CMS-BPH-20-001

CMS-BPH-20-001 ; CERN-EP-2020-110
Measurement of the CP-violating phase ${\phi_{\mathrm{s}}}$ in the ${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} }$ channel in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
5 July 2020
Phys. Lett. B 816 (2021) 136188
Abstract: The CP-violating weak phase ${\phi_{\mathrm{s}}}$ and the decay width difference $\Delta\Gamma_{\mathrm{s}}$ between the light and heavy $\mathrm{B^{0}_{s}}$ mass eigenstates are measured with the CMS detector at the LHC in a sample of 48 500 reconstructed ${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} }$ events. The measurement is based on a data sample corresponding to an integrated luminosity of 96.4 fb $^{-1}$ , collected in proton-proton collisions at $\sqrt{s} =$ 13 TeV in 2017-2018. To extract the values of ${\phi_{\mathrm{s}}}$ and $\Delta\Gamma_{\mathrm{s}}$ , a time-dependent and flavor-tagged angular analysis of the ${\mu^{+}\mu^{-}} {\mathrm{K^{+}}\mathrm{K^{-}}}$ final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ${\phi_{\mathrm{s}}} = -11 \pm 50 {\,\text{(stat)}} \pm 10 {\,\text{(syst)}}$ mrad and $\Delta\Gamma_{\mathrm{s}} = 0.114 \pm 0.014 {\,\text{(stat)}} \pm 0.007 {\,\text{(syst)}}$ ps $^{-1}$ , in agreement with the standard model predictions. When combined with the previous CMS measurement at $\sqrt{s} =$ 8 TeV, the following values are obtained: ${\phi_{\mathrm{s}}} = -21 \pm 45$ mrad, $\Delta\Gamma_{\mathrm{s}} = 0.1073 \pm 0.0097$ ps $^{-1}$ , a significant improvement over the 8 TeV result.
Links: e-print arXiv:2007.02434 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Definition of the three angles ${\theta _\mathrm {T}}$ , ${\psi _\mathrm {T}}$ , and ${\varphi _\mathrm {T}}$ describing the topology of the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ decay.
png pdf	Figure 2: The invariant mass distribution of the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The vertical bars on the points represent the statistical uncertainties. The solid line represents a projection of the fit to data (as discussed in Section 5, solid markers), the dashed line corresponds to the signal, the dotted line to the combinatorial background, and the long-dashed line to the peaking background from $\mathrm{B}^{0} \to \mathrm{J}/\psi \, {\mathrm{K^{*(892)}}}^0 \to {\mu^{+} \mu^{-}} \,\mathrm{K^{+}} \pi^{-}$ , as obtained from the fit. The distribution of the differences between the data and the fit, divided by the combined uncertainty in the data and the best fit function for each bin (pulls) is displayed in the lower panel.
png pdf	Figure 3: The ${ct}$ distribution (left) and its uncertainty (right) for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2.
png pdf	Figure 3-a: The ${ct}$ distribution for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2.
png pdf	Figure 3-b: The uncertainty in ${ct}$ for the ${\mathrm{B^{0}_{s}} \to \mathrm{J}/\psi \,\phi \to {\mu^{+} \mu^{-}} \, {\mathrm{K^{+}} \mathrm{K^{-}}}}$ candidates in data. The notations are as in Fig. 2.
png pdf	Figure 4: Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2017 (left) and 2018 (right) data samples. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distributions between the data and the fit function in each bin are shown in the lower panels.
png pdf	Figure 4-a: Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2017 data sample. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distribution between the data and the fit function in each bin is shown in the lower panel.
png pdf	Figure 4-b: Results of the calibration of the per-event mistag probability ${\omega _{\text {evt}}}$ based on ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}} \to {\mu^{+} \mu^{-}} \,\mathrm{K^{\pm}}}$ decays from the 2018 data sample. The vertical bars represent the statistical uncertainties. The solid line shows a linear fit to data (solid markers). The pull distribution between the data and the fit function in each bin is shown in the lower panel.
png pdf	Figure 5: The angular distributions $\cos {\theta _\mathrm {T}}$ (left), $\cos {\psi _\mathrm {T}}$ (middle), and ${\varphi _\mathrm {T}}$ (right) for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2.
png pdf	Figure 5-a: The $\cos {\theta _\mathrm {T}}$ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2.
png pdf	Figure 5-b: The $\cos {\psi _\mathrm {T}}$ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2.
png pdf	Figure 5-c: The ${\varphi _\mathrm {T}}$ angular distribution for the $\mathrm{B^{0}_{s}}$ candidates and the projections from the fit. The notations are as in Fig. 2.
png pdf	Figure 6: The two-dimensional likelihood contours at 68% CL in the ${\phi _{\mathrm {s}}}$ - ${\Delta \Gamma _{\mathrm {s}}}$ plane, for the CMS 8 TeV (dashed line), 13 TeV (dotted line), and combined (solid line) results. The SM prediction is shown with the diamond marker [1,3].

Tables
png pdf	Table 1: Angular and time-dependent terms of the signal model.
png pdf	Table 2: Calibrated opposite-side muon tagger performance evaluated using ${\mathrm{B^{\pm}} \to \mathrm{J}/\psi \,\mathrm{K^{\pm}}}$ events in the 2017 and 2018 data samples. The uncertainties shown are statistical only.
png pdf	Table 3: Results of the fit to data. Statistical uncertainties are obtained from the increase in $-\log{\mathcal {L}}$ by 0.5, whereas systematic uncertainties are described below and summarized in Table 4.
png pdf	Table 4: Summary of the systematic uncertainties. The dashes ({\text {--}}) mean that the corresponding uncertainty is not applicable. The total systematic uncertainty is obtained as the quadratic sum of the individual contributions.

Summary

The CP-violating phase

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

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

$\mathrm{B^{0}_{s}}$ meson mass eigenstates are measured using a total of 48 500

${\mathrm{B^{0}_{s}}\to\mathrm{J}/\psi\,\phi(1020) \to \mu^{+}\mu^{-}\,{\mathrm{K^{+}}\mathrm{K^{-}}} }$ signal events, collected by the CMS experiment at the LHC in proton-proton collisions at

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

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

$\mathrm{B^{0}_{s}}$ meson at the time of production. A novel opposite-side muon tagger based on deep neural networks has been developed to maximize the sensitivity of the present analysis. A high tagging power of

${\approx}$ 10% is achieved, aided by the requirement of an additional muon in the signal sample imposed at the trigger level.

The CP-violating phase is measured to be

${\phi_{\mathrm{s}}} = -11 \pm 50 {\,\text{(stat)}} \pm 10 {\,\text{(syst)}}$ mrad, consistent both with the SM prediction

${\phi_{\mathrm{s}}} = {-36.96\,^{+0.72}_{-0.84}}$ mrad [1] and with the absence of CP violation in the mixing-decay interference. The decay width difference between the

$\mathrm{B^{0}_{s}}$ mass eigenstates is measured to be

$\Delta\Gamma_{\mathrm{s}}= 0.114 \pm 0.014 {\,\text{(stat)}} \pm 0.007 {\,\text{(syst)}}$ ps

$^{-1}$ , consistent with the theoretical prediction

$\Delta\Gamma_{\mathrm{s}} = 0.091 \pm 0.013$ ps

$^{-1}$ [3]. In addition, the CP-violating parameter

$|\lambda|$ and the average lifetime of the heavy and light

$\mathrm{B^{0}_{s}}$ mass eigenstates, as well as their mass difference, have been measured. The uncertainties in all these measurements are dominated by the statistical components.

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

$\sqrt{s} =$ 8 TeV [13], yielding

${\phi_{\mathrm{s}}} = -21 \pm 45$ mrad and

$\Delta\Gamma_{\mathrm{s}}= 0.1073 \pm 0.0097$ ps

$^{-1}$ . These results are significantly more precise than those from the previous CMS measurement at 8 TeV, and can be used to further constrain possible new-physics effects in

$\mathrm{B^{0}_{s}}$ meson decay and mixing.

References
1	The CKMfitter Group Collaboration	Predictions of selected flavour observables within the Standard Model	PRD 84 (2011) 033005	1106.4041
2	C.-W. Chiang et al.	New physics in $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ : a general analysis	JHEP 04 (2010) 031	0910.2929
3	A. Lenz and G. Tetlalmatzi-Xolocotzi	Model-independent bounds on new physics effects in non-leptonic tree-level decays of B-mesons	(12, 2019)	1912.07621
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 $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ 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	ATLAS Collaboration	Time-dependent angular analysis of the decay $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ and extraction of $\Delta\Gamma_{\mathrm{s}}$ and the CP-violating weak phase $\phi_{\mathrm{s}}$ by ATLAS	JHEP 12 (2012) 072	1208.0572
10	ATLAS Collaboration	Flavor tagged time-dependent angular analysis of the $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ decay and extraction of $\Delta\Gamma_{\mathrm{s}}$ and the weak phase $\phi_{\mathrm{s}}$ in ATLAS	PRD 90 (2014) 052007	1407.1796
11	ATLAS Collaboration	Measurement of the CP-violating phase $\phi_{\mathrm{s}}$ and the $\mathrm{B^{0}_s}$ meson decay width difference with $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ decays in ATLAS	JHEP 12 (2016) 072	1601.03297
12	ATLAS Collaboration	Measurement of the $CP$ -violating phase $\phi_s$ in $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\phi$ decays in ATLAS at 13 TeV	Submitted to EPJC	2001.07115
13	CMS Collaboration	Measurement of the CP-violating weak phase $\phi_{\mathrm{s}}\$ and the decay width difference $\Delta\Gamma_{\mathrm{s}}\$ using the $\mathrm{B_s \to J/\psi \phi} \$ decay channel in pp collisions at $\sqrt{s} =$ 8 TeV	PLB 757 (2016) 97	CMS-BPH-13-012 1507.07527
14	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{\mathrm{s}}$ in ${\mathrm{\overline{B}}^0}s \to \mathrm{J}/\psi\pi^+\pi^-$ decays	PLB 713 (2012) 378	1204.5675
15	LHCb Collaboration	Measurement of CP violation and the $\mathrm{B^{0}_s}$ meson decay width difference with $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\mathrm{K}^+\mathrm{K}^-$ and $\mathrm{B^{0}_s} \to \mathrm{J}/\psi\pi^+\pi^-$ decays	PRD 87 (2013) 112010	1304.2600
16	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{\mathrm{s}}$ in ${\mathrm{\overline{B}}^0}s\to \mathrm{J}/\psi\pi^+\pi^-$ decays	PLB 736 (2014) 186	1405.4140
17	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
18	LHCb Collaboration	First study of the CP-violating phase and decay-width difference in $\mathrm{B^{0}_s} \to \psi(2\text{S})\phi$	PLB 762 (2016) 253	1608.04855
19	LHCb Collaboration	Measurement of the CP-violating phase $\phi_{\mathrm{s}}$ in ${\mathrm{\overline{B}}^0}s \to {\mathrm{D^+}}s\mathrm{D^{-}}s$ decays	PRL 113 (2014) 211801	1409.4619
20	A. S. Dighe, I. Dunietz, and R. Fleischer	Extracting CKM phases and $\mathrm{B^{0}_s}$ -- ${\mathrm{\overline{B}}^0}s$ mixing parameters from angular distributions of non-leptonic B decays	EPJC 6 (1999) 647	hep-ph/9804253
21	A. S. Dighe, I. Dunietz, H. J. Lipkin, and J. L. Rosner	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	volume 1031999
23	CMS Collaboration	Performance of the 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	1508.07749
27	H. Voss, A. Hocker, J. Stelzer, and F. Tegenfeldt	TMVA, the toolkit for multivariate data analysis with ROOT	in XIth International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT)	physics/0703039
28	R. Fruhwirth	Application of Kalman filtering to track and vertex fitting	NIMA 262 (1987) 444
29	Particle Data Group, M. Tanabashi et al.	Review of particle physics	PRD 98 (2018) 030001
30	CMS Collaboration	Description and performance of track and primary-vertex reconstruction with the CMS tracker	JINST 9 (2014) P10009	CMS-TRK-11-001 1405.6569
31	T. Sjostrand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
32	CMS Collaboration	Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements	EPJC 80 (2020) 4	CMS-GEN-17-001 1903.12179
33	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
34	D. J. Lange	The EvtGen particle decay simulation package	NIMA 462 (2001) 152
35	E. Barberio, B. van Eijk, and Z. W\cas	PHOTOS --- a universal Monte Carlo for QED radiative corrections in decays	CPC 66 (1991) 115
36	E. Barberio and Z. W\cas	PHOTOS --- a universal Monte Carlo for QED radiative corrections: version 2.0	CPC 79 (1994) 291
37	GEANT4 Collaboration	GEANT4 --- A simulation toolkit	NIMA 506 (2003) 250
38	F. Chollet et al.	Keras
39	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
40	D. Kingma and J. Ba	Adam: A method for stochastic optimization	(12, 2014)	1412.6980
41	W. Verkerke and D. Kirkby	The roofit toolkit for data modeling	2003
42	N. L. Johnson	Systems of frequency curves generated by methods of translation	Biometrika 36 (1949) 149
43	M. Rosenblatt	Remarks on some nonparametric estimates of a density function	Ann. Math. Statist. 27 (1956) 832
44	E. Parzen	On estimation of a probability density function and mode	Ann. Math. Statist. 33 (1962) 1065