Dark Matter collisions with the Human Body

Interactions of 60 GeV WIMPs on various nuclei in the human body

Katherine Freese, Christopher Savage
We investigate the interactions of Weakly Interacting Massive Particles (WIMPs) with nuclei in the human body. We are motivated by the fact that WIMPs are excellent candidates for the dark matter in the Universe. Our estimates use a 70 kg human and a variety of WIMP masses and cross-sections. The contributions from individual elements in the body are presented and it is found that the dominant contribution is from scattering off of oxygen (hydrogen) nuclei for the spin-independent (spin-dependent) interactions. For the case of 60 GeV WIMPs, we find that, of the billions of WIMPs passing through a human body per second, roughly ~10 WIMPs hit one of the nuclei in the human body in an average year, if the scattering is at the maximum consistent with current bounds on WIMP interactions. We also study the 10-20 GeV WIMPs with much larger cross-sections that best fit the DAMA, COGENT, and CRESST data sets and find much higher rates: in this case as many as 105 WIMPs hit a nucleus in the human body in an average year, corresponding to almost one a minute.

A variety of astrophysical observations has shown conclusively that the majority of the matter in the Universe consists of an unknown nonluminous, nonbaryonic component.
Understanding the nature of this dark matter is one of the major outstanding problems of astrophysics and particle physics.
Most cosmologists believe that the solution to this puzzle lies in the discovery of a new type of fundamental particle. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak interactions with ordinary matter.
Possible WIMP candidates include supersymmetric particles and Kaluza-Klein particles motivated by theories with extra dimensions.
These particles are thought to have masses in the range 1 GeV – 10 TeV, consistent with their being part of an
electroweak theory.
Searches for WIMPs [1-3] include direct detection laboratory experiments, which look for the elastic scattering of WIMPs in the Galaxy as they pass through terrestrial detectors situated in deep underground sites.
These efforts are ongoing worldwide.
Currently there are intriguing hints of discovery with the DAMA [4], CoGeNT [5, 6], and CRESST [7] experiments although no consensus has been reached in the community. The null results of a host of other experiments, including CDMS [8] and XENON [9, 10] have been used to place bounds on the scattering rates of WIMPs as a function of WIMP mass. In the standard framework used in this work, there is a strong tension between the results of the first three experiments and the null results of the latter two.
Many efforts in both the experimental and theoretical directions are ongoing to understand these discrepancies; in this paper we will simply use the currently published results of these experiments.
In this paper we consider this same elastic scattering of WIMPs with nuclei in the human body.
Billions of WIMPs pass through our bodies every second, yet most of them pass through unimpeded.
Only rarely does WIMP actually hit one of our nuclei.
To perform our analysis we will assume a human of 70 kg and consider a variety of WIMP masses in
the GeV-TeV range.
First we will study 60 GeV WIMPs with the maximum scattering cross-section allowed by the null results of the XENON and CDMS experiments.
Then we will turn to the lower mass WIMPs (10-20 GeV) that provide the best fits to the hints of discovery in DAMA, CRESST, and COGENT as well as TeV benchmark cases again compatible with the null result experiments.
The scattering rate of WIMPs with an element (indexed by k) in a human body of mass Mbody is given by1

where Nk is the number of nuclei of that element in the body, with mk the nuclear mass and fk the mass fraction of that element; nχ is the number density of WIMPs, with mχ the WIMP mass and ρχ the local dark matter mass density; f(v) is the WIMP velocity distribution; and σk(v) is the (velocity-dependent) WIMP-nucleus scattering cross-section(…..)
(……)
In conclusion, we have studied the interactions of WIMPs with nuclei in a human body of mass 70 kg. We examined the contributions from a variety of elements in the body and found that the dominant contribution is from scattering off of oxygen nuclei for spin-independent (SI) interactions and hydrogen nuclei for spin-dependent (SD) interactions.
For a canonical case of 60 GeV WIMP mass and the maximum elastic scattering cross-sections compatible with the experimental bounds from XENON and CDMS, we found that on average five WIMPs hit one of the nuclei in the human body in a year via SI scattering and 30 via SD scattering. We also studied the 10-20 GeV WIMPs with much larger cross-sections that best fit the DAMA, COGENT, and CRESST data sets, and found much higher rates: in this case as many as 105 WIMPs hit a nucleus in the human body in an average year, corresponding to almost one a minute.
Read more: arxiv.org/pdf

2 thoughts on “Dark Matter collisions with the Human Body

  1. Physiological effects? At first reading I found the article scary 🙂 scattered? Would it be any different on a spaceship?

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