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  1. J

    Invariant pT

    What's the definition of invariant pT in a 2->2 process? I know how to calculate the invariant mass in this case, but I am not sure about pT.
  2. J

    Cosmic rays affecting the LHC

    I've heard of cosmic rays affecting measurements made at the LHC in the context of muons. Is it just muons that can reach the detectors or is there background from other particles as well? Why are muons a background but not electrons? How significant is it? Thanks.
  3. J

    Cherenkov radiation - phase velocity not group velocity

    Why must the charged particle that leads to Cherenkov radiation travel faster than the phase velocity of light not the group velocity of light? One of the sides of the triangle that is used to define cosθ is v=c/n i.e. the phase velocity. I don't see why it's one rather than the other. Thanks!
  4. J

    W/Z production cross sections

    I had a look at the production cross sections for W/Z at hadron colliders. These differ as a function of energy with the W x-sec being consistently ~10 times larger than the Z cross sections. Why is the W cross section so much larger? I think the coupling strength is similar and the mass...
  5. J

    Monte Carlo in high energy physics

    Why is it necessary to use Monte Carlo methods in high energy physics? There is Feynman calculus to evaluate matrix elements for various interactions and the relativistic Fermi's Golden Rule for decays and scattering to obtain a decay width or differential cross section. What are we...
  6. J

    Wavefn symmetry requirement

    Both Rho^0 and Pi^0 are bosons so require an overall symmetric wavefn. However, they are in different spin states: the Pi is in the anti-symmetric S=0 state and the Rho is in one of the symmetric S=1 states. Which other part of the overall wavefn (color, flavor, spatial) differs between the two...
  7. J

    Weak force coupling to left-handed particles

    The W couples to left-handed particles only. What about the Z? Is it the same? Thanks in advance!
  8. J

    Understanding the Kolmogorov–Smirnov test

    Dear all, I am using some software to perform a two-sample Kolmogorov–Smirnov test. Specifically, I am testing the compatibility of two histograms. The function returns a single number that is 1 for a perfect match (when I compare the histogram to itself) and somewhere between 0.05 to 0.25...
  9. J

    Partial wave analysis - incoming/outgoing?

    In the chapter on partial wave analysis in Griffiths's Introduction to Quantum Mechanics, he considers a spherically symmetric potential and says that for large r, the radial part of Schrodinger's equation becomes, \frac{d^{2}u}{dr^{2}}≈-k^{2}u with a general solution of...
  10. J

    Intrinsic parity of particles

    A quark and antiquark have opposite parity. The quark is customarily taken to have positive parity. I understand this to mean that Pf = f, where f is the wavefunction of the quark and Pg = -g, where g is the wavefunction of the antiquark. Does this mean that P acting on an antiquark...
  11. J

    Bending power - magnet units question

    I am reading a paper where the bending power of a dipole magnet is described as 2 Tm. Is that Tesla*meter? Is bending power actually power i.e. Work/Time? Can someone explain this physical quantity to me, please?
  12. J

    Simple group theory vocabulary issue

    I am reading about group theory in particle physics and I'm slightly confused about the word "representation". Namely, it is sometimes said that the three lightest quarks form a representation of SU(3), or that the three colors do. But at the same time, it is said that a group can be...
  13. J

    Parity violation in weak decays

    I am confused about when and to what extent parity is violated in weak decays. On the one hand, there's Wu's famous experiment where electrons are emitted preferentially in one direction. This parity violation can be said to be maximal, since all electrons are emitted in one direction...
  14. J

    Parity violation in weak decays

    Homework Statement I am confused about parity violation in weak decays. I learned about Wu's famous experiment and how it demonstrates that parity is violated in weak decays. However, when I am doing a course problem on nuclear β-decay, then it still necessary to conserve parity...
  15. J

    Natural units question

    I'm slightly confused about natural units. Take mass as an example: I can measure something in kg's, but then decide to convert to MeV/c^2, for instance. To do that I would multiply the quantity in kg by 3*10^8 squared and divide by 10^6*1.6*1-^(-19) i.e. the SI values of the constants. If I...
  16. J

    Parity - what does it matter?

    The parity operator has eigenvalues of +/- 1 and particles can have intrinsic parity of +/- 1. What does it matter? Does a P=-1 particle behave physically different from a P=+1 particle? Is parity a useful concept only in the sense that one can check if an interaction conserves parity (parity...
  17. J

    Polarization and helicity states

    At the beginning of cpt 9, Griffiths states that massive bosons have three polarization states (m_s = 1, 0, -1), but massless ones have only two (m_s = 1, -1). Are these polarization states the same thing as helicity states? I.e. the W/Z would have 3 helicity states and the photon only 2?
  18. J

    Drell Yan process [Broken] The Feynman diagram for Drell Yan has a gamma-star or a Z as the mediator. Does gamma-star simply mean a photon with a sizeable amount of energy? Is there a well-defined point in the energy of the mediator when...
  19. J

    Lepton universality

    I'd just like to clarify something I read on Wikipedia: "The branching ratio of the common purely leptonic tau decays are: 17.82% for decay into a tau neutrino, electron and electron antineutrino; 17.39% for decay into a tau neutrino, muon and muon antineutrino. The similarity...
  20. J

    Quantifying the statistical error in a counting experiment

    I need to find the statistical error in a counting experiment. Specifically, a decay can proceed via option A or option B and I need to find the branching ratio BR_a=(N_a)/(N_a+N_b). If I were to do this counting experiment multiple times my results for BR_a would follow the binomial...