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!