Category: Observation

This weekend, I’ve been taking shifts. Specifically, I’ve filled the position known as “Liaison” during the swing period, from 4 pm to midnight. The Liaison’s job is to facilitate communication between the detector group – BaBar – and the accelerator operators. There is a popular perception in my field, which has some truth, of a historical “rivalry” between these two groups. Accelerator physicists are interested in pushing the machine up in performance, possibly creating a high-background environment not suitable for high-efficiency data-taking. The detector physicists want stable conditions with low backgrounds, so they can keep their data logging rates reasonable and maintain a low-noise environment for easier data analysis. Liaison’s job is to pass concerns between the groups, and settle matters of dispute if they arise.

Shifts are the way you get close to your experiment if, like me, you were an undergrad on a different experiment when this one was built. Combined with my detector role, I have not felt this close to BaBar since my last detector service role. It’s refreshing, not only to be reminded where you data really comes from, but to play a modest role in making it happen.

It’s always a little painful. You have to eat questionable food from Safeway, or Quiznos. You drink some coffee, then too much, so that by the time you get home all you can do is think about are diamond sensor background rates while not sleeping. You’re a little too groggy in the morning, a little too sharp in the afternoon. During the quiet moments, when the operators are engrossed in tune space or bunch patterns, you fill the time with work you should have done during the week or the occasional odd posting in the electronic log.

Above all, however, you’re reminded about what a talented crew of people make it possible to probe the frontier of nature. For a moment, you might even get to be part of that crew.

A few months ago, the television program “Mythbusters” tackled a series of baseball myths, ranging from whether a corked bat makes a difference to the performance of a hitter, to whether sliding into a base is faster than just slowing down and landing on it. Overall, I was pretty impressed with the experiments they devised. More than once, the Mythbusters remarked on how the data they were collecting were the real story, where the real science happens. That kind of recognition of the importance of gathering and analyzing data warms my heart.

One myth they tried to tackle was the following: it’s possible to knock the hide off a baseball in a normal pitching/hitting environment. In their setup, they loaded baseballs into an air cannon and fired them at a stationary bat. The technical reason for doing so, I suspect, was that this pitching/hitting rig was not wholly reliable and the precision timing needed to hit the faster pitches was beyond the rig’s capability. They concluded from this setup – fast ball, fixed bat – that it was not possible to knock the skin off a baseball under normal conditions. In their experiment, the ball had to be traveling at about 437 mph in order to lose its skin after striking the bat.

As a particle physicist, I see this as a unique opportunity to think about fixed-target vs. colliding beam experiments. When you’re attempting to go for raw collision energy, without expending more energy than is necessary in any one part of the experiment, you should go for a “colliding beam” experiment. This is when both the target and the bullet are moving toward one another, relative to the reference frame of the laboratory. In baseball, the lab frame is the stadium, and in that frame we know that the bat and the ball are both moving when the ball gets hit.

Colliding beam experiments are typically held in contrast to the “fixed-target” experiment, in which the target is stationary (in the lab frame) and the bullet is moving. The Mythbusters conducted the experiment which doesn’t happen in baseball (unless the hitter bunts): they fired baseballs at a stationary, rather than a moving, bat. Could this explain why they concluded that the pitcher would have to be super-human in order to get the energy needed to part hide from baseball?

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