LUX-ZEPLIN detector records potential dark
A single high-energy event at the LUX-ZEPLIN dark matter detector has physicists exploring non-standard particle models, including higgsinos and
Physicists are analyzing a potential dark matter particle detection from the LUX-ZEPLIN (LZ) experiment. The single event, announced on 1 September, has about a 1-in-200 chance of being a random fluke.
The LZ detector in South Dakota uses a large tank of liquid xenon to search for dark matter. It looks for collisions between dark matter particles and xenon atomic nuclei, which should produce flashes of light captured by surrounding cameras. The collaboration recorded only one such flash.
An anomalous high-energy event
The signal's energy was higher than expected for a standard weakly interacting massive particle (WIMP). Henning Flaecher at the University of Bristol, part of the LZ group, calls it an anomalous event. "It's not what you would expect from the most general dark matter models," he says. The lack of accompanying lower-energy collisions makes a simple 'vanilla' WIMP unlikely.
Since the announcement, theorists have published numerous papers examining the data. Juri Smirnov at the University of Liverpool notes the volume of work reflects the event's informative energy profile, not a consensus on a discovery. "If it persists, its energy already tells us quite a lot about types of physical processes that could produce it," Smirnov says.
The higgsino candidate
A leading explanation is the higgsino, a non-standard WIMP from supersymmetry theory. In this framework, every known particle has a 'superpartner' with different spin. The higgsino would be the superpartner of the Higgs boson.
JiJi Fan at Brown University states the higgsino is the simplest remaining WIMP explanation for the LZ signal. It gives rise to a wealth of signals that could be searched for at different experimental frontiers. Its predicted signature-a single high-energy event without lower-energy collisions-matches the LZ data.
However, the most basic higgsino model fitting the detection appears ruled out by other experiments. This suggests any higgsino responsible would need a much higher mass than previously thought.
Exploring extra dimensions and beyond
Other models propose dark matter originating from extra spatial dimensions. Lisa Randall at Harvard University, a co-author on one such study, says these models were already under investigation for other physics puzzles. In some sense, the data looks like it's calling out for something like this: it avoids the pre-existing constraints and fits quite naturally.
An extra-dimensional dark matter particle could explain the LZ event and address the long-standing mystery of fundamental particle masses. Other theories propose an entire dark sector containing multiple types of dark particles.
The search for confirmation
Currently, no model can be singled out as correct. Smirnov cautions, I don't think the data currently justify saying one of these is 'the' explanation. Some models make additional predictions, which will help narrow the field as researchers seek more data.
The LZ team and other collaborations worldwide continue analyzing data for confirming events. JiJi Fan reflects that such anomalies provide concrete targets for theoretical and experimental inquiry. Whether the LZ event is confirmed or not, the exploration it has sparked will fuel long-term research into dark matter's nature.
