B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 1/19 Welcome to Lepton Moments 2006! B. Lee Roberts Department of Physics.

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 1/19

Welcome to Lepton Moments 2006!

B. Lee RobertsDepartment of Physics

Boston University

http://g2pc1.bu.edu/lept06

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 2/19

Magnetic Dipole moments started with a proposal by Otto Stern to study space quantization:

Z. Phys. 7, 249 (1921)

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 3/19

First Result from Otto Stern and Walter Gerlach

Z. Phys. 8, 110 (1922)

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 4/19

ohne Magnetfeldmit Magnetfeld

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 5/19

(in modern language)

(and in English)

By 1924 they had published 3 papers plus this review article.

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 6/19

Phipps and Taylor found the same effect in Hydrogen

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 7/19

Dirac Equation Predicts g=2

Non-relativistic reduction of the Dirac Equation for an electron in a weak magnetic field.

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 8/19

But … the hydrogen hyperfine structure not as expected …

Phys. Rev. 71, 914 (1947)

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 9/19

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 10/19

Kusch and Foley, PR 72, 1256 (1947), gs ≠ 2 ???

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 11/19

SchwingerThe new Hamiltonian is superior to the original one in essentially three ways:

•it involves the experimental electron mass, rather than the unobservable mechanical mass;

•an electron now interacts with the radiation field only in the presence of an external field…

•the interaction of an electron with an external field is now subject to a finite radiative correction.

These discrepancies can be accounted for by a small additional electron spin magnetic moment.

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 12/19

Dirac + Pauli moment

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 13/19

Radiative corrections change g

Dirac Stern-Gerlach

Schwinger Kusch-Foley

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 14/19

Beyond The SM Value for electron and muon anomalies?

e vrs. : relative contribution of heavier things

e,

e*,

e,

e,

e,

e, e,

e,

e,

e,e,?S

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 15/19

Electric and Magnetic Dipole MomentsPhys. Rev. 78 (1950)

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B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 17/19

Transformation Properties of Electric and Magnetic Dipole Moments

An EDM implies both P and T are violated. An EDM at a measureable level would imply non-standard model CP.

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 18/19

However, it should be emphasized that while such arguments are appealing from the point of view of symmetry, they are not necessarily valid.

Ultimately the validity of all such symmetry arguments must rest on experiment.

Phys. Rev. 109, 225 (1958)

B. Lee Roberts, Welcome and Overview – Lepton Moments 2006 - 19 June 2006 - p. 19/19

Norman Ramsey –

A brief History of the search for a permanent EDM of the neutron