From underground detectors to cosmic secrets: Exploring dark matter-nucleon interactions

In a brand new research, scientists report outcomes from the PandaX-4T experiment, setting stringent limits on dark matter–nucleon interactions utilizing low-energy information and the Migdal impact, ruling out important parameter space for a thermal relic dark-matter mannequin.

Darkish matter is among the nice mysteries in science, eluding direct detection and defying conventional fashions. It’s so shrouded in thriller that we do not even know what dark matter particles are and what their mass is.

It is because dark matter particles do not work together with gentle, making them not possible to detect. The main candidates for dark matter particles are axions and weakly interacting huge particles (WIMPs).

Within the depths of the China Jinping Underground Laboratory, the PandaX-4T experiment stands as a beacon within the quest to unravel the mysteries of dark matter. The experimental program employs ‘xenon detectors’ to discover dark matter, research neutrinos, and examine new physics, similar to neutrinoless double beta decay.

Now, scientists have reported progress within the seek for dark-matter–nucleon interactions utilizing the PandaX-4T. The findings are printed in Physical Review Letters.

The PandaX-4T experiment and the Migdal impact

On the coronary heart of the PandaX-4T experiment lies a state-of-the-art dual-phase xenon time projection chamber (TPC) housing a considerable 3.7 tons of liquid xenon inside a delicate quantity. This subtle chamber serves as the first area for particle interactions.

Co-author Dr. Ran Huo from the Shandong Institute of Superior Expertise defined, “For gentle dark matter, the utmost power the dark matter can switch to the xenon nuclei is proportional to the dark matter mass squared.”

“When the dark matter mass is under a number of GeV, the recoil power resulting from dark matter collision with the xenon nuclei has virtually no likelihood of exceeding the power threshold of the detector.”

The PandaX-4T experiment leverages the Migdal impact to beat this problem by enhancing the experiment’s sensitivity, significantly to low-mass dark matter particles under 3 GeV, in an try to probe dark matter-nucleon interactions.

The Migdal impact includes the potential ionization or excitation of electrons within the atoms, making up the fabric (on this case, xenon) by means of which dark matter passes. The nucleons (protons and neutrons) inside the atomic nuclei expertise interactions with dark matter particles.

These interactions can result in the excitation or ionization of electrons within the surrounding atoms. Consequently, these electrons can purchase energies above keV. When these energized electrons go by means of liquid xenon, they generate detectable indicators indicative of electron recoils within the detector.

“Merely talking, the Migdal impact helps us to increase our attain for dark matter lots under 3 GeV to probe the dark matter-nucleon interactions,” stated Dr. Yong Yang, co-author of the research from Shanghai Jiao Tong College.

A thermal dark matter mannequin

In a thermal dark matter mannequin, dark matter particles are assumed to have been in thermal equilibrium with the primordial soup of particles within the early universe. Because the universe expanded and cooled, these particles decoupled from the thermal bathtub whereas preserving a sure abundance.

This course of is akin to a freeze-out, the place the dark matter particles freeze into their noticed abundance.

The thermal dark matter mannequin is especially interesting as a result of it offers a pure mechanism for explaining the noticed relic abundance of dark matter within the universe. The ‘annihilation’ or decay of those particles within the early universe would have produced the right density of dark matter we observe in the present day.

This mannequin typically includes the consideration of particular forms of particles, similar to weakly interacting huge particles (WIMPs) or different candidates with comparable properties.

“Our experiment was primarily designed for WIMP-like dark matter, by which case the ‘force-mediator’ (particle answerable for transmitting the power between dark matter and ordinary matter) is assumed to be very heavy, so the interplay is extraordinarily short-ranged,” famous Dr. Yang.

PandaX-4T mannequin’s flexibility aids in reproducing the noticed quantity of dark matter by means of the annihilation of dark matter particles into normal mannequin particles through the early universe, showcasing a various parameter space.

PandaX-4T’s focused strategy utilized optimized low-energy information to set strict constraints on dark matter-nucleon interplay power for darkish lots starting from 0.03 to 2 GeV.

“The brand new evaluation instantly assessments a sort of thermal dark matter mannequin—dark matter pairs annihilating into bizarre matter by way of the darkish photon within the early universe—and eliminates substantial parameter space that was beforehand thought of believable,” defined Dr. Huo.

Primarily, the research refines our understanding by limiting the potential situations for dark matter interactions by way of the darkish photon, which is the mediator.

Constructing on discoveries

The experiment’s success in scrutinizing dark matter particles inside the 0.03 to 2 GeV vary affords helpful insights, refining our comprehension of a thermal dark matter mannequin.

The researchers spotlight two attainable avenues for future research with the PandaX-4T.

“We purpose to boost publicity, by means of elevated information or a bigger xenon goal, to delve into decrease dark matter–nucleon interplay cross-sections.”

“This expanded publicity holds the potential to elucidate the intricacies of the background within the low-energy area, predominantly influenced by cathode electrodes and micro-discharging noise,” stated Dr. Huo.

“On the opposite aspect, our research has no sensitivity for this interplay for darkish matter lighter than 30 MeV, under which the Migdal impact can not assist us anymore. This implies we want new detection strategies,” acknowledged Dr. Yang.

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