Harris VargheseMSc Physics

CUSAT

MATTERMatter is the stuff around youMatter is anything that has mass and takes up space.

ANTIMATTERantimatter is material composed of antiparticles, which have the same mass as particles of ordinary matter but opposite charges, as well as other particle properties such as lepton and baryon numbers. It can be considered as a perfect counter part of matter.

Outline of the Seminar

• Origin of the Concept• Matter antimatter imbalance in the universe• Production and storing of antimatter• Applications of antimatter

ORIGIN

Dirac hole theory

Paul A.M. Dirac

In 1928 Dirac wrote down an equation that combined quantum theory and special relativity to describe the behaviour of an electron moving at a relativistic speed.

But the equation posed a problem: Dirac's equation could have two solutions, one for an electron with positive energy, and one for an electron with negative energy.

•It would make matter unstable.

•Dirac considered vacuum as negative levels filled with electrons.

• So missing of an electron from the energy level would result in a positive charged hole (particle).

•So a gamma ray could produce an electron and a hole (positron).

•Positron can be considered as an electron travelling backwards in time.

Dirac Hole theory is not perfect, it was later replaced by more advanced quantum field theory.

• The term antimatter was first used by Arthur Schuster in 1898.

• In 1928, British Physicist Paul Dirac predicted the existence of positrons.

• In 1932 Carl D. Anderson discovered that cosmic-ray collisions produced these particles in a cloud chamber.

• The antiproton and antineutron were found by Emilio Segre and Owen Chamberlain in 1955 using a Bevatron.

MATTER ANTIMATTER ASYMMETRY

MISSING ANTIMATTER

• According to the theory of big bang, it should have produced equal amount of matter and antimatter.

• It would have resulted in total annihilation of matter and antimatter, leaving the universe as wandering radiations.

• But somehow matter survived!

Antimatter Galaxies

• Immediately after Big bang by the natural rules of chance there would have been some regions with slight excess of matter and other with antimatter.

• These antimatter galaxies if exist, they would be observationally identical, making them impossible to detect.

Alpha Magnetic Spectrometer

• It is an experiment module that is mounted on the International Space Station (ISS).

• It is designed to measure antimatter in cosmic rays.

• Any observations of an antihelium nucleus would provide evidence for the existence of antimatter in space.

i. The universe begins with a small preference for matter.

ii. The universe was originally perfectly symmetric, but somehow a set of phenomena contributed to a small imbalance in favour of matter.

There are other theories which are based on the view that matter and antimatter are not perfect counter parts, there is some asymmetry.

CP Symmetry

• CP is the combination of two other more fundamental symmetries, charge conjugation and parity. C transforms a particle into its antiparticle, while the P creates the mirror image of a physical system.

• All the physical laws and interaction will be same, i.e. Nature will treat matter and antimatter same.

CP Violation

• CP Violation was first discovered in the decay patterns of neutral kaons.

• In the study of neutral kaons, two particle species were found, having apparently identical masses but very different lifetimes.

• These particles have different decay modes. One (KS) decaying to two pions (+ve CP) and other (Kl) to three pions (-ve CP).

• But decay into two pions were observed after the possible lifetime for short life kaons. That the -ve CP particles decay as +ve CP particles.

• It was believed that in Nature, CP cannot be changed but the above observation demonstrates a violation of that conviction.

• Further CP symmetry violation were observed in quark oscillations and incorporated into quark mixing theory.

• It was observed that neutral kaons can transform into their antiparticle and vice versa.

• But these oscillations were not observed in equal rates.

• Antimatter to matter conversion were faster, so an equal mix of particle will result in an excess of matter.

• Similar violations were observed for B mesons also.

• However, more CP violation must be observed in order to explain the universe's matter dominance.

• Therefore, physicists are looking to find CP violation in other particles, such as neutrinos.

• Since CP symmetry is not valid for all interaction, this makes matter and antimatter not so perfect counterparts.

• So it would be the reason for matter dominance in the universe.

PRODUCTION AND STORAGE

Natural Sources

• Many different kinds of antiparticles are also produced by Cosmic rays.

• Positrons are produced naturally in β+ decays of radioactive isotopes (K-40).

• Antimatter are found in solar flares and galactic centres.

• Produced above thunderstorms by the gamma-ray flashes created by electrons accelerated by strong electric fields in the clouds.

Artificial Sources

• Proton-antiproton pairs are made by firing high energy protons at metal targets (lead, iridium).

• Positrons can also be similarly produced (using electron beam) or by exposing metal target (gold) to short ultra intense laser.

Antiproton Decelerator (AD)•Focusing magnets keeps the antiprotons in the track.

•Strong electric fields slow them down.

•Passing them through clouds of electron (cooling) reduces the sideways motion and the spread in energy.

Currently it serves experiments at CERN which are

• ACE – To study biological effects of antiprotons• AEGIS – To measure the Earth’s gravitational

acceleration on anti-hydrogen• ATRAP – Comparing hydrogen and anti-hydrogen• ALPHA – Spectroscopy analysis of anti-hydrogen• ASACUSA – Compares matter and antimatter using

anti-helium

Storing Antimatter

• Antiparticles will annihilate on the contact with the walls of the container.

• Antimatter in the form of charged particle can be stored in vacuum contained by using combination of electric field and magnetic field.

• Dipole moment is induced on neutral molecules and are trapped by magnetic fields in vacuum.

APPLICATIONS

Positron Emission Tomography (PET)

• PET scan is an imaging test that helps reveal how your tissues and organs are functioning. It uses a radioactive drug (tracer) to show this activity.

• The positron emitted by the tracer annihilate with an electron to produce two gamma rays, it allows the detection of the tracer.

• A computer analyzes the gamma rays and uses the information to create an image map of the organ or tissue being studied with the help of CT scan.

As Fuel

• Matter-antimatter propulsion will be the most efficient propulsion ever developed.

• Pure Antimatter rockets - Antiproton annihilation reactions produce charged and uncharged pions, in addition to neutrinos and gamma rays. The charged pions can be channelled by a magnetic nozzle, producing thrust.

• thermal antimatter rocket - the energy or heat from the annihilation is harnessed to create an exhaust from a propellant.

• All the antimatter ever produced get annihilated by contact with matter could only give enough energy to power an ordinary lamp for a few minutes.

Antimatter Detonation

• One gram of antimatter reacting with its ordinary matter counterpart gives 1.8e^14 J.

• Where 1 kiloton TNT equivalent = 4.184e^12 joules.

• Antimatter weapons are not thought to currently exist due to the cost of production and the limited technology available to produce and contain antimatter in sufficient quantities for it to be a useful weapon.

References

• Frank Close : Antimatter, oxford university press, 2010

• http://home.cern/topics/antimatter• http://www.nevis.columbia.edu/daedalus/motiv/

cp.html• Gordon Fraser: Antimatter the ultimate mirror,

Cambridge university press, 2002• S,Sahoo, RK Agrawalla and M Goswami: Antimatter in

the universe, physics education

Pair production• Pair production is the creation of an elementary

particle and its antiparticle• In order for pair production to occur, the

incoming energy of the interaction must be above a threshold in order to create the pair – at least the total rest mass energy of the two particles – and that the situation allows both energy and momentum to be conserved and also all quantum numbers should be conserved

• The probability of pair production in photon-matter interactions increases with photon energy and also increases approximately as the square of atomic number of the nearby atom

Penning Trap•The Penning Trap was named after Frans Michel Penning by Hans Georg Dehmelt who built the first trap.

•Penning traps use a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially.

•The particle oscillate due to the electric field and rotates by the effects of magnetic field