PHY106Quarks, Leptons and Force Intro

PHY106Quarks, Leptons and Force Intro - What IS Matter...

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What IS Matter ? Matter is all the “stuff” around you! Here’s the picture we’re going to uncover (not all today though) Matter Matter Leptons Charged Charged Neutrinos Neutrinos Forces Weak Weak EM EM Strong Strong Gravity Gravity Hadrons Baryons Baryons Mesons Mesons Quarks Anti-Quarks
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The Quarks – a Recap Proton u u d Quarks Antiquarks Q = +2/3 Q = -1/3 Q = -2/3 Q = +1/3 u d c s t b u c t d s b Quarks can have 3 color values: red , green & blue Quarks have total spin S = ½ ( S Z = -½ or +½ ) Anti-quarks have the same mass as their quark does. Hadrons = Baryons + Mesons Baryons (antibaryons) contain 3 quarks (3 antiquarks) Mesons contain a quark and an antiquark
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Why quarks? Murray Gell-Mann 1969 Nobel Prize in Physics Why should nature be this complicated? To simplify the picture, and still account for this plethora of particles which were observed, Murray Gell-Mann proposed all these particles were composed of just 3 smaller constituents, called quarks.
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But even Gell-Mann doubted that they were real… An excerpt from Gell-Mann’s 1964 paper: “A search for stable quarks of charge –1/3 or +2/3 and/or  stable di-quarks of charge –2/3 or +1/3 or +4/3 at the  highest energy accelerators  would help to reassure us of  the  non-existence of real quarks”. In 1969, an experiment at SLAC uncovered the first evidence that protons in fact had substructure
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If neutrons & protons are not fundamental, what about electrons? Are they made up of smaller constituents also ? As far as we can tell, electrons appear to be indivisible. As far as we can tell, electrons appear to be indivisible.
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Leptons Electrons belong to a general class of particles, called “ Leptons As far as we can tell, the leptons are “fundamental”.
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PHY106Quarks, Leptons and Force Intro - What IS Matter...

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