Fundamental particles, the Standard Model, and beyond

We know today that the matter around us is built of point-like objects, quarks and leptons with an experimental upper limit for their size of 10-18m. A total number of six quarks, six anti-quarks as well as six leptons and six anti-leptons have been established experimentally. These fundamental building blocks are arranged in three "families" and we have convincing arguments that this set of families is complete. The behaviour of these elementary particles is governed by four fundamental interactions, namely gravitation, electromagnetic, weak and strong interaction. The interactions between particles are meditated by so-called field bosons, which are the graviton, photon, W- and Z bosons, and the gluon, respectively.

The number of particles and corresponding anti-particles created during the "big-bang" was equal and most particle/anti-particle pairs annihilated. However, a very small imbalance, or spontaneous symmetry breaking, resulted in a small excess of the matter of today's universe.

Modern theoretical and experimental research in particle physics has succeeded to unite the electromagnetic, weak and strong interactions into a unified scheme, called the Standard Model, which is able to describe a large set of experimental data on the properties of elementary particles and simple composites thereof. One of the priorities of this field is the search for the so-called Higgs-Boson, which is thought to be responsible for the masses of the elementary particles.

The Standard Model has many parameters for which values cannot be predicted within the framework of the model and therefore have to be introduced empirically. This shortcoming, together with other theoretical arguments, makes an extension of the Standard Model necessary. Experimental evidence of Physics beyond the Standard Model was only recently provided by the observation of neutrino oscillations, which prove that neutrinos have mass, contrary to the fact that neutrinos are massless within the Standard Model. There are other indications from astro-particle physics that so-called "cold dark matter" exists, requiring the existence of new particles, which are not part of the Standard Model. Due to these facts the search for physics beyond the Standard Model is a major priority of modern experimental and theoretical particle physics.

Future experiments at Fermilab in the U.S. and the LHC at CERN will be able to study the Higgs Boson and establish more physics beyond the standard model.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

be concerned with, fundamental symmetries and interactions, quarks, leptons, have convincing arguments, be meditated by, field boson, graviton, W- and Z bosons, gluon, annihilate, succeed to, priorities, Higgs-Boson, empirically, shortcoming, neutrino oscillations

Exercise 2. Answer the questions:

1. What is Particle and Nuclear Physics concerned with?

2. What is the matter around us built of?

3. What has been established experimentally?

4. What is the behaviour of these elementary particles governed by?

5. What are the interactions between particles meditated by?

6. What has modern theoretical and experimental research in particle physics succeeded to unite?

Exercise 3. Match the left part with the right:

1. The interactions between particles	a. a major priority of modern experimental and theoretical particle physics.
2. The Standard Model has many parameters for which values cannot be predicted	b. the search for the so-called Higgs-Boson, which is thought to be responsible for the masses of the elementary particles.
3. One of the priorities of this field is	c. within the framework of the model and therefore have to be instructed empirically.
4. Due to these facts the search for physics beyond the Standard Model is	d. are meditated by so-called field bosons, which are the graviton, photon, W- and Z bosons, and the gluon respectively.

Exercise 4. Open brackets using the right words:

The number of particles and corresponding anti-particles (created/inverted) during the "big-bang" was (different/equal) and most particle/anti-particle (groups/pairs) annihilated. However, a very small (imbalance/balance), or spontaneous symmetry breaking, (resulted in/resulted from) a small excess of the matter of today's universe.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe elementary particle; quark; lepton; gravitation; boson using the suggested words and expressions:

elementary particle cannot be described as a compound; a particle which in the present state of knowledge; and is thus one of the fundamental constituents; of all matter. example: Elementary particle – a particle which in the present state of knowledge cannot be described as a compound and is thus on of the fundamental constituents of all matter.

quark having charges; one of the hypothetical basic particles; whose magnitudes are 1/3 or 2/3 of the electron charge; in theory may be built up; from which many of the elementary particles

lepton smaller than the proton mass; a fermion having a mass; which interacts with electromagnetic and gravitational fields

gravitation between all masses; the mutual attraction; in the universe

boson obeys Bose-Einstein statistics; a particle that; includes photons, pi mesons and all nuclei; having an even number of particles with integer spin

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: A total number of six quarks, six anti-quarks as well as six leptons and six anti-leptons have been established experimentally.

2. Question: ____________________________________ ?

Answer: These fundamental building blocks are arranged in three "families".

3. Question: ____________________________________ ?

Answer: Due to these facts the search for physics beyond the Standard Model is a major priority of modern experimental and theoretical particle physics.

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: scheme; on; research; simple; able; succeeded; simple; strong:

Modern theoretical and experimental ______ in particle physics has ______ to unite the electromagnetic, weak and ______ interactions into a unified ______, called the Standard Model, which is ______ to describe a large set ______ experimental data ______ the properties of elementary particles and ______ composites thereof.

Exercise 2. Fill in the table with words from the text. Group the synonyms:

govern	call
to be concerned with	invent
world	up-to-date
name	big
arguments	lack
create	cool
pair	main
small	rule
modern	to be interested in
research	facts
scheme	little
large	plan
datum	consider
think	meanings
many	do
cold	thanks to
values	learn
shortcoming	peace
other	couple
make	investigation
evidence	information
due to	tests
experiments	proof
study	cool
major	another

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Modern theoretical and experimental research in particle physics”

“Fundamental particles”

“The Standard Model”

Lesson 6

The Reading Module

Read the text: Particle Physics

Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. It is also called high energy physics, because many elementary particles do not occur under normal circumstances in nature, but can be created and detected during energetic collisions of other particles, as is done in particle accelerators. Research in this area has produced a long list of particles.

Subatomic particles

An image showing 6 quarks, 6 leptons and the interacting particles, according to the Standard Model.

Modern particle physics research is focused on subatomic particles, which have less structure than atoms. These include atomic constituents such as electrons, protons, and neutrons (protons and neutrons are actually composite particles, made up of quarks), particles produced by radiative and scattering processes, such as photons, neutrinos, and muons, as well as a wide range of exotic particles.

Strictly speaking, the term particle is a misnomer because the dynamics of particle physics are governed by quantum mechanics. As such, they exhibit wave-particle duality, displaying particle-like behavior under certain experimental conditions and wave-like behavior in others (more technically they are described by state vectors in a Hilbert space). Following the convention of particle physicists, "elementary particles" refer to objects such as electrons and photons, with the understanding that these "particles" display wave-like properties as well.

All the particles and their interactions observed to date can almost be described entirely by a quantum field theory called the Standard Model. The Standard Model has 40 species of elementary particles (24 fermions, 12 vector bosons, and 4 scalar bosons), which can combine to form composite particles, accounting for the hundreds of other species of particles discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature, and that a more fundamental theory awaits discovery. In recent years, measurements of neutrino mass have provided the first experimental deviations from the Standard Model.

Particle physics has had a large impact on the philosophy of science. Some particle physicists adhere to reductionism, a point of view that has been criticized and defended by philosophers and scientists. Part of the debate is described below.

The idea that all matter is composed of elementary particles dates to at least the 6^th century BC. The philosophical doctrine of atomism and the nature of elementary particles were studied by ancient Greek philosophers such as Leucippus, Democritus and Epicurus; ancient Indian philosophers such as Kanada, Dignāga and Dharmakirti; medieval scientists such as Alhazen, Avicenna and Algazel; and early modern European physicists such as Pierre Gassendi, Robert Boyle and Isaac Newton. The particle theory of light was also proposed by Alhazen, Avicenna, Gassendi and Newton. These early ideas were founded in abstract, philosophical reasoning rather than experimentation and empirical observation.

In the 19^th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was composed of a single, unique type of particle. Dalton and his contemporaries believed these were the fundamental particles of nature and thus named them atoms, after the Greek word atomos, meaning "indivisible". However, near the end of the century, physicists discovered that atoms were not, in fact, the fundamental particles of nature, but conglomerates of even smaller particles. The early 20th century explorations of nuclear physics and quantum physics culminated in proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn), and nuclear fusion by Hans Bethe in the same year. These discoveries gave rise to an active industry of generating one atom from another, even rendering possible (although not profitable) the transmutation of lead into gold. They also led to the development of nuclear weapons. Throughout the 1950s and 1960s, a bewildering variety of particles were found in scattering experiments. This was referred to as the "particle zoo". This term was deprecated after the formulation of the Standard Model during the 1970s in which the large number of particles was explained as combinations of a (relatively) small number of fundamental particles.