Transcript From the Infinite to the Infinitely Small: Probing the

Particle Physics at the
Energy Frontier
Tevatron→LHC
&
The Very Early Universe
Tony Liss
Air Force Institute of Technology
April 10, 2008
Two Views of the Universe
• High energy physicists study the
smallest, most fundamental objects
and the forces between them.
• Cosmologists study what there is on
the largest possible scales and try to
understand how it got that way.
But these two very different approaches
address many of the same questions: What is
the Universe made of & how does it behave?
The High-Energy View
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
Unification of the Forces
Electric
Magnetic
Weak
Strong
“Low
Energy”
Higgs Bosons
born here
Electromagnetic
Electroweak
“High
Energy”
“Very
(very)High
Energy”
Theory (“Standard
Model”) works up to
~here
…And you may notice that gravity isn’t in
this picture… STRING THEORY???
Cosmology, Particle Physics, the
Universe and All That
Successes of Particle Physics
+ Big Bang
• Light elements (H to Li) were made in
the early universe
– And we can calculate how much!
About 1 He nucleus for every
10 protons (25% by mass)
Predicted abundance depends
on density of “baryons” –
particles made of 3 quarks
(like a proton or a neutron)
astron.berkeley.edu/~mwhite/darkmatter/bbn.html
The grey band is where the measured & calculated abundances are.
But Wait!
Recent cosmological
measurements put the density
of the universe here.
Most of the universe
is not normal
(“baryonic”) matter!
Dark Matter
(Not a New Idea)
Speed of stuff out here
Doesn’t match
luminous matter in
here!
There’s DARK MATTER in Galaxies!!
Dark Matter In Between
Galaxies Too!
Motion of a
galaxy out here
Doesn’t agree with
luminous matter in
here
The “Hydra” Galactic Cluster
Wmatter ~ 0.3 from
galactic clusters
Studying the Universe at Accelerators
Accelerate particles to
very high energies and
smack them together.
E=Mc2 : Make new stuff
and study how it
behaves.
Fermi National Accelerator Laboratory
This picture shows a proton
and antiproton colliding to
make a pair of top quarks.
Top quarks were discovered 14
years ago at Fermilab
Michael Goodman
Hadron-Hadron Collisions
• Proton-antiproton (Tevatron) or
proton-proton (LHC) collisions:
Each collision (“event”) is between the hadron
constituents. What can happen is…EVERYTHING
Cross Sections
The total pp
cross section is
here at ~1011!
This happens
only once in
~1010 collisions
Data Taking (TeVatron)
p
p
Protons & antiprotons
collide at ~2.5 MHz
0.25Hz of W/Z
production
~100 Hz of
high ET jets
~100 Hz of
b-quark
production
.0002 Hz of top
quark
production
?? Hz of
new physics
20%
“Acceptance”
Prescale/20
10%
“Acceptance”
1%
“Acceptance”
10%
“Acceptance”
??
“Acceptance”
~20% Analysis
Mode
85% to
analysis
~1% Analysis
Mode
~40% Analysis
Mode
?? Analysis
Mode
~10-2 Hz for
analysis
~0.4 Hz for
analysis
~10-2 Hz for
analysis
~10-5 Hz for
analysis
The CDF Detector at FNAL
 The
Mass of the Top Quark
 The Mass of the W Boson
Measuring the Top Mass
There are many subtleties
to improve S/B and
resolution, but basically…
p, E
Measure p, E
for each of the
decay objects
M top c 
2
E
 E j 2  E j3   c
2
j1
2
p
j1
 p j 2  p j3 
2
Measuring the Top Mass
Mtop  171.9  2.0 GeV/c
2
Measuring the W Boson Mass
W
e
e
W
MW  80.413  0.048 GeV/c2


A Window
on
the
Higgs!
t
H
W
W
b
2
MW  Mtop
Experimental
bound (LEP)
W
W
W
MW  ln M Higgs
The result is marginally inconsistent
with the SM… SUSY????
Making Higgs Bosons
Finding The Higgs
The Higgs “couples to mass”, so it’s preferred decay
channel depends on its (unknown) mass. As if life
were not difficult enough…
Looking for Higgs (is hard)
H  bb (x10!)
No Higgs…yet
SUSY
• Every quark, lepton and force
carrier has a SUSY partner
(sparticles).
– Sparticles would be made
copiously in the early (HOT)
universe.
– They all decay away quickly,
except for the lightest one
(neutralino), which can’t.
– The dark matter might be made
up of neutralinos!!
Make SUSY
particles at an
accelerator:
pp  
www.science.doe.gov/hep/EME2004/03-what-is.html
Another Reason to Believe in SUSY?
• Einstein’s dream of a “Unified Field
Theory”, now needs SUSY:
EM
weak
No SUSY
SUSY
strong
Energy
Energy
Searching for SUSY – an example
SUSY models come in many different flavors, but one
characteristic of many of them is signatures with
large “Missing ET” – Undetectable particles whose
momentum is unmeasured.
In these diagrams
“charginos” and
“neutralinos” are produced.
In their subsequent
decay, the lightest
“neutralino” is produced
but remains undetected.
Searching for Charginos &
Neutralinos
The data
Backgrounds
What the signal
would look like (if
it were there)
No SUSY So Far
• Many searches, no sightings…
• The
hunt continues…
• At LHC there is 7x more “reach”
(E=Mc2) for making SUSY particles.
• But maybe SUSY isn’t the right
model…
• We can find it anyway if M<E/c2!
On to the LHC!
ATLAS Detector at CERN
ATLAS is VERY BIG
ATLAS
A (simulated) Higgs event in
ATLAS
A Black Hole in ATLAS
The Universe as We Know It
This is NOT what we
thought as recently as
10 years ago!!
73%
Our fabulously successful
“Standard Model of
particle physics” explains
only 4% of the universe…
So far…
Perspective
• Our theories of cosmology and particle
physics are extremely successful, but leave
significant open questions.
• As new phenomena are discovered, we
adapt the theories and test them with
experiments & observations.
• The next ten years of accelerator
experiments and cosmological
measurements are guaranteed to bring new
insights and new surprises!