1. The search for the God Particle
The Higgs Boson
The search for the God Particle

2. The Standard Model
Most successful description of fundamental particles and forces
Provides a theoretical framework incorporating all known particles and forces (except gravity)

3. Forces Electromagnetic Strong Weak
Gravity (not actually included in the standard model)

4. Quantum Field Theory (QFT)
A theory of fields that is consistent with quantum mechanics
Utilizes gauge particles which travel back and forth between charged particles (in the case of the electromagnetic field), and are the origin of force
Electroweak theory
Incorporates Quantum ElectroDynamics (QED) and theory of weak interactions
Quantum ChromoDynamics (QCD) is the QFT for color force

5. Fundamental Particles
6 Quarks:
top, bottom, charmed, strange, up, down
6 Leptons:
electron, muon, tau, and their neutrinos
6 bosons
Electromagnetic force: photon
Strong force: gluon
Weak force: W+, W-, Z
Gravitational: graviton

6. Shortcomings of the Standard Model
Doesn’t incorporate gravity
Doesn’t explain the masses of the particles
Why should something as simple as a quark even have a mass
Why do they have different masses
For instance, photons are massless, but the W and Z particles are huge
Why there is such a range of masses
Doesn’t explain the origin of mass

7. Criteria for a New Theory
Explain the symmetry breaking between electromagnetism and the weak force
Describe a mechanism for imparting mass to particles
Cannot introduce any new physics

8. Enter the Higgs Field
There is a Higgs field that fills the universe (a scalar field)
Any particles that pass through this field distort it
This distortion slows the particles down, preventing them from travelling at the speed of light
This is, in fact, the particle’s mass
Analog to physics in solids – an electron moving through a positively charged crystal lattice acts as if it is 40 times more massive

9. The Higgs Boson
Since the Higgs field is a quantum field, it has it’s own carrier particle, the Higgs boson
The Higgs has spin 0, because the Higgs field is a scalar field
If it had a spin, there would be a preferred direction, which there is not
In fact, the Higgs boson is the analog of the phonon in crystals; it is a perturbation in the field itself, without a particle
Might be a top – antitop combination

10. The Higgs Boson (cont.)
Causes W and Z bosons to be massive, which limits the range of the weak force
Photons are not affected, so they are massless, travel at the speed of light, and have an infinite range
In other words, the symmetry of the electroweak force is broken

11. The Mass of the Higgs Boson
The mass of the Higgs particle is important because different theories predict different masses
Experiments at the LEP showed that the mass of the Higgs must be > 113 GeV
Supersymmetric: < 130
Standard model: < 170
Technicolor: > 160

12. Finding the Higgs
Basically, you accelerate protons and antiprotons in opposite directions
When they come together, they annihilate in a burst of energy
This energy forms a Higgs particle, which then decays
The decay particles are picked up by a detector, and their velocities are measured
Using conservation of momentum and energy, physicists work backwards to find the mass of the Higgs

13. Decay Process for the Higgs
Higgs is heavy, so it can decay into almost anything
Branching ratios are strongly dependent on the Higgs mass, thus making a variety of tagging and detection algorithms necessary

14. Summary of Decays Available
Indistinguishable jets produced, but important for Higgs production
Decay into gluon pair
Gluon Decay
Weak branching ratio but clean signature
Decay into photon through higher order processes
Two Photon Decay
Coupling strongest to top quark (unless mH<2MT)
Decay into any fermion
Fermionic Decay
Decay into Z or W boson
Vector Boson Decay
Diagram
Remarks
Description
Higgs Decay Process

15. History of the Higgs Peter Higgs proposed the idea in 1964
The SSC was built, in large part, to look for the Higgs. However, the project was terminated in 1993
In 2000, the LEP collider was scheduled for shutdown
However, the physicists decided to max the collider in a final bid to find the Higgs
They found 5 possible appearances, but the collider was shut down without the Higgs having been found

16. History of the Higgs (Cont.)
It was hoped that Fermilab would be able to detect the Higgs, but that turned out to not be the case
LHC at CERN should be finished in 2007 and should be able to detect it

17. Conclusion The Higgs boson gives particles mass
To be consistent, the standard model requires the existence of the Higgs boson
The mass of the Higgs boson will pick out the most valid theory
Finding the Higgs boson is not trivial. Further searches will increase the precision of current measured values, and provide a better estimate for the Higgs mass

18. Conclusion (Cont.)
If and when the Higgs is discovered, it will be one of the most important discoveries in particle physics
Finding the Higgs boson will further the longer-term goal of unifying all forces
There are other theories to explain how particles get their mass - proving that the Higgs boson does not exist would be just as scientifically valuable as proving that it does

19. Higgs Himself

20. Dismantling the LEP

21. Computer reconstruction of a possible Higgs decay

22. Part of the LHC (under construction)

23. Bibliography
The God Particle: If the Universe is the Answer, What Is the Question?, by Leon Lederman, Dick Teresi, Houghton Mifflin Co; (January 1993)
htttp://physicsweb.org/article/world/12/12/12/1
htttp://physicsweb.org/article/news/4/9/2