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Register a new userThe Search for Dark Matter
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Laura Baudis
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The dark matter problem is almost a century old. Since the 1930s evidence has been growing that our cosmos is dominated by a new form of non-baryonic matter, that holds galaxies and clusters together and influences cosmic structures up to the largest observed scales. At the microscopic level, we still do not know the composition of this dark, or invisible matter, which does not interact directly with light. The simplest assumption is that it is made of new particles that interact with gravity and at most weakly with known elementary particles. I will discuss searches for such new particles, both space- and Earth-bound including those placed in deep underground laboratories. While a dark matter particle hasnt been yet identified, even after decades of concerted efforts, new technological developments and experiments have reached sensitivities where a discovery might be imminent, albeit certainly not guaranteed.
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We propose an X-ray mission called Xenia to search for decaying superweakly interacting Dark Matter particles (super-WIMP) with a mass in the keV range. The mission and its observation plan are capable of providing a major break through in our understanding of the nature of Dark Matter (DM). It will confirm, or reject, predictions of a number of particle physics models by increasing the sensitivity of the search for decaying DM by about two orders of magnitude through a wide-field imaging X-ray spectrometer in combination with a dedicated observation program. The proposed mission will provide unique limits on the mixing angle and mass of neutral leptons, right handed partners of neutrinos, which are important Dark Matter candidates. The existence of these particles is strongly motivated by observed neutrino flavor oscillations and the problem of baryon asymmetry of the Universe. In super-WIMP models, the details of the formation of the cosmic web are different from those of LambdaCDM. The proposed mission will, in addition to the search for decaying Dark Matter, provide crucial insight into the nature of DM by studying the structure of the cosmic web. This will be done by searching for missing baryons in emission, and by using gamma-ray bursts as backlight to observe the warm-hot intergalactic media in absorption.
Results are presented from a reanalysis of the entire five-tower data set acquired with the Cryogenic Dark Matter Search (CDMS II) experiment at the Soudan Underground Laboratory, with an exposure of 969 kg-days. The analysis window was extended to a recoil energy of 150 keV, and an improved surface-event background-rejection cut was defined to increase the sensitivity of the experiment to the inelastic dark matter (iDM) model. Three dark matter candidates were found between 25 keV and 150 keV. The probability to observe three or more background events in this energy range is 11%. Because of the occurrence of these events the constraints on the iDM parameter space are slightly less stringent than those from our previous analysis, which used an energy window of 10-100 keV.
We report results of a search for light (<10 GeV) particle dark matter with the XENON10 detector. The event trigger was sensitive to a single electron, with the analysis threshold of 5 electrons corresponding to 1.4 keV nuclear recoil energy. Considering spin-independent dark matter-nucleon scattering, we exclude cross sections sigma_n>3.5x10^{-42} cm^2, for a dark matter particle mass m_{chi}=8 GeV. We find that our data strongly constrain recent elastic dark matter interpretations of excess low-energy events observed by CoGeNT and CRESST-II, as well as the DAMA annual modulation signal.
Multiple astrophysical and cosmological observations show that the majority of the matter in the universe is non-luminous. It is not made of known particles, and it is called dark matter. This is one of the few pieces of concrete experimental evidence of new physics beyond the Standard Model. Despite decades of effort, we still know very little about the identity of dark matter; it remains one of the biggest outstanding mysteries facing particle physics. Among the numerous proposals to explain its nature, the Weakly Interacting Massive Particle (WIMP) scenario stands out. The WIMP scenario is based on a simple assumption that dark matter is in thermal equilibrium in the early hot universe, and that the dark matter particles have mass and interactions not too different from the massive particles in the Standard Model. Testing the WIMP hypothesis is a focus for many experimental searches. A variety of techniques are employed including the observation of WIMP annihilation, the measurement of WIMP-nucleon scattering in terrestrial detectors, and the inference of WIMP production at high energy colliders. In this article, we will focus on the last approach, and in particular on WIMP dark matter searches at the Large Hadron Collider. Authors note: this paper (and references therein) correspond to the version that was submitted to the joint issue of Nature Physics and Nature Astronomy in January 2017.
Dark Matter (DM) detection prospects at future e+e- colliders are reviewed under the assumption that DM particles are fermions of the Majorana or Dirac type. Although the discussion is quite general, one will keep in mind the recently proposed candidate based on an excess of energetic photons observed in the center of our Galaxy with the Fermi-LAT satellite. If one assume that DM couples to a Zprime, using radiative return events e+e-->XX+photon, one could observe a spectacular signal at a TeV e+e- collider. This result relies on the ability of using highly polarized beams to eliminate a large part of the W exchange background. Prospects of discovery at LHC using mono-jets are also discussed and appear promising. In the second part, one assumes that DM particles annihilate through Higgs particles, either the SM boson h or MSSM type bosons called H, A. A promising scenario emerges, where one has e+e-->HA, with H decaying into hh, while A decays invisibly in most of the cases.
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