September 17, 2004  


BABAR’s New Leadership: A Cosmic Coincidence

By Heather Rock Woods

Two reddish-haired Canadians are taking over BaBar.

David MacFarlane, on leave from UC San Diego, will become spokesperson the week of September 20, and Chris Hearty from the University of British Columbia is the new physics analysis coordinator.

Chris Hearty (shown left), new BaBar physics analysis coordinator, and David MacFarlane, new BaBar spokesperson. (Photo by Diana Rogers)

“It’s a conspiracy,” Hearty joked.

“It’s just a cosmic coincidence,” MacFarlane said.

The 600-person collaboration works hard to ensure smooth continuity by training new leaders before their terms start. MacFarlane’s family has relocated here for his two-year term, and Hearty has frequent travel plans during his one-year term to see his wife, who teaches near Vancouver.

The first order of business was to celebrate BaBar’s success at the formidable International Conference on High Energy Physics (ICHEP) in Beijing last August, where the collaboration presented some 64 conference papers—an unusually high number—and participated with 22 parallel session talks and one plenary session talk.

 “It’s very satisfying to us that we were able to bring so much new physics and new data to the table,” MacFarlane said. “The conference summary speaker noted that the results from both B-factories (BaBar and Belle in Japan) were the highlight of the conference.”

The results reflect a broad range of contributions, including a doubled data set in the last year, a new method for storing data to more quickly reach the physics analysis groups, a new data quality group, a very active physics analysis community and an efficient internal review process.

A high spot was BaBar’s presentation on the discovery of direct CP violation in the B meson particle, announced by the collaboration weeks earlier (see  Physicists found a large asymmetry, or CP violation, in how frequently B particles perished into a particular set of particles compared to the frequency for the antimatter anti-B particles. Picture a cookie jar with equal numbers of white cookies with chocolate chips (matter) and chocolate cookies with white chips (antimatter).  When you go to eat these unusual cookies that started with one chip each, you count 900 chocolate chips but only 700 white chips. This behavior difference may be part of the reason we are made of matter instead of antimatter.

“Belle presented their results at the conference and confirmed our result. This was a real milestone for the B-factories,” MacFarlane said.

Another conference highlight is the search for asymmetry in penguin modes, a rare class of decay from B mesons to other particles. The BaBar experiment is pursuing intriguing hints that penguin modes reveal new physics that are unaccounted for in the Standard Model, the bible of known particles and interactions.

“This is clearly going to be a hot topic over the next year,” Hearty said.

If the Standard Model is correct, penguin modes should have the exact same amount of asymmetry as the now well-studied decay process involving what are called charmonium states. Experimental data from both B experiments, presented in Beijing, show the penguin modes appear to have less asymmetry than the charmonium modes.

“The data are continuing to hint there may be new physics here, perhaps supersymmetry,” MacFarlane said. However, the current measurement lacks enough statistical significance to be sure. He hopes the experiments will accumulate enough data to be convincing in time for ICHEP 2006 in Moscow.

Another mystery that remains is the existence of pentaquarks, particles made of five quarks—not the usual two or three. Two nuclear physics experiments claimed to have seen pentaquarks last year. Since then about half of the world’s big particle physics experiments, including BABAR, have not seen signals for pentaquarks at that mass, while the other half have.

“The jury’s still out at this point,” MacFarlane said.  “We have a huge data set, we should be producing pentaquarks.”

The BABARians will also be looking for other new particles using spectroscopy, a way of analyzing data based on the mass of particles. This method has already turned up two new particles in the past 18 months at both BABAR and Belle.

“Theorists give us a lot of input in where to look for new particles,” Hearty said.

Pinning down the alpha angle will also be an important goal for the next run, to get a more precise measurement and better understanding of this complicated quantity. Alpha, beta and gamma are the three angles in the unitarity triangle, which summarizes what is known about electroweak interactions with bottom quarks. Comparing new direct measurements of alpha with indirect measurements of alpha could again open a window on new physics. (see

During the current accelerator downtime, BaBar is making major upgrades to the detector, replacing one third of the muon system.  Failures in the old muon system degraded the detector’s ability to efficiently identify muons. The remainder of the muon system will be replaced during next summer’s downtime.

“We’re unbuilding the detector and rebuilding it.  It’s a big deal,” Hearty said.

The next run is scheduled to begin October 15 and run to July 1, 2005. “We’re hoping to record another 100 inverse femtobarns or more,” MacFarlane said. “That would be a substantial increase in our data sample.”

Hearty hopes to make analyzing those reams of new data easier and faster by providing the core tools and data that the analysis groups need including central schedules so groups can complete their work and get it through the review process in time to present at major conferences.

“We’d like to have a good show of new physics analyses at the Lepton Photon conference in June,” he said. 




The Stanford Linear Accelerator Center is managed by Stanford University for the US Department of Energy

Last update Wednesday September 15, 2004 by Emily Ball