The Personal Blog of Stephen Sekula

Seeing what is not visible

What a week. Busy, busy, busy! Let’s start at the beginning.

BaBar is engrossed in its fifth run, which we aptly denote “Run 5”. A lot of things changed in the accelerator and detector when we shutdown for the 2004 upgrade last fall. It’s critical, given such changes, to validate the outpouring data by applying hard physics analysis to it. That’s what BaBar has been doing for weeks now. This week, MIT student Yi and me used his sample of D*+ –> pi+ D0 –> K pi+ pi pi+, which has inherently HUGE statistics, to understand the BaBar tracking system. Along with other measurements that have been or are being made, we are coming to an understanding of our new efficiencies in this Run.

Out of sheer interest, I decided to see if I could spot differences in our tracking system between Run 3 and Run 5 by imaging our detector. How do you do this, when you can’t crack it open or go and x-ray it from the outside? Simple: x-ray it from the inside. One of the properties of the quantum of light, the photon, is that in the presence of matter it can produce a electron-positron pair. Since this must happen in material, you can “see what cannot be seen” by looking for the emerging electron and positron and tracking their trajectories back to their point of origin. Thus, one can radiograph the inner detector system. See the sample image below:

Finally, the Congress passed the Energy Policy act of 2005. This is the first time both houses of Congress have agreed, on schedule, on a comprehensive energy policy for the nation. This is also the first time the energy bill hasn’t had to be rolled into an omnibus bill, to be passed en masse, or passed well beyond the fiscal year deadline, for at least two years. I’m still waiting to see the final text of the post-conference bill, the one actually passed by both houses.