CMS-PAS-B2G-20-002

CMS-PAS-B2G-20-002
Search for W' decaying to a vector-like quark and a top or bottom quark in the all-jets final state
CMS Collaboration
March 2021

Abstract: A search for a heavy W' boson resonance decaying to one B or T vector-like quark and a top or bottom quark, respectively, is presented. The analysis is performed using proton-proton collision data collected from the year 2016 to 2018 with the CMS detector at the LHC. The data correspond to an integrated luminosity of 137 fb $^{-1}$ at a center-of-mass energy of 13 TeV. Both decay channels result in a final state with a top quark, a Higgs or Z boson, and a b quark, each produced with significant energy. The all-hadronic decays of both the Higgs boson and the top quark are considered. The final-state jets, some of which correspond to merged decay products of a boosted top quark and a Higgs or Z boson, are selected using jet substructure techniques, which help to suppress standard model backgrounds. A W' boson signal would appear as a narrow peak in the invariant mass distribution of these three jets. No significant deviation in data with respect to the standard model background predictions is observed. The 95% confidence level upper limits on the cross section for W' boson production and the subsequent decay into a top quark, Higgs or Z boson, and b quark are set as a function of the W' boson mass, for several vector-like quark mass hypotheses. We exclude a W' boson in this channel with a mass below 3.2 TeV given benchmark model assumptions, and additionally present limits based on generalizations of these assumptions. This is the first search for a W' boson in this channel using the full 2016 to 2018 CMS data.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Dominant diagrams for the signal model considered in the analysis. The analysis assumes equal branching fractions for W' boson to tB and bT and 50% for each VLQ to qH and qZ for the benchmark model.
png pdf	Figure 1-a: Dominant diagram for tB production in the considered signal model. The analysis assumes equal branching fractions for the B-VQL to bH and bZ for the benchmark model.
png pdf	Figure 1-b: Dominant diagram for bT production in the considered signal model. The analysis assumes equal branching fractions for the T-VQL to tH and tZ for the benchmark model.
png pdf	Figure 2: Normalized distributions of the discriminating variables in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tHb signal MC simulation for the tHb analysis. Each variable distribution in this set of figures is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 2-a: Normalized distribution of the $m_{\mathrm{SD}}(\mathrm{T})$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tHb signal MC simulation for the tHb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 2-b: Normalized distribution of the imageMD $_{\mathrm{top}}$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tHb signal MC simulation for the tHb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 2-c: Normalized distribution of the $m_{\mathrm{SD}}(\mathrm{H})$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tHb signal MC simulation for the tHb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 2-d: Normalized distribution of the Dbtag variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tHb signal MC simulation for the tHb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 3: Normalized distributions of the discriminating variables in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tZb signal MC simulation for the tZb analysis. Each variable distribution in this set of figures is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 3-a: Normalized distribution of the $m_{\mathrm{SD}}(\mathrm{T})$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tZb signal MC simulation for the tZb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 3-b: Normalized distribution of the imageMD $_{\mathrm{top}}$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tZb signal MC simulation for the tZb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 3-c: Normalized distribution of the $m_{\mathrm{SD}}(\mathrm{Z})$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tZb signal MC simulation for the tZb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 3-d: Normalized distribution of the $\tau_{21}$ variable in ${\mathrm{t} {}\mathrm{\bar{t}}}$ , QCD, and tZb signal MC simulation for the tZb analysis. In this distribution, the variable is required to pass a loosened event selection that preserves same-jet variable correlations.
png pdf	Figure 4: Cut profile diagram used for background estimation. The signal region is labeled C, the A and B regions are used for the purpose of creating the ${TF({p_{\mathrm {T}}},\eta)}$ , and F is the validation region. After a senisitivity comparison, K and H are additionally used as validation regions. The loose, medium, and tight tag definitions are given in Table 1.
png pdf	Figure 5: Background closure for the reconstructed W' boson invariant mass in region F (upper left), K (upper right), and H (bottom) for the purpose of validation in the tHb analyses. The lower panels show the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 5-a: Background closure for the reconstructed W' boson invariant mass in region F for the purpose of validation in the tHb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 5-b: Background closure for the reconstructed W' boson invariant mass in region K for the purpose of validation in the tHb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 5-c: Background closure for the reconstructed W' boson invariant mass in region H for the purpose of validation in the tHb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 6: Background closure for the reconstructed W' boson invariant mass in region F (upper left), K (upper right), and H (bottom) for the purpose of validation in the tZb analyses. The lower panels show the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 6-a: Background closure for the reconstructed W' boson invariant mass in region F for the purpose of validation in the tZb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 6-b: Background closure for the reconstructed W' boson invariant mass in region K for the purpose of validation in the tZb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 6-c: Background closure for the reconstructed W' boson invariant mass in region H for the purpose of validation in the tZb analyses. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 7: Reconstructed W' boson mass distributions ( ${m_{\mathrm {\mathrm{t} \mathrm{H} \mathrm{b}}}}$ (top), and ${m_{\mathrm {\mathrm{t} \mathrm{Z} \mathrm{b}}}}$ (bottom)) in the signal region with estimated backgrounds, and several signal benchmarks. The uncertainties shown in the hatched region contain both statistical and systematic uncertainties of all background components. The lower panels show the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 7-a: Reconstructed W' boson mass distribution ($ {m_{\mathrm {\mathrm{t} \mathrm{H} \mathrm{b}}}})in the signal region with estimated backgrounds, and several signal benchmarks. The uncertainties shown in the hatched region contain both statistical and systematic uncertainties of all background components. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 7-b: Reconstructed W' boson mass distribution (( ${m_{\mathrm {\mathrm{t} \mathrm{Z} \mathrm{b}}}}$ ) in the signal region with estimated backgrounds, and several signal benchmarks. The uncertainties shown in the hatched region contain both statistical and systematic uncertainties of all background components. The lower panel shows the difference between the number of events observed in the data and the predicted background, divided by the systematic uncertainty in the background and the statistical uncertainty in the data added in quadrature.
png pdf	Figure 8: The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm$ 1 and ${\pm}$ 2 $\sigma _{exp}$ uncertainties in the expected limit. The limits for low- (top), medium- (center), and high- (bottom) mass VLQ mass ranges are shown.
png pdf	Figure 8-a: The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm$ 1 and ${\pm}$ 2 $\sigma _{exp}$ uncertainties in the expected limit. The limits for the low-mass VLQ range are shown.
png pdf	Figure 8-b: The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm$ 1 and ${\pm}$ 2 $\sigma _{exp}$ uncertainties in the expected limit. The limits for the medium-mass VLQ range are shown.
png pdf	Figure 8-c: The W' boson 95% CL production cross section limits. The expected limits (dashed) and observed limits (solid), as well as the W' boson theoretical cross section and the PDF and scale normalization uncertainties are shown. The bands around the expected limit represent the $\pm$ 1 and ${\pm}$ 2 $\sigma _{exp}$ uncertainties in the expected limit. The limits for the high-mass VLQ range are shown.
png pdf	Figure 9: Generalized exclusion maps for hypotheses other than the benchmark model for the expected (top) and observed (bottom) limits, which assumes equal fraction of VLQ (B, T) flavor and equal VLQ branching ratio to qZ and qH. The VLQ flavor assumption (left) is generalized by varying the fraction of qB and qT from the W' decay between 0 and 1. The VLQ branching ratio (right) is generalized by varying the VLQ $\to$ qH and VLQ $\to$ qZ branching ratios.
png pdf	Figure 9-a: Generalized exclusion maps for hypotheses other than the benchmark model for the expected limits, which assumes equal fraction of VLQ (B, T) flavor and equal VLQ branching ratio to qZ and qH. The VLQ flavor assumption is generalized by varying the fraction of qB and qT from the W' decay between 0 and 1.
png pdf	Figure 9-b: Generalized exclusion maps for hypotheses other than the benchmark model for the expected limits, which assumes equal fraction of VLQ (B, T) flavor and equal VLQ branching ratio to qZ and qH. The VLQ branching ratio is generalized by varying the VLQ $\to$ qH and VLQ $\to$ qZ branching ratios.
png pdf	Figure 9-c: Generalized exclusion maps for hypotheses other than the benchmark model for the observed limits, which assumes equal fraction of VLQ (B, T) flavor and equal VLQ branching ratio to qZ and qH. The VLQ flavor assumption is generalized by varying the fraction of qB and qT from the W' decay between 0 and 1.
png pdf	Figure 9-d: Generalized exclusion maps for hypotheses other than the benchmark model for the observed limits, which assumes equal fraction of VLQ (B, T) flavor and equal VLQ branching ratio to qZ and qH. The VLQ branching ratio is generalized by varying the VLQ $\to$ qH and VLQ $\to$ qZ branching ratios.

Tables
png pdf	Table 1: Selection regions used in the analysis. The AK8 jet discriminator and mass selections are explicitly defined here.
png pdf	Table 2: The signal efficiency (in percent) from the three VLQ mass ranges considered in the analysis. The efficiency is given for both the tHb and tZb final states considering the corresponding selection.
png pdf	Table 3: Sources of systematic uncertainty that affect the final distributions. Sources that list the systematic variation as $\pm$ 1 $\sigma$ have a shape effect which is dependent on the variable given in the parentheses, while those that list the variation in percent are rate uncertainties with the range of values specifying the year-to-year envelope.

Summary

A search for a heavy W' boson decaying to a B or T vector-like quark and a top or b quark, respectively, has been presented. The data correspond to an integrated luminosity of 137 fb

$^{-1}$ collected between 2016 and 2018 with the CMS detector at the LHC. The signature considered for both decay modes is a top quark and a Higgs or Z boson, both decaying hadronically, and a b quark jet. Boosted heavy-resonance identification techniques are used to select the event signature of three energetic jets and to suppress standard model backgrounds. No significant deviation from the standard model background prediction has been observed. Cross section upper limits on W' boson production in the top quark, Higgs or Z boson, and b quark decay mode are set as a function of the W' boson mass, for several vector-like quark mass hypotheses. A W' boson with a mass below 3.2 TeV is excluded at 95% CL given benchmark model assumptions.

References
1	M. Schmaltz and D. Tucker-Smith	Little Higgs theories	Ann. Rev. of Nucl. and Part. Sci. 55 (2005) 229	hep-ph/0502182
2	T. Appelquist, H.-C. Cheng, and B. A. Dobrescu	Bounds on universal extra dimensions	PRD 64 (2001) 035002	hep-ph/0012100
3	R. N. Mohapatra and J. C. Pati	Left-right gauge symmetry and an 'isoconjugate' model of CP violation	PRD 11 (1975) 566
4	CMS Collaboration	Search for heavy gauge W' boson in events with an energetic lepton and large missing transverse momentum at $\sqrt{s} =$ 13 TeV	PLB 770 (2017) 278	CMS-EXO-15-006 1612.09274
5	ATLAS Collaboration	Search for a new heavy gauge boson resonance decaying into a lepton and missing transverse momentum in 36 fb $^{-1}$ of $pp$ collisions at $\sqrt{s} =$ 13 TeV with the ATLAS experiment	EPJC 78 (2018) 401	1706.04786
6	CMS Collaboration	Search for a heavy resonance decaying to a pair of vector bosons in the lepton plus merged jet final state at $\sqrt{s}=$ 13 TeV	JHEP 05 (2018) 088	CMS-B2G-16-029 1802.09407
7	ATLAS Collaboration	Search for WW/WZ resonance production in $\nu$ qq final states in pp collisions at $\sqrt{s} =$ 13 TeV with the ATLAS detector	JHEP 03 (2018) 042	1710.07235
8	CMS Collaboration	Searches for $\mathrm{W'}$ bosons decaying to a top quark and a bottom quark in proton-proton collisions at 13 TeV	JHEP 08 (2017) 029	CMS-B2G-16-016 1706.04260
9	ATLAS Collaboration	Search for $W' \rightarrow tb$ decays in the hadronic final state using pp collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector	PLB 781 (2018) 327	1801.07893
10	CMS Collaboration	Search for single production of a vector-like T quark decaying to a Z boson and a top quark in proton-proton collisions at $\sqrt{s} =$ 13 TeV	PLB 781 (2018) 574	CMS-B2G-17-007 1708.01062
11	CMS Collaboration	Search for single production of vector-like quarks decaying to a b quark and a Higgs boson	JHEP 06 (2018) 031	CMS-B2G-17-009 1802.01486
12	ATLAS Collaboration	Search for pair- and single-production of vector-like quarks in final states with at least one $Z$ boson decaying into a pair of electrons or muons in $pp$ collision data collected with the ATLAS detector at $\sqrt{s} =$ 13 TeV	PRD 98 (2018), no. 11, 112010	1806.10555
13	CMS Collaboration	Search for single production of vector-like quarks decaying into a b quark and a W boson in proton-proton collisions at $\sqrt s =$ 13 TeV	PLB 772 (2017) 634	CMS-B2G-16-006 1701.08328
14	CMS Collaboration	Search for pair production of vector-like quarks in the bWbW channel from proton-proton collisions at $\sqrt{s} =$ 13 TeV	PLB 779 (2018) 82	CMS-B2G-17-003 1710.01539
15	CMS Collaboration	Search for vector-like T and B quark pairs in final states with leptons at $\sqrt{s} =$ 13 TeV	JHEP 08 (2018) 177	CMS-B2G-17-011 1805.04758
16	CMS Collaboration	A search for bottom-type, vector-like quark pair production in a fully hadronic final state in proton-proton collisions at $\sqrt{s} =$ 13 TeV	PRD 102 (2020) 112004	CMS-B2G-19-005 2008.09835
17	ATLAS Collaboration	Combination of the searches for pair-produced vector-like partners of the third-generation quarks at $\sqrt{s} =$ 13 TeV with the ATLAS detector	PRL 121 (2018), no. 21, 211801	1808.02343
18	K. Agashe, R. Contino, and A. Pomarol	The minimal composite Higgs model	NPB 719 (2005) 165	hep-ph/0412089
19	D. Barducci et al.	Exploring drell-yan signals from the 4d composite higgs model at the lhc	JHEP 04 (2013) 152	1210.2927
20	D. Barducci and C. Delaunay	Bounding wide composite vector resonances at the lhc	JHEP 02 (2016) 55	1511.01101
21	N. Vignaroli	New W $'$ signals at the LHC	PRD 89 (2014) 095027	1404.5558
22	CMS Collaboration	CMS luminosity measurements for the 2016 data taking period	CMS-PAS-LUM-17-001	CMS-PAS-LUM-17-001
23	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $\sqrt{s} =$ 13 TeV	CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
24	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $\sqrt{s} =$ 13 TeV	CMS-PAS-LUM-18-002	CMS-PAS-LUM-18-002
25	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
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	M. Cacciari, G. P. Salam, and G. Soyez	The anti- ${k_{\mathrm{T}}}$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
28	M. Cacciari, G. P. Salam, and G. Soyez	Fastjet user manual	EPJC 72 (2012) 1896	1111.6097
29	D. Bertolini, P. Harris, M. Low, and N. Tran	Pileup per particle identification	JHEP 10 (2014) 059	1407.6013
30	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
31	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
32	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
33	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
34	P. Nason	A new method for combining NLO QCD with shower Monte Carlo algorithms	JHEP 11 (2004) 040	hep-ph/0409146
35	S. Frixione, P. Nason, and G. Ridolfi	A positive-weight next-to-leading-order Monte Carlo for heavy flavour hadroproduction	JHEP 09 (2007) 126	0707.3088
36	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
37	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
38	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
39	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
40	T. Sjostrand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
41	CMS Collaboration	Investigations of the impact of the parton shower tuning in Pythia 8 in the modelling of $\mathrm{t\overline{t}}$ at $\sqrt{s}=$ 8 and 13 TeV	CMS-PAS-TOP-16-021	CMS-PAS-TOP-16-021
42	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
43	GEANT4 Collaboration	GEANT4--a a simulation toolkit	NIM506 (2003) 250
44	CMS Collaboration	Jet algorithms performance in 13 TeV data	CMS-PAS-JME-16-003	CMS-PAS-JME-16-003
45	CMS Collaboration	Identification of heavy, energetic, hadronically decaying particles using machine-learning techniques	JINST 15 (2020) P06005	CMS-JME-18-002 2004.08262
46	M. Dasgupta, A. Fregoso, S. Marzani, and G. P. Salam	Towards an understanding of jet substructure	JHEP 09 (2013) 029	1307.0007
47	A. J. Larkoski, S. Marzani, G. Soyez, and J. Thaler	Soft Drop	JHEP 05 (2014) 146	1402.2657
48	CMS Collaboration	A Cambridge-Aachen (C-A) based jet algorithm for boosted top-jet tagging	CDS
49	CMS Collaboration	Search for massive resonances decaying into $WW$ , $WZ$ , $ZZ$ , $qW$ , and $qZ$ with dijet final states at $\sqrt{s}=$ 13 TeV	PRD 97 (2018) 072006	CMS-B2G-17-001 1708.05379
50	CMS Collaboration	Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV	JINST 13 (2018) P05011	CMS-BTV-16-002 1712.07158
51	J. Thaler and K. Van Tilburg	Maximizing boosted top identification by minimizing N-subjettiness	JHEP 02 (2012) 093	1108.2701
52	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
53	J. S. Conway	Incorporating nuisance parameters in likelihoods for multisource spectra	in Proceedings, PHYSTAT 2011 workshop on statistical issues related to discovery claims in search experiments and unfolding, CERN, January 2011	1103.0354
54	CMS Collaboration	Measurement of the inelastic proton-proton cross section at $\sqrt{s}=$ 13 TeV	JHEP 07 (2018) 161	CMS-FSQ-15-005 1802.02613
55	R. J. Barlow and C. Beeston	Fitting using finite Monte Carlo samples	CPC 77 (1993) 219