# Recent content by BenLillie

1. ### Question: What is Virtuality for a Virtual Photon?

The technical definition of virtuality is just the amount by which the particle is off it's mass shell. That is, for a photon of 4-momentum Q^{mu} then Q^2, the 4-momentum squared, should be zero since the photon is massless. The amount by which it is not is what we call the virtuality. For a...
2. ### How could 2nd and 3rd gen. quarks be possibly discovered?

The question "what is energy" is a pretty difficult one to answer in general. In the particle collision context you're talking about there are basically two types of energy to think about: the mass of the particles and their kinetic energy. Let's say we have an accelerator that collides...
3. ### Quark masses

All quark and lepton masses are free parameters in the Standard Model. There have certainly been many attempts to explain them with a more fundamental theory. People have constructed models that could explain various features of the observed particle spectrum, and some of those models are...
4. ### Detection of Elementary Particles

A good place to start for an introduction to collider detectors is at the particle adventure: http://particleadventure.org/particleadventure/frameless/modern_detect.html That section gives a very introductory overview of how collider experments work and how the data is interpreted.
5. ### Weak decay

Remember that the branching ratio of a decay mode is just the width into that mode divided by the total width. The decay rate is just the inverse of the width. So all you need the total width, and then the branching ratios give you all the partial widths.
6. ### Ring Accelerator

I've usually heard the Tevatron and similar accelerators referred to as just "synchrotrons", but it must mean the same thing. One important difference is that a cyclotron (at least the first ones) were solid disks rather than rings. A constant magnetic field is used to create the circular...
7. ### *if* the higgs can not be found

Haelfix is absolutely correct. Also, the fact that you have to introduce new degrees of freedom to evade the unitarity bound leads to one of the famous "no lose theorems" for the LHC. Basically, if the Higgs isn't there to be found, then there must be something else that couples to Ws and Zs...
8. ### *if* the higgs can not be found

No need to worry, it's a minor point :) But, the LHC can, in fact, find a Standard Model Higgs up to masses of about 1 TeV. There is a bound coming from unitarity of longitudinal W scattering that requires the Higgs mass to be < 850 GeV, hence the statement that the LHC will find a SM Higgs...
9. ### From Atoms to Quarks and Beyond: A historical panorama

I glanced at it quickly, but it seems quite good. I'll try to read it more closely later.
10. ### *if* the higgs can not be found

A small correction to what PhysicsMonkey said - if the only fundamental particles are those we know of, plus the Higgs, then it *will* be found at the LHC. This is due to the fact that, in the SM, there is an upper bound to the Higgs mass, and that is below the highest mass Higgs the LHC can...
11. ### Standard Model help requested .

For anyone looking for a slightly more technical book, there is a compilation called "The Rise of the Standard Model", edited by Hoddeson, Brown, Riordan, and Dresden. It contains semi-technical (there are a few formulae and plots, nothing too intense) papers by a lot of the people who were...
12. ### Do Gravitons exist?

I believe that the correct statement is that, while there is no direct evidence that the graviton exists, we would all be a bit surprised if it doesn't. As for detecting gravitons at the CERN: The LHC certainly is not being built for doing that - it's looking mainly for the Higgs, and more...
13. ### Particle/Anti-Particle question

Nothing prevents them from annihilating. In fact, the way you entangle them in the first place is by producing them in pairs from collisions or decays of other particles (sort of reverse annihilation), and they then fly apart. If you like, that's what keeping them from annihilating, the fact...
14. ### Particle/Anti-Particle question

Yes, you certainly can entangle a particle/anti-particle pair. I don't know if this has ever been done with electrons (and, as mathman said, it's not a relevant question for photons), but take a look at the description of the BaBar and Belle experiments. Their measurements depend on entangling...
15. ### Supersymmetric Particles

Supersymmetry relates degrees of freedom. The muon has four, and the pions only 3 (now that I think about it, the neutral pion can't be SUSY to a charged particle anyway, so really 2). That's 4 fermionic degrees of freedom for 2 scalar d.o.f, so it seems like you would need to find 2 more...