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From the Director: Turning the Page

(Photo - Persis Drell) At 12:43 p.m. on Monday the B Factory completed the program of delivering physics data to BaBar. In the remaining few hours of the day, the PEP-II team continued to explore the limits of accelerator physics by pushing the low-energy beam current to a new world-record of 3.213 A.

While intense analysis of the unique BaBar data sample will continue for a number of years, Monday’s events bring to an end the operational phase for PEP-II and mark a fundamental transition for SLAC as a national user facility. By turning this important page in the history of SLAC as the host for one of the world's premier particle physics facilities, it is timely to reflect both on the accomplishments and the future direction for the particle physics and astrophysics program at the laboratory.

The B Factory was born out of an ambitious goal of exploring contributions to the origins of the dominance of matter over antimatter in the universe today. It is the PEP-II team who has turned this dream into a reality. Through their extraordinary dedication, innovation and creativity we not only achieved, but in fact far surpassed, the ambitious goals for the B Factory program. The resulting data sample has been a key part in advancing our understanding of matter–antimatter asymmetries and the elegant picture of quantum interference that underlies its origins.

The success of the B Factory program has also depended critically on the development of a truly international experimental team, the BaBar Collaboration. SLAC has been privileged to host an outstanding group of 600 users from 11 countries and 76 institutions worldwide. The BaBar team, working in close collaboration with PEP-II and SLAC, has built and operated the BaBar detector, and continues to produce beautiful physics results at an unprecedented rate. At this writing some 335 journal articles, spanning topics from CP violation and rare decays of B mesons, to charm and tau properties, to initial-state radiation, two-photon physics and the spectroscopy of exotic states, have been emerged from the B Factory data.

The Standard Model incorporates a natural mechanism for generating asymmetries in the behavior of matter versus antimatter particles through intrinsic properties of the weak interaction. The long lifetime of the B meson and the relatively large probability for matter–antimatter oscillations in the evolution of B mesons presented an ideal laboratory for testing these ideas. Quantum interference between competing decay pathways for neutral B and anti-B mesons results in large and testable asymmetries. The Standard Model predictions have been exquisitely tested with the B Factory data. We have shown with high precision that the Cabibbo-Kobayaski-Maskawa (CKM) model and the Unitarity Triangle consistently describe both indirect measurements of rates, representing the lengths of the sides, with CP asymmetry measurements, providing us with a measure of the interior angles of the triangle: beta, alpha and gamma.

PEP-II achieved design luminosity within a remarkable 18 months of turn-on, allowing BaBar to establish the validity of CKM picture by summer 2001. Eventually the head-room built into the original design and investments in upgrades allowed PEP-II to raise both the peak and integrated luminosity capability of the machine well beyond the initial goals. These improvements opened up the opportunity to greatly expand the BaBar physics program. Through precision measurements of the quark couplings, an expanded program of measuring CKM angles, and measurements of rates and CP violation in rare b-quark to s-quark penguin decays, have brought the search for physics beyond the Standard Model to a new quantitative level. The increasing number of overlapping constraints can be played off each other to surgically constrain the influence of such new physics in quantum loops and rare or forbidden decays. Together the suite of measurements provides a powerful legacy for the B Factory data in the era of new discoveries at the energy frontier with the LHC.

Indeed, the ability to explore the flavor couplings of supersymmetry or other new physics, should discoveries emerge at the LHC, is the primary motivation behind the SuperB proposal pursued by INFN in Europe and the Super KEKB upgrade project at KEK. SuperB, in particular, with factors of 100 increase in luminosity, would be a powerful addition to the tools available for exploring new physics in the next decade.

Turning a page in the history of operating particle physics facilities on site also signals a change in direction and role for the particle physics and astrophysics program at SLAC. We envision a program that is founded on a major involvement in the energy frontier, in particular ATLAS and the upgrades for the sLHC and eventually a detector for a future linear collider. The particle astrophysics effort will rest on a foundation of GLAST, soon to be launched for a 5–10 year observing program, and LSST, as well as exploration of exciting opportunities in a next generation ground-based gamma-ray observatory. Accelerator research will vigorously pursue ILC development and a broader suite of high gradient and far-field plasma wakefield acceleration techniques. The end of B Factory operations thus signals the beginning of a process of re-inventing the role of SLAC as a national user laboratory for HEP. This program will be, as always, driven by exciting science opportunities aligned with the national program. Turning the page therefore represents both an opportunity to savor the accomplishments of the B Factory, while also marking a new beginning for the SLAC HEP program.

—Persis Drell, SLAC Today, April 11, 2008