Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - LDMThExp (Going Beyond the WIMP: From Theory to Detection of Light Dark Matter)

Teaser

The identity of dark matter (DM) is still unknown. For more than three decades, significant theoretical and experimental efforts have been directed towards the search for a Weakly Interacting Massive Particle (WIMP), often overlooking other possibilities. The lack of an...

Summary

The identity of dark matter (DM) is still unknown. For more than three decades, significant theoretical and experimental efforts have been directed towards the search for a Weakly Interacting Massive Particle (WIMP), often overlooking other possibilities. The lack of an unambiguous positive signal, at indirect- and direct-detection experiments and at the LHC, stresses the need to expand on other theoretical possibilities, and more importantly, to develop new experimental capabilities. Indeed it is conceivable that the WIMP paradigm has been misleading, and other theoretically motivated scenarios must be explored vigorously.

This project focuses on light, sub-GeV dark matter. In addition to novel theoretical paradigms that point to DM in the low-mass regime, several new strategies to directly detect dark matter particles with MeV to GeV mass, far below standard direct detection capabilities, are studied. In particular, techniques to search for ionized electrons or chemical bond-breaking are considered. Both possibilities are revolutionary and require new dedicated technologies and experiments. Sensitivity to one or few electrons has been established before this project in noble gas detectors and the PI has derived the first direct-detection limits on MeV to GeV dark matter using XENON10 data, demonstrating proof-of-principle. Similar detection methods in crystals which will significantly enhance the sensitivity to light dark matter provide a major goal in this project. Significant efforts are required to lay the theoretical foundation of light DM and to study in depth and develop the various possibilities to directly detect it. The proposal is centered around these efforts.

The innovative theoretical paradigms and novel avenues to experimentally detect sub-GeV DM, open up a new and groundbreaking field of research. The proposal at hand takes the necessary steps, and offers the opportunity to pave the way and enable the discovery of such a particle, if it exists.

Work performed

Since the beginning of the ERC project, significant progress has been made on three fronts:

1. Theoretical model building and cosmological implications. New models and cosmological dynamics of light dark sectors and light dark matter have been studied. Such models have deep implications to dynamics in the early universe and may explain, as the PI showed, the observed baryon-anti-baryon asymmetry, the dark matter density and the hierarchy between the weak scale (of order 100 times the mass of the proton) and the quantum gravity scale (which lies 16 orders of magnitude above the weak scale).

2. Direct detection of light dark matter through electron recoils. One of the main goals of the ERC project is to devise new methods to search for light, sub-GeV dark matter. In 2011, several new strategies to directly detect dark matter particles with MeV to GeV mass, far below standard direct detection capabilities, were suggested by the PI. Since the beginning of the project, the PI and his colleagues reported on a new breakthrough in devising a CCD-based detector with a single-electron sensitivity, realizing the PI\'s ideas and allowing for a the search of sub-GeV dark matter (i.e. with masses below that of the proton) . A new collaboration, SENSEI, composed of theorist and experimentalists, has began searching for such dark matter with first results already published.

3. Direct detection of light dark matter through nuclear recoils. Light dark matter may interact with protons rather than electrons. Measuring such interactions requires new technologies and the development of ultra-low threshold detectors would be considered a breakthrough in the field. The PI has published a study of a new and novel way to make such a search for light dark matter (and possibly solar neutrinos), via the study of chemical-bond breaking. The theoretical tools and prospective reach were calculated and discussed thoroughly. The PI further wrote a first paper suggesting an experimental setup which employs the measurement of color-centers produced in crystals, allowing for such an ultra-low threshold detector that would realize the idea of detecting light dark matter through bond-breaking interactions.

Final results

Both technologies discussed in (2) and (3) exhibit beyond the state of the art progress. The SENSEI experiment is planned to deploy a new line of skipper-CCD detectors at the SNOLAB mine, later this year. New results, digging deep into uncharted territory in the dark matter parameter space, are expected to appear in late 2019. Meanwhile, a new lab which explores the color-center idea presented by the PI has been opened. Through a joint theoretical-experimental collaboration, this technology will hopefully materialize to allow for the search of light dark matter scatterings with nucleons.