Learn Physics Online: THE LARGE HADRON COLLIDER -UNVEILING THE SECRETS OF UNIVERSE

This is a project on one of the most sophisticated instruments ever constructed by human beings -the Large Hadron Collider, which has recently resumed functioning after a brief period of inactivity, in March 2010.

What is the Large Hadron Collider?

The Large Hadron Collider (LHC) is the largest and the most complex instrument (27 KM long) ever made. It is developed by CERN (The European Organisation for Nuclear Research) and is stationed in the Switzerland-France border almost 100 m underground. It is a particle accelerator which is created to study the smallest particle known-the building block of the universe.

Two beams of subatomic particles –Hadrons- protons or lead ions are made to travel in the opposite directions inside the particle accelerator, with gaining energy in each lap. It is expected that the LHC will create the conditions resembling the ones that prevailed in the universe after the Big Bang. This may be created when the two beams are collided at a very high energy. Groups of physicists from many countries analyse the changes occurring in the collider-particles that are created in the collision using detectors in different experiments.

The LHC is created with an expectation that it will help the physicists to go deep in to the heart of matter and describe the working of the universe.

The current accepted theory about the evolution of universe is that the universe originated from an extremely violent explosion-the Big Bang, since which the universe has been cooling and becoming less energetic. The matter and forces with which the world is made up condensed out of this ball of energy in the very early cooling processes. The data collected from the analysis of the results of the experiments may be able to describe the origin of the universe without any apprehensions.

LARGE HADRON COLLIDER

WORKING OF THE LARGE HADRON COLLIDER

When in full power many trillions of protons will speed around the LHC accelerator ring, 11,245 times a second traveling at 99.99 % the speed of light. It is capable of engineering up to a maximum of 600 million collisions every second.

Systems to control extreme temperatures
During the collision, when two proton beams hit, the temperature generated will be 1,00,000 times hotter than the inner part of the sun, but concentrated in a very small space. These collisions will produce up to 7TeV (tn electron volts), 7 times higher energy of those produced by the previous experiments. At the same time, superfluid helium is circulated around LHC’s accelerator ring by the cooling system thus keeping the machine at -271.3 degrees C.

Data collection
The detectors of the LHC are the most sophisticated instruments ever constructed. These devices can measure the particles with micron precision. To collect the data of the collisions, many devices have been engineered to measure the passage time of a particle to a few billionths of a second. Trigger system registers the position of particles to millionths of a metre.

Analysis of experimental results
Many thousands of computers around the world has been harnessed in a large computing network called ‘The Grid’, which will hold the information and findings from the LHC.

LHC TUNNEL

OBJECTIVES

There exist various opinions among the scientists about the results of the collisions. One of the many theories which are expected to be tested by LHC is the theory by scientist Peter Higgs. The different type of fundamental particles of which the matter is made of has very different masses, but particles that make up light (photons) have no mass at all. According to the theory of Higgs mechanism, whole space is filled with Higgs field and by interacting with this field particles acquire mass. Those particles which interact strongly are heavier and those which interact feebly are lighter. Higgs field has at least one particle associated with it –Higgs boson. If such a particle exists, experiments at LHC will detect it .

The LHC was built to find the answers for the unanswered questions in particle physics. The Standard Model of Particle Physics contains the detailed descriptions about the building blocks of the universe and the interactions among them. The results from the experiments in LHC may help to fill the gaps and missing knowledge in the standard model.

The ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid) experiments will explain the unsolved questions like what is the origin of mass, why do small particles weigh the amount they do and why some particles have no mass at all. The ATLAS and CMS experiments will look for the super-symmetric particles dark matter and dark energy which are believed to make up 96 % of the universe.

ATLAS DETECTOR

The universe is made of atoms; which contain nucleus composed of protons and neutrons which in turn are made of particles called quark bound together by gluons. This bond is extremely strong. But during the initial stages of the evolution of universe the temperature was too high and energetic for gluons to be able to hold quarks strongly together. The theories suggest that during the few microseconds after Big Bang the universe would have consisted of a very hot and dense mixture of quarks and gluons called quark-gluon plasma. By recreating the conditions after the Big Bang during the collision, the Large Hadron Collider could help in supplementing this theory and to analyse the properties if the quark-gluon plasma.

Another result which the experiment is expected to testify is the existence of extra dimensions as proposed by Einstein and String Theory which may become visible at very high energy.

CURRENT STATUS

The experiments in the Large Hadron Collider were started in September 2008, 9 days after which an explosion at the laboratory forced the machine to be shut down for essential repair works.

The experiments in the LHC were restarted in March 2010 after the repair works. The machine is designed to allow collisions of maximum 7 TeV beams of protons, but the laboratory managers decided to operate it at half the power until the end of 2011. The machine will be then shut down for another year for further maintenance works so as to ensure that it can work at full power in 2013 without further breaking down.

ATLAS (A Toroidal LHC ApparauS) detector
Size: 46 m long, 25 m high and 25 m wide. The ATLAS detector is the largest volume particle detector ever constructed.
Weight: 7000 tonnes
Location: Meyrin, Switzerland

GLOSSARY

Gluons
Gluons are elementary expressions of quark interaction, and are indirectlyinvolved with the binding of protons and neutrons together in atomic nucleithrough the strong force.

Hadron
A hadron is a composite particle made of quarks held together by the strongforce. Hadrons are categorized into two families: baryons, and mesons.

Higgs Boson
Higgs boson (also called God’s Particle) is a hypothetical (yet to bediscovered) massive scalar elementary particle predicted to exist by theStandard Model in particle physics. The existence of Higgs boson was proposedby a U K scientist Peter Higgs.

Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of the nucleus of an atom.

Quark-gluon plasma
This is a phase which exists at extremely high temperature and density. This phase consists of free quarks and gluons, which are several of the basic building blocks of matter.