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THE reason the Universe contains so much more matter than antimatter remains
as mysterious as ever, following ambiguous results from an experiment designed
to find out.

For the past two years, the Babar experiment at the Stanford Linear
Accelerator Center in Palo Alto, California, has been comparing particles called
B mesons with their antimatter partners to see if they are exact mirror images.
Its first official result, presented on Monday, is about as unhelpful as it
could be.

It all comes down to measuring a single number known as sin2b. If the B meson
and the anti-B meson are precise mirror images it should be zero. If the
particles are not鈥攁 condition known as charge-parity violation鈥攕in2b
should be somewhere around 0.7. Babar鈥檚 measurement comes out slap in the middle
of this range at 0.34, with a sizeable experimental uncertainty.

鈥淲hat we鈥檝e got right now would be a number from hell, if it was the last
thing that we could do,鈥� says Steward Smith of Princeton University, spokesman
for the Babar team. The measurement could equally well agree with either zero or
0.7, he says.

Babar researchers studied the decays of some 23 million B-anti-B pairs.
鈥淔ortunately, we鈥檙e just beginning,鈥� Smith says. Within six months the
researchers hope to double the number of measurements and reduce the uncertainty
enough to say more definitely whether B mesons show CP violation. So far, only
particles called K mesons are known to break the symmetry between matter and
antimatter鈥攕uggesting that they could have been created in unequal amounts
during the big bang.