physics at the highest energies Joe Lykken Fermi National Accelerator Laboratory
slides + more info • http://theory.uchicago.edu/~smaria/aaas05-colliders/
• particles accelerated to high energies can probe sub-atomic distances • so particle accelerators are super-microscopes
particle alchemy • when particles collide, some of their energy can be converted into new particles: E = mc 2 • so accelerators produce particles which do not normally exist on Earth. • the higher the energy, the heavier the particles that we can produce:
collisions at MeV energies MeV = million electron volts the first circular particle accelerator, built by Lawrence and Livingston in 1932 accelerated protons to 1.2 MeV diameter = 11 inches! collisions at MeV energies can produce nuclear reactions
collisions at GeV energies GeV = billion electron volts collisions at GeV energies can produce antimatter, quarks, neutrinos, etc Fermilab booster and antiproton source
collisions at TeV energies TeV = trillion electron volts collisions at TeV energies may produce • Higgs bosons • superparticles • dark matter underground tunnel of the 14 TeV Large Hadron Collider in Geneva
major themes of particle physics today • the quantum vacuum • the dark side • the origin of space and time
the Standard Model • 57 elementary particles • matter + forces
a universe full of Higgs the Standard Model conjectures: • the existence of a Higgs energy field • the Higgs field permeates the entire universe • particles react to the Higgs field and get mass these are bold conjectures!
Higgs vs the quantum vacuum Problems: • where is the Higgs particle? • a Higgs field doesn’t seem to be consistent with a quantum vacuum • some important new physics is missing in this story!
Higgs and new physics • is there a Higgs? how many Higgs? • what is the new physics that reconciles Higgs (or something like it) with the quantum vacuum? supersymmetry? new forces? extra dimensions? none of the above? we will know soon by probing the TeV energies:
countdown to LHC supercollider LHC magnets in the tunnel CMS detector at CERN
countdown to LHC supercollider ATLAS detector installation at CERN
the particles we know make up only 4% of the universe! can we use supercolliders to solve the mysteries of dark matter and dark energy?
what is dark energy? • a dark energy field permeates the entire universe - what is it? • unlike magnetic or electric fields, it accelerates the expansion of the universe • could be just gravity, but then Einstein was wrong! • could be the Higgs field, but then why isn’t it much more intense?
the universe could be bigger than we know: • could have extra spacetime dimensions • could have extra quantum dimensions • this second possibility implies supersymmetry
supersymmetry
superparticles • supersymmetry is a fundamental principle which can be built into the laws of particle physics • it predicts that every particle has a partner superparticle • but no superparticles have been seen yet
supersymmetry has other profound implications: • supersymmetry suppresses quantum effects, quiets the quantum vacuum • with other ingredients, supersymmetry can make quantum mechanics consistent with gravity superstrings
supersymmetry and dark matter • lightest neutralino is a combination χ 0 ˜ 1 of the superpartners of the photon, Z and Higgs • in most models, this is the stable LSP • mass ~ 100 GeV - 1 TeV • our best guess for dark matter!
a superconducting solution: can we understand all or some of the dark matter constituents in the laboratory? we will need a Linear Collider for this
are we one particle away from understanding dark matter? choose one: - neutralino - axion - wimpZILLA - LKP let’s imagine - sterile neutrino a different history...
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what is the mysterious bright matter? Answer: 57 new elementary particles + 2 new forces in this 4% slice!
• why shouldn’t there be 57 components for the dark matter sector? (don’t all have to be stable) • won’t understand dark sector until you understand all of this • emphasizes need for multiple overlapping experimental and observational approaches
the origin of space and time question for the LHC supercollider: • do extra dimensions play a role with the Higgs and electroweak physics?
what? extra dimensions? • are there more spatial dimensions than the three that we see? • if so, why haven’t we seen them?
microscopic extra dimensions a simple example: the tightrope walker sees the tightrope as having only one spatial dimension the tightrope walker can only move in one direction, (back and forth)
but an ant on a tightrope can move both back and forth AND around a circle the ant sees an extra dimension = an extra tiny circle at every point along the tightrope
three fundamental but very distinct physical arguments point towards extra dimensions: • spacetime is dynamical • string theory • the particle zoo
spacetime is dynamical • Einstein figured out in 1911 that spacetime is curved and distorted by matter and energy • there is no reason to suppose that the dynamical history of spacetime is simple • the number of accessible spatial dimensions at any given energy scale is something you have to measure
in string theory electrons, quarks, photons, gravitons, neutrinos, etc are all different vibrations of one kind of microscopic string: the superstring
• string theory is very elegant mathematically • but if we take string theory seriously, it makes a prediction that there are many extra dimensions of space
the particle zoo • 57 different elementary particles related to each other in complicated ways • can we map part/all of these patterns onto the shape of the extra dimensions?
how do you detect an extra dimension? maria spiropulu • even if extra dimensions make sense in theory, it still isn’t physics until you find a way to detect them in experiments • this depends upon what is the physical mechanism that is hiding them • let’s explore Oskar Klein’s idea that extra dimensions are hidden because they are tiny
Kaluza-Klein modes • if the extra dimension is tiny, we will not see a particle’s motion around it • so we will interpret the momentum from this motion as a contribution circle with radius R to the particle’s mass • quantum mechanics says that this momentum is quantized: it has to m = n be a multiple of 1 / R R • we call this new heavy particle a Kaluza-Klein mode
one small problem: Fermilab theorists • we don’t know which particles can move in the extra dimensions • string theory suggests that perhaps none of the particles that we are made of can move in extra dimensions!
the braneworld only gravitons and exotics move in the “bulk” of the extra dimensional universe ordinary particles are trapped on a brane and can’t move in the extra dimensions
• if the braneworld idea is correct, the extra dimensions may be large! • they may affect the Higgs, or even cosmology. • perhaps only experiments with gravity or gravitons will detect the presence of extra dimensions Savas Dimopoulos Lisa Randall Nima Arkani-Hamed Gia Dvali Raman Sundrum
extra dimensions at colliders • particle accelerators are our most powerful tools for exploring extra dimensions • if Klein’s idea of tiny extra dimensions is correct, we can still detect them as long as their size is no smaller than .00000000000000001 centimeters! • if the braneworld or related ideas are correct, we can produce Kaluza-Klein modes at particle colliders like the LHC and ILC
the origin of space and time long term questions: • what is string theory? • where do space and time come from? • what is the origin and fate of the universe?
the era of supercolliders • we have recovered from the Hole in Texas • the supercollider era begins with LHC 2007 • Higgs, supersymmetry, extra dimensions? • dark matter in the laboratory?
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