# Search for CP violation using triple product asymmetries in $\Lambda^{0}_{b}\to pK^{-}\pi^{+}\pi^{-}$, $\Lambda^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $\Xi^{0}_{b}\to pK^{-}K^{-}\pi^{+}$ decays

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## Abstract

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.

## Figures and captions

 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. Fig1a.pdf [30 KiB] HiDef png [391 KiB] Thumbnail [131 KiB] Fig1b.pdf [30 KiB] HiDef png [396 KiB] Thumbnail [132 KiB] Fig1c.pdf [30 KiB] HiDef png [387 KiB] Thumbnail [131 KiB] Fig1d.pdf [30 KiB] HiDef png [389 KiB] Thumbnail [131 KiB] 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. Fig2a.pdf [29 KiB] HiDef png [360 KiB] Thumbnail [124 KiB] Fig2b.pdf [29 KiB] HiDef png [357 KiB] Thumbnail [124 KiB] Fig2c.pdf [29 KiB] HiDef png [356 KiB] Thumbnail [123 KiB] Fig2d.pdf [29 KiB] HiDef png [363 KiB] Thumbnail [125 KiB] 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. Fig3a.pdf [24 KiB] HiDef png [356 KiB] Thumbnail [129 KiB] Fig3b.pdf [24 KiB] HiDef png [359 KiB] Thumbnail [130 KiB] Fig3c.pdf [24 KiB] HiDef png [359 KiB] Thumbnail [129 KiB] Fig3d.pdf [24 KiB] HiDef png [355 KiB] Thumbnail [129 KiB] 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. Fig4a.pdf [15 KiB] HiDef png [144 KiB] Thumbnail [36 KiB] Fig4b.pdf [15 KiB] HiDef png [130 KiB] Thumbnail [33 KiB] 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. Fig5a.pdf [14 KiB] HiDef png [133 KiB] Thumbnail [33 KiB] Fig5b.pdf [15 KiB] HiDef png [128 KiB] Thumbnail [33 KiB] 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. Fig6a.pdf [26 KiB] HiDef png [338 KiB] Thumbnail [124 KiB] Fig6b.pdf [26 KiB] HiDef png [352 KiB] Thumbnail [124 KiB] 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]. Fig7a.pdf [26 KiB] HiDef png [137 KiB] Thumbnail [29 KiB] Fig7b.pdf [25 KiB] HiDef png [135 KiB] Thumbnail [28 KiB] Fig7c.pdf [24 KiB] HiDef png [126 KiB] Thumbnail [28 KiB] Fig7d.pdf [25 KiB] HiDef png [124 KiB] Thumbnail [28 KiB] 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]. Fig8a.pdf [25 KiB] HiDef png [124 KiB] Thumbnail [28 KiB] Fig8b.pdf [26 KiB] HiDef png [139 KiB] Thumbnail [29 KiB] Fig8c.pdf [25 KiB] HiDef png [125 KiB] Thumbnail [28 KiB] Fig8d.pdf [22 KiB] HiDef png [113 KiB] Thumbnail [25 KiB] 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]. Fig9a.pdf [25 KiB] HiDef png [131 KiB] Thumbnail [29 KiB] Fig9b.pdf [25 KiB] HiDef png [134 KiB] Thumbnail [29 KiB] Fig9c.pdf [25 KiB] HiDef png [133 KiB] Thumbnail [28 KiB] Fig9d.pdf [26 KiB] HiDef png [140 KiB] Thumbnail [29 KiB] 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]. Fig10a.pdf [23 KiB] HiDef png [124 KiB] Thumbnail [28 KiB] Fig10b.pdf [25 KiB] HiDef png [132 KiB] Thumbnail [28 KiB] Fig10c.pdf [25 KiB] HiDef png [132 KiB] Thumbnail [28 KiB] Fig10d.pdf [21 KiB] HiDef png [110 KiB] Thumbnail [25 KiB] Animated gif made out of all figures. PAPER-2018-001.gif Thumbnail

## Tables and captions

 Selection window for control samples used to assess systematic uncertainties and for selection criteria optimization. Table_1.pdf [51 KiB] HiDef png [29 KiB] Thumbnail [4 KiB] tex code 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. Table_2.pdf [57 KiB] HiDef png [28 KiB] Thumbnail [5 KiB] tex code 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. Table_3.pdf [59 KiB] HiDef png [33 KiB] Thumbnail [5 KiB] tex code 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 ${\mathrm{\,GeV\!/}c^2}$ . Table_4.pdf [49 KiB] HiDef png [136 KiB] Thumbnail [20 KiB] tex code 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 $|\Phi|$. Table_5.pdf [50 KiB] HiDef png [290 KiB] Thumbnail [47 KiB] tex code 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 ${\mathrm{\,GeV\!/}c^2}$ . Table_6.pdf [51 KiB] HiDef png [88 KiB] Thumbnail [6 KiB] tex code 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 $|\Phi|$. Table_7.pdf [49 KiB] HiDef png [194 KiB] Thumbnail [32 KiB] tex code

Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.