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Feb
19
comment Does a muon detector on Earth's surface correctly measure the mean lifetime of a muon?
Nice question. I supervised a muon decay lab course, and when a student asked me this for the first time, I had a really hard time finding the answer. Now I like to ask my students this question to give them something to think about :-).
Jan
15
comment How to find SUSY with near-degenerate masses?
@annav: Thanks, I forgot to take the random boost of the initial state into account! That could help, even without additional emitted particles. Still, just from experience, there are parameter ranges areas where its not enough and a e.g. multilepton search is just not sensitive.
Jan
15
comment How to find SUSY with near-degenerate masses?
@anna v: True, that's why I wrote comfortably detect. The problem is for one the trigger, you have a minimal $p_T$ threshold to trigger on single electrons or muons, and if it's too low, you have to run prescaled (I think at the moment at ATLAS the lowest is at 10 GeV, and then 18 GeV, but I'm not sure). The other thing is that (assuming your event triggered on something) you don't know the trigger efficiencies very well below 15 or 10 GeV (because they were determined e.g. from $Z\rightarrow\ell\ell$. So very often, you can't use those soft leptons as you'd like.
Jan
15
asked How to find SUSY with near-degenerate masses?
Jan
15
asked How to measure (missing) transverse energy
Jan
6
comment Moving Between Degenerate Vacua?
What I was trying to say was, I think the symmetry breaking only implies that you are anywhere in the circle, not that you are in a certain fixed point. I don't know how you move around in the valley, or if there is a physical meaning to the "angular position" but I'd like to know, too.
Jan
5
comment Moving Between Degenerate Vacua?
I guess you're asking whether the state moves around in the valley, or if it stays fixed ("remains broken" in the same orientation), and if it stays fixed, what keeps it there? ... I'm not sure, so I just leave this as a comment. But I think you can have a different value of the field (position in the valley) at every point in space, and it doesn't matter which one it is, because you can't measure the field directly. What matters is the form of the potential - the position of the minimum gives you the higgs VEV, the curvature (oscillations up the walls) creates the gauge boson masses.
Dec
13
comment String Theory- Are strings the end? What are they made of?
@MBN: I guess they think it's settled that they are made of strings.
Dec
13
awarded  Yearling
Dec
10
reviewed Reviewed The effect of dark lines in the Sun's spectrum on reflected paint/ color
Dec
10
comment What is quark transverse momentum?
Possibly a duplicate of "What is p_T? (transverse momentum?)", does that link answer your question?
Dec
10
comment How to understand exciton?
The radius of the exciton is larger because the eff. mass of the hole is smaller than the proton mass (The Bohr radius is $a_0 = \hbar\,/\,\mathbf{m_e}\, c \,\alpha$). And the difference between the hole and the positron is that the positron is a real particle ($e^+$), whereas the hole is a quasiparticle. It's a collective behavior of the material's electrons that looks like it is a particle.
Dec
10
comment How to understand exciton?
@KabaT: The hole is basically an atom that is missing an electron. But that picture is not quite accurate, since the atom is fixed in the lattice, but the hole moves around. A better picture would be to imagine a hole in the electron cloud that moves around as if it were a particle. Or think of it as an air bubble: When you excite an electon above the gap, you have a "droplet of water" in the upper band, and a "bubble of air" of same volume in the lower band. It is an absense of water, but behaves like a droplet...
Dec
8
awarded  Custodian
Dec
8
reviewed No Action Needed when water falls to the ground and forms a puddle, where does most of the energy go?
Dec
8
answered How to understand exciton?
Dec
8
answered What is anti-time?
Dec
8
comment $D$ and $H$ in macroscopic Maxwell's equation: auxiliary or constitutive?
@HuiZhang right, thanks, fixed it.
Dec
8
revised $D$ and $H$ in macroscopic Maxwell's equation: auxiliary or constitutive?
fixed typo
Dec
8
answered $D$ and $H$ in macroscopic Maxwell's equation: auxiliary or constitutive?