particle physics at the energy frontier
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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 ViewThe matter around us is made up of “quarks” and “leptons”
And held together by four forces, each with a force carrier:
A proton is made of U U D
Add an electron to make a hydrogen atom Electromagnetic
StrongWeak
Gravity
Unification of the Forces
ElectricMagneticWeakStrong
ElectromagneticElectroweak
“Low Energy”
“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???
Part way to Einste
in’s
dream!
Higgs Bosons born here
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!
astron.berkeley.edu/~mwhite/darkmatter/bbn.html
Predicted abundance depends on density of “baryons” – particles made of 3 quarks (like a proton or a neutron)
About 1 He nucleus for every 10 protons (25% by mass)
The grey band is where the measured & calculated abundances are.
But Wait!
Most of the universe is not normal (“baryonic”) matter!
Recent cosmological measurements put the density of the universe here.
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
matter ~ 0.3 from galactic clusters
Studying the Universe at AcceleratorsAccelerate particles to very high energies and smack them together.
E=Mc2 : Make new stuff and study how it behaves.
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
Fermi National Accelerator Laboratory
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
1% “Acceptance”
~1% Analysis Mode
~10-2 Hz for analysis
10% “Acceptance”
~40% Analysis Mode
~10-5 Hz for analysis
?? “Acceptance”
?? Analysis Mode
20% “Acceptance”
~20% Analysis Mode
~10-2 Hz for analysis
Prescale/20 10%
“Acceptance”
85% to analysis
~0.4 Hz for analysis
The CDF Detector at FNAL
The Mass of the Top Quark
The Mass of the W Boson
Measuring the Top Mass
,p E
2 22 21 2 3 1 2 3top j j j j j jM c E E E c p p p
There are many subtleties to improve S/B and resolution, but basically…
Measure for each of the decay objects
,p E
Measuring the Top Mass
2171.9 2.0 GeV/ctopM
Measuring the W Boson MassW e
eW
280.413 0.048 GeV/cWM
A Window on the Higgs!
Experimental bound (LEP)
2W topM M lnW HiggsM M
W W
W
HW W
t
b
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)
(x10!)H bb
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!!
www.science.doe.gov/hep/EME2004/03-what-is.html
Make SUSY particles at an accelerator:
pp
E=Mc2 happening
here!
Another Reason to Believe in SUSY?
• Einstein’s dream of a “Unified Field Theory”, now needs SUSY:
Energy Str
eng
th o
f fo
rce
No SUSY
Energy Str
eng
th o
f fo
rce
SUSYEM
weakstrong
Searching for SUSY – an exampleSUSY 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
What the signal would look like (if it were there)
The data
Backgrounds
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
Dar
k M
atte
r
Dar
k En
ergy
This is NOT what we thought as recently as 10 years ago!!
Our fabulously successful “Standard Model of particle physics” explains only 4% of the universe…
So far…
Ato
ms
73%
4%
23%
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!
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