Ralph** Sinkus**, Dissertation, Fachbereich Physik der Universität Hamburg, 1996 :
## "Measurement of the Proton Structure Function F_{2} from the 1994 HERA Data using a Neutral Network for the Identification of the Scattered Lepton"

#### Summary

The proton structure function *F*_{2} is measured from deep inelastic positron-proton scattering in the kinematic range 5 ≤ *Q*² ≤ 40 GeV² and 1 · 10^{-4} ≤ *x* ≤ 6 · 10^{-3} using the '94 ZEUS data. This measurement extends the kinematic region so far studied to lower values of *x* and *Q*². For the event selection a neural network is used which efficiently identifies the scattered positron in the final state and reduces the contribution from background events significantly. For the training of the neural network a new approach to error function minimization is developed. When compared to the *F*_{2} measurement using the '93 ZEUS data the errors on the *F*_{2} are typically reduced by a factor 2. It is further shown that the value of the predicted power behavior of *F*_{2} as a function of the *x* at fixed *Q*² from the BFKL leading-order approximation does not match the data for 5 ≤ *Q*² ≤ 40 GeV² when fitting a function *F*_{2} ∼ *x*^{-λ}. The double-leading-logarithmic approximation of the DGLAP evolution equation reproduces the *Q*² behavior of λ within errors. The predicted *Q*² behavior of *F*_{2} at fixed values of *y* from the BFKL and the DGLAP evolution equations are compared and shown to differ significantly in their curvature. It is demonstrated that the current errors on *F*_{2} need to be reduced by at least an additional factor 2 at lower *Q*² and by a factor ∼ 4 at larger *Q*² to uniquely distinguish between the predicted behavior of *F*_{2} from both evolution equations.