麻豆淫院

Dark matter, a type of matter that does not emit, absorb, or reflect light, is predicted to account for most of the universe's mass. While theoretical predictions hint at its abundance, detecting this elusive matter has so far proved to be very difficult, leaving its composition and origin a mystery.

One widely explored hypothesis is that dark matter consists of weakly interacting massive particles, or WIMPs for short. These particles are theorized to only interact with ordinary matter via gravity and potentially via weak nuclear forces.

The LUX-ZEPLIN (LZ) experiment is a large-scale research effort aimed at searching for signals associated with the presence of WIMPs using a sophisticated detector known as a dual-phase xenon time projection chamber. The researchers involved in the experiment recently published their most recent in a paper in 麻豆淫院ical Review Letters, which places more stringent constraints on lighter dark matter particles that could have gained energy after colliding with cosmic rays.

"The main scientific goal of this work was to explore the possibility of detecting lighter dark matter particles than conventional WIMPs," Yongheng Xu, part of the LZ collaboration, told 麻豆淫院.

"Lighter dark matter particles are challenging to probe in conventional settings without boosting. The conceptualization took shape through ongoing discussions with theorists, which helped refine the concept and identify feasible experimental signatures in the LZ Experiment."

The LZ experiment has already made significant strides in the search for hypothetical dark matter particles. Recently, the LZ collaboration set the most stringent constraints to date on WIMPs, yet the detector employed in the experiment can also be used to search for other dark matter candidates.

"The detector exhibits an unprecedented sensitivity towards a wide variety of new or rare physical phenomena, and we intend to fully exploit this in expanding the search for particle dark matter," explained Aiham Al Musalhi, part of the LZ collaboration.

"Interactions with low-mass dark matter particles can be tricky to detect, so we consider a scenario where scatters with cosmic rays in the Milky Way impart enough energy to lift them into a more accessible energy regime. It's sort of like camping outside a baseball stadium to catch stray home runs."

The detector employed by the LZ collaboration is a dual-phase liquid xenon time projection chamber, a chamber filled with liquid and gaseous xenon, located at the Sanford Underground Research Facility (SURF) in South Dakota. This detector can detect tiny flashes of light and the ionization signals that are produced when particles interact with xenon atoms.

"In our search, we looked for rare nuclear recoil events that could be caused by dark matter particles accelerated to relativistic speed by cosmic rays鈥攁n unconventional but promising signature beyond standard dark matter models," explained Xu.

As part of the LZ experiment, Xu, Al Musalhi and their colleagues have been searching for specific low-energy signatures in the data collected at SURF. These are the signatures that they would expect to arise from collisions between dark matter particles and nuclei in the dense liquid xenon inside their detector.

"We're able to observe these signatures in our dual-phase xenon time projection chamber, which is capable of detecting individual photons and electrons via two arrays of photomultiplier tubes," explained Al Musalhi.

"The nature of these signals鈥攚hich differs depending on the dark matter candidate being considered鈥攊s well-predicted by much theoretical work in the literature, as well as simulations informed by cosmic ray measurements."

While the researchers did not observe any excess events that could be linked to the interactions they were probing, they ultimately placed new constraints on dark matter particles that could be boosted by collisions with cosmic rays. In future experimental runs, they will increase the time for which the detector is running, while also searching for other dark matter candidates.

"At present, we are achieving remarkable agreement between our data and the background models," said Xu. "This highlights our detailed understanding of the detector and its response. This level of control not only lends confidence to our null result, but it also enables us to set meaningful constraints on a previously unexplored region of parameter space鈥攈elping to steer future dark matter searches toward more promising directions."

The new results published by the LZ collaboration could soon inform other searches for cosmic ray-boosted dark matter particles with masses below 1 GeV/c虏. In fact, the team placed new constraints on the extent to which these particles could interact with ordinary matter, ruling out interactions stronger than 3.9脳10鈦宦陈� cm虏 with a 90% confidence level.

"As with any search for rare physical phenomena, a null result is not necessarily a bad thing; it tells us where not to look (which models we have now tested and ruled out)," said Al Musalhi. "We've excluded a substantial amount of parameter space for these particular models, though there is much left to probe over a longer operation timeline and with larger next-generation detectors."

The LZ collaboration is still working to further improve the sensitivity of the detector presently located at SURF. In the future, the experiment could test the validity of various other dark matter models, potentially shedding new light on the nature of dark matter.

"Having developed a deep understanding of our wonderful detector, we would like to push its capabilities even further," said Xu. "We're excited to turn this powerful instrument toward a broader range of new physics that leads to rare and exotic phenomena in our detector, continuing the search for new physics hiding in the quietest corners of the universe."

The LZ experiment is expected to continue running up until 2028. By collecting even more data, the researchers could further narrow down the parameter space that future dark matter searches should focus on.

"There is always more to be done in improving this analysis, such as leveraging the directionality of the galactic cosmic rays with respect to the Earth's rotation, which would produce a sidereal diurnal modulation of the signal, to narrow the scope further," added Al Musalhi.

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