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FYO7 SLAC S CIENCE AND T ECHNOLOGY S ELF E VALUATION
A more precise measurements of CP violation in B decays to double-charm final states
BDD(bar),
The time-dependent CP violation in the decay Bρ 0 ρ 0 ,
The semileptonic branching fractions in B decays.
The CP violation measurements in the decays BDD are consistent with the Standard Model and
rule out large direct CP violation in this mode. The time-dependent CP asymmetry measurement in
Bρ 0 ρ 0 represents a major step in removing the ambiguities in the determination of the angle α. The
measurements continue to hold to the CKM picture, which imposes significant constraints on models
of physics beyond the Standard Model, including the supersymmetric extensions of the Standard
Model.
Search for the Effects of Physics Beyond the Standard Model: A key element of the BABAR
physics program is seeking the effects of New Physics through loop-dominated rare decays of B
mesons. A clean set of observables sensitive to the effects of New Physics are time-dependent CP
violating parameters in the so-called b → sss penguin diagrams containing virtual quarks and vector
0 0
bosons. While such modes, including B → ϕK
, 0 0
B → η′ K and a number of related channels, should
show the same CP asymmetry as the benchmark charmonium result for sin2β, they are also sensitive
to New Physics at high mass scales BABAR has performed a comprehensive set of measurements of
CP asymmetries in these channels. BABAR presented new results based on Runs 1-5, including a
complete time-dependent Dalitz analysis of the decay BΚπ + π − . The “naïve” average of the
measurements continues to show a nearly 2.5 standard deviation discrepancy with the predictions of
the Standard Model. Improving precision of these measurements is among the highest priorities of
the experiment.
A set of measurements of the decays ΒD (∗) τν, which complete the semileptonic picture of B meson
decays, provide yet another window on physics beyond the Standard Model, owing to dependence of
the branching fractions on the mass of the charged Higgs. At current uncertainty levels, the data is
consistent with the Standard Model.
Analysis and Simulation Tools: The BABAR collaboration has developed or contributed to many
analysis and simulation software tools now in use in high energy physics and other fields. In FY07,
the Stat Pattern Recognition package for multivariate classification and “data mining,” that is now
maintained as open-source software and used outside HEP, was further developed with additional
capabilities, and was used to provide significant improvements in particle identification performance.
BABAR members contributed to a similar package, TMVA, which is also now in wide use.
The RooFit package for data modeling, developed within BABAR to address complex requirements of
time-dependent CP fits, continues to be developed. It is now distributed as part of the ROOT system,
almost universally used in high energy physics and increasingly adopted in other scientific
communities.
In FY07 BABAR members also contributed to the validation of new releases of the standard particleinteraction
simulation toolkit, GEANT4, widely used in HEP, nuclear physics, medical imaging, and
beyond. A BABAR collaborator is also a member of the core GEANT4 development team.
Objective 1.2 Leadership in Science and Technology
The BABAR experiment at SLAC is the leading experimental program in the US and among the
leading programs worldwide, focused on investigating CP symmetry breaking using the decays of B
mesons. The collaboration includes 543 physicists from 77 institutions in 10 countries: the US,
Canada, France, Germany, Italy, Netherlands, Norway, Russia, Spain and UK. There are also 520
associate members. The BABAR collaboration, with a young researcher base of about 150 PhD
graduate students and 90 postdoctoral research associates, is one of the leading institutions
worldwide that trains future high energy physicists.
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