## Measurement and QCD Analysis of Neutral and Charged Current Cross Sections at HERA |

The H1 experiment at HERA was designed to measure the details of proton sub-structure at the very highest energies using positrons (e

The NC and CC cross section data in e^{+}p and e^{-}p
scattering are complementary in probing different types of
quark inside the proton.
In this paper, the H1 experiment has been used to explore
this complementarity. The huge kinematic coverage of the
high Q^{2} data, together with equally precise recent
low Q^{2}
data have allowed a determination of the
behavior of *quark* and
*gluon* *parton distribution functions * (PDF),
using H1 data alone. Five components of proton structure are extracted
simultaneously. The first is the * up-type * quark density, U,
corresponding
to up quarks together with their heavier cousins, the charm quarks. Secondly,
there is the * down-type * quark density, D, corresponding to the sum of
down and strange quarks. The * anti-up-type * (Ubar) and
* anti-down-type * (Dbar) quarks make up the third and fourth components.
The fifth type is the gluons that bind the proton together.
The resulting PDFs are shown in the figure.
They are compared with those obtained
by the MRST and CTEQ groups, who perform global fits to deep-inelastic
scattering data together with various other results.
The comparison is remarkably good, given
the many differences in terms of the data sets used, the theoretical
input and the assumptions made.

The NC photon exchange process
measures the sum of all quark densities weighted by their
squared charges. On the other hand,
* Z * exchange and its
quantum-mechanical interference with the photon measures the
difference between quarks and anti-quarks.
Furthermore, the dominant components of the * Z * exchange and
interfernce contributions act with opposite sign for positron and electron
scattering and can therefore be separated from photon exchange by comparing
data from the two beam charges.
These properties were exploited in an
earlier H1 publication
to make a first measurement of the *xF _{3}*
structure function, which basically measures the

The NC analysis analysis is extended to lower energies of the scattered
electron than has previously been possible. This has allowed a determination
of the longitudinal structure function, F_{L}, for the first time in
this large momentum transfer range. The results are fully consistent
with the prediction for F_{L} obtained from the PDFs extracted in
the fit to the full data.

*Last Update 04.04.2003*