CMS-EXO-16-039

CMS-EXO-16-039 ; CERN-EP-2017-097
Search for new physics in the monophoton final state in proton-proton collisions at $ \sqrt{s} = $ 13 TeV
CMS Collaboration
12 June 2017
J. High Energy Phys. 10 (2017) 073
Abstract: A search is conducted for new physics in a final state containing a photon and missing transverse momentum in proton-proton collisions at $ \sqrt{s} = $ 13 TeV. The data collected by the CMS experiment at the CERN LHC correspond to an integrated luminosity of 12.9 fb$^{-1}$. No deviations are observed relative to the predictions of the standard model. The results are interpreted as exclusion limits on the dark matter production cross sections and parameters in models containing extra spatial dimensions. Improved limits are set with respect to previous searches using the monophoton final state. In particular, the limits on the extra dimension model parameters are the most stringent to date in this channel.
Links: e-print arXiv:1706.03794 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading-order diagrams of the simplified DM model (left), electroweak-DM effective interaction (center), and graviton (G) production in the ADD model (right), with a final state of $\gamma $ and large ${ {p_{\mathrm {T}}} ^\text {miss}} $.
png pdf	Figure 1-a: Leading-order diagrams of the simplified DM model, with a final state of $\gamma $ and large ${ {p_{\mathrm {T}}} ^\text {miss}} $.
png pdf	Figure 1-b: Leading-order diagrams of the electroweak-DM effective interaction, with a final state of $\gamma $ and large ${ {p_{\mathrm {T}}} ^\text {miss}} $.
png pdf	Figure 1-c: Leading-order diagrams of the graviton (G) production in the ADD model, with a final state of $\gamma $ and large ${ {p_{\mathrm {T}}} ^\text {miss}} $.
png pdf	Figure 2: The ${p_{\mathrm {T}}^{\gamma }}$ (left) and ${ {p_{\mathrm {T}}} ^\text {miss}} $ (right) distributions for the candidate sample, compared with estimated contributions from SM backgrounds. In the legends, "others'' includes the contribution from $\gamma$+jets, $\mathrm{ W } \to \ell \nu $, ${\mathrm{ Z } (\to \ell \overline {\ell })}$+${\gamma }$, and $\mathrm{ t \bar{t} }\gamma$ backgrounds. The background uncertainties include statistical and systematic components. The last bin includes the overflow. The lower panel shows the ratio of data and SM background predictions, where the hatched band shows the systematic uncertainty.
png pdf	Figure 2-a: The ${p_{\mathrm {T}}^{\gamma }}$ distribution for the candidate sample, compared with estimated contribution from SM backgrounds. In the legend, "others'' includes the contribution from $\gamma$+jets, $\mathrm{ W } \to \ell \nu $, ${\mathrm{ Z } (\to \ell \overline {\ell })}$+${\gamma }$, and $\mathrm{ t \bar{t} }\gamma$ backgrounds. The background uncertainties include statistical and systematic components. The last bin includes the overflow. The lower panel shows the ratio of data and SM background predictions, where the hatched band shows the systematic uncertainty.
png pdf	Figure 2-b: The ${ {p_{\mathrm {T}}} ^\text {miss}} $ distribution for the candidate sample, compared with estimated contribution from SM backgrounds. In the legend, "others'' includes the contribution from $\gamma$+jets, $\mathrm{ W } \to \ell \nu $, ${\mathrm{ Z } (\to \ell \overline {\ell })}$+${\gamma }$, and $\mathrm{ t \bar{t} }\gamma$ backgrounds. The background uncertainties include statistical and systematic components. The last bin includes the overflow. The lower panel shows the ratio of data and SM background predictions, where the hatched band shows the systematic uncertainty.
png pdf	Figure 3: The ratio of 95% CL cross section upper limits to theoretical cross section ($\mu _{95}$), for DM simplified models with vector (left) and axial-vector (right) mediators, assuming $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1. Expected and observed $\mu _{95} = $ 1 contours are overlaid. The region below the observed contour is excluded.
png pdf	Figure 3-a: The ratio of 95% CL cross section upper limits to theoretical cross section ($\mu _{95}$), for DM simplified models with vector mediators, assuming $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1. Expected and observed $\mu _{95} = $ 1 contours are overlaid. The region below the observed contour is excluded.
png pdf	Figure 3-b: The ratio of 95% CL cross section upper limits to theoretical cross section ($\mu _{95}$), for DM simplified models with axial-vector mediators, assuming $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1. Expected and observed $\mu _{95} = $ 1 contours are overlaid. The region below the observed contour is excluded.
png pdf	Figure 4: The 90% CL exclusion limits on the $\chi $-nucleon spin-independent (left) and spin-dependent (right) scattering cross sections involving vector and axial-vector operators, respectively, as a function of the ${m_{\text {DM}}}$. Simplified model DM parameters of $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1 are assumed. The region to the upper left of the contour is excluded. On the plots, the median expected 90% CL curve overlaps the observed 90% CL curve. Also shown are corresponding exclusion contours, where regions above the curves are excluded, from the recent results by CDMSLite [39], LUX [40], PandaX [41], CRESST-II [42], PICO-60 [43], IceCube [44], PICASSO [45] and Super-Kamiokande [46] Collaborations.
png pdf	Figure 4-a: The 90% CL exclusion limits on the $\chi $-nucleon spin-independent scattering cross sections involving vector and axial-vector operators, respectively, as a function of the ${m_{\text {DM}}}$. Simplified model DM parameters of $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1 are assumed. The region to the upper left of the contour is excluded. On the plots, the median expected 90% CL curve overlaps the observed 90% CL curve. Also shown are corresponding exclusion contours, where regions above the curves are excluded, from the recent results by CDMSLite [39], LUX [40], PandaX [41] and CRESST-II [42] Collaborations.
png pdf	Figure 4-b: The 90% CL exclusion limits on the $\chi $-nucleon spin-dependent scattering cross sections involving vector and axial-vector operators, respectively, as a function of the ${m_{\text {DM}}}$. Simplified model DM parameters of $ g_{\mathrm{q}}= $ 0.25 and $ g_{\text{DM}}= $ 1 are assumed. The region to the upper left of the contour is excluded. On the plots, the median expected 90% CL curve overlaps the observed 90% CL curve. Also shown are corresponding exclusion contours, where regions above the curves are excluded, from the recent results by PICO-60 [43], IceCube [44], PICASSO [45] and Super-Kamiokande [46] Collaborations.
png pdf	Figure 5: The 95% CL expected and observed lower limits on $\Lambda $ as a function of ${m_{\text {DM}}}$, for a dimension-7 operator EFT model.
png pdf	Figure 6: The 95% CL upper limits on the ADD graviton production cross section, as a function of ${M_D}$ for $n=3$ extra dimensions.
png pdf	Figure 7: Lower limit on ${M_D}$ as a function of $n$, the number of ADD extra dimensions.

Tables
png pdf	Table 1: Summary of estimated background and observed candidate events. The quoted uncertainties for the background estimates are obtained by adding the systematic and statistical uncertainties in quadrature.
png pdf	Table 2: Summary of relative systematic uncertainties (%) for different background estimates. The middle column indicates the component of the estimated SM background that is affected by each uncertainty.
png pdf	Table 3: The 95% CL observed and expected lower limits on ${M_D}$ as a function of $n$, the number of ADD extra dimensions.

Summary

Proton-proton collisions producing large missing transverse momentum and a high transverse momentum photon have been investigated to search for new phenomena, using a data set corresponding to 12.9 fb$^{-1}$ of integrated luminosity recorded at $ \sqrt{s} = $ 13 TeV at the CERN LHC. No deviations from the standard model predictions are observed. Constraints are set on the production cross sections for dark matter and large extra dimension gravitons at 95% confidence level, which are then translated to limits on the parameters of the individual models. For the simplified dark matter production models considered, the search excludes mediator masses of up to 700 GeV for low-mass dark matter. For an effective dimension-7 photon-dark matter contact interaction, values of $\Lambda$ up to 600 GeV are excluded. For the ADD model with extra spatial dimensions, values of the fundamental Planck scale up to 2.31-2.49 TeV, depending on the number of extra dimensions, are excluded. These are the most stringent limits to date using the monophoton final state.

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