cern.ch

Observation of the suppressed $\Lambda_b^0\to D p K^-$ decay with $D\to K^+ \pi^-$ and measurement of its $C P$ asymmetry

[to restricted-access page]

Information

Tools

Abstract

A study of $\Lambda_b^0$ baryon decays to the $DpK^-$ final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of 9 fb$^{-1}$ collected with the LHCb detector. Two $\Lambda_b^0$ decays are considered, $\Lambda_b^0\to DpK^-$ with $D\to K^-\pi^+$ and $D\to K^+\pi^-$, where $D$ represents a superposition of $D^0$ and $\overline{D}^0$ states. The latter process is expected to be suppressed relative to the former, and is observed for the first time. The ratio of branching fractions of the two decays is measured, and the $C P$ asymmetry of the suppressed mode, which is sensitive to the CKM angle $\gamma$, is also reported.

Figures and captions

Distributions of the invariant mass for selected (left) $\Lambda ^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} p K ^- $ and (right) $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ candidates in the full phase space (black points) corresponding to the favoured and suppressed decays, respectively. The total fit model, as described in the text, is indicated by the solid blue line, and individual components are indicated.

 Fig1a.pdf [30 KiB]
HiDef png [462 KiB]
Thumbnail [371 KiB]
*.C file
Fig1a.pdf
Fig1b.pdf [24 KiB]
HiDef png [348 KiB]
Thumbnail [308 KiB]
*.C file
Fig1b.pdf

Distributions of the invariant mass for (left) $\Lambda ^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} p K ^- $ and (right) $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ candidates, corresponding to the favoured and suppressed decays, respectively, in the restricted phase-space region $M^2(p K ^- )<5 \text{ Ge V} ^2 /c^4 $. The fit, as described in the text, is overlaid.

 Fig2a.pdf [30 KiB]
HiDef png [460 KiB]
Thumbnail [383 KiB]
*.C file
Fig2a.pdf
Fig2b.pdf [24 KiB]
HiDef png [367 KiB]
Thumbnail [342 KiB]
*.C file
Fig2b.pdf

Distributions of the invariant mass for (left) $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ and (right) $\overline{ \Lambda} {}^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} \overline p K ^+ $ candidates in the full phase space (black points), corresponding to separation of the suppressed decay sample by $\Lambda ^0_ b $ flavour. The fit, as described in the text, is indicated by the solid blue line, and individual components are indicated.

 Fig3a.pdf [24 KiB]
HiDef png [358 KiB]
Thumbnail [319 KiB]
*.C file
Fig3a.pdf
Fig3b.pdf [24 KiB]
HiDef png [354 KiB]
Thumbnail [321 KiB]
*.C file
Fig3b.pdf

Distributions of the invariant mass for (left) $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ and (right) $\overline{ \Lambda} {}^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} \overline p K ^+ $ candidates in the restricted phase-space region (black points), where the separation is made according to the $\Lambda ^0_ b $ flavour. The fit, as described in the text, is indicated by the solid blue line, and individual components are indicated.

 Fig4a.pdf [21 KiB]
HiDef png [325 KiB]
Thumbnail [293 KiB]
*.C file
Fig4a.pdf
Fig4b.pdf [22 KiB]
HiDef png [339 KiB]
Thumbnail [302 KiB]
*.C file
Fig4b.pdf

Phase space of the (left) $\Lambda ^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} p K ^- $ and (right) $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ candidates having a mass between 5600 and 5640 $\text{ Me V /}c^2$ . No background subtraction is applied.

 Fig5a.pdf [66 KiB]
HiDef png [204 KiB]
Thumbnail [116 KiB]
*.C file
Fig5a.pdf
Fig5b.pdf [24 KiB]
HiDef png [133 KiB]
Thumbnail [79 KiB]
*.C file
Fig5b.pdf

Invariant-mass projections of the $\Lambda ^0_ b $ phase space in (left) $M( D p )$, (middle) $M( p K ^- $), and (right) $M( D K ^- $) for the $\Lambda ^0_ b \rightarrow [ K ^- \pi ^+ ]_{D} p K ^- $ candidates.

 Fig6a.pdf [17 KiB]
HiDef png [131 KiB]
Thumbnail [80 KiB]
*.C file
Fig6a.pdf
Fig6b.pdf [17 KiB]
HiDef png [130 KiB]
Thumbnail [76 KiB]
*.C file
Fig6b.pdf
Fig6c.pdf [17 KiB]
HiDef png [140 KiB]
Thumbnail [84 KiB]
*.C file
Fig6c.pdf

Invariant-mass projections of the $\Lambda ^0_ b $ phase space in (left) $M( D p )$, (middle) $M( p K ^- $), and (right) $M( D K ^- $) for the $\Lambda ^0_ b \rightarrow [ K ^+ \pi ^- ]_{D} p K ^- $ candidates.

 Fig7a.pdf [17 KiB]
HiDef png [135 KiB]
Thumbnail [78 KiB]
*.C file
Fig7a.pdf
Fig7b.pdf [17 KiB]
HiDef png [137 KiB]
Thumbnail [80 KiB]
*.C file
Fig7b.pdf
Fig7c.pdf [17 KiB]
HiDef png [133 KiB]
Thumbnail [83 KiB]
*.C file
Fig7c.pdf

Relative efficiency correction as a function of position within the $\Lambda ^0_ b $ phase space, obtained from simulated samples.

 Fig8.pdf [40 KiB]
HiDef png [309 KiB]
Thumbnail [495 KiB]
*.C file
Fig8.pdf

Animated gif made out of all figures.

 PAPER-2021-027.gif
Thumbnail
thumbnail_PAPER-2021-027.gif

Tables and captions

Signal $\Lambda ^0_ b $ yields obtained from fits to the invariant-mass distributions, $M(Dp K ^- )$, for the favoured and suppressed decay samples in the two phase-space regions.

 Table_1.pdf [68 KiB]
HiDef png [25 KiB]
Thumbnail [12 KiB]
tex code 		Table_1.pdf

Absolute uncertainties on the ratio of branching fractions, $R$, and $ C P$ asymmetry, $A$, related to the sources of systematic uncertainty studied. The statistical and total systematic uncertainties are also shown.

 Table_2.pdf [72 KiB]
HiDef png [170 KiB]
Thumbnail [77 KiB]
tex code 		Table_2.pdf

Created on 26 April 2024.