Rare top quark decays at a 100 TeV proton–proton collider: \(t \rightarrow bWZ\) and \(t\rightarrow hc\)
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Abstract
We investigate extremely rare top quark decays at a future proton–proton collider with centre-of-mass energy of 100 TeV. We focus on two decay modes: radiative decay with a Z boson, \(t \rightarrow b WZ\), and flavour-changing neutral decay with a Higgs boson, \(t \rightarrow h c\), the former being kinematically suppressed with a branching ratio of \({\mathscr {O}}(10^{-6})\) (Altarelli et al., Phys Lett B 502:125–132, 2001), and the latter highly loop-suppressed, with a branching ratio of \({\mathscr {O}}(10^{-15})\) (Aguilar-Saavedra, Acta Phys Polon B 35:2695–2710, 2004). We find that \(t \rightarrow b WZ\) will be very challenging to observe in top quark pair production, even within well-motivated beyond-the-standard model scenarios. For the mode \(t\rightarrow h c\) we find a stronger sensitivity than that obtained by any future LHC measurement by at least one order of magnitude.
1 Introduction
The top quark’s large mass suggests that it may be intimately-connected to the mechanism of electroweak symmetry breaking (EWSB). Furthermore, it is unique as a colour-charged particle because of the fact that it decays before hadronizing. The top quark decays mostly through the channel \(t\rightarrow b W\) with much smaller contributions from other SM processes. The QCD production of top quarks at the Large Hadron Collider (LHC) is expected to be high, with \(\sigma (pp \rightarrow t{\bar{t}}) \simeq 950\) pb at 14 TeV centre-of-mass energy [3], and would be 40 times larger at a proton collider with a centre-of-mass energy of 100 TeV (e.g. the Future Circular hadron-hadron Collider – FCC-hh [4, 5]). Given its large production rates, the top quark provides simultaneously interesting tests of QCD (through its production mechanisms) and of electroweak physics (through its decay channels). The Tevatron has already measured several properties of the top following its discovery, and the LHC is already adding further precision measurements. The purpose of the present study is to investigate to which extent a FCC-hh can provide valuable information to our knowledge of the top quark properties and couplings. Here, we focus on the potential for the observability of the radiative SM decay mode, \(t \rightarrow bWZ\), and on the decay of the top quark through the direct interaction between the top and charm together with the Higgs boson, i.e. \(t\rightarrow h c\).
The decay of the top quark to a bottom quark, a Z and a W boson, \(t \rightarrow bWZ\), received some attention 20 years ago, with several studies addressing its rate and potential sensitivity to new physics [1, 6, 7, 8, 9]. A peculiar feature of this process is that it occurs near the kinematical threshold: \(m_t \simeq m_b \,+\, m_W \,+\, m_Z\) and is thus suppressed within the Standard Model (SM), predicted to be \({\mathscr {O}}(10^{-6})\). In the studies of Refs. [1, 6, 8], it was pointed out that one has to take into account the finite widths of the Z and W bosons when calculating this decay mode. Indeed, if the widths are ignored, the current particle data group nominal values [10] of the particles involved: \(m_t \simeq 173.1\) GeV, \(m_b \simeq 4.18\) GeV, \(m_Z \simeq 91.19\) GeV and \(m_W \simeq 80.39\) GeV would imply \(m_t < m_b + m_W + m_Z\) and would suggest a kinematically-forbidden decay. Nevertheless, if the gauge boson widths are properly taken into account the decay can proceed. This leads to \({\mathscr {O}}(10^4)\) top quark pair production events containing the decay during the lifetime of the high-luminosity LHC (HL-LHC) with an integrated luminosity of 3000 fb\(^{-1}\), inclusively over the decays of the Z and W bosons. Consequently, the process will likely be impossible to observe at the LHC. However, given the substantial increase in cross section at the FCC-hh this channel is expected to yield \({\mathscr {O}}(10^6)\) events, justifying a more detailed investigation into its observability.
Flavour-changing neutral (FCN) decays of the top quark appear at one loop and have a strong suppression due to the Glashow–Iliopoulos–Maiani (GIM) mechanism and second-third generation mixing [2, 11, 13, 14]. Within the SM, this suppression leads to the following branching ratios: \(\mathrm {BR}(t \rightarrow \gamma c) \sim 10^{-14}\), \(\mathrm {BR}(t \rightarrow gc ) \sim 10^{-12}\), \(\mathrm {BR}(t \rightarrow Z c) \sim 10^{-14}\) and \(\mathrm {BR}(t \rightarrow h c ) \sim 10^{-15}\) [2], rendering them unobservable at the current and future colliders. Consequently, the measurement of such processes within current capabilities would clearly signal the presence of BSM phenomena. Here, we focus on the transition \(t \rightarrow h c\), where the new physics effect is treated as an effective interaction between the top quark, the charm quark and the Higgs boson.
This paper is organised as follows: in Sect. 2 we consider theoretical aspects of the \(t \rightarrow bWZ\) decay and construct a simple phenomenological analysis to assess its observability at the FCC-hh within the SM. To complement this analysis, we study the allowed size of an enhancement to the decay rate due to the presence of a charged heavy scalar boson contribution, given current experimental constraints. Subsequently, in Sect. 3, we analyse the decay \(t \rightarrow h c\), taking into account the effective coupling h-t-c and extract a bound by looking at a clean final state at the FCC-hh, with \(h\rightarrow \gamma \gamma \). Finally, we present our conclusions in Sect. 4.
2 Top quark decays to bWZ
2.1 Theoretical considerations
2.1.1 Defining the final state
The ‘cleanest’ channels in which the process \(t \rightarrow bWZ\) contributes are those containing multiple leptons. Here we will focus on the cases \(t \rightarrow b e^+ \nu _e \mu ^+\mu ^-\) and \(t \rightarrow b jj \mu ^+\mu ^-\), which receive contributions from other intermediate states in addition to \(t \rightarrow bWZ\). We examine the observability of these processes by looking at the particle content in the final states only and we do not attempt to separate the \(t \rightarrow bWZ\) contribution.^{1}
The ratio of branching ratios defines the \(t \rightarrow bWZ\) as described in the main text. The results of Ref. [1] are only provided in 5 GeV intervals
\(m_t\) (GeV) | \(R'\) | R (Ref. [1]) |
---|---|---|
170 | \(1.55 \times 10^{-6}\) | \(1.53(4)\times 10^{-6}\) |
171 | \(1.62 \times 10^{-6}\) | – |
172 | \(1.71 \times 10^{-6}\) | – |
173 | \(1.79 \times 10^{-6}\) | – |
174 | \(1.89 \times 10^{-6}\) | – |
175 | \(2.00 \times 10^{-6}\) | \(1.96(5)\times 10^{-6}\) |
2.1.2 Next-to-leading order corrections
Since the decay process occurs close to the top mass threshold, it is interesting to investigate the impact of next-to-leading order (NLO) QCD corrections. To consider a scenario which might be realistic in a phenomenological study, we examine corrections to the decay process \(t \rightarrow b e^+ \nu _e \mu ^+ \mu ^-\), with the invariant mass of \(\mu ^+\mu ^-\) pair taken to lie above 70 GeV to remove the photon contribution, \(\gamma \rightarrow \mu ^+\mu ^-\). We use MG5_aMC@NLO to calculate the SM decay width, \(\Gamma \), setting \(m_t = 173\) GeV and varying the bottom mass between 0.2 and 5.2 GeV. In Fig. 1 we show the variation of the decay width as a function of the input bottom mass. In addition, we also present the ratio between the NLO and the leading order (LO) corrections in the lower inset. It is evident that the NLO corrections reduce the branching ratio by about 10%. The impact of increasing the b-quark mass is larger at NLO than at LO, which is due to the phase space becoming even more restricted close to the top mass threshold. Given the null results of the phenomenological analyses (see below), we do not consider higher-order corrections in more detail.
2.2 Phenomenological analysis for \(t\rightarrow bWZ\)
2.2.1 The three-lepton final state
Using the assumption that the missing transverse momentum is primarily due to the undetected neutrino from the “signal” top quark decay and using the mass-shell condition \(m_t^2 = (p_\nu + p_{\ell ^{'+}} + p_{\ell ^{+}} + p_{\ell ^{-}} + p_b)^2\) we obtain a quadratic equation, and hence two solutions, for the z-component of the neutrino momentum. We use these solutions to reconstruct two corresponding values of the total invariant mass using momenta of the reconstructed top quarks. We require that both of these values lie within [350, 700] GeV.
To assess the detection prospects of this process we consider the background arising from \(pp \rightarrow t{\bar{t}} Z\), where all three particles are taken to be on-shell in this case. Using the aforementioned basic cuts, and the LO cross sections for the signal, \(\sigma _{\mathrm {signal}} \simeq 3.00 \times 10^{-5}\) pb, and for the background contribution to the final state considered here (i.e. including branching ratios) \(\sigma _{t{\bar{t}} Z} \simeq 0.10\) pb, we find an estimate of \({\mathscr {O}}(5)\) events for the signal and \({\mathscr {O}}(5000)\) events for the \(t{\bar{t}} Z\) at an integrated luminosity of 10 ab\(^{-1}\), a ballpark estimate of the FCC-hh end-of-lifetime data sample. This implies that this channel will be impossible to observe during the FCC-hh lifetime, and we do not consider it here any further.
2.2.2 The two-lepton final state
2.3 Heavy charged Higgs bosons
We simulate these two processes at LO using MG5_aMC@NLO and assume that the new scalar only possesses these two interactions. Hence, using the results obtained in the aforementioned articles [25, 26], we derive constraints for the maximum and minimum allowed values of the decay width at LO. These are shown in Fig. 3. Evidently the enhancement factor is moderate over the range of scalar boson masses considered, with a maximal value of \({\mathscr {O}}(2)\) for a heavy charged Higgs boson mass of \(\sim 200\) GeV. Hence we can conclude that the addition of a heavy charged scalar cannot render this process observable at a 100 TeV collider. Note that due to the interference of the SM diagrams with the charged scalar diagrams, which can be negative, the decay width can possess values lower than those of the SM.
3 Top quark decays to Higgs boson-charm quark
3.1 The h-t-c coupling
Here we focus on the resulting top quark decay \(t \rightarrow h c\), induced by couplings of the above kind. We also note that these couplings can lead to other interesting final states [27]. Various studies have already examined this process at the LHC [14, 27, 28], with the current best experimental constraint on BR(\(t\rightarrow hc\)) at the LHC being \(0.22\%\) at 95% C.L., coming from ATLAS 13 TeV data (36.1 fb\(^{-1}\)) in the di-photon channel [29]. The corresponding best constraint at CMS is currently \(0.47\%\) through \(h\rightarrow b {\bar{b}}\) decays [31]. Naive extrapolation of the 13 TeV ATLAS result [29] to the high-luminosity LHC demonstrates that an integrated luminosity of 3000 fb\(^{-1}\) implies an ultimate constraint of BR(\(t\rightarrow hc\)) \(\lesssim 0.019\%\) through the \(h\rightarrow \gamma \gamma \) channel alone.^{5} It is important to note here that the LHC analyses do not consider the tagging of charm jets in the derivation of these constraints. This implies that these limits are associated with the crucial assumption that the \(t \rightarrow h u\) decay will be either absent or sub-dominant with respect to \(t \rightarrow h c\). Alternatively, one can use these analyses to impose constraints on \(t \rightarrow h u\), assuming \(t\rightarrow hc\) is absent or sub-dominant.
In the present study we will analyse the prospect of constraining \(\mathrm {BR}(t \rightarrow h c)\) and \(\lambda _{ct}^h\) through top quark pair production at the FCC-hh. To the best of our knowledge this represents the first estimate for a constraint on this coupling at the FCC-hh. Among all the decay channels, the one expected to provide the strongest contribution in the combination for the constraint is the one involving the transition \(h \rightarrow \gamma \gamma \), and therefore we will focus on it in the present study. In our analysis we consider both the scenario with and that without charm-jet tagging, with values for the tagging efficiencies motivated by current LHC considerations [32].
3.2 Phenomenological analysis for \(t\rightarrow hc\)
We have implemented the interaction described by Eq. (6) in a UFO [33] model which we interface to MG5_aMC@NLO to generate signal \(pp \rightarrow t{\bar{t}} \rightarrow (hc) {\bar{t}}\) (and the charge-conjugate process) events. We also generate parton-level events for the backgrounds using MG5_aMC@NLO and perform shower and hadronization using HERWIG 7 as before. The background processes considered include those that include a Higgs boson in association with other particles: \(pp \rightarrow t {\bar{t}} h\), \(pp \rightarrow h j j W^\pm \) and those that contain non-resonant di-photon production: \(pp \rightarrow t {\bar{t}} \gamma \gamma \), \(pp \rightarrow \gamma \gamma j j W^\pm \), where the W bosons were decayed to electrons or muons. Generation-level cuts were applied on the non-resonant photon samples: the photon transverse momentum was required to lie in \(p_{T,\gamma } > 10\) GeV, the distance between either a jet and a photon or between two photons \(\Delta R (\gamma , \mathrm {~j~or}~\gamma ) > 0.1\) and the invariant mass of the two photons to satisfy \(M_{\gamma \gamma } \in [110, 140]\) GeV. In all background samples we asked for the generation-level cuts on the jets and final-state leptons of \(p_T > 20\) GeV. The jets have been merged to the HERWIG 7 parton shower at tree level using the MLM method via the FxFx add-on module [34].^{6}
The starting signal and background cross sections considered in the analyses of the top quark pair production search for the \(t\rightarrow hc\) decay. For simplicity, we have rescaled the leading-order cross sections for all processes by a k-factor of 2. This approximation does not have a significant impact on our conclusions. The second and third columns show the generation-level cross sections for the hadronic and semi-leptonic cases, respectively, see main text for further details. The signal cross sections are shown for \(\lambda ^h_{ct} = 0.1\), which we take here as a “working value”
Process | \(\sigma _\mathrm {gen}^{\mathrm {had.}}\) (pb) | \(\sigma _\mathrm {gen}^{\mathrm {s.l.}}\) (pb) |
---|---|---|
\(pp \rightarrow t{\bar{t}} \rightarrow (hc) {\bar{t}} +\) h.c. | 0.332 | 0.122 |
\(pp \rightarrow t {\bar{t}} h\) | 0.044 | 0.030 |
\(pp \rightarrow h j j W^\pm \) | 0.022 | 0.070 |
\(pp \rightarrow t {\bar{t}} \gamma \gamma \) | 0.042 | 0.028 |
\(pp \rightarrow \gamma \gamma j j W^\pm \) | 1.294 | 0.424 |
We identify photons and leptons by requiring \(p_T > 25\) GeV, within \(|\eta | < 2.5\) in both cases. We assume flat identification efficiencies of b-jets of 70% and of c-jets of 20% and ask for them to have \(p_T > 25\) GeV and lie within \(|\eta | < 2.5\) GeV.^{7} We consider mis-tagging rates for light jets to b-jets of 1%, and to c-jets of 0.5%. The rate of mis-identification of b-jets to c-jets was taken to be 12.5% and the rate for the converse was taken to be 10% [32]. We do not consider mis-tagging of light jets to photons in our analysis. We do not apply any detector effects such as momentum smearing and we assume that jets, leptons and photons are detected with 100% efficiency within the considered coverage.^{8}
A summary of the selection criteria of the analysis for each of the channels considered for the \(pp \rightarrow t{\bar{t}} \rightarrow (hc) {\bar{t}}\) process. The final invariant mass cut, on \(m_{\gamma \gamma c}\) allows identification of the signal top quark
Exactly one b-jet, \(p_T > 25\) GeV, \(|\eta | < 2.5\), \(P_{b\rightarrow b} = 0.7\), \(P_{c\rightarrow b} = 0.1\), \(P_{l\rightarrow b} = 0.01\), \(\ge 2\) photons, \(p_T > 25\) GeV, \(|\eta | < 2.5\), | |
Hadronic: | Semi-leptonic: |
\(\ge 1\) light jets, | \(\ge 1\) leptons, \(p_T > 25\) GeV, \(|\eta | < 2.5\). |
top: combine b-jet + 1, 2 light jets. | solve for \(p^z_\nu \) using mass constraint. |
With c -tagging: | No c -tagging: |
\(P_{c\rightarrow c} = 0.2\), \(P_{l\rightarrow c} = 0.005\), \(P_{b\rightarrow c} = 0.125\). | no charm jets. |
\(m_\mathrm {top,~reco} \in [150, 200]\) GeV, \(m_{\gamma \gamma c} \in [160, 190]\) GeV. |
The expected signal and background events at an integrated luminosity of \({\mathscr {L}} = 10~\mathrm {ab}^{-1}\) after applying the analyses in the search for the \(t \rightarrow hc\) decay. The resulting event yields are shown for the case where charm-jet tagging is considered for the hadronic and semi-leptonic cases, see main text for further details. As before, the signal cross sections are shown for the working value \(\lambda ^h_{ct} = 0.1\)
\({\mathscr {L}} = 10~\mathrm {ab}^{-1}\) | ||
---|---|---|
Process | \(N_{\hbox {c-tag}}^{\mathrm {had.}}\) | \(N_{\hbox {c-tag}}^{\mathrm {s.l.}}\) |
\(pp \rightarrow t{\bar{t}} \rightarrow (hc) {\bar{t}} +\) h.c. | 22952 | 10260 |
\(pp \rightarrow t {\bar{t}} h\) | 1816 | 689 |
\(pp \rightarrow h j j W^\pm \) | 7 | 1 |
\(pp \rightarrow \gamma \gamma j j W^\pm \) | 211 | 2 |
\(pp \rightarrow t {\bar{t}} \gamma \gamma \) | 107 | 39 |
As for Table 4, but without charm-jet tagging
\({\mathscr {L}} = 10~\mathrm {ab}^{-1}\) | ||
---|---|---|
Process | \(N_{\hbox {no c-tag}}^{\mathrm {had.}}\) | \(N_{\hbox {no c-tag}}^{\mathrm {s.l.}}\) |
\(pp \rightarrow t{\bar{t}} \rightarrow (hc) {\bar{t}} +\) h.c. | 191871 | 61124 |
\(pp \rightarrow t {\bar{t}} h\) | 26533 | 6962 |
\(pp \rightarrow h j j W^\pm \) | 66 | 19 |
\(pp \rightarrow \gamma \gamma j j W^\pm \) | 7130 | 164 |
\(pp \rightarrow t {\bar{t}} \gamma \gamma \) | 1598 | 478 |
We summarise the main features of the analysis in Table 3. The resulting event yields after applying the analyses are shown in Tables 4 and 5 for the cases with and without charm tagging, respectively, at an integrated luminosity of \({\mathscr {L}} = 10~\mathrm {ab}^{-1}\).
3.3 Constraints for \(t\rightarrow hc\)
To take into account the effect of the presence of systematic uncertainties, we assume that they only affect the total number of background events, B, by inducing a systematic uncertainty \(\Delta B = \alpha B\), with \(\alpha \ge 0\) parameterising the effect. We add this in quadrature to the statistical uncertainty on the expected number of events. We therefore show results for values of \(\alpha \) corresponding to no systematics (\(\alpha =0\)) to demonstrate the ultimate precision at the future collider, low systematic uncertainty (\(\alpha = 0.05\)), and high systematic uncertainty (\(\alpha = 0.2\)). For the ATLAS analysis of [29] we have deduced that the current systematic uncertainty would correspond to \(\alpha \simeq 0.063\) and we derive results for an extrapolation to the high-luminosity LHC data set (3000 fb\(^{-1}\)) either using this value or setting \(\alpha = 0\) as the best-case scenario.
The 95% C.L. upper limits as calculated by each of the phenomenological analyses of this article for a 100 TeV FCC-hh with an integrated luminosity of 10 ab\(^{-1}\) corresponding to the systematic uncertainty parameter values \(\alpha = (0, 0.05, 0.2)\) as described in the main text. We give the limits on the branching ratios for the top quark as a percentage of the total as well as the associated values of the coupling, \(\lambda _{ct}^h\). The results for BR(\(t \rightarrow hc\)) are also given graphically in Fig 4
Analysis | Hadr. | Semi-lept. |
---|---|---|
With c-tagging | ||
\(\lambda _{ct}^h\) \(\times 10^{-3}\) | (6.42, 10.15, 19.40) | (7.40, 9.52, 17.08) |
BR in \(10^{-3}\)% | (1.08, 2.70, 9.91) | (1.44, 2.39, 7.69) |
No c-tagging | ||
\(\lambda _{ct}^h\) \(\times 10^{-3}\) | (4.43, 13.61, 27.15) | (5.38, 11.32, 22.36) |
BR in \(10^{-3}\)% | (0.52, 4.99, 19.42) | (0.76, 3.38, 13.17) |
4 Conclusions
We have investigated the rare top quark decay processes \(t \rightarrow bWZ\) and \(t \rightarrow h c\) at a future circular hadron collider running at 100 TeV with 10 ab\(^{-1}\) of integrated luminosity. We have demonstrated that it will be extremely challenging to observe a final state in which the \(t \rightarrow bWZ\) process contributes. This is true even in the case of the presence of new physics contributions allowed by current LHC constraints. On the other hand, the \(t \rightarrow h c\) decay can be constrained to \({\mathscr {O}}(10^{-3})\%\), either with or without considering charm-jet tagging. This estimate is an order of magnitude more stringent than a high-luminosity LHC extrapolation and will allow us to constrain the off-diagonal top quark-charm quark Yukawa couplings to \(\lambda _{ct}^h \sim {\mathscr {O}}(10^{-3})\).
The extremely rare decay modes we have investigated in the present article constitute two of the many interesting ones for top quarks. A future high-energy collider will be able to provide information on other processes, such as \(t \rightarrow cWW\), \(t \rightarrow q \gamma \), \(t \rightarrow q Z\), \(t \rightarrow c \gamma \gamma \) and \(t \rightarrow c ZZ\). We leave investigations of such modes to future work.
Footnotes
- 1.
This separation is not possible due to interference of the \(t \rightarrow bWZ\) contribution with other diagrams.
- 2.
Charge-conjugate processes are taken into account from this point on by multiplying by the appropriate symmetry factors.
- 3.
Defined as usual \(\Delta R = \sqrt{\Delta \eta ^2 + \Delta \phi ^2}\), where \(\eta \) is the pseudo-rapidity and \(\phi \) is the azimuthal angle.
- 4.
We employ this method to “groom” the jets, removing soft radiation.
- 5.
This is obtained by extrapolating the number of events for the signal and backgrounds from 36.1 to 3000 fb\(^{-1}\), assuming that the experimental details and analysis remain unchanged.
- 6.
Further details on the usage of this module for tree-level merging will available in a future release of the HERWIG 7 manual.
- 7.
- 8.
As discussed in, e.g., [36], better forward detector coverage for b-jet or photon identification, up to \(|\eta |\sim 3-3.5\) may increase signal efficiency at a future 100 TeV collider. In the present analysis we chose to be conservative, allowing identified objects only within \(|\eta | < 2.5\).
- 9.
The naive statistical combination employed here adds the Gaussian significances linearly: \(\sigma _\mathrm {total} = \sum _{i=1}^k \frac{\sigma _i}{\sqrt{k}}\). This provides a conservative estimate of the combined significance [37].
- 10.
These estimates are in agreement with the HL-LHC projections found in Ref. [30].
- 11.
The increase in signal cross section from 13 TeV to 100 TeV is \(\sim 40\), whereas for the \(pp \rightarrow t{\bar{t}}h\) background this increase is \(\sim 70\). Given that we are now considering 10 ab\(^{-1}\) versus 3 ab\(^{-1}\) at the HL-LHC, the naive increase in significance is \(\sim ( 40/\sqrt{70}) \times \sqrt{10/3} \sim 9 \), which would imply an order of magnitude improvement on the branching ratio measurements from 13 to 100 TeV, provided the kinematical structure scales in a similar way for signal and background.
Notes
Acknowledgements
We would like to thank Michael Spannowsky for useful discussions. AP acknowledges support by the ERC Grant ERC-STG-2015-677323.
References
- 1.G. Altarelli, L. Conti, V. Lubicz, The t\(\rightarrow \) WZ b decay in the standard model: a critical reanalysis. Phys. Lett. B 502, 125–132 (2001). arXiv:hep-ph/0010090 ADSCrossRefGoogle Scholar
- 2.J.A. Aguilar-Saavedra, Top flavor-changing neutral interactions: Theoretical expectations and experimental detection. Acta Phys. Polon. B 35, 2695–2710 (2004). arXiv:hep-ph/0409342 ADSGoogle Scholar
- 3.M. Czakon, P. Fiedler, A. Mitov, Total top-quark pair-production cross section at hadron colliders through \(\cal{O}(\alpha _S^4)\). Phys. Rev. Lett. 110, 252004 (2013). arXiv:1303.6254 ADSCrossRefGoogle Scholar
- 4.M. L. Mangano et al, Physics at a 100 TeV pp collider: standard model processes, CERN Yellow Report, pp. 1–254 (2017). arXiv:1607.01831
- 5.R. Contino et al., Physics at a 100 TeV pp collider: Higgs and EW symmetry breaking studies, CERN Yellow Report, pp. 255–440 (2017). arXiv:1606.09408
- 6.G. Mahlon, S.J. Parke, Finite width effects in top quark decays. Phys. Lett. B 347, 394–398 (1995). arXiv:hep-ph/9412250 ADSCrossRefGoogle Scholar
- 7.E.E. Jenkins, The Rare top decays \(t \rightarrow b W^{+} Z\) and \(t \rightarrow c W^{+} W^{-}\). Phys. Rev. D 56, 458–466 (1997). arXiv:hep-ph/9612211 ADSCrossRefGoogle Scholar
- 8.G. Mahlon, Theoretical expectations in radiative top decays. In: Thinkshop on Top Quark Physics for Run II Batavia, Illinois, October 16–18, 1998 (1998). arXiv:hep-ph/9810485
- 9.J.L. Diaz Cruz, D.A. Lopez Falcon, Testing models with nonminimal Higgs sector through the decay t \(\rightarrow \) q + W Z. Phys. Rev. D 61, 051701 (2000). arXiv:hep-ph/9911407 ADSCrossRefGoogle Scholar
- 10.Particle Data Group collaboration, C. Patrignani et al., Review of particle physics. Chin. Phys. C40, 100001 (2016)Google Scholar
- 11.G. Eilam, J.L. Hewett, A. Soni, Rare decays of the top quark in the standard and two Higgs doublet models. Phys. Rev. D 44, 1473–1484 (1991)ADSCrossRefGoogle Scholar
- 12.J. Baglio, A. Djouadi, R. Groeber, M. Mühlleitner, J. Quevillon et al., The measurement of the Higgs self-coupling at the LHC: theoretical status. JHEP 1304, 151 (2013). arXiv:1212.5581
- 13.B. Mele, S. Petrarca, A. Soddu, A new evaluation of the t \(\rightarrow \) cH decay width in the standard model. Phys. Lett. B 435, 401–406 (1998). arXiv:hep-ph/9805498 ADSCrossRefGoogle Scholar
- 14.N. Craig, J.A. Evans, R. Gray, M. Park, S. Somalwar, S. Thomas et al., Searching for \(t \rightarrow c h\) with multi-leptons. Phys. Rev. D 86, 075002 (2012). arXiv:1207.6794 ADSCrossRefGoogle Scholar
- 15.J. Alwall, M. Herquet, F. Maltoni, O. Mattelaer T. Stelzer, MadGraph 5: going beyond. JHEP 1106, 128 (2011). arXiv:1106.0522
- 16.J. Alwall, R. Frederix, S. Frixione, V. Hirschi, F. Maltoni et al., The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations. JHEP 1407, 079 (2014). arXiv:1405.0301
- 17.M. Cacciari, G.P. Salam, Dispelling the \(N^{3}\) myth for the \(k_t\) jet-finder. Phys. Lett. B 641, 57–61 (2006). arXiv:hep-ph/0512210 ADSCrossRefGoogle Scholar
- 18.M. Cacciari, G.P. Salam, G. Soyez, FastJet user manual. Eur. Phys. J. C 72, 1896 (2012). arXiv:1111.6097 ADSCrossRefGoogle Scholar
- 19.S. Gieseke, D. Grellscheid, K. Hamilton, A. Papaefstathiou, S. Platzer et al., Herwig++ 2.5 Release Note. arXiv:1102.1672
- 20.K. Arnold, L. d’Errico, S. Gieseke, D. Grellscheid, K. Hamilton et al., Herwig++ 2.6 Release Note. arXiv:1205.4902
- 21.J. Bellm, S. Gieseke, D. Grellscheid, A. Papaefstathiou, S. Platzer et al., Herwig++ 2.7 release note. arXiv:1310.6877
- 22.J. Bellm et al., Herwig 7.0/Herwig++ 3.0 release note. Eur. Phys. J. C76, 196 (2016). arXiv:1512.01178 ADSCrossRefGoogle Scholar
- 23.J. Bellm et al., Herwig 7.1 release note. arXiv:1705.06919
- 24.J.M. Butterworth, A.R. Davison, M. Rubin, G.P. Salam, Jet substructure as a new Higgs search channel at the LHC. Phys. Rev. Lett. 100, 242001 (2008). arXiv:0802.2470 ADSCrossRefGoogle Scholar
- 25.ATLAS collaboration, G. Aad et al., Search for charged Higgs bosons in the \(H^{\pm } \rightarrow tb\) decay channel in \(pp\) collisions at \(\sqrt{s}=8 \) TeV using the ATLAS detector. JHEP 03, 127 (2016). arXiv:1512.03704
- 26.ATLAS collaboration, G. Aad et al., Search for a charged Higgs boson produced in the vector-boson fusion mode with decay \(H^\pm \rightarrow W^\pm Z\) using \(pp\) collisions at \(\sqrt{s}=8\) TeV with the ATLAS experiment. Phys. Rev. Lett. 114, 231801 (2015). arXiv:1503.04233
- 27.D. Atwood, S. K. Gupta, A. Soni, Constraining the flavor changing Higgs couplings to the top-quark at the LHC. JHEP10, 57 (2014). arXiv:1305.2427
- 28.J.A. Aguilar-Saavedra, G.C. Branco, Phys. Lett. B 495, 347 (2000). https://doi.org/10.1016/S0370-2693(00)01259-4. arXiv:hep-ph/0004190 ADSCrossRefGoogle Scholar
- 29.ATLAS collaboration, M. Aaboud et al., Search for top quark decays \(t\rightarrow qH\), with \(H\rightarrow \gamma \gamma \), in \(\sqrt{s}=13\) TeV \(pp\) collisions using the ATLAS detector. JHEP 10, 129 (2017). arXiv:1707.01404
- 30.ATLAS collaboration, Sensitivity of ATLAS at HL-LHC to flavour changing neutral currents in top quark decays \(t \rightarrow cH\), with \(H\gamma \gamma \). arXiv:ATL-PHYS-PUB-2013-012
- 31.CMS collaboration, A.M. Sirunyan et al., Search for the flavor-changing neutral current interactions of the top quark and the Higgs boson which decays into a pair of b quarks at \(\sqrt{s}=\) 13 TeV. arXiv:1712.02399
- 32.Performance and calibration of the JetFitterCharm algorithm for c-jet identification, Tech. Rep. ATL-PHYS-PUB-2015-001. CERN, Geneva (2015)Google Scholar
- 33.C. Degrande, C. Duhr, B. Fuks, D. Grellscheid, O. Mattelaer, T. Reiter, UFO—the universal Feyn rules output. Comput. Phys. Commun. 183, 1201–1214 (2012). arXiv:1108.2040 ADSCrossRefGoogle Scholar
- 34.R. Frederix, S. Frixione, A. Papaefstathiou, S. Prestel, P. Torrielli, A study of multi-jet production in association with an electroweak vector boson. JHEP 02, 131 (2016). arXiv:1511.00847
- 35.A. Lenz, M. Spannowsky G. Tetlalmatzi-Xolocotzi, Phys. Rev. D 97(1), 016001 (2018). https://doi.org/10.1103/PhysRevD.97.016001, arXiv:1708.03517 [hep-ph]
- 36.A. Papaefstathiou, K. Sakurai, Triple Higgs boson production at a 100 TeV proton-proton collider. JHEP 02, 006 (2016). arXiv:1508.06524
- 37.S.A. Stouffer et al., The American soldier: adjustment during army life, vol. I, pp. xii, 599. Ann. Am. Acad. Political Soc. Sci. 265, 173–175 (1949)Google Scholar
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