physics at the highest energies Joe Lykken Fermi National - - PowerPoint PPT Presentation

Joe Lykken Fermi National Accelerator Laboratory

physics at the highest energies

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:

• so accelerators produce particles which do

not normally exist on Earth.

• the higher the energy, the heavier the

particles that we can produce:

E = mc2

collisions at MeV energies

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 MeV = million electron volts

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

underground tunnel of the 14 TeV Large Hadron Collider in Geneva

• Higgs bosons
• superparticles
• dark matter

major themes

• f 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

CMS detector at CERN LHC magnets in the tunnel

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?

• 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?

what is dark energy?

• could have extra spacetime dimensions
• could have extra quantum dimensions
• this second possibility implies

supersymmetry

the universe could be bigger than we know:

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 suppresses quantum

effects, quiets the quantum vacuum

• with other ingredients, supersymmetry

can make quantum mechanics consistent with gravity

supersymmetry has other profound implications:

superstrings

supersymmetry and dark matter

• lightest neutralino is a combination
• f 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!

˜ χ0

1

can we understand all or some of the dark matter constituents in the laboratory? we will need a Linear Collider for this

a superconducting solution:

choose one:

• neutralino
• axion
• wimpZILLA
• LKP
• sterile neutrino

let’s imagine a different history... are we one particle away from understanding dark matter?

uppose at we wer reatures of e dark...

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?

• are there more spatial dimensions than

the three that we see?

• if so, why haven’t we seen them?

what? extra dimensions?

microscopic extra dimensions

a simple example: the tightrope walker sees the tightrope as having only

• ne spatial dimension

the tightrope walker can

• nly 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

• 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?

the particle zoo

how do you detect an extra dimension?

• 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

maria spiropulu

• 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 to the particle’s mass

• quantum mechanics says that this

momentum is quantized: it has to be a multiple of

• we call this new heavy particle a

Kaluza-Klein mode

Kaluza-Klein modes

circle with radius R

m = n R

1/R

• ne small problem:
• 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!

Fermilab theorists

• rdinary particles are trapped on a brane and can’t move in the

extra dimensions

• nly gravitons and exotics

move in the “bulk” of the extra dimensional universe

the braneworld

• 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 Gia Dvali Lisa Randall Raman Sundrum Nima Arkani-Hamed

• 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

extra dimensions at colliders

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?

• we have recovered from the Hole in Texas
• the supercollider era begins with LHC 2007
• Higgs, supersymmetry, extra dimensions?
• dark matter in the laboratory?

the era of supercolliders