New algorithms for identifying the flavour of ${\mathrm {B}} ^0$ mesons using pions and protons

Information

LHCb-PAPER-2016-039
CERN-EP-2016-251
arXiv:1610.06019 [PDF]

(Submitted on 19 Oct 2016)
Eur. Phys. J. C77 (2017) 238
Inspire 1492731

Tools

Abstract

Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 \rightarrow D^- \pi^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.

Figures and captions

Mass distribution of $ B ^0 \rightarrow D^-\pi^+$ candidates with fit projections overlaid. Data points (black dots) correspond to the $ B ^0$ candidates selected in the 2 $ fb^{-1}$ data sample collected at $\sqrt{s} =8 \mathrm{ Te V} $. The solid blue curve represents the total fit function which is the sum of signal (red dashed) and combinatorial background (green dash-dotted).	Fig1.pdf [26 KiB] HiDef png [221 KiB] Thumbnail [178 KiB] *.C file
Distribution of the BDT output of signal (correct-tag decision) and background (wrong-tag decision) tagging particles, for (left) $\rm SS$ $\pi $ and (right) $\rm SS$ $ p $ taggers. In case of multiple tagging candidates per $ B ^0$ candidate, only the candidate with the highest BDT output value is shown.	Fig2a.pdf [19 KiB] HiDef png [963 KiB] Thumbnail [496 KiB] *.C file
	Fig2b.pdf [19 KiB] HiDef png [883 KiB] Thumbnail [461 KiB] *.C file
Measured average mistag fraction in bins of (left) $\rm SS$ $\pi $ and (right) $\rm SS$ $ p $ BDT output. The plots are obtained with the test sample of background-subtracted $ B ^0 \rightarrow D^-\pi^+$ candidates. The green-shaded area shows the confidence range within $\pm 1\sigma$.	Fig3a.pdf [16 KiB] HiDef png [107 KiB] Thumbnail [91 KiB] *.C file
	Fig3b.pdf [16 KiB] HiDef png [122 KiB] Thumbnail [97 KiB] *.C file
(top left) Distribution of the mistag probability $\eta^\rm SS\pi $ and (top right) measured mistag fraction $\omega$ as a function of $\eta^\rm SS\pi $. (bottom left) Distribution of the mistag probability $\eta^\rm SS p $ and (bottom right) measured mistag fraction $\omega$ as a function of $\eta^\rm SS p $. The green-shaded area shows the 68% confidence range.	Fig4a.pdf [14 KiB] HiDef png [96 KiB] Thumbnail [95 KiB] *.C file
	Fig4b.pdf [15 KiB] HiDef png [122 KiB] Thumbnail [92 KiB] *.C file
	Fig4c.pdf [14 KiB] HiDef png [93 KiB] Thumbnail [89 KiB] *.C file
	Fig4d.pdf [15 KiB] HiDef png [131 KiB] Thumbnail [100 KiB] *.C file
Mixing asymmetry in bins of mistag probability using the $\rm SS$ $\pi $ tagger.	Fig5a.pdf [6 KiB] HiDef png [130 KiB] Thumbnail [116 KiB] *.C file
	Fig5b.pdf [6 KiB] HiDef png [128 KiB] Thumbnail [118 KiB] *.C file
	Fig5c.pdf [16 KiB] HiDef png [126 KiB] Thumbnail [115 KiB] *.C file
	Fig5d.pdf [16 KiB] HiDef png [117 KiB] Thumbnail [104 KiB] *.C file
	Fig5e.pdf [15 KiB] HiDef png [111 KiB] Thumbnail [106 KiB] *.C file
Mixing asymmetry in bins of mistag probability using the $\rm SS$ $ p $ tagger.	Fig6a.pdf [15 KiB] HiDef png [134 KiB] Thumbnail [121 KiB] *.C file
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	Fig6d.pdf [15 KiB] HiDef png [117 KiB] Thumbnail [113 KiB] *.C file
	Fig6e.pdf [16 KiB] HiDef png [112 KiB] Thumbnail [106 KiB] *.C file
Animated gif made out of all figures.	PAPER-2016-039.gif Thumbnail

Tables and captions

Expected correlation between the flavour of a $ B $ meson and the hadronization products.	Table_1.pdf [34 KiB] HiDef png [33 KiB] Thumbnail [15 KiB] tex code
Loose selection requirements for the $\rm SS$ $\pi $ and $\rm SS$ $ p $ algorithms. The variables used as input for the BDT classifiers are indicated by \checkmark.	Table_2.pdf [72 KiB] HiDef png [116 KiB] Thumbnail [58 KiB] tex code
Calibration parameters for the $\rm SS$ $\pi $ , $\rm SS$ $ p $ and $\rm SScomb$ taggers where the first uncertainties are statistical and the second are systematic.	Table_3.pdf [37 KiB] HiDef png [59 KiB] Thumbnail [26 KiB] tex code
Tagging efficiencies and tagging power of the $\rm SS$ $\pi $ , $\rm SS$ $ p $ and $\rm SScomb$ algorithms. The $\rm SScomb$ efficiencies are shown splitting the sample in candidates tagged exclusively by $\rm SS$ $\pi $ or $\rm SS$ $ p $ , or by both. As explained in the text, there is a large overlap between the $\rm SS$ $\pi $ and $\rm SS$ $ p $ taggers.	Table_4.pdf [39 KiB] HiDef png [67 KiB] Thumbnail [34 KiB] tex code
Calibration parameters for the $ B ^0 \rightarrow K ^+ \pi ^- $ decay sample. Uncertainties are statistical only.	Table_5.pdf [38 KiB] HiDef png [39 KiB] Thumbnail [16 KiB] tex code
Systematic uncertainties on the calibration parameters of $\rm SS$ $\pi $ , $\rm SS$ $ p $ and $\rm SScomb$ taggers. The total systematic uncertainty is the squared sum of all contributions. A dash indicates a value negligible with respect to the quoted precision.	Table_6.pdf [32 KiB] HiDef png [109 KiB] Thumbnail [48 KiB] tex code
Systematic uncertainties related to the decay-time model. A dash indicates a value negligible with respect to the quoted precision.	Table_7.pdf [31 KiB] HiDef png [47 KiB] Thumbnail [22 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [1 MiB]
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2016-039. The files are: Supplementary.pdf : An overview of the extra figures .pdf, .png, .eps, .C : The figures in variuous formats	Fig7a.pdf [16 KiB] HiDef png [134 KiB] Thumbnail [124 KiB] *C file
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