Particle Physics help please

http://core.physicsinfo.co.uk/download.php?file=1520



http://core.physicsinfo.co.uk/download.php?file=1524

For q18iv I can't see how the total mass increase in the reaction is caused by the kinetic energy of the kaon minus.

Thanks for any help

The kaon minus is the only one moving before the collision, so it is the only one with any kinetic energy. Therefore the energy in order to cause the gain in mass is provided by the kaon minus. The proton is stationary, so it doesn't have any energy input during the collision.

The reaction happened due to kaon minus colliding with the stationary proton, so I suppose the KE of the kaon minus caused the whole reaction. But I don't get how the gain in mass occurred. Energy-mass is conserved, so a mass increase must mean an energy decrease, but we can't really see this from the question. However they never said in the question that the products of the reaction are actually moving. So I guess initially there's KE of the Kaon minus and afterwards there's just the products formed, so mass formed, but these have no KE due to no movement as the question just said "produced". I hate ambiguous questions like these as they should've mentioned whether the products are moving or not.

Yeah the energy from the kaon minus did cause it. But you have to think about conservation of momentum - for momentum to be conserved, they couldn't all be stationary after the collision, so you have to infer that they did move. The koan minus had momentum cause it has mass and it was moving. The proton did not. Therefore in order for momentum to be conserved the products had to move. The mass increased which means that the energy did decrease, in order for mass-energy to also be conserved.

I'm interested in that part. How did the energy decrease?

Because of E=mc^2. Mass can change into the equivalent amount of energy, and energy can change back into the equivalent amount of mass. That's why in some collisions photons are the product, because all the mass of the colliding particles becomes energy (in the form of a photon). Mass and energy can interchange, that's how we came to have matter. When the universe was at the point of singularity there was energy. The energy changed into matter (which has mass).

Another thing to remember is that when particles travel at relativistic speeds (close to the speed of light), so that they cannot go above the speed of light, energy has to be converted into mass. SO at very high speeds the mass of particles increases.

Oh okay, make sense now, thanks.

Btw has anything ever travel beyond the speed of light? Or is it that any object cannot go beyond it? Just curious.

No problem

Nope nothing can go beyond the speed of light. Experiments were carried out, but they found that the mass increased enough to never let the speed go beyond the speed of light - it's almost a cosmic speed limit. When more energy is given to particles the mass just goes higher and higher.

Okay thanks

That's ok. Hope it helps

For the same last question last part on that same paper, it says on the MS conservation of quark number. Since when was this a conservation law and how? See attached. There are 5 quarks on the LHS but 7 on the RHS.

Also how can we say that strangeness is conserved if we aren't fully sure that the interaction is a strong interaction? They never mentioned it.

Why can't you say lepton number conserved?

THANKS

Well anti-quarks will have a quark number of -1 and quarks a quark number of +1. So the LHS has +4 and so does the RHS. So quarks have to be conserved just like leptons are.

Strangeness is a component of strange quarks. It's not about whether there is a strong interaction or not. All strange quarks have a strangeness of -1 and all anti-strange quarks have a strangeness of +1. The interaction will always involve the strong nuclear force when quarks are involved, if that's what you meant by strong interaction.

There are no leptons in the interaction, which is why they cannot be conserved. There are only baryons and mesons, which are made out of quarks. Lepton conservation, while correct, is irrelevant to this question because it doesn't involve leptons.

hope this helps

My books for Physics mentioned nothing about this quark number business.

LHS= (-1) + 4(1)
=+3

RHS= 5(+1) +2(-1)
=+3

LHS=RHS


What I mean about the strong interaction is that in a strong interaction strangeness is conserved while in a weak interaction strangeness may be conserved or change by plus or minus 1. Hence it does matter if the interaction is strong or weak. How do you even know if an interaction is strong or not?

Neither does mine but I just assumed it was conserved.

Ah right yeah I was one out, but it's still conserved on both sides .

Oh I see what you mean sorry! Erm I'm not sure I thought a strong interaction just occurred when there were quarks involved. Maybe I have that wrong. I didn't think strangeness had an effect on whether it was a strong or weak interaction. I thought weak interactions only occurred with leptons.

So you were right

That's a really good table for the exchange bosons

Exchange bosons aren't on my spec, so I won't bother with them.

Oh I do edexcel and we learnt them. We didn't need to know anything about them, just that they exist and their names. It makes other stuff easier to understand.

Each of the four forces of nature (strong nuclear, weak nuclear, gravity and electromagnetic) have corresponding exchange bosons. They are in the last column of the table you posted. The strong nuclear force has the gluon, the weak nuclear has W+ W- and Z bosons, gravity has gravitons which are only theoretical at present, as there is no experimental evidence for them yet, and electromagnetic have the photon. That's basically all you need to know.

It is this strong nuclear force that holds quarks together to make baryons & mesons (hadrons), as the gluons are exchanged between the quarks inside hadrons. The strong nuclear force is not exerted on leptons, which is why they don't make larger particles like the quarks do.

Even though you don't need to know about them, having knowledge about them does make it easier to understand why certain particles can/cannot exist in nature.

Strange. I do Edexcel as well, they aren't on the spec at all. See attached, it doesn't mention exchange bosons.

So exchange particles make up those four forces of nature? It's hard to imagine them though, like with the gravitational force around Earth I imagine the gravitational field lines around it. I'm guessing gravitons are like tiny dots buliding the field lines and forming them? What I'm trying to say is that how do you imagine these exchange particles? Any analogy?

Also, how did the symmetry of the model predict the top and bottom quark?

Thanks