Beauty in the Universe

Innermost SpaceHigh Energy Particle Physics is a study of the smallest pieces of matter.

It investigates the deepest and most fundamental aspects of nature.

It investigates (among other things) the nature of the universe immediately after the Big Bang.

It also explores physics at temperatures not common for the past 15 billion years (or so).

Periodic Table

u

du u

d d

Proton Neutron Electron

Gluons hold quarks togetherPhotons hold atoms together

Helium Neon

All atoms are madeof protons, neutronsand electrons

tb

cs

ud

While quarks have similar electric charge, they have vastly different masses (but zero size!)

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Why three dimensions?

What gives particles their mass?

Are there new forces and symmetries that we don’t yet know?

Are the forces and particles of which we do know just different faces of a deeper, unifying principle?

=e2/ħc

Fermi National Accelerator Laboratory

(a.k.a. Fermilab)

• Begun in 1968

• First beam 1972 (200, then 400 GeV)

• Upgrade 1983 (900 GeV)

• Upgrade 2001 (980 GeV)

Jargon alert: 1 Giga Electron Volt (GeV) is 100,000 times more energy than the particle beam in your TV.

If you made a beam the hard way,it would take 1,000,000,000 batteries

Increasing ‘Violence’ of Collision

ExpectedNumber

ofEvents

Run II

Run I

Increased reach for discovery physicsat highest masses

Huge statistics for precision physicsat low mass scales

Formerly rare processesbecome high statisticsprocesses

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The Main Injector upgrade was completed in 1999.

The new accelerator increases the number of possible collisions per second by 10-20.

DØ and CDF have undertaken massive upgrades to utilize the increased collision rate.

Run II began March 2001

How Do You Detect Collisions?• Use one of two large multi-purpose particle

detectors at Fermilab (DØ and CDF).

• They’re designed to record collisions of protons colliding with antiprotons at nearly the speed of light.

• They’re basically cameras.

• They let us look back in time.

Typical Detector (Now)

30’

30’

50’

• Weighs 5,000 tons• Can inspect

10,000,000 collisions/second

• Will record 50 collisions/second

• Records approximately 10,000,000 bytes/second

• Will record 1015 (1,000,000,000,000,000) bytes in the next run (1 PetaByte).

Remarkable Photos

This collision is the most violentever recorded (and fully understood). It required thatparticles hit within 10-19 m or 1/10,000 the size of a proton

In this collision, a top and anti-top quark were created,helping establish their existence

Modern Cosmology• Approximately 15 billion years

ago, all of the matter in the universe was concentrated at a single point

• A cataclysmic explosion (of biblical proportions perhaps?) called the Big Bang caused the matter to fly apart.

• In the intervening years, the universe has been expanding, cooling as it goes.

4x10-12 seconds

Now (13.7 billion years)

Stars form(1 billion years)

Atoms form (380,000 years)

Nuclei form (180 seconds)

??? (Before that)

Nucleons form (10-10 seconds)

Quarks differentiate (10-34 seconds?)

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Why three dimensions?

What gives particles their mass?

Are there new forces and symmetries that we don’t yet know?

Are the forces and particles of which we do know just different faces of a deeper, unifying principle?

Back to the Mysteries

In 1964, Peter Higgs postulated a physics mechanism which gives all particles their mass.

This mechanism is a field which permeates the universe.

If this postulate is correct, then one of the signatures is a particle (called the Higgs Particle). Fermilab’s Leon Lederman co-authored a book on the subject called The God Particle.

top

bottom

Undiscovered!

Higgs: An Analogy

Hunting for HiggsFor technical reasons, we look for Higgs

bosons in association with a W or Z boson.

b jet

electron

neutrino(MET)

In the region where the Higgs boson is expected, we expect it to decay nearly-exclusively into b-quarks

bbH

Symmetries

Translational

Rotational

More Complex Symmetries

In a uniform gravitational field, a ball’s motion is independent of vertical translation.

The origin from where potential energy is chosen is irrelevant.

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2

2

1 2

The equations of motion are “symmetric under vertical or horizontal translations.”

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Complex Familiar Symmetries

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Complex Familiar Symmetries

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Complex Familiar Symmetries

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Reflections: x -x

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Complex Familiar Symmetries

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Rotations:

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Complex Familiar Symmetries

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Complex Familiar Symmetries

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Bottom Line:

Electromagnetic force exhibits a symmetry under:

Translation Rotation Reflection Charge Congugation (and many others)

Fermions and Bosons

Fermions: matter particles ½ integer spin

Bosons: force particles integer spin

Unfamiliar Symmetries

One possible symmetry that is not yet observed is the interchange of fermions (spin ½ particles) and bosons (integral spin particles)

Equation = Fermions + Bosons

Equation = Fermions + Bosons

Known equation

Interchanged equation (pink green)

Unfamiliar Symmetries

One possible symmetry that is not yet observed is the interchange of fermions (spin ½ particles) and bosons (integral spin particles)

Equation = Fermions + Bosons

Known equation

Equation = Fermions + Bosons

Interchanged equation (pink green) + Fermions + Bosons

+ Fermions + Bosons

This New Symmetry is called SuperSymmetry (SUSY)

SUSY Consequence

• SUSY quark “squark”

• SUSY lepton “slepton”

• SUSY boson “bosino”

The Golden Tri-lepton SuperSymmetry Signature

This is the easiest to observe signature for SUSY.

No excess yet observed.

muons

electron

neutrino

The Conundrum of Gravity

• Why is gravity so much weaker (~10-35×) the other forces?

– Completely unknown

• One possibility is that gravity can access more dimensions than the other forces

The Dimensionality of Space Affects a Force’s Strength

• Gauss Law AdEQ

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3D

Are More Dimensions Tenable?

• Newton’s Law of Gravity

• Clearly indicates a 3D space structure.

Or does it?

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Nature of Higher Dimensions

• What if the additional dimensions had a different shape?

• What if the additional dimensions were small?

Access to Additional Dimensions

• What if gravity alone had access to the additional dimensions?

Access to Additional Dimensions

• What if gravity alone had access to the additional dimensions?

A Model with “n” Dimensions.• Gravity communicating with

these extra dimensions could produce an unexpectedly large number of electron or photon pairs.

• Thus, analysis of the production rate of electrons and photon provides sensitivity to these extra dimensions.

• Large energies are required to produce such pairs.

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Once again there are interesting events!

(way out on the mass tail.)

ee pair pair

photonselectrons

Data-Model Comparison

Data-Model Comparison

Summary

• Particle physics allows us to study some of the deepest mysteries of reality.

• We know a whole bunch of stuff.

• The things we don’t know, we’re studying like mad.

• The mysteries mentioned here are unsolved. We need help.

Send students.

www-d0.fnal.gov/~lucifer/PowerPoint/Teacher_Colloquium.ppt

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