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CMS-PAS-EXO-16-046

Search for new physics with dijet angular distributions in proton-proton collisions at $\sqrt{s}= $ 13 TeV and constraints on dark matter and other models

CMS Collaboration

July 2017

Abstract: A search is presented for new physics using measurements of dijet angular distributions from proton-proton collisions at $\sqrt{s}= $ 13 TeV, constraining models of quark contact interactions, extra spatial dimensions, quantum black holes, and dark matter. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 35.9 fb$^{-1}$. The measured distributions are found to be in agreement with predictions from perturbative quantum chromodynamics (QCD) that include electroweak corrections. In a benchmark model, valid to next-to-leading order in QCD, in which only left-handed quarks participate, contact interactions are excluded up to a scale of 13.1 and 17.4 TeV for destructive or constructive interference, respectively. The most stringent lower limits to date are set on the scale of graviton exchange. In the Giudice-Rattazzi-Wells convention, virtual graviton exchange is excluded up to a scale of 10.6 TeV at 95% confidence. The production of quantum black holes is excluded for masses below 8.3 and 6.0 TeV, depending on the model. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter particles with quark coupling $g_{\text{q}} = 1.0$, dark matter coupling $g_{\text{DM}} = 1.0$, and masses between 2.5 and 5.0 TeV are excluded.

Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, EPJC 78 (2018) 789. The superseded preliminary plots can be found here.

Figures
png pdf	Figure 1: Normalized $ {\chi _{\text {dijet}}} $ distributions shown for the unfolded data compared to NLO predictions (black dotted line). The error bars represent statistical and experimental systematic uncertainties combined in quadrature. Theoretical uncertainties are indicated as gray bands. Also shown are the predictions for QCD+CI with $\Lambda _{\mathrm {LL}}^{+}= $ 13 TeV (blue dashed-dotted lines), QCD+ADD with $\Lambda _{\mathrm {T}}\ (\mathrm {GRW})\ =$ 10 TeV (orange dashed lines), QCD+QBH with $n_{\mathrm {ED}}= $ 6 and $M_{\mathrm {QBH}}= $ 8 TeV (green dashed-dotted lines), and QCD+DM with $M_{\mathrm {Med}} = $ 4.5TeV and $g_{\text {q}} =1.0$ (red solid lines).
png pdf	Figure 2: The 95% CL upper limits on the universal quark coupling $g_{\text {q}}$ as a function of mass for a leptophobic axial-vector or vector DM mediator with $g_{\text {DM}}=1.0$ and $m_{\text {DM}}= $ 1 GeV. The observed limits (solid), expected limits (dashed) and their variation at the 1 and 2 standard deviation levels (shaded bands) are shown. A dotted horizontal line shows the coupling strength for a benchmark DM mediator with $g_{\text {q}}=1.0$.
png pdf	Figure 3: The 95% CL observed (blue) and expected (light blue) excluded regions in the plane of dark matter mass vs. mediator mass, for a (top) vector mediator and an (bottom) axial-vector mediator for a DM benchmark model with $g_{\text {DM}}=1.0$ and $g_{\text {q}}=1.0$ are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements and MadDM version 2.0.6 [65,66].
png pdf	Figure 3-a: The 95% CL observed (blue) and expected (light blue) excluded regions in the plane of dark matter mass vs. mediator mass, for a vector mediator for a DM benchmark model with $g_{\text {DM}}=1.0$ and $g_{\text {q}}=1.0$ are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements and MadDM version 2.0.6 [65,66].
png pdf	Figure 3-b: The 95% CL observed (blue) and expected (light blue) excluded regions in the plane of dark matter mass vs. mediator mass, for a axial-vector mediator for a DM benchmark model with $g_{\text {DM}}=1.0$ and $g_{\text {q}}=1.0$ are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements and MadDM version 2.0.6 [65,66].

Tables
png pdf	Table 1: Summary of leading experimental and theoretical uncertainties on the normalized $ {\chi _{\text {dijet}}} $ distributions in %. While the statistical analysis represents each uncertainty through a change in the $ {\chi _{\text {dijet}}} $ distribution correlated among all $ {\chi _{\text {dijet}}} $ bins, this table summarizes each uncertainty by a representative percentage to demonstrate the relative contributions. For the lowest and highest dijet mass bins, the relative shift is given for the lowest $ {\chi _{\text {dijet}}} $ bin. In the highest dijet mass bin, the dominant experimental contribution corresponds to the statistical uncertainty, while the dominant theoretical contribution is from the uncertainty in QCD scales.
png pdf	Table 2: Observed and expected exclusion limits at 95% CL for various CI, ADD, QBH, and DM models. The 68% ranges of expectation for the expected limit are given as well. For the DM vector mediator, couplings $g_{\text {DM}}=1$, $g_{\text {q}}=1$ and a DM mass of 1GeV are assumed and a range of masses instead of a lower limit is quoted.

Summary

Normalized dijet angular distributions have been measured with the CMS detector over a wide range of dijet invariant masses. The distributions are found to be in agreement with predictions of perturbative quantum chromodynamics and are used to set lower limits on the contact interaction scale for a variety of quark compositeness models, extra spatial dimensions, quantum black hole production, and simplified models of a quark and dark matter interactions. For the first time, a lower limit at the 95% confidence level of $g_{\text{q}}>1$ on the universal quark coupling of a dark matter mediator with masses between 2.5 and 5.0 TeV for (axial-)vector mediators is set in a region that is not accessible through dijet resonance searches. The lower limits for the contact interaction scale $\Lambda$ range from 9.1 to 22.2 TeV. The lower limits for the scales of ADD models, $\Lambda_{\mathrm{T}}$ (GRW) and $M_{\mathrm{S}}$ (HLZ), are in the range of 8.9-12.6 TeV, and are the most stringent set of limits available. Quantum black hole production scales in the ADD $n_{\textrm{ED}} = $ 6 model of up to 8.3 TeV and in the Randall-Sundrum $n_{\textrm{ED}}= $ 1 model of up to 6.0 TeV are excluded.

Additional Figures
png pdf	Additional Figure 1: The 95% CL upper limits on the universal quark coupling $g_{\text {q}}'$ as a function of the mass of a DM mediator that only decays to quarks from CMS dijet narrow resonance search (CMS-PAS-EXO-16-056), boosted dijet resonance search (CMS-PAS-EXO-17-001), and dijet chi analysis (CMS-PAS-EXO-16-046) with 35.9 fb$^{-1}$. The red and light red lines correspond to the observed and expected limits from the dijet narrow resonance search. The green and light green lines correspond to the observed and expected limits from the boosted dijet resonance search. A dashed horizontal line at $g_{\text {q}}'=$ 0.4 indicates the lower border of the region for which the resonance width is $>$ 10% such that the sensitivity for the dijet resonance searches might fade away. The blue and light blue lines correspond to the observed and expected limits from the dijet chi analysis. A dotted horizontal line shows the coupling strength $g_{\text {q}}'= $ 1.0, which is the benchmark quark coupling chosen by the dijet chi analysis.
png pdf	Additional Figure 2: Same as Fig.-aux 1 but with log scale for the x-axis.
png pdf	Additional Figure 3: The 95% CL observed (blue) and expected (light blue) exclusion regions in the plane of dark matter mass vs. mediator mass, for a (top) vector mediator and an (bottom) axial-vector mediator for a DM benchmark model with $g_{\text {DM}}=$ 1.0 and $g_{\text {q}}= $ 1.0, are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements. The exclusion regions are also compared to the 95% CL observed (red) and expected (light red) exclusion regions from the CMS monojet search with 12.9 fb$^{-1}$ (CMS-EXO-16-037).
png pdf	Additional Figure 3-a: The 95% CL observed (blue) and expected (light blue) exclusion regions in the plane of dark matter mass vs. mediator mass, for a vector mediator for a DM benchmark model with $g_{\text {DM}}=$ 1.0 and $g_{\text {q}}= $ 1.0, are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements. The exclusion regions are also compared to the 95% CL observed (red) and expected (light red) exclusion regions from the CMS monojet search with 12.9 fb$^{-1}$ (CMS-EXO-16-037).
png pdf	Additional Figure 3-b: The 95% CL observed (blue) and expected (light blue) exclusion regions in the plane of dark matter mass vs. mediator mass, for an axial-vector mediator for a DM benchmark model with $g_{\text {DM}}=$ 1.0 and $g_{\text {q}}= $ 1.0, are compared to constraints from the cosmological relic density of DM (light gray) determined from astrophysical measurements. The exclusion regions are also compared to the 95% CL observed (red) and expected (light red) exclusion regions from the CMS monojet search with 12.9 fb$^{-1}$ (CMS-EXO-16-037).

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