Search for flavour-changing neutral current interactions of the top quark and the Higgs boson in events with a pair of $\tau$-leptons in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration
JHEP 2306 (2023) 155, 2023.

Abstract (data abstract)
Search for flavour-changing neutral current interactions of the top quark and the Higgs boson in events with a pair of $\tau$-leptons in pp collisions at $\sqrt{s}=13$TeV with the ATLAS detector A search for flavour-changing neutral current (FCNC) $tqH$ interactions involving a top quark, another up-type quark ($q=u, c$), and a Standard Model (SM) Higgs boson decaying into a $\tau$-lepton pair ($H\rightarrow \tau^+\tau^-$) is presented. The search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$TeV that corresponds to an integrated luminosity of 139 fb$^{-1}$ recorded with the ATLAS detector at the Large Hadron Collider. Two processes are considered,single top quark FCNC production in association with a Higgs boson ($pp\rightarrow tH$), and top quark pair production in which one of top quarks decays into $Wb$ and the other decays into $qH$ through the FCNC interactions. The search selects events with two hadronically decaying $\tau$-lepton candidates ($\tau_{h}$) or at least one $\tau_{h}$ with an additional lepton (e,$\mu$), as well as multiple jets. Event kinematics are used to separate signal from the background through a multivariate discriminant. A slight excess of data is observed with a significance of 2.3$\sigma$ above the expected SM background, and 95% CL upper limits on the $t\to qH$ branching ratios are derived. Observed (expected) 95% CL upper limits are set on the $t\to cH$ and $t\to uH$ branching ratios of $9.4 \times 10^{-4}\, (4.8^{+2.2}_{-1.4}\times 10^{-4})$ and $6.9\times 10^{-4}\, (3.5^{+1.5}_{-1.0}\times 10^{-4})$, respectively. The corresponding combined observed (expected) upper limits on the dimension-6 operator Wilson coefficients in the effective $tqH$ couplings are $C_{c\phi} <1.35\, (0.97)$ and $C_{u\phi} <1.16\, (0.82)$, respectively.

  • Figure 1a

    Data from Figure 1 (a)

    10.17182/hepdata.130958.v1/t1

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1b

    Data from Figure 1 (b)

    10.17182/hepdata.130958.v1/t2

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1c

    Data from Figure 1 (c)

    10.17182/hepdata.130958.v1/t3

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1d

    Data from Figure 1 (d)

    10.17182/hepdata.130958.v1/t4

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1e

    Data from Figure 1 (e)

    10.17182/hepdata.130958.v1/t5

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1f

    Data from Figure 1 (f)

    10.17182/hepdata.130958.v1/t6

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1g

    Data from Figure 1 (g)

    10.17182/hepdata.130958.v1/t7

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1h

    Data from Figure 1 (h)

    10.17182/hepdata.130958.v1/t8

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 1i

    Data from Figure 1 (i)

    10.17182/hepdata.130958.v1/t9

    Leading tau Pt distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying...

  • Figure 2a

    Data from Figure 2 (a)

    10.17182/hepdata.130958.v1/t10

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2b

    Data from Figure 2 (b)

    10.17182/hepdata.130958.v1/t11

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2c

    Data from Figure 2 (c)

    10.17182/hepdata.130958.v1/t12

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2d

    Data from Figure 2 (d)

    10.17182/hepdata.130958.v1/t13

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2e

    Data from Figure 2 (e)

    10.17182/hepdata.130958.v1/t14

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2f

    Data from Figure 2 (f)

    10.17182/hepdata.130958.v1/t15

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2g

    Data from Figure 2 (g)

    10.17182/hepdata.130958.v1/t16

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2h

    Data from Figure 2 (h)

    10.17182/hepdata.130958.v1/t17

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 2i

    Data from Figure 2 (i)

    10.17182/hepdata.130958.v1/t18

    Di-tau mass distributions obtained before the fit to data (Pre-Fit) showing the expected background and tuH signals after applying fake...

  • Figure 3a

    Data from Figure 3 (a)

    10.17182/hepdata.130958.v1/t19

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{\ell}\tau_{had}\tau_{had}$ region, Other...

  • Figure 3b

    Data from Figure 3 (b)

    10.17182/hepdata.130958.v1/t20

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{\ell}\tau_{had}$-1j region, Other...

  • Figure 3c

    Data from Figure 3 (c)

    10.17182/hepdata.130958.v1/t21

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{\ell}\tau_{had}$-2j region, Other...

  • Figure 3d

    Data from Figure 3 (d)

    10.17182/hepdata.130958.v1/t22

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{h}\tau_{lep}\tau_{had}$-2j region, Other...

  • Figure 3e

    Data from Figure 3 (e)

    10.17182/hepdata.130958.v1/t23

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{h}\tau_{lep}\tau_{had}$-3j region, Other...

  • Figure 3f

    Data from Figure 3 (f)

    10.17182/hepdata.130958.v1/t24

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{\ell}\tau_{had}\tau_{had}$SS region, Other...

  • Figure 3g

    Data from Figure 3 (g)

    10.17182/hepdata.130958.v1/t25

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{h}\tau_{had}\tau_{had}$-2j region, Rare...

  • Figure 3h

    Data from Figure 3 (h)

    10.17182/hepdata.130958.v1/t26

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{h}\tau_{had}\tau_{had}$-3j region, Rare...

  • Figure 3i

    Data from Figure 3 (i)

    10.17182/hepdata.130958.v1/t27

    BDT output distributions obtained from a signal+background fit to the data for the tuH search in the $t_{h}\tau_{had}\tau_{had}$-3jSS region, Rare...

  • Figure 4a

    Data from Figure 4 (a)

    10.17182/hepdata.130958.v1/t28

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{\ell}\tau_{had}\tau_{had}$ region, Other...

  • Figure 4b

    Data from Figure 4 (b)

    10.17182/hepdata.130958.v1/t29

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{\ell}\tau_{had}$-1j region, Other...

  • Figure 4c

    Data from Figure 4 (c)

    10.17182/hepdata.130958.v1/t30

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{\ell}\tau_{had}$-2j region, Other...

  • Figure 4d

    Data from Figure 4 (d)

    10.17182/hepdata.130958.v1/t31

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{h}\tau_{lep}\tau_{had}$-2j region, Other...

  • Figure 4e

    Data from Figure 4 (e)

    10.17182/hepdata.130958.v1/t32

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{h}\tau_{lep}\tau_{had}$-3j region,Other MC...

  • Figure 4f

    Data from Figure 4 (f)

    10.17182/hepdata.130958.v1/t33

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{\ell}\tau_{had}\tau_{had}$SS region, Other...

  • Figure 4g

    Data from Figure 4 (g)

    10.17182/hepdata.130958.v1/t34

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{h}\tau_{had}\tau_{had}$-2j region, Rare...

  • Figure 4h

    Data from Figure 4 (h)

    10.17182/hepdata.130958.v1/t35

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{h}\tau_{had}\tau_{had}$-3j region, Rare...

  • Figure 4i

    Data from Figure 4 (i)

    10.17182/hepdata.130958.v1/t36

    BDT output distributions obtained from a signal+background fit to the data for the tcH search in the $t_{h}\tau_{had}\tau_{had}$-3jSS region, Rare...

  • Figure 5a

    Data from Figure 5 (a)

    10.17182/hepdata.130958.v1/t37

    95% CL upper limits on $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$ for the individual searches as well as their combination, assuming $\mathcal{B}(\mathrm{t}\to\mathrm{uH}) = 0$. The...

  • Figure 5b

    Data from Figure 5 (b)

    10.17182/hepdata.130958.v1/t38

    95% CL upper limits on $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ for the individual searches as well as their combination, assuming $\mathcal{B}(\mathrm{t}\to\mathrm{cH}) = 0$. The...

  • Figure 6a (Observed Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t39

    Observed upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6a (Expected Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t40

    Expected upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6a (Expected $+2\sigma$ Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t41

    Expected $+2\sigma$ upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6a (Expected $+1\sigma$ Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t42

    Expected $+1\sigma$ upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6a (Expected $-1\sigma$ Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t43

    Expected $-1\sigma$ upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6a (Expected $-2\sigma$ Branching fraction)

    Data from Figure 6 (a)

    10.17182/hepdata.130958.v1/t44

    Expected $-2\sigma$ upper limits at 95% CL on the branching fractions in the plane of $\mathcal{B}(\mathrm{t}\to\mathrm{uH})$ and $\mathcal{B}(\mathrm{t}\to\mathrm{cH})$.

  • Figure 6b (Observed Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t45

    Observed upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Figure 6b (Expected Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t46

    Expected upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Figure 6b (Expected $+2\sigma$ Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t47

    Expected $+2\sigma$ upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Figure 6b (Expected $+1\sigma$ Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t48

    Expected $+1\sigma$ upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Figure 6b (Expected $-1\sigma$ Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t49

    Expected $-1\sigma$ upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Figure 6b (Expected $-2\sigma$ Anomalous couplings)

    Data from Figure 6 (b)

    10.17182/hepdata.130958.v1/t50

    Expected $-2\sigma$ upper limits at 95% CL on the anomalous couplings in the plane of $C_{\mathrm{c\phi}}$ and $C_{\mathrm{u\phi}}$.

  • Yields, leptonic channels

    Table 6

    10.17182/hepdata.130958.v1/t51

    Predicted and observed yields in each of the analysis regions considered in leptonic channel.

  • Yields, hadronic channels

    Table 6

    10.17182/hepdata.130958.v1/t52

    Predicted and observed yields in each of the analysis regions considered in hadronic channel.

  • Systematics, FCNC

    Table 7

    10.17182/hepdata.130958.v1/t53

    Absolute uncertainties on $\mathcal{B}(\mathrm{t}\to\mathrm{qH})$ obtained from the combined fit to the data.

  • Fit, FCNC

    Table 8

    10.17182/hepdata.130958.v1/t54

    Summary of 95% CL upper limits on $\mathcal{B}(\mathrm{t}\to\mathrm{qH})$, significance and best-fit branching ratio in the signal regions. The values in...

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