Looking through the heart of matter
Dr Manjit Kaur

The foundation of our modern understanding of structure of matter was laid at the turn of the 20th century when some of the most important scientific discoveries took place. The discovery of the electron by J.J. Thomson followed by the discovery of atomic nucleus by Ernest Rutherford, gave structure to the matter.

Until then the entire matter in the universe was conceived to be created from atoms, treated as tiny, irreducible, ultimate particles. The discovery revolutionised the urge of scientists to explore the interiors of atom which are too tiny for humans to peer into.

The naïve way to do so was to smash it and see what lies inside! Physicists started by initiating systematic investigations in which one particle was used as a fast moving probe called projectile, to smash or bounce off from another particle, called the target. Such scientific experiments called “scattering experiments” began to provide clue to the interiors of these tiny particles.

To completely break up the target, the projectiles needed to be highly energetic. Scientists developed huge and complex machines called particles accelerators which could increase the speed of these tiny particles to match the speed of light. As the energy of particles increased, scattering experiments were able to probe deeper and deeper inside the target particle to reveal increasingly finer details.

Soon it was established that atom contains protons, neutrons and electrons making the interior of these tiny particles visible. The end of 1960s saw the discovery of the quarks — the building blocks of protons and neutrons, collectively called nucleons. A strong force is responsible for keeping the quarks together inside the nucleons. This force is transmitted by the gluons.

The success story of scattering experiments continued and they continued to serve as important research tools. The elementary, point-like electrons proved to be ideal “probes” for analysing the complex structure of matter.

Over the years, physicists and engineers planned, designed and built the hi-tech accelerators to perform precision measurements of the properties of particles and their constituents, the quarks and gluons. In 1971 the Norwegian physicist Bjørn H. Wiik in Germany proposed the construction of one such machine which would use electrons as probes for viewing protons — facility that would allow physicists to discover the deepest structure of the proton and the fundamental forces of nature, the proton being the essential component of matter around us.

The proposal well taken and pursued by the scientific community led to the construction of Hadron Electron Ring Accelerator (HERA) in Hamburg in Germany. The accelerator was housed in a 6.3 km-long tunnel, 25 metres beneath the ground and collided electrons having 27.5 Giga electron-volts of energy with protons possessing 920 Giga electron-volts of energy.

The HERA ring passes through four immense underground halls named as North, South, East & West where huge apparatus called detectors are positioned to register the electron-proton collisions and investigate the most minute building blocks of matter.

The detector is a general term used for a device that detects particles or radiation. In 1992, the first two experiments went into operation - H1 in the North Hall and ZEUS in the South Hall. Both experiments were designed to unravel the internal structure of proton and to study the fundamental forces of nature.

In 1995, the third experiment named HERMES was installed in East Hall to investigate the spin of the protons. And finally in 1998, the fourth experiment called HERA-B was started. These detectors weighed from 400 metric tons to 3600 metric tons.

Such complex and difficult experiments cannot be undertaken by a single country both due to technological as well as financial resources. The detectors are therefore designed and constructed by large international teams. H1 had 330 physicists from 37 institutes in 12 countries. ZEUS has 360 members, 51 institutes and 12 countries and similar are the numbers for other experiments.

ZEUS is one of the four experiments at HERA in which the Department of Physics, Panjab University, Chandigarh is taking part. The participation is supported by the Department of Science & Technology, India and Max Planck Institute, Germany.

Nowhere else in the world such a unique experiment exists which registers the collision of electrons and protons at such high energy. The two independent research teams on H1 and ZEUS experiments make measurements to confirm and compliment each other’s findings. A picture of the ZEUS detector gives an idea of complexity and intricacies of this research.

After 15 years of successful operation of HERA, Germany’s largest research instrument, the data taking ended in summer 2007. The analysis of the recorded measurement data will be completed over the next decade giving a comprehensive overall picture of the interior of proton and the forces confining the quarks within it, with a precision unmatched by any other accelerator in the world for many years to come.

The writer, Professor-in-Physics & Fellow, Panjab University, is a member of the ZEUS team

THIS UNIVERSE
PROF YASH PAL

I am curious to know the radius of a rainbow. Is it equal to the radius of the Earth — or the Sun? Also, please tell me why sometimes we see two rainbows, one within the other?

Rainbow is seen when sunlight coming from behind us falls on tiny spherical droplets of water hanging in the atmosphere. Let us consider its interaction with a single droplet.

The light is bent and broken into its constituent colours while getting into the droplet. It then falls on the backside of the droplet and is reflected back through “total internal reflection”. After this it emerges from the drop at an angle towards the person watching the rainbow.

It can be shown that most of the rays going through these deflections and dispersions would be those for which the angle of deviation is minimum.

This angle can be calculated from the refractive index of water and comes out to be 42°. This holds for all droplets in the air.

As a consequence the rainbow is seen as an arc that makes an angle of 42°. The distance of the droplet from the observer does not enter. It could be at any distance in the atmosphere. Thus the rainbow is not “located” at any well-defined distance.

It is seen in a well-defined direction. It is detectable by naked eye because of the cooperation of all the droplets in that direction. Since the drops of water are confined to the troposphere of the atmosphere you could say with certainty that the distance from which the rainbow light comes to us is also so confined.

You are also curious about the phenomenon of multiple rainbows sometime seen.

The second rainbow at a wider angle results from the light that after entering a droplet suffers not just one reflection at its back, but three total internal reflections before emerging! Multiple rainbows can be seen only when the atmosphere is very clean.

Water-soaked region in space

Scientists looking at a fledgling solar system have observed for the first time how water, considered a necessary ingredient for life, begins to make its way to newly forming planets.

They peered at an embryonic star called IRAS 4B located in our Milky Way galaxy about 1,000 light years from earth in the constellation Perseus. A light year is about 6 trillion miles, the distance light travels in a year.

NASA’s Spitzer Space Telescope enabled them to find quantities of water vapor equal to five times the volume of all the oceans on earth that had rained down onto a dusty disk around the star where planets are believed to form. — Reuter

Trends
Diamonds tell of early earth

Diamonds more than 4 billion years old — nearly as old as the Earth itself — have been discovered in Western Australia, giving scientists vital clues about the early history of our planet.

Found trapped in zircon crystals in the Jack Hills region, the small gems are the oldest identified fragments of the Earth’s crust and their existence suggests the Earth may have cooled faster than previously thought, experts said on Wednesday.

The time between the creation of the Earth around 4.5 billion years ago and the formation of the oldest known rocks some 500 million years later is known as the Hadean period — the “dark ages” of geology. Many geologists have traditionally thought of it as a time when the surface of the planet was a mass of molten lava. But the discovery of the ancient diamonds, reported in the journal Nature, challenges that view.

Google tour of galaxies

The heavens are only a few mouse clicks away with Google Inc.’s latest free tool. A new feature in Google Earth, the company’s satellite imagery-based mapping software, allows users to view the sky from their computers.

The tool provides information about various celestial bodies, from stars to planets, and includes imagery from the Hubble Space Telescope and other sources.

It also allows users to take virtual tours through galaxies, including the Milky Way, from any point on Earth they choose. “By working with some of the industry’s leading experts, we’ve been able to transform Google Earth into a virtual telescope,” Lior Ron, a Google product manager, said in a statement. — AP

Orchids of Dino era

Fossilised orchid pollen on the back of a bee preserved in amber has offered the first evidence that these delicate flowers existed around the time of the dinosaurs, U.S. researchers said on Wednesday.

Biologists at Harvard University said the ancient pollen, found in a clump on a now-extinct worker bee, means orchids are much older than previously thought.

While orchids are the largest and most diverse plant family on earth, they have been largely absent from the fossil record, said Harvard researcher Santiago Ramirez, whose study appears in the journal Nature.

Orchids package their pollen in structures called pollinia, which consist of masses of pollen grains. It was that structure that caught Ramirez’ eye.

“It is very distinct. Because of its shape and form, we were able to identify it right away,” Ramirez said in a telephone interview. — Reuter