CMS-TOP-22-007

CMS-TOP-22-007 ; CERN-EP-2024-085
Searches for violation of Lorentz invariance in $ \mathrm{t} \overline{\mathrm{t}} $ production using dilepton events in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
23 May 2024
Phys. Lett. B 857 (2024) 138979
Abstract: A search for violation of Lorentz invariance in the production of top quark pairs ($ \mathrm{t} \overline{\mathrm{t}} $) is presented. The measured normalized differential $ \mathrm{t} \overline{\mathrm{t}} $ production cross section, as a function of the sidereal time, is examined for potential modulations induced by Lorentz-invariance breaking operators in an effective field theory extension of the standard model (SM). The cross section is measured from collision events collected by the CMS detector at a center-of-mass-energy of 13 TeV, corresponding to an integrated luminosity of 77.8 fb$ ^{-1} $, and containing one electron and one muon. The results are found to be compatible with zero, in agreement with the SM, and are used to place upper limits at 68% confidence level on the magnitude of the Lorentz-violating couplings ranging from 1-8 $ \times $ 10$^{-3} $. This is the first precision test of the isotropy in special relativity with top quarks at the LHC, restricting further the bounds on such couplings by up to two orders of magnitude with respect to previous searches conducted at the Tevatron.
Links: e-print arXiv:2405.14757 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Distribution of the number of b jets in data and simulation, after the event selection, (left) in 2016 and (right) in 2017 samples. The hatched band includes statistical and systematic uncertainties in the predictions. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 1-a: Distribution of the number of b jets in data and simulation, after the event selection, (left) in 2016 and (right) in 2017 samples. The hatched band includes statistical and systematic uncertainties in the predictions. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 1-b: Distribution of the number of b jets in data and simulation, after the event selection, (left) in 2016 and (right) in 2017 samples. The hatched band includes statistical and systematic uncertainties in the predictions. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 2: Prefit (upper) and postfit (lower) distributions of the number of b jets in sidereal hour bins, in 2016 and 2017 data. The gray band reflects the statistical and systematic uncertainty predicted in each bin, including correlations across bins. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 2-a: Prefit (upper) and postfit (lower) distributions of the number of b jets in sidereal hour bins, in 2016 and 2017 data. The gray band reflects the statistical and systematic uncertainty predicted in each bin, including correlations across bins. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 2-b: Prefit (upper) and postfit (lower) distributions of the number of b jets in sidereal hour bins, in 2016 and 2017 data. The gray band reflects the statistical and systematic uncertainty predicted in each bin, including correlations across bins. The vertical bars associated with the data points represent their statistical uncertainty. The lower panels show the ratio of the observed data event yields to those expected from simulation.
png pdf	Figure 3: The normalized differential cross section for $ \mathrm{t} \overline{\mathrm{t}} $ as a function of sidereal time, using combined 2016-2017 data. The error bars show statistical, as well as statistical and systematic uncertainties, including correlations across bins.
png pdf	Figure 4: Comparison of systematic and statistical uncertainties, where the former are grouped according to the treatment of time dependence:\ uniform (flat luminosity component, background normalization, theory), correlated (trigger, luminosity stability and linearity, pileup, and MC statistical uncertainty), or uncorrelated (other experimental uncertainties) across sidereal time bins.
png pdf	Figure 5: Number of $ \mathrm{t} \overline{\mathrm{t}} $ events reconstructed in the SME hypothesis divided by the number of events in the SM hypothesis, as a function of the number of b jets and sidereal time, for the four directions of the $ c_L $ coefficients. The uncertainty band represents the MC statistical uncertainty in the sample used to compute the SME hypothesis. The sinusoidal variation is arising from the $ f(t) $ dependence on sidereal time, while smaller structures reflect the number of b jets in each sidereal time bin.
png pdf	Figure 6: Fitted SME coefficients and their 68 and 95% CL, measured in fits of single coefficients while the coefficients corresponding to the three other directions are left floating, within the $ c_L $, $ c_R $, $ c $, and $ d $ families. The error bar includes statistical and systematic uncertainties. Fitting a single coefficient, with the others fixed to the SM value, leads to negligible changes in the results.
png pdf	Figure 7: Uncertainty breakdown for SME fits of single coefficients while the coefficients corresponding to the three other directions are left floating, by splitting according to the treatment of time dependence: flat across sidereal time (flat luminosity component, background normalization, theory), correlated in sidereal time bins (trigger, luminosity stability and linearity, pileup, MC statistical uncertainty, single top quark decay in the SME), systematics uncorrelated in sidereal time bins (other experimental uncertainties), and statistical uncertainty.

Tables
png pdf	Table 1: Event yields in data and MC simulation in 2016-2017, after selection. The uncertainties include statistical and systematic sources, with correlations.
png pdf	Table 2: Summary of the systematic uncertainties and their correlation scheme between 2016 and 2017 data sets, and between sidereal time bins. Sources marked with an asterisk are only included in the SME fits. Sources marked with a dagger are uniform and correlated in sidereal time.
png pdf	Table 3: Expected and observed 68% confidence level interval measured for the SME fits of single coefficients while the others are fixed to their SM value, and while coefficients for the three other directions are floating.

Summary

A search for violation of Lorentz invariance has been performed using top quark pairs ($ \mathrm{t} \overline{\mathrm{t}} $), requiring the presence of one muon and one electron in the events. Data collected in 2016-2017 with the CMS detector corresponding to an integrated luminosity of 77.8 fb$ ^{-1} $ are used. A measurement of the $ \mathrm{t} \overline{\mathrm{t}} $ normalized differential cross section as a function of sidereal time is performed. The Lorentz invariance assumption is tested by measuring 16 sets of Wilson coefficients within the standard model extension, an effective field theory predicting a modulation of the $ \mathrm{t} \overline{\mathrm{t}} $ cross section with sidereal time. Measurements of the Lorentz-violating couplings are found to be compatible with the standard model hypothesis. The precision of the results ranges from less than 1 $ \times $ 10$^{-3} $ to 8 $ \times $ 10$^{-3} $ for the measured coefficients. This constitutes the most precise test of the isotropy in special relativity using top quarks at a hadron collider.

References
1	V. A. Kostelecky and S. Samuel	Spontaneous breaking of Lorentz symmetry in string theory	PRD 39 (1989) 683
2	R. Gambini and J. Pullin	Nonstandard optics from quantum space-time	PRD 59 (1999) 124021	gr-qc/9809038
3	M. Pospelov and C. Tamarit	Lifshitz-sector mediated SUSY breaking	JHEP 01 (2014) 048	1309.5569
4	D. Colladay and V. A. Kostelecky	CPT violation and the standard model	PRD 55 (1997) 6760	hep-ph/9703464
5	D. Colladay and V. A. Kostelecky	Lorentz-violating extension of the standard model	PRD 58 (1998) 116002	hep-ph/9809521
6	V. A. Kostelecky and N. Russell	Data tables for Lorentz and CPT violation	Rev. Mod. Phys. 83 (2011) 11	0801.0287
7	ZEUS Collaboration	Search for effective Lorentz and CPT violation using ZEUS data	PRD 107 (2023) 092008	2212.12750
8	KLOE-2 Collaboration	Test of CPT and Lorentz symmetry in entangled neutral kaons with the KLOE experiment	PLB 730 (2014) 89	1312.6818
9	H. Nguyen	CPT results from KTeV	in Proc. 2nd Meeting on CPT and Lorentz Symmetry: Bloomington IN, USA, 2001 link	hep-ex/0112046
10	FOCUS Collaboration	Charm system tests of CPT and Lorentz invariance with FOCUS	PLB 556 (2003) 7	hep-ex/0208034
11	BaBar Collaboration	Search for CPT and Lorentz violation in $ {\mathrm{B}^0} \overline{\mathrm{B}}^{0} $ oscillations with dilepton events	PRL 100 (2008) 131802	0711.2713
12	D0 Collaboration	Search for violation of CPT and Lorentz invariance in $ \mathrm{B}_{s}^{0} $ meson oscillations	PRL 115 (2015) 161601	1506.04123
13	LHCb Collaboration	Search for violations of Lorentz invariance and CPT symmetry in \HepParticle$ {\mathrm{B}} $(s)0 mixing	PRL 116 (2016) 241601	1603.04804
14	D0 Collaboration	Search for violation of Lorentz invariance in top quark pair production and decay	PRL 108 (2012) 261603	1203.6106
15	A. Carle, N. Chanon, and S. Perries	Prospects for Lorentz invariance violation searches with top pair production at the LHC and future hadron colliders	EPJC 80 (2020) 128	1908.11256
16	M. S. Berger, V. A. Kostelecky, and Z. Liu	Lorentz and CPT violation in top-quark production and decay	PRD 93 (2016) 036005	1509.08929
17	CMS Collaboration	HEPData record for this analysis	link
18	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
19	CMS Tracker Group Collaboration	The CMS Phase-1 pixel detector upgrade	JINST 16 (2021) P02027	2012.14304
20	CMS Collaboration	Development of the CMS detector for the CERN LHC Run 3	Accepted by JINST, 2023	CMS-PRF-21-001 2309.05466
21	CMS Collaboration	Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	JINST 15 (2020) P10017	CMS-TRG-17-001 2006.10165
22	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
23	CMS Collaboration	Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC	JINST 16 (2021) P05014	CMS-EGM-17-001 2012.06888
24	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
25	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
26	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
27	CMS Collaboration	Performance of reconstruction and identification of $ \tau $ leptons decaying to hadrons and $ \nu_{\!\tau} $ in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 13 TeV	JINST 13 (2018) P10005	CMS-TAU-16-003 1809.02816
28	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in $ {\mathrm{p}\mathrm{p}} $ collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
29	CMS Collaboration	Performance of missing transverse momentum reconstruction in proton-proton collisions at $ \sqrt{s}= $ 13 TeV using the CMS detector	JINST 14 (2019) P07004	CMS-JME-17-001 1903.06078
30	M. Cacciari, G. P. Salam, and G. Soyez	FASTJET user manual	EPJC 72 (2012) 1896	1111.6097
31	CMS Collaboration	Measurements of inclusive W and Z cross sections in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV	JHEP 01 (2011) 080	CMS-EWK-10-002 1012.2466
32	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ k_{\mathrm{T}} $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
33	CMS Collaboration	Identification of heavy-flavour jets with the CMS detector in $ {\mathrm{p}\mathrm{p}} $ collisions at 13 TeV	JINST 13 (2018) P05011	CMS-BTV-16-002 1712.07158
34	CMS Collaboration	Performance summary of AK4 jet b tagging with data from proton-proton collisions at 13 TeV with the CMS detector	CMS Detector Performance Note CMS-DP-2023-005, 2023 CDS
35	S. Alioli, P. Nason, C. Oleari, and E. Re	A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG \textscbox	JHEP 06 (2010) 043	1002.2581
36	T. Sjöstrand et al.	An introduction to PYTHIA8.2	Comput. Phys. Commun. 191 (2015) 159	1410.3012
37	M. Czakon and A. Mitov	\textsctop++: a program for the calculation of the top-pair cross-section at hadron colliders	Comput. Phys. Commun. 185 (2014) 2930	1112.5675
38	CMS Collaboration	Measurement of the differential cross section for top quark pair production in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s} = $ 8 TeV	EPJC 75 (2015) 542	CMS-TOP-12-028 1505.04480
39	CMS Collaboration	Measurement of differential cross sections for top quark pair production using the lepton+jets final state in proton-proton collisions at 13 TeV	PRD 95 (2017) 092001	CMS-TOP-16-008 1610.04191
40	CMS Collaboration	Differential cross section measurements for the production of top quark pairs and of additional jets using dilepton events from $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 13 TeV	Submitted to JHEP, 2024	CMS-TOP-20-006 2402.08486
41	N. Kidonakis and N. Yamanaka	Higher-order corrections for $ {\mathrm{t}\mathrm{W}} $ production at high-energy hadron colliders	JHEP 05 (2021) 278	2102.11300
42	J. Alwall et al.	The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations	JHEP 07 (2014) 079	1405.0301
43	R. Frederix and S. Frixione	Merging meets matching in MC@NLO	JHEP 12 (2012) 061	1209.6215
44	P. Kant et al.	\textschathor for single top-quark production: Updated predictions and uncertainty estimates for single top-quark production in hadronic collisions	Comput. Phys. Commun. 191 (2015) 74	1406.4403
45	T. Gehrmann et al.	$ {\mathrm{W^+}\mathrm{W^-}} $ production at hadron colliders in next to next to leading order QCD	PRL 113 (2014) 212001	1408.5243
46	J. M. Campbell, R. K. Ellis, and C. Williams	Vector boson pair production at the LHC	JHEP 07 (2011) 018	1105.0020
47	J. Alwall, S. de Visscher, and F. Maltoni	QCD radiation in the production of heavy colored particles at the LHC	JHEP 02 (2009) 017	0810.5350
48	R. Gavin, Y. Li, F. Petriello, and S. Quackenbush	FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order	Comput. Phys. Commun. 182 (2011) 2388	1011.3540
49	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
50	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
51	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
52	GEANT4 Collaboration	GEANT 4--a simulation toolkit	NIM A 506 (2003) 250
53	S. van der Meer	Calibration of the effective beam height in the ISR	ISR Report CERN-ISR-PO-68-31, 1968
54	P. Grafström and W. Kozanecki	Luminosity determination at proton colliders	Prog. Part. Nucl. Phys. 81 (2015) 97
55	CMS Collaboration	Precision luminosity measurement in proton-proton collisions at $ \sqrt{s}= $ 13 TeV in 2015 and 2016 at CMS	EPJC 81 (2021) 800	CMS-LUM-17-003 2104.01927
56	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s}= $ 13 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
57	CMS BRIL Collaboration	The Pixel Luminosity Telescope: a detector for luminosity measurement at CMS using silicon pixel sensors	EPJC 83 (2023) 673	2206.08870
58	CMS Collaboration	Search for charged-lepton flavor violation in top quark production and decay in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 13 TeV	JHEP 06 (2022) 082	CMS-TOP-19-006 2201.07859
59	CMS Collaboration	Measurement of the $ \mathrm{t} \overline{\mathrm{t}} $ production cross section, the top quark mass, and the strong coupling constant using dilepton events in $ {\mathrm{p}\mathrm{p}} $ collisions at $ \sqrt{s}= $ 13 TeV	EPJC 79 (2019) 368	CMS-TOP-17-001 1812.10505
60	CMS Collaboration	Measurement of the cross section for top quark pair production in association with a W or Z boson in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	JHEP 08 (2018) 011	CMS-TOP-17-005 1711.02547
61	ATLAS and CMS Collaborations, and LHC Higgs Combination Group	Procedure for the LHC Higgs boson search combination in Summer 2011	Technical Report CMS-NOTE-2011-005, ATL-PHYS-PUB-2011-11, 2011
62	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
63	CMS Collaboration	The CMS statistical analysis and combination tool: \textsccombine	Submitted to Comput. Softw. Big Sci, 2024	CMS-CAT-23-001 2404.06614
64	S. Baker and R. D. Cousins	Clarification of the use of chi-square and likelihood functions in fits to histograms	NIM 221 (1984) 437
65	L. Demortier	$ p $ values and nuisance parameters	in Proc. LHC Workshop on Statistical Issues for LHC Physics (PHYSTAT-LHC): Geneva, 2007 link
66	M. Jones	Computation of WGS84 geodetic coordinates and azimuths at the LHC interaction points	CERN TS/SU-ACG Activity Report, 2005 EDMS Document 32274 (2005) 7