Neutralino Dark Matter in Minimal Supergravity: Direct Detection vs. Collider Searches

TL;DR

This work evaluates direct detection prospects for relic neutralinos within the minimal supergravity (mSUGRA) framework, using a $^{73}$Ge detector to compute event rates from scalar and spin interactions and comparing them to relic-density and collider constraints. The authors derive the neutralino–nucleus scattering formalism, incorporate nucleon matrix elements and nuclear form factors, and fold the cross section with a standard halo velocity distribution to obtain $R$. They show that large $\tan\beta$ regions yield substantial detection rates, often in cosmologically favored parts of parameter space, implying that direct detection could provide the first SUSY signal in these cases, while collider searches remain essential for full coverage and cross-checks. The study highlights complementary discovery channels and quantifies uncertainties that affect the interpretation of direct-detection results in the context of SUSY parameter space, relic density, and flavor constraints such as $B\to X_s\gamma$.

Abstract

We calculate expected event rates for direct detection of relic neutralinos as a function of parameter space of the minimal supergravity model. Numerical results are presented for the specific case of a $^{73}$Ge detector. We find significant detection rates ($R> 0.01$ events/kg/day) in regions of parameter space most favored by constraints from $B\to X_sγ$ and the cosmological relic density of neutralinos. The detection rates are especially large in regions of large $\tanβ$, where many conventional signals for supersymmetry at collider experiments are difficult to detect. If the parameter $\tanβ$ is large, then there is a significant probability that the first direct evidence for supersymmetry could come from direct detection experiments, rather than from collider searches for sparticles.

Figures (9)

• Figure 1: A plot of contours of neutralino scattering events/kg/day in a $^{73}$Ge detector, for mSUGRA parameters $A_0=0$, $\tan\beta =2$ and a) $\mu <0$ and b) $\mu >0$, in the $m_0\ vs.\ m_{1/2}$ plane. The regions labelled TH are excluded by theoretical considerations, while the EX regions are excluded by collider searches for SUSY particles. The region to the right of the solid contour is excluded by $\Omega h^2>1$. We also show contours of neutralino relic density $\Omega h^2=0.15$ and $0.4$; the region in between is favored by models of a MDM universe.
• Figure 2: Same as Fig. 1, except for $\tan\beta =10$. Below the dotted contour is where $\Omega h^2<0.025$.
• Figure 3: Same as Fig. 1, except for $\tan\beta =35$. Note, however, the expanded scale relative to Fig. 1 and 2.
• Figure 4: A plot of neutralino scattering events/kg/day in a $^{73}$Ge detector, for mSUGRA parameters $m_0 ,m_{1/2} ,A_0 =$150, 200, and 0 GeV versus $\tan\beta$ for $\mu <0$ and $\mu >0$.
• Figure 5: A plot of the ratio of neutralino scattering events from the spin-spin interaction over that from scalar interactions for mSUGRA parameters $m_0 ,m_{1/2} ,A_0 =$150, 200, and 0 GeV, versus $\tan\beta$ for $\mu <0$ and $\mu >0$.