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Physicists confirm existence of new 'exotic' matter


Scientists at the Large Hadron Collider beauty (LHCb) Collaboration at CERN in Geneva have successfully verified the existence of a new “exotic” type of particle that was hitherto unusual to the Standard Model (SM) of particle physics.

The discovery thus prompts further refinements to SM theories. 

 


In search of the 'ghost' particle

More than six years ago, the Belle Collaboration – a team of 400 physicists and engineers from all over the world – reported the discovery of Z(4430), a particle that had only been theoretical up to that point.

Hadrons (composite particles held together by strong forces) have traditionally been classified as either mesons or baryons. Baryons result when three quarks – the smallest “building blocks” of matter – combine; protons and neutrons fall under this category. On the other hand, when quarks pair up with their “anti-quarks” (particles with the same mass, but opposite charges), mesons are formed instead. Some examples of mesons are pions and kaons, which are usually found in the decay of man-made particles (such as in particle accelerators).

However, Z(4430) was a unique case: it appeared to be made up of two quarks and two anti-quarks. According to the Belle Collaboration, this particle emerged as “a tantalizing peak” in particles that resulted from the decay of B mesons.

"Some experts argued that Belle's initial analysis was naïve and prone to arrive at an unjustified conclusion," explained physics professor Tomasz Skwarnicki. "As a result, many physicists concluded that there was no good evidence to prove this particle was real."

As a result of this revelation, others set out to find strong evidence proving the “ghost” particle's existence. Another international team, BaBar, caused quite a stir in the scientific community some time after the Belle Collaboration published its findings.

"BaBar didn't prove that Belle's measurements and data interpretations were wrong," said Skwarnicki. "They just felt that, based on their data, there was no need to postulate existence of this particle."

This prompted Belle to conduct further, more intensive analysis of their data, and managed to find statistically significant evidence for Z(4430)'s existence. However, it was the LHCb that was able to conclusively prove that the “ghost” particle was certainly no ghost, using data from both Belle and Babar.

"This experiment is the clincher, showing that particles made up of two quarks and two anti-quarks actually exist," said Skwarnicki, one of the lead authors of the LHCb's paper. "There used to be less-clear evidence for the existence of such a particle, with one experiment being questioned by another. Now we know this is an observed structure, instead of some reflection or special feature of the data."

Rigorous testing

How did the LHCb come up with “unambiguous” results? Through hard (and extremely careful) work.

After examining and analyzing more than 25,000 decays of B mesons (which were selected from 180 trillion proton-proton collisions in the Large Hadron Collider), the LHCb confirmed the existence of Z(4430) with an “overwhelming” signal significance of 13.9 sigma. Compared to Belle's calculations – which had a significance of 5.2 sigma – LHCb's findings are indeed the missing pieces in this physics puzzle.

"Because the data sample was so large, it forced us to use statistically powerful analysis that could, in turn, measure properties in an unambiguous manner,” said Professor Sheldon Stone, who leads the team of SU researchers at CERN.

“It's great to finally prove the existence of something that we had long thought was out there." — TJD, GMA News
Tags: lhc, cern, physics