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DATE: 2015 Nov. 12th 15:30-

PLACE:large meeting room, J-PARC research building

TITLE: Muon (g-2) at Fermilab: Preparing for Takeoff

LANGUAGE: English

SPEAKER: Prof. B Lee Roberts
(Boston University)

CONTACT: Prof. Shunzo Kumano, j-parc-pn-seminar-(AT)-ml.post.kek.jp

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Abstract:

Measurements of the magnetic moments of the electron and muon were 

intertwined with the development of the “modern physics” of the 20th 

century. The measurements are expressed in terms of the g-value, the 

proportionality constant between the magnetic moment and the spin, ¥vec{

mu}= g (Qe ¥hbar/2m) ¥vec{s}

For leptons the factor g is greater than the Dirac value of 2 because of 

radiative corrections. Thus g has an anomalous part, g =2(1+ a), or 

equivalently a = (g-2)/2. The anomaly is dominated by the lowest-order (

Schwinger) term, a = α/2π ≃ 0.00116. For the muon it is necessary to 

include contributions from QED, the strong interaction and the 

electroweak gauge bosons. To measure the anomaly, polarized muons are 

injected into a precision magnetic storage ring with average field 

uniformity of one part per million (ppm). The frequency that the spin 

turns relative to the momentum is measured, along with the magnetic 

field felt by the muon beam. The muon anomaly measured at Brookhaven 

appears to be larger than the Standard-Model value by more than three 

standard deviations. To clarify whether this is evidence for New Physics 

or not, Fermilab E989 will reduce the total experimental error from 540 

parts per billion (ppb) to 140 ppb. This requires reducing the total 

systematic error on the muon spin rotation frequency, and the systematic 

error on the magnetic field, each to a precision of 70 ppb. This 

measurement also requires an increase in statistics over the BNL 

experiment by a factor of 21, for a total of 2×1011 analyzed events. The 

precision storage ring has been moved from Brookhaven to Fermilab, and 

is now operational. The magnet shimming has now begun, and detector 

installation is scheduled in mid-2016. Data collection should begin in 

early 2017. I will explain the technique, and the large number of 

improvements that are being employed in the new experiment, and show 

pictures of relocation of the 14 m diameter superconducting coils, and 

the reconstruction at Fermilab.