Teachers colloquium

Upload
dheerajkumar 
Category
Education

view
124 
download
3
Embed Size (px)
description
Transcript of Teachers colloquium
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!)
Mys
terie
s of t
he Q
uant
um U
niver
se
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
1
10
100
1000
The Main Injector upgrade was completed in 1999.
The new accelerator increases the number of possible collisions per second by 1020.
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 multipurpose 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 1019 m or 1/10,000 the size of a proton
In this collision, a top and antitop 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.
4x1012 seconds
Now (13.7 billion years)
Stars form(1 billion years)
Atoms form (380,000 years)
Nuclei form (180 seconds)
??? (Before that)
Nucleons form (1010 seconds)
Quarks differentiate (1034 seconds?)
Mys
terie
s of t
he Q
uant
um U
niver
se
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 coauthored 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 nearlyexclusively into bquarks
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.
hgv
hmgmv
2
2
1 2
The equations of motion are “symmetric under vertical or horizontal translations.”
h
r
qqV
o
21
4
1
Complex Familiar Symmetries
r
r1
r2
x
y
 21
21
4
1
rr
qqV
o
r2
r1
Complex Familiar Symmetries
r
r1
r2
x
yTranslations: x x + x y y + y
 21
21
4
1
rr
qqV
o
Complex Familiar Symmetries
r
r1
r2
x
y
x
y
Reflections: x x
y y
 21
21
4
1
rr
qqV
o
Complex Familiar Symmetries
r
r1
r2
Rotations:
x
y
 21
21
4
1
rr
qqV
o
Complex Familiar Symmetries
r
r1
r2
Charge Flip: q q
x
y
Vrr
rr
qqV
oo

))((
 21
21
21
21
4
1
4
1
 21
21
4
1
rr
qqV
o
Complex Familiar Symmetries
r
r1
r2
x
y
 21
21
4
1
rr
qqV
o
V
rr
rr
qqV
oo

))((
 21
21
21
21
4
1
4
1
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 Trilepton 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 (~1035×) 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
o
encl
r
QE encl
o2
1 24
1
r
QE encl
o
2D
3D
Are More Dimensions Tenable?
• Newton’s Law of Gravity
• Clearly indicates a 3D space structure.
Or does it?
221
r
mGmF
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.
p
pG
qq’
e
e
Once again there are interesting events!
(way out on the mass tail.)
ee pair pair
photonselectrons
DataModel Comparison
DataModel 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.
wwwd0.fnal.gov/~lucifer/PowerPoint/Teacher_Colloquium.ppt
Available at Amazon, BarnesandNoble.com + local book stores