Complementary Search of Fermionic Absorption Operators at Hadron Collider and Direct Detection Experiments

TL;DR

This work formulates fermionic dark sector absorption interactions via a quark–neutrino–chi EFT with five leading Lorentz structures and studies their collider and direct-detection signatures. By evaluating mono-photon, mono-jet, and mono-Z channels at the LHC, the authors extract current and projected limits on the operator scales $\Lambda_i$, finding that mono-Z leptonic decays often provide the strongest collider constraints, reaching $\Lambda \sim \mathcal{O}(\text{TeV})$ for light $m_\chi$. They then connect these collider probes to nuclear-target absorption on nuclei, deriving SI and SD scattering rates and comparing with DD experiments; light targets like Borexino yield especially strong SD bounds, while heavy-nucleus detectors excel for SI bounds depending on the operator. Overall, the paper demonstrates a complementary landscape where collider searches constrain DS absorption operators in regions where direct-detection and neutrino experiments are less sensitive, and vice versa, highlighting the tensor operator as a particularly rich case with competing SI and SD contributions. The results guide future explorations at HL-LHC/HE-LHC and inform cross-experimental strategies for probing light dark-sector fermions via absorption mechanisms.

Abstract

Instead of the energy recoil signal at direct detection experiments, dark fermion appears as missing energy at hadron colliders. For a fermionc dark sector particle that coupled with quarks and neutrino via absorption operators, its production at collider is accompanied by an invisible neutrino. We study in details the mono-$X$ (photon, jet, and $Z$) productions at the Large Hadron Collider (LHC). We start from the quark-level absorption operators to make easy comparison between the collider and direct detection experiments. In other words, we study the model-independent constraints on a dark fermion with absorption operator. In addition, the interplay and comparison with the possible detection at the neutrino experiments, especially Borexino, is also briefly discussed. We find that light nuclear target can provide the stronger constraints on both spin-dependent and spin-independent absorption operators.

Figures (21)

• Figure 1: Feynman diagrams of the mono-$\gamma$ process for (a) the signal operators and (b) the irreducible background.
• Figure 2: The normalized parton-level distributions of the photon polar angle ($\theta_\gamma$) (a) and transverse momentum ($p_{T,\gamma}$) (b) in the laboratory frame with the center-of-mass energy $\sqrt{s} = 13\,{\rm TeV}$. The panel (c) is the total background and signal cross sections as functions of the center-of-mass energy $\sqrt{\hat{s}}$ at the parton level. In all the above panels, the signals (colorful non-solid curves) are obtained with parameters $m_\chi = 0\,{\rm GeV}$ and $\varLambda_i = 1\,{\rm TeV}$ while the background (black-solid curve) stands for the irreducible contribution from the channel $q\bar{q} \to \gamma Z(\nu\nu)$.
• Figure 3: Light panel: Validation of our simulation for the missing transverse momentum distribution. The experimental data are (black line) taken from Ref. ATLAS:2020uiq and our results (red triangle) have been renormalized by multiplying an overall constant. Right panel: The expected 95% C.L. exclusion limits at LHC-13.
• Figure 4: Feynman diagrams contributing to the mono-jet events. The panels (a), (b) and (c) are for the signal operators (green dot) while (d), (e) and (f) are for the irreducible background.
• Figure 5: The normalized parton-level distributions of the polar angle ($\theta_j$) (a) and transverse momentum ($p_{T,j}$) (b) in the laboratory frame with center of mass energy $\sqrt{s} = 13\,{\rm TeV}$. (c): The signal and background total cross sections as functions of the center-of-mass energy at the parton level, $\sqrt{\hat{s}}$. In all three panels, the signal (colorful non-solid curves) are shown for parameters $m_\chi = 0\,{\rm GeV}$ and $\varLambda_i = 1\,{\rm TeV}$, and the background (black-solid curve) stands for the irreducible channel $q\bar{q}'/qg \to j Z(\nu\nu)$.