Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector

TL;DR

ATLAS analyzes monojet events in $pp$ collisions at $\sqrt{s}=7$ TeV with $\mathcal{L}=4.7\,\mathrm{fb}^{-1}$ to search for dark matter pair production and large extra dimensions. The analysis uses four overlapping signal regions defined by $E_T^{\mathrm{miss}}$ and leading-jet $p_T$, with backgrounds constrained by data-driven control regions for $Z/W$+jets, multijet, and non-collision sources, complemented by MC for other processes. No excess is observed and 95% CL limits are set on LED via the $(4+n)$-dimensional Planck scale $M_D$ and on WIMP production via EFT suppression scales $M_*$; the results are translated to WIMP-nucleon cross sections and annihilation rates $\langle\sigma v\rangle$, enabling comparisons with direct and indirect detection. The study highlights EFT validity caveats at high energies while demonstrating the complementary role of collider searches in probing light-WIMP regimes and providing stringent constraints on beyond-Standard-Model monojet signatures.

Abstract

A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at sqrt(s)=7 TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 inverse femtobarn. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles.

Figures (7)

• Figure 1: Kinematic distributions in the control regions corresponding to SR1 (labelled CR1) are shown. The upper row is the leading electron and muon $p_{\mathrm{T}}$ distribution for $Z\rightarrow e^+ e^-$+jets (left) and $Z\rightarrow \mathrm{\mu^+ \mu^-}$+jets (right) and shows distributions after SR1 cuts on jets and $E_{\mathrm{T}}^{\mathrm{miss}}$. The lower row is the missing transverse momentum distribution $E_{\mathrm{T}}^{\mathrm{miss}, \not e}$ for $W\rightarrow e\nu$+jets (left) and $E_{\mathrm{T}}^{\mathrm{miss}}$ for $W\rightarrow \mu\nu$+jets (right) also after SR1 jet and $E_{\mathrm{T}}^{\mathrm{miss}}$ cuts.
• Figure 2: Kinematic distributions for signal regions SR1 on the left and SR4 on the right. Signal distributions for ADD and WIMP samples for cross sections equal to the excluded values are drawn as dashed lines on top of the predicted background distributions. The electroweak backgrounds (see equation \ref{['eq:bg:2']}) are determined in bins of the variable that is plotted.
• Figure 3: Left: Visible cross sections in SR4 as a function of $M_\mathrm{D}$ as predicted by the effective ADD theory, for $n=2,4,6$ extra dimensions. The coloured bands correspond to the theoretical systematic uncertainties (PDF, ISR/FSR, scale). The horizontal lines are the expected and observed cross-section limits at 95% CL, taking into account experimental systematic uncertainties fully correlated between signal and background, as well as uncertainties on the luminosity estimate, trigger efficiency, and MC statistical uncertainties. The inclusion of signal uncertainties here increases the cross-section limits compared to those given in table \ref{['tab:bg']}, which exclude signal uncertainties. Right: 95% CL lower limits on $M_\mathrm{D}$ for different numbers of extra dimensions based on SR4. Observed and expected limits including all but the theoretical signal uncertainties are shown as solid and dashed lines, respectively. The grey $\pm 1 \sigma$ band around the expected limit is the variation expected from statistical fluctuations and experimental systematic uncertainties on SM and signal processes. The impact of the theoretical uncertainties is shown by the red small-dashed $\pm 1 \sigma$ limits. The previous ATLAS limit Aad:2011xw is also shown for comparison.
• Figure 4: ATLAS lower limits at 90% CL on $M_*$ for different masses of $\chi$---the region below the limit lines is excluded. The 90% instead of the 95% CL lower limits are plotted because the former are used in the following figures \ref{['fig:wimp:2']} and \ref{['fig:wimp:3']}. Observed and expected limits including all but the theoretical signal uncertainties are shown as dashed black and red solid lines, respectively. The grey $\pm 1 \sigma$ band around the expected limit is the variation expected from statistical fluctuations and experimental systematic uncertainties on SM and signal processes. The impact of the theoretical uncertainties is shown by the thin red dotted $\pm 1 \sigma$ limit lines around the observed limit. The $M_*$ values at which WIMPs of a given mass would result in the required relic abundance are shown as rising green lines (taken from Goodman:2010ku), assuming annihilation in the early universe proceeded exclusively via the given operator. The shaded light-grey regions in the bottom right corners indicate where the effective field theory approach breaks down Goodman:2010ku. The plots for D1, D5, D8 are based on SR3, those for D9 and D11 on SR4.
• Figure 5: Inferred 90% CL ATLAS limits on spin-independent WIMP-nucleon scattering. Cross sections are shown versus WIMP mass $m_\chi$. In all cases the thick solid lines are the observed limits excluding theoretical uncertainties; the observed limits corresponding to the WIMP-parton cross section obtained from the $-1\sigma_{\mathrm{theory}}$ lines in figure \ref{['fig:wimp:1']} are shown as thin dotted lines. The latter limits are conservative because they also include theoretical uncertainties. The ATLAS limits for operators involving quarks are for the four light flavours assuming equal coupling strengths for all quark flavours to the WIMPs. For comparison, 90% CL limits from the XENON100 2012arXiv1207.5988X, CDMSII PhysRevLett.106.131302, CoGeNT Aalseth:2010vx, CDF 2012PhRvL108u1804A, and CMS CmsPreprint experiments are shown.