Disentangling flavor violation in the top-Higgs sector at the LHC

  • Admir GreljoEmail author
  • Jernej F. Kamenik
  • Joachim Kopp
Open Access


We study the LHC phenomenology of flavor changing Yukawa couplings between the top quark, the Higgs boson, and either an up or charm quark. Such tuh or tch couplings arise for instance in models in which the Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied thj decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on \( \mathrm{\mathcal{B}} \)(thu) are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on tuh and tch couplings, setting the limits of \( \mathrm{\mathcal{B}} \)(thu) < 0.7% and \( \mathrm{\mathcal{B}} \)(thc) < 1.2%.

We then investigate the sensitivity of future searches in the multilepton channel and in the fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between tuh couplings, for which anomalous single top production is relevant, and tch couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic t + h production and thj decay can be competitive with the multilepton search at 100 fb−1 of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging thj decays. Our sensitivity estimates on \( \mathrm{\mathcal{B}} \)(thu) (\( \mathrm{\mathcal{B}} \)(thc)) at 100 fb−1 of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are 0.22% (0.33%), 0.15% (0.19%) and 0.36% (0.48%), respectively.


Beyond Standard Model Higgs Physics Heavy Quark Physics Rare Decays 


Open Access

This article is distributed under the terms of the Creative Commons Attribution License (CC-BY 4.0), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited.


  1. [1]
    R. Harnik, J. Kopp and J. Zupan, Flavor Violating Higgs Decays, JHEP 03 (2013) 026 [arXiv:1209.1397] [INSPIRE].ADSCrossRefGoogle Scholar
  2. [2]
    CMS collaboration, Combined multilepton and diphoton limit on tcH, CMS-PAS-HIG-13-034 (2014).
  3. [3]
    J.A. Aguilar-Saavedra and G.C. Branco, Probing top flavor changing neutral scalar couplings at the CERN LHC, Phys. Lett. B 495 (2000) 347 [hep-ph/0004190] [INSPIRE].ADSCrossRefGoogle Scholar
  4. [4]
    N. Craig, J.A. Evans, R. Gray, M. Park, S. Somalwar et al., Searching for tch with Multi-Leptons, Phys. Rev. D 86 (2012) 075002 [arXiv:1207.6794] [INSPIRE].ADSGoogle Scholar
  5. [5]
    Y. Wang, F.P. Huang, C.S. Li, B.H. Li, D.Y. Shao et al., Constraints on flavor-changing neutral-current Htq couplings from the signal of tH associated production with QCD next-to-leading order accuracy at the LHC, Phys. Rev. D 86 (2012) 094014 [arXiv:1208.2902] [INSPIRE].ADSGoogle Scholar
  6. [6]
    K.-F. Chen, W.-S. Hou, C. Kao and M. Kohda, When the Higgs meets the Top: Search for tch 0 at the LHC, Phys. Lett. B 725 (2013) 378 [arXiv:1304.8037] [INSPIRE].ADSCrossRefGoogle Scholar
  7. [7]
    D. Atwood, S.K. Gupta and A. Soni, Constraining the flavor changing Higgs couplings to the top-quark at the LHC, arXiv:1305.2427 [INSPIRE].
  8. [8]
    P. Agrawal, S. Bandyopadhyay and S.P. Das, Multilepton Signatures of the Higgs Boson through its Production in Association with a Top-quark Pair, Phys. Rev. D 88 (2013) 093008 [arXiv:1308.3043] [INSPIRE].ADSGoogle Scholar
  9. [9]
    CMS collaboration, A search for anomalous production of events with three or more leptons using 19.5/fb of \( \sqrt{s} \) =8 TeV LHC data, CMS-PAS-SUS-13-002 (2013).
  10. [10]
    ATLAS collaboration, Search for flavor-changing neutral currents in tcH, with H → γγ and limit on the tcH coupling, ATLAS-CONF-2013-081 [ATLAS-COM-CONF-2013-090] (2013).
  11. [11]
    ATLAS collaboration, Search for top quark decays tqH with H → γγ using the ATLAS detector, JHEP 06 (2014) 008 [arXiv:1403.6293] [INSPIRE].ADSGoogle Scholar
  12. [12]
    CMS collaboration, Search for the standard model Higgs boson decaying to tau pairs produced in association with a W or Z boson, CMS-PAS-HIG-12-053 (2013).
  13. [13]
    C.S. Li, R.J. Oakes and T.C. Yuan, QCD corrections to tW + b, Phys. Rev. D 43 (1991) 3759 [INSPIRE].ADSGoogle Scholar
  14. [14]
    J. Drobnak, S. Fajfer and J.F. Kamenik, Flavor Changing Neutral Coupling Mediated Radiative Top Quark Decays at Next-to-Leading Order in QCD, Phys. Rev. Lett. 104 (2010) 252001 [arXiv:1004.0620] [INSPIRE].ADSCrossRefGoogle Scholar
  15. [15]
    C. Zhang and F. Maltoni, Top-quark decay into Higgs boson and a light quark at next-to-leading order in QCD, Phys. Rev. D 88 (2013) 054005 [arXiv:1305.7386] [INSPIRE].ADSGoogle Scholar
  16. [16]
    M. Czakon, P. Fiedler and A. Mitov, Total Top-Quark Pair-Production Cross Section at Hadron Colliders Through \( O\left(\alpha \frac{4}{S}\right) \), Phys. Rev. Lett. 110 (2013) 252004 [arXiv:1303.6254] [INSPIRE].ADSCrossRefGoogle Scholar
  17. [17]
    A.D. Martin, W.J. Stirling, R.S. Thorne and G. Watt, Parton distributions for the LHC, Eur. Phys. J. C 63 (2009) 189 [arXiv:0901.0002] [INSPIRE].ADSCrossRefGoogle Scholar
  18. [18]
    Y. Wang, private communication.Google Scholar
  19. [19]
    N.D. Christensen and C. Duhr, FeynRules - Feynman rules made easy, Comput. Phys. Commun. 180 (2009) 1614 [arXiv:0806.4194] [INSPIRE].ADSCrossRefGoogle Scholar
  20. [20]
    J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer and T. Stelzer, MadGraph 5 : Going Beyond, JHEP 06 (2011) 128 [arXiv:1106.0522] [INSPIRE].ADSCrossRefGoogle Scholar
  21. [21]
    T. Sjöstrand, S. Mrenna and P.Z. Skands, PYTHIA 6.4 Physics and Manual, JHEP 05 (2006) 026 [hep-ph/0603175] [INSPIRE].ADSCrossRefGoogle Scholar
  22. [22]
    DELPHES 3 collaboration, J. de Favereau et al., DELPHES 3, A modular framework for fast simulation of a generic collider experiment, JHEP 02 (2014) 057 [arXiv:1307.6346] [INSPIRE].CrossRefGoogle Scholar
  23. [23]
    LHC Higgs Cross Section Working Group collaboration, S. Heinemeyer et al., Handbook of LHC Higgs Cross Sections: 3. Higgs Properties, arXiv:1307.1347 [INSPIRE].
  24. [24]
    P. Meade and M. Reece, BRIDGE: Branching ratio inquiry/decay generated events, hep-ph/0703031 [INSPIRE].
  25. [25]
    A.L. Read, Presentation of search results: The CL(s) technique, J. Phys. G 28 (2002) 2693 [INSPIRE].ADSCrossRefMathSciNetGoogle Scholar
  26. [26]
    CMS collaboration, 2HDM scenario, H to hh and A to Zh, CMS-PAS-HIG-13-025 (2013).
  27. [27]
  28. [28]
    ATLAS collaboration, Sensitivity of ATLAS at HL-LHC to flavour changing neutral currents in top quark decays tcH, with H → γγ, ATL-PHYS-PUB-2013-012 (2013).
  29. [29]
    S. Jadach, Z. Was, R. Decker and J.H. Kuhn, The tau decay library TAUOLA: Version 2.4, Comput. Phys. Commun. 76 (1993) 361 [INSPIRE].ADSCrossRefGoogle Scholar
  30. [30]
    CMS collaboration, Performance of tau-lepton reconstruction and identification in CMS, 2012 JINST 7 P01001 [arXiv:1109.6034] [INSPIRE].ADSGoogle Scholar
  31. [31]
    S. Khatibi and M.M. Najafabadi, Probing the Anomalous FCNC Interactions in Top-Higgs Final State and Charge Ratio Approach, Phys. Rev. D 89 (2014) 054011 [arXiv:1402.3073] [INSPIRE].ADSGoogle Scholar
  32. [32]
    M. Farina, C. Grojean, F. Maltoni, E. Salvioni and A. Thamm, Lifting degeneracies in Higgs couplings using single top production in association with a Higgs boson, JHEP 05 (2013) 022 [arXiv:1211.3736] [INSPIRE].ADSGoogle Scholar
  33. [33]
    D.E. Kaplan, K. Rehermann, M.D. Schwartz and B. Tweedie, Top Tagging: A Method for Identifying Boosted Hadronically Decaying Top Quarks, Phys. Rev. Lett. 101 (2008) 142001 [arXiv:0806.0848] [INSPIRE].ADSCrossRefGoogle Scholar
  34. [34]
    T. Plehn, G.P. Salam and M. Spannowsky, Fat Jets for a Light Higgs, Phys. Rev. Lett. 104 (2010) 111801 [arXiv:0910.5472] [INSPIRE].ADSCrossRefGoogle Scholar
  35. [35]
    T. Plehn, M. Spannowsky, M. Takeuchi and D. Zerwas, Stop Reconstruction with Tagged Tops, JHEP 10 (2010) 078 [arXiv:1006.2833] [INSPIRE].ADSCrossRefGoogle Scholar
  36. [36]
    Y.L. Dokshitzer, G.D. Leder, S. Moretti and B.R. Webber, Better jet clustering algorithms, JHEP 08 (1997) 001 [hep-ph/9707323] [INSPIRE].ADSCrossRefGoogle Scholar
  37. [37]
    M. Cacciari, G.P. Salam and G. Soyez, FastJet User Manual, Eur. Phys. J. C 72 (2012) 1896 [arXiv:1111.6097] [INSPIRE].ADSCrossRefGoogle Scholar
  38. [38]
    T. Gleisberg, S. Hoeche, F. Krauss, M. Schonherr, S. Schumann et al., Event generation with SHERPA 1.1, JHEP 02 (2009) 007 [arXiv:0811.4622] [INSPIRE].ADSCrossRefGoogle Scholar
  39. [39]
    S. Schumann and F. Krauss, A Parton shower algorithm based on Catani-Seymour dipole factorisation, JHEP 03 (2008) 038 [arXiv:0709.1027] [INSPIRE].ADSCrossRefGoogle Scholar
  40. [40]
    T. Gleisberg and S. Hoeche, Comix, a new matrix element generator, JHEP 12 (2008) 039 [arXiv:0808.3674] [INSPIRE].ADSCrossRefGoogle Scholar
  41. [41]
    S. Hoeche, F. Krauss, S. Schumann and F. Siegert, QCD matrix elements and truncated showers, JHEP 05 (2009) 053 [arXiv:0903.1219] [INSPIRE].ADSCrossRefGoogle Scholar
  42. [42]
    M. Schonherr and F. Krauss, Soft Photon Radiation in Particle Decays in SHERPA, JHEP 12 (2008) 018 [arXiv:0810.5071] [INSPIRE].ADSCrossRefGoogle Scholar
  43. [43]
    ATLAS collaboration, Measurement of multi-jet cross sections in proton-proton collisions at a 7 TeV center-of-mass energy, Eur. Phys. J. C 71 (2011) 1763 [arXiv:1107.2092] [INSPIRE].ADSGoogle Scholar
  44. [44]
    J.M. Butterworth, A.R. Davison, M. Rubin and G.P. Salam, Jet substructure as a new Higgs search channel at the LHC, Phys. Rev. Lett. 100 (2008) 242001 [arXiv:0802.2470] [INSPIRE].ADSCrossRefGoogle Scholar
  45. [45]
    J. Baglio, A. Djouadi, R. Gröber, M.M. Mühlleitner, J. Quevillon et al., The measurement of the Higgs self-coupling at the LHC: theoretical status, JHEP 04 (2013) 151 [arXiv:1212.5581] [INSPIRE].ADSCrossRefGoogle Scholar
  46. [46]
    T. Hahn, Automatic loop calculations with FeynArts, FormCalc and LoopTools, Nucl. Phys. Proc. Suppl. 89 (2000) 231 [hep-ph/0005029] [INSPIRE].ADSCrossRefGoogle Scholar
  47. [47]
    A. Djouadi, W. Kilian, M. Muhlleitner and P.M. Zerwas, Production of neutral Higgs boson pairs at LHC, Eur. Phys. J. C 10 (1999) 45 [hep-ph/9904287] [INSPIRE].ADSCrossRefGoogle Scholar
  48. [48]
    ATLAS collaboration, Search for exotic same-sign dilepton signatures (bquark, T 5/3 and four top quarks production) in 4.7/fb of pp collisions at \( \sqrt{s} \) = 7 TeV with the ATLAS detector, ATLAS-CONF-2012-130 [ATLAS-COM-CONF-2012-163] (2012).

Copyright information

© The Author(s) 2014

Authors and Affiliations

  • Admir Greljo
    • 1
    Email author
  • Jernej F. Kamenik
    • 1
    • 2
  • Joachim Kopp
    • 3
  1. 1.Jožef Stefan InstituteLjubljanaSlovenia
  2. 2.Faculty of Mathematics and PhysicsUniversity of LjubljanaLjubljanaSlovenia
  3. 3.Max Planck Institut für KernphysikHeidelbergGermany

Personalised recommendations