RHUL group :: BaBar activities
In 1994 the Royal Holloway group joined the BABAR experiment at PEP-II, SLAC. PEP-II is a high luminosity, asymmetric B-factory and the primary aim of BABAR is to make precision measurements of CP violation in weak decays of the B meson. 
Since data taking began in May 1999, BABAR has amassed a sample of nearly 
400 million B decays and shown first evidence for CP violation in B meson decays. 

Electromagnetic Calorimeter (EMC)
A high quality electromagnetic calorimeter is an essential feature of BABAR. The UK groups in the collaboration built the forward endcap of this calorimeter including the associated electronics, trigger and data acquisition.
EMC hardware
EMC software
We carried out radiation damage studies for the calorimeter's CsI crystals. We are involved in the day-to-day operation and monitoring of the EMC and the calorimeter trigger (EMT).
We played a major role in the production of trigger software for the electromagnetic trigger (EMT). We have made important contributions to calorimeter energy calibration using Virtual Compton Scattering (VCS) events.

Physics studies

It is the primary goal of the Babar experiment to measure the sides and the angles of the CKM Unitarity Triangle, and to test the Standard Model picture of CP violation. The large sample of B decays collected by the experiment also permits precision studies of B meson decays. In addition, Babar collects a huge sample of tau decays.

CP Violation
sin(2Beta)
Gamma
We have been involved in the measurement of sin(2Beta), where Beta is one of the angles of the CKM Unitarity Triangle. We pioneered the early analysis of the golden decay mode B0 -> J/Psi Ks. More recently, we developed the CP analysis of the decay B0-> etacKs.
The measurement of the angle gamma of the Unitarity triangle is both theoretically and experimentally challenging. We are involved in the analysis of decays of the form B -> D(*)K(*) which are anticipated to provide a promising approach to this measurement. Initially, we have performed  a measurement of the branching fraction for the decay B+->D0K*+.
sin(2Beta+gamma)

We have played a leading role in the measurement of sin(2Beta+gamma) using the partially reconstructed decay B0 -> D*pi.

B Physics
Branching Ratios
Hadronic Mass Moments
We have measured branching fractions for numerous B meson decays (B0 -> J/Psi Ks,  B -> etac K, B- -> D0K*-, B0-> D*a1). These results all improve on the precision of previous measurements, as well as validating the selection of these decays for future studies of CP violation.
We have led the measurement of the hadronic mass distribution in semileptonic B decays. Moments of this distribution can be compared with the predictions of Heavy Quark Effective Theory (HQET). The results can be used to improve the determination of Vcb and the mass of the b quark.
b -> s gamma
The branching ratio for the decay b ->s gamma provides stringent constraints on physics beyond the Standard Model. It also provides information on the same HQET parameters determined from the mass moments in semileptonic decays. We select a data sample in which one of the B mesons is fully reconstructed and use the other B to measure the b -> s gamma branching fraction. This new technique is expected to provide the most reliable measurement of the branching fraction and the photon energy spectrum within a few years as more data is collected.

Tau Physics

We are pioneering the search for the lepton family number violating decay tau -> e gamma. Although the Standard Model expectation for this decay rate is extremely small, some extensions can lead to decay rates within experimental reach. We are also leading the analysis of the decay tau -> K*nu. Hadronic tau decays involving kaons can allow theoretically clean measurements of the strange quark mass and of the CKM matrix element Vus.

People
References / Theses
PhD students:
David Hopkins
Sudan Paramesaran
Adam Wren

Group publications
Postdocs: 
Henning Flaecher
Fabrizio Salvatore

Academic staff:
Glen Cowan
Tania McMahon