The Form Factors of the Nucleons: Present Status - Fisica
The Form Factors of the Nucleons: Present Status - Fisica
The Form Factors of the Nucleons: Present Status - Fisica
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Two-photon exchange is next term to <strong>the</strong> Born approximation. Affects<br />
form factor observables through interference between <strong>the</strong> single- and<br />
two-photon processes. Requires third form factor, and modification <strong>of</strong><br />
G Ep and G Mp .<br />
with:<br />
u(p, λN) (GM γμ − F2Pμ /M + F3 γ·K Pμ /M2 ~ ~<br />
) u(p, λN) ~ ~ ~ ~<br />
GM = GM + δGM, and GE = GE + δGE, YM ≡ Re (δGM/GM); YE ≡ Re (δGE/GM); Y3≡ (ν/M2 Define<br />
~<br />
~<br />
) Re (F3/GM) <strong>The</strong>n, in double-polarization experiments, <strong>the</strong> measured Pt/Pl ratio<br />
Contains 3 additional terms from two-photon exchange<br />
P /P =<br />
t l<br />
2ε<br />
τ(1+<br />
ε)<br />
<br />
<br />
<br />
<br />
<br />
G<br />
M<br />
E<br />
G<br />
+ Y<br />
E<br />
<br />
2/17/2013 C.F. Perdrisat SAEMP Trento 2013<br />
43<br />
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<br />
G<br />
M<br />
E<br />
G<br />
<br />
<br />
<br />
<br />
<br />
Y<br />
M<br />
+<br />
1<br />
2ε<br />
1+<br />
ε<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
G<br />
M<br />
E<br />
G<br />
<br />
<br />
<br />
<br />
<br />
Y<br />
3
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