Search for flavour-changing neutral-current couplings between the top quark and the Higgs boson in multi-lepton final states in 13 TeV $pp$ collisions with the ATLAS detector

The ATLAS collaboration
CERN-EP-2024-070, 2024.

Abstract (data abstract)
- CERN-LHC. A search is presented for flavour-changing neutral-current interactions involving the top quark, the Higgs boson and an up-type quark ($q=u,c$) with the ATLAS detector at the Large Hadron Collider. The analysis considers leptonic decays of the top quark along with Higgs boson decays into two $W$ bosons, two $Z$ bosons or a $\tau^{+}\tau^{-}$ pair. It focuses on final states containing either two leptons (electrons or muons) of the same charge or three leptons. The considered processes are $t\bar{t}$ and $Ht$ production. For the $t\bar{t}$ production, one top quark decays via $t\to Hq$. The proton-proton collision data set analysed amounts to 140 fb$^{-1}$ at $\sqrt{s}=13$ TeV. No significant excess beyond Standard Model expectations is observed and upper limits are set on the $t\to Hq$ branching ratios at 95\,\% confidence level, amounting to observed (expected) limits of $\mathcal{B}(t\to Hu)<2.8\,(3.0) \times 10^{-4}$ and $\mathcal{B}(t\to Hc)<3.3\,(3.8) \times 10^{-4}$. Combining this search with other searches for $tHq$ flavour-changing neutral-current interactions previously conducted by ATLAS, considering $H\to b\bar{b}$ and $H\to\gamma\gamma$ decays, as well as $H\to\tau^{+}\tau^{-}$ decays with one or two hadronically decaying $\tau$-leptons, yields observed (expected) upper limits on the branching ratios of $\mathcal{B}(t\to Hu)<2.6\,(1.8) \times 10^{-4}$ and $\mathcal{B}(t\to Hc)<3.4\,(2.3) \times 10^{-4}$.

  • SR$2\ell$ Dec pre-fit background composition

    Figure 3 (a) in the paper

    10.17182/hepdata.150998.v1/t1

    Pre-fit background composition of the SR$2\ell$ Dec. The table shows the event yields as opposed to just the percentages of...

  • SR$2\ell$ Prod pre-fit background composition

    Figure 3 (b) in the paper

    10.17182/hepdata.150998.v1/t2

    Pre-fit background composition of the SR$2\ell$ Prod. The table shows the event yields as opposed to just the percentages of...

  • SR$3\ell$ Dec pre-fit background composition

    Figure 3 (c) in the paper

    10.17182/hepdata.150998.v1/t3

    Pre-fit background composition of the SR$3\ell$ Dec. The table shows the event yields as opposed to just the percentages of...

  • SR$3\ell$ Prod pre-fit background composition

    Figure 3 (d) in the paper

    10.17182/hepdata.150998.v1/t4

    Pre-fit background composition of the SR$3\ell$ Prod. The table shows the event yields as opposed to just the percentages of...

  • SR$2\ell$ Dec $H_\text{T}(\text{jets})$ post-fit

    Figure 6 (a) in the paper

    10.17182/hepdata.150998.v1/t5

    Post-fit plot of $H_\text{T}(\text{jets})$ in the SR$2\ell$ Dec from a signal-blinded background-only fit.

  • SR$2\ell$ Prod $m(t_\text{SM}, b\text{-jet}_0)$ post-fit

    Figure 6 (b) in the paper

    10.17182/hepdata.150998.v1/t6

    Post-fit plot of $m(t_\text{SM}, b\text{-jet}_0)$ in the SR$2\ell$ Prod from a signal-blinded background-only fit.

  • SR$3\ell$ Dec $m(\ell_\text{OS},\ell_\text{SS,1})$ post-fit

    Figure 6 (c) in the paper

    10.17182/hepdata.150998.v1/t7

    Post-fit plot of $m(\ell_\text{OS},\ell_\text{SS,1})$ in the SR$3\ell$ Dec from a signal-blinded background-only fit.

  • SR$3\ell$ Prod $m(\ell_\text{OS},\ell_\text{SS,1})$ post-fit

    Figure 6 (d) in the paper

    10.17182/hepdata.150998.v1/t8

    Post-fit plot of $m(\ell_\text{OS},\ell_\text{SS,1})$ in the SR$3\ell$ Prod from a signal-blinded background-only fit.

  • SR$2\ell$ Dec $D_\text{NN}(tHc)$ post-fit

    Figure 7 (a) in the paper

    10.17182/hepdata.150998.v1/t9

    Post-fit plot of $D_\text{NN}(tHc)$ in the SR$2\ell$ Dec from the full fit to data.

  • SR$2\ell$ Prod $D_\text{NN}(tHc)$ post-fit

    Figure 7 (b) in the paper

    10.17182/hepdata.150998.v1/t10

    Post-fit plot of $D_\text{NN}(tHc)$ in the SR$2\ell$ Prod from the full fit to data.

  • SR$3\ell$ Dec $D_\text{NN}(tHc)$ post-fit

    Figure 7 (c) in the paper

    10.17182/hepdata.150998.v1/t11

    Post-fit plot of $D_\text{NN}(tHc)$ in the SR$3\ell$ Dec from the full fit to data.

  • SR$3\ell$ Prod $D_\text{NN}(tHc)$ post-fit

    Figure 7 (d) in the paper

    10.17182/hepdata.150998.v1/t12

    Post-fit plot of $D_\text{NN}(tHc)$ in the SR$3\ell$ Prod from the full fit to data.

  • CR$2\ell$ HF$e$ $p_\text{T}(\ell_1)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t13

    Post-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ HF$e$ from the full fit to data.

  • CR$2\ell$ HF$\mu$ $p_\text{T}(\ell_1)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t14

    Post-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ HF$\mu$ from the full fit to data.

  • CR$2\ell$ $t\bar{t}V$ $p_\text{T}(\ell_1)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t15

    Post-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ $t\bar{t}V$ from the full fit to data.

  • CR$3\ell$ HF$e$ $p_\text{T}(\ell_2)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t16

    Post-fit plot of $p_\text{T}(\ell_2)$ in the CR$3\ell$ HF$e$ from the full fit to data.

  • CR$3\ell$ HF$\mu$ $p_\text{T}(\ell_2)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t17

    Post-fit plot of $p_\text{T}(\ell_2)$ in the CR$3\ell$ HF$\mu$ from the full fit to data.

  • CR$3\ell$ $t\bar{t}W$ $p_\text{T}(b\text{-jet}_0)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t18

    Post-fit plot of $p_\text{T}(b\text{-jet}_0)$ in the CR$3\ell$ $t\bar{t}W$ from the full fit to data.

  • CR$3\ell$ $t\bar{t}Z$ $p_\text{T}(b\text{-jet}_0)$ post-fit

    Figure 8 in the paper

    10.17182/hepdata.150998.v1/t19

    Post-fit plot of $p_\text{T}(b\text{-jet}_0)$ in the CR$3\ell$ $t\bar{t}Z$ from the full fit to data.

  • Upper limits on $\mathcal{B}(t\to Hu)$

    Figure 9 (a) in the paper

    10.17182/hepdata.150998.v1/t20

    Observed and expected upper exclusion limits on the branching ratio $\mathcal{B}(t\to Hu)$ for different analyses and their statistical combination.

  • Upper limits on $\mathcal{B}(t\to Hc)$

    Figure 9 (b) in the paper

    10.17182/hepdata.150998.v1/t21

    Observed and expected upper exclusion limits on the branching ratio $\mathcal{B}(t\to Hc)$ for different analyses and their statistical combination.

  • Table 6

    Table 6 in the paper

    10.17182/hepdata.150998.v1/t22

    Post-fit normalisation factors of free-floating background processes and the signal normalisation.

  • Table 7

    Table 7 in the paper

    10.17182/hepdata.150998.v1/t23

    Post-fit predicted and observed yields in all $2\ell$SS signal and control regions. Pre-fit signal contributions for a signal cross section...

  • Table 8

    Table 8 in the paper

    10.17182/hepdata.150998.v1/t24

    Post-fit predicted and observed yields in all $3\ell$ signal and control regions. Pre-fit signal contributions for a signal cross section...

  • Table 9

    Table 9 in the paper

    10.17182/hepdata.150998.v1/t25

    Expected upper limits on $\mathcal{B}(t\to Hq)$ for the nominal fit and alternative fit configurations. One contains the full phase space...

  • Table 10

    Table 10 in the paper

    10.17182/hepdata.150998.v1/t26

    Expected and observed upper limits on $\mathcal{B}(t\to Hq)$ and $|C_{u\phi}^{qt,tq}|$ for the full fit containing all systematic uncertainties.

  • SR$2\ell$ Dec $H_\text{T}(\text{jets})$ pre-fit

    Figure 2 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t27

    Pre-fit plot of $H_\text{T}(\text{jets})$ in the SR$2\ell$ Dec from a signal-blinded background-only fit.

  • SR$2\ell$ Prod $m(t_\text{SM}, b\text{-jet}_0)$ pre-fit

    Figure 2 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t28

    Pre-fit plot of $m(t_\text{SM}, b\text{-jet}_0)$ in the SR$2\ell$ Prod from a signal-blinded background-only fit.

  • SR$3\ell$ Dec $m(\ell_\text{OS},\ell_\text{SS,1})$ pre-fit

    Figure 2 (c) in the auxiliary material

    10.17182/hepdata.150998.v1/t29

    Pre-fit plot of $m(\ell_\text{OS},\ell_\text{SS,1})$ in the SR$3\ell$ Dec from a signal-blinded background-only fit.

  • SR$3\ell$ Prod $m(\ell_\text{OS},\ell_\text{SS,1})$ pre-fit

    Figure 2 (d) in the auxiliary material

    10.17182/hepdata.150998.v1/t30

    Pre-fit plot of $m(\ell_\text{OS},\ell_\text{SS,1})$ in the SR$3\ell$ Prod from a signal-blinded background-only fit.

  • SR$2\ell$ Dec $D_\text{NN}(tHu)$ post-fit

    Figure 3 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t31

    Post-fit plot of $D_\text{NN}(tHu)$ in the SR$2\ell$ Dec from the full fit to data.

  • SR$2\ell$ Prod $D_\text{NN}(tHu)$ post-fit

    Figure 3 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t32

    Post-fit plot of $D_\text{NN}(tHu)$ in the SR$2\ell$ Prod from the full fit to data.

  • SR$3\ell$ Dec $D_\text{NN}(tHu)$ post-fit

    Figure 3 (c) in the auxiliary material

    10.17182/hepdata.150998.v1/t33

    Post-fit plot of $D_\text{NN}(tHu)$ in the SR$3\ell$ Dec from the full fit to data.

  • SR$3\ell$ Prod $D_\text{NN}(tHu)$ post-fit

    Figure 3 (d) in the auxiliary material

    10.17182/hepdata.150998.v1/t34

    Post-fit plot of $D_\text{NN}(tHu)$ in the SR$3\ell$ Prod from the full fit to data.

  • SR$2\ell$ Dec $D_\text{NN}(tHc)$ pre-fit

    Figure 4 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t35

    Pre-fit plot of $D_\text{NN}(tHc)$ in the SR$2\ell$ Dec from the full fit to data.

  • SR$2\ell$ Prod $D_\text{NN}(tHc)$ pre-fit

    Figure 4 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t36

    Pre-fit plot of $D_\text{NN}(tHc)$ in the SR$2\ell$ Prod from the full fit to data.

  • SR$3\ell$ Dec $D_\text{NN}(tHc)$ pre-fit

    Figure 4 (c) in the auxiliary material

    10.17182/hepdata.150998.v1/t37

    Pre-fit plot of $D_\text{NN}(tHc)$ in the SR$3\ell$ Dec from the full fit to data.

  • SR$3\ell$ Prod $D_\text{NN}(tHc)$ pre-fit

    Figure 4 (d) in the auxiliary material

    10.17182/hepdata.150998.v1/t38

    Pre-fit plot of $D_\text{NN}(tHc)$ in the SR$3\ell$ Prod from the full fit to data.

  • SR$2\ell$ Dec $D_\text{NN}(tHu)$ pre-fit

    Figure 6 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t39

    Pre-fit plot of $D_\text{NN}(tHu)$ in the SR$2\ell$ Dec from the full fit to data.

  • SR$2\ell$ Prod $D_\text{NN}(tHu)$ pre-fit

    Figure 6 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t40

    Pre-fit plot of $D_\text{NN}(tHu)$ in the SR$2\ell$ Prod from the full fit to data.

  • SR$3\ell$ Dec $D_\text{NN}(tHu)$ pre-fit

    Figure 6 (c) in the auxiliary material

    10.17182/hepdata.150998.v1/t41

    Pre-fit plot of $D_\text{NN}(tHu)$ in the SR$3\ell$ Dec from the full fit to data.

  • SR$3\ell$ Prod $D_\text{NN}(tHu)$ pre-fit

    Figure 6 (d) in the auxiliary material

    10.17182/hepdata.150998.v1/t42

    Pre-fit plot of $D_\text{NN}(tHu)$ in the SR$3\ell$ Prod from the full fit to data.

  • CR$2\ell$ HF$e$ $p_\text{T}(\ell_1)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t43

    Pre-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ HF$e$ from the full fit to data.

  • CR$2\ell$ HF$\mu$ $p_\text{T}(\ell_1)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t44

    Pre-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ HF$\mu$ from the full fit to data.

  • CR$2\ell$ $t\bar{t}V$ $p_\text{T}(\ell_1)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t45

    Pre-fit plot of $p_\text{T}(\ell_1)$ in the CR$2\ell$ $t\bar{t}V$ from the full fit to data.

  • CR$3\ell$ HF$e$ $p_\text{T}(\ell_2)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t46

    Pre-fit plot of $p_\text{T}(\ell_2)$ in the CR$3\ell$ HF$e$ from the full fit to data.

  • CR$3\ell$ HF$\mu$ $p_\text{T}(\ell_2)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t47

    Pre-fit plot of $p_\text{T}(\ell_2)$ in the CR$3\ell$ HF$\mu$ from the full fit to data.

  • CR$3\ell$ $t\bar{t}W$ $p_\text{T}(b\text{-jet}_0)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t48

    Pre-fit plot of $p_\text{T}(b\text{-jet}_0)$ in the CR$3\ell$ $t\bar{t}W$ from the full fit to data.

  • CR$3\ell$ $t\bar{t}Z$ $p_\text{T}(b\text{-jet}_0)$ pre-fit

    Figure 8 in the auxiliary material

    10.17182/hepdata.150998.v1/t49

    Pre-fit plot of $p_\text{T}(b\text{-jet}_0)$ in the CR$3\ell$ $t\bar{t}Z$ from the full fit to data.

  • $tHu$ fit NP ranking

    Figure 10 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t50

    Ranking of fit nuisance parameters according to their impact on the post-fit $tHu$ signal normalisation when fixed to $\pm1\sigma$

  • $tHc$ fit NP ranking

    Figure 10 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t51

    Ranking of fit nuisance parameters according to their impact on the post-fit $tHc$ signal normalisation when fixed to $\pm1\sigma$

  • Upper limits on $\mathcal{B}(t\to Hu)$ per final state

    Figure 12 (a) in the auxiliary material

    10.17182/hepdata.150998.v1/t52

    Expected upper exclusion limits on the branching ratio $\mathcal{B}(t\to Hu)$ for each individual final state and the full analysis.

  • Upper limits on $\mathcal{B}(t\to Hc)$ per final state

    Figure 12 (b) in the auxiliary material

    10.17182/hepdata.150998.v1/t53

    Expected upper exclusion limits on the branching ratio $\mathcal{B}(t\to Hc)$ for each individual final state and the full analysis.

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