadrons is studied in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\scriptscriptstyle\rm NN}} $ $=$ 8.16 TeV with the LHCb detector at the LHC. The measurement uses an integrated luminosity of $12.2\pm0.3\,nb^{-1} $ for the proton beam projecting into the LHCb detector (positive rapidity) and $18.6\pm0.5\,nb^{-1} $ for the lead beam projecting into the LHCb detector (negative rapidity). Nuclear effects in proton-lead data are probed by double-differential cross-sections, forward-to-backward cross-section ratios and nuclear modification factors of the beauty hadrons. The double-differential cross-sections are measured as function of the beauty hadron transverse momentum and rapidity in the nucleon-nucleon centre-of mass frame. Forward-to-backward cross-section ratios and nuclear modification factors indicate a significant nuclear suppression at positive rapidity compared to $pp$ collisions and compared to negative rapidity. The baryon-to-meson ratio of $\Lambda ^0_ b $ over $ B ^0$ is reported as well and exhibits a value consistent with the same measurements in $pp$ collisions at positive rapidity, whereas tensions are observed at negative rapidity.

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Mass fit results for the $ B ^+ \!\rightarrow \overline{ D }{} {}^0 \pi ^+ $ decay for (left) $ p\mathrm{Pb}$ and (right) $\mathrm{Pb}p$ . The solid blue line, the solid green line, the cross-shaded area, the brown shaded area and the red shaded area represent the total fit, the signal component, the partially reconstructed background the combinatorial background and misidentified background, respectively.

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Mass fit results for the $ B ^+ \!\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ decay for (left) $ p\mathrm{Pb}$ and (right) $\mathrm{Pb}p$ . The solid blue line, the solid green line, the cross-shaded area, the brown shaded area and the red shaded area represent the total fit, the signal component, the partially reconstructed background the combinatorial background and misidentified background, respectively.

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Mass fit results for the $ B ^0 \!\rightarrow D ^- \pi ^+ $ decay for (left) $ p\mathrm{Pb}$ and (right) $\mathrm{Pb}p$ . The solid blue line, the solid green line, the cross-shaded area, the brown shaded area and the red shaded area represent the total fit, the signal component, the partially reconstructed background the combinatorial background and misidentified background, respectively.

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Mass fit results of $\Lambda ^0_ b \!\rightarrow \Lambda ^+_ c \pi ^- $ for the $\Lambda ^0_ b \!\rightarrow \Lambda ^+_ c \pi ^- $ decay for (left) $ p\mathrm{Pb}$ and (right) $\mathrm{Pb}p$ . The solid blue line, the solid green line, the cross-shaded area, the brown shaded area and the red shaded area represent the total fit, the signal component, the partially reconstructed background the combinatorial background and misidentified background, respectively.

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Production cross-section of $ B ^+ $ mesons as a function of (left) $ p_{\mathrm{T}}$ in $y$ bins and (right) $y$ integrated over $ p_{\mathrm{T}}$ . The bars (boxes) show statistical (systematic) uncertainties.

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Production cross-section of $ B ^0 $ mesons as function of (left) $ p_{\mathrm{T}}$ in $y$ bins and (right) $y$ integrated over $ p_{\mathrm{T}}$ . The bars (boxes) show statistical (systematic) uncertainties.

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Production cross-section of $\Lambda ^0_ b $ baryons as a function of (left) $ p_{\mathrm{T}}$ in $y$ bins and (right) $y$ integrated over $ p_{\mathrm{T}}$ . The bars (boxes) show statistical (systematic) uncertainties.

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Production cross-section ratios of $\Lambda ^0_ b $ baryons over $ B ^0 $ and $ B ^0 $ over $ B ^+ $ (top) as a function of $y$ integrated over $ p_{\mathrm{T}}$ and as a function of $ p_{\mathrm{T}}$ for (bottom left) $2.5<y<3.5$ and (bottom right) $-3.5<y<-2.5$. The bars (boxes) show statistical (systematic) uncertainties.

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Forward-backward ratio $R_{\rm FB}$ of $ B ^+ $ as a function of (left) $ p_{\mathrm{T}}$ and as a function of (right) $y$ in proton-lead collisions compared with HELAC-onia calculations using different nPDF sets. For the data points, the bars (boxes) represent the statistical (systematic) uncertainties. The rapidity range $2.5<| y |<3.5$ represents the common range between the $ p\mathrm{Pb}$ and $\mathrm{Pb}p$ data samples studied in this analysis.

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$R_{\rm FB}$ of $ B ^0 $ as a function of (left) $ p_{\mathrm{T}}$ and as a function of (right) $y$ in proton-lead collisions. The bars (boxes) represent the statistical (systematic) uncertainties.

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$R_{\rm FB}$ of $\Lambda ^0_ b $ as a function of (left) $ p_{\mathrm{T}}$ and of (right) $y$ in proton-lead collisions. The bars (boxes) represent the statistical (systematic) uncertainties.

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$R_{\rm FB}$ of (red) $ B ^+ $, (blue) $ B ^0 $ and (green) $\Lambda ^0_ b $ as a function of (left) $ p_{\mathrm{T}}$ and of (right) $y$ in proton-lead collisions. The bars (boxes) represent the statistical (systematic) uncertainties.

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$R^{\Lambda ^0_ b / B ^0 }_{\text{pPb}}$ as a function of (left) $ p_{\mathrm{T}}$ and of (right) $y$ in $p$Pb and Pb$p$ collisions. The bars (boxes) represent the statistical (systematic) uncertainties.

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$R_{ p\mathrm{Pb} }$ of $ B ^+ $ mesons as function of (top) $y$ and as function of $ p_{\mathrm{T}}$ in (bottom left) $p$Pb and (bottom right) Pb$p$ compared with HELAC-onia calculations using different nPDF sets as well as with the measurement of nonprompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $R_{ p\mathrm{Pb} }$. For the data points, the bars (boxes) represent the statistical (systematic) uncertainties.

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Tables and captions

Signal yields in the $ p_{\mathrm{T}} $ range $2< p_{\mathrm{T}} <20 {\mathrm{\,GeV\!/}c} $, and the rapidity range $1.5< y <3.5$ for $ p\mathrm{Pb}$ and $-4.5< y <-2.5$ for $\mathrm{Pb}p$ .

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Summary of systematic uncertainties (in %) for the measured cross-sections for different decay modes in $ p\mathrm{Pb}$ . The ranges correspond to the minimum and maximum values over the $ p_{\mathrm{T}}$ and $ y$ bins of the beauty hadrons.

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Summary of systematic uncertainties (in %) for the measured cross-sections for different decay modes in $\mathrm{Pb}p$ . The ranges correspond to the minimum and maximum values over the $ p_{\mathrm{T}}$ and $ y$ bins of the beauty hadrons.

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