Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Single-nucleon experiments   We discuss the Jefferson Lab low momentum transfer data on moments of the
nucleon spin structure functions $g_1$ and $g_2$ and on single charged pion
electroproduction off polarized proton and polarized neutron. A wealth of data
is now available, while more is being analyzed or expected to be taken in the
upcoming years. Given the low momentum transfer selected by the experiments,
these data can be compared to calculations from Chiral Perturbation theory, the
effective theory of strong force that should describe it at low momentum
transfer. The data on various moments and the respective calculations do not
consistently agree. In particular, experimental data for higher moments
disagree with the calculations.The absence of contribution from the $\Delta$
resonance in the various observables was expected to facilitate the
calculations and hence make the theory predictions either more robust or valid
over a larger $Q^2$ range. Such expectation is verified only for the Bjorken
sum, but not for other observables in which the $\Delta$ is suppressed.
Preliminary results on pion electroproduction off polarized nucleons are also
presented and compared to phenomenological models for which contributions from
different resonances are varied. Chiral Perturbation calculations of these
observables, while not yet available, would be valuable and, together with
these data, would provide an extensive test of the effective theory.

23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
28
The categories of this paper are: alg-geom