Quarks Leptons Bosons the LHC and all that
Quarks, Leptons, Bosons, the LHC and all that. Tony Liss OLLI Lecture September 23, 2008
Some HE Physicist Principles • We are reductionists (and proud of it!) – Our worldview is that there a small number of fundamental constituents, interacting via a small number of forces, that make up the Universe as we know it. – This picture has worked extremely well for about 2000 years. – The modern version has been untangled using particle beams of ever increasing energy.
The Standard Model The matter around us is made up of “quarks” and “leptons” A proton is made of uud Add an electron to make a hydrogen atom Electromagnetic Strong Weak And held together by four forces, each with a force carrier: ? ? Gravity
The Standard Model The matter around us is made up of “quarks” and “leptons” Helium Atom particleadventure. org The marriage of quantum mechanics and special relativity required that antiparticles exist.
Why High Energy? • From quantum theory we know l ~ 1/p Wavelength is inversely proportional to momentum If you want to see small things you need short wavelengths (that’s why electron microscopes were invented) and short wavelengths means high momentum (and energy). • From relativity we know E=Mc 2 If you want to create a heavy particle (large M) you need a lot of energy.
Unification of the Forces Electric Magnetic Weak Strong Electromagnetic “Low Energy” w t r Pa d s ’ in e t s in E o t y a Higgs Bosons born here? m a e r ! Electroweak “High Energy” Theory works up to ~here That’s the region we want to probe with the LHC. “Very (very)High Energy”
H N- L CER C
Fermilab Protons & antiprotons collide at 2 Te. V (2 x 1012 electron volts) The worlds highest energy particle accelerator!!
Fermilab Makes Top Quarks The heaviest known elementary particle. Discovered in 1994! Why is it so heavy? ? We don’t know
The Large Hadron Collider 2. 7 mi The world’s largest, highest energy, accelerator 300 feet underground outside of Geneva, Switzerland. The LHC collides intense beams of protons 40 million times per second at “ 14 Te. V”
France Grapes Switzerland Cows
Inside the Tunnel
ATLAS Detector at CERN
ATLAS is VERY BIG
ATLAS
Who Is ATLAS? • ATLAS is one of four large experiments at LHC – The ATLAS collaboration consists of • • ~2500 physicists including ~700 graduate students from 169 different institutions in 37 different countries ATLAS is a United Nations of particle physics.
ATLAS, The Movie http: //atlas. ch
Some of What LHC Can Study • Higgs Boson – Understanding M • Supersymmetry – Dark Matter? • Extra Dimensions – Quantum Gravity/String Theory • Dark Energy – We don’t even know how to look for this • Heavy gauge bosons – New forces? • Precision top quark studies – New physics? • Diboson production – From the Higgs? • Quark and lepton substructure – Are fundamental particles fundamental? • etc.
Let’s Pick Two • Higgs Boson • Supersymmetry
What is “The Higgs”? • Named after Peter Higgs • It “gives mass” to the fundamental particles (if, in fact, it exists) Without the Higgs (or something) theory requires that all these fundamental particles have M=0. But we know that’s not the case.
F=Ma The idea is that the Higgs field exists throughout all space. As particles try to move through this field they interact with it and are “slowed down”. Heavier particles are those that interact more strongly M=F/a In quantum mechanics there is a particle associated with a field (quantum of the field). The photon is the quantum of the electromagnetic field. The Higgs boson is the quantum of the Higgs Field.
Finding the Higgs • The Higgs “couples to mass” – It decays to the heaviest particles available Hard, but copious Easy, but rare
This is a simulation of the production and decay of a Higgs to two Z bosons. The Z bosons themselves decay, one to a pair of electrons and the other to a pair of muons. m+ m- e+ e-
Supersymmetry (SUSY) • Every quark, lepton and force carrier has a SUSY partner (sparticles). Make SUSY particles at an accelerator: – Sparticles would be made copiously in the early (HOT) universe. – They all decay away quickly, except for the lightest one (neutralino), which has nowhere to go. www. science. doe. gov/hep/EME 2004/03 -what-is. html
Why is this an attractive idea? SUSY & Unified Forces Strength of force • SUSY helps with unifying the forces. Einstein’s dream of a “Unified Field • • SUSY is a necessary ingredient of quantum gravity theories. Theory”, now needs SUSY: • We know that the universe is filled with dark matter. No SUSY EM matter is not made of quarks and leptons – the – Dark Standard Model has no dark matter candidates. – Dark matter interacts very weakly with normal matter weak (or else we would have found it already). strong – The lightest SUSY particle is a perfect candidate. Energy
Dark Matter
Dark Matter’s Everywhere In Galaxies And clusters of galaxies Speed of stuff Motion out here of a galaxy out here Doesn’t match luminous matter in here! Doesn’t agree with luminous matter in here The “Hydra” Galactic Cluster
Physics 211 • Momentum is “conserved” – Before the protons collide they have equal and opposite momentum: The total momentum is zero. – Therefore: The total momentum of all the stuff created in the collision must also be zero.
A Simulated SUSY Event Missing momentum carried away by invisible particle
About Those Black Holes… • Creating microscopic black holes at the LHC would be – A MAJOR BREAKTHROUGH IN SCIENCE! – INCREDIBLY EXCITING – NOBEL PRIZE STUFF – NOT AT ALL DANGEROUS – REALLY
About Black Holes • The microscopic black holes that might be created at LHC are so small they evaporate instantly according to Steven Hawking. – But what if Hawking’s wrong? • Cosmic rays reach much higher energies than the LHC and have been having collisions for billions of years – any black holes created have not done much damage.
About Black Holes • Black holes don’t suck everything in. – Only stuff inside the Schwarzschild radius. – If the sun suddenly became a black hole, the Earth’s orbit would not change (but we’d get very cold). The Schwarzschild radius of the sun is 3 kilometers. – The Schwarzschild radius of a 1 Te. V black hole is about 10 -18 m – that’s about 1/1000 th of the size of a proton. • There’s nothing around such a black hole for it to suck in!
Final Words • After 25 years of planning and 15 years of design and construction, the LHC is finally about to turn on. • This is the chance of a lifetime. • Our understanding of the way the Universe works is about to be revolutionized. – We just don’t know exactly how…
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