Cross-check using non-prompt displaced tracks
We use the combined likelihood fitting procedure to measure the kaon fraction around prompt Ds±/D± mesons.
The fitter includes the KKπ invariant mass and KKπ impact parameter distributions; the TOF and dE/dx distributions of the tracks in the cone for identifying various particle types.
In order to test that the fitting procedure gives sensible results, we test the fitter on a sample for which we have a good estimate of the expected kaon fraction.
For this test we use a sample of displaced tracks with impact parameter in the range 200μm < d0 < 2mm, in a cone of radius ΔR = 0.7 around the reconstructed KKπ candidates.
In the fitting procedure, we measure the kaon fraction fK around the various D components (i.e. prompt, secondary and background), but for this study we are mainly interested in the kaon fraction around the secondary Ds±/D± component produced in B decays.
Basically, the cross-check involves comparing the measured fraction of kaons produced in B decays with predictions of the Monte Carlo event generators.
Since the prompt D± fraction in the data sample is ~94% we do not have sufficient statistics in the secondary D± component for this study.
However, we can do the crosscheck more reliably using the secondary Ds± component that is about 25% of the total Ds± component.
For this study, we do not split the sample of displaced tracks into opposite-sign and same-sign charge tracks since we are not particularly interested in studying charge correlations in the displaced sample.
We compare the measured kaon fraction around secondary Ds± component obtained from the fitting procedure with the kaon fraction around secondary Ds± mesons found in a generic bb-bar sample generated using the PYTHIA event generator.
The kaon fraction measured in ranges of pT is listed in the table below:
The plot below shows a graphical representation of the results:
The results of the study show that the measured kaon fraction around the secondary Ds± component (produced in B decays) is similar to the predictions of the PYTHIA event generator.
This study provides a very useful cross-check of the fitter that is used in the charm fragmentation study.
Note:
Kaons can be produced in B decays in various ways that depend on the B branching fractions and production fractions.
For a direct comparison of the kaon fraction (measured around the secondary Ds± component) with the B branching fractions, the various production fractions for B+/B0 vs Bs0 and the external Ds± emission will have to be accounted for correctly.
Since accounting for all the above mentioned factors is not feasible, we use a generic bb-bar sample for the comparative study instead of comparing directly with B → K X branching fractions.
We expect that all the factors mentioned above are taken into account correctly while generating the generic bb-bar sample using the default decay table in PYTHIA.