in proton-antiproton collisions tended
to move in the direction of the protons.
Antitop quarks, the antimatter version
of the top quark, generally moved back
the other way.
A later look with more CDF data, about
half of what will be collected by the end
of September, only strengthened the statistics, and DZero has also reported this
unexpected preference. The anomaly is
too strong to square with the predictions
of quantum chromodynamics, one of the
theories rolled into the standard model.
A bookie taking bets that the CDF
asymmetry is a fluke could post odds
just shy of one in a thousand — about a
“three sigma” result, in the language of
physicists. That’s not good enough to say
anything for sure, but it has stirred up
some excitement.
“I find this forward-backward asymmetry tantalizing because both experiments saw it,” says Christopher Hill, a
theoretical physicist at Fermilab.
Hill has an explanation for this unusual
behavior, worked out in full mathematical detail by Harvard physicist Matthew
Schwartz and colleagues in a paper posted
online June 15 at arXiv.org. Two top
quarks might behave like a pair of electrons in a superconductor, a material with
no resistance to the flow of electricity. A
new particle could unite the pair, which,
in this theory, play the role of the Higgs by
explaining the origin of mass.
Then again, adding in the full dataset
could also wipe out this anomaly.
“We can’t make any claim yet, but we
should have a more definitive look at this
thing by next summer,” says Dan Amidei,
a member of the CDF team and a physicist at the University of Michigan in Ann
Arbor. “My greatest worry is not that it
goes away with more data, but that it
remains a hint and we never know what
it was.”
Other curiosities on the table include
jets of particles with energies between
120 and 160 GeV, which could be the
remnants of a new, unexplained particle (not the Higgs). CDF saw the jets,
but DZero didn’t. DZero, meanwhile, has
uncovered an unexplained preference
for the production of the matter version
Higgs in hiding though the tevatron is out of the running to discover the higgs boson, analyses of the atom smasher’s remaining data may further limit this elusive particle’s potential mass.
recent findings at the large hadron collider suggest the higgs mass is below 145 GeV.
Possible mass range for the Higgs
Excluded
by LEP Collider
Possible
masses
Excluded by LHC
Excluded
by Tevatron
Excluded by
Tevatron’s indirect
measurements
Lighter
114
GeV
145 156
Heavier
177 185
Exclusion = 95% con;dence
of the muon — an overweight cousin of
the electron — over the antimatter version. This tricky measurement hasn’t
been repeated by the CDF team.
Convincing the wider physics community that these oddities are real will
be difficult. The LHC has already begun
to investigate them; early results, presented in July at a meeting in Grenoble,
France, contain no signs of anything out
of the ordinary, contradicting the Tevatron results.
“I think they’re embarrassing rubbish,” says Wilczek, who favors supersymmetry as an extension of the
standard model. “You really have to do
contortions to make these things consistent with what we know, and I find it
hard to believe that Mother Nature has
such poor taste.”
Future frontiers
Even though the LHC is currently running at half its intended strength, that
international machine will soon be the
sole collider pushing the high-energy
frontier in search of never-before-seen
particles. No one else can compete with
its collisions.
Without its famed atom smasher,
Fermilab is shifting its focus to other
areas, including the activities of already
discovered particles. Next year, the lab
will shut down temporarily to transplant
some of the Tevatron’s bits and pieces
into other experiments and to upgrade
its accelerator complex for a ne w generation of experiments that require intense
beams packed with tremendous numbers
of particles, just not at such high energies.
Beams that once fed the Tevatron will
be reconfigured to churn out muons for
projects including Muon g- 2. By exam-
ining the strange behavior of muons in
magnetic fields, this project could point
to certain versions of supersymmetry.
Explore more
s For info on proposed future colliders:
arxiv.org/abs/0909.3240
