AtlasPublic Web 
Internal TWiki
|
Studies of new Higgs boson interactions through nonresonant $HH$ production in the $b\bar{b}\gamma\gamma$ final state in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector ATLAS-CONF-2023-050 18 August 2023
|
||
| Content | Preview | |
|---|---|---|
| Main document (CDS record) - internal | pdf from CDS | |
| Figures Tables | - | |
| Abstract | ||
| A search for nonresonant Higgs boson pair production in the $b\bar{b}\gamma\gamma$ final state is performed using 140 fb$^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The analysis strategy is optimised to probe anomalous values of the Higgs ($H$) boson self-coupling modifier $\kappa_\lambda$ and of the quartic $HHVV$ ($V=W,Z$) coupling modifier $\kappa_{2V}$. No significant excess above the expected background from Standard Model processes is observed. An observed upper limit $\mu_{HH}<4.0$ is set at 95% confidence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confidence intervals for the coupling modifiers are $-1.4<\kappa_\lambda<6.9$ and $-0.5<\kappa_{2V}<2.7$, assuming all other Higgs boson couplings except those under study are fixed to the Standard Model predictions. The results are also interpreted in the Standard Model effective field theory and Higgs effective field theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this final state based on the full Run 2 dataset. | ||
| Figures | ||
|
Figure 01a: BDT score distributions for simulated ggF and VBF HH→bb̄γγ signal events and simulated background events from nonresonant diphoton production and singly-produced Higgs bosons decaying to γγ for the (a) low and (b) high mass regions. The data in the mγγ sidebands are also shown as a comparison to nonresonant diphoton production. All distributions are normalised to unity. The vertical dashed lines correspond to the thresholds used to define the event categories. Events with a BDT score between 0 and the lowest threshold (thick dashed line) are discarded. Events passing the lowest threshold are categorized as Low Mass i, i = 1..4 (High Mass i, i = 1..3), with a higher category index i corresponding to higher BDT scores and more signal-like events. png (128kB) pdf (25kB) |
 |
|
|
Figure 01b: BDT score distributions for simulated ggF and VBF HH→bb̄γγ signal events and simulated background events from nonresonant diphoton production and singly-produced Higgs bosons decaying to γγ for the (a) low and (b) high mass regions. The data in the mγγ sidebands are also shown as a comparison to nonresonant diphoton production. All distributions are normalised to unity. The vertical dashed lines correspond to the thresholds used to define the event categories. Events with a BDT score between 0 and the lowest threshold (thick dashed line) are discarded. Events passing the lowest threshold are categorized as Low Mass i, i = 1..4 (High Mass i, i = 1..3), with a higher category index i corresponding to higher BDT scores and more signal-like events. png (128kB) pdf (25kB) |
 |
|
|
Figure 02a: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (105kB) pdf (35kB) |
 |
|
|
Figure 02b: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (97kB) pdf (36kB) |
 |
|
|
Figure 02c: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (87kB) pdf (35kB) |
 |
|
|
Figure 02d: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (50kB) pdf (36kB) |
 |
|
|
Figure 02e: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (99kB) pdf (36kB) |
 |
|
|
Figure 02f: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (49kB) pdf (34kB) |
 |
|
|
Figure 02g: Comparison between the diphoton invariant mass distribution in data (points with error bars) and the background-only fit (solid line) for the four low mass (a-d) and three high mass (e-g) categories of the HH→bb̄γγ search. In each of the low mass (high mass) regions, a higher category index corresponds to higher BDT scores and more signal-like events. The peaks near 125 GeV are due to single-Higgs-boson production. png (46kB) pdf (33kB) |
 |
|
|
Figure 03a: Observed (solid line) and expected (dashed line) value of -2lnΛ as a function of (a) κλ and (b) κ2V, when all other coupling modifiers (including, respectively, κ2V or κλ) are fixed to their SM predictions. png (71kB) pdf (24kB) |
 |
|
|
Figure 03b: Observed (solid line) and expected (dashed line) value of -2lnΛ as a function of (a) κλ and (b) κ2V, when all other coupling modifiers (including, respectively, κ2V or κλ) are fixed to their SM predictions. png (68kB) pdf (24kB) |
 |
|
|
Figure 04: Likelihood contours at 68% (solid line) and 95% (dashed line) CL in the (κλ, κ2V) parameter space, when all other coupling modifiers are fixed to their SM predictions. The corresponding expected contours are shown by the teal and yellow shaded regions. The SM prediction is indicated by the star, while the best-fit value is denoted by the black cross. png (74kB) pdf (54kB) |
 |
|
|
Figure 05a: Likelihood contours at 68% (solid line) and 95% (dashed line) CL in the (a) cgghh vs chhh and (b) ctthh vs chhh HEFT parameter space, with the remaining coefficient fixed to its SM value. The corresponding expected contours are shown by the teal and yellow shaded regions. The SM prediction is indicated by the star, while the best-fit value is denoted by the black cross. png (76kB) pdf (66kB) |
 |
|
|
Figure 05b: Likelihood contours at 68% (solid line) and 95% (dashed line) CL in the (a) cgghh vs chhh and (b) ctthh vs chhh HEFT parameter space, with the remaining coefficient fixed to its SM value. The corresponding expected contours are shown by the teal and yellow shaded regions. The SM prediction is indicated by the star, while the best-fit value is denoted by the black cross. png (71kB) pdf (60kB) |
 |
|
|
Figure 06: The observed (filled circles) and expected (hollow circles) 95% CL upper limits on the HH ggF production cross-section in the Standard Model and for seven HEFT benchmark points defined in Ref. [90]. The expected constraints are obtained from a background hypothesis with σHH = 0. The teal and yellow colored bands indicate the ± 1σ and ± 2σ variations on the expected limit due to statistical and systematic uncertainties. The predicted cross-sections of each of the models under consideration are shown by the red crosses. The contribution from VBF production to the total HH production cross-section is neglected. png (62kB) pdf (26kB) |
 |
|
|
Figure 07: Likelihood contours at 68% (solid line) and 95% (dashed line) CL in the cH☐ vs cH SMEFT parameter space. The corresponding expected contours are shown by the teal and yellow shaded regions. The SM prediction is indicated by the star, while the best-fit value is denoted by the black cross. png (72kB) pdf (70kB) |
 |
|
|
Figure 08: Summary of the expected (blue) and observed (orange) one-dimensional constraints at 68% (solid error bars) and 95% (dashed error bars) CL on the coefficients of selected HEFT (top) and SMEFT (bottom) operators describing Higgs boson interactions affecting HH production through gluon-gluon fusion. The results are obtained from one dimensional scans of the profile log-likelihood under the assumption that all other Wilson coefficients are fixed to their SM values. The contribution from VBF HH production is neglected. png (92kB) pdf (67kB) |
 |
|
| Tables | ||
|
Table 01: Summary of the nominal Higgs-boson pair signal, single-Higgs-boson background and continuum background event samples used in this article. The generator used in the simulation, the parton distribution function (PDF) set, and the set of tuned parameters (tune) are also provided. More details are given in the text and in Ref. [17]. png (321kB) pdf (52kB) |
 |
|
|
Table 02: Breakdown of the dominant systematic uncertainties on the expected μHH upper limit at 95% CL. The impact of the uncertainties corresponds to the relative variation of the expected upper limit when re-evaluating the profile likelihood ratio after fixing the nuisance parameter in question to its best-fit value, while all remaining nuisance parameters remain free to float. Only systematic uncertainties with an impact of at least 0.1% are shown. png (20kB) pdf (37kB) |
 |
|
|
Table 03: The number of expected events (estimated using simulation) from HH signals with various κλ and κ2V hypotheses and single Higgs boson production, as well as the number of expected events from the continuum background. For comparison, the number of data events observed in the 120 GeV < mγγ < 130 GeV window is also shown. The uncertainties on the HH signals and single Higgs boson backgrounds include the systematic uncertainties discussed in Section 6. Asymmetric uncertainties arise primarily from the theory calculation of the SM ggF HH cross-section and the large heavy flavour uncertainty on the ggH single Higgs yield parametrized by a lognormal distribution. The uncertainty in the continuum background is given by the sum in quadrature of the statistical uncertainty from the fit to the data and the spurious signal uncertainty. png (55kB) pdf (65kB) |
 |
|
|
Table 04: The observed and expected 95% CL constraints on the HEFT Wilson coefficients, obtained from one-dimensional scans of the profile log-likelihood under the assumption that all other Wilson coefficients are fixed to their SM values. The contribution from VBF HH production is subdominant to that from ggF and is neglected. png (11kB) pdf (42kB) |
 |
|
|
Table 05: The definitions of the seven HEFT benchmark points described in Ref. [90]. png (13kB) pdf (32kB) |
 |
|
|
Table 06: The observed and expected 95% CL constraints on the SMEFT Wilson coefficients, obtained from one dimensional scans of the profile log-likelihood under the assumption that all other Wilson coefficients are fixed to their SM values. The contribution from VBF production is neglected. png (10kB) pdf (42kB) |
 |
|
