Category: experimental physics

Could DAMA’s ‘Dark Matter Signal’ Simply Be Poorly Analyzed Noise?

“To date, DAMA has shown that a non-constant signal exists with 13-sigma significance. (5-sigma is normally the gold standard for experimental physics.) If they made their overall event rate publicly available, it would be easy to check — even just by eye — whether the modulation is real or whether there’s a noise floor that’s changing over time. Until they release their data, we cannot have any confidence that they haven’t fallen through this loophole.

As Nicola Rossi pointed out, “if the background is either increasing or decreasing an artificial modulation is introduced in the residual rate and it interferes with a possible real modulation.” Whether DAMA’s signal is real, and how strong it is if it is real, cannot be established without independently checking this very basic piece of raw data. If the data shows an annual growth in their noise of even just a few percent, their signal will vanish entirely.”

For around 20 years now, one and only one experiment has claimed to have directly detected a signal that would be consistent with dark matter: the DAMA collaboration. By looking for collisions with their targets that yield a specific amount of energy in their detector, they run similarly to a large number of complementary detectors. But only DAMA has seen a signal, and they have steadfastly refused to release either their raw data or their analysis pipeline, making independent verification difficult. Two attempts at verification, COSINE and ANAIS, have failed to reproduce their signal.

Earlier this month, a new paper came out contending that simply a poor analysis of their noise could mimic this signal at the full 13-sigma significance. Is DAMA too good to be true?

Dark Matter Search Discovers A Spectacular Bonus: The Longest-Lived Unstable Element Ever

“Whenever you build an experiment that can take you beyond your previous sensitivity limits, you open yourself up to the possibility of discovery. In robustly detecting this extraordinarily rare decay with a longer lifetime than any other we’ve ever seen, the XENON collaboration has demonstrated how capable their apparatus is. Although it was designed to search for dark matter, it’s also sensitive to a number of other possibilities which might herald rare or even entirely new physics.

While the direct detection of the longest-lived unstable decay is an incredible feat, its implications go far beyond a simple discovery. It’s a demonstration of XENON’s sensitivity, and its ability to tease out even a tiny signal against a well-understood, low-magnitude background. It gives us every reason to be hopeful that, if nature is kind, XENON may reveal some of its even more profound secrets.”

Naturally-occurring xenon is made up of nine isotopes. While only one of them was known to be unstable, transmuting into barium through double beta decay, some of the isotopes should theoretically be unstable to decays through an even rarer pathway: double electron capture. For the first time, double electron capture has now been observed in the element xenon, thanks to the incredible work and the unprecedented detector sensitivities provided by the experiment XENON1T. Xenon-124 has now broken the record, and is officially the longest-lived unstable isotope ever to have its decay measured.

This discovery showcases the extreme versatility of the XENON collaboration’s detector, and should make us hopeful for an even greater prize. Here’s why.