CMS-PAS-FTR-18-041

CMS-PAS-FTR-18-041
CP-violation studies at the HL-LHC with CMS using $\mathrm{B^0_s}$ decays to $\mathrm{J}/\psi\phi(1020)$
CMS Collaboration
December 2018

Abstract: We have estimated the expected sensitivity on the CP-violating phase $\phi_s$ measured in the decay channel $\mathrm{B^0_s} \to \! \mathrm{J}/\psi\phi(1020)$ in pp collisions with the CMS detector at the end of the HL-LHC data-taking with 3 ab $^{-1}$ of collected data. The sensitivity on $\phi_s$ mainly depends on the collected statistics, on the flavour-tagging power, and on the proper-decay-time resolution. The study is performed using fully simulated signal events and toy Monte Carlo experiments, for a few assumed tagging scenarios. The sensitivity on $\phi_s$ is expected to be in the 5-6 mrad range, which improves the current world average uncertainty by a factor of five.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Left: invariant mass resolution in the Phase 2 sample compared with Phase 1 case. Right: $c\tau$ uncertainty distribution in 2012 data (blue) and Phase 2 MC (red) samples. The better performance of Phase 2 w.r.t. 2012 data is due to the Phase 2 tracker.
png	Figure 1-a: Left: invariant mass resolution in the Phase 2 sample compared with Phase 1 case. Right: $c\tau$ uncertainty distribution in 2012 data (blue) and Phase 2 MC (red) samples. The better performance of Phase 2 w.r.t. 2012 data is due to the Phase 2 tracker.
png	Figure 1-b: Left: invariant mass resolution in the Phase 2 sample compared with Phase 1 case. Right: $c\tau$ uncertainty distribution in 2012 data (blue) and Phase 2 MC (red) samples. The better performance of Phase 2 w.r.t. 2012 data is due to the Phase 2 tracker.
png pdf	Figure 2: Left: variation of the $\phi _s$ statistical uncertainty as function of the tagging power ( $\epsilon D^2$ ) see equation (1), measured in different flavour tagging scenarios. A function proportional to $1/\sqrt {\epsilon D^2}$ is shown to describe the behaviour of the $\phi _s$ uncertainty in the selected range. Right: 68% confidence level (CL) contour from the fit of a toy MC pseudo-experiment generated in the tagging scenario $c$ . The contour combines statistical and systematic uncertainties. The black cross represents the SM expectations [2][1].
png	Figure 2-a: Left: variation of the $\phi _s$ statistical uncertainty as function of the tagging power ( $\epsilon D^2$ ) see equation (1), measured in different flavour tagging scenarios. A function proportional to $1/\sqrt {\epsilon D^2}$ is shown to describe the behaviour of the $\phi _s$ uncertainty in the selected range. Right: 68% confidence level (CL) contour from the fit of a toy MC pseudo-experiment generated in the tagging scenario $c$ . The contour combines statistical and systematic uncertainties. The black cross represents the SM expectations [2][1].
png	Figure 2-b: Left: variation of the $\phi _s$ statistical uncertainty as function of the tagging power ( $\epsilon D^2$ ) see equation (1), measured in different flavour tagging scenarios. A function proportional to $1/\sqrt {\epsilon D^2}$ is shown to describe the behaviour of the $\phi _s$ uncertainty in the selected range. Right: 68% confidence level (CL) contour from the fit of a toy MC pseudo-experiment generated in the tagging scenario $c$ . The contour combines statistical and systematic uncertainties. The black cross represents the SM expectations [2][1].

Tables
png pdf	Table 1: Statistical uncertainty of $\phi _s$ obtained from toy MC pseudo-experiments for different scenarios of flavour tagging.

Summary

The CMS sensitivity for the measurement of the CP-violating phase

$\phi_s$ in the HL-LHC era has been estimated using simulated data and MC toy pseudo-experiments corresponding to the 3 ab

$^{-1}$ of integrated luminosity. The offline selection of signal events and the analysis strategy are similar to what was used in the past except for the tagging performance, for which three different scenarios have been considered. Assuming the new tagging power (

$\epsilon D^2$ ) to be in the range 1.2-2.4%, and a total of 9 million

$\mathrm{B^0_s}$ candidates, we expect the

$\phi_s$ statistical uncertainty to be 5-6 mrad at the end of Phase 2 data taking, which improves the current world average uncertainty by a factor of five.

References
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