Inelastic dark matter at DAMA, CDMS and Future Experiments Page: 1 of 4
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Inelastic Dark Matter at DAMA, CDMS and Future Experiments
David R. Smith' and Neal Weinerb*
'Center for Theoretical Physics, Massachusetts Institute of Technology,
Cambridge, MA, USA
bDepartment of Physics, University of Washington,
Seattle, WA, USA
The DAMA annual modulation signature, interpreted as evidence for a spin-independent WIMP coupling,
seems in conflict with null results from CDMS. However, in models of "inelastic dark matter", the experiments are
compatible. Inelastic dark matter can arise in supersymmetric theories as the real component of a sneutrino mixed
with a singlet scalar. In contrast with ordinary sneutrino dark matter, such particles can satisfy all experimental
constraints while giving the appropriate relic abundance. We discuss the modifications to the signal seen at
DAMA, in particular noting the strong suppression of low energy events in both modulated and unmodulated
components. We discuss future experiments, with emphasis on distinguishing inelastic dark matter from ordinary
dark matter, and stressing the significance of experiments with heavy target nuclei, such as xenon and tungsten.1. Introduction
Recently the DAMA collaboration has reported
evidence from four years of study of an annual
modulation signal consistent with a WIMP [1].
The data satisfy the six requirements of a WIMP
signal in that it is a modulation of the single hit
rate, contained entirely in the low energy bins,
with the appropriate shape, phase, period, and
amplitude that are expected. Studies of possible
systematic errors have turned up no candidates
to explain the modulation [2].
At the same time, the CDMS collaboration
has reported no evidence for a WIMP signal in
their experiment [3,4], claiming a conflict with
DAMA as interpreted as a WIMP coupled with
spin-independent (SI) interactions at 99.8%, even
given no assumptions about the background [4].
Given this conflict, and the absence of a clear
source of systematic error, it is worthwhile to con-
sider alternative forms of dark matter, with dif-
ferent interaction properties from the neutralino.
The neutralino is a very appealing candidate,
both because it arises in a motivated theory (su-
persymmetry) and because it naturally has the
*This work was partially supported by the DOE under
contract DE-FGO3-96-ER40956.right relic abundance. In looking for a alterna-
tive theory, we would like to retain both of these
features, while still explaining the discrepancy be-
tween CDMS and DAMA.
1.1. Inelastic Dark Matter
Let us consider "inelastic dark matter" (iDM)
[5]. We assume the presence of two particles Xi
and X2, such that m - m i2 > 0. We further
assume that Xi constitutes the dark matter in the
galaxy, and that Xi can only scatter off of nuclei
by making an inelastic transition to X2. That
is, the allowed scattering is XiN -> X2N. Let
us emphasize that the inelasticity is not due to a
nuclear transition, but instead in the final state of
the dark matter particle, itself.
It is quite simple to construct models of this
type, but we will address this later. For now, let
us focus on the kinematical changes which occur
in a scattering experiment. The central differ-
ence from ordinary elastic scattering is the re-
quirement on the velocity ) for a scattering to
occur:o226(mnN -+ mx)
mNmx(1)
where mN is the mass of the target nucleus. The
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Smith, David R. & Weiner, Neal. Inelastic dark matter at DAMA, CDMS and Future Experiments, report, August 22, 2002; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc785584/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.