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This chapter begins by covering: kinematics for fixed target and HERA collider experiments; essential features of DIS experiments and detectors; and how DIS events are selected and the raw data corrected to give cross-sections. It then summarizes nucleon structure function data from the classic DIS experiments, including some early HERA data. The next topics covered are measurement of the longitudinal structure function and the contribution of heavy flavours (particularly charm) to the proton structure function. The chapter ends with a brief account of structure function data — viewed as virtual-photon proton cross-sections — in the ‘transition region’ between photoproduction and deep inelastic scattering.

This chapter outlines the extensions to the formalism to allow for W and Z exchange at high Q² in NC and CC processes, and to allow for polarization of the electron or positron beams. The extensions for the unpolarized case are treated first, paying particular attention to the relationships of the structure functions to the PDFs via the electroweak couplings. High-Q² HERA data are then discussed and the importance of their contribution to determining PDFs outlined. The next section extends the formalism to NC and CC processes with polarized electrons or positrons. This is followed by an outline of contribution of HERA data to the precision measurement of electroweak parameters. An appendix gives more detail on the formalism for high-Q² NC DIS.

This chapter presents the determination of structure functions and parton distributions from deep inelastic lepton-nucleon scattering, both for the case of charged lepton-nucleon and the case of neutrino-nucleon scattering. The focus is on the results obtained by the HERA experiments. The direct measurements as well as the indirect extraction of the gluon density from scaling violations are discussed. Information obtained from sum rules and from hadron-hadron scattering is briefly summarized, followed by a discussion of global QCD fits of the parton densities based on all available information.

Paul Broca observed that in a series of patients with aphasia, a condition which causes a loss of language, there was a concomitant paralysis of the right side of the body. At first it was often assumed that these individuals were left-handed — in effect restoring some form of conceptual symmetry to an otherwise asymmetric brain. The precise nature of hemispheric specialisation is still far from clear, and is complicated by a number of observations. A complete and adequate theory of cerebral lateralisation must not only explain how and why language is typically located in the left hemisphere and visuo-spatial processing of complex images is typically located in the right hemisphere. The chapter adds that the so-called HERA model, hemispheric encoding/retrieval asymmetry, poses many problems for neuropsychology and, given the importance of semantic memory in language usage, those questions are likely also to be important for understanding the evolution of language. In addition, the chapter discusses the nature of handedness.

Quantum chromodynamics the quantum gauge theory of strong interactions is presented: SU(3) being the (colour) symmetry group. The colour content of strongly interacting particles is described. Gluons, the field particles, carry colour so that they mutually interact – unlike photons. Renormalization leads to the coupling strength declining at large four momentum transfer squared q² and to binding of quarks in hadrons at small q². The cutoff in the range of the strong interaction is shown to be due to this low q² behaviour, despite the gluon being massless. In high energy interactions, say proton-proton collisions, the initial process is a hard (high q²) parton+parton to parton+parton process. After which the partons undergo softer interactions leading finally to emergent hardrons. Experiments at DESY probing proton structure with electrons are described. An account of electroweak unification completes the book. The weak interaction symmetry group is SU_L(2), L specifying handedness. This makes the electroweak symmetry U(1)⊗SUL(2). The weak force carriers, W^± and Z⁰, are massive, which is at odds with the massless carriers required by quantum gauge theories. How the BEH mechanism resolves this problem is described. It involves spontaneous symmetry breaking of the vacuum with scalar fields. The outcome are massive gauge field particles to match the W^± and Z⁰ trio, a massless photon, and a scalar field with a massive particle, the Higgs boson. The experimental programmes that discovered the vector bosons in 1983 and the Higgs in 2012 are described, including features of generic detectors. Finally puzzles revealed by our current understanding are outlined.