Scores of theory papers now chase a lone xenon flash too energetic for a plain WIMP

The denominator is one event. It gives one energy value, and fitting a model curve would take a spectrum ^[24]. The other figure in circulation is the 1-in-200 chance New Scientist reports for the burst being a fluke rather than dark matter, which works out to 0.5 per cent ^[4][23]. That figure compares the flash against background. Ranking the models now competing to explain it is a different question ^[25].

Energy alone still narrows the field, because the candidates differ in what should accompany a high-energy recoil. "It's an anomalous event," said Henning Flaecher of the University of Bristol, a member of the LZ group ^[6]. "It's not what you would expect from the most general dark matter models," he said ^[7]. On Flaecher's account, a high-energy hit with no lower-energy collisions alongside it makes it exceedingly unlikely that the particle, if it exists, is a vanilla WIMP ^[8].

So the higgsino went into scores of abstracts. It is a non-vanilla WIMP from supersymmetry, the framework in which every known particle has a superpartner with similar properties and different spin, and it would be the superpartner of the Higgs boson ^[11]. A higgsino event is predicted to arrive without a host of lower-energy collisions, and that fits what LZ saw ^[14]. JiJi Fan of Brown University calls it the simplest WIMP explanation still available ^[12]. "It gives rise to a wealth of signals that could be searched for at different experimental frontiers," Fan said ^[13]. The basic version is in trouble already: constraints from other experiments appear to rule out the simplest higgsino model that would explain the LZ detection, so the mass would have to be much higher than expected ^[15].

Several other papers put the particle in extra dimensions, using models already under study for other problems in particle physics, according to Lisa Randall of Harvard University, a co-author of one of them ^[16]. "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," Randall said ^[17]. Such a candidate could fit the LZ detection and also explain why the fundamental particles have the masses they do, she said ^[18]. Other proposals sketch a whole dark matter sector with multiple types of dark particle ^[19].

Juri Smirnov of the University of Liverpool said the pile of papers is not theorists declaring their belief that the event is a true dark matter discovery. It reflects instead that, if the signal persists, its energy already tells them quite a lot about the types of physical processes that could produce it ^[10]. He also said: "I don't think the data currently justify saying one of these is 'the' explanation" ^[20]. Some of the models come with additional predictions, and Smirnov said those will be particularly useful in picking through so many ideas ^[21]. In New Scientist's account, the work so far is theory papers and continuing analysis at the detectors, with no collaboration in it having changed what it searches for ^[26].