View of the Tevatron at Fermilab. (Image courtesy of Fermilab)
By James Dacey
With the sheer scale of its machinery and its extensive international collaborations, accelerator physics is now a highly visible part of mainstream science. A recent episode at Fermilab reminded me, however, that the scientific results could never be as clear-cut as the facilities that produced them. I couldn’t help but feel a little bit frustrated by this, but perhaps that says more about my short concentration span.
Earlier this week, we reported new findings from Fermilab’s D0 experiment, which claimed to have gathered the strongest evidence yet for CP violation beyond the Standard Model. CP violation helps to explain the fundamental difference between the behaviour of a particle and its antiparticle. It explains why matter survived in the universe after the Big Bang, when matter and antimatter were created in equal amounts and should have annihilated completely.
So as you can see the implications of this research were fairly humongous. Hence physicsworld.com and a whole load of other sites covered the story.
However, last Monday – without us realizing – a rival experiment at the Tevatron had already poured cold water on the D0 celebrations by saying that the results were void. Let me explain.
D0 had looked for asymmetry in the production of muons from the decay of B mesons and anti B mesons, and they reported a CP violation that was 3.2 standard deviations larger than what is predicted by the Standard Model.
The particle physics community got very excited because their results had included decent measurements, for the first time, of the decay of Bs mesons, which theorists have long touted as an excellent place to look for CP violation. It seemed that the physics was finally moving beyond the Standard Model.
But before D0 had time to wind down their celebrations, Gavril Girgiu of the CDF experiment was in Turin addressing a particle physics conference about the CDF analysis of the same meson decays. The difference was that CDF had seen nothing out of the ordinary in their results, and their sample size was twice as large – from 5.2 femtobarn of Bs decays, they record CP violation that is within 0.8 standard deviations of the Standard Model.
Now, don’t get me wrong here. I fully realize that experimental physics can only ever move forwards by the proposition of new phenomena followed by its confirmation by other experiments. But, given the expectation that surrounds particle physics – fuelled largely by the high profile of its facilities – I just couldn’t help but feel a bit frustrated by these events. It was just a reminder that despite all the exciting questions and mind-blowing implications of particle physics, the real science so often boils down to more mundane concepts like statistical significance.
Perhaps there is a better way for the particle physics community to communicate that this part of the science can be fun too?
The danger is that people like me, who are intrigued by this weird and fascinating area of science, have come to expect every new result to be as certain as the facilities that have produced them.