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This thesis will focus on quarks and gluons, which are the only particles in the SM that directly experience the strong nuclear force. There are six types, or flavours of quarks: up ( u ), down ( d ), strange ( s ), charm ( c ), bottom ( b ) and top ( t ). These can be divided into light quarks ( u , d , s ) and heavy quarks ( c , b , t ), which have much greater masses than the light quarks (masses are given in Table 1.3). Gluons are massless and serve as the mediators of the strong interaction. Interestingly, quarks and gluons only occur within hadrons, and cannot be isolated or otherwise removed from hadrons. This peculiar feature of the strong interaction is known as confinement, and understanding how it emerges from QCD is one of the great problems of modern physics. All approaches to this problem must invariably deal with hadrons, which are how quarks and gluons manifest themselves in nature. 

## 1.2.2 The Quark Model 

In 1964, Gell-Mann [51] and Zweig [131] independently introduced the quark model, which proposes that hadrons are not fundamental particles. Rather, they are composite objects composed of more fundamental particles, which Gell-Mann called quarks. At the time, all known hadrons could be explained in terms of just three types of quarks ( u , d , s ), and their 

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