More is Less!

Control-room-225x300 Aidan Randle-Conde over at Quantum Diaries:

Life is full of uncertainty. And so is particle physics. No matter how sophisticated our models are or how good our understanding is there are still things we don’t know. This is research after all. Uncertainty is a huge part of everything we do.

Every time we make a measurement of anything, we have to give in our result, by saying “It’s this much, give or take that much”, and we refer to the “that much” as the uncertainty. (This has nothing to do with the famous Heisenberg uncertainty!) There are four main sources of uncertainty in our measurements:

– Statistical uncertainty
– Model dependent uncertainty
– Uncertainty from other measurements
– Systematic uncertainty

The statistical uncertainty simply comes from having low numbers of events to work with and we can reduce this uncertainty by recording more data. This is why we love luminosity so much, and why we spend thousands of hours babysitting the detector.

The model dependent uncertainty comes from our choice of physical model and usually limited by how well we can simulate different models of physics. For a lowly experimental physicist like me the best thing to do is ask the theorists for these uncertainties. They’re often larger than we’d like, but that’s the price we pay for having access to cutting edge models.

The uncertainty from other measurements is usually included when we expect another measurement to more precise in the future. (We can hope!) A good example is the uncertainty on luminosity. As our understanding of the detector improves, this uncertainty can decrease.

The final uncertainty, the systematic uncertainty, is the one that keeps physicists awake at night.