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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.
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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
http://www.slac.stanford.edu/slac/media-info/20040802/). 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
http://www2.slac.stanford.edu/tip/2004/jun04/babar.htm).
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.
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