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Home > iSGTW - 26 May 2010 > Feature - New result could shed light on the existence of the Universe

Feature - New result could shed light on the existence of the Universe


The DZero collaboration has found evidence for a new effect which could explain the matter-antimatter asymmetry of nature. CP violations, such as this effect, are in disagreement with the predictions of the theoretical framework known as the Standard Model of particles and their interactions. The effect ultimately may help to explain why the universe is filled with matter while antimatter disappeared shortly after the Big Bang. Image courtesy of the DZero collaboration. 

The Big Bang should have created a universe with equal amounts of matter and anti-matter. Instead, we only see antiparticles when they are produced in nuclear reactions, cosmic rays, and particle colliders.

The dominance of matter that we observe in the universe is possible only if there is ‘CP violation’ – differences in the behavior of particles and antiparticles. Although physicists first observed certain forms of CP violation decades ago, those differences were consistent with the Standard Model of particle physics, and far too small to explain the apparent imbalance between matter and antimatter.

Now, scientists with the DZero collaboration at Fermilab have found evidence for significant CP violation in the behavior of particles containing bottom quarks. And they did it using grid computing.

The new result indicates a one percent difference between the production of pairs of muons and pairs of antimuons in the decay of B mesons. If confirmed by further observations and analysis, this result could represent an important step towards understanding the dominance of matter in our universe.

“This exciting new result provides evidence of deviations from the present theory in the decays of B mesons, in agreement with earlier hints,” said Dmitri Denisov, co-spokesperson for the DZero experiment. Last year, both the DZero and CDF detectors – separate detector experiments at the Tevatron collider – observed such hints in studying particles made of a bottom quark and a strange quark.

The DZero detector records particles emerging from high-energy proton-antiproton collisions produced by the Tevatron. For this measurement of CP violation, scientists analyzed hundreds of trillions of collisions collected over the last eight years. Image courtesy of Fermilab.

When matter and anti-matter particles collide at high-energies, they turn into energy, producing new particles and antiparticles. The DZero result is based on data the experiment recorded over the last eight years - hundreds of trillions of collisions between protons and antiprotons in the Tevatron collider.

DZero collaborators perform the data analysis for the experiment using a variety of computational resources, including Open Science Grid and EGEE.

“Computing resources are playing a very important role in particle physics with many exciting results, including di-muon charge asymmetry, obtained with heavy use of grid,” Denisov said.

To avoid any bias, the DZero physicists performed the data analysis ‘blind.’ Only after a long period of verification of the analysis tools did the DZero physicists look at the full data set.

Then, using unique features of their precision detector and newly developed analysis methods, the DZero scientists demonstrated that the probability that this measurement can be explained by any known effect is below 0.1 percent (3.2 standard deviations).

“Many of us felt goose bumps when we saw the result,” said Stefan Soldner-Rembold, co-spokesperson of DZero. “We knew we were seeing something beyond what we have seen before and beyond what current theories can explain.”

—Miriam Boon, iSGTW, with excerpts from Fermilab DZero press release
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