Measurement of dijet angular distributions and search for beyond the standard model physics in proton-proton collisions at $\sqrt{s}$ = 13 TeV

Abstract

A measurement is presented of dijet angular distributions in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data collected with the CMS detector at the CERN LHC and corresponding to an integrated luminosity of 138 fb$^{-1}$. For the first time, the dijet angular distributions, corrected for detector effects, are compared with the predictions of perturbative quantum chromodynamics at next-to-next-to-leading order, including next-to-leading-order electroweak corrections. While data are generally found to be in agreement with predictions, a small difference in shape of the normalized distributions is seen for dijet masses ranging from 2.4 to 4.8 TeV and above 6 TeV. The distributions are used to search for proposed signatures of quark compositeness, extra spatial dimensions, quantum black holes, dark-matter mediators, axion-like particles, and anomalous gluon couplings. The most stringent limits to date are set for most of these scenarios. Quark contact interactions are excluded at 95% confidence level (CL) up to a scale of 17 (37) TeV for destructive (constructive) interference in a benchmark scenario, valid to next-to-leading order in quantum chromodynamics, and in which only left-handed quarks participate. The coupling of axion-like particles to the gluon, $c_{\text{g}}/f_{\text{a}}$, is constrained to be lower than 0.42 TeV$^{-1}$ at 95% CL. The anomalous triple-gluon coupling, $C_{\text{G}}/Λ^2$, in a standard model effective field theory is constrained to be lower than 0.0076 TeV$^{-2}$ at 95% CL.

Figures (8)

• Figure 1: Example diagrams of dijet production processes in QCD and BSM physics. Upper row: $t$-channel quark-gluon scattering in QCD (left), quark-quark scattering via a BSM contact interaction (center left), quark pair production through an $s$-channel BSM resonance (center right), and quark pair production through gravitons in models with extra spatial dimensions (right). Lower row: quark pair production through a quantum black hole (left), gluon pair production through an axion-like particle (center), and gluon pair production with a dimension-6 effective field theory anomalous gluon coupling operator (right). A description of the symbols in the diagrams is given in Section \ref{['sec:bsm']}.
• Figure 2: Normalized $\chi_{\text{dijet}}$ distributions for the $M_{\mathrm{jj}}$ bins up to 4.8$\,\text{Te\spaceV}$. The data distributions at the detector level (points) are compared to NNLO predictions, corrected for the detector response (black dotted lines). The vertical bars on the points represent statistical and experimental systematic uncertainties combined in quadrature. The horizontal bars show the bin widths. Theoretical uncertainties are indicated with the blue bands. The prediction from various BSM scenarios, with parameter values given in the legend, are shown by the different dot-dashed lines. The lower plots display the ratio of the data to the NNLO QCD + NLO EW predictions.
• Figure 3: Normalized $\chi_{\text{dijet}}$ distributions for the $M_{\mathrm{jj}}$ bins above 4.8$\,\text{Te\spaceV}$. Notations as in Fig. \ref{['fig:data_results_detector1']}.
• Figure 4: The 95% $\text{CL}$ upper limits on the universal quark coupling $g_{\text{q}}$ as functions of a vector or axial-vector mediator mass, with $g_{\text{DM}}=1.0$ and $m_{\text{DM}}=1\,\text{Ge\spaceV}\xspace$. The observed (solid line) and expected (dashed line) limits and their 68% and 95% confidence intervals (shaded bands) are shown. A dashed horizontal line shows the coupling strength for a benchmark DM mediator with $g_{\text{q}}=1$. Results are compared to the previous searches using dijet angular CMS:2018ucw (blue dotted line) and dijet mass CMS:2019gwf (red dotted line) distributions. The vertical scale on the right axis gives the corresponding values of $\Gamma/m_{\text{med}}$.
• Figure 5: The 95% $\text{CL}$ upper limits on the ALP gluon coupling (upper) in linear EFT, $c_\text{g}$, as functions of the characteristic energy scale, $f_\text{a}$, assuming $m_\text{a}=1\,\text{Me\spaceV}\xspace$. Only $\chi_{\text{dijet}}$ distributions with $M_{\mathrm{jj}}\xspace<f_\text{a}$ are used to obtain the limits on $c_\text{g}$. The 95% $\text{CL}$ upper limits on the anomalous triple-gluon coupling (lower), $C_\text{G}$, in SMEFT as functions of the BSM physics energy scale, $\Lambda$. Only $\chi_{\text{dijet}}$ distributions with $M_{\mathrm{jj}}\xspace<\Lambda$ are used to obtain the limits on $C_\text{G}$. The observed limits (solid lines), expected limits (dashed lines), and their 68% and 95% confidence intervals (shaded bands) are shown.