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Karteikarten

Theory

Johanna Blomqvist Physics Englisch 101 Karten

Theory

Karten in diesem Stapel (101)

  1. 1What are the fundamental matter constituents?Quarks and leptons
  2. 2Which are the fundamental forces in nature?Gravity, strong force, electromagnetic force, weak force
  3. 3What is the origin of Klein-Gordon & Driac equations?The relativistiv interpretation of the Schrödinger. KG: spin 0-particles, Dirac: 1/2- spin particles
  4. 4What is the interpretation of the negative solutions of the Dirac equation?Negative occupied states, leading to antiparticles
  5. 5How are the positrons described in Dirac's hole theory?The process of removing a an electron with energy -E and -p cannot be distinguished from adding a p, E-particle. Thus Dirac predicted a s=+- 1/2, e+ with opposite charge
  6. 6Which are the basic Feynman diagrams for the processes where an electron either emits or absorbs a photon?Which are the basic Feynman diagrams for the processes where an electron either emits or absorbs a photon?
  7. 7How is annihilation and pair production described by feynman diagrams?How is annihilation and pair production described by feynman diagrams?
  8. 8What is the connection between range of force and mass of the force carrier?R inverse M, when M->0, R->inf
  9. 9What kind of reaction is described using the Yukawa potential?Interaction through the exchange of a massive particle. If M->0, R->inf, Y becomes the coulomb potential
  10. 10What are natural units in physics and how does one convert them into SI units?All units can be described as powers of energy, since h=c=1. Restored by dimensional analysis
  11. 11What is the centre-of-mass frame of a system of particles?When sum(p)=0
  12. 12What is the CM frame of a single particle?In the particle.
  13. 13How is the invariant mass of a system of particles defined?Tillgänglig energi i systemet. W2CM=W2Lab
  14. 14How is the mass of a decaying particle determined from measurement of the decay products?W2intial=W2final
  15. 15What is the threshold energy for a reaction?The energy needed to achieve the reaction
  16. 16How does the reaction rate depend of the reaction cross sec?R=Lsigmar=nb*vi*Nt*sigmar = J*Nt*sigmar
  17. 17What is luminosity?J*N, N=number of particles luminated, J=flux=nb*vi
  18. 18What is "collision length"?The mean distance travelled before a a collision occurs. =1/(nm*sigma), nm=number of nuclei per unit volume
  19. 19When is it relevant to care about the differential cross-sectin?When the internal structure of the target is important or is being examined
  20. 20Why is elementary particle physics called high energy physics?Small wavelengths => high p => high energy
  21. 21Why are electrons preferably accelerated in linear accelerators?Electrons which are accelerated radially loose a lot of energy to synchrotron radiation
  22. 22What is a cyclotron?A split circle with a an ion source in the middle. Oscillating magnetic field gives an oscillating potential difference which gives the particle a push when it passes
  23. 23What characterises a synchrotron?Circle with several magnets around. B-field that changes to keep radius, E-field gives pushes
  24. 24Why is it an advantage to use collisions rather than fixed target machines if you wnat to serach for new particles?Higher energies (double the beam energy). Products often produced at rest, easier to detect
  25. 25What is produced in the dominant interaction of photons with matter?Pair production: an electron-positron pair
  26. 26Which of the particles electron, muon or charged pion has the longest range in a detector, assuming the all have the same momentum?The muon has no strong interaction with nuclei. Hard to deflect due to their mass
  27. 27What kind of detector can be used to localize particle tracks to within 0.1mmDrift chambers
  28. 28Why are some detectors placed in a strong magnetic field?Because the particle tracks bend, and from that one can calculate momentum and sign of the charge
  29. 29Why are calorimenters placed at larger distances from the interaction point than drift chambers in a multi-purpose detector at a collider?Because calorimeters measure energy and momentum, and you want to do the drift chamber stuff before that
  30. 30Where are the muon detectors placed in a multipurpose detector at a collider?Furthest away, cause they reach the furthes
  31. 31How many lepton generations exist in nature?3
  32. 32Which interactions affect leptons?Weak and electromagnetic. (Neutrinos only weak)
  33. 33Why did Pauli propose the existence of a neutral, very light lepton?Because of the energy spectra in nuclear beta decay. Ee- should be fixed, it is not, it has a range.
  34. 34What is the Feynman diagram for the process whereby the existance of a neutral lepton was first shown experimentally?anti-ve+p => n+e+
  35. 35How could the neutrino mass be determined from a direct measurement?Energy-momentum conservation of beta-decay ("missing" energy)
  36. 36What do we mean by "universality of weak interactions" for leptons?The charged leptons are identical except for important mass effects, and decay in similar ways.
  37. 37What are neutrino oscillations?The phenomenon that neutrios can oscillate between different flavours
  38. 38Is the characteristic oscillation length the same for solar and atmospheric neturinos? Why?Yes. Wavelength prop L/E. Different L (distance from source) and energies
  39. 39What are the hadrons?Quarks combine to hadrons. Hadrons are divided into muons and baryons
  40. 40Why are the so-called "strange particles" K and A strange?It was assumed that particles produced by the strong force should also decay with it. This was not the case. These decay by the weak force
  41. 41What is a hadron resonace and how can it be produced?It is a highly unstable exited- hadron state, created from ultra relitavistic collisions
  42. 42How does one determine the mass of a resonance if the decay products are known?From the invariant massa nd the maximum value of the Breit-Wigner resonance formula
  43. 43What quantum numbers enter into "spectroscopic notation"2s+1LJ
    L - angular momentum between quarks
    S - sum of quark spin
    J = L+S
  44. 44What is the parity of a quark-antiquark system?(-1)^L
  45. 45What do we mean when we say that a conservation law is multiplicative?That the product is conserved, not the sum
  46. 46What is hypercharge?Y=B+S+C+b+T
  47. 47How is I3 defined?1/2*(N(u)-N(d))
  48. 48What do we mean by saying that isospin is conserved in strong interaction?That strong interaction does not change a flavour
  49. 49What is a weight diagram?A placement of particles in a Y(I3)-diagram
  50. 50How are the light meson with spin 0 organized in a nonet?Light mesons with spin 0 = pi, pi+, pi-
    eta,eta
    K, K-, K0, K0-
  51. 51How are the lightest mesons with spin 1/2 organized in a nonet?Light mesons with spin 1 = K0*, K0*-, K*-, k*+, rho+,-,0, omega, phi.
  52. 52What is an octet and a declupet?strange(I3) (Sfrom 0->-3, I3 from +1 -> -1). Octet is declupet without the superbaryons
  53. 53How can we get indications of the mass differences between u,d, and s quarks?Difference betweeen quark compositions in the decouplet and octate, and then taking the mean.
  54. 54What is the timescale for strong interactions?10^-22 - -24s
  55. 55What is the timescale for electromagnetic interactions?10^-16 - -21
  56. 56What is the timescale for weak interactions?10^-7 - -13
  57. 57Why was the quantum number colour introduced?Because hadrons like qqq (with equal spin! were found, and because of pauli there must be some distinction
  58. 58What are gluons and how many different kinds exist?Quanta of the colour field - carriers of force- 8 different
    (gluons have color in twos)
  59. 59In which ways are gluons similar (different) to (from) photons.Gluons are the gauge bosons in QCD, photons in QED. Massless spin -1, coupling to conserved charges. Photons however are themselves neutral, but gluons have a nonzero value of the color charge to which they couple
  60. 60What is meant by "running" of the strong coupling constant?The decrease of the strong coupling constant at shorter distances
  61. 61What is mean by asymptotic freedom?Bonds between particles asymptotically tends towards the expected value as energy increases and distance decreases
  62. 62What is meant by confinement?Only color singlets exist as free particles (colour neutrals)
  63. 63How can the number of colour degrees of freedom be verifed experimentally?Ratio between cross-section of e+e- --> mymy- or hadrons include a 3 - degrees of freedom
  64. 64What kinds of experiments allow for determination of the proton form factor?Muon and electron scattering experiment?
  65. 65What would the proton form factors be if the proton was a spin1/2 Dirac particle?The proton would be point-like
  66. 66What kind of experiment could demonstrate the existance of point-like partons within the protons?Deep inelastic scattering
  67. 67What are the parton distribution functions and why are they important in current hadron-collider experiments?It is the probability density for finding a particle with a certain longitudinal momentum fraction x at resolution scale Q^2
  68. 68What are "charged current" reactions?Reactions involving W bosons
  69. 69What are semi-leptonic charged current reactions?Reactions that mix hadrons and leptons
  70. 70What is the idea behind "lepton-quark symmetry"?That quarks behave like leptons in reactions (eg Feynman diagrams)
  71. 71Why was quark mixing (Cabibbo mixing) introduced?To explain naturally occuring decays that mix quarks from different generations
  72. 72What is meant by Cabibbo suppression?That Wus and Wcd are supressed by factors compared to Wud and Wcs
  73. 73How is Cabibbo mixing modified by the introduction of the third quark family?Must allow mixing between all lower 3 quarks with the upper ones
  74. 74What kind of processes can teach us about the couplings Vub and Vcb?CKM-matrix contains information about the strength of flavour-changing weak decays
  75. 75How can the top quark life time be estimated from its mass?=hbar/gamma=hbar/mass
  76. 76What are the consequences of the very short top quark life timeIt implies that the g(ud) and g(cb) are suppressed
  77. 77What are "neutral weak currents"?Interactions with Zbosons
  78. 78Which combinations of leptons or quarks couple to the z at the fundamental level?Leptons and anti-leptons
  79. 79Do Natural currents change quark flavour?NO
  80. 80Do charged currents change quark flavour?Yes
  81. 81What is the weak mixing angle?It is the angle by which spontaneous summetry breaking rotates the original W and B vector boson plane, producing as a result the Z boson and photon. Also a relationship between Mz and mW
  82. 82Local gauge invariance requires the existance of a long range field. What are the gauge bosons of this field in QED?The gauge field of QED is the electromagnetic field. Hence, the bosons are photons
  83. 83What are the gauge bosons in the unified electroweak theory? Are they all physicals particles?It couples to the Ws and Z (and give them mass), but does not touch the photon.
  84. 84How do the couplings of the Higgs to fermions depend on the mass of the fermions?g(Hff)=sqrt(2)*gw(mphoton/mw)
  85. 85How do we think that precence of a Higgs field makes the electroweak gauge bosons massive?They move within the field, creating a "mass inertia". They get heavier the faster they move.
  86. 86What is helicity?The projection of the angular momentum onto the direction of linear momentum
  87. 87What is the helicity of the neutrino and anti-neutrino?Neutrinos are very fast => left-handed (-1)
    Fast anti-neutrinos are therefore right-handed (+1)
  88. 88Why does the pion+ decay to a muon+ rather than a e+Because of helicity. If it decays to an antineutrino, which is RH, and a lepton, which then has to be RH. It then has to be a slow lepton, and electrons move fast
  89. 89How can the Kaon0 and its anti-particle be converted to each other by higher order processes?You woulf violate strangeness, which is okay in weak interactions, so by two weak decaus to each other
  90. 90How do we know that the observed states Ks and KL are not CP eigenstates?CP is not conserved
  91. 91Are there other particle-anti-particle systems where CP violation has been observed?B0, anti B0
  92. 92What are strangeness oscillations?Produced particles, such as an K0 with s=1, can, if allowed to travel through free space, to reach a point where it does not have definite strangeness. It can then oscillate between 1 and -1
  93. 93What is the CPT theorem?Charge conjugation, parity and time reversal invariance
  94. 94What evidence do we have for the existance of dark matter?Astronomical observations of galaxies rotational curves, and of velocities from redshift, does not match the visible/expected materia. There must be mass we cannot see.
  95. 95What is gauge coupling unification, and what are the short-coming of the George-Glashow model?I unifies the three gauge interactions which define EM, W and S interactions- The GG predicts proton decay, which has not been observed.
  96. 96What is the hierarchy problem and why is it a problem?The scale of the gravity force is much weaker compared to EW, W and S
  97. 97What is mean by SUSY? Why must SUSY be broken?Each fermion has a bosonic partner. SUSY predicts that the pairs have equal mass. But then we should have observed them, which we have not
  98. 98What observational and theoretical issues can SUSY help solve?The hierarchy problem. Many flavours of string theory and GUT
  99. 99How could the Higgs sector change in SUSY senarios?2 complex Higgs doublets instead of 1
    8 degrees of freedom instead of 4
    => 5 physical higgs bosons
  100. 100How could we infer that we produced a dark matter particle in a collider experiment?Missing transverse energy (like neutrinos)
  101. 101What typ of experiment could demonstrate that neutrinos are Majorano particles?Majorano - the fermions are their own anti-particles. An observation of neutrinoless double beta decay would prove this. OR direct detection of nuclear recoil against invisible particles

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Beschreibung
Physics Karteikarten am Theory, erstellt von Johanna Blomqvist am 14/03/2017.
Erstellt von
Johanna Blomqvist · Mär 2017
Aktualisiert
14 Mär 2017
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