Science & Technology

The China Dark Matter Experiment Listens to the Sound of Cosmology From a Laboratory Deep Underground

The schematic setup of the subsequent technology CDEX experiment in CJPL-II. Credit score: ©Science China Press

Quite a few compelling evidences from astroparticle physics and cosmology point out that the main matter part in the Universe is darkish matter, accounting for about 85% with the remaining 15% is odd matter. However, individuals nonetheless know little about darkish matter, together with its mass and different properties. Many fashions predict darkish matter particles may couple to odd particle at weak interplay degree, so it’s potential to seize the sign of darkish matter particle in the direct detection experiment.

The scientific targets of the China Dark matter Experiment (CDEX) are on direct detection of gentle darkish matter and neutrino-less double beta decay with p-type level contact germanium (PPCGe) detectors at the China Jinping Underground Laboratory (CJPL). The measurable power spectra induced by the elastic scattering between darkish matter particles and goal nucleons in CDEX detector system may give us the info of darkish matter mass, spin, and different properties.

Elastic scattering between darkish matter particles and goal nucleons. Credit score: ©Science China Press

The evaluation of the present darkish matter experiments is normally mannequin dependent, and plenty of fashions past the customary mannequin have predicted the existence of darkish matter, akin to super-symmetry mannequin and extra-dimension mannequin. Due to the selection of physics fashions, the constraints obtained from identical experimental knowledge can’t be utilized instantly to different fashions, which brings problems to bodily interpretations.

Cosmology observations have verified that the main half of darkish matter is the non-relativistic chilly darkish matter, and as a end result, the momentum switch in the scattering course of between darkish matter particles and nucleons is just about a whole bunch of MeV, a lot decrease than the electroweak scale (~250 GeV). It’s subsequently appropriate to use efficient discipline idea to analyze the interplay between darkish matter and odd matter. Two various schemes have been proposed lately to examine totally different potential interactions, specifically non-relativistic efficient discipline idea (NREFT) and chiral efficient discipline idea (ChEFT). An efficient idea accommodates all potential interactions allowed by given symmetric rules, so it could possibly model-independently scale back the complicacy of evaluation.

In the darkish matter direct detection experiments, what is usually targeted on are the spin-independent (SI) and spin-dependent (SD) scattering evaluation, whereas EFT may give extra momentum-dependent or velocity-dependent interplay which aren’t considered normally. Benefiting from the low electrical noise of PCCGe, the evaluation threshold of CDEX-1B and CDEX-10 each attain 160 eV, which may largely enhance the detection sensitivity for gentle darkish matter.

Primarily based on the knowledge set of CDEX-1B and CDEX-10, CDEX collaboration presents new limits for the couplings of WIMP-nucleon arising from NREFT and ChEFT. In the nonrelativistic efficient discipline idea method, they enhance over the present bounds in the low mχ area. In the chiral efficient discipline idea method, they for the first time prolonged the restrict on WIMP-pion coupling to the mχ< 6 GeV/c2 area.

(a) Exclusion limits of totally different coupling coefficients of NREFT; (b) Exclusion limits of WIMP-pion scattering cross part. Credit score: ©Science China Press

Associated outcomes have been revealed on-line entitled “First experimental constraints on WIMP couplings in the efficient discipline idea framework from CDEX” on Science China-Physics, Mechanics & Astronomy (Sci. China-Phys. Mech. Astron. 64, 281011 (2021)).[1] Prof. Y. F. Zhou from the Institute of Theoretical Physics, Chinese language Academy of Sciences wrote a overview article for this publication.[2]

The operation and evaluation of CDEX-1B and CDEX-10 are coming to the finish, and the subsequent technology of experiments CDEX-100/CDEX-1T are underneath preparation now. The decrease background degree and enchancment of PPCGe efficiency can elevate the sensitivity of direct detection experiment. Whereas the subsequent technology experiment of CDEX can uncover darkish matter stays unknown, however the thriller of darkish matter will encourage increasingly researchers to pursue its research till the day when this profound thriller of the Universe might be solved.

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