CMS-PAS-BPH-20-001

CMS-PAS-BPH-20-001
Measurement of the CP violating phase $\phi_{\text{s}}$ in the $\mathrm{B}_s \to \mathrm{J}/\psi\,\phi(1020) \to \mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
March 2020

Abstract: The CP violating weak phase $\phi_{\text{s}}$ , and the decay width difference $\Delta\Gamma_{\text{s}}$ between the light and heavy $\mathrm{B_s}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of reconstructed $\mathrm{B}_s \to \mathrm{J}/\psi\,\phi(1020) \to \mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ decays. The measurement is based on a data set corresponding to an integrated luminosity of 96.4 fb $^{-1}$ , collected in proton-proton collisions at a center-of-mass energy of 13 TeV in 2017-2018. To extract the values of $\phi_{\text{s}}$ and $\Delta\Gamma_{\text{s}}$ , a time-dependent and flavor-tagged angular analysis of the $\mu^+\mu^-\,\mathrm{K}^+\mathrm{K}^-$ final state is performed. The analysis employs a novel opposite-side muon flavor tagger based on machine learning techniques, which, in conjunction with a dedicated tagging trigger, allowed to reach an unprecedented tagging power. The measurement yields $\phi_{\text{s}} =$ -0.011 $\pm$ 0.050 (stat) $\pm$ 0.010 (syst) rad, and $\Delta\Gamma_{\text{s}} =$ 0.114 $\pm$ 0.014 (stat) $\pm$ 0.007 (syst) ps $^{-1}$ , in agreement with the standard model predictions. When combined with our previous measurement at a center-of-mass energy of 8 TeV, the following values are obtained: $\phi_{\text{s}} =$ -0.021 $\pm$ 0.045 rad, $\Delta\Gamma_{\text{s}} =$ 0.1074 $\pm$ 0.0097 ps $^{-1}$ , a significant improvement over the 8 TeV result.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 816 (2021) 136188. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Definition of the three angles ${\theta _\text {T}}$ , ${\psi _\text {T}}$ , and ${\varphi _\text {T}}$ describing the topology of the ${\mathrm{B_s} \to \mathrm{J}/\psi \,\phi(1020)\to {\mu^{+} \mu^{-}} {\mathrm{K^{+}} \mathrm{K^{-}}}}$ decay.
png pdf	Figure 2: The invariant mass distribution of the ${\mathrm{B_s} \to \mathrm{J}/\psi \,\phi(1020)\to {\mu^{+} \mu^{-}} {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The solid line represents a fit to data (solid markers), the dashed green line corresponds to the signal, while the dashed red (magenta) line corresponds to the combinatorial (peaking) background, as obtained by the fit. The distribution of the pulls between the data and the fit for each bin is displayed in the bottom panel.
png pdf	Figure 3: The ${ct}$ distribution (left) and its uncertainty (right) of the ${\mathrm{B_s} \to \mathrm{J}/\psi \,\phi(1020)\to {\mu^{+} \mu^{-}} {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The solid line represents a fit to data (solid markers), the dashed green line corresponds to the signal, while the dashed red (magenta) line corresponds to the combinatorial (peaking) background, as obtained by the fit. The distribution of the pulls between the data and the fit for each bin is displayed in the bottom panel.
png pdf	Figure 3-a: The ${ct}$ distribution (left) and its uncertainty (right) of the ${\mathrm{B_s} \to \mathrm{J}/\psi \,\phi(1020)\to {\mu^{+} \mu^{-}} {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The solid line represents a fit to data (solid markers), the dashed green line corresponds to the signal, while the dashed red (magenta) line corresponds to the combinatorial (peaking) background, as obtained by the fit. The distribution of the pulls between the data and the fit for each bin is displayed in the bottom panel.
png pdf	Figure 3-b: The ${ct}$ distribution (left) and its uncertainty (right) of the ${\mathrm{B_s} \to \mathrm{J}/\psi \,\phi(1020)\to {\mu^{+} \mu^{-}} {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The solid line represents a fit to data (solid markers), the dashed green line corresponds to the signal, while the dashed red (magenta) line corresponds to the combinatorial (peaking) background, as obtained by the fit. The distribution of the pulls between the data and the fit for each bin is displayed in the bottom panel.
png pdf	Figure 4: Results of the calibration of the per-event mistag rate ${\omega _{\text {evt}}}$ performed using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ decays in data collected in 2017 (left) and in 2018 (right). The solid line shows a linear fit to data (solid markers). The distributions of the pulls between the data and the fitted function in each bin are displayed in the lower panels.
png pdf	Figure 4-a: Results of the calibration of the per-event mistag rate ${\omega _{\text {evt}}}$ performed using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ decays in data collected in 2017 (left) and in 2018 (right). The solid line shows a linear fit to data (solid markers). The distributions of the pulls between the data and the fitted function in each bin are displayed in the lower panels.
png pdf	Figure 4-b: Results of the calibration of the per-event mistag rate ${\omega _{\text {evt}}}$ performed using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ decays in data collected in 2017 (left) and in 2018 (right). The solid line shows a linear fit to data (solid markers). The distributions of the pulls between the data and the fitted function in each bin are displayed in the lower panels.
png pdf	Figure 5: The angular distributions $\cos {\theta _\text {T}}$ (left), $\cos {\psi _\text {T}}$ (middle), and ${\varphi _\text {T}}$ (right) of the $\mathrm{B_s}$ candidates. The solid line represents the fit to data (solid markers), the dashed green line corresponds to signal, while the dashed red (magenta) line shows the combinatorial (peaking) background. The pull distributions between the data and the fit function in each bin are shown in the lower panels.
png pdf	Figure 5-a: The angular distributions $\cos {\theta _\text {T}}$ (left), $\cos {\psi _\text {T}}$ (middle), and ${\varphi _\text {T}}$ (right) of the $\mathrm{B_s}$ candidates. The solid line represents the fit to data (solid markers), the dashed green line corresponds to signal, while the dashed red (magenta) line shows the combinatorial (peaking) background. The pull distributions between the data and the fit function in each bin are shown in the lower panels.
png pdf	Figure 5-b: The angular distributions $\cos {\theta _\text {T}}$ (left), $\cos {\psi _\text {T}}$ (middle), and ${\varphi _\text {T}}$ (right) of the $\mathrm{B_s}$ candidates. The solid line represents the fit to data (solid markers), the dashed green line corresponds to signal, while the dashed red (magenta) line shows the combinatorial (peaking) background. The pull distributions between the data and the fit function in each bin are shown in the lower panels.
png pdf	Figure 5-c: The angular distributions $\cos {\theta _\text {T}}$ (left), $\cos {\psi _\text {T}}$ (middle), and ${\varphi _\text {T}}$ (right) of the $\mathrm{B_s}$ candidates. The solid line represents the fit to data (solid markers), the dashed green line corresponds to signal, while the dashed red (magenta) line shows the combinatorial (peaking) background. The pull distributions between the data and the fit function in each bin are shown in the lower panels.
png pdf	Figure 6: The two-dimensional likelihood contours at 68% CL in the ${\phi _{\text {s}}}$ - ${\Delta \Gamma _{\text {s}}}$ plane, for the CMS 8 TeV (dashed green line), 13 TeV (dashed blue line), and the combined (solid red line) results. The SM prediction is shown as the black rectangle.

Tables
png pdf	Table 1: Angular and time-dependent terms of the signal model.
png pdf	Table 2: Calibrated OS muon tagger performance evaluated using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ events in 2017 and 2018 data sets.
png pdf	Table 3: Results of the fit to data with the statistical uncertainties coming from the fit. The description of the systematic uncertainties is detailed below and summarized in Table 4.

Summary

The weak phase

${\phi_{\text{s}}}$ and the decay width difference

$\Delta\Gamma_{\text{s}}$ between the light and heavy

$\mathrm{B_s}$ meson mass eigenstates are measured using a total of 48 500

${\mathrm{B_s} \to\mathrm{J}/\psi\,\phi{1020} \to \mu\mu{\mathrm{K^{+}}\mathrm{K^{-}}} }$ candidates, collected by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of

$\sqrt{s} =$ 13 TeV, corresponding to an integrated luminosity of {96.4 fb

$^{-1}$ } . Events are selected using a trigger that requires an additional muon, which is exploited to infer the flavor of the

$\mathrm{B_s}$ meson at production time. A novel opposite-side muon tagger based on deep neural networks has been developed to maximize the sensitivity of the present analysis, and allowed to achieve an unprecedented tagging power of

$\approx$ 10%, aided by the requirement of the additional muon in the signal sample.

The weak phase is measured to be

${\phi_{\text{s}}} =$

$-$ 0.011

$\pm$ 0.050 (stat)

$\pm$ 0.010 (syst) rad, consistent both with the SM prediction, and with the absence of CP violation in the mixing-decay interference. The decay width difference between the

$\mathrm{B_s}$ mass eigenstates is measured to be

$\Delta\Gamma_{\text{s}}=$ 0.114

$\pm$ 0.014 (stat)

$\pm$ 0.007 (syst) ps

$^{-1}$ , consistent with the theoretical predictions. In addition, the CP violating parameter

$|{\lambda}|$ , and the average lifetime of the heavy and light

$\mathrm{B_s}$ mass eigenstates, as well as their mass difference have been measured. All measurements are dominated by the statistical uncertainties.

The results presented in this note are further combined with those obtained by CMS at

$\sqrt{s} =$ 8 TeV [19], yielding

${\phi_{\text{s}}} =$

$-$ 0.021

$\pm$ 0.045 rad and

$\Delta\Gamma_{\text{s}}=$ 0.1074

$\pm$ 0.0097 ps

$^{-1}$ . These results are significantly more precise than those from the previous CMS measurement, and allow to further constrain possible contributions from new physics in the

$\mathrm{B_s}$ meson decay and mixing.

References
1	J. Charles et al.	Predictions of selected flavour observables within the Standard Model	PRD 84 (2011) 033005	1106.4041
2	C.-W. Chiang et al.	New physics in $B_s^0 \to J/\psi \phi$ : a general analysis	JHEP 04 (2010) 031
3	A. Lenz and U. Nierste	Numerical Updates of Lifetimes and Mixing Parameters of B Mesons		1102.4274
4	D0 Collaboration	Measurement of $\mathrm{B^0_{s}}$ Mixing Parameters from the Flavor-Tagged Decay $\mathrm{B^0_{s}} \to \mathrm{J}/\psi \phi$	PRL 101 (2008) 241801	0802.2255
5	D0 Collaboration	Measurement of the CP-violating phase $\phi_{\mathrm{s}}^{\mathrm{J}/\psi \phi}$ using the flavor-tagged decay $\mathrm{B_s^0} \rightarrow \mathrm{J}/\psi \phi$ in 8 $fb$ ^{-1} of p $\overline{\textrm{p}}$ collisions	PRD 85 (2012) 032006	1109.3166
6	CDF Collaboration	First Flavor-Tagged Determination of Bounds on Mixing-Induced CP Violation in $\mathrm{B^0_{s}} \to \mathrm{J}/\psi \phi$ Decays	PRL 100 (2008) 161802	0712.2397
7	CDF Collaboration	Measurement of the CP-violating phase $\beta_{\mathrm{s}}^{\mathrm{J}/\psi\phi}$ in $\mathrm{B^0_s} \to \mathrm{J}/\psi \phi$ decays with the CDF II detector	PRD 85 (2012) 072002	1112.1726
8	CDF Collaboration	Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set	PRL 109 (2012) 171802	1208.2967
9	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{s}$ in $\mathrm{\overline{B}^0_s} \to \mathrm{J}/\psi\pi^+\pi^-$ decays	PLB 713 (2012) 378	1204.5675
10	LHCb Collaboration	Measurement of CP violation and the $\mathrm{B_s^0}$ meson decay width difference with $\mathrm{B_s^0} \to \mathrm{J}/\psi \mathrm{K}^+\mathrm{K}^-$ and $\mathrm{B_s^0}\to \mathrm{J}/\psi\pi^+\pi^-$ decays	PRD 87 (2013) 112010	1304.2600
11	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{s}$ in $\mathrm{\overline{B}_s^0}\to \mathrm{J}/\psi\pi^+\pi^-$ decays	PLB 736 (2014) 186	1405.4140
12	LHCb Collaboration	Precision measurement of CP violation in $\mathrm{B^0_s} \to \mathrm{J}/\psi\mathrm{K}^+\mathrm{K}^-$ decays	PRL 114 (2015) 041801	1411.3104
13	ATLAS Collaboration	Time-dependent angular analysis of the decay $\mathrm{B_{s}^{0}} \to \mathrm{J}/{\psi\phi}$ and extraction of $\Delta \Gamma_{\mathrm{s}}$ and the CP-violating weak phase $\phi_{s}$ by ATLAS	JHEP 12 (2012) 072	1208.0572
14	ATLAS Collaboration	Flavor tagged time-dependent angular analysis of the $\mathrm{B_s^0} \rightarrow \mathrm{J}/\psi \phi$ decay and extraction of $\Delta \Gamma_{\mathrm{s}}$ and the weak phase $\phi_{s}$ in ATLAS	PRD 90 (2014) 052007	1407.1796
15	ATLAS Collaboration	Measurement of the CP-violating phase $\phi_{s}$ and the $\mathrm{B_s}$ meson decay width difference with $\mathrm{B_s^0} \rightarrow \mathrm{J}/\psi \phi$ decays in ATLAS	JHEP 12 (2016) 072	1601.03297
16	ATLAS Collaboration	Measurement of the $CP$ -violating phase $\phi_s$ in $B^0_s \to J/\psi\phi$ decays in ATLAS at 13 TeV		2001.07115
17	LHCb Collaboration	First study of the CP-violating phase and decay-width difference in $\mathrm{B^0_s} \to\psi\text{(2S)} \phi$	PLB 762 (2016) 253	1608.04855
18	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{s}$ in $\mathrm{\overline{B}_s^0}\to \mathrm{J}/\psi{\mathrm{D^+}}s\mathrm{D^{-}}s$ decays	PRL 113 (2014) 211801	1409.4619
19	CMS Collaboration	Measurement of the CP-violating weak phase $\phi_{s}\$ and the decay width difference $\Delta \Gamma_{\mathrm{s}}\$ using the $\mathrm{\overline{B}_s^0}\to \mathrm{J}/\psi \, \phi$ decay channel in pp collisions at $\sqrt{s} =$ 8 TeV	PLB 757 (2016) 97	CMS-BPH-13-012 1507.07527
20	A. Dighe et al.	Extracting CKM phases and $\mathrm{B^0_s} - \mathrm{\bar{B}_s}$ mixing parameters from angular distributions of non-leptonic B decays	EPJC 6 (1999) 647	hep-ph/9804253
21	A. Dighe et al.	Angular distributions and lifetime differences in $\mathrm{B^0_s} \to \mathrm{J}/\psi \phi$ decays	PLB 369 (1996) 144	hep-ph/9511363
22	G. C. Branco, L. Lavoura, and J. P. Silva	CP Violation	Int. Ser. Monogr. Phys. 103 (1999)1
23	CMS Collaboration	Performance of CMS muon detector and muon reconstruction with proton-proton collisions at $\sqrt{s} =$ 13 TeV	JINST 13 (2018) P06015	CMS-MUO-16-001 1804.04528
24	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
25	CMS Collaboration	The CMS Experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
26	I. Antcheva et al.	ROOT -- A C++ framework for petabyte data storage, statistical analysis and visualization	CPC 180 (2009) 2499
27	A. Hoecker et al.	TMVA: Toolkit for Multivariate Data Analysis	PoS ACAT (2007) 040	physics/0703039
28	R. Fruhwirth	Application of Kalman filtering to track and vertex fitting	NIMA 262 (1987) 444
29	Particle Data Group Collaboration	Review of Particle Physics	PRD 98 (2018) 030001
30	T. Sjostrand et al.	An Introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
31	D. Lange	The EvtGen particle decay simulation package	NIMA 462 (2001) 152
32	E. Barberio et al.	PHOTOS -- a universal Monte Carlo for QED radiative corrections in decays	CPC 66 (1991) 115
33	E. Barberio and Z. W\cas	PHOTOS -- a universal Monte Carlo for QED radiative corrections: version 2.0	CPC 79 (1994) 291
34	GEANT4 Collaboration	GEANT4--A simulation toolkit	NIMA 506 (2003) 250
35	M. Pivk and F. R. Le Diberder	SPlot: A Statistical tool to unfold data distributions	NIMA 555 (2005) 356	physics/0402083
36	F. Chollet et al.	Keras	link
37	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
38	D. P. Kingma and J. Ba	Adam: A method for stochastic optimization		1412.6980
39	W. Verkerke and D. P. Kirkby	The RooFit toolkit for data modeling	in Statistical Problems in Particle Physics, Astrophysics and Cosmology (PHYSTAT 05): Proceedings, Oxford, 2005	physics/0306116
40	N. L. Johnson	Systems of frequency curves generated by methods of translation	Biometrika 36 (1949) 149
41	P. Ongmongkolkul et al.	iminuit---a Python interface to C++ MINUIT2	2012 \url https://github.com/iminuit/iminuit
42	F. James and M. Roos	Minuit---a system for function minimization and analysis of the parameter errors and correlations	CPC 10 (1975) 343