cern.ch

Measurement of the mass and lifetime of the $\Omega_b^-$ baryon

[to restricted-access page]

Abstract

A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm9$ $\Omega_b^-\to\Omega_c^0\pi^-$, $\Omega_c^0\to pK^-K^-\pi^+$ decays. Using the $\Xi_b^-\to\Xi_c^0\pi^-$, $\Xi_c^0\to pK^-K^-\pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $\Omega_b^-$ baryon are measured to be \begin{align*} \frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\ \tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06 {\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $\tau_{\Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{\Omega_b^-}-m_{\Xi_b^-}$, and the corresponding $\Omega_b^-$ mass, which yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5 {\rm MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6 {\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.

Figures and captions

Invariant mass distribution for (left) $\Xi ^0_ c \rightarrow p K ^- K ^- \pi ^+ $ and (right) $\POmega ^0_ c \rightarrow p K ^- K ^- \pi ^+ $ candidates over the full $X_b$ fit regions. The corresponding simulations (sim.) are overlaid. The vertical arrows indicate the signal regions, and the horizontal ones show the sideband regions.

XcMassComp.pdf [27 KiB]
HiDef png [171 KiB]
Thumbnail [54 KiB]
*.C file
XcMassComp.pdf

Results of the simultaneous mass fit to the signal and calibration modes. The fitted $\POmega ^-_ b $ combinatorial (comb.) background yield is very small, and not clearly visible.

Omb2Om[..].pdf [20 KiB]
HiDef png [326 KiB]
Thumbnail [92 KiB]
*.C file
Omb2OmcPi_OmbFit_def_Y0.pdf
Xib2Xi[..].pdf [21 KiB]
HiDef png [267 KiB]
Thumbnail [78 KiB] *.C file
Xib2XicPi_OmbFit_def_Y0.pdf

Results of the simultaneous mass fit to the $\POmega ^-_ b $ signal in the four decay time bins, as indicated in each plot.

Omb2Om[..].pdf [19 KiB]
HiDef png [288 KiB]
Thumbnail [86 KiB]
*.C file
Omb2OmcPi_OmbFit_Omb_tbin_0.pdf
Omb2Om[..].pdf [18 KiB]
HiDef png [282 KiB]
Thumbnail [85 KiB] *.C file
Omb2OmcPi_OmbFit_Omb_tbin_1.pdf
Omb2Om[..].pdf [18 KiB]
HiDef png [271 KiB]
Thumbnail [83 KiB] *.C file
Omb2OmcPi_OmbFit_Omb_tbin_2.pdf
Omb2Om[..].pdf [19 KiB]
HiDef png [277 KiB]
Thumbnail [83 KiB] *.C file
Omb2OmcPi_OmbFit_Omb_tbin_3.pdf

Results of the simultaneous mass fit to the $\Xi ^-_ b $ signal in the four decay time bins, as indicated in each plot.

Xib2Xi[..].pdf [21 KiB]
HiDef png [280 KiB]
Thumbnail [81 KiB]
*.C file
Xib2XicPi_OmbFit_Xib_tbin_0.pdf
Xib2Xi[..].pdf [21 KiB]
HiDef png [271 KiB]
Thumbnail [80 KiB] *.C file
Xib2XicPi_OmbFit_Xib_tbin_1.pdf
Xib2Xi[..].pdf [20 KiB]
HiDef png [274 KiB]
Thumbnail [83 KiB] *.C file
Xib2XicPi_OmbFit_Xib_tbin_2.pdf
Xib2Xi[..].pdf [20 KiB]
HiDef png [259 KiB]
Thumbnail [78 KiB] *.C file
Xib2XicPi_OmbFit_Xib_tbin_3.pdf

Corrected signal yield ratio as a function of decay time, along with a fit to an exponential function. The horizontal bars indicate the bin sizes, and are not an indication of the uncertainty.

CorrYi[..].pdf [14 KiB]
HiDef png [73 KiB]
Thumbnail [21 KiB]
*.C file
CorrYieldRatio_XibOverOmb_def.pdf

Animated gif made out of all figures.

PAPER-2016-008.gif
Thumbnail
thumbnail_PAPER-2016-008.gif

Tables and captions

Results of the fit to data for each decay time bin, and the relative efficiency. The uncertainties are statistical only.

Table_1.pdf [43 KiB]
HiDef png [49 KiB]
Thumbnail [8 KiB]
tex code
Table_1.pdf

Summary of systematic uncertainties in $\delta m$ and the lifetime ratio. When two values are indicated, the first is a correction, and the second is the uncertainty.

[Error creating the table]

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