Particle physics

Particle physics is a branch of physics that studies the elementary subatomic constituents of matter and radiation, and their interactions. The field is also called high energy physics, because many elementary particles do not occur under ambient conditions on Earth. They can only be created artificially during high energy collisions with other particles in particle accelerators.

What particle physics studies

Everyday matter is built from a short list of parts. Atoms hold electrons and a nucleus of protons and neutrons, which are made of smaller particles called quarks. Particle physicists ask what the smallest parts are and what forces act between them.

The work joins theory and experiment. Theorists predict what should happen, and experimenters test the predictions. When the two disagree, something new may be waiting to be found.

The Standard Model

The Standard Model is the main theory of the field. It was developed in the early 1970s and has explained almost all experimental results since then. It sorts the known particles into groups.

• Quarks. There are six: up, down, charm, strange, top, and bottom.
• Leptons. There are six: the electron, the muon, the tau, and a neutrino for each.
• Gauge bosons. These carry forces. The photon carries the electromagnetic force, the gluon carries the strong force, and the W and Z bosons carry the weak force.
• The Higgs boson. It comes from a field that gives mass to elementary particles.

The ATLAS and CMS teams at CERN announced the Higgs boson on 4 July 2012. It appears in only about one in a billion collisions, so finding it took careful statistics and a great deal of data.

Open questions

The Standard Model works well, yet it is incomplete. Each open question below is a possible research path.

• Dark matter. It appears to make up about 27 percent of the universe, while the matter we know makes up about 5 percent.
• Neutrino mass. The basic Standard Model needs neutrinos to have no mass. Neutrino oscillations, honored by the 2015 Nobel Prize in Physics, show that they have some.
• Matter and antimatter. The early universe should have made equal amounts of both, yet almost no antimatter remains.
• Gravity. The Standard Model covers three of the four fundamental forces and leaves gravity out.

How experiments work

Most heavy particles do not occur in daily life, so scientists make them. An accelerator uses electric fields to speed up charged particles and magnets to steer them. In a collider, two beams meet head on, and the energy of the crash can turn into new particles.

CERN, the European laboratory near Geneva, runs the Large Hadron Collider. It is a ring of superconducting magnets 27 kilometers around, in a tunnel about 100 meters underground. It started in 2008 and now collides protons at 13.6 TeV. Four large detectors sit at the collision points: ATLAS, CMS, ALICE, and LHCb.

A detector works like a huge digital camera built in layers. Inner layers track charged particles, other layers measure energy, and outer layers catch muons. Other labs include Fermilab and Brookhaven in the United States, DESY in Germany, and KEK in Japan.

How the data are analyzed

A collider makes more collisions than anyone can store, so fast electronics keep only the interesting events. Analysts count events that match a pattern, plot them in histograms, and compare the plots with a prediction. A peak above a smooth curve may mark a new particle. Chance can fake a peak, so a team must show that the excess is very unlikely to be a fluke.

You can try this yourself. The CERN Open Data portal shares real data and tools from LHC experiments, including event displays and guides for full analyses. The Particle Data Group publishes the Review of Particle Physics, a reference for checking results against accepted values.

Applications and spin-offs

Tim Berners-Lee invented the World Wide Web at CERN in 1989 to help scientists share information. On 30 April 1993 CERN put the web software in the public domain, which helped the web spread.

Medicine also gains. The first PET image at CERN dates from 1977. CERN accelerator know-how helped design two of the four dual ion therapy centers in Europe, which treat cancer with beams of protons and carbon ions. Detector chips built for particle tracking have also led to color X-ray imaging.

Learning, teaching, and research

To find related pages here, use this link: Search this wiki for Particle physics.

How a student can start. Begin with the Standard Model chart and the four forces. Algebra, trigonometry, and basic statistics come first. Calculus and vectors come next. Later, linear algebra, special relativity, and quantum mechanics open the deeper theory. Learn some Python too, since analysis uses code.

Classroom activities. A cloud chamber is a simple detector. Many classroom versions use a cold plate cooled with dry ice and a vapor of isopropyl alcohol. Charged particles leave thin trails of droplets that students can see, sketch, and sort by shape.

Project ideas.

• Use CERN Open Data to plot the mass of muon pairs and find the peaks.
• Look up ten particles in the Particle Data Group tables and compare mass, charge, and lifetime.
• Write a short report on one open question and list the experiments that test it.

Research directions. These include the open questions above and new tools for data analysis.

Discussion questions, essay ideas, and learning related AI prompt ideas

Discussion questions

• Why must physicists build huge machines to study the smallest things?
• What should a team show before it claims a new particle?

Essay ideas

• Explain how basic research at CERN led to the World Wide Web and to medical tools.
• Compare the roles of theory and experiment in finding the Higgs boson.

AI prompt ideas

• Explain the Standard Model to a high school student, then quiz me with five questions.
• Help me plan a short analysis of CERN Open Data, and ask me questions where my plan is vague.

Readings from Wikipedia

• Particle physics
• Standard Model
• Elementary particle
• Quark
• Lepton
• Gauge boson
• Higgs boson
• Large Hadron Collider
• CERN
• Particle accelerator
• Particle detector
• Cloud chamber
• Dark matter
• Neutrino oscillation
• Baryon asymmetry
• Particle Data Group
• Positron emission tomography
• Proton therapy

See also

Physics Atomic physics Beyond the Standard Model High pressure physics Fundamental interaction Introduction to quantum mechanics List of accelerators in particle physics List of particles Magnetic Monopole Micro black hole Nuclear physics Astrophysics

Resonance (particle physics) Rochester conference Standard model (mathematical formulation) Stanford Physics Information Retrieval System Subatomic particle Timeline of particle physics Unparticle physics Cosmology Mathematics Research Open research Teaching

External links

• CERN
• CERN Open Data portal
• Particle Data Group
• Fermilab
• DESY
• KEK
• Brookhaven National Laboratory
• International Particle Physics Outreach Group