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We present measurements of the Branching Fraction and photon energy spectrum in B → X{sub S}[gamma] decays in a sample of 89 million B{bar B} pairs collected at the BABAR detector at Stanford Linear Accelerator Center's PEP-II asymmetric B-factory. Results from a fully-inclusive and a sum of 38 exclusive final states techniques are presented and found to be consistent with the Standard Model calculations, as well as experimental results obtained from semileptonic B → X{sub c}lv decays.
The electromagnetic penguin process b [yields] s[gamma] is very interesting to theorists because it can be used to constrain contributions from new physics that could enter at the one loop level. The high statistics of B[bar B] events collected at the BABAR experiment make a measurement of this rare decay possible. The branching fraction of a sum of exclusive b [yields] s[gamma] decay modes is measured as a function of the strange hadronic mass. This is a large step toward the measurement of the b [yields] s[gamma] rate.
The b [yields] s[gamma] decay represents a possible electromagnetic ''loop'' penguin decay of the B meson. This FCNC process is of high theoretical interest because various scenarios of new physics are expected to have contributions at the same (one loop) level as the Standard Model. The large sample of B[bar B] meson decays collected by the BaBar experiment makes a precision measurement of this rare decay possible. In conjunction with Standard Model predictions at the 10% level, it brings new physics effects into the realm of detection--or seriously constrains models that could predict them. A fully inclusive technique is presented to study the b [yields] s[gamma] transition as a function of photon energy, using 88.5 [+-] 1.0 x 10[sup 6] B[bar B] meson decays collected by the BaBar experiment in the years 2000 to 2002. The expected statistical and systematic uncertainties have been fully determined which enables first comparisons with theoretical predictions and other experimental results. It also lays the basis for the determination of the inclusive branching fraction [Beta](B [yields] X[sub s][gamma]) and the measurement of the photon energy spectrum.
Using a sample of 383 million B{bar B} events collected by the BABAR experiment, they measure sums of seven exclusive final states B → X{sub d(s)}[gamma], where X{sub d}(X{sub s}) is a non-strange (strange) charmless hadronic system in the mass range 0.6-1.8 GeV/c2. After correcting for unmeasured decay modes in this mass range, they obtain a branching fraction for b → d[gamma] of (7.2 ± 2.7(stat.) ± 2.3(syst.)) x 10−6. Taking the ratio of X{sub d} to X{sub s} they find [Lambda](b → d[gamma])/[Lambda](b → s[gamma]) = 0.033 ± 0.013(stat.) ± 0.009(syst.), from which they determine.
Recent BaBar results on rare B decays involving flavour-changing neutral currents are presented. New measurements of the CP asymmetries in b 2!s[gamma] decays are reported as well as b 2!sll− branching ratio measurements.
I discuss recent results in radiative B decays from the Belle and BaBar collaborations. I report new measurements of the decay rate and CP asymmetries in b → s[gamma] and b → d[gamma] decays, and measurements of the photon spectrum in b → s[gamma]. Radiative penguin decays are flavour changing neutral currents which do not occur at tree level in the standard model (SM), but must proceed via one loop or higher order diagrams. These transitions are therefore suppressed in the SM, but offer access to poorlyknown SM parameters and are also a sensitive probe of new physics. In the SM, the rate is dominated by the top quark contribution to the loop, but non-SM particles could also contribute with a size comparable to leading SM contributions. The new physics effects are potentially large which makes them theoretically very interesting, but due to their small branching fractions they are typically experimentally challenging.
We present a feasibility study for a new analysis for extracting the angle of the Unitarity Triangle from the study of the neutral B meson decays. We reconstruct the decay channel B° → {bar D}°K*° with the K*° → K?− and the {bar D}° → K{sub S}?+?− using a D° Dalitz analysis technique. The sensitivity to the angle comes from the interference of the b → c and b → u processes contributing to the same final state and by the fact that the B°({bar B}°) can be unambiguously identified through the sign of electric charge of the kaon from K*°({bar K}*°) decay. The impact of the result of such analysis is evaluated for the actual BaBar statistics.
The author discusses two recent results in b → s[gamma] decays from BABAR. The first is a measurement of the branching fraction and photon energy spectrum in the B meson frame of the decay B → X{sub s[gamma]}. The second result probes the photon polarization via time-dependent CP violation in neutral B decays to K*°{gamma}.