Dark Matter
Overview

It has been well established for decades that the majority of the matter in the Universe is dark. This dark matter is the gravitational glue that holds together galaxies and galaxy clusters and is the key ingredient in the successful cold dark matter (CDM) paradigm of structure formation. Observations of the CMB and of the light element abundances from big bang nucleosynthesis indicate that most of the dark matter is non-baryonic; a new form of matter outside of the Standard Model of particle physics. Many possibilities for dark matter have been proposed. The Dark Matter MA focuses on the hypothesis that the dark matter is a cold relic of the big bang, a new Weakly Interacting Massive Particle, or WIMP. Its goal is to understand the nature of dark matter, in particular, to confirm or refute the hypothesis that dark matter consists of WIMPs, and if discovered, to understand how they fit into extensions of the Standard Model of particle physics. Several attractive extensions of the standard model, most notably supersymmetry (SUSY) predict the existence of WIMPs with properties remarkably in accordance with those needed to obtain the current matter density.

A variety of observations and experiments in the next decade should either confirm, or come close to excluding, the WIMP hypothesis. After many years of effort, experiments based on direct detection of relic WIMPs via scattering with nuclei in sensitive, low-background detectors are finally reaching the sensitivity needed to probe the expected region of WIMP parameter space in SUSY and other models. If the WIMP was produced in the primordial soup of the big bang, it should also be produced in collisions of high-energy particles at facilities such as the LHC. WIMPs may be identified by their missing energy signatures at colliders. Finally, the products of WIMP annihilations in the cosmos can be observed by detectors of high- or low-energy photons, positrons, antiprotons, or high-energy neutrinos. These indirect detection techniques are now reaching the sensitivities needed to probe the signals expected from WIMP annihilations.

Activities
In order to achieve its goals, the Dark Matter MA initially supported the following activities:
  • The COUPP program, including analyzing data, supporting the operations for COUPP-60kg and preparing for the construction of a larger COUPP detectors (COUPP 500kg). The COUPP and Picasso experiments have now merged to form the PICO collaboration and are concentrating upon the development of the PICO-250l experiment.
  • Improving the performance of P-type Point Contact (PPC) detectors and use them to obtain definitive constraints on low-mass dark matter.
  • Created the Dark Matter Hub, which convenes a group of experts to analyze and assimilate evidence from direct detection, indirect detection, and colliders about the nature of dark matter.
  • Work with the other MAs to constrain the masses of neutrinos (the one already detected dark matter component) with careful studies of the matter distribution in the Universe.

Dark matter direct detection experiments
Since the inception of the "Pushing Cosmology to the Edge' PFC, the Dark Matter MA has become involved in three additional dark matter direct detection experiments:
DAMIC (Dark Matter in CCDs)

In cooperation with the Detector Development MA, this experiment uses large CCD chips with extraordinarily low backgrounds in order to probe very small WIMP masses.

DarkSide
This is a Noble Liquid experiment utilizing Argon in a Time Projection Chamber (TPC) as its target nuclei. Due to its ability to use pulse height discrimination to eliminate electron backgrounds, DarkSide is able to achieve excellent background reduction.

XENON-1T
This is a Xenon filled TPC based Noble Liquid detector. XENON-1T is the successor to the XENON-100 experiment and will have over 1 ton of target material and over 2 tons of total Xenon.