A search for $C$P and $P$ violation using triple-product asymmetries is performed with $\Lambda^{0}_{b}\to pK^{-}\pi^{+}\pi^{-}$, $\Lambda^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $\Xi^{0}_{b}\to pK^{-}K^{-}\pi^{+}$ decays. The data sample corresponds to integrated luminosities of 1.0fb$^{-1}$ and 2.0fb$^{-1}$, recorded with the LHCb detector at centre-of-mass energies of 7TeV and 8TeV, respectively. The $CP$- and $P$-violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from $CP$ or $P$ symmetry is found. The first observation of $\Lambda^{0}_{b}\to pK^{-}\chi_{c0}(1P)(\to\pi^{+}\pi^{-}, K^{+}K^{-})$ decay is also reported.
Distributions of the $p K ^- \pi ^+ \pi ^- $ invariant mass in the four samples defined by the $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) flavour and the sign of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The results of the fit are overlaid as described in the legend. The contribution of the cross-feeds to the fit results is barely visible but is found to be nonnegligible. |
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Distributions of the $p K ^- K ^+ K ^- $ invariant mass in the four samples defined by the $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) flavour and the sign of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The results of the fit are overlaid as described in the legend. The contribution of the cross-feeds to the fit results is barely just visible but is found to be nonnegligible. |
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Distributions of the $p K ^- K ^- \pi ^+ $ invariant mass in the four samples defined by the $\Xi ^0_ b $ ( $\overline \Xi {}_ b ^0$ ) flavour and the sign of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The results of the fit are overlaid as described in the legend. The contribution of the $ B ^0 \rightarrow K ^- K ^+ K ^+ \pi ^- $ cross-feed to the fit results is barely visible but is found to be nonnegligible. |
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The asymmetries using binning schemes (left) A and (right) B for the $\Lambda ^0_ b \rightarrow p K ^- \pi ^+ \pi ^- $ decay. For $ a_P^{\widehat{T}\text{-odd}}$ ( $ a_ C P ^{\widehat{T}\text{-odd}}$ ), the values of the $\chi^2$ /ndf for the $P$-symmetry ( $ C P$ -symmetry) hypothesis, represented by a dashed line, are quoted. |
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The asymmetries using binning schemes (left) C and (right) D for $\Lambda ^0_ b \rightarrow p K ^- K ^+ K ^- $ decay. For $ a_P^{\widehat{T}\text{-odd}}$ ( $ a_ C P ^{\widehat{T}\text{-odd}}$ ), the values of the $\chi^2$ /ndf for the $P$-symmetry ( $ C P$ -symmetry) hypothesis, represented by a dashed line, are quoted. |
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The left (right) plot shows the distribution of the $\pi^+\pi^-$ ($K^{+}K^{-}_{\textrm{fast}}$) reconstructed invariant mass for $\Lambda ^0_ b $ candidates selected within $\pm2\sigma$ of the $\Lambda ^0_ b $ mass peak. The results of the fit for different signal and background components are overlaid as described in the legend. |
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Background-subtracted distributions of $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) candidates in different regions of phase space of the $\Lambda ^0_ b \rightarrow p K ^- \pi ^+ \pi ^- $ decay for different values of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The background subtraction is performed using the $sPlot$ technique [27]. |
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Background-subtracted distributions of $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) candidates in different regions of phase space of the $\Lambda ^0_ b \rightarrow p K ^- \pi ^+ \pi ^- $ decay for different values of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The background subtraction is performed using the $sPlot$ technique [27]. |
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Background-subtracted distributions of $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) candidates in different regions of phase space of the $\Lambda ^0_ b \rightarrow p K ^- K ^+ K ^- $ decay for different values of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The background subtraction is performed using the $sPlot$ technique [27]. |
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Background-subtracted distributions of $\Lambda ^0_ b $ ( $\overline{\Lambda} {}^0_ b $ ) candidates in different regions of phase space of the $\Lambda ^0_ b \rightarrow p K ^- K ^+ K ^- $ decay for different values of $ C_{\widehat{T}}$ ( $\overline{ C}_{\widehat{T}}$ ). The background subtraction is performed using the $sPlot$ technique [27]. |
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Animated gif made out of all figures. |
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Selection window for control samples used to assess systematic uncertainties and for selection criteria optimization. |
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Measurements of the $ C P$ - and $P$-violating observables $ a_ C P ^{\widehat{T}\text{-odd}}$ and $ a_P^{\widehat{T}\text{-odd}}$ , together with their statistical and systematic uncertainties. |
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Sources of systematic uncertainty and their relative contributions to the total uncertainty. Where present, the value in brackets shows the systematic uncertainty assigned to the measurement in specific phase-space regions. |
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Definition of the 14 regions that form scheme A for the $\Lambda ^0_ b \rightarrow p K ^- \pi ^+ \pi ^- $ decay. Bins $1-4$ focus on the region dominated by the $\Delta(1232)^{++}\rightarrow p\pi ^+ $ resonance. The other 10 bins are defined to study regions where $p K ^- $ resonances are present on either side of the $f_0(980)\rightarrow \pi ^+ \pi ^- $ or $\overline{ K }{} {}^{*}(892)^{0} \rightarrow K ^- \pi ^+ $ resonances. Further splitting depending on $|\Phi|$ is performed to reduce potential dilution of asymmetries, as suggested in Ref. [14]. Masses are in units of $ {\mathrm{ Ge V /}c^2}$ . |
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Measurements of $ a_P^{\widehat{T}\text{-odd}}$ and $ a_ C P ^{\widehat{T}\text{-odd}}$ in specific phase-space regions for the $\Lambda ^0_ b \rightarrow p K ^- \pi ^+ \pi ^- $ decay. Each value is obtained through an independent fit to the candidates in the corresponding region of the phase space. Scheme A is defined in Table 4 and divides the phase space according to dominant resonant contributions, while scheme B consists of twelve non-overlapping bins of width $\pi/12$ in $|\Phi|$. |
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Definition of the seven regions that form scheme C for the $\Lambda ^0_ b \rightarrow p K ^- K ^+ K ^- $ decay. The scheme is defined to study regions where $ p K_{\rm slow}^-$ resonances are present ($1-3$) on either side of the $\Phi\rightarrow K ^+ K ^- $ resonances. Masses are in units of $ {\mathrm{ Ge V /}c^2}$ . |
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Measurements of $ a_P^{\widehat{T}\text{-odd}}$ and $ a_ C P ^{\widehat{T}\text{-odd}}$ in specific phase-space regions for the $\Lambda ^0_ b \rightarrow p K ^- K ^+ K ^- $ decay. Each value is obtained through an independent fit to the candidates in the corresponding region of the phase space. Scheme C is defined in Table 6 and divides the phase space according to dominant resonant contributions, while scheme D consists of ten non-overlapping bins of width $\pi/10$ in $|\Phi|$. |
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Created on 18 May 2024.