New Experiments Will Shed Light On Matter And Antimatter

Jul 22, 2004

If the laws of physics were precisely the same for matter and antimatter, you wouldn't be reading this. All matter, as we know it, would have been converted into light after the Big Bang. To explore the fundamental differences between matter and antimatter, physicists need a vast amount of data. In early July, the PEP-II accelerator at the Stanford Linear Accelerator Center, one of the world's chief suppliers of these data, reached a new milestone: It is delivering three times as many particle collisions per second as the machine was designed to produce.

"This remarkable achievement allows us to perform much more precise measurements that will shed light on matter-antimatter asymmetries," said physicist Marcello Giorgi, a spokesman for the BaBar collaboration, which has just published its 100th paper based on data from PEP-II. "These asymmetries are fundamental features of the laws of nature that played a major role in the evolution of the universe."

The Big Bang, according to the most basic physical laws, created equal amounts of matter and antimatter. Whenever a particle of matter meets its antimatter twin, they annihilate each other, leaving behind only a burst of energy.

The particles of energy ­ photons ­ zipping through the universe today are evidence that a lot of annihilations took place. However, the fact that we are here is proof that the annihilation was incomplete: There is one particle of matter for every billion photons. It's the cause of this one-in-a-billion imbalance that scientists are trying to understand.

Researchers designed PEP-II to collide electrons and their antimatter counterparts, positrons, at the precise energy that produces an abundance of short-lived pairs of particles and antiparticles called B mesons, which decay spontaneously into other particles of matter and antimatter. Because the B meson is relatively heavy, it can decay into matter and antimatter in more ways than lighter particles can. If there were no difference between matter and antimatter, both the B meson and the anti-B meson would decay at exactly the same rate.

Some decay patterns are very rare. The BaBar collaboration has seen some decays only a few times in 10 million events. Were it not for the multitude of B mesons PEP-II is providing, studies of such unusual particle behavior would be impossible.

In addition, a bigger data sample means better results. If you can only flip a penny 10 times and you get heads seven times, you could conclude that it will turn up heads 70 percent of the time. But if you flip the penny 100 times, you're likely to see that heads turns up closer to half the time.

The 600 physicists from around the world in the BaBar collaboration are now working around the clock to see what insights the new data hold. Matthew Graham, a University of Wisconsin postdoctoral fellow, is among those studying a process that caused excitement when a rival collaboration called Belle, which is based at a Japanese accelerator laboratory, announced a result that has just a 1 percent chance of agreeing with the currently prevailing theory, known as the Standard Model. BaBar's result at that time had a 60 percent chance of agreeing with the Standard Model. The discrepancy could simply be due to statistical chance, or it could be much-sought-after evidence of the Standard Model's Achilles' heel.

Both collaborations have significantly more data for this round of analysis, so it wouldn't be a surprise to see the results change when both collaborations present their latest results in mid-August at the International Conference on High Energy Physics, to be held this year in Beijing.

Ultimately, as Giorgi points out, both collaborations "are on the same adventure. We hope to open a window on new laws of physics."

Relevant Web URLs:

Stanford Report, July 21, 2004: news-service.stanford.edu/news/2004/july21/luminosity-721.html
BaBar Collaboration Home Page: www.slac.stanford.edu/BFROOT/
BaBar Public Information: www-public.slac.stanford.edu/babar/

Source: Stanford Linear Accelerator Center

Explore further: Better thermal-imaging lens from waste sulfur

add to favorites email to friend print save as pdf

Related Stories

The debut of the antihydrogen beam

Mar 07, 2014

The standard model of particle physics suggests that matter and antimatter are equal and opposite in every way. Yet the observable Universe is made almost entirely of matter—an asymmetry that remains one ...

Recommended for you

Better thermal-imaging lens from waste sulfur

8 hours ago

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Robotics goes micro-scale

19 hours ago

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

User comments : 0

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Robotics goes micro-scale

(Phys.org) —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Chronic inflammation linked to 'high-grade' prostate cancer

Men who show signs of chronic inflammation in non-cancerous prostate tissue may have nearly twice the risk of actually having prostate cancer than those with no inflammation, according to results of a new study led by researchers ...

Cosmologists weigh cosmic filaments and voids

(Phys.org) —Cosmologists have established that much of the stuff of the universe is made of dark matter, a mysterious, invisible substance that can't be directly detected but which exerts a gravitational ...