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| CMS-EXO-17-017 ; CERN-EP-2018-219 | ||
| Search for physics beyond the standard model in high-mass diphoton events from proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| 1 September 2018 | ||
| Phys. Rev. D 98 (2018) 092001 | ||
| Abstract: A search for physics beyond the standard model is performed using a sample of high-mass diphoton events produced in proton-proton collisions at $\sqrt{s} = $ 13 TeV. The data sample was collected in 2016 with the CMS detector at the LHC and corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The search is performed for both resonant and nonresonant new physics signatures. At 95% confidence level, lower limits on the mass of the first Kaluza-Klein excitation of the graviton in the Randall-Sundrum warped extra-dimensional model are determined to be in the range of 2.3 to 4.6 TeV, for values of the associated coupling parameter between 0.01 and 0.2. Lower limits on the production of scalar resonances and model-independent cross section upper limits are also provided. For the large extra-dimensional model of Arkani-Hamed, Dimopoulos, and Dvali, lower limits are set on the string mass scale $ {M_{\mathrm{S}}} $ ranging from 5.6 to 9.7 TeV, depending on the model parameters. The first exclusion limits are set in the two-dimensional parameter space of a continuum clockwork model. | ||
| Links: e-print arXiv:1809.00327 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ; | ||
| Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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| Figures | |
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Figure 1:
The product of the event selection efficiency ($\varepsilon $) and the detector acceptance (A) is shown as a function of signal resonance mass $ {m_{\mathrm {X}}} $ for the $ {{\Gamma _{\mathrm {X}}} / {m_{\mathrm {X}}}} = 1.4\times 10^{-4}$ signal width hypothesis. The total (black), EBEB (red), and EBEE (blue) curves are shown for the spin (J) hypotheses $\mathrm {J}=$ 0 (solid) and $\mathrm {J}= $ 2 (dashed). |
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Figure 2:
Observed diphoton invariant mass spectra for the EBEB (left) and EBEE (right) categories. Also shown are the results of a likelihood fit to the background-only hypothesis. The shaded region shows the one standard deviation uncertainty band associated with the fit, reflecting the statistical uncertainty of the data. The lower panels show the difference between the data and fit, divided by the statistical uncertainty in the data points. |
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Figure 2-a:
Observed diphoton invariant mass spectrum for the EBEB category. Also shown are the results of a likelihood fit to the background-only hypothesis. The shaded region shows the one standard deviation uncertainty band associated with the fit, reflecting the statistical uncertainty of the data. The lower panel shows the difference between the data and fit, divided by the statistical uncertainty in the data points. |
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Figure 2-b:
Observed diphoton invariant mass spectrum for the EBEE category. Also shown are the results of a likelihood fit to the background-only hypothesis. The shaded region shows the one standard deviation uncertainty band associated with the fit, reflecting the statistical uncertainty of the data. The lower panel shows the difference between the data and fit, divided by the statistical uncertainty in the data points. |
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Figure 3:
Expected and observed 95% CL upper limits on the production cross section for RS gravitons of mass $ {m_\mathrm {{\mathrm {G}}}} $ and three values of ${\tilde{k}}$ (left) and for spin-0 resonances of mass $ {m_{\mathrm {S}}} $ produced via gluon fusion for the three width hypotheses (right). The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-a:
Expected and observed 95% CL upper limits on the production cross section for RS gravitons of mass $ {m_\mathrm {{\mathrm {G}}}} $ and ${\tilde{k}} = $ 0.01. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-b:
Expected and observed 95% CL upper limits on the production cross section for spin-0 resonances of mass $ {m_{\mathrm {S}}} $ produced via gluon fusion for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-4} $. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-c:
Expected and observed 95% CL upper limits on the production cross section for RS gravitons of mass $ {m_\mathrm {{\mathrm {G}}}} $ and ${\tilde{k}} = $ 0.1. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-d:
Expected and observed 95% CL upper limits on the production cross section for spin-0 resonances of mass $ {m_{\mathrm {S}}} $ produced via gluon fusion for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-2} $. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-e:
Expected and observed 95% CL upper limits on the production cross section for RS gravitons of mass $ {m_\mathrm {{\mathrm {G}}}} $ and ${\tilde{k}} = $ 0.2. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 3-f:
Expected and observed 95% CL upper limits on the production cross section for spin-0 resonances of mass $ {m_{\mathrm {S}}} $ produced via gluon fusion for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 5.6 {\times} 10^{-2}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEB (left) and EBEE (right) categories for the three width hypotheses. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-a:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEB category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-4}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-b:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEE category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-4}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-c:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEB category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-2}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-d:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEE category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 1.4 {\times} 10^{-2}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-e:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEB category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 5.6 {\times} 10^{-2}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 4-f:
Expected and observed 95% CL upper limits on the fiducial cross section for the resonant $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ process. Shown are the results in the EBEE category for $\Gamma_{\mathrm{X}}/m_{\mathrm{X}} = 5.6 {\times} 10^{-2}$. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. |
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Figure 5:
The diphoton invariant mass distributions in the EBEB (left) and EBEE (right) categories for the SM diphoton background prediction and the fake background measurement compared to the data. The last bin includes the overflow. The error bars on the points indicate the statistical uncertainty. The upper (lower) plots show the pre-fit (post-fit) background estimates. The hatched bands indicate the total pre- or post-fit systematic uncertainties. Invariant mass distributions from two signal scenarios are superimposed on the lower plots. The bottom panels show the pull distributions, indicating the difference between the data and background prediction, divided by the uncertainty in the background, with error bars representing the statistical uncertainty and shaded bands showing the one standard deviation systematic uncertainty, normalized by the statistical uncertainty. |
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Figure 5-a:
The diphoton invariant mass distributions in the EBEB (left) and EBEE (right) categories for the SM diphoton pre-fit background prediction and the fake background measurement compared to the data. The last bin includes the overflow. The error bars on the points indicate the statistical uncertainty. The hatched band indicates the total systematic uncertainties. The bottom panels show the pull distributions, indicating the difference between the data and background prediction, divided by the uncertainty in the background, with error bars representing the statistical uncertainty and shaded bands showing the one standard deviation systematic uncertainty, normalized by the statistical uncertainty. |
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Figure 5-b:
The diphoton invariant mass distributions in the EBEB (left) and EBEE (right) categories for the SM diphoton post-fit background prediction and the fake background measurement compared to the data. The last bin includes the overflow. The error bars on the points indicate the statistical uncertainty. The hatched bands indicate the total systematic uncertainties. Invariant mass distributions from two signal scenarios are superimposed on the plots. The bottom panels show the pull distributions, indicating the difference between the data and background prediction, divided by the uncertainty in the background, with error bars representing the statistical uncertainty and shaded bands showing the one standard deviation systematic uncertainty, normalized by the statistical uncertainty. |
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Figure 6:
The 95% CL exclusion limits for the continuous graviton model in the clockwork framework over the $k$-$M_5$ parameter space. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. The shaded region with $k > M_5$ denotes the area where the theory becomes nonperturbative. |
| Tables | |
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Table 1:
Exclusion lower limits obtained on the mass scale $ {M_{\mathrm {S}}} $ (in units of TeV) for various conventions used in the calculation of the ADD large extra dimensional scenario, as described in Section 4. The total asymmetric uncertainties are shown on the expected limits. |
| Summary |
|
A search has been performed for physics beyond the standard model in high-mass diphoton events from proton-proton collisions at a center-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 35.9 fb$^{-1}$ collected by the CMS detector in 2016. A resonant peak in the diphoton invariant mass spectrum could indicate the existence of a new scalar particle, such as a heavy Higgs boson, or of a Kaluza-Klein excitation of the graviton in the Randall-Sundrum model of warped extra dimensions. A nonresonant excess could be a signature of large extra dimensions, in the scenario by Arkani-Hamed, Dimopoulos, and Dvali, or a continuum clockwork model. The data are found to be in agreement with the predicted background from standard model sources, and no evidence for new physics is seen. Masses below 2.3-4.6 TeV are excluded at 95% confidence level for the excited state of the Randall-Sundrum graviton, for a coupling parameter in the range 0.01 $ < \tilde{k} < $ 0.2. Limits are also set on the production of scalar resonances, and model-independent cross section limits have been extracted as a function of diphoton invariant mass for any resonant $\gamma \gamma$ production process. These results extend the sensitivity of the previous search performed by the CMS experiment [19] and are compatible with those reported by the ATLAS Collaboration in Ref. [18]. In the large extra-dimensional model of Arkani-Hamed, Dimopoulos, and Dvali, exclusion limits on the string mass scale are set in the range 5.6 $ < {M_{\mathrm{S}}} < $ 9.7 TeV, depending on the specific model convention. These results extend the current best lower limits on $ {M_{\mathrm{S}}} $ from the diphoton channel as presented in Ref. [18]. Additionally, the first exclusion limits are set in the two-dimensional parameter space of a continuum clockwork model. |
| Additional Figures | |
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Additional Figure 1:
The product of the event selection efficiency ($\varepsilon $) and the detector acceptance (A) is shown as a function of signal resonance mass $m_{\mathrm {X}}$ for the $\Gamma _{\mathrm {X}}/ m_{\mathrm {X}} = 1.4\times 10^{-2}$ signal width hypothesis. The total (black), EBEB (red), and EBEE (blue) curves are shown for the spin (J) hypotheses $\mathrm {J}=$ 0 (solid) and $\mathrm {J}=$ 2 (dashed). |
png pdf |
Additional Figure 2:
The product of the event selection efficiency ($\varepsilon $) and the detector acceptance (A) is shown as a function of signal resonance mass $m_{\mathrm {X}}$ for the $\Gamma _{\mathrm {X}}/ m_{\mathrm {X}} = 5.6\times 10^{-2}$ signal width hypothesis. The total (black), EBEB (red), and EBEE (blue) curves are shown for the spin (J) hypotheses $\mathrm {J}=$ 0 (solid) and $\mathrm {J}=$ 2 (dashed). |
png pdf |
Additional Figure 3:
The 95% CL exclusion limits for the continuous graviton model in the clockwork framework over the $k$-$M_5$ parameter space using a linear $k$-axis scale. The shaded bands represent the 1 and 2 standard deviation uncertainty in the expected limit. The shaded region with $k > M_5$ denotes the area where the theory becomes nonperturbative. |
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Additional Figure 4:
An event display of the highest invariant mass diphoton event recorded in 2016 at 1840 GeV in the EBEB category. The two photons are represented by the red ECAL energy deposits. |
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Additional Figure 5:
The $K$ factor as a function of $m_{\gamma \gamma}$ in the EBEB category. The $K$ factor is defined as the ratio of the predicted MCFM NNLO $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ cross section to that of SHERPA. The renormalization and factorization scales have been set to $m_{\gamma \gamma}$ (black) and varied simultaneously by factors of 0.5 (blue) and 2.0 (red). |
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Additional Figure 6:
The $K$ factor as a function of $m_{\gamma \gamma}$ in the EBEE category. The $K$ factor is defined as the ratio of the predicted MCFM NNLO $ {\mathrm {p}} {\mathrm {p}}\to \gamma \gamma $ cross section to that of SHERPA. The renormalization and factorization scales have been set to $m_{\gamma \gamma}$ (black) and varied simultaneously by factors of 0.5 (blue) and 2.0 (red). |
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