95 lines
5.2 KiB
HTML
95 lines
5.2 KiB
HTML
<h2>Weak Interaction and nuclear decay</h2>
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<p>There are more particles after the decay than just the proton,
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there is an electron and a new particle that has not been introduced
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yet. This new particle is the neutrino (which is italian and means
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“the small neutral one”). As its name suggests, it is electrically
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neutral. It has no color charge either, so it does not interact
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strongly. It only interacts with this new force, the weak force, and
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because the weak force is so weak, it is extremely difficult to
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detect. It has been detected, for the first time in 1956, 26 years
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after it had been predicted. It also differs from the quarks and the
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electron in that its mass has not been measured, it is so light that
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there are only upper limits on its mass. The best, up do date limit is
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about 1/250 of the mass of the electron.</p>
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<img src="neutron_decay.png">
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<p>This figure shows what happens in the beta decays, the neutron
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turns into a proton, an electron and this new particle, the
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neutrino. For now the interaction is a “black box”, we know what comes
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in and what comes out, but what happens in between?</p>
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<h2>Charged Messengers</h2>
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<p>The other forces had messenger particles, the photon[ref] for
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electromagnetism and the gluons[ref] for strong interactions, this is
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also true for the weak force, and like for the other two forces, the
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messenger is a boson[ref]. There is an important difference though,
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the messenger particles for the weak force are very heavy, and there
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are three of them. Their weight is the reason that this force is so
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weak. This sounds counter-intuitive, right? We won’t dive into this,
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so if you want to know more, head over here->[READ MORE?]. The
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messenger particles are called the W bosons, there are two of them,
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one with positive electric charge and one with negative charge, and
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there is also a neutral one, which is called Z and which will be
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explained later.</p>
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<p>What actually happens in this "black box", is that the neutron
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turns into a proton and a [W-] boson, and the [W-] boson decays into
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an electron and a neutrino. The W boson is very heavy, its mass is
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about 80 times that of the proton, and it will only exist for an
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extremely short time (we cannot explain this with what we have
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explained so far, but you might want to keep reading until we explain
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the second and third generations of matter to understand the short
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lifetime of the W). As we know neither the proton nor the neutron is
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fundamental, so we can still look closer at the neutron becoming the
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proton and the [W-] boson. The neutron is made up of one up-quark and
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two down-quarks, and what happens is that one of the down-quarks turns
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into an up-quark and the [W-] boson. This is the extent to which the
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Standard Model is describing this weak interaction, the down-quark
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turning into an up-quark and a [W-] boson and the decay of the
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[W-]. These two interactions are “black boxes”, perhaps there is
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something more fundamental occurring if one just looks closely enough,
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nobody knows that as of today, again this is for someone (maybe you)
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to find out! </p>
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<p>So far the matter particles that have been introduced are the
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electron, the up and down-quarks and the neutrino. The quarks are
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connected in that they can interact strongly with each other, and they
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are connected to the electron by the electromagnetic force. But the
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matter particles are grouped into quarks and leptons, the leptons (so
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far) being the electron and the neutrino[[, muon, tau and their
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respective neutrino]]. The weak force really gives the connection that
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motivates giving the electron and the neutrino this common name,
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leptons, as it allows electrons to turn into neutrinos and the other
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way around. It also connects the two types of quarks in the same way,
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allowing the up-quark to turn into the down-quark as mentioned.</p>
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<h2>Neutral messenger and discovery</h2>
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<p>The third messenger of the weak force is the Z boson, which is
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about as massive as the W bosons, 90 times as massive as the
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proton. But unlike the W bosons, it is not charged. Both the Z and the
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W bosons were discovered at CERN, and their discovery is one of the
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major accomplishments of both CERN and the Standard Model. It is
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remarkable because the masses of the particles were predicted, and the
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Z boson, unlike the W bosons, was not involved in the weak
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interactions that were known, [but was a consequence of the theory and
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no experiment had seen any indication of its existence when it was
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predicted, can you explain this one]. Both the W bosons and the Z
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boson were discovered in 1983, and the two persons responsible for the
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experiments, Rubbia and van der Meer, got the Nobel prize for this
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just one year after the discovery, in 1984. </p>
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<h2>Outlook</h2>
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<p>Is this it? For what we know, yes. What we know by now is
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sufficient to explain everything that surrounds us, from the atoms and
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nuclei being formed, quarks glued together, down to things as rare and
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obscure as nuclear decay and radiation. Is this the whole picture? Not
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quite. We have not explained antimatter, and then there are some
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really strange particles turning up in cosmic rays. And, in the end,
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you might want to learn about the Higgs as well. Read on!</p>
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