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Author Topic: Are heavy partlicles made of combinations of lighter particles?  (Read 1659 times)

Offline Eric A. Taylor

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When they play with particle accelerators they make some really heavy particles like strange quarks and muons.These quickly decay into collections of lighter particles. Does this mean that the heavy particles are made of the lighter ones?

I know under some conditions a neutron can become an electron and a proton. What happens at the quark level when this happens? Does one of the down quarks shed an electron and become an up quark? How is this possible considering the electron has a charge of -1, while +2/3 and the down quark -1/3 for a sum of +1/3?


Offline imatfaal

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(-1/3) - (-1) = (2/3) --> down quark less w- boson goes to up quark - says it better than I could.

Offline Soul Surfer

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Yes and no!  There are three generations of heavier particles for example the electron the muon and the tau (together with their neutrinos)are identical particles except for their weight.  there are similarly three generations of quarks;  normal(up and down), strange and charm, top and bottom.   The succeeding generations are best thought of as exited states of the lowest mass ones. 

Higher mass particles can decay into a range of lower mass particles subject to an array of conservation laws but that does not mean that they are made up of these particles to start with because in many cases there are a set of possible decay paths that are available to any particle and a set of statistical rules defines the probability of each of them,  the production of many of the more interesting particles can have a very low probability and so many experiments have to be done before a statistically significant set of results to identify this particle can be built up.

Offline chrisdsn

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The general viewpoint wouldn't be that the heavier particles are made up of the lighter
ones (it's not like you add two downs to get a strange). However, quarks come in several
flavours ( up, down, strange, charm, bottom, top) and the Weak force can mediate the
change in flavour of a quark. The force carriers for the weak force (the W and Z bosons)
are are massive (as opposed to photons and gluons which mediate the electromagnetic
and strong nuclear forces, which are massless). This means it takes *energy* to make them
(E = mc^2, after all). So in a high energy accelerator you have enough energy density to
make the transformation of an up (say) into a larger mass quark likely. It is an *transformation" however, and not two quarks coming together to form a composite particle.

Due to "Quantum Weirdness", however, systems are allowed to make transformations that require higher energy than they have as long as it is for a very short time (a form of the Heisenberg uncertainty principle). As such, even the "low energy" particles such as the proton and neutron, which we naively think of as being made of up and down quarks,  will also have some strange quark content on average (the amount is an area of active current research).

Offline syhprum

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It is an interesting point that the mass of the Up and Down quarks in as much they can be ascertained only form a small part of the mass of the Proton, the remainder comes from the mass equivalent of the energy of the Gluon's.

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