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Thread: Basic questions about neutrino

  1. #1 Basic questions about neutrino 
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    1) A neutrino has no charge.
    What is understood by that ? A neutron has no charge because it has both charges. The same applies to neutrinos, or is a completely different kind of mass/matter intented?
    If yes, what kind
    If no: a neutrino is contained in a neutron, what keeps the two charges together in a neutrino?

    2)I read that a neutrino is detected by pair emission, how do they understand if the cause has been a neutrino or EMR
    3)How do you shoot a neutrino in a chosen direction?
    Thanks


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  3. #2  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by logic View Post
    1) A neutrino has no charge.
    What is understood by that ? A neutron has no charge because it has both charges. The same applies to neutrinos, or is a completely different kind of mass/matter intented?
    A neutron is a composite particle (made of 3 quarks whose electrical charges sum to zero and whose color charges sum to "white"/neutral).

    A neutrino is a fundamental particle. As far as we know it has no internal structure. It has zero charge.

    If no: a neutrino is contained in a neutron, what keeps the two charges together in a neutrino?
    Neutrinos are not contained in neutrons. As far as we know, neutrons consist of quarks and gluons.

    2)I read that a neutrino is detected by pair emission, how do they understand if the cause has been a neutrino or EMR
    Neutrinos are detected when they interact via the weak force. There are various ways this can occur. They can interact with an atom via the reverse of beta decay causing positrons and neutrons to be emitted. The positron can then annihilate with an electron generation pairs of (gamma ray?) photons. The neutron can also interact with other atoms causing further radiation to be emitted. Alternatively, they can impart momentum to another particle; if this causes the second particle to travel fast than light in the medium then Cherenkov (sp?) radiation will be emitted. There are other routes as well.

    A lot of effort is made to screen out other possible sources of detection events. This is why neutrino detectors are typically deep underground, surrounded by rocks of low radioactivity. It is still possible that other events can be detected. Sometimes these can be identified because of the energy of the generated photons, etc.

    3)How do you shoot a neutrino in a chosen direction?
    In the famous OPERA experiment, they start with a beam of particles that can be controlled (i.e. protons) and aim these at a large lump of graphite. Neutrinos are generated (indirectly) and, because of conservation of momentum, most will have the same direction as the original beam.


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    Quote Originally Posted by Strange View Post
    A neutrino is a fundamental particle. As far as we know it has no internal structure. It has zero charge.
    You did not ask directly the basic question: if it has no internal structure it is a new kind of mass/matter, the first example of mass without charge. Is that correct? If you mean so it opens up a Pandora box. A neutrino can be annihilated only by an antineutrino.Is that correct? If so, is that yet another type of mass/matter?

    Neutrinos are not contained in neutrons. As far as we know, neutrons consist of quarks and gluons.
    When a neutron is not bound it splits into a proton, electron and neutrino, is that correct? If a neutrino has non-zero mass, and this mass is different from charged mass, how can it be created in the process?
    There are various ways this can occur.
    . Alternatively, they can impart momentum to another , etc.
    . Neutrinos are generated (indirectly) and, because of conservation of momentum, most will have the same direction as the original beam.
    How do you create a neutrino indirectly, or, anyway, apart from breaking up a neutron?
    If they are generated in the graphite (by collision I suppose, but I'llwait for your answer) why should they shoot out at light speed ?
    How can you direct a beam to graphite and produce a beam in a direction so precise that hits a target 500 km away?
    If neutrinos slip through the whole earth, why shouldn't they slip through Opera's detectors? what traps them in bulk?
    Thanks for your attention.
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by logic View Post
    You did not ask directly the basic question: if it has no internal structure it is a new kind of mass/matter, the first example of mass without charge. Is that correct?
    I am not aware of any reason mass and charge have to be associated. Z0 bosons also have mass and no charge.

    A neutrino can be annihilated only by an antineutrino.Is that correct?
    All particles can only annihilate with their anti-particles. Because of conservation laws (all quantum numbers - spin, charge, color, lepton number, etc - have to be conserved).

    When a neutron is not bound it splits into a proton, electron and neutrino, is that correct?
    It decays into a proton, electron and (electron) antineutrino. I think this is because one of the quarks changes flavour via the weak interaction.

    If a neutrino has non-zero mass, and this mass is different from charged mass, how can it be created in the process?
    Mass is just mass.

    How do you create a neutrino indirectly, or, anyway, apart from breaking up a neutron?
    In the case of the OPERA experiment, the intermediate products are mesons. I assume these (being also composite particles) decay via a similar mechanism to neutrons. But I don't know the details.

    If they are generated in the graphite (by collision I suppose, but I'llwait for your answer) why should they shoot out at light speed ?
    Conservation of momentum. They are lighter than the original protons and so they have a corresponding higher velocity for a given energy.

    How can you direct a beam to graphite and produce a beam in a direction so precise that hits a target 500 km away?
    I'm pretty sure the beam spreads out pretty widely but I have not seen any figures for this.

    If neutrinos slip through the whole earth, why shouldn't they slip through Opera's detectors? what traps them in bulk?
    They are only able to detect a tiny fraction. In the OPERA experiment, there were about proton collisions (which should have generated a similar number of neutrinos) and 16,000 detections. Similarly, the "massive" burst of neutrinos detected from the 1987 supernova amounted to ... 24 events.

    Thanks for your attention.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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