Marina PartIII

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Information about Marina PartIII

Published on October 16, 2007

Author: Lindon



A first path towards unification: from hadrons to quarks:  A first path towards unification: from hadrons to quarks Circa 1950, the first particle accelerators began to uncover many new particles, at a much faster rate than cosmic ray experiments. Most of these particles are unstable and decay very quickly, and hence had not been seen in cosmic rays. Could all these particles be fundamental? Slide2:  Symmetry operations on an octahedron illustrate the theory of quarks. Theorist Murray Gell-Mann (and, independently, Yuval Ne'eman) discovered a theory that organized all the particles into families with properties mathematically the same as those of a "group of eight" in abstract algebra. Gell-Mann called it "The Eightfold Way." When physicists recognized that underlying fundamental particles could explain the eightfold pattern, the idea of quarks was born. In the 1970s, experiments at the Department of Energy's SLAC showed that quarks were not just mathematical constructs but real building blocks of protons and neutrons. M. Gell-Mann and the eightfold way  quarks were established as the fundamental building blocks of hadrons Slide3:  Quarks and leptons: the building blocks Ordinary matter Cosmic rays/ particle physics accelerators 1974 The discovery of charm:  1974 The discovery of charm the fourth quark was discovered simultaneously on the West Coast, at DOE’s SLAC, using the MARK I detector, (above left) and on the East Coast, at DOE’s Brookhaven Laboratory. Physicist Burton Richter, (left), led the SLAC team, and Sam Ting led the Brookhaven group, (right). sc Our path towards elementary constituents: does it end here?:  Our path towards elementary constituents: does it end here? Fundamental forces I:  Fundamental forces I The electromagnetic force binds electrons to atomic nuclei (clusters of protons and neutrons) to form atoms. Electromagnetic force Weak force gravity This is the force that is part of our everyday life but is the only one that does not fit in the quantum theory that I am describing Fundamental forces II: the strong force:  Fundamental forces II: the strong force Each quark carries one of the three types of "strong charge," also called "color charge." These charges have nothing to do with the colors of visible light. There are eight possible types of color charge for gluons. Just as electrically-charged particles interact by exchanging photons, in strong interactions color-charged particles interact by exchanging gluons. Force in the microworld: :  Force in the microworld: interactions proceed via the exchange of a force-carrier called bosons. Particles transmit forces among each other by exchanging force-carrying particles called bosons. These force mediators carry discrete amounts of energy, called quanta, from one particle to another. You could think of the energy transfer due to boson exchange as something like the passing of a basketball between two players Bosons: the force carriers:  Bosons: the force carriers electroweak unification:  electroweak unification Standard Model of ElectroWeak interactions (Glashow, Salam, Weinberg): unification of em and weak forces W inferred from b decay etc no experimental evidence of the Z at that time W, Z mass  100 GeV  weak force is weak and short range BUT the SM construction applies only to massless particles unless the minimum energy state is non zero …. this implies that a ‘particle’ called ‘Higgs’ exists. experimental evidence:  experimental evidence 1973: discovery of weak neutral currents at CERN in nme scattering interactions (indirect evidence for the Z boson) The theory was in good shape but there was still a lot to verify The mystery of mass:  The mystery of mass When you get on the scale in the morning, you may be hoping that it registers a smaller number than the day before -- you may be hoping that you've lost weight. It's the quantity of mass in you, plus the force of gravity, that determines your weight. But what determines your mass? That's one of the most-asked, most-hotly pursued questions in physics today. Many of the experiments circulating in the world's particle accelerators are looking into the mechanism that gives rise to mass. We are hoping to find the "Higgs boson." Higgs, they believe, is a particle, or set of particles, that might give others mass. The hunt for the Higgs particle(s):  The hunt for the Higgs particle(s) This is the remaining piece of the puzzle that is yet to be discovered: LHC, the most powerful pp collider is being built at CERN to discover this object and, maybe, some even more exotic matter! CERN Putting it all together:  Putting it all together The Standard Model summarizes the current knowledge in Particle Physics and is consistent with an impressive amount of very precise data. It is the quantum theory that explains all our present observations of the subatomic world on the basis of two fundamental components the theory of strong interactions (quantum chromodynamics or QCD) the unified theory of weak and electromagnetic interactions (electro-weak). Are we done?:  Are we done? We do not think so: Mass hierarchy is a big mystery mt/mu 108 the n mass  quark mass different scale Why are there 3 families? A more complete theory may be looming at the horizon! What about gravity? What is next?:  What is next? the coupling constant are not really “constant” a1 em a2 weak a3 strong at ~ TeV scale the “coupling constants” start to deviate from the SM predictions if there is SUSY expect to see “sparticles” at ~ TeV energy A deeper level of unification? Final remark: the study of these fundamental particles can be seen as a search for our origins:  Final remark: the study of these fundamental particles can be seen as a search for our origins particle accelerator = time machine recreate at microscopic scale the physics soon after the Big Bang

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