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Study of the decay $B^+ \rightarrow K^+\pi^0$ at LHCb

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Abstract

This analysis investigates the capability of LHCb to study the decay mode $ B ^+ \!\rightarrow K ^+ \pi ^0 $ {}. This serves as a prototype analysis for decay channels with similar topologies, such as the $ B ^0 \!\rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^0 $ , the $\Lambda ^0_ b \!\rightarrow \Lambda \gamma $ , and the $ B ^0 \!\rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^0 \gamma $ decays, which involve photons in the final state and lack a reconstructed decay vertex. There is significant interest in these channels due to their sensitivity to effects of physics beyond the standard model. The proton-proton collision data set collected in 2011--2012, corresponding to 3.0 $\,fb^{-1}$ of integrated luminosity, is studied. An analysis strategy is developed to mitigate the effects of low trigger efficiency and large combinatorial background leading to the reconstruction of $72\pm26$ signal events with a statistical significance of $3.7\sigma.$ Based on the findings of this study, a dedicated software trigger is being developed for use in the next data-taking period scheduled for later this year, when the LHC centre-of-mass energy will be increased.

Figures and captions

MT-DOCA and the reconstructed $ B ^+ \!\rightarrow K ^+ \pi ^0 $ {} decay topology.

MTD_with.pdf [28 KiB]
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*.C file
MTD_with.pdf

Signal and background distributions of $\log_{10}(\chi^2 _{\text{MT-DOCA}})$ for 2012 conditions. The signal contribution from simulated data is shown in hatched blue, and the background contribution from mass sidebands in the recorded data is shown in hatched red.

mtdChi[..].pdf [14 KiB]
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*.C file
mtdChi2LogPlot.pdf

Mass distribution of the reconstructed candidates, selected from the entire data set. The data are drawn as black points. The fit to the $ B ^+$ reconstructed mass is drawn as a solid blue line. The signal component is drawn in dashed blue, the combinatorial background is drawn in dashed purple, and the low-mass background is drawn in dashed magenta.

massFit.pdf [18 KiB]
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massFit.pdf

Reconstructed $ B ^+$ mass distribution from simulated data of $ B ^+ \!\rightarrow K ^+ \pi ^0 $ {} decays that pass the selection requirements.

mgdMass.pdf [16 KiB]
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mgdMass.pdf

Distribution of the classifier response variable. The signal contribution from simulated data is shown in solid blue, and the background contribution from experimental data is shown in hatched red.

BDTRes[..].pdf [22 KiB]
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*.C file
BDTResponseLarge.pdf

Animated gif made out of all figures.

CONF-2015-001.gif
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thumbnail_CONF-2015-001.gif

Created on 11 December 2018.Citation count from INSPIRE on 11 December 2018.