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Measurement of the properties of the $\Xi_b^{*0}$ baryon

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Abstract

We perform a search for near-threshold $\Xi_b^0$ resonances decaying to $\Xi_b^- \pi^+$ in a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by the LHCb experiment. We observe one resonant state, with the following properties: \begin{eqnarray*} m(\Xi_b^{*0}) - m(\Xi_b^-) - m(\pi^+) &=& 15.727 \pm 0.068 (\mathrm{stat}) \pm 0.023 (\mathrm{syst}) \mathrm{MeV}/c^2, \Gamma(\Xi_b^{*0}) &=& 0.90 \pm 0.16 (\mathrm{stat}) \pm 0.08 (\mathrm{syst}) \mathrm{MeV} . \end{eqnarray*} This confirms the previous observation by the CMS collaboration. The state is consistent with the $J^P=3/2^+$ $\Xi_b^{*0}$ resonance expected in the quark model. This is the most precise determination of the mass and the first measurement of the natural width of this state. We have also measured the ratio \begin{align*} \frac{\sigma(pp \to \Xi_b^{*0} X){\cal{B}}(\Xi_b^{*0} \to \Xi_b^- \pi^+)}{\sigma(pp \to \Xi_b^- X)} = 0.28 \pm 0.03 (\mathrm{stat}) \pm 0.01 (\mathrm{syst}) . \end{align*}

Figures and captions

Mass spectra of (left) $\Xi ^0_ c $ and (right) $\Xi ^-_ b $ candidates after all selection requirements are imposed, except for the one on the mass that is plotted. The vertical dashed lines show the selection requirements used in forming $\Xi ^-_ b $ and $\Xi ^{*0}_ b $ candidates.

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paperPlot-mXic.pdf
paperP[..].pdf [18 KiB]
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paperPlot-mXib.pdf

Distribution of $\delta m$. Right-sign candidates (RS, $\Xi ^-_ b \pi ^+ $) are shown as points with error bars, and wrong-sign candidates (WS, $\Xi ^-_ b \pi ^- $) as a histogram. A single narrow structure is seen in the right-sign data.

 paperP[..].pdf [19 KiB]
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paperPlot-dm-wideRange.pdf

Distribution of $\delta m$ along with the results of the fit described in the text.

 paperP[..].pdf [31 KiB]
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paperPlot-dm-fit.pdf

Distribution of $\delta m$, using only events in which one or more of the $\Xi ^-_ b $ decay products pass the L0 hadron trigger requirements. The results of the fit are overlaid.

 paperP[..].pdf [30 KiB]
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paperPlot-dm-fit-L0TOS.pdf

Invariant mass spectrum of selected $\Xi ^0_ c \pi ^- $ candidates. The fit described in the text is overlaid. The $\Xi ^-_ b $ signal peak and background from combinatorial events are clearly visible, accompanied by small contributions from the peaking background processes $\Xi ^-_ b \rightarrow \Xi ^0_ c \rho^-$ and $\Xi ^-_ b \rightarrow \Xi ^0_ c K ^- $.

 Xib2Xi[..].pdf [30 KiB]
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Xib2Xic0Pi_def_L0Had_Y0_05022016.pdf

Animated gif made out of all figures.

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Tables and captions

Systematic uncertainties, in units of $ {\mathrm{ Me V /}c^2}$ (mass) and $\mathrm{ Me V}$ (width).

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Relative systematic uncertainties on the production ratio.

 Table_2.pdf [46 KiB]
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Created on 10 July 2020.