cern.ch

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

[to restricted-access page]

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]
Fig1a.pdf
Fig1b.pdf [30 KiB]
HiDef png [396 KiB]
Thumbnail [132 KiB]
Fig1b.pdf
Fig1c.pdf [30 KiB]
HiDef png [387 KiB]
Thumbnail [131 KiB]
Fig1c.pdf
Fig1d.pdf [30 KiB]
HiDef png [389 KiB]
Thumbnail [131 KiB]
Fig1d.pdf

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]
Fig2a.pdf
Fig2b.pdf [29 KiB]
HiDef png [357 KiB]
Thumbnail [124 KiB]
Fig2b.pdf
Fig2c.pdf [29 KiB]
HiDef png [356 KiB]
Thumbnail [123 KiB]
Fig2c.pdf
Fig2d.pdf [29 KiB]
HiDef png [363 KiB]
Thumbnail [125 KiB]
Fig2d.pdf

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]
Fig3a.pdf
Fig3b.pdf [24 KiB]
HiDef png [359 KiB]
Thumbnail [130 KiB]
Fig3b.pdf
Fig3c.pdf [24 KiB]
HiDef png [359 KiB]
Thumbnail [129 KiB]
Fig3c.pdf
Fig3d.pdf [24 KiB]
HiDef png [355 KiB]
Thumbnail [129 KiB]
Fig3d.pdf

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]
Fig4a.pdf
Fig4b.pdf [15 KiB]
HiDef png [130 KiB]
Thumbnail [33 KiB]
Fig4b.pdf

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]
Fig5a.pdf
Fig5b.pdf [15 KiB]
HiDef png [128 KiB]
Thumbnail [33 KiB]
Fig5b.pdf

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]
Fig6a.pdf
Fig6b.pdf [26 KiB]
HiDef png [352 KiB]
Thumbnail [124 KiB]
Fig6b.pdf

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]
Fig7a.pdf
Fig7b.pdf [25 KiB]
HiDef png [135 KiB]
Thumbnail [28 KiB]
Fig7b.pdf
Fig7c.pdf [24 KiB]
HiDef png [126 KiB]
Thumbnail [28 KiB]
Fig7c.pdf
Fig7d.pdf [25 KiB]
HiDef png [124 KiB]
Thumbnail [28 KiB]
Fig7d.pdf

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]
Fig8a.pdf
Fig8b.pdf [26 KiB]
HiDef png [139 KiB]
Thumbnail [29 KiB]
Fig8b.pdf
Fig8c.pdf [25 KiB]
HiDef png [125 KiB]
Thumbnail [28 KiB]
Fig8c.pdf
Fig8d.pdf [22 KiB]
HiDef png [113 KiB]
Thumbnail [25 KiB]
Fig8d.pdf

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]
Fig9a.pdf
Fig9b.pdf [25 KiB]
HiDef png [134 KiB]
Thumbnail [29 KiB]
Fig9b.pdf
Fig9c.pdf [25 KiB]
HiDef png [133 KiB]
Thumbnail [28 KiB]
Fig9c.pdf
Fig9d.pdf [26 KiB]
HiDef png [140 KiB]
Thumbnail [29 KiB]
Fig9d.pdf

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]
Fig10a.pdf
Fig10b.pdf [25 KiB]
HiDef png [132 KiB]
Thumbnail [28 KiB]
Fig10b.pdf
Fig10c.pdf [25 KiB]
HiDef png [132 KiB]
Thumbnail [28 KiB]
Fig10c.pdf
Fig10d.pdf [21 KiB]
HiDef png [110 KiB]
Thumbnail [25 KiB]
Fig10d.pdf

Animated gif made out of all figures.

PAPER-2018-001.gif
Thumbnail
thumbnail_PAPER-2018-001.gif

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
Table_1.pdf

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
Table_2.pdf

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
Table_3.pdf

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
Table_4.pdf

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
Table_5.pdf

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
Table_6.pdf

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
Table_7.pdf

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