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| CMS-PAS-EXO-20-001 | ||
| Search for W$ \gamma $ resonances using hadronic decays of Lorentz-boosted W bosons in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| March 2021 | ||
| Abstract: A search for W$ \gamma $ resonances in the mass range between 700 and 6000 GeV is presented. The W boson is reconstructed via its hadronic decay, with the final-state products forming a single, large-radius jet, owing to a large Lorentz boost of the W boson. The search is based on proton-proton collision data at $\sqrt{s} = $ 13 TeV, collected with the CMS detector in 2016-2018, corresponding to an integrated luminosity of 137 fb$^{-1}$. The W$ \gamma $ invariant mass spectrum is parameterized with a smoothly falling background function and examined for the presence of resonance-like signals. No significant excesses above the predicted background are observed. Model-specific limits at 95% confidence level on the production cross section times branching fraction to the W$ \gamma $ channel are set for narrow resonances and for resonances with an intrinsic width equal to 5% of their mass, for spin-0 and spin-1 hypotheses, ranging between 0.11 and 35 fb. These are the most restrictive limits to date on the existence of such resonances. Model-independent limits on the production cross section times branching fraction to the W$ \gamma $ channel times signal acceptance are also set for minimum W$ \gamma $ mass thresholds between 1500 and 8000 GeV, allowing for testing more general models predicting production of a photon in association with a jet consistent with a hadronic W or Z boson decay. | ||
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Links:
CDS record (PDF) ;
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These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Definitions of the signal and control region in data, based on the jet mass ${m_\mathrm {J}^\text {SD}}$. The stacked filled histograms represent dominant backgrounds from simulation, normalized to the $ {p_{\text {T}}^{\gamma}} $ spectrum in the signal region. Red (black) points correspond to data in the signal (control) region. Benchmark spin-0 signal distributions, normalized to a cross section of 2 pb, for two mass (1 and 3.5 TeV) and two width (narrow, N, and broad, B) hypotheses are shown with dashed lines. The two lower panels show the data-to-simulation ratio in the control and signal regions. |
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Figure 2:
Distribution of some of the kinematic variables used in the analysis. Upper row: $ {p_{\text {T}}^{\gamma}} $ (left), ${m_{{\mathrm {J}\gamma}}}$ (right); middle row: $ {\eta _\mathrm {J}} $ (left), $\cos^*\theta _\gamma $ (right); lower row: $ {p_{\text {T}}^{\gamma}} / {m_{{\mathrm {J}\gamma}}} $ (left), ${\tau _{21}}$ (right). The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. The discrepancy seen in the ${\tau _{21}}$ variable in the control region and either signal region or simulation is due to the correlation of the $N$-subjettiness variable with the jet mass. The control region data are therefore not used in the optimization of the ${\tau _{21}}$ selection. |
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Figure 2-a:
Distribution of the $ {p_{\text {T}}^{\gamma}} $ kinematic variable.The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. |
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Figure 2-b:
Distribution of the ${m_{{\mathrm {J}\gamma}}}$ kinematic variable. The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. |
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Figure 2-c:
Distribution of the $ {\eta _\mathrm {J}} $ kinematic variable.The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. |
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Figure 2-d:
Distribution of the $\cos^*\theta _\gamma $ kinematic variable.The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. |
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Figure 2-e:
Distribution of the $ {p_{\text {T}}^{\gamma}} / {m_{{\mathrm {J}\gamma}}} $ kinematic variable.The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. |
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Figure 2-f:
Distribution of the ${\tau _{21}}$ kinematic variable. The notations are the same as in Fig. 1, except that the yield in the control region is normalized to that in the signal region. The discrepancy seen in the control region and either signal region or simulation is due to the correlation of the $N$-subjettiness variable with the jet mass. The control region data are therefore not used in the optimization of the ${\tau _{21}}$ selection. |
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Figure 3:
Signal acceptance ${\cal A}$ (upper left), the product of signal acceptance and selection efficiency ${\cal A}\varepsilon $ (upper right), and W tagging efficiency (lower) for spin-0 (solid lines) and spin-1 (dashed lines) resonances, for the narrow (red) and broad (blue) hypotheses. The curves are obtained by fitting the set of discrete mass points, for which simulated signal samples are available, with fourth-order polynomials. For the W tagging efficiency, also shown is an average value obtained for the different spin and width hypotheses (the green curve with the hatched uncertainty band). |
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Figure 3-a:
Signal acceptance ${\cal A}$ for spin-0 (solid lines) and spin-1 (dashed lines) resonances, for the narrow (red) and broad (blue) hypotheses. The curves are obtained by fitting the set of discrete mass points, for which simulated signal samples are available, with fourth-order polynomials. Figure 3-b |
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Figure 3-b:
Signal acceptance ${\cal A}$ (upper left), the product of signal acceptance and selection efficiency ${\cal A}\varepsilon $ (upper right), and W tagging efficiency (lower) for spin-0 (solid lines) and spin-1 (dashed lines) resonances, for the narrow (red) and broad (blue) hypotheses. The curves are obtained by fitting the set of discrete mass points, for which simulated signal samples are available, with fourth-order polynomials. For the W tagging efficiency, also shown is an average value obtained for the different spin and width hypotheses (the green curve with the hatched uncertainty band). |
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Figure 3-c:
W tagging efficiency for spin-0 (solid lines) and spin-1 (dashed lines) resonances, for the narrow (red) and broad (blue) hypotheses. The curves are obtained by fitting the set of discrete mass points, for which simulated signal samples are available, with fourth-order polynomials. Also shown is an average value obtained for the different spin and width hypotheses (the green curve with the hatched uncertainty band). |
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Figure 4:
Background-only fit to data (black points) with the chosen background function. The green and yellow bands show, respectively, the 68 and 95% confidence level statistical uncertainties in the fit. The lower panel contains the pull distribution, defined as the difference between the data yield and the background prediction, divided by the combined uncertainty in both. Expected signal shapes are also shown in the lower panel for three different resonance mass hypotheses, 1000 GeV (red), 2600 GeV (cyan), and 4000 GeV (green) and for both narrow (solid) and broad (dashed) cases. Signal normalizations are set to 15, 1, and 0.3 fb, respectively, for illustration purpose. In the limit setting procedure, the optimal values of the background parameters are refitted for each signal mass hypothesis to account for the uncertainties associated with the background prediction. |
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Figure 5:
Expected and observed 95% CL limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma)$ for the spin-0 (upper row) and spin-1 (lower row) resonances for the narrow (left column) and broad (right column) resonance cases. |
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Figure 5-a:
Expected and observed 95% CL limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma)$ for the spin-0 resonances for the narrow resonance cases. |
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Figure 5-b:
Expected and observed 95% CL limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma)$ for the spin-0 resonances for the broad resonance cases. |
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Figure 5-c:
Expected and observed 95% CL limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma)$ for the spin-1 resonances for the narrow resonance cases. |
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Figure 5-d:
Expected and observed 95% CL limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma)$ for the spin-1 resonances for the broad resonance cases. |
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Figure 6:
Observed background-only fit $p$-values for spin-0 (left) and spin-1 (right) resonance hypotheses. The largest excess observed at 1580 GeV, corresponds to a local significance of 2.8 (3.1) standard deviations ($\sigma $) for narrow (broad) signals, for both spin hypotheses. |
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Figure 6-a:
Observed background-only fit $p$-values for the spin-0 resonance hypothesis. The largest excess observed at 1580 GeV, corresponds to a local significance of 2.8 (3.1) standard deviations ($\sigma $) for narrow (broad) signals. |
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Figure 6-b:
Observed background-only fit $p$-values for the spin-1 resonance hypothesis. The largest excess observed at 1580 GeV, corresponds to a local significance of 2.8 (3.1) standard deviations ($\sigma $) for narrow (broad) signals. |
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Figure 7:
Expected and observed 95% CL model-independent limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma) {\cal A}$ (left) and $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma) {\cal A} \epsilon _{\rm W tag}$ (right), as a function of the minimum invariant mass requirement on the ${\mathrm {J}\gamma}$ system. |
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Figure 7-a:
Expected and observed 95% CL model-independent limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma) {\cal A}$, as a function of the minimum invariant mass requirement on the ${\mathrm {J}\gamma}$ system. |
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Figure 7-b:
Expected and observed 95% CL model-independent limits on $\sigma {\cal B}(X \rightarrow \mathrm{W} \gamma) {\cal A} \epsilon _{\rm W tag}$, as a function of the minimum invariant mass requirement on the ${\mathrm {J}\gamma}$ system. |
| Tables | |
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Table 1:
Systematic uncertainties affecting the signal description. Uncertainties marked with the dagger affect both the yield and the shape of the signal distribution, while the rest only affect the signal yield. In case the uncertainty is different for various data taking periods, the three numbers given in the second column correspond to the 2016/2017/2018 data taking, while the third column shows the combined uncertainties across the three years, taking into account the year-to-year correlations. The effect on the signal yield is the same for all the hypotheses studied. |
| Summary |
| In summary, a search for W$ \gamma $ resonances in the mass range between 700 and 6000 GeV has been presented. The W boson is reconstructed via its hadronic decay, with the final-state products forming a single, large-radius jet, owing to a large Lorentz boost of the W boson. The search is based on the proton-proton collision data at $\sqrt{s} = $ 13 TeV, collected with the CMS detector in 2016-2018, corresponding to an integrated luminosity of 137 fb$^{-1}$. No significant excesses above the smoothly falling background is observed. Limits at 95% confidence level on the production cross section times branching fraction for W$ \gamma $ resonances are set for narrow and broad (with the intrinsic width equal 5% of their mass) resonances, ranging from 21 (32) fb to 0.15 (0.23) fb for the narrow (broad) spin-0 hypothesis, and from 20 (35) fb to 0.11 (0.13) fb for the spin-1 hypotheses. The results reported are the most restrictive limits to date on the existence of such resonances. In addition, model-independent limits are also set on the production cross section times branching fraction times signal acceptance, as a function of the minimum invariant mass of the jet-photon system, offering a possibility to interpret these results in the context of other models predicting similar signatures. |
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