Underground experiments in Italy search for violation of the Pauli exclusion principle

They have found no signs of the event yet.
Loukia Papadopoulos
Can the Pauli exclusion principle be violated.jpg
Can the Pauli exclusion principle be violated?

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Deep in Italy’s Gran Sasso mountains, in the National Institute for Nuclear Physics’ (INFN) underground laboratories, researchers have been searching for proof of a very small violation of a fundamental quantum tenet called the Pauli exclusion principle, according to an article by Phys.org published on Monday.

The principle, that is applied to everything, dictates that electrons can only arrange themselves in certain specific ways in atoms. These arrangements make it so we are made of solid matter.

"It is ubiquitous—you, me, we are Pauli-exclusion-principle-based," says Catalina Curceanu, a member of the physics think-tank, the Foundational Questions Institute, FQXi, and the lead physicist on the experiments at INFN. 

"The fact we cannot cross walls is another practical consequence."

A violation of a fundamental principle

But some speculative models of physics, beyond the standard model, suggest that the principle may be violated. "Many of these violations are naturally occurring in so-called 'noncommutative' quantum-gravity theories and models, such as the ones we explored in our papers," said Curceanu. 

"The analysis we reported disfavors some concrete realizations of quantum gravity.”

Curceanu and her colleagues discovered that signs that the exclusion principle had been violated could be picked up in lab experiments on Earth. 

Underground experiments in Italy search for violation of the Pauli exclusion principle
The Pauli exclusion principle dictates the arrangement of electrons.

Their research is called the VIP-2 (Violation of the Pauli Principle) lead experiment and is conducted in a lab housed underground because the radiation signature from such a process will be so faint, it would otherwise be drowned out by the general background radiation on Earth from cosmic rays. 

"Our laboratory ensures what is called 'cosmic silence,' in the sense that the Gran Sasso mountain reduces the flux of cosmic rays by a million times," said Curceanu. 

"Our signal has a possible rate of just one or two events per day, or less," explained Curceanu. 

In addition to working deep underground the scientists need to make sure materials used in the experiment do not emit any radiation themselves and the apparatus used are shielded from radiation from the mountain rocks.

Interesting experiments

The combination of these settings allow the researchers to undertake some pretty interesting experiments.

"What is extremely exciting is that we can probe some quantum-gravity models with such a high precision, which is impossible to do at present-day accelerators," said Curceanu.

As of yet, the team has found no evidence for the violation of the Pauli principle but that hasn’t stopped them from setting ambitious plans to extend their research to other quantum-gravity applications.

"On the experimental side, we will use new target materials and new analysis methods, to search for faint signals to unveil the fabric of spacetime," said Curceanu.

"What is extremely exciting is that we can probe some quantum-gravity models with such a high precision, which is impossible to do at present-day accelerators," Curceanu added. "This is a big leap, both from theoretical and experimental points of view."

Their work appears in two papers in the journals Physical Review Letters (published on September 19, 2022) and Physical Review D (accepted for publication on December 7, 2022).