The identification of charm jets is achieved at LHCb for data collected in 2015--2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities used in the tagging algorithm. The charm-tagging efficiency is reported as a function of the transverse momentum of the jet. The measured efficiencies are compared to those obtained from simulation and found to be in good agreement.
Depictions of the flavour-enhanced data samples used in this analysis. The jets labelled probe are retained for further analysis. Sub-figures depict (top left) the heavy-flavour-enriched sample and (top right) the light-parton mis-tag enriched sample, as well as the further enriched (bottom left) charm and (bottom right) beauty sub-samples. Some additional requirements are applied but not included in the labeling; see text for details. |
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Background-subtracted (left) invariant mass and (right) $\log\chi^2_{\text{IP}} $ projections and fit results for all (top) $ D ^0 \rightarrow K ^- \pi ^+ $ and (bottom) $ D ^+ \rightarrow K ^- \pi ^+ \pi ^+ $ candidates associated with jets reconstructed in the efficiency-reporting region. The background uncertainties, which are included in the error bars, predominantly affect the displaced components. |
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Probability density functions for (left) $m_{\rm cor}({\rm DV})$ and (right) $N_{\rm trk}({\rm DV})$ used in the fits for (solid green) charm, (dashed red) beauty, and (dotted blue) light-parton jets. |
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DV (left) corrected mass and (right) track multiplicity projections of fits to the flavour-enriched jet samples: (top-to-bottom) beauty-enriched sub-sample, charm-enriched sub-sample, and heavy-flavour-enriched sample fit with data-driven corrections. |
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Detector-response matrices for (left) $ D ^0 $-, (right) $ D ^+ $- and (bottom) DV-tagged charm jets. The shading represents the interval-to-interval migration probabilities ranging from (white) 0 to (black) 1 such that each row sums to unity when the underflow and overflow bins are included. Jets with true (reconstructed) $ p_{\mathrm{T}} (j)$ in the 20--100 $\text{ Ge V}$ region but whose reconstructed (true) $ p_{\mathrm{T}} (j)$ is either below 15 $\text{ Ge V}$ or above 100 $\text{ Ge V}$ are included in the unfolding but not shown graphically. |
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Charm-tagging efficiency in intervals of $ p_{\mathrm{T}}$ determined from (blue triangles) $ D ^0 \rightarrow K ^- \pi ^+ $ and (red squares) $ D ^+ \rightarrow K ^- \pi ^+ \pi ^+ $ decays, as well as (black circles) the weighted average. The points are offset in each $ p_{\mathrm{T}}$ interval to aid visibility. |
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The (left) invariant mass and (right) $\chi^2_{\text{IP}} $ projections of example fits for (top) $ D ^0 \rightarrow K ^- \pi ^+ $ and (bottom) $ D ^+ \rightarrow K ^- \pi ^+ \pi ^+ $ candidates. |
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Branching and fragmentation fractions used to obtain the total charm yields from $ D ^0 \rightarrow K ^- \pi ^+ $ and $ D ^+ \rightarrow K ^- \pi ^+ \pi ^+ $ decays. The PDG [19] averages are used for both branching fractions. Charm fragmentation fractions are based on the global averages reported in Ref. [20], but have been updated as detailed in the text. The fragmentation fractions are inclusive of feed down from excited charm states. |
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Relative systematic uncertainties (%) on the tagging efficiencies determined using the $ D ^0 $ and $ D ^+ $ decays as well as their weighted combination. Ranges of uncertainties are given when the value depends on the $ p_{\mathrm{T}} (j) $ interval. The total systematic uncertainty is evaluated as the sum in quadrature of the uncertainties from all sources. |
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Charm-tagging efficiencies (%) determined in intervals of $ p_{\mathrm{T}} (j) $. First and second uncertainties are statistical and systematic, respectively. |
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Created on 14 December 2021.