CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-B2G-17-009 ; CERN-EP-2017-338
Search for single production of vector-like quarks decaying to a b quark and a Higgs boson
JHEP 06 (2018) 031
Abstract: A search is presented for single production of heavy vector-like quarks (B) that decay to a Higgs boson and a b quark, with the Higgs boson decaying to a highly boosted $ \mathrm{b\bar{b}} $ pair reconstructed as a single collimated jet. The analysis is based on data collected by the CMS experiment in proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The data are consistent with background expectations, and upper limits at 95% confidence level on the product of the B quark cross section and the branching fraction are obtained in the range 1.28-0.07 pb, for a narrow B quark with a mass between 700 and 1800 GeV. The production of B quarks with widths of 10, 20 and 30% of the resonance mass is also considered, and the sensitivities obtained are similar to those achieved in the narrow width case. This is the first search at the CERN LHC for the single production of a B quark through its fully hadronic decay channel, and the first study considering finite resonance widths of the B quark.
Figures & Tables Summary References CMS Publications
Figures

png pdf
Figure 1:
The leading-order Feynman diagram for the production of a single vector-like B quark in association with a b quark and light-flavour quark, and its decay to a Higgs boson and a b quark.

png pdf
Figure 2:
The b-tagged subjet multiplicity of AK8 jets in events passing preselection criteria. The lower panel shows the ratio of data to the MC background prediction. The normalization of the contributions from signals at $ {m_{{{\mathrm {B}}}}}= $ 1 and 1.8 TeV is multiplied by a factor of 500. Background events are normalized to data. Only the statistical uncertainties are taken into consideration here, and they are too small to be visible.

png pdf
Figure 3:
Multiplicity of forward jets before event categorization. The normalization of the signal contributions is multiplied by a factor of 500. The simulated background predictions are normalized to data. The lower panel shows the ratio of data to background. We show only the statistical uncertainties.

png pdf
Figure 4:
Distribution in the reconstructed B quark mass, after applying all selections to events with no forward jets (left) and to events with at least one forward jet (right), compared to the background distributions estimated before fitting. The upper and lower plots refer to the low- and high-mass $ {m_{{{\mathrm {B}}}}} $ analyses, respectively. The expectations for signal MC events are given by the blue histogram lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratios of observations to background expectations are given in the lower panels, together with the total uncertainties prior to fitting, indicated by the grey-hatched band.

png pdf
Figure 4-a:
Distribution in the reconstructed B quark mass, after applying all selections to events with no forward jet, compared to the background distributions estimated before fitting. The plot refers to the low-mass $ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue histogram lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of observations to background expectations is given in the lower panel, together with the total uncertainties prior to fitting, indicated by the grey-hatched band.

png pdf
Figure 4-b:
Distribution in the reconstructed B quark mass, after applying all selections to events with at least one forward jet, compared to the background distributions estimated before fitting. The plot refers to the low-mass $ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue histogram lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of observations to background expectations is given in the lower panel, together with the total uncertainties prior to fitting, indicated by the grey-hatched band.

png pdf
Figure 4-c:
Distribution in the reconstructed B quark mass, after applying all selections to events with no forward jet, compared to the background distributions estimated before fitting. The plot refers to the high-mass $ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue histogram lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of observations to background expectations is given in the lower panel, together with the total uncertainties prior to fitting, indicated by the grey-hatched band.

png pdf
Figure 4-d:
Distribution in the reconstructed B quark mass, after applying all selections to events with at least one forward jet, compared to the background distributions estimated before fitting. The plot refers to the high-mass $ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue histogram lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of observations to background expectations is given in the lower panel, together with the total uncertainties prior to fitting, indicated by the grey-hatched band.

png pdf
Figure 5:
Distribution in the reconstructed B quark mass after applying all selections to events with no forward jets (left) and to events with at least one forward jet (right), compared to the background distributions estimated after fitting. The upper and lower plots refer to the low- and high-$ {m_{{{\mathrm {B}}}}} $ analyses, respectively. The expectations for signal MC events are given by the blue lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratios of the observations to background expectations are given in the lower panels, together with the total uncertainties after fitting, indicated by the grey-hatched band.

png pdf
Figure 5-a:
Distribution in the reconstructed B quark mass after applying all selections to events with no forward jet, compared to the background distributions estimated after fitting. The plot refers to the low-$ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of the observations to background expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.

png pdf
Figure 5-b:
Distribution in the reconstructed B quark mass after applying all selections to events with at least one forward jet, compared to the background distributions estimated after fitting. The plot refers to the low-$ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of the observations to background expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.

png pdf
Figure 5-c:
Distribution in the reconstructed B quark mass after applying all selections to events with no forward jet, compared to the background distributions estimated after fitting. The plot refers to the high-$ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of the observations to background expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.

png pdf
Figure 5-d:
Distribution in the reconstructed B quark mass after applying all selections to events with at least one forward jet, compared to the background distributions estimated after fitting. The plot refers to the high-$ {m_{{{\mathrm {B}}}}} $ analysis. The expectations for signal MC events are given by the blue lines. Different contributions to background are indicated by the colour-filled histograms. The grey-hatched error band shows total uncertainties in the background expectation. The ratio of the observations to background expectations is given in the lower panel, together with the total uncertainties after fitting, indicated by the grey-hatched band.

png pdf
Figure 6:
The median observed and expected 95% CL upper limits on the product of the B quark production cross section and branching fraction as a function of the signal mass, assuming narrow-width resonances (upper-left) and widths of 10 (upper-right), 20 (lower-left), and 30% (lower-right) of the resonance mass for the B quark. The results are shown for the combination of 0 and $ > $0 forward-jet categories. The continuous red curves correspond to the theoretical expectations for singlet and doublet models.

png pdf
Figure 6-a:
The median observed and expected 95% CL upper limits on the product of the B quark production cross section and branching fraction as a function of the signal mass, assuming narrow-width resonances. The results are shown for the combination of 0 and $ > $0 forward-jet categories. The continuous red curves correspond to the theoretical expectations for singlet and doublet models.

png pdf
Figure 6-b:
The median observed and expected 95% CL upper limits on the product of the B quark production cross section and branching fraction as a function of the signal mass, assuming a width of 10% of the resonance mass for the B quark. The results are shown for the combination of 0 and $ > $0 forward-jet categories. The continuous red curves correspond to the theoretical expectations for singlet and doublet models.

png pdf
Figure 6-c:
The median observed and expected 95% CL upper limits on the product of the B quark production cross section and branching fraction as a function of the signal mass, assuming a width of 20% of the resonance mass for the B quark. The results are shown for the combination of 0 and $ > $0 forward-jet categories. The continuous red curves correspond to the theoretical expectations for singlet and doublet models.

png pdf
Figure 6-d:
The median observed and expected 95% CL upper limits on the product of the B quark production cross section and branching fraction as a function of the signal mass, assuming a width of 30% of the resonance mass for the B quark. The results are shown for the combination of 0 and $ > $0 forward-jet categories. The continuous red curves correspond to the theoretical expectations for singlet and doublet models.
Tables

png pdf
Table 1:
Cross sections for $ {\mathrm {p}} {\mathrm {p}}\to {{\mathrm {B}}} {\mathrm {b}} {\mathrm {q}}$, with the ratio $\Gamma _{{{\mathrm {B}}}}/ {m_{{{\mathrm {B}}}}}$ fixed to 1% (NWA). The couplings and branching fractions in simplified models are calculated using the equations in the text. The uncertainties in the production cross sections correspond to the halving and doubling of the QCD renormalization and factorization scales

png pdf
Table 2:
Cross sections for $ {\mathrm {p}} {\mathrm {p}}\to {{\mathrm {B}}} {\mathrm {b}} {\mathrm {q}}$ for three values of the $\Gamma _{{{\mathrm {B}}}}/ {m_{{{\mathrm {B}}}}} $ ratio. The conditions assume that singlets and doublets have $\kappa _{{\mathrm {W}}} = \kappa _{{\mathrm {Z}}} = \kappa _{{\mathrm {H}}}\equiv \kappa $, $\kappa _{{\mathrm {W}}} = $ 0 and $\kappa _{{\mathrm {Z}}} = \kappa _{{\mathrm {H}}}\equiv \kappa $, respectively. For each $\Gamma _{{{\mathrm {B}}}}/ {m_{{{\mathrm {B}}}}} $, we provide the values of $\tilde\sigma _\text {AW}$ and of the physical cross sections for both the singlet and doublet models, $\sigma _\text {S}$ and $\sigma _\text {D}$ respectively. The uncertainties in the production cross sections correspond to the halving and doubling of the QCD renormalization and factorization scales. The values of $\kappa $ are listed in the parentheses.

png pdf
Table 3:
Summary of systematic uncertainties in background events. The quantification of the effects quoted in the table reflects the uncertainties in the event yields. All uncertainties are considered in the simulated background events, except the one on background estimation that affects only the data-based estimate of the multijet process. All the systematic uncertainties apply to both categories of forward-jet multiplicity, except for the case of the modelling of the forward jets, where the first entry corresponds to the category with no forward jets, and the second entry to the category with at least one jet in the forward region.

png pdf
Table 4:
Observed and expected fitted number of events in the signal ranges of 700 $ < {m_{{{\mathrm {B}}}}} < $ 1500 and 1500 $ < {m_{{{\mathrm {B}}}}} < $ 1800 GeV, and expected signal at $ {m_{{{\mathrm {B}}}}}= $ 1000 and 1800 GeV. The multijet background is obtained from data, while the yields for the other sources of background are obtained from MC simulation. The combined statistical and systematic uncertainties correspond to the quadrature of the statistical and systematic uncertainties.
Summary
A search has been presented for electroweak production of vector-like B quarks with charge $-1/3\,e$, decaying to a bottom quark and a Higgs boson (H). The analysis uses a data sample corresponding to an integrated luminosity of 35.9 fb$^{-1}$ , collected in pp collisions at $\sqrt{s} = $ 13 TeV.

No significant deviations are observed relative to the standard model prediction, and upper limits are placed on the product of the cross section and the branching fraction of the B quark.

Expected and observed limits at 95% confidence level vary from 1.20 to 0.07 pb and from 1.28 to 0.07 pb, respectively, for B quark masses in the range considered, which extends from 700 to 1800 GeV. The search is performed under the hypothesis of a singlet or doublet B quark of narrow width decaying to Hb with a branching fraction of approximately 25%. The possibility of having non-negligible resonant widths is also studied. Limits obtained on the production of B quarks with widths of 10, 20, and 30% of the resonance mass are comparable to those found for the narrow-width approximation. This search extends existing knowledge on vector-like quarks, by interpreting the results in a new theoretical framework with non-negligible resonance widths, and investigating the final state with a bottom quark and a Higgs boson for the first time.
References
1 ATLAS Collaboration Observation of a new particle in the search for the standard model Higgs boson with the ATLAS detector at the LHC PLB 716 (2012) 1 1207.7214
2 CMS Collaboration Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC PLB 716 (2012) 30 CMS-HIG-12-028
1207.7235
3 ATLAS and CMS Collaborations Combined measurement of the Higgs boson mass in pp collisions at $ \sqrt{s}= $ 7 and 8 TeV with the ATLAS and CMS experiments PRL 114 (2015) 191803 1503.07589
4 J. A. Aguilar-Saavedra, R. Benbrik, S. Heinemeyer, and M. P\'erez-Victoria Handbook of vectorlike quarks: mixing and single production PRD 88 (2013) 094010 1306.0572
5 M. Schmaltz and D. Tucker-Smith Little Higgs review Ann. Rev. Nucl. Part. Sci. 55 (2005) 229 hep-ph/0502182
6 D. B. Kaplan and H. Georgi SU(2) x U(1) breaking by vacuum misalignment PLB 136 (1984) 183
7 H. Georgi, D. B. Kaplan, and P. Galison Calculation of the composite Higgs mass PLB 143 (1984) 152
8 M. J. Dugan, H. Georgi, and D. B. Kaplan Anatomy of a composite Higgs model NPB 254 (1985) 299
9 J. A. Aguilar-Saavedra Identifying top partners at LHC JHEP 11 (2009) 030 0907.3155
10 A. De Simone, O. Matsedonskyi, R. Rattazzi, and A. Wulzer A first top partner hunter's guide JHEP 04 (2013) 004 1211.5663
11 M. Buchkremer, G. Cacciapaglia, A. Deandrea, and L. Panizzi Model independent framework for searches of top partners NPB 876 (2013) 376 1305.4172
12 G. D. Kribs, T. Plehn, M. Spannowsky, and T. M. P. Tait Four generations and Higgs physics PRD 76 (2007) 075016 0706.3718
13 S. Banerjee, M. Frank, and S. K. Rai Higgs data confronts sequential fourth generation fermions in the Higgs triplet model PRD 89 (2014) 075005 1312.4249
14 ATLAS and CMS Collaborations Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at $ \sqrt{s}= $ 7 and 8 TeV JHEP 08 (2016) 045 1606.02266
15 O. Eberhardt et al. Joint analysis of Higgs decays and electroweak precision observables in the standard model with a sequential fourth generation PRD 86 (2012) 013011 1204.3872
16 CMS Collaboration Searches for Higgs bosons in pp collisions at $ \sqrt{s} = $ 7 and 8 TeV in the context of four-generation and fermiophobic models PLB 725 (2013) 36 CMS-HIG-12-013
1302.1764
17 ATLAS Collaboration Search for vector-like B quarks in events with one isolated lepton, missing transverse momentum and jets at $ \sqrt{s}= $ 8 TeV with the ATLAS detector PRD 91 (2015) 112011 1503.05425
18 ATLAS Collaboration Search for pair production of a new heavy quark that decays into a W boson and a light quark in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector PRD 92 (2015) 112007 1509.04261
19 ATLAS Collaboration Search for pair and single production of new heavy quarks that decay to a Z boson and a third-generation quark in pp collisions at $ \sqrt{s}= $ 8 TeV with the ATLAS detector JHEP 11 (2014) 104 1409.5500
20 ATLAS Collaboration Search for single production of a vector-like quark via a heavy gluon in the 4b final state with the ATLAS detector in pp collisions at $ \sqrt{s} = $ 8 TeV PLB 758 (2016) 249 1602.06034
21 ATLAS Collaboration Search for single production of vector-like quarks decaying into Wb in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector EPJC. 76 (2016) 442 1602.05606
22 ATLAS Collaboration Search for the production of single vector-like and excited quarks in the Wt final state in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector JHEP 02 (2016) 110 1510.02664
23 CMS Collaboration Search for vector-like charge 2/3 T quarks in proton-proton collisions at $ \sqrt{s} = $ 8 TeV PRD 93 (2016) 012003 CMS-B2G-13-005
1509.04177
24 CMS Collaboration Search for pair-produced vectorlike B quarks in proton-proton collisions at $ \sqrt{s} = $ 8 TeV PRD 93 (2016) 112009 CMS-B2G-13-006
1507.07129
25 CMS Collaboration Search for top-quark partners with charge 5/3 in the same-sign dilepton final state PRL 112 (2014) 171801 CMS-B2G-12-012
1312.2391
26 CMS Collaboration Search for single production of vector-like quarks decaying to a Z boson and a top or a bottom quark in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 05 (2017) 029 CMS-B2G-16-001
1701.07409
27 CMS Collaboration Search for single production of a heavy vector-like T quark decaying to a Higgs boson and a top quark with a lepton and jets in the final state PLB 771 (2017) 80 CMS-B2G-15-008
1612.00999
28 CMS Collaboration Search for electroweak production of a vector-like quark decaying to a top quark and a higgs boson using boosted topologies in fully hadronic final states JHEP 04 (2017) 136 CMS-B2G-16-005
1612.05336
29 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
30 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
31 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
32 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
33 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
34 CMS Collaboration Pileup removal algorithms CMS-PAS-JME-14-001 CMS-PAS-JME-14-001
35 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
36 CMS Collaboration Jet algorithms performance in 13 TeV data CMS-PAS-JME-16-003 CMS-PAS-JME-16-003
37 CMS Collaboration Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV Submitted to \it JINST CMS-BTV-16-002
1712.07158
38 S. D. Ellis, C. K. Vermilion, and J. R. Walsh Techniques for improved heavy particle searches with jet substructure PRD 80 (2009) 051501 0903.5081
39 S. Catani, Y. L. Dokshitzer, M. H. Seymour, and B. R. Webber Longitudinally-invariant k$ _\perp $-clustering algorithms for hadron-hadron collisions NPB 406 (1993) 187
40 M. Dasgupta, A. Fregoso, S. Marzani, and G. P. Salam Towards an understanding of jet substructure JHEP 09 (2013) 029 1307.0007
41 A. J. Larkoski, S. Marzani, G. Soyez, and J. Thaler Soft drop JHEP 05 (2014) 146 1402.2657
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 T. Sjostrand et al. An introduction to PYTHIA 8.2 CPC 191 (2015) 159 1410.3012
44 P. Skands, S. Carrazza, and J. Rojo Tuning PYTHIA 8.1: the Monash 2013 tune Euro. Phys. J. C 74 (2014) 3024 1404.5630
45 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements Euro. Phys. J. C 76 (2016) 155 CMS-GEN-14-001
1512.00815
46 P. Nason A new method for combining NLO QCD with shower Monte Carlo algorithms JHEP 11 (2004) 040 hep-ph/0409146
47 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
48 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with parton shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
49 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
50 M. Czakon and A. Mitov Top++: A program for the calculation of the top-pair cross-section at hadron colliders CPC 185 (2014) 2930 112.5675
51 Y. Li and F. Petriello Combining QCD and electroweak corrections to dilepton production in FEWZ PRD 86 (2012) 094034 1208.5967
52 C. Degrande et al. UFO --- The Universal FeynRules Output CPC 183 (2012) 1201 1108.2040
53 O. Matsedonskyi, G. Panico, and A. Wulzer On the interpretation of top partners searches JHEP 12 (2014) 097 1409.0100
54 NNPDF Collaboration Parton distributions from high-precision collider data EPJC 77 (2017) 663 1706.00428
55 GEANT4 Collaboration $ GEANT4--a $ simulation toolkit NIMA 506 (2003) 250
56 C. Y. Chen, S. Dawson, and E. Furlan Vectorlike fermions and Higgs effective field theory revisited PRD 96 (2017) 015006 1703.06134
57 J. Pumplin et al. New generation of parton distributions with uncertainties from global QCD analysis JHEP 07 (2002) 012 hep-ph/0201195
58 CMS Collaboration CMS luminosity measurements for the 2016 data taking period CMS-PAS-LUM-17-001 CMS-PAS-LUM-17-001
59 M. Botje et al. The PDF4LHC Working Group Interim Recommendations 1101.0538
60 S. Alekhin et al. The PDF4LHC Working Group Interim Report 1101.0536
61 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
62 T. Junk Confidence level computation for combining searches with small statistics NIMA 434 (1999) 435 hep-ex/9902006
63 A. L. Read Presentation of search results: the $ CL_s $ technique in Durham IPPP Workshop: Advanced Statistical Techniques in Particle Physics, p. 2693 Durham, UK, March, 2002 [JPG 28 (2002) 2693]
64 G. Cowan, K. Cranmer, E. Gross, and O. Vitells Asymptotic formulae for likelihood-based tests of new physics EPJC 71 (2011) 1554 1007.1727
65 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,Geneva, Switzerland 17-20 January 2011, p. 115 2011 1103.0354
Compact Muon Solenoid
LHC, CERN