Chromo-dynamics PHYS328 Term Project Sertaç balatlı Middle East Technical University may 17, 2019 Sertaç balatlı (METU)Chromo-dynamicsMay 17, / 20

Content 1 Introduction brief of standart model color charges Confinement Asymptotic Freedom 2 Conclusion Conclusion Chromo-dynamics Sertaç balatlı (METU)2 / 20

IntroductionHistorical view The idea of chromo-dynamics * Quantum chromadynamics shortly called QCD is the modern theory of strong interaction. Historically bases of QCD are description of ordinary matter,what protons and neutrons are made of, how they interact. **In 1973 the concept of colour as the source of a “strong field” was developed into the theory of QCD by European physicists Harald Fritzsch and Heinrich Leutwyler, together with American physicist Murray Gell-Mann. ( Nobel Prize at 1969) *** In 2004 Nobel Prize in Physics David J. Gross (University of California, Santa Barbara), David Politzer (Caltech) and Frank Wilczek (MIT) were honored "for the discovery of asymptotic freedom in the theory of the strong interaction Chromo-dynamics May 17, 2019 Sertaç balatlı (METU)3 / 20

Standart model Brief of standard model * the standard model which is the model of fundamental structure of matter: everything in the universe is found to be made from a few basic building blocks called fundamental particles, governed by four fundamental forces,insight into the Our best understanding of how these particles and three of the forces are related to each other is encapsulated in the Standard Model of particle physics. The roots of the model based of in 1930s theories and discoveries in physics like quantum mechanics. Developed in the early 1970s, it has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Over time and through many experiments, the Standard Model has become established as a well-tested physics theory. Chromo-dynamics Sertaç balatlı (METU)May 17, 2019

Standart model The theory Chromo-dynamics May 17, 2019 Emircan Elikkaya (METU)5 / 20 Fermions: which are particles consist of quarks and leptons. there are twelve fermions which can be considered as the particle building blocks of matter. The name of fermion comes from Italian physicist Enrico Fermi and they obey a statistical rule described by him

Standart model The theoryThe theory Quarks : The word "quark" originally cames from in the the novel Finnegans Wake written by the Irish author James Joyce (1882–1941). The protagonist of the book is a publician named Humphrey Chimpden Earwicker who dreams that he is serving beer to a drunken seagull. Instead of asking for "three quarts for Mister Mark" the inebriated bird says "three quarks for Muster Mark". Because the pre-standard model theory was complete with only three quarks, the name made some sense. The full standard model today needs six quarks. The six flavors of quarks are named as up, down, strange, charm, top, and bottom. Sertaç balatlı (METU) Chromo-dynamics May 17, / 20

Standart model The theoryThe theory Leptons: leptons are the other six fermions, the name derived from the Greek word λεπτός (leptos) meaning thin, delicate, lightweight, or small. These particles don't need to bind to each other, Originally leptons were considered the "light" particles and the hadrons as the "heavy" particles, but the discovery of the tau lepton in 1975 broke that rule. The tau (the heaviest lepton) is almost twice as massive as a proton (the lightest hadron). Chromo-dynamics Emircan Elikkaya (METU)May 17, / 20 Sertaç balatlı (METU)

Standart modelThe theory Chromo-dynamics Sertaç balatlı (METU)May 17, / 20 Bosons: Boson is a type of particle that obeys the rules of Bose-Einstein statistics. These bosons also have a quantum spin with contains an integer value, such as 0, 1, -1, -2, 2, etc. The name boson comes from the surname of Indian physicist Satyendra Nath Bose Bosons are sometimes called force particles, because it is the bosons that control the interaction of physical forces, such as electromagnetism and possibly even gravity itself.

Standart modelThe theory Chromo-dynamics Sertaç balatlı (METU)May 17, / 20

color charges The new kind of charges’ color charges’ The proton and the neutron are composite and built up of quarks which has been known since the 1960s. However, strangely enough, it was not possible to produce free quarks. Today we know there are six different kinds, or “flavors,” of quarks— denoted u, d, s, c, b, and t, for: up, down, strange, charmed, bottom, and top. Of these, only up and down quarks play a significant role in the structure of ordinary matter. The other, much heavier quarks are all unstable. Quarks have electric charges which are a fraction of the proton’s, –1/3 or +2/3, a strange feature which has not yet been explained. Each quark, in addition to an electric charge, also has a special property which, like its electric charge, is quantized, that is, it can only take on certain values. This property is called color charge, owing to its similarity to the concept of color. Chromo-dynamics Sertaç balatlı (METU) May 17, / 20

color charges Chromo-dynamics Sertaç balatlı (METU)May 17, / 20 A quark of any one of the six flavors can also carry a unit of any of the three color charges red, blue or green. For every quark there is an antiquark in the same way as the electron has an antiparticle, the positron. Antiquarks have the color charges antired, antiblue or antigreen. Aggregates of quarks, which can exist freely, are color neutral.

color charges Sertaç balatlı (METU) May 17, / 20 ** The three quarks in the proton (u, u and d) have different color charges so that the total color charge is white (or neutral). In the same way as electrically neutral molecules can form bonds (through the attraction between their positive and negative parts) the exchange of force between protons and neutrons in the nucleus occurs through the color forces that leak out from their quarks and force-carrying particles. Although the different quark flavors all have different masses, the theory is perfectly symmetrical with respect to the three colors. This color symmetry is described by the Lie group SU(3).

What is the Evidence for Color? One of the most convincing arguments for color comes from a comparison of the cross sections for the two processes: If we forget about how the quarks turn into hadrons then the graphs (amplitudes) for the two reactions only differ by the charge of the final state fermions (muons or quarks). We are assuming that the CM energy of the reaction is large compared to the fermion masses. color charges * If color plays no role in quark production then the ratio of cross sections should only depend on the charge (Q) of the quarks that are produced. **However, if color is important for quark production then the above ratio should be multiplied by the number of colors (3).

color charges *For example, above b-quark threshold but below top-quark threshold we would expect:

**SU(3) is the group of 3 × 3 unitary matrices with determinant 1. This is the symmetry group of the strong force. What this means is that, as far as the strong force is concerned, the state of a particle is given by a vector in some vector space on which elements of SU(3) act as linear (in fact unitary) operators. We say the particle "transforms under some representation of SU(3)". For example, since elements of SU(3) are 3 × 3 matrices, they can act on column vectors by matrix multiplication. This gives a 3-dimensional representation of SU(3). Quarks transform under this representation of SU(3), and because it's 3-dimensional we say quarks come in 3 colors: red, green and blue. This is just an amusing way of talking about the 3 column vectors SU(3) Sertaç balatlı (METU)

SU(3)

Confinement and Asymptotic Freedom In QCD we know that strong force decreases at very small quark-quark separation asymptotic freedom strong force increases as quarks are pulled apart. quark confinement Experimental Evidence for confinement *Did not observe free quarks **Quarks confined within hadrons

Strong Interaction Dynamics Gluons attract each other - self-interactions Colour force lines pulled together in QCD

References Chromo-dynamics Sertaç balatlı (METU)May 17, / 20