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How do we know quarks aren't just parts of broken-up protons

  1. Jun 10, 2015 #1
    Please be esy on me for asking what seems a very silly question but i have only just started reading about this sort of thing very recently. I can only learn by asking so please bear with me. thanks

    My question is, how do we know when we have found a new particle, for example when physicists used a colider to smash protons how do we know the pieces are not just pieces of broken protons, how do we know we had found the different quarks?

    please be give an answer in laymans terms, i dont work in science i am just an enthusiast. thanks
     
  2. jcsd
  3. Jun 10, 2015 #2

    DEvens

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    Welcome to the forum.

    It's not really possible to give a "layman's terms" answer because the situation involves technical aspects. It's like asking to explain parking a car without referring to the motion of a car.

    But here goes.

    The basic idea of particle colliders is to adjust the energy and see what comes out. At a really simple level, as you slowly increase the energy you get more kinds of interactions.

    Think about colliding two protons just for example. They will have an energy available due to their kinetic energy. The mass of an electron is a certain amount. When the energy available in colliding two electrons becomes greater than twice this mass (refer to relativity and equivalence of mass and energy) then the collision can spit out an electron and a positron. And you can see these fly away. When that happens you see the chance of a reaction increase strongly. This chance is expressed as a cross section (an area) and the cross section is a function of energy. When you reach twice the mass of an electron you see a sharp increase in cross section. This is usually called a resonance.

    The same happens when you get enough energy to create a proton-anti-proton pair. Or a neutron-anti-neutron pair.

    Now the complicated bits. When you get enough energy to produce a quark-anti-quark pair, you can make such a pair. And you see another resonance. And this pair comes out as an unstable particle. You can infer the characteristics of this particle by what it decays into, and how long that takes. You scan energy, see the increased reaction cross section, collect the decay products, and infer what decayed. And you scan up in energy and infer that there are six quarks with particular symmetries.

    Now it's a very complicated business because there are quite a few combinations of quarks, in a variety of energy states, that can be produced. And they can decay into a variety of end products. And the inferring of characteristics from those decay products is pretty complicated.

    So, fundamentally, it's banging things together to see what parts come out. And inferring the structure from the characteristics of those parts.
     
  4. Jun 10, 2015 #3

    ChrisVer

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    Can you explain what you mean by broken up proton pieces?
     
  5. Jun 10, 2015 #4
    I think i shall read some more as i undertsand some of what you are saying but not entirely. thankyou, i will work this out after reading it again after i have learned a bit more. nice one.
     
  6. Jun 10, 2015 #5

    What i mean by broken up pieces is how do we know quarks are an actual new particle and not just three pieces of a smashed up proton. If i throw glass (imagine glass is one single particle) and it breaks into three pieces, i still have parts of glass not a new material.

    So if i smash a proton how do i know ive found a new thing and not just broken that proton into three pieces?
     
  7. Jun 10, 2015 #6

    ChrisVer

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    OK then, it goes under @DEvens answer.
    In many cases you don't even observe those particles, but instead you observe their decay products...
    Their products will show you those particles masses after you measure their momenta and identify them.
     
    Last edited: Jun 10, 2015
  8. Jun 10, 2015 #7

    jtbell

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    When you take different identical glasses and break them, they shatter into different collections of pieces, with different numbers, shapes and sizes.

    When you take different protons and "break" them, they "shatter" in a limited number of ways which correspond to rearrangements of a small number of internal components with a limited set of properties. All up quarks have the same fundamental properties, as do all down quarks, and there are always two up quarks and one down. Any "new" quarks produced in a process can be traced to new quark-antiquark pairs produced out of the energy which was used to smash the original protons together.
     
  9. Jun 11, 2015 #8
    Take another but similar way of thinking than yours. Take a house and break it up. You get stones. The stone alone and the house alone don't have the same properties. In some way each stone is effectively a part of the house but it is not like a house. It's the same with people. Each of us has a character, an identity. But all together we built communities that do not obligatorily reflect our personal opinion and way to be.
     
  10. Jun 11, 2015 #9

    meBigGuy

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    I think the whole point is that if something is the end of the line, it can't be broken. If it can be broken, it must be made of something that can be split. The goal is to get to something that can't be broken, then you know you are at the basic building blocks. So, whatever you can break a proton into, it isn't a proton anymore so it needs a name. It turns out there aren't many things they can break into, so it's easy to name them. If there were lots of possibilities (like the house example) it would be harder to name them meaningfully.
     
  11. Jun 11, 2015 #10
    Simple analogy, say i have a piece of plastic and break it i still just have pieces of plastic not anything new. So i was asking can the same be said for quarks? Or do quarks have completely different properties then a broken proton?

    I am very new to this, it is just an interest i have got into since reading about the universe on the larger scale. Now the small stuff is just as interesting to me.

    So go easy on me ladies/gents.

    Thanks
     
  12. Jun 11, 2015 #11

    meBigGuy

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    Quarks have completely different properties than protons, so they aren't just "small protons".

    The fact that you can break up plastic means it is made of smaller things (molecules). Molecules can be broken up so they must be smaller things (atoms). Atoms ..... etc etc. Where does it stop? Particle physics searches for the answer. If you can split it, it's not a base component.
     
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