# Search results

1. ### Path integrals

Quantum Mechanics and Path Integrals: Emended Edition by Richard P. Feynman (Author), Albert R. Hibbs (Author), Daniel F. Styer (Editor)
2. ### 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.
3. ### Cosmic rays affecting the LHC

Thanks to you both!
4. ### 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.
5. ### Cherenkov radiation - phase velocity not group velocity

Thanks for the reply! But again, is there a qualitative way of understanding why it's phase velocity not group velocity? True, refraction of light is also controlled by c/n - the phase velocity. Refraction can be understood from Fermat's principle, but again I don't know why it's one type of...
6. ### 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!
7. ### 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...
8. ### 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...
9. ### Wavefn symmetry requirement

Actually i think i know what the answer is. Since the quarks inside the mesons are distinguishable (antiquark and quark) then their combination doesn't have a symmetry requirement.
10. ### Wavefn symmetry requirement

I was mixing it up yes! So but taking the overall wavefn of the quarks then. As fermions they must be anti-symmetric overall. If the spins are different for the two mesons, then what else is also different?
11. ### 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...

13. ### 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!
14. ### 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...
15. ### Partial wave analysis - incoming/outgoing?

Thanks! The operator yields the momentum for the first term and (-1)*momentum for the second. A negative magnitude for momentum does not make sense, so therefore it is to be evaluated for times t<0 making it the incoming wave. Is that the argument?
16. ### 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...
17. ### Intrinsic parity of particles

Thanks for the reply! If both chirality and helicity are flipped for both particle and antiparticle, then what's the consequence of them having opposite relative parity? Doesn't the +1 eigenvalue case mean that the function is left unchanged under the parity operation?
18. ### 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...
19. ### 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?
20. ### Parity violation in weak decays

As an example, consider the La_{57} (J^P=2^-) → Ce_{58} (J^P=0^+) decay and I'd like to figure out what the angular momentum and spin state of the electron-neutrino system is. I get the right answer, when I require l=1 as this carries P=-1 making P conserved and S_{enu}=1 to conserve angular...
21. ### Simple group theory vocabulary issue

Thanks! That cleared it up.
22. ### 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...
23. ### 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...
24. ### Parity violation in weak decays

But in Wu's experiment, ALL the electrons come out in one direction making parity MAXIMALLY violated.
25. ### 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...
26. ### Natural units question

OK, so I've figured out that the answer is no I shouldn't multply by 3*10^8 squared again. The mass would be the same number in MeV/c^2 as it is in MeV, only in the latter case it's measured in natural units. But to rephrase my question: if the number didn't change when going from MeV/c^2 to...
27. ### 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...
28. ### 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...
29. ### 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?
30. ### Drell Yan process

Thank you for your replies! For massive particles, a real particle is one which lies on mass shell i.e. E^2-p^2*c^2=m^2*c^4. For a virtual particle the equals sign doesn't apply and one can get different values for m other than the true value of m. However, a photon is massless, so what...