# Tag Info

108

Ah, I know this one! What's in a proton? A proton is really made of quantum fields. Remember that. Any time you hear any other description of the composition of a proton, it's just some approximation of the behavior of quantum fields in terms of something people are likely to be more familiar with. We need to do this because quantum fields behave in very ...

34

You can't consider a proton just as three quarks (called valence quarks, because they determine the quantum numbers) because virtual quarks and antiquarks are constantly being created and anhilated via strong force. So a proton is more like a quark sea. In fact, this process gives most part of the proton's mass (the valence quarks are just the 2% of the ...

19

There is a rigorous formal analysis which lets you do this. The true problem, of course allows both the proton and the electron to move. The corresponding Schrödinger equation thus has the coordinates of both as variables. To simplify things, one usually transforms those variables to the relative separation and the centre-of-mass position. It turns out that ...

18

A neutron is not a proton and an electron lumped together (as your question seems to suggest you think) A hydrogen atom is a bound state of an electron and a proton (bound by the electromagnetic force) whereas a neutron is a bound state of three quarks (bound by the strong force). You might be tempted to think that a neutron is also a bound state of an ...

14

There is an electrostatic repulsion between the protons in the nucleus. However, there is also an attraction due to another kind of force besides electromagnetism, namely the so-called "strong nuclear interaction". The strong nuclear interaction ultimately boils down to the forces between the "colorful" quarks inside the protons - and neutrons. It is ...

14

The question you are asking has been answered in terms of popularized description. The real physics picture is not simple and depends a lot on a number of experimental measurements by many experiments. If you look at figure 9.18 of the link you will see that the composition of the proton changes according to the momentum transfer from the probing particle. ...

13

Great question. The electric field creates such a strong force that it would be very hard to move large amounts of just one type of charge. So astrophysical systems do generally eject equal numbers of protons and electrons. In particular, the solar wind is electrically neutral. So these cosmic rays are created in very nearly equal numbers, but by the ...

13

The wording of the question suggests that the electrons were the first objects or particles whose charge required the people to establish the sign convention. But that's obviously not the case. The electron was discovered by J. J. Thomson in 1897 but for much more than a century before that moment, people had already been studying electric (and magnetic) ...

12

I assume you're talking of the hydrogen atom; the hamiltonian of the nucleus + electron system is $$H = \frac{p_e^2}{2 m _e} + \frac{p_n^2}{2 m _n} - \frac{e^2}{|r_e - r_n|}.$$ You can do a change of coordinates (center of mass coordinates) $$\vec{R} = \frac{m_e \vec{r}_e + m_n \vec{r}_n}{m_e+m_n} \\ \vec{r} = r_e -r_n$$ and find the conjugate momenta to ...

11

These collisions don't produce significant amount of light in the visible range, so the easy answer is "no". They also take place in a vacuum, inside a beampipe which is itself buried in a detector apparatus that is ten meters plus on a side and packed full of stuff with no room for a human. That said, there are several ways in which a high energy ...

11

what does this mean lifetime signify ? This is the experimental lower limit on the proton lifetime. What it means is just because we havn't seen a proton decay, it doesn't mean that it can't. What does the proton decompose into? This probably depends what theoretical model you look at, but it seems that crucially it must conserve the quantity ...

10

Masses and coupling between quarks are free parameters in the standard model, so there is not real explanation to that fact. About the measurment: you can have a look at this wikipedia article about Penning traps which are devices used for precision measurements for nucleus. Through the cyclotron frequency (Larmor factor) we can obtain the mass of the ...

10

The real problem here is that when things get really, really small, they don't behave like the world we see around us. That can make a lot of what goes on in that weird world quite hard to grasp. The diagram is misleading. Protons aren't really round, grey blobs, and quarks aren't really little spheres that sit inside them. Down at the subatomic level, ...

8

The proton ($uud$) turns into a neutron ($ddu$). Up and down quarks don't have equal charges; the up is $+\frac{2}{3}e$ and the down is $-\frac{1}{3}e$. By the way, such an operation has a name - isospin symmetry transformation - corresponding to an approximate SU(2) symmetry that makes the proton and neutron have almost similar masses.

8

The neutron is made of two down quarks and an up quark; the proton of two up quarks and a down quark. This leads to two effects that differentiate their masses. One is that the up and down quark themselves have different masses. The other is that the proton is charged, and so quantum corrections involving virtual photons affect its mass. The details are ...

7

The goal of such a treatment is to induce damages in the cells of the tumor by mean of ionizing radiation. These radiations can be X-rays (photons), electron, proton or things like carbon ions. The problem is: if you try to irradiate a tumor, you first have to go through normal tissues and the risk is to damage them also. Photons will transfer energy ...

7

Blue. The proton is way smaller than a wavelength of visible light. But blue light has a shorter wavelength than any other visible color, red light is longer wavelength, blue is shorter, other colors in the middle somewhere. White light is a mixture of all the colors of light, all the wavelengths in the visible range. If you illuminate the proton ...

6

As @dmckee says the problem is complicated. It is complicated because it is not a solution of a potential describing one force, but a balance between electromagnetic forces and the strong force that is keeping the quarks within the nucleons. (In the nucleus the strong force is like a type of Van der waals potential, a higher order interaction, overflowing ...

6

On the level of QED and above, the equality of the charges has no theoretical explanation. But it is extremely well established experimentally, as even small deviations would add up to huge amounts of electricity in bulk matter. On the level of the standard model, the value of the charges of the up and down quark comes from simple arithmetic from those of ...

6

Hmmm...some back-of-the-envelope calculations: The depth of the air column at sea level is $14\text{ lbs/in}^2 = 2 \times 10^5\text{ g/cm}^2$, so neglecting space-charge effects and assuming minimum ionization the whole way we get about $4 \times 10^5\text{ MeV} = 0.4\text{ TeV}$ energy loss. We are actually above minimum ionization, so we can multiply that ...

6

A neutron is a fermion, a hydrogen atom is a boson. This is related to the fact that a neutron decays into three fermions rather than two which is what you seem to think. A neutron is composed of three valence quarks, $u,d,d$, while a hydrogen atom is made out of $u,u,d,e^-$. The internal size of a neutron is about $10^{-14}$ meters while the internal size ...

6

A proton is made of two up quarks and a down quark, whereas a neutron is made of two down quarks and an up quark. The quark masses contribute very little of the actual mass of the proton and neutron, which mostly arises from energy associated with the strong interactions among the quarks. Still, they do contribute a small fraction, and the down quark is ...

6

A proton is a bound state of three quarks. The quarks themselves are (as far as we know) pointlike, but because you have the three of them bound together the proton has a finite size. It doesn't have a sharp edge any more than an atom has a sharp edge, but an edge is conventionally defined at a radius of 0.8768 femtometres. Protons are spherical in the same ...

6

Such a process is forbidden by energy conservation: the proton is the lightest baryon (that is the lightest bound state of three quarks). hawking radiation finds it's energy by reducing the energy of the black hole, but there is not lighter baryon state for the proton to go to. Baryon number violating proton decay processes are theorized, but have not been ...

5

Most proton-proton collisions will be elastic: throw in two protons and two protons will come out, deflected at some angle. But the more interesting collisions are those where individual constituents of the proton (quarks, antiquarks, or gluons) interact. For instance, all the interesting high-energy proton-proton collisions at the LHC are really collisions ...

5

Consider two independent systems, two distant atoms, for example. Each atom has is own angular momentum $J_1$ and $J_2$. If these atoms are different and distant (non interacting), then the QM variables are separated, the total wave function becomes a product of the two atomic wave functions, and the total system angular momentum is a sum of the two. The ...

5

The electron and muon really do have different interactions with the proton (Sect. 4.4), so that there is physics beyond the Standard Model. That there is physics beyond the standard model we know from other discrepancies too, as the massive neutrinos with their oscillations and discrepancies in CP violation expectations. If this is a correct ...

5

The Standard Model which has been decided upon after a thorough experimental observation of the interactions of particles at the micro level, i.e. the space and energy dimensions where quantum mechanics reigns, has as a main pillar the quark model. The quark model started with the above observation: that if the particles were plotted in two dimensions ...

Only top voted, non community-wiki answers of a minimum length are eligible