Harvard BABAR Group
Faculty:
Masahiro Morii
Ex-Postdocs: Stephen Bailey, Eunil Won, Jinwei Wu
Graduate students: Kris Chaisanguanthum, Corry Lee
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Harvard BABAR Group
Faculty:
Masahiro Morii |
The BABAR Experiment operated between 1999 and 2008 at the PEP-II Electron Positron Storage Ring at Stanford Linear Accelerator Center (SLAC). PEP-II collided electrons and positrons at the center-of-mass energy of 10.58 GeV, so-called the Υ(4S) resonance, to produce a large number of B mesons, and their decays are observed by the BABAR Detector. The accelerator provided very high luminosity (1.2×1034 cm-2s-1), with the electron and positron beams having different energies (9 GeV for electrons, 3.1 GeV for positrons) in the laboratory frame. The final-state B mesons are therefore boosted toward the direction of the electron beam momentum. This “asymmetric” collision scheme makes it possible to measure the proper decay time of the B mesons through their flight lengths, thereby allowing BABAR to detect time-dependent CP asymmetry in various decays of B mesons. Such measurements have provided strong constraints on the imaginary phase of the Cabbibo-Kobayashi-Maskawa matrix, the origin of the CP violation in the Standard Model, for which we had very limited experimental data.
During the 9-year operation, the BABAR Experiment accumulated an integrated luminosity of 531 fb-1, of which 433 fb-1 was recorded on the Υ(4S) resonance. Measurements with improved accuracies and in a wider variety of decay modes will follow in the next few years.
Several upgrade projects took place during the lifetime of the BABAR Experiment, enabling the detector to take data at increasingly luminosities delivered by PEP-II. The Harvard BABAR group played a leading role in the Level-1 Trigger upgrade project.
 Prototype ZPD module |
 Production ZPD system in the BABAR Electronics House, with Harvard postdocs Bailey (left) and Won. |
The Z-PT Discriminator (ZPD) modules we have developed at Harvard are described in Ref. [1].