Quark model 4-20 Aug 2018.pptx

qaurk model

1. The quark model [email protected] 20 th August 2018

2. The Quark Model : 1964 In 1964 Gell-Mann and Zweig independently proposed that all hadrons are in fact composed of even more elementary constituents, which Gell-Mann called quarks. The quarks come in three types (or “ flavors ”), forming a triangular “Eightfold- Way” pattern The Up Quark The Down Quark The Strange Quark  

3. Murray Gell-Mann

4. George Zweig

5. The Quarks The u (for “up”) quark carries a charge of and a strangeness of zero; the d (“down”) quark carries a charge of and ; the s ( “ strange”) quark has and  

6. The antiquark To each quark ( ) there corresponds an antiquark ( ), with the opposite charge and strangeness .  

7. The Quark Model The quark model represents a relatively simple picture of the internal structure of subatomic particles and makes predictions of their production and decay. It uses a minimum of adjusted quark parameters and has great predictive power e.g. for the composite particle : masses, magnetic moments and life times. There are no contradictions to this model known so far , but few questions remains!!!

8. The Quark Model The quark model asserts that Every baryon is composed of three quarks (and every antibaryon is composed of three antiquarks) Every meson is composed of a quark and an antiquark. With these two rules it is easier to construct the baryon decuplet and the meson octet.

9. Baryon decuplet qqq Q S Baryon uuu 2 . Delta ++ uud 1 ... Delta + udd .. Delta neutral ddd -1 ... Delta - uus 1 -1 ... Sigma + uds -1 ... Sigma neutral dds -1 -1 ... Sigma - uss -2 ... Xi neutral dss -1 -2 ... Xi - sss -1 -3 …Omega - qqq Q S Baryon uuu 2 uud 1 udd ddd -1 uus 1 -1 uds -1 dds -1 -1 uss -2 dss -1 -2 sss -1 -3

10. The meson nonet Q S Meson Name Pi - neutral 1 Pion -1 Pion Eta 1 1 Kaon+ 1 Kaon neutral -1 -1 Kaon- -1 Anti-Kaon ? ? Phi Q S Meson Name Pi - neutral 1 Pion -1 Pion Eta 1 1 Kaon+ 1 Kaon neutral -1 -1 Kaon- -1 Anti-Kaon ? Phi

11. The same combination of quarks can result in a number of different particles The delta-plus : and the proton are both composed of ; the and the are both This absurdity can be explained as analogy with the hydrogen atom. As the hydrogen atom (electron plus proton) has many different energy levels, so a given collection of quarks can bind together in many different ways.  

12. H owever the various energy levels in the electron/proton system are relatively close together and hence all of them are represented as “hydrogen ,” The energy spacings for different states of a bound quark system are very large, and hence regarded as distinct particles. Thus, in principle, an infinite number of hadrons can be constructed out of only three quarks.

13. Problems with the Quark model Quark confinement : For reasons not yet known, quarks are absolutely confined within baryons and mesons Even though all quarks are stuck inside hadrons, still, they are accessible to experimental study. When a proton was probed using neutrino beams at CERN - known as “deep inelastic scattering” , most of the incident particles pass right through, whereas a small number bounced back sharply.

14. This means that the charge of the proton is concentrated in small lumps However, in the case of the proton the evidence suggests three lumps instead of one. This is a strong support for the quark model

15. (a) In Rutherford scattering the number of particles deflected through large angles indicates that the atom has internal structure (a nucleus). (b) In deep inelastic scattering the number of particles deflected through large angles indicates that the proton has internal structure (quarks). The dashed lines show what you would expect if the positive charge were uniformly distributed over the volume of (a) the atom, (b) the proton.

16. Mesons are quark anti quark pairs Baryons are quark triplets

17. Theoretical objection to the quark model Quark Model appears to violate the Pauli exclusion principle . According to Pauli’s exclusion principle no two electrons can occupy the same state. However the exclusion principle applies to all particles of half-integer spin . In particular, the exclusion principle should apply to quarks, which carry spin 1/2. is supposed to consist of three identical u quarks in the same state; it (and also the ( ddd ) and the ( sss )) appear to be inconsistent with the Pauli principle.  

18. Along with flavour, quark got the colour( quantum no.) In 1964, O. W. Greenberg proposed a way out of this dilemma He suggested that quarks not only come in three flavours (u, d, and s) but each of these also comes in three colours (“red,” “green,” and “blue,” say). To make a baryon, we take one quark of each colour, then the three u’s in are no longer identical ( one is red, one is green, and one is blue). The exclusion principle applies only to identical particles!!  

19. The November Revolution And Its Aftermath The November Revolution began with the discovery of a new subatomic particle, the J/ψ meson , a particle with an unusually narrow width at 3095 MeV. on November 10, 1974 two groups (one, a MIT group doing experiment on the east coast at Brookhaven National Laboratory, U.S.A. and the other a SLAC- Berkeley group doing experiment on the west coast at Stanford Linear accelerator centre, U.S.A) simultaneously announced the discovery of a new particle at 3095 MeV whose lifetime was about 1000 times longer than that of other particles of comparable mass.

20. Samual Ting at Brookhaven National Laboratory, U.S.A.

21. Burton Richter of SLAC

22. The discovery was announced by both groups together on  11 November 1974 , and the particle's name was combined to in order to acknowledge that both groups had equal parts in its discovery. For this discovery, the heads of both research groups, Burton Richter of SLAC and Samuel Ting of BNL, were awarded the 1976 Nobel Prize in Physics.  

23. Computer reconstruction of a psi-prime decay (the Mark I detector), making a near-perfect image of the Greek letter psi.

24. Till then mesons were discovered, and only three types of quarks: up, down and strange were known. The importance of the J/ψ meson discovery is that it was the first particle discovered that contained a quark never seen before, the charm quark. In fact, this meson is a bound state of one charm quark and one anti-charm quark. The existence of the charm quark was speculated as early as 1964, but this was the first time it was actually seen in an experiment .

25. This discovery sparked a revolution - the November Revolution , named after the month in which the discovery was announced - because it revealed a new path towards understanding the structure of matter, namely, that all hadrons, including the protons and neutrons, were actually composite particles made of quarks . Before that, many physicists were highly sceptic of the quark model, but the discovery of the J/ψ meson managed to convince most of them of the model's validity.

26. In the years following 1974, major advances in particle physics were made. Other composite particles, which were made from a combination of the charm quark and one or two of the up , down and strange quarks, were discovered, which provided even more evidence for the charm quark and the quark model. In 1975, two more quarks - the top and bottom - were hypothesized, and in 1977, the bottom quark was discovered at Fermi Lab.

27. Intermediate Vector Bosons There are three intermediate vector bosons, two of them charged ( and one neutral ( ). Their masses were calculated to be and In January 1983 the discovery of the W with mass was reported by Carlo Rubbia’s and five months later the same team announced discovery of the  

28. Standard Model

29. The Standard Model describes what matter is made of and how it holds together. It rests on two basic ideas: all matter is made of particles, and these particles interact with each other by exchanging other particles associated with the fundamental forces. The basic grains of matter are  fermions  and the force carriers are  bosons . The names of these two classes refer to their spin – or angular momentum. Fermions have half-integer spin whereas bosons have integer values 

30. The Standard Model (SM ) Since the sixties physicists have been looking for new particles. Up to now about 200 particles (most of which are not fundamental) have been discovered and categorized. - 6 quarks - 6 leptons (the best-known lepton is the electron) - Force carrier particles (like the photon) Experiments have verified the SM predictions with high precision and the particles predicted by SM have been experimentally found . BUT…gravity is not included in SM .

31. Standard Model In the current view, all matter is made out of three kinds of elementary particles: leptons, quarks, and mediators . There are six leptons, classified according to their charge (Q), electron number ( Le, muon number ( Lµ), and tau number ( L ). They fall naturally into three families or generations  

32. Standard Model

33. Lepton Classification First Generation Second Generation Third Generation First Generation Second Generation Third Generation

34. There are six antileptons, with all the signs reversed. The positron, for example , carries a charge of +1 and an electron number - 1. So there are really 12 leptons

35. Quark Classification There are six “ flavors ” of quarks, which are classified according to charge (Q), strangeness (S), charm (C), beauty (B), and truth (T ). The quarks also fall into three generations

36. Quark Classification First Generation Second Generation Third Generation First Generation Second Generation Third Generation

37. For every particle there exists its antiparticle and hence we have six antiquarks. All signs are reversed in the table of antiquarks. Every quark and antiquark comes in three colours , so there are ( for quarks for antiquarks 36 of them in all.  

38. Mediators Every interaction has its mediators Photon for the electro- magnetic force Two W’s and a Z for the weak force strong force? Pion ?? The discovery of heavy mesons indicated that, protons and neutrons could now exchange rho’s and eta’s and K’s and phi’s and all the rest of them.

39. The quark model suggested that the mediator can be complicated and the particle which is exchanged between two quarks, in a strong process is called the gluon, and in the Standard Model there are eight gluons. The gluons themselves carry colour , and therefore can not exist as isolated particles. We can detect gluons only within hadrons, or in colourless combinations with other gluons ( glueballs ). The deep inelastic scattering experiments showed that roughly half the momentum of a proton is carried by electrically neutral constituents , presumably gluons

40. Quark “confinement” disallows the presence of free quarks. Only “white” hadrons are allowed. This is a property of the strong interactions. But what happens when a quark-antiquark pair is stretched ? Answer: The colour force field is stretched , until it “snaps ”, producing new quarks

41. The three generations of quarks and leptons, in order of increasing mass.

42. Generations of Matter Mass increases from first generation to the next Going down in each generation, the charges are: +2/3, -1/3, 0, -1 These are all in multiples of the elementary charge

43. The Fundamental Building Blocks

44. The Four Fundamental Forces These forces include interactions that are attractive or repulsive, decay and annihilation. Strong Weak Electromagnetic Gravity

45. Force Strength Theory Mediator Strong 10 Chromodynamics Gluon Electromagnetic Electrodynamics Photon Weak Flavordynamics W and Z Gravitational Geometrodynamics Graviton Force Strength Theory Mediator Strong 10 Chromodynamics Gluon Electromagnetic Electrodynamics Photon Weak Flavordynamics W and Z Gravitational Geometrodynamics Graviton

46. The Strong Force The strongest of the 4 forces Is only effective at distances less than 10 -15 meters (about the size of the nucleus) Holds quarks together This force is carried by gluons

47. Strong Force P rotons and neutrons are bound together in the nucleus of an atom This is due to the residual strong force that is binding the quarks together in each of the baryons

48. The strong interaction is hypothesized to be mediated by massless particles called gluons, those are exchanged between quarks, antiquarks, and other gluons . Gluons, in turn, are thought to interact with quarks and gluons as all carry a type of charge called  colour charge. Colour charge is analogous to electromagnetic charge, but it comes in three types rather than one ( red, green, blue) that results in a different type of force, with different rules of behaviour . These rules are detailed in the theory of quantum chromodynamics (QCD), which is the theory of quark-gluon interactions .  

49. Strong force: gluons Gluons interact with quarks Gluons interact with other gluons

50. Masters of Quantum Mechanics Paul Dirac

51. Quantum Mechanics The word “quantum” (Latin, “how much”) refers to a discrete unit that quantum theory assigns to certain physical quantities, such as the energy of an atom at rest, or the electric charge, angular momenta etc..The discrete values of these physical quantities are identified by quantic numbers. The relativistic formulation of Quantum Mechanics was done by P.A.M. Dirac in 1928, who also predicted the existence of the positron and antimatter.

52. Quantic numbers Spin : I n quantum mechanics the spin of a particle is related to an angular momentum which has non-classical features. It can not be associated to a rotation, but only refers to the presence of angular momentum. Isospin : It is a quantum number related to the strong interaction, it was introduced to explain the symmetry in particles strongly interacting and led to the discovery and understanding of quarks (Yang-Mills theory).

53. Contd … Flavour quantic numbers: specific numbers for different particles species, as the leptonic and barionic number, or charm, strangeness, bottomness, topness. Electric charge Conservation laws: the occurrence or not of the different decays and interactions is governed by conservation laws of the quantic numbers.

54. 58 Conservation Laws and Symmetries Physicists like to have clear rules or laws that determine whether a certain process can occur or not. It seems that everything occurs in nature that is not forbidden. Certain conservation laws are already familiar from our study of classical physics. These include mass-energy, charge, linear momentum, and angular momentum. These are absolute conservation laws: they are always obeyed.

55. 59 Additional Conservation Laws These are helpful in understanding the many possibilities of elementary particle interactions. Some of these laws are absolute, but others may be valid for only one or two of the fundamental interactions.

56. 60 Baryon Conservation In low-energy nuclear reactions, the number of nucleons is always conserved. Empirically this is part of a more general conservation law . It assignes a new quantum number called baryon number that has the value B = +1 for baryons and − 1 for antibaryons, and 0 for all other particles. The conservation of baryon number requires the same total baryon number before and after the reaction . Although there are no known violations of baryon conservation, there are theoretical indications that it was violated sometime in the beginning of the universe when temperatures were quite high. This is thought to account for the dominance of matter over antimatter in the universe today.

57. 61 Lepton Conservation The leptons are all fundamental particles , and there is a conservation of leptons for each of the three kinds (families) of leptons. The number of leptons from each family is the same both before and after a reaction. We let for the electron and the electron neutrino; for their antiparticles; and for all other particles. We assign the quantum numbers for the muon and its neutrino and for the tau and its neutrino similarly. Thus three additional conservation la ws are added.  

58. 62 Strangeness In the early 1950s physicists had considerable difficulty understanding the numerous observed reactions and decays. For example, the behavior of the K mesons seemed very odd. There is no conservation law for the production of mesons, but it appeared that K mesons, as well as the Λ and Σ baryons, were always produced in pairs in the proton reaction studied most often, namely the reaction. In addition, the very fast decay of the π meson into two photons (10 −16 s) is the preferred mode of decay. One would expect the K meson to also decay into two photons very quickly, but it does not. The long and short decay lifetimes of the K are 10 −8 and 10 −10 s, respectively.  

59. 63 The New Quantum Number: Strangeness Strangeness, S , is conserved in the strong and electromagnetic interactions, but not in the weak interaction. The kaons have lambda and sigmas have , the xi has , and the omega has When the strange particles are produced by the strong interaction, they must be produced in pairs to conserve strangeness.  

60. 64 Contd … π can decay into two photons by the strong interaction, it is not possible for K to decay at all by the strong interaction. The K is the lightest particle, and there is no other strange particle to which it can decay. It can decay only by the weak interaction, which violates strangeness conservation. Because the typical decay times of the weak interaction are on the order of 10 − 10 s, this explains the longer decay time for K . Only violations are allowed by the weak interaction.  

61. 65 Hypercharge One more quantity, called hypercharge , has also become widely used as a quantum number. The hypercharge quantum number is defined by Hypercharge, the sum of the strangeness and baryon quantum numbers, is conserved in strong interactions. The hypercharge and strangeness conservation laws hold for the strong and electromagnetic interactions, but are violated for the weak interaction.  

62. 66 Symmetries Symmetries lead directly to conservation laws. Three symmetry operators called parity, charge conjugation , and time reversal are considered.

63. Quantum Electrodynamics In particle physics,  quantum electrodynamics  ( QED ) is the   relativistic  quantum field theory of electrodynamics . It describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved. QED mathematically describes all phenomena involving electrically charged particles interacting by means of exchange of photons and represents the quantum counterpart of classical electromagnetism giving a complete account of matter and light interaction.

64. In other words, QED can be described as a perturbation theory of the electromagnetic quantum vacuum. Richard Feynman called it "the jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the electron and the Lamb shift of the energy levels of  hydrogen.

65. Electromagnetic force e - e - Photon The repulsive force that two approaching electrons “feel” Photon is the particle associated to the electromagnetic force “smallest bundle” of force

66. Photon exchange Feynman Diagram e- e- e- e- g

67. Here, two electrons enter, a photon passes between them and the two then exit. This diagram, then, describes the interaction between two electrons In the classical theory it is the Coulomb repulsion of like charges (if the two are at rest). In QED this process is called Moller scattering In QED, the interaction is “mediated by the exchange of a photon ,” Time

68. One can twist these “Feynman diagrams” around into any topological configuration . Time

69. As per the convention, a particle line running “backward in time” (as indicated by the arrow) is to be interpreted as the corresponding antiparticle going forward (the photon is its own antiparticle. In this process an electron and a positron annihilate to form a photon, which in turn produces a new electron-positron pair . An electron and a positron went in, an electron and a positron came out This represents the interaction of two opposite charges: their Coulomb attraction. In QED this process is called Bhabha scattering.

70. Pair annihilation