The Particle Adventure

Eternal questions The search for the fundamental The atom Is the atom fundamental? Is the nucleus fundamental? Are protons and neutrons
fundamental? The modern atom model The scale of the atom What are we looking for? The standard model The standard model quiz

Quarks and leptons Matter & antimatter What is antimatter? Quarks The naming of quarks Hadrons, baryons and mesons Leptons Lepton decays Lepton type conservation Lepton decay quiz Neutrinos Quiz - What particles are made of

The four interactions How does matter interact? The unseen effect Electromagnetism Residual EM force What about the nucleus? Strong Color charge Quark confinement Quarks emit gluons Residual strong force Weak Electroweak Gravity Interaction summary Quantum mechanics The Pauli Exclusion Principle Fermions and bosons A lot to remember End of section

Testing a theory Searching for the atom's structure Rutherford's result Rutherford's analysis How physicists experiment Deflected probe

Detecting the world A better microscope Wavelength - The cave Wavelength - The moral Wavelength and resolution explained The physicists tool: The accelerator Waves and particles The world's meterstick Mass and energy Energy-mass conversion

Accelerators How to obtain particles to accelerate Accelerating particles Accelerating particles: Animation Accelerator design Fixed target experiments Colliding beam experiment A linear or circular accelerator What makes particles go in a circle? Advantages of accelerator design Major accelerators The event Detectors Detector shapes

Modern detectors Typical detector components Measuring charge and momentum Detector cross section Quiz - Particle tracks The computer reconstruction A quark/gluon event The end End of section

The Role of the Higgs Boson The Theory of 1964 The Boson What is the Mass of the Boson? Collisions at the Large Hadron Collider can produce many things

The Announcement Fireworks on the 4th of July The Higgs Boson decays into other particles Easy to Detect How a Higgs boson "event" might look in ATLAS An example of an actual event with a possible Higgs decay

What is the Mechanism giving mass to fundamental particles? What is the Mechanism giving mass to fundamental particles? Part 2 How Does the Higgs Boson get its Mass?

Finding the Mass of the Higgs Boson Finding the Mass of the Higgs Boson, Part 2 Finding the mass of the Higgs from its Decay Products The data for Higgs boson come with a background Time evolution of Higgs Boson Data The Data for Higgs Boson Decaying to two photons

Shortcomings of the first data Is this particle really the Higgs Boson? Does it swim and quack like a duck? Where does most of the mass of the universe come from?

If there was no Higgs? So if there was no Higgs, what would the universe be like?

Is this Higgs Boson the Higgs Boson of the Standard Model? There is more to life than the Higgs Boson! End of section

Beyond the standard model The standard model as a theory Three generations Grand Unified Theory Forces and the Grand Unified Theory Supersymmetry String theory Extra dimensions Dark Matter End of section

What is decay? Radioactivity Radioactive particles Confusion about decays A look into the nucleus If it can happen, it will Half life Missing mass Particle decay mediators Virtual particles Different interactions Annihilations Bubble chamber and decays Neutron beta decays Electron / positron annhiliation Top production End of section

Higgs Boson Discovered > The Mass of the Higgs Boson > The Data for Higgs Boson Decaying...

The Data for Higgs Boson Decaying to two photons

The decays to two photons (H → γ+γ) have much larger backgrounds, but the signal clearly stands out.

The bottom plot shows the same data, but with the background subtracted out, so you only see the signal. Now the bump at around 125 GeV is even more apparent! © CERN

This is another invariant mass histogram, but this time for the Higgs decaying to two photons. As you can see, the background is very large compared to the previous plot. That's because there are many more processes that produce two photons than four leptons.

The dashed red line represents the background, while the solid red line represents the sum of the background and signal. As you can see, the data agree very well with a new particle at around 125 GeV.