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### Counting experiments

All measurements in particle physics ultimately come down to counting events.  How many events of type X did you see?  Of those, how many have property Y?  What fraction of X events did you miss because your detector is imperfect (it always is), and does that fraction have a dependence on Y?  How often does process Z come into your sample by accident, and does that too depend on Y?  It it through such careful counting, and then accounting, that we find the true production rates and true kinematic distributions, and use them to determine parameters of physical theories.

This week, the United States has been engaged in a set of really huge counting experiments — our federal elections!  According to the numbers I could find, something like 118.76 million people voted for either Barack Obama or John McCain in this year’s general election.  This election turned out to be not especially close, but some others did.  In particular, in the Minnesota Senate race, 1,211,542 people voted for Norm Coleman, and 1,211,206 voted for Al Franken.  That’s a 336-vote difference out of 2,422,748 votes cast for the two of them, 0.014%, and that’s not even worrying about the effects of independent candidate Dean Barkley (437,377).

Compare this to some of the most challenging measurements in particle physics:

W boson mass: 80.398 +- 0.025 GeV (0.031%)

Z boson mass: 91.1876 +- 0.0023 GeV (0.0025%)

Anomalous muon magnetic moment: (11659208 +- 6) x 10^(-10) (0.000051%)

Achieving this level of precision on these measurements has required many years and many graduate students.  And now we’re supposed to do the same in a matter of a few days to get the election results?  Good luck, Minnesota!

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