Lots of news is there about India based Neutrino Observatory. So it becomes an important topic for bot prelims and mains.
First we need to understand certain concepts
Standard Model
Significance of discovery of Higgs Boson
The particle, a boson, was first found last July and many thought that it might not be the correct boson, but once scientists finished recent testing an affirmative judgment was made. They were on the right track.
This discovery is huge to the scientific community because it gives validity to The Standard Model of Physics, which is authoritative theory for particle physics. The only element or particle that is part of the Standard model and hasn't been discovered is the Higgs boson, until now.
The confirmation was crucial because the model dictates how the basic pieces of matter act together. If it was proved incorrect, or that the there was no Higgs boson, the way modern scientists look at particle physics would be completely altered, therefore changing many of the current technological assumptions.
Dark Energy, Dark Matter
In the early 1990's, one thing was fairly certain about the expansion of the Universe. It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the Universe had to slow. The Universe is full of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.
What Is Dark Energy?
More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.
What Is Dark Matter?
By fitting a theoretical model of the composition of the Universe to the combined set of cosmological observations, scientists have come up with the composition that we described above, ~68% dark energy, ~27% dark matter, ~5% normal matter. What is dark matter?
We are much more certain what dark matter is not than we are what it is.
Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.
Neutrinos
Neutrinos are one of the fundamental particles which make up the universe. They are also one of the least understood.
Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.
Three types of neutrinos are known; there is strong evidence that no additional neutrinos exist, unless their properties are unexpectedly very different from the known types. Each type or "flavor" of neutrino is related to a charged particle (which gives the corresponding neutrino its name). Hence, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau (elementary particles are frequently labelled with Greek letters, to confuse the layman). The table below lists the known types of neutrinos (and their electrically charged partners).
First we need to understand certain concepts
Standard Model
Under the Standard Model, which has been pieced together by physicists over the last 70 years, the universe is believed to be made up of matter (four per cent atoms and 27 per cent "dark matter" that we cannot observe or explain) and energy (68 per cent "dark energy").
The model explains the way 17 subatomic particles are bound together to create atoms and then matter by three the four fundamental forces of nature: the strong nuclear force, the weak nuclear force and electromagnetism. It excludes the fourth force: gravity.
The particles fit into two categories:
1. bosons, which transmit forces, and
2. fermions, which make up matter.
Fermions consist of 6 quark varieties and 6 lepton varieties. Every lepton has a corresponding neutrino (an energy-carrying particle of very low mass and high velocity) and all these particles also have antimatter versions, which behave in the same way, but annihilate upon contact with matter, converting the mass of both particles into pure energy.
Nearly all matter is formed by two types of quark – the up quark and the charm quark – and one type of lepton: the electron. The remaining four quarks (top, down, strange and bottom quarks) and five leptons (electron neutrino, muon, muon neutrino, tau and tau neutrino) are simply larger versions of those three main particle types.
Bosons come in four categories which mediate the three fundamental forces mentioned above.
1. The most familiar boson is the photon which mediates electromagnetism, which is responsible for the phenomena of electricity, magnetism and light.
2. W bosons and Z bosons mediate the weak nuclear force and
3. gluons mediate the strong nuclear force which binds quarks together into larger particles such as neutrons and protons.
The existence of the Higgs boson is also predicted by the Standard Model and it has been found recently. It is thought to be the particle responsible for the mechanism by which all the other particles acquire mass.
The graviton is another hypothetical boson which could mediate the force of gravity. If it were ever found, the Standard Model could finally be replaced by the elusive Theory of Everything, which would unite all four fundamental forces of nature.
The particle, a boson, was first found last July and many thought that it might not be the correct boson, but once scientists finished recent testing an affirmative judgment was made. They were on the right track.
This discovery is huge to the scientific community because it gives validity to The Standard Model of Physics, which is authoritative theory for particle physics. The only element or particle that is part of the Standard model and hasn't been discovered is the Higgs boson, until now.
The confirmation was crucial because the model dictates how the basic pieces of matter act together. If it was proved incorrect, or that the there was no Higgs boson, the way modern scientists look at particle physics would be completely altered, therefore changing many of the current technological assumptions.
Dark Energy, Dark Matter
In the early 1990's, one thing was fairly certain about the expansion of the Universe. It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the Universe had to slow. The Universe is full of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.
What Is Dark Energy?
More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.
What Is Dark Matter?
By fitting a theoretical model of the composition of the Universe to the combined set of cosmological observations, scientists have come up with the composition that we described above, ~68% dark energy, ~27% dark matter, ~5% normal matter. What is dark matter?
We are much more certain what dark matter is not than we are what it is.
- First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 27% required by the observations.
- Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them.
- Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.
Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.
Neutrinos
Neutrinos are one of the fundamental particles which make up the universe. They are also one of the least understood.
Neutrinos are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a "weak" sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.
Three types of neutrinos are known; there is strong evidence that no additional neutrinos exist, unless their properties are unexpectedly very different from the known types. Each type or "flavor" of neutrino is related to a charged particle (which gives the corresponding neutrino its name). Hence, the "electron neutrino" is associated with the electron, and two other neutrinos are associated with heavier versions of the electron called the muon and the tau (elementary particles are frequently labelled with Greek letters, to confuse the layman). The table below lists the known types of neutrinos (and their electrically charged partners).
|
Neutrino
|
ne
|
nm
|
nt
|
|
Charged Partner
|
electron (e)
|
muon (m)
|
tau (t)
|
The results of recent neutrino experiments have opened the door to learning much more about neutrinos and their habits. In 2011, researchers turned on the first set of detectors at the Daya Bay Reactor Neutrino Experiment in southern China, hoping to make a key measurement that would help them understand how one type of neutrino turns into another.
In March 2012, after only seven months of taking data, the Daya Bay scientists announced success: They nailed the measurement of theta one-three, one of three so-called “mixing angles” that describe the oscillation of neutrinos between one flavor and another. Previous experiments had shown that theta one-three had to be small, and scientists had begun to wonder whether this mixing angle might be zero. The Daya Bay result, in combination with other neutrino measurements in Japan, South Korea, France and the United States, showed that the angle is small, but definitely not zero.
When the size of that angle was announced, neutrino physicists from around the world cheered. The result opened up the possibility that neutrinos behave differently than antineutrinos, which in turn might help explain the preponderance of matter over antimatter in the universe.
Now scientists are gearing up for new neutrino studies that could lead to answers to some big questions:
- If you could put neutrinos on a scale, how much would they weigh?
- Are neutrinos their own antiparticles?
- Are there more than three kinds of neutrinos?
- Do neutrinos get their mass the same way other elementary particles do?
- Why is there more matter than antimatter in the universe?
How do we know they are there at all?
Wily neutrinos usually avoid contact with matter, but every so often, they crash into an atom to produce a signal that allows us to observe them. Fredrick Reines first detected them in 1956, garnering himself a Nobel prize in 1995.
Most commonly, experiments use large pools of water or oil. When neutrinos interact with electrons or nuclei of those water or oil molecules, they give off a flash of light that sensors can detect.
Some extra Gyaan:
String Theory
In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings. In string theory, the different types of observed elementary particles arise from the different quantum states of these strings. In addition to the types of particles postulated by the standard model of particle physics, string theory naturally incorporates gravity, and is therefore a candidate for a theory of everything, a self-contained mathematical model that describes all fundamental forces and forms of matter. Aside from this hypothesized role in particle physics, string theory is now widely used as a theoretical tool in physics, and it has shed light on many aspects of quantum field theory and quantum gravity
Quantum field theory
In theoretical physics, quantum field theory (QFT) is a theoretical framework for constructing quantum mechanical models of subatomic particles in particle physics and quasiparticles in condensed matter physics, by treating a particle as an excited state of an underlying physical field. These excited states are called field quanta. For example, quantum electrodynamics (QED) has one electron field and one photon field, quantum chromodynamics (QCD) has one field for each type of quark, and in condensed matter there is an atomic displacement field that gives rise to phonon particles. Ed Witten describes QFT as "by far" the most difficult theory in modern physics
Questions
1. neutrinos are called ghost particles because?
a. they have no mass
b. since they have no charge they are difficult to detect
c. they rarely interact with matter
Q2. Why neutrino detectors are installed deep underground?
a. they are found deep inside the earth
b. so that neutrinos are not confused for cosmic rays
c. the detectors emit harmful radiations
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