M3L2: Why particle research?

"There is nothing new to be discovered in physics now. All that remains is more and more precise measurement."

— Lord Kelvin

“Today's science is tomorrow's technology.”

— Edward Teller

In the last lecture, we tried to understand, how does research in particle physics, helps to develop new technologies. With example of Hybrid Pixel detector technology, we tried to understand how governments can promote Knowledge based economy

WHAT IS KNOWLEDGE-BASED ECONOMY? The knowledge-based economy or innovation driven economy is the one that uses Knowledge as a product to drive its economy.

While I gave a very small bird view of how can we apply the technology used to capture the events in LHC, CERN claims that its technologies find application in many other fields. The list is very large

1.    to explore the fundamental nature of matter

2.    materials sciences

3.    semiconductor circuit lithography

4.    historical research & the restoration

5.    to study biological molecules and other materials like protein structure analysis

6.    pharmaceutical research & drug development

7.    real-time visualization of chemical reactions & biochemical processes

8.    food sterilization

9.    medical isotope production

10. simulation of cancer treatments

11. reliability testing of nuclear weapons

12. scanning of shipping containers

13. proposed combination of PET and MRI imaging

14. improved sound quality in archival recordings

15. parallel computing

16. ion implantation for strengthening materials

17. curing of epoxies and plastics

18. data mining and simulation

19. international relations

20. nuclear waste transmutation

21. remote operation of complex facilities

Thus, research in particle physics cater diverse sectors of the national economy such as industry. 

Information technology

Medical instrumentation

Electronics

Communications

Biophysics

Finance

Based on this spillover effect, that the particle research creates on various branches of economy, shouldn’t India carry out this kind of research on its own soil? Most of the Nobel prize in physics prizes in physics have gone to research in atomic and subatomic particles. Ever wondered, why India doesn’t have a place in one of this?

In order to do research in particle physics, we need a facility known as synchro-cyclotron. India has recently developed a synchrotron facility known as Variable Energy Cyclotron Center (VECC) to do particle research of its kind in Kolkata. It has a collaboration with the European Organization for Nuclear Research. The Centre houses a 224 cm cyclotron—the first of its kind in India—which has been operational since 16 June 1977. It provides proton, deuteron, alpha particle and heavy ion beams of various energies to other institutions.

India has now become an associate member of CERN. How will this help to promote precision manufacturing and advanced manufacturing under Make in India program?

Do you know? CERN has recently proposed to build a successor to the Large Hadron Collider consisting of a 100km-diameter cyclotron capable of smashing subatomic particles together with 10 times more energy than the LHC. The proposed project is called Future Circular cyclotron Collider.

What research do they carry out in particle research?

All of us know that matter is made up of atoms and molecules. It is made up of proton, electron and neutron. This was proposed first by Dalton. He tried to develop a model of an atom, although it was vague compared to what we know now. The developments in his model are captured under the standard model of physics. However, even after so many developments, the standard model of physics doesn’t answer the following questions.

[1] What is mass?

Why do particles weigh the amount they do? Why do some particles have no mass at all? There are no established answers to these questions, but one explanation is the Higgs boson. First hypothesised in 1964, it has yet to be observed.

[2] What is dark matter/dark energy?

Everything we see in the universe is made up of ordinary matter, but that forms only 4 per cent of the universe. Dark matter and dark energy are believed to make up the remaining 96 per cent, but they're incredibly difficult to detect and study, other than through the gravitational forces they exert.

[3] Why is there no more antimatter?

Antimatter is like a twin version of matter, but with opposite electric charge. At the birth of the universe, equal amounts of matter and antimatter should have been produced in the Big Bang. But when matter and antimatter particles meet, they annihilate each other, transforming into energy. Somehow, a tiny fraction of matter must have survived to form the universe we live in today, with hardly any antimatter left. Why does nature appear to have this bias for matter over antimatter?

[4] How did quarks form particles just after the Big Bang?

Protons and neutrons (which make up the atomic nucleus) are made of quarks, which are bound together by other particles called gluons. The bond is so strong that quarks are never seen in isolation. Collisions with lead ions in the Alice detector will generate temperatures more than 100,000 times hotter than the Sun's core, possibly freeing the quarks from their bonds with the gluons. This should create a state of matter called quark-gluon plasma, which probably existed just after the Big Bang.

[5] Are there more than three dimensions?

Einstein showed that the three dimensions of space are related to time. Subsequent theories propose that further hidden dimensions of space may exist -- for example, string theory implies that there are additional spatial dimensions yet to be observed. These may become detectable at very high energies, so data from all the detectors will be carefully analyzed to look for signs of extra dimensions.

In order to search for these answers, they do research. The most famous labs, where this research is carried out in collaboration with other countries are

1.    Fermilabs

2.    CERN

Now the scientists had a question. A proton is made up of 2 up quarks and one down quark. Each ‘up quark’ has 2 MeV of mass and each ‘down quark’ has 4 Mev of mass, so the total mass of the proton should be 8 Mev. Yet the total mass of a proton is 938 MeV

So how can a proton be that heavy when its constituent particles weigh only a fraction of its actual weight?

As per the equation E=mc², mass and energy are interconvertible. So, are they completely different or is mass a confined form of energy? What is that energy that fills up the spaces between the quarks? In 1964, Peter Higgs proposed that this space is occupied by an Energy Field and it permeates the entire universe (fill up the entire universe just like some syrup or liquid)

In order to know this, if such energy field exists, they developed LHC. In LHC experiment, when the two protons were smashed, they got completely segregated into many other sub-sub atomic particles. Scientists could find this particle, that showed the feature of acting as a glue to combine the quarks and gluons and form a proton. They were named as Higgs Boson. These individual particles remain stable only for 10^-22 seconds and fills up the space between the individual quarks. This space is called as the Higgs field.

Higgs boson particles do not spin. In case of protons and electrons, they spin continuously

Recently, CERN also got a nobel prize for discovery of neutrinos.

What are neutrinos? And how can we use them? From UPSC point of view, the most important thing is, how can we use this for public welfare.

The story starts from 1930. Back in that time, when the scientists were trying to make a nuclear bomb, they discovered that law of conservation of mass and law of conservation of energy are not obeyed in certain atomic reactions (known as Beta decay of elements)

The assumed that this imbalance is caused by certain particles that carry very little mass. This makes it hard to find them. They are also neutral. They therefore called them as baby neutrons or simply neutrinos.

After World war II, scientist who participated in Manhattan project continued to make experiments. Now they shifted their zone of experiments from the nuclear bomb to the nuclear reactor.  And they could see, that in early seconds of operation of reactor, gamma rays are fluctuating. This means that there are certain particles that are interfering with it. One among those scientists was Cowan Reines

Cowan believed that in the early phase, when the nuclear process is started, both the electron and the anti-electron (recognized as positron) are released. They annihilate each other and release Gamma radiation. However, what causes these fluctuations in the Gamma radiations could not be explained. To balance this fluctuation, he put the mass and energy of the tiny particle, that was called as neutrinos. And surprisingly, the equation got balanced.

                                      N⁰ ® p⁺ + e^- + n_{e (missing)}

                                      p⁺ + n_{t (missing)}  ® e⁺ + N⁰

Thus, Cowan Reines made a hypothesis that a particle, known as neutrino exists. But now the research community wants to see it.

To do, scientists at Fermilabs and CERN started working on it.

1.    In the year 1975, scientists at the Linear accelerator at Fermilab (USA), detected one beam of neutrinos for which they won Nobel prize in physics in the year 1975. They called them as electron neutrino (n_e) 

2.    Then in the year 1988, scientists at CERN also detected a beam of neutrinos by decay of pi-meson for which they got Nobel prize in Physics in the year 1988. They called them as muon neutrino (n_m)

So, the question that came to the minds of scientists was, how many types of neutrinos exist? Two were discovered. So, are there only two neutrinos or three or four?

To find an answer to it, they shifted their gaze to the point where they started…

Back before second world war, the scientists saw neutrinos adjoined with Gamma radiation. This means that there is some relation between both of them as they are found to originate together. This mean, neutrinos remember their origin.

In order to see if any other kinds of neutrinos exist, scientists started to look at Gamma radiation. I hope you are aware of the fact that this is produced during nuclear reactions. Now since the core of the sun is also undergoing nuclear reactions, scientists were hopeful to find a pool of neutrinos coming out of the sun along with the gamma radiation. But something else happened.

The scientists had theoretically calculated an ‘x’ amount of it to reach us through Standard Solar model. However, while experimenting, they could actually detect Neutrinos that were only ¹/₃^rd or ¹/₄^th of theoretical calculations.

What does this mean? Some believed that the calculations were wrong. Some believed that calculations were right but the reading was wrong. An Italian scientist Bruno Pontecorvo belonged to the latter class of scientists.

He claimed, “All neutrinos are of same source (same elementary particles) … They only change flavors (states/oscillations)”. He meant that there should be three kinds of neutrinos. Since we are detecting only 1/3^rd, this doesn’t mean our theoretical calculations are wrong. It means, we are able to detect only one neutrino while three different forms of neutrinos exist. He called them tau neutrino (n_t), muon neutrino (n_m) and electron neutrino (n_e)

So, since we have already discovered, muon neutrino (n_m) (CERN – year 1988) and electron neutrino (n_e) (Fermilabs – year 1975), the remaining 2/3^rd should be made up of tau neutrino (n_t).

In the race to discover and detect the third unknown neutrino, both CERN and Fermilabs made giant investments.

CERN started with experimenting with Laboratori Nazionali del Gran Sasso (LNGS). CERN is in Geneva in Switzerland while LNGS is at Green Sasso in Italy, at the distance of 451 kms from itself. While, its comptetitor Fermilabs started working on Deep Underground Neutrino Experiment (DUNE). In the year 2015, DUNE research Fermilabs conducted an experiment with the international Long-Baseline Neutrino Facility (LBNF) at the Sanford Underground Research Facility in South Dakota.

We will return back to the experiment conducted by CERN. In that experiment, they could find that neutrinos arrived faster than the speed of light. (although the gap was 60 billionth of a second). And could they detect Tau neutrinos? The answer was finally Yes.

Now it was the turn of Fermilabs.

While CERN could not stretch its tunnel beyond 451 kms, Fermilab has an advantage. They could make a tunnel that was around 1300 kms long. On their way, the particles did something incredible — they changed identities. The experiment at Fermilab was designed to generate only muon-flavored neutrinos. By the time they reached the Sanford underground research facility, they changed into electron and tau neutrinos. This means, they can oscillate and that, all the three flavors viz. electron neutrino, tau neutrino and muon neutrino do not have the same masses. However, this has raised one more question for the scientists, the quest for the answer still continues

Neutrinos do not seem to get their masses the way other particles do—through the Higgs boson. This is due to the fact, that neutrinos have masses about a million times lighter than other particles of their class, such as electrons. In short, they do not fit in the standard model of an atom. Then what is the mechanism that makes neutrinos? Does this mean, that everything we learn about neutrinos in the coming years will contribute to a new branch of physics?

Neutrinos decay differently, when they interact with matter than with antimatter. This phenomenon is known as charge conjugation–parity (CP) violation. Neutrinos may be the first fundamental particles that are identical to its antiparticle. Such particles that are identical to their antiparticles are known as ‘Majorana’. Scientists in international research community have already started putting efforts to find the fourth neutrino, which they call as sterile neutrino. Although results are negative, based on the data obtained from Ice Cube laboratory, the hope still exists. Japan is making even more powerful neutrino detector, ‘HYPER-KAMIOKANDE’. One another super giant neutrino lab also exists in Antarctica known as Ice cube neutrino lab. For more details, refer Cherenkov radiation in Astrophysics-II

So, summarizing what we have learnt. What do we know about neutrinos?

·         Neutrinos are elementary particles that have no electric charge. They are among the most abundant particles in the universe.

·         They are very light. A neutrino weighs at least a million times less than an electron, but the precise mass is still unknown.

·         In nature, they are produced in great quantities in the sun and in smaller quantities in the Earth. In the laboratory, scientists can make neutrino beams with particle accelerators.

·         Neutrinos pass harmlessly right through matter, and only very rarely do they collide with other matter particles.

·         There are three types of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos.

·         The laws of quantum mechanics allow a neutrino of one type to turn into another one as the neutrino travels long distances. And they can transform again and again. This process is called neutrino oscillation.

·         Understanding neutrino oscillations is the key to understanding neutrinos and their role in the universe.

Potential applications of Neutrinos in engineering applications

(1) Monitoring nuclear non-proliferation

In nuclear reactors, the amount of plutonium builds up as the uranium fuel is used, and the number and characteristics of antineutrinos emitted by plutonium differ significantly from the number of antineutrinos emitted by uranium. This makes it possible for a specially designed detector monitoring the antineutrino flux from a nuclear reactor core to analyze the content of the reactor and verify that no tampering has occurred with the reactor fuel.

(2) A way to 'x-ray' the Earth to find cavities of mineral and oil deposits.

Neutrinos change the way they spin depending on how far they have traveled and how much matter they have passed through. So, geophysicists have proposed that analyzing the way a beam of neutrinos are spinning after passing through pockets of the Earth could reveal where mineral deposits are.

(3) Faster global communication.

Scientists have proven that it's possible to encode a message in neutrinos using binary code. But there are complications preventing this kind of communication from taking off. The particles are so hard to detect that the receiver would need a giant neutrino detector to get the message. The neutrino beam would also need to be extremely powerful to travel a long distance.

(4) A way for scientists to detect dark matter.

The IceCube lab has built a neutrino detector in Antarctica that has detected extremely high-energy neutrinos. The scientists have observed that some neutrinos come from space and are produced from things like supermassive black holes and particularly violent star deaths that produce gamma ray bursts. But the scientists also think them to be coming from decaying dark matter in nearby galaxies or from the cores of the Sun or Earth.

(5)  Communication with extra-terrestrial life. This one is a little far-fetched, but since it is possible to encode messages in neutrinos, theoretically those encoded neutrinos could be beamed into space. Currently, scientists don't have the ability to beam neutrinos that far, and any aliens on the receiving end would have to be able to decode the message.

India too has shown interest to work on neutrinos. Can you write an essay on how will it create demand for sophisticated instruments, advanced materials and precision manufacturing?