# Tag Info

## Hot answers tagged experimental-physics

9

Fill a garden hose with water. Hold both ends closed, and walk to the "higher" pond. Have someone helping you hold the end of the hose under water. Now walk to the other pond (still holding the end of the hose shut). Hold the hose near the surface of the pond - you should feel water pressing against your finger. Make a very small opening and observe the ...

6

A resonance (in the particle physics or related physics sense) and an unstable particle is exactly the same thing. The object has some complex mass and the imaginary part determines the decay width (and decay rate). But these two terms describe different aspects of the same thing. "A particle" refers to the object, the particle species (in your URL's case, ...

3

Yes, it is hocus pocus from scientific reporters. Going to the original press release from the experimenters: Common sense says the object is either wave-like or particle-like, independent of how we measure it. But quantum physics predicts that whether you observe wave like behavior (interference) or particle behavior (no interference) depends only on ...

3

It is worth stressing that black holes are predictions of classical General Relativity models. Our experimental data have established that the underlying level of nature is quantum mechanical. There is a large body of research on quantizing gravity and unifying the three forces studied with particle physics experiments with the gravitational force. String ...

3

This is speculating - but if your slides are of non-uniform thickness, or they are bent as a result of the pinching, they will present a different path length in one leg of the interferometer (and therefore give rise to a shift in the fringe pattern). This may become clear by looking at this diagram: In the diagram on the left, the total path length is ...

3

It means that when the neutrinos hit electrons, the electrons are moving preferentially in the same directions that the neutrinos were moving. So when we are building a water Cherenkov detector for solar neutrinos, the Cherenkov signal will be coming from the direction of the sun. This is very advantageous to suppress background and because of the daily and ...

2

I don't know nearly enough QFT to address the background or implications of your question. However, I'd basically answer yes to your first two questions, but it depends a little on your definition. A single phonon mode is not localized in space. However a wave packet can in principle be built up of a small range of frequencies, giving a fairly well defined ...

2

This is to be read in conjunction with the answer by Lubos The particle data group has compiled a lot of crossections in this paper, whence I have copied a particular plot, fig 49.5. Squareroot(s) in GeV The blue part are the resonances that were found during the sixties , and are typical of other resonances in scattering ...

2

Stokes Law is not going to apply in this situation because the water flow around the ball will be turbulent not laminar. The way to see this is to calculate the Reynold's number. For a sphere this is approximately given by: $$Re \approx \frac{\rho_wdv}{\mu}$$ If we feed in $\rho_w = 1000$ kg/m$^3$, $d = 0.00317$ m, $v = 37$ m/s and $\mu = 0.001$ Pa.s ...

2

Measuring T-line power flow from the ground without contact is tricky, especially near the tower. The tower is a solidly grounded structure and tends to sink the EM fields to ground, and the conductors are far from your position (high in the air). Better to move to mid-span where there is no tower and the conductors are closer to the ground. Also better to ...

2

When you say "improves the reliability", well that is not clear at all, because you have reduced your sample size and possibly introduced an (unknown) bias. Median filtering is typically used where you do not fully understand the noise properties of your sample and where there may be cases of results that are way out from the expected result because of rare ...

2

As far as I know the 33 cm difference is the current champ for the measurement. The stability of part(s) in $10^{18}$ is only achieved after running for a certain length of time, and averaging out white frequency noise. Their actual result was obtained over a period of time (40,000s and 100,000s for the high and low measurements) and was 37 ± 15cm. They ...

1

Assuming the question is about creating superpositions of eigenstates of the atomic Hamiltonian, one can do this by shining coherent electromagnetic radiation at the frequency $\omega$, such that $E = \hbar \omega$ is the energy difference between the two atomic states. This causes Rabi oscillations, so that the quantum state oscillates between the ground ...

1

are the decay products produced totally probabilistic or can we "tune" an accelerator to increase the probability of a particular decay channel occuring? Once a particle is produced, it decays completely independently of its production. The only dependence on production occurs when, for instance, a particle is produced in an entangled state and ...

1

Although Supersymmetry (SUSY) - under certain assumptions - predicts the existence of Dark Matter (DM) candidate, the signals for DM are not specific to SUSY. Fist, how to detect DM at the LHC: DM will not be detected by the experiments directly as it is believed (reasonable assumption) to not interact with regular matter. Therefore the only way of ...

1

This answer is based on Floris' insight that the slides might be bent. Let's say the laser hits the slide at an angle of $\theta$ and travels through the panel at an angle of $\theta'=\sin^{-1}({n_a\over n_s}\sin(\theta))$. Let's assume the curvature is light enough that the laser essentially exits parallel to how it entered. I am also going to assume you ...

1

At a guess, the effect rises from the fact that your interferometer is not properly aligned. The presence of linear, rather than circular, fringes suggests that there is an angular misalignment. Then moving the wedge causes a lateral shift in the intersection point of the beam and the angled slide, which results in a shift in the apparent position of the ...

1

Experimental physicists are very visual people. They are more interested in seeing the wavefunction. Calculating it is the work of a theoretical physicist. "Catching sight of the elusive wavefunction", would be a good read for you at this point. As you proceed with Griffiths, you will see that in experiments we measure certain quantities, called the ...

1

The wave function is connected to an experimentally observable value through its complex conjugate square, which gives the probability of an interaction or a decay happening; from this a crossection for the interaction can be predicted, number of events versus some variable in appropriate units. Example: the experiment can measure very many decays of the ...

1

You need to keep the amount of time the same as well. The change in momentum of a system is equal to impulse delivered to it, which is just the time-integral of the force: $$\Delta \vec{p} = \vec{J} = \int_{t_1}^{t_2} \vec{F} \, dt = \vec{F} \Delta t \text{ (if \vec{F} is constant with respect to t.)}$$ So just having $\vec{F}$ constant isn't enough; ...

1

I use this arrangement in my introductory classes when time allows, but not for momentum. I call it the "work-energy mini-lab". (It's a mini-lab because I don't expect a detailed write-up and guide the class through some of the harder analysis.) Some things to note. By measuring how far the mass hanger has to drop you get the distance over which the ...

1

In superfluid helium-4, the phonon excitation spectrum includes a mode which has the same energy and momentum as a neutron with a speed of about 440 m/s (wavelength $\lambda \approx 9\,Å$). You can create a neutron beam which contains only 9 Å neutrons by starting with cold neutrons and being clever with diffraction from crystals. If you send these ...

1

You seem to be onto something. This research paper on arxiv suggests a linear relation between the hall coefficient and temperature for a certain strongly disordered metal; the analysis probably does not apply in your case with copper, but was included because it is interesting, is current research and deals with the relation between the hall coefficient and ...

1

The smallest possible black hole that could be observed would be one with a mass on the scale of the Planck mass (~ 22 µg) and a radius on the scale of the Planck length (really small). Thermodynamics makes it impractical to pack multiple particles into such a small space, so the best bet would be to accelerate elementary particles to have relativistic mass ...

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