Potential dark matter detection sparks hope in search for elusive substance

Matthew Kapust/Sanford Underground Research Laboratory

An international team of scientists says it has detected an intriguing signal that could hint at evidence of dark matter , offering a clue that might bring the mystery of the elusive substance one step closer to a solution.

Dark matter makes up about 85% of all the matter in the universe and is about five times as abundant as ordinary matter, which makes up stars, planets and everything else that scientists can see. Dark matter is invisible because it does not absorb or reflect light, but it does interact with regular matter, and its gravitational effects are needed to explain the structure of the universe.

Li (utoronto), Ima/ESA/NASA

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For nearly half a century — since American astronomers Vera Rubin and W. Kent Ford provided some of the strongest evidence for dark matter’s existence — scientists have tried to identify the unseen substance, more recently using sophisticated devices designed to detect potential candidates.

One of these devices is the LUX-ZEPLIN, or LZ, experiment — a detector containing 7 active metric tons of liquid xenon that’s in a former gold mine nearly a mile (about 1.5 kilometers) below Earth’s surface at the Sanford Underground Research Facility in South Dakota. The detector registered an unusual particle interaction in June 2023 that generated a flash of light and cautious excitement.

The LZ collaboration is an international group of 250 scientists and engineers from 39 institutions. After months of analysis, the team estimates only a 0.5% chance that a known source of interference caused the event — making this signal the most compelling hint of dark matter the instrument has ever recorded.

However, in scientific terms, claiming a discovery requires a much higher degree of confidence. “One event, by itself, is not enough,” Alvine Kamaha, an assistant professor of physics at the University of California, Los Angeles, said in an email.

“We need to see whether additional events appear as we collect more data and whether the statistical significance of the observation increases,” said Kamaha, a member of the LZ collaboration who helped build the LZ detector.

Sam Eriksen, a senior research associate of physics at the University of Bristol and member of the LZ collaboration, presented the findings September 1 at the TeV Particle Astrophysics 2026 conference in Japan, and the team has submitted a study for publication in the scientific journal Physical Review Letters.

The researchers are already working on further analysis that could potentially increase the statistical significance of the event. The threshold to claim a discovery in particle physics is known as 5-sigma, which means about a 1 in 3.5 million chance of a statistical fluke rather than a real hint of dark matter. The analysis is currently at 2.6-sigma, or a 1 in 200 chance of a fluke.

A definitive detection of dark matter would be “a major breakthrough,” Kamaha said. “We know that dark matter plays a fundamental role in the formation of galaxies and the large-scale structure of the universe, but we still do not know what it actually is,” she said. “It’s exciting because it would open an entirely new area of particle physics.”

There are several candidates for what dark matter could be, including primordial black holes or an undiscovered particle. Detectors such as the LZ experiment search for a class of hypothetical particles called weakly interacting massive particles, or WIMPs.

If they exist, WIMPs pass through regular matter without interacting with it, and vast numbers of them could pass unnoticed through a human body every second. On rare occasions, however, one such particle could collide with an atomic nucleus and produce a tiny recoil — precisely the kind of event the LZ experiment is designed to detect.

The detector uses highly purified liquid xenon . Researchers selected this element because its atoms have heavy nuclei that make it a particularly sensitive target for WIMPs. Collisions in xenon produce signals the detector can easily measure.

The LZ experiment is located deep underground and equipped with protective layers to shield it from cosmic rays and other sources of radiation, which could produce signals similar to dark matter. However, this background noise can only be reduced, not eliminated.

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“You’re always going to be in a situation where it’s possible that events occurring in your detector are due to more conventional mechanisms,” said Rick Gaitskell, Hazard Professor of Physics at Brown University in Providence, Rhode Island, and the spokesperson for the LZ experiment.

Potential dark matter collisions are believed to be extremely rare. “Our understanding is that dark matter is so weakly interacting with conventional material,” Gaitskell added, “that even in a detector of the scale of the LZ experiment we need to look for periods of months or years per single interaction.”

The LZ collaboration spotted the 2023 event through an analysis of 220 days of data, collected between March 2023 and April 2024. The researchers are now working through a more recent dataset spanning 700 days, Gaitskell said, hoping it contains further collisions that could help determine whether the 2023 event was a dark matter interaction.

For this larger analysis, the team is also introducing techniques to avoid unconscious bias, for example by inserting “synthetic events” in the data. These look like genuine dark matter interactions to the analysis team and are only removed after the analysis is completed.

“A possible detection brings a lot of tension between the excitement of the experiment working the way we imagined it would, with the worry that we could make mistakes, or just simply be fooled by something rare and new or coincidental happening in the detector,” said Kimberly Palladino, a professor of physics at England’s University of Oxford and a member of the LZ collaboration, in an email. “It’s a little like having a crush on someone as a teenager where you tell yourself to act cool, but have the tendency to over-interpret every little gesture they make.”

However, Palladino warned, history is also littered with experiments that have seen one or two unexplained events that are never fully understood. If the new LZ data contains new potential dark matter collisions, similar experiments also designed to detect dark matter, such as the XENONnT in Italy and the PandaX-4T in China , could provide an independent test of the results.

Finding dark matter would bring scientists a big step closer to understanding what the universe is made of and how it evolved from the big bang to present day.

“But a lot more scientists will need to study dark matter to understand its properties in a variety of different experiments, and then using that information, run astrophysical simulations of our universe,” Palladino added. “There are many theories about what dark matter can be, and there may be multiple types of dark matter.”

The LZ experiment’s potential detection of dark matter is intriguing but needs confirmation, according to Tim M.P. Tait, a professor in the department of physics and astronomy at the University of California, Irvine, who’s not part of the LZ collaboration.

“Only time can tell whether they will see more events as the detector accumulates more data, or if this will turn out to be a temporary statistical fluke,” Tait added in an email. He noted that the LZ event occurred at a much higher energy than most models expect for WIMPs, meaning dark matter could “turn out to be more weird and wonderful than even we had originally imagined.”

Tracy Slatyer, a professor of physics at the Massachusetts Institute of Technology, agrees that further data analysis is needed to understand whether the LZ event is dark matter. “If this is dark matter,” Slatyer, who is not involved with the LZ collaboration, added in an email, “the fact that the event is at quite a high energy, without accompanying events at lower energy, is very interesting.”

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The energy measured in the LZ event indicates how much the xenon nucleus recoiled due to the potential interaction with the dark matter. A high-energy dark matter particle, Slatyer explained, would already reveal quite a bit about the nature of dark matter and how it interacts with ordinary particles. Other experiments could potentially help pin down its properties further.

“There would be a lot still to do and learn, but if this really is a dark matter signal,” she said, “this could be a key that unlocks a great deal of information about new physics, as well as giving us a new way to measure the behavior of dark matter in the neighborhood of the Earth and possibly more broadly through the cosmos.”

马修·卡普斯特/桑福德地下研究实验室

一个国际科学家团队表示，他们探测到了一种有趣的信号，这可能暗示着暗物质存在的证据，为揭开这种难以捉摸的物质之谜提供了线索。

暗物质约占宇宙所有物质的85%，其含量约为普通物质（构成恒星、行星以及科学家可见的一切物质）的五倍。暗物质不吸收也不反射光，因此是不可见的，但它确实会与普通物质相互作用，其引力效应对于解释宇宙的结构至关重要。

李（多伦多大学），IMA/ESA/NASA

美国宇航局哈勃望远镜探测到疑似“暗星系”

近半个世纪以来——自从美国天文学家维拉·鲁宾和W·肯特·福特提供了暗物质存在的最有力证据以来——科学家们一直在试图识别这种看不见的物质，最近更是使用旨在探测潜在候选物质的精密设备。

其中一台设备是LUX-ZEPLIN（简称LZ）实验装置——一个位于南达科他州桑福德地下研究设施的废弃金矿中、地表以下近1.5公里（1英里）的探测器，内含7吨活性液氙。该探测器于2023年6月记录到一次不寻常的粒子相互作用，引发了一次闪光，并引起了人们谨慎的关注。

LZ合作组是由来自39个机构的250名科学家和工程师组成的国际团队。经过数月的分析，该团队估计已知干扰源导致该事件的可能性仅为0.5%——这使得该信号成为该仪器记录到的最令人信服的暗物质迹象。

然而，从科学角度来看，宣称一项发现需要更高的置信度。“单凭一次事件是不够的，”加州大学洛杉矶分校物理学助理教授阿尔维娜·卡马哈在一封电子邮件中写道。

“我们需要观察随着我们收集更多数据，是否会有其他事件出现，以及观测结果的统计显著性是否会提高，”LZ 合作组成员、LZ 探测器建造者 Kamaha 说。

布里斯托尔大学物理学高级研究员、LZ合作组成员萨姆·埃里克森于9月1日在日本举行的2026年TeV粒子天体物理学会议上公布了研究结果，该团队已向科学期刊《物理评论快报》提交了相关研究论文。

研究人员已着手进行进一步分析，以期提高该事件的统计显著性。粒子物理学中，一项发现的显著性阈值被称为5σ，这意味着统计上的偶然性而非暗物质真实存在的概率约为350万分之一。目前的分析结果为2.6σ，即偶然性的概率约为200分之一。

卡玛哈表示，对暗物质的明确探测将是“一项重大突破”。她说：“我们知道暗物质在星系的形成和宇宙的大尺度结构中起着至关重要的作用，但我们仍然不知道它究竟是什么。这令人兴奋，因为它将开辟粒子物理学的一个全新领域。”

关于暗物质的可能构成，目前有几种候选理论，包括原初黑洞或尚未发现的粒子。诸如LZ实验之类的探测器正在寻找一类被称为弱相互作用大质量粒子（WIMP）的假想粒子。

如果弱相互作用重粒子（WIMP）存在，它们可以穿过普通物质而不与之发生相互作用，而且每秒钟都有大量的WIMP在人体内悄无声息地穿过。然而，在极少数情况下，其中一个WIMP可能会与原子核碰撞并产生微小的反冲——这正是LZ实验旨在探测的那种事件。

该探测器使用高纯度液态氙。研究人员选择这种元素是因为其原子核较重，使其成为弱相互作用重粒子（WIMP）的特别灵敏的靶标。氙中的碰撞会产生探测器可以轻松测量的信号。

LZ实验装置位于地下深处，并配备了防护层以屏蔽宇宙射线和其他辐射源，这些辐射源可能会产生类似暗物质的信号。然而，这种背景噪声只能降低，而无法消除。

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“你总会遇到这样的情况：探测器中发生的事件可能是由更传统的机制引起的，”罗德岛州普罗维登斯布朗大学的哈扎德物理学教授、LZ实验发言人里克·盖茨克尔说。

人们认为暗物质碰撞极其罕见。“我们了解到，暗物质与常规物质的相互作用非常弱，”盖茨克尔补充道，“即使在LZ实验这样规模的探测器中，我们也需要数月甚至数年的时间才能探测到一次相互作用。”

LZ合作组通过分析2023年3月至2024年4月间收集的220天的数据，发现了2023年的事件。盖茨克尔表示，研究人员目前正在分析一个涵盖700天的更新数据集，希望其中包含更多碰撞事件，以帮助确定2023年的事件是否是暗物质相互作用。

为了进行这项更全面的分析，研究团队还引入了一些避免无意识偏见的技术，例如在数据中插入“合成事件”。这些事件在分析团队看来与真实的暗物质相互作用非常相似，只有在分析完成后才会将其移除。

“探测到目标的可能性带来了很大的矛盾：一方面，我们为实验能够按预期进行而感到兴奋；另一方面，我们又担心会犯错，或者仅仅是被探测器中发生的罕见、新颖或偶然事件所蒙蔽，”英国牛津大学物理学教授、LZ合作组成员金伯利·帕拉迪诺在电子邮件中写道。“这有点像青少年时期暗恋某人，你告诉自己要表现得酷一点，但却总是忍不住过度解读对方的每一个小动作。”

然而，帕拉迪诺警告说，历史上也充斥着一些实验，这些实验都曾观测到一两个无法解释的事件，而这些事件至今仍未被完全理解。如果新的LZ数据包含新的潜在暗物质碰撞，那么其他旨在探测暗物质的类似实验，例如意大利的XENONnT和中国的PandaX-4T，可以对实验结果进行独立检验。

发现暗物质将使科学家们在了解宇宙的构成以及它如何从大爆炸演化到今天方面迈出一大步。

帕拉迪诺补充说：“但还需要更多科学家通过各种不同的实验来研究暗物质，以了解其特性，然后利用这些信息来运行我们宇宙的天体物理模拟。关于暗物质究竟是什么，目前有很多理论，而且可能存在多种类型的暗物质。”

加州大学欧文分校物理与天文系教授蒂姆·MP·泰特（Tim MP Tait）表示，LZ实验有可能探测到暗物质，这令人感兴趣，但还需要进一步证实。泰特教授并非LZ合作组的成员。

“只有时间才能证明，随着探测器积累更多数据，他们是否会观测到更多此类事件，或者这是否只是一个暂时的统计偶然现象，”泰特在一封电子邮件中补充道。他指出，LZ事件发生的能量远高于大多数WIMP模型的预期，这意味着暗物质“可能比我们最初想象的还要奇特和美妙”。

麻省理工学院物理学教授特雷西·斯莱特也认为，需要进一步的数据分析来判断LZ事件是否属于暗物质。斯莱特教授并未参与LZ合作项目，她在电子邮件中补充道：“如果这确实是暗物质，那么该事件能量很高，且没有伴随低能量事件，这一点非常有趣。”

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科学家认为我们银河系中神秘的光芒可能来自暗物质。这意味着什么？

LZ事件中测得的能量表明了氙核由于与暗物质的潜在相互作用而产生的反冲量。斯莱特解释说，高能暗物质粒子已经能够揭示暗物质的本质及其与普通粒子相互作用的诸多信息。其他实验或许有助于进一步确定其性质。

“还有很多事情要做，很多东西要学，”她说，“但如果这真的是暗物质信号，这可能是一把钥匙，可以解开大量关于新物理学的信息，并为我们提供一种新的方法来测量地球附近乃至整个宇宙中暗物质的行为。”