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Interactions / Weak / Strong / Decay = confusion! Watch

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    First of all, is interaction completely different to decay? Because all hadrons interact by the strong interaction, and yet they can decay into leptons (i.e. in Beta + or - decay) and I thought leptons only felt the weak interaction. So do hadrons "interact" by the strong interaction (and by "interaction", I'm guessing it means they feel the force), and they decay by the weak interaction. So...it's implied that all decay is by the weak interaction - the strong interaction can't change quark type, so surely nothing can decay into another product if there's no changing of quark type at all? However, I've been told that mesons can "interact" with baryons and change a proton to a neutron and vice versa. Why is that the strong interaction? I know it involves hadrons but there's been a quark change - u to d or vice versa!? VERY confusing. Also, if Beta decay involves a proton or neutron decaying, then surely that's the weak interaction? But I thought hadrons didn't feel the weak interaction? And does the W boson actually decay into an electron/neutrino pair or does it exchange charge/momentum with the pair?

    Very confused.
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    Im quite confused myself but ill add something to help

    Hadrons interact through the strong force and through electromagnetic if charged. All hadrons decay through the weak interaction except the proton which is stable.
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    (Original post by laughingbagel)
    First of all, is interaction completely different to decay? Because all hadrons interact by the strong interaction, and yet they can decay into leptons (i.e. in Beta + or - decay) and I thought leptons only felt the weak interaction. So do hadrons "interact" by the strong interaction (and by "interaction", I'm guessing it means they feel the force), and they decay by the weak interaction. So...it's implied that all decay is by the weak interaction - the strong interaction can't change quark type, so surely nothing can decay into another product if there's no changing of quark type at all? However, I've been told that mesons can "interact" with baryons and change a proton to a neutron and vice versa. Why is that the strong interaction? I know it involves hadrons but there's been a quark change - u to d or vice versa!? VERY confusing. Also, if Beta decay involves a proton or neutron decaying, then surely that's the weak interaction? But I thought hadrons didn't feel the weak interaction? And does the W boson actually decay into an electron/neutrino pair or does it exchange charge/momentum with the pair?

    Very confused.
    Right, you seem to be very flustered and confused; let me see if I can clear up any issues you may have with particle Physics.

    Hadrons are composed of two sub-group particles, Baryons and Mesons of which the quark compositions are different; Baryons each have three quarks and Mesons each have a quark and a corresponding anti-quark.

    Leptons are just leptons for now at A level. You only need to know about Electrons and perhaps Muons, both of which have corresponding neutrinos/anti - neutrinos.

    Now, Hadrons interact via the strong nuclear force; interaction is not the same as decay please don't mix these up. Anyway, an example of an interaction between two hadrons would be between two protons; when they interact they exchange a virtual photon. Two protons are then consequently emitted.

    However, Hadrons can also decay via the weak nuclear force. For now, all you need to know is that a proton can be changed into a neutron or vice versa (This is as a result of a neutron rich nucleus or electron capture which I'll come onto) To help you know which particle is exchanged and which particles "come out" as it were, think about it like this:

    If a proton is changing into a neutron then the exchange particle will snatch the positive charge from the proton and hence transfer it to the emitted leptons - in this case a positron and a neutrino would be emitted and a neutron on the other side (Since baryons and mesons are separated in feynman diagrams). Now you may ask, why doesn't an anti-neutrino form? Well consider conservation laws:

    p \rightarrow n + e^+ + V_e

    Here we can see that if it were an anti-electron neutrino, then the lepton number would not balance since a positron has a lepton number of -1 and a neutrino has a lepton number of +1. The stuff's gotta balance; the same with charge - check it if you like, but I know it's balanced.

    A neutron could alternatively change into a proton; this would just produce the opposite (A W- Boson, Proton, Electron and Anti-Neutrino). This is perhaps more commonly known as Beta decay.

    There are a few strange interactions which you may need to take note of, for instance, something which I mentioned earlier was electron capture; this is when a proton and electron collide, therefore:

    p + e^- \rightarrow n + V_e

    The conservation laws are still firmly in place; the only slight mishap of conservation that you must accept is that when a strange particle (A Kaon for instance) decays via the weak nuclear force, strangeness doesn't have to be conserved.

    Well I really hope I helped out a bit - anything else you need help with please quote me again
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    (Original post by Femto)
    Right, you seem to be very flustered and confused; let me see if I can clear up any issues you may have with particle Physics.

    Hadrons are composed of two sub-group particles, Baryons and Mesons of which the quark compositions are different; Baryons each have three quarks and Mesons each have a quark and a corresponding anti-quark.

    Leptons are just leptons for now at A level. You only need to know about Electrons and perhaps Muons, both of which have corresponding neutrinos/anti - neutrinos.

    Now, Hadrons interact via the strong nuclear force; interaction is not the same as decay please don't mix these up. Anyway, an example of an interaction between two hadrons would be between two protons; when they interact they exchange a virtual photon. Two protons are then consequently emitted.

    However, Hadrons can also decay via the weak nuclear force. For now, all you need to know is that a proton can be changed into a neutron or vice versa (This is as a result of a neutron rich nucleus or electron capture which I'll come onto) To help you know which particle is exchanged and which particles "come out" as it were, think about it like this:

    If a proton is changing into a neutron then the exchange particle will snatch the positive charge from the proton and hence transfer it to the emitted leptons - in this case a positron and a neutrino would be emitted and a neutron on the other side (Since baryons and mesons are separated in feynman diagrams). Now you may ask, why doesn't an anti-neutrino form? Well consider conservation laws:

    p \rightarrow n + e^+ + V_e

    Here we can see that if it were an anti-electron neutrino, then the lepton number would not balance since a positron has a lepton number of -1 and a neutrino has a lepton number of +1. The stuff's gotta balance; the same with charge - check it if you like, but I know it's balanced.

    A neutron could alternatively change into a proton; this would just produce the opposite (A W- Boson, Proton, Electron and Anti-Neutrino). This is perhaps more commonly known as Beta decay.

    There are a few strange interactions which you may need to take note of, for instance, something which I mentioned earlier was electron capture; this is when a proton and electron collide, therefore:

    p + e^- \rightarrow n + V_e

    The conservation laws are still firmly in place; the only slight mishap of conservation that you must accept is that when a strange particle (A Kaon for instance) decays via the weak nuclear force, strangeness doesn't have to be conserved.

    Well I really hope I helped out a bit - anything else you need help with please quote me again
    Thank you! So would you call this decay: pion + proton --> kaon + sigma ? The particles produced are at a higher rest energy than the reactants, there's no decay into leptons, and there's no direct quark change - just annihilation and pair production of quarks. So wouldn't this just be interaction?
 
 
 
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