Shedding Light on the Dark Sector with Direct WIMP Production

TL;DR

This work analyzes direct WIMP production at the ILC via the radiative process $e^+e^-\to\chi\chi\gamma$, connecting cosmology through the relic annihilation cross section to collider observables. By factorizing the cross section with ISR and introducing a model-dependent but shape-normalized function $f(s)$, the authors provide a framework that accommodates both model-independent inputs and concrete particle physics models. They study two benchmark scenarios, SUSY with a Bino LSP and a UED-like spin-1 WIMP, and quantify the 500 GeV ILC reach, mass determinations, and the ability to discriminate between models using the photon energy spectrum, particularly when beam polarization is available. The results show substantial discovery potential and precise parameter extraction, with polarization playing a crucial role in both discovery reach and model discrimination, thereby offering a feasible path to unravel the nature of dark matter at colliders.

Abstract

A Weakly Interacting Massive Particle (WIMP) provides an attractive dark matter candidate, and should be within reach of the next generation of high-energy colliders. We consider the process of direct WIMP pair-production, accompanied by an initial-state radiation photon, in electron-positron collisions at the proposed International Linear Collider (ILC). We present a parametrization of the differential cross section for this process which conveniently separates the model-independent information provided by cosmology from the model-dependent inputs from particle physics. As an application, we consider two simple models, one supersymmetric, and another of the "universal extra dimensions" (UED) type. The discovery reach of the ILC and the expected precision of parameter measurements are studied in each model. In addition, for each of the two examples, we also investigate the ability of the ILC to distinguish between the two models through a shape-discrimination analysis of the photon energy spectrum. We show that with sufficient beam polarization the alternative model interpretation can be ruled out in a large part of the relevant parameter space.

Figures (6)

• Figure 1: Values of the quantity $\sigma_{an}$ allowed at the $3\sigma$ level as a function of the WIMP mass $M_\chi$, and for different values of the WIMP spin $S_\chi$. The lower (upper) band is for models where $s$-wave ($p$-wave) annihilation dominates. We use the constraint $\Omega_{\rm dm} h^2 = 0.1143\pm 0.0034$, which results from the combination of data from WMAP-5, Type Ia supernovae and baryon acoustic oscillations Komatsu:2008hk.
• Figure 2: Feynman diagrams for the WIMP pair-production in the SUSY benchmark model (a,b) and the UED benchmark model (c,d).
• Figure 3: The reach of a 500 GeV electron-positron collider with an integrated luminosity of ${\cal L}_{\rm int} = 500\ {\rm fb}^{-1}$ for discovery of our two benchmark models: (a) SUSY and (b) UED. Blue (red) lines correspond to unpolarized (polarized with $P_{e^-}=0.8$, $P_{e^+}=0.6$) beams. Solid (dashed) lines indicate $5\sigma$ ($3\sigma$) significance. Also shown are $\kappa_e$ contours in the (a) $(M_\chi,M_{\tilde{e}_R})$ or (b) $(M_\chi,M_{E_R})$ parameter plane.
• Figure 4: Expected precision of the model parameter measurement in the two benchmark scenarios: (a) SUSY and (b) UED. The notation and labelling are the same as in Fig. \ref{['fig:1']}.
• Figure 5: Plots illustrating the ability of the ILC to discriminate between the two benchmark scenarios using the radiative WIMP production process.