Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session Y10: Invited Session: History of the G2 from 1947 to Present |
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Sponsoring Units: FHP DPF Chair: Robert Crease, Stonybrook University Room: 204 |
Tuesday, April 8, 2014 1:30PM - 2:06PM |
Y10.00001: Study of Electron G-2 From 1947 To Present Invited Speaker: Toichiro Kinoshita In 1947 Kusch and Foley discovered in the study of Zeeman splitting of Ga atom that the electron g-factor was about 0.2\% larger than the value 2 predicted by the Dirac equation. Soon afterwards Schwinger showed that it can be explained as the effect of radiative correction. His calculation, in the second order perturbation theory of the Lorentz invariant formulation of renormalized quantum electrodynamics, showed that the electron has an excess magnetic moment $a_e \equiv (g-2)/2 = \alpha/(2\pi)$, where $\alpha$ is the fine structure constant, in agreement with the measurement within 3\%. Thus began a long series of friendly competition between experimentalists and theorists to improve the precision of $a_e$. Over the period of more than 60 years measurement precision of $a_e$ was improved by more than $10^4$ by the spin precession technique, and further $10^3$ by the Penning trap experiments. In step with the progress of measurement, the theory of $a_e$, expressed as a power series in $\alpha$, has been pushed to the fifth power of $\alpha$. Including small contributions from hadronic effects and weak interaction effect and using the best non-QED value of $\alpha$: $\alpha^{-1} = 137.035 999 049 (90)$, one finds $a_e (theory) = 1 159 652 181.72 (77) \times 10^{-12}$. The uncertainty is about $0.66~ppb$, where $1~ppb = 10^{-9}$. The intrinsic uncertainty of theory itself is less than $0.1~ppb$. The over all uncertainty comes mostly from the uncertainty of non-QED $\alpha$ mentioned above, which is about $0.66~ppb$. This is in good agreement with the latest measurement: $a_e (experiment) = 1 159 652 180.73 (28) \times 10^{-12}$. The uncertainty of measurement is $0.24~ppb$. An alternate approach to test QED is to assume the validity of QED (and the Standard Model of particle physics) and obtain $\alpha$ by solving the equation $a_e (experiment) = a_e (theory)$. This yields $\alpha^{-1} (a_e) = 137.035 999 172 7 (342)$, whose uncertainty is $0.25 ~ppb$, better than $\alpha$ obtained by any other means. Although comparison of theory and experiment of $a_e$ began historically as a test of the validity of QED, it has now evolved into a precision test of fine structure constant at the level exceeding $1~ppb$, which may be regarded as a test of internal consistency of quantum mechanics as a whole. [Preview Abstract] |
Tuesday, April 8, 2014 2:06PM - 2:42PM |
Y10.00002: The First CERN Muon g-2 Experiment Invited Speaker: Richard Garwin The Summary of the 16 June 1965 publication of this experiment in \textit{Il Nuovo Cimento} reads, ``The anomalous part of the gyromagnetic ratio, \textbf{a }$\equiv $ 1/2 (g-2) of the muon has been measured by determining the precession $\theta ~=$~\textbf{a}$\omega_{0}$$B^{\mathrm{-}}t$ for 100 MeV/c muons as a function of storage time $t$ in a known static magnetic field of the form $B$~$=$~$B_{0}$(1$+$\textit{ay}$+$\textit{by}$^{2}+$\textit{cy}$^{3}+$\textit{dy}$^{4})$. The result is \textbf{a}$_{exp}$~$=$~(1162 $\pm$ 5) $\cdot$ 10$^{-6}$ compared with the theoretical value \textbf{a}$_{th}$~$=$~$\alpha $/2$\pi +$0.76$\alpha ^{2}$/$\pi^{2}$ $=$ 1165 $\cdot$ 10$^{-6}$. This agreement shows that the muon obeys standard quantum electrodynamics down to distances $\sim$ 0.1 fermi. Details are given of the methods used to store muons for $\sim$ 10$^{3}$ turns in the field, and of measuring techniques and precautions necessary to achieve the final accuracy. Some of the methods of orbit analysis, magnet construction shimming and measurement, polarization analysis, and digital timing electronics may be of more general interest.'' The paper is available in full at http://www.fas.org/rlg/060065{\%}20Nuovo{\%}20Cimento.pdf The authors valued highly the presentation of experimental details, which will be the emphasis of this talk, recounting the motivation of choices made with the tools and technology of that era. [Preview Abstract] |
Tuesday, April 8, 2014 2:42PM - 3:18PM |
Y10.00003: The BNL Muon G-2 Experiment And Beyond Invited Speaker: Yannis Semertzidis |
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