10 - H1 - Desy

Chapter 1
Theoretical framework
This chapter introduces the theoretical basis needed for the understanding of prompt
photon production in photoproduction. In sections 1.1 and 1.2 the theoretical introduction
to the Standard Model and the electron-proton scattering is given. Prompt photon
theory and summary of recent studies is presented in sections 1.3 and 1.4. The chapter is
finished with discussion of the prompt photon analysis motivation. Finally, the goals for
the described work are defined in section 1.5 setting the foundament for the discussion
following in next chapters.
1.1 The standard model
The Standard Model (SM) is the experimentally well-tested theory of the particle physics
based on fundamental particles and their interactions. Within this model, fundamental
particles can be classified according to three basic types: quarks, leptons and gauge bosons
(the carriers of force). The quarks and leptons, which in turn are divided into three
generations, are members of a family of particles called fermions (particles with half
integer spin). The properties of these fundamental fermions are summarized in table 1.1.
Experimentally six different types of quarks, known as flavours, have been observed: up
(u), down (d), charm (c), strange (s), top (t) and bottom (b) are grouped into three
generations. The left handed (L) quarks, which have the spin oppositely aligned with the
direction of motion, are grouped into the doublets. The right handed (R) quarks, where
the spin is aligned with the direction of motion, are grouped into singlets.
( ) ( ) ( )
u c t
, , , u
d s b R , d R , c R , s R , t R , b R (1.1)
L
L
L
All visible matter is composed of the first generation particles, e.g. protons and neutrons
are made out of u and d quarks. Quarks have never been observed as free isolated states,
but only exist in bound states, e.g. baryons represent the bound states of three quarks
(qqq), and mesons, the bound state of the quark-antiquark (q¯q) pairs.
Leptons are spin 1/2 particles which can be observed as free particles. Analogous to the