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Dorfan Today: Physics at its Best

Last Tuesday, the BaBar experiment announced a major result: for the first time ever, they had seen neutral D-mesons transition into anti-neutral D-mesons. The existence of this process, also referred to as "D mixing," has been the subject of debate by physicists for over thirty years and many current and former high-energy physics experiments have searched for it. The observation of such a rare event is a testament to the tremendous efforts of both the BaBar researchers and the SLAC accelerator staff. Without the impressive performance of the PEP-II accelerator and the Babar detector, and the superb caliber of the Babar physics analysis teams, this result would not have been possible.

So what is the value of this new result?

The Standard Model of particle physics, which describes so successfully the ordinary matter particles and the fundamental interactions between them, is one of the greatest scientific triumphs of the twentieth century. The Model resulted from the intimate interplay of ground-breaking discoveries (many made at SLAC) and brilliant theoretical insights and strategies. Notwithstanding its remarkable success at describing the luminous (as opposed to dark) realms of our vast Universe, we know that the Standard Model cannot be fully correct. Ever more precise measurements and/or the elucidation of yet unobserved phenomena (like BaBar's first observation of D mixing), allow us to probe the Model yet more incisively. This new result leaves open an intriguing question about the origin of the effect. Is it due to the known physics of the Standard Model, or is it due to new processes previously unseen? Knowledge builds on knowledge, and in the coming months, we are likely to see a flurry of new theoretical work from researchers worldwide to interpret these observations. Allied and confirming measurements from other high-energy experiments, such Belle at KEK and CLEO at Cornell, will soon add crucial information to help increase our understanding.

This is physics at its best: while it is exciting to "be the first" to produce a new result, the ultimate value of our research is in understanding Nature at an increasingly deeper level, and a collaborative effort is now launched to interpret the repercussions of the BaBar result. While it is too soon to know if the level of D mixing being observed requires new physics or not, the Babar observation has thrust this issue front and center on our ever-inquisitive minds... so stay tuned.

The D-mixing result from BaBar is but one more telling example of what we can expect to learn from the Babar data. There is an immense dataset already established by the experiment and, by the end of 2008, we will double it. Our colleagues at KEKB and Belle have amassed an equivalently huge dataset, and are likewise in the process of doubling it. Notwithstanding the prodigious publication rate of the Babar experiment (about one journal paper a week), in reality the collaboration has only skimmed the surface of this vast ocean of data. Trawling the data will continue for many years after the end of data taking in 2008 and who knows what treasures will be netted. As I said before, knowledge builds on knowledge, and the results from the operating Tevatron at FNAL and from the Large Hadron Collider at CERN, expected to begin data-taking in 2008, will help tease out secrets still buried in the two huge B Factory datasets. New information will guide us towards new methods and directions of navigating through this wonderful resource.

SLAC, as always, is keeping up the pressure on the boundaries of understanding and the huge store of data from BaBar guarantees many more years of stress for the Standard Model.

—Jonathan Dorfan, March 19, 2007