CMS-TOP-12-031

CMS-TOP-12-031 ; CERN-EP-2016-249
Measurement of the mass difference between top quark and antiquark in pp collisions at $\sqrt{s} =$ 8 TeV
CMS Collaboration
29 October 2016
Phys. Lett. B 770 (2017) 50
Abstract: The invariance of the standard model (SM) under the CPT transformation predicts equality of particle and antiparticle masses. This prediction is tested by measuring the mass difference between the top quark and antiquark ( $\Delta m_{\mathrm{t}} = m_{\mathrm{t}} - m_{\overline{\mathrm{t}}}$ ) that are produced in pp collisions at a center-of-mass energy of 8 TeV, using events with a muon or an electron and at least four jets in the final state. The analysis is based on data corresponding to an integrated luminosity of 19.6 fb $^{-1}$ collected by the CMS experiment at the LHC, and yields a value of $\Delta m_{\mathrm{t}} = -0.15 \pm 0.19\, \mathrm{(stat)} \pm 0.09\, \mathrm{(syst)}$ GeV, which is consistent with the SM expectation. This result is significantly more precise than previously reported measurements.
Links: e-print arXiv:1610.09551 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Comparison of the data to simulation for the transverse momenta of the four leading jets in each event for $\ell ^+$ +jets events (left) and $\ell ^-$ +jets events (right). The last bin of each distribution includes all jets with ${p_{\mathrm {T}}} >$ 530 GeV. The bin-by-bin ratio of the observed to the simulated spectra one is shown at the bottom of each plot. The uncertainties are purely statistical. The total simulated event yields are normalized to the observed yields in the data, while keeping the relative fractions of the individual components fixed.
png pdf	Figure 1-a: Comparison of the data to simulation for the transverse momenta of the four leading jets in each event for $\ell ^+$ +jets events. The last bin of each distribution includes all jets with ${p_{\mathrm {T}}} >$ 530 GeV. The bin-by-bin ratio of the observed to the simulated spectra one is shown at the bottom of each plot. The uncertainties are purely statistical. The total simulated event yields are normalized to the observed yields in the data, while keeping the relative fractions of the individual components fixed.
png pdf	Figure 1-b: Comparison of the data to simulation for the transverse momenta of the four leading jets in each event for $\ell ^-$ +jets events. The last bin of each distribution includes all jets with ${p_{\mathrm {T}}} >$ 530 GeV. The bin-by-bin ratio of the observed to the simulated spectra one is shown at the bottom of each plot. The uncertainties are purely statistical. The total simulated event yields are normalized to the observed yields in the data, while keeping the relative fractions of the individual components fixed.
png pdf	Figure 2: Comparison between the data and simulation for the fitted top quark mass of the jet-quark assignment with the smallest $\chi ^2$ (top) and these smallest $\chi ^2$ values (bottom), for $\ell ^+$ +jets events (left) and $\ell ^-$ +jets events (right). The last bin of the top quark mass distributions includes all masses above 980 GeV. The bin-by-bin ratio of the observed spectrum to the simulated one is shown at the bottom of each plot. The uncertainties are purely statistical.
png pdf	Figure 2-a: Comparison between the data and simulation for the fitted top quark mass of the jet-quark assignment with the smallest $\chi ^2$ , for $\ell ^+$ +jets events. The last bin of the distribution includes all masses above 980 GeV. The bin-by-bin ratio of the observed spectrum to the simulated one is shown at the bottom of the plot. The uncertainties are purely statistical.
png pdf	Figure 2-b: Comparison between the data and simulation for the fitted top quark mass of the jet-quark assignment with the smallest $\chi ^2$ , for $\ell ^-$ +jets events. The last bin of the distribution includes all masses above 980 GeV. The bin-by-bin ratio of the observed spectrum to the simulated one is shown at the bottom of the plot. The uncertainties are purely statistical.
png pdf	Figure 2-c: Comparison between the data and simulation for the smallest $\chi ^2$ values, for $\ell ^+$ +jets events. The bin-by-bin ratio of the observed distribution to the simulated one is shown at the bottom of the plot. The uncertainties are purely statistical.
png pdf	Figure 2-d: Comparison between the data and simulation for the smallest $\chi ^2$ values, for $\ell ^-$ +jets events. The bin-by-bin ratio of the observed distribution to the simulated one is shown at the bottom of the plot. The uncertainties are purely statistical.
png pdf	Figure 3: Width of the pull distribution (left) and bias on the estimated top quark mass (right) as a function of the generated top quark mass for $\ell$ +jets events. The dashed blue line represents the ideal outcome.
png pdf	Figure 3-a: Width of the pull distribution as a function of the generated top quark mass for $\ell$ +jets events. The dashed blue line represents the ideal outcome.
png pdf	Figure 3-b: Bias on the estimated top quark mass as a function of the generated top quark mass for $\ell$ +jets events. The dashed blue line represents the ideal outcome.
png pdf	Figure 4: Residual bias on the estimated top quark mass as a function of the generated top quark mass using $\ell ^+$ +jets events (left) and $\ell ^-$ +jets events (right) after the inclusive $\ell$ +jets calibration. The dashed blue line represents the ideal outcome.
png pdf	Figure 4-a: Residual bias on the estimated top quark mass as a function of the generated top quark mass using $\ell ^+$ +jets events after the inclusive $\ell$ +jets calibration. The dashed blue line represents the ideal outcome.
png pdf	Figure 4-b: Residual bias on the estimated top quark mass as a function of the generated top quark mass using $\ell ^-$ +jets events after the inclusive $\ell$ +jets calibration. The dashed blue line represents the ideal outcome.

Tables
png pdf	Table 1: Expected and observed yield of events passing the full selection of $\mathrm{ e }^{+}$ +jets, $\mathrm{ e }^{-}$ +jets, $\mu^{+}$ +jets, and $\mu^{-}$ +jets channels. Simulations are used to obtain the expected number of events except for the QCD multijet background, which is derived from data, as described in the text. The uncertainties on the event numbers are statistical and reflect the limited number of events in simulation or data for the individual processes.
png pdf	Table 2: Summary of systematic uncertainties on $\Delta m_{\mathrm{ t } }$ . For each contribution, the first value is the observed systematic shift, whereas the second number is the uncertainty of the shift due to the limited number of generated events. In all cases, the larger among the two is considered as the final systematic uncertainty and is indicated in the bold font. The total uncertainty is obtained from the sum in quadrature of the individual terms.

Summary

Data collected by the CMS experiment in pp collisions at

$\sqrt{s} =$ 8 TeV and corresponding to an integrated luminosity of 19.6

$\pm$ 0.5 fb

$^{-1}$ have been used to measure the difference in mass between the top quark and antiquark. The measured value is

$\Delta m_{\mathrm{t}} = -0.15 \pm 0.19\, \mathrm{(stat)} \pm 0.09\, \mathrm{(syst)}$ GeV. This result improves in precision upon previously reported measurements [9-12] by more than a factor of two. It is in agreement with the expectations from CPT invariance, requiring equal particle and antiparticle masses.

References
1	S. Glashow	Partial-symmetries of weak interactions	Nucl. Phys. 22 (1961) 579
2	S. Weinberg	A model of leptons	PRL 19 (1967) 1264
3	A. Salam	Weak and electromagnetic interactions	Conf. Proc. C 680519 (1968) 367
4	Particle Data Group, C. Patrignani et al.	Review of particle physics	CPC 40 (2016) 100001
5	D. Colladay and V. A. Kosteleck\'y	CPTviolation and the standard model	PRD 55 (1997) 6760
6	G. Barenboim and J. Lykken	A model of CPT violation for neutrinos	PLB 554 (2003) 73
7	R. S. Raghavan	A new model of solar neutrinos in manifest violation of CPT invariance	JCAP 0308 (2003) 002
8	V. A. Kosteleck\'y and R. Potting	CPT and strings	Nucl. Phys. B 359 (1991) 545
9	CDF Collaboration	Measurement of the mass difference between top and anti-top quarks at CDF	PRD 106 (2013) 152001	1103.2782
10	D0 Collaboration	Direct measurement of the mass difference between top and antitop quarks	PRD 84 (2011) 052005	1106.2063
11	CMS Collaboration	Measurement of the mass difference between top and antitop quarks	JHEP 06 (2012) 109, ,%\%CITATION = ARXIV:1204.2807;\%\%	CMS-TOP-11-019 1204.2807
12	ATLAS Collaboration	Measurement of the mass difference between top and anti-top quarks in $pp$ collisions at $\sqrt{s} =$ 7 TeV using the ATLAS detector	PLB 728 (2013) 363	1310.6527
13	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004,.%\%CITATION = JINST,3,S08004;\%\%	CMS-00-001
14	DELPHI Collaboration	Measurement of the mass and width of the $\mathrm{ W }\$ boson in $\mathrm{ e }^{+}\mathrm{ e }^{-}$ collisions at $\sqrt{s} =$ 161-209 GeV	EPJD 55 (2008) 1, ,%\%CITATION = 0803.2534;\%\%	0803.2534
15	CMS Collaboration	Performance of CMS muon reconstruction in pp collision events at $\sqrt{s} =$ 7 TeV	JINST 7 (2012) P10002	CMS-MUO-10-004 1206.4071
16	CMS Collaboration	Energy calibration and resolution of the CMS electromagnetic calorimeter in pp collisions at $\sqrt{s} =$ 7 TeV	JINST 8 (2013) P09009	CMS-EGM-11-001 1306.2016
17	CMS Collaboration	Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $\sqrt{s} =$ 8 TeV	JINST 10 (2015) P06005	CMS-EGM-13-001 1502.02701
18	CMS Collaboration	CMS luminosity based on pixel cluster counting---Summer 2013 update	CMS-PAS-LUM-13-001	CMS-PAS-LUM-13-001
19	J. Alwall et al.	MadGraph 5: going beyond	JHEP 06 (2011) 128	1106.0522
20	T. Sjostrand, S. Mrenna, and P. Skands	PYTHIA 6.4 physics and manual	JHEP 05 (2006) 026	hep-ph/0603175
21	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
22	S. Alioli, P. Nason, C. Oleari, and E. Re	A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX	JHEP 06 (2010) 043	1002.2581
23	S. Alioli, P. Nason, C. Oleari, and E. Re	NLO single-top production matched with shower in POWHEG: $s$ - and $t$ -channel contributions	JHEP 09 (2009) 111, , [Erratum: \DOI10.1007/JHEP02(2010)011]	0907.4076
24	E. Re	Single-top Wt-channel production matched with parton showers using the POWHEG method	EPJC 71 (2011) 1547	1009.2450
25	S. Frixione and B. R. Webber	The MC@NLO 3.4 event generator		0812.0770
26	G. Corcella et al.	HERWIG 6: an event generator for hadron emission reactions with interfering gluons (including supersymmetric processes)	JHEP 01 (2001) 010	hep-ph/0011363
27	GEANT4 Collaboration	GEANT4---a simulation toolkit	NIMA 506 (2003) 250
28	K. Melnikov and F. Petriello	Electroweak gauge boson production at hadron colliders through $\mathcal{O}(\alpha_s^2$ )	PRD 74 (2006) 114017	hep-ph/0609070
29	M. Czakon, P. Fiedler, and A. Mitov	The total top quark pair production cross-section at hadron colliders through $\mathcal{O}(\alpha_s^4)$	PRL 110 (2013) 252004	1303.6254
30	N. Kidonakis	NNLL threshold resummation for top-pair and single-top production		1210.7813
31	CMS Collaboration	Commissioning of the particle-flow reconstruction in minimum-bias and jet events from pp collisions at 7 TeV	CDS
32	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063, ,%\%CITATION = 0802.1189;\%\%	0802.1189
33	CMS Collaboration	Determination of jet energy calibration and transverse momentum resolution in CMS	JINST 6 (2011) 11002	CMS-JME-10-011 1107.4277
34	CMS Collaboration	Missing transverse energy performance of the CMS detector	JINST 6 (2011) 09001	CMS-JME-10-009 1106.5048
35	CMS Collaboration	Measurement of the $\mathrm{ t \bar{t} }\$ production cross section in the $\mathrm{ e } \mu$ channel in proton-proton collisions at $\sqrt{s} =$ 7 and 8 TeV	Submitted to JHEP	CMS-TOP-13-004 1603.02303
36	CMS Collaboration	Identification of b-quark jets with the CMS experiment	JINST 8 (2013) 04013, ,%\%CITATION = ARXIV:1204.2807;\%\%	CMS-BTV-12-001 1211.4462
37	CMS Collaboration	Measurement of differential top-quark pair production cross sections in pp colisions at $\sqrt{s} =$ 7 TeV	EPJC 73 (2013) 2339	CMS-TOP-11-013 1211.2220
38	CMS Collaboration	Measurement of the differential cross section for top quark pair production in pp collisions at $\sqrt{s} =$ 8 TeV	EPJC 75 (2015) 542	CMS-TOP-12-028 1505.04480
39	CMS Collaboration	Measurement of the $\mathrm{t}\overline{{\mathrm{t}}}$ production cross section in the all-jets final state in pp collisions at $\sqrt{s} =$ 8 TeV	EPJC 76 (2016) 128	CMS-TOP-14-018 1509.06076
40	CMS Collaboration	Measurement of the top quark mass using proton-proton data at $\sqrt{s} =$ 7 TeV and 8 TeV	PRD 93 (2016) 072044	CMS-TOP-14-022 1509.04044
41	P. Van Mulders	Calibration of the jet energy scale using top quark events at the LHC	PhD thesis, Vrije Universiteit, Brussel, 2010
42	J. D'Hondt et al.	Fitting of event topologies with external kinematic constraints in CMS	CMS Note 2006/023
43	S. Blyweert	Measurement of the top-quark mass and the mass difference between top and anti-top quarks at the LHC	PhD thesis, Vrije Universiteit, Brussel, 2014
44	The ATLAS, CDF, CMS and D0 Collaborations	First combination of Tevatron and LHC measurements of the top-quark mass		1403.4427
45	R. G. Miller	The jackknife---a review	Biometrika 61 (1974) 1
46	CMS Collaboration	Measurements of the $\mathrm{ t \bar{t} }\$ production cross section in lepton+jets final states in pp collisions at 8 $TeV$ and ratio of 8 to 7 TeV cross sections		CMS-TOP-12-006 1602.09024
47	CMS Collaboration	Measurement of the lepton charge asymmetry in inclusive W production in pp collisions at $\sqrt{s} =$ 7 TeV	JHEP 04 (2011) 050	CMS-EWK-10-006 1103.3470
48	CMS Collaboration	Measurement of inclusive W and Z boson production cross sections in pp collisions at $\sqrt{s} =$ 8 TeV	PRL 112 (2014) 191802	CMS-SMP-12-011 1402.0923
49	CMS Collaboration	Measurement of the $t$ -channel single-top-quark production cross section and of the $\|V_{\mathrm{t }\mathrm{b }}\|$ CKM matrix element in pp collisions at $\sqrt{s} =$ 8 TeV	JHEP 06 (2014) 090	CMS-TOP-12-038 1403.7366
50	P. M. Nadolsky et al.	Implications of CTEQ global analysis for collider observables	PRD 78 (2008) 013004	0802.0007