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Measurement of $B^+$, $B^0$ and $\Lambda_b^0$ production in $p\mkern 1mu\mathrm{Pb}$ collisions at $\sqrt{s_{NN}} = 8.16 \ \rm TeV$

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Abstract

The production of $B^+$, $B^0$ and $\Lambda_b^0$ hadrons is studied in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}}=8.16 {\rm TeV}$ recorded with the LHCb detector at the LHC. The measurement uses a dataset corresponding to an integrated luminosity of $12.2\pm0.3 \mathrm{nb}^{-1}$ for the case where the proton beam is projected into the LHCb detector (corresponding to measuring hadron production at positive rapidity) and $18.6\pm0.5 \mathrm{nb}^{-1}$ for the lead beam projected into the LHCb detector (corresponding to measuring hadron production at negative rapidity). Nuclear effects are probed through 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 a 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. The ratio of $\Lambda_b^0$ over $B^0$ production cross-sections is reported and is consistent with the corresponding measurement in $pp$ collisions.

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Invariant mass distribution of $ B ^+ $ candidates reconstructed in the $ B ^+ \rightarrow \overline{ D } {}^0 \pi ^+ $ decay for (left) $ p\mkern 1mu\mathrm{Pb}$ and (right) $\mathrm{Pb}\mkern 1.5mu p$ collisions, with the fit result superimposed. 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 $ B ^+ \rightarrow \overline{ D } {}^0 K ^+ $ decays, respectively.

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Invariant mass distribution of $ B ^+ $ candidates reconstructed in the $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ decay for (left) $ p\mkern 1mu\mathrm{Pb}$ and (right) $\mathrm{Pb}\mkern 1.5mu p$ collisions, with the fit result superimposed. 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 $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ $ decays, respectively.

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Invariant mass distribution of $ B ^0 $ candidates reconstructed in the $ B ^0 \rightarrow D ^- \pi ^+ $ decay for (left) $ p\mkern 1mu\mathrm{Pb}$ and (right) $\mathrm{Pb}\mkern 1.5mu p$ collisions, with the fit result superimposed. 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 $ B ^0 \rightarrow D ^- K ^+ $ decays, respectively.

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Invariant mass distribution of $\Lambda ^0_ b $ candidates reconstructed in the $\Lambda ^0_ b \rightarrow \Lambda ^+_ c \pi ^- $ decay for (left) $ p\mkern 1mu\mathrm{Pb}$ and (right) $\mathrm{Pb}\mkern 1.5mu p$ collisions, with the fit result superimposed. 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 $\Lambda ^0_ b \rightarrow \Lambda ^+_ c K ^- $ decays, 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 vertical bars (boxes) show statistical (total) 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 vertical bars (boxes) show statistical (total) 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 vertical bars (boxes) show statistical (total) uncertainties.

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Production cross-section ratios of $\Lambda ^0_ b $ baryons over $ B ^0 $ mesons and of $ B ^0 $ mesons over $ B ^+ $ mesons (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 vertical bars (boxes) show statistical (total) uncertainties.

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Forward-backward ratio, $R_{\rm FB}$, for $ B ^+ $ mesons as a function of (left) $ p_{\mathrm{T}}$ and (right) $y$ in proton-lead collisions compared with HELAC-onia calculations using different nPDF sets. For the data points, the vertical bars (boxes) represent the statistical (total) uncertainties. The rapidity range $2.5<| y |<3.5$ represents the common range between the $ p\mkern 1mu\mathrm{Pb}$ and $\mathrm{Pb}\mkern 1.5mu p$ data samples studied in this analysis.

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

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

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Forward-backward ratio, $R_{\rm FB}$, of (red) $ B ^+ $, (blue) $ B ^0 $ mesons and (green) $\Lambda ^0_ b $ baryons as a function of (left) $ p_{\mathrm{T}}$ and (right) $y$ in proton-lead collisions. The vertical bars (boxes) represent the statistical (total) uncertainties. Data points are shifted horizontally for better visibility.

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Ratio of nuclear modification factors, $R^{\Lambda ^0_ b / B ^0 }_{ p\mkern 1mu\mathrm{Pb} }$, as a function of (left) $ p_{\mathrm{T}}$ and (right) $y$ in $ p\mkern 1mu\mathrm{Pb} $ and $\mathrm{Pb}\mkern 1.5mu p $ collisions. The vertical bars (boxes) represent the statistical (total) uncertainties.

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Nuclear modification factor, $R_{ p\mkern 1mu\mathrm{Pb} }$, for $ B ^+ $ mesons as function of (top) $y$ and as a function of $ p_{\mathrm{T}}$ in (bottom left) $ p\mkern 1mu\mathrm{Pb} $ and (bottom right) $\mathrm{Pb}\mkern 1.5mu p $ compared with HELAC-onia calculations using different nPDF sets as well as with the measurement of $R_{ p\mkern 1mu\mathrm{Pb} }$ for nonprompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production. For the data points, the vertical bars (boxes) represent the statistical (total) uncertainties.

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Tables and captions

Signal yields in the range $2< p_{\mathrm{T}} <20\text{ Ge V /}c $ and $1.5< y <3.5$ ($-4.5< y <-2.5$) for $ p\mkern 1mu\mathrm{Pb}$ ( $\mathrm{Pb}\mkern 1.5mu p$ ) collisions. Uncertainties are statistical only.

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Summary of systematic uncertainties (in %) for the measured cross-sections for different decay modes in $ p\mkern 1mu\mathrm{Pb}$ . The ranges correspond to the minimum and maximum values over the $ p_{\mathrm{T}}$ and $ y$ bins of the measurement.

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Summary of systematic uncertainties (in %) for the measured cross-sections for different decay modes in $\mathrm{Pb}\mkern 1.5mu p$ . The ranges correspond to the minimum and maximum values over the $ p_{\mathrm{T}}$ and $ y$ bins of the measurement.

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Differential cross-sections of $ B ^+ $ , $ B ^0$ and $\Lambda ^0_ b $ production in bins of $ p_{\mathrm{T}}$ and $y$, $\frac{{\rm d}^2\sigma}{{\rm d} p_{\mathrm{T}} {\rm d}y}( \upmu\text{b} /[ \text{ Ge V /}c ])$, and in bins of $y$ integrated over $2< p_{\mathrm{T}} <20\text{ Ge V /}c $, $\frac{{\rm d}\sigma}{{\rm d}y} ( \upmu\text{b} )$. The first uncertainty is statistical and the second systematic.

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Forward-backward ratios, $R_{\rm FB}$, of $ B ^+ $ , $ B ^0$ and $\Lambda ^0_ b $ production in bins of $ p_{\mathrm{T}}$ and integrated over $2.5<|y|<3.5$. The first uncertainty is statistical and the second systematic.

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Ratios of nuclear modification factors, $R^{\Lambda ^0_ b / B ^0 }_{ p\mkern 1mu\mathrm{Pb} }$, in bins of $ p_{\mathrm{T}}$ and integrated over $2.5<|y|<3.5$, for $ p\mkern 1mu\mathrm{Pb} $ and $\mathrm{Pb}\mkern 1.5mu p $ samples. The first uncertainty is statistical and the second systematic.

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Nuclear modification factor, $R_{ p\mkern 1mu\mathrm{Pb} }$, of $ B ^+ $ production in $ p\mkern 1mu\mathrm{Pb} $ and $\mathrm{Pb}\mkern 1.5mu p $ collisions, in bins of $ p_{\mathrm{T}}$ for the range $2.5<|y|<3.5$. The first uncertainty is statistical and the second systematic.

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Created on 19 October 2019.