Maverick dark matter at colliders

TL;DR

The paper investigates collider probes of a maverick dark matter scenario where the WIMP is the only new particle accessible at the LHC and interacts with quarks via a higher-dimensional axial-vector operator. Using an effective field theory framework constrained by the observed relic density, it studies X X̄ + jet production and contrasts it with SM backgrounds, finding that the signal tends to produce harder jets and greater hadronic activity. Through Monte Carlo simulations with detector effects and conservative cuts, it estimates discovery reach and outlines data-driven strategies to constrain or observe such WIMPs at the Tevatron and LHC. The results suggest a realistic potential to constrain or discover maverick dark matter in the low to moderate mass range, while highlighting uncertainties related to background modeling and optimization that could affect the exact reach.

Abstract

Assuming that dark matter is a weakly interacting massive particle (WIMP) species X produced in the early Universe as a cold thermal relic, we study the collider signal of pp or ppbar -> XXbar + jets and its distinguishability from standard-model background processes associated with jets and missing energy. We assume that the WIMP is the sole particle related to dark matter within reach of the LHC--a "maverick" particle--and that it couples to quarks through a higher dimensional contact interaction. We simulate the WIMP final-state signal XXbar + jet and dominant standard-model (SM) background processes and find that the dark-matter production process results in higher energies for the colored final state partons than do the standard-model background processes, resulting in more QCD radiation and a higher jet multiplicity. As a consequence, the detectable signature of maverick dark matter is an excess over standard-model expectations of events consisting of large missing transverse energy, together with large leading jet transverse momentum and scalar sum of the transverse momenta of the jets. Existing Tevatron data and forthcoming LHC data can constrain (or discover!) maverick dark matter.

Figures (7)

• Figure 1: The upper panel indicates the value of $G_A$ as a function of the WIMP mass $M_X$ necessary to result in a relic abundance of $\Omega_X h^2 = 0.11$ if the interaction Lagrangian is given by Eq. (\ref{['interactionlagrangian']}). Shown for comparison is the value of the Fermi coupling constant, $G_F$. For the effective field theory of Sect. \ref{['EFT']} to be valid, the mass of $\Psi_\mu$ in Eq. (\ref{['uvcomplete']}) must be below the solid curve and above the dashed (Tevatron) and dotted (LHC) horizontal lines in the bottom panel. The vertical dashed and dotted lines indicate the rough kinematic reach for dark-matter production for the indicated hadron collider. The kinks in the curves around $M_X = 170$ GeV correspond to the opening of the top quark production channel, allowing for weaker couplings (top panel) and consequently requiring larger $M_{\psi}'s$ (bottom panel).
• Figure 2: Representative Feynman diagrams (at the parton level) for the processes $pp\rightarrow X\bar{X}+\textrm{ jet}$ (left), $pp\rightarrow \nu\bar{\nu} +\textrm{ jet}$ (center), and $pp\rightarrow l^+\nu+\textrm{ jet}$ (right).
• Figure 3: Upper panel: Suppression factors as a function of the WIMP mass. The broken curves track the kinematic and parton flux suppression for the indicated hadron colliders, normalized to unity at a mass of 10 GeV. The solid curve represents the suppression due to the decrease in $G_A$ as $M_X$ increases (again normalized to unity at a mass of 10 GeV). The total suppression as a function of mass is the product of the two factors. Lower panel: $X \bar{X}$ + jet signal cross section as a function of the $X$ mass and the cross sections for the background processes at the LHC (dottel lines) and the Tevatron (dashed lines).The background processes for the indicated colliders are, from top to bottom, $l^+$ jet, $l^-$ jet, $\nu\bar{\nu}$ jet, and $t\bar{t}$. (The cross sections for $l^+$ jet and $l^-$ jet at the Tevatron are nearly indistinguishable.) The kinks in the curves around $M_X = 170$ GeV correspond to the opening up of the top quark production channel, allowing for weaker couplings (top panel) and correspondingly lower cross sections (bottom panel).
• Figure 4: The normalized distributions of the transverse momentum of the leading parton for the standard-model background (dark region) and the maverick dark-matter signal (light region) at the Tevtron (left) and the LHC (right). The insert in each the figure shows the distribution of events for which the leading parton has transverse momentum satisfying $p_{T} \geq p_{T,\textrm{min}}$. The signal has been generated with $M_X=5$ GeV at the Tevatron and $M_X=50$ GeV at the LHC.
• Figure 5: Distributions for the number of jets (after the $p_T$ and $\slashed{E}_T$ cuts discussed in the text) for signal and background processes at the Tevatron for a WIMP mass of $5$ GeV (left) and the LHC for a WIMP mass of $50$ GeV (right). For each case, the sum of the background processes are shown in the upper panels, and the signal distributions in the lower panels.