The calibration system for the E989 experiment at Fermilab

The muon anomaly (g ­ 2)/2 has been measured to 0.54 parts per million by E821 experiment at Brookhaven Lab, and at present there is a 3 to 4 standard deviation difference between the SM and experimental values. A new muon (g ­ 2) experiment, E989, is being prepared at Fermilab that will improve the experimental error by a factor of four to clarify this difference. A central component to reach this fourfold improvement in accuracy is the high­ precision laser calibration system which should monitor the gain fluctuations of the Calorimeter Photodetectors at 0.04% accuracy.