The Standard Model of Particle Physics describes the basic building blocks of matter known to us with impressive accuracy. And yet we know: It does not completely represent nature and therefore cannot be the ultimate, all-encompassing theory. To discover the physics beyond the Standard Model – we call it “new physics” – extremely precise experiments and measurements are needed, combined with extremely precise calculations. PRECISION is therefore the guiding theme of PRISMA+ – and this exhibition.
In our first module, you can playfully get to know the many facets of PRECISION. They form the common thread of our exhibition and are presented in the other thematic modules. We also take you on a fascinating journey of discovery through the world of the very small and the very large. Because the research at PRISMA+ extends over 45 orders of magnitude – from a radiation source at the edge of the universe to the inside of a proton.
Further Information:
The Standard Model of Particle Physics – the building blocks of nature
For around 60 years, physics has been working with the “Standard Model of Particle Physics” – a theory of particles and interactions that can explain and predict many phenomena very accurately. But not all of them.
The Standard Model of Particle Physics is, so to speak, the building kit of nature – the number of building blocks is very manageable.
Detailed information on the Standard Model of Particle Physics can be found here.
In the 3sat media library you will also find a Film from the “nano” program from April 30, 2021, which shows how the Standard Model of Particle Physics can be imagined as a “building” with many rooms – starting at minute five.
Physics of Extremes – from Quark to Supernova
The research at PRISMA+ extends over 45 orders of magnitude. From the smallest building blocks of matter to the most distant objects in space. The scientists in Mainz primarily investigate the extreme dimensions.
But why is research even interested in such unimaginably small things as quarks as elementary building blocks of matter? We cannot see them and they seemingly play no major role in everyday phenomena. And yet it is the case that they explain our world and also have a meaning for the very large structures!
Here is an example:
Blue giants are stars that can reach about 50 times the mass of the sun. Most conventional models assume that such massive stars should collapse into black holes. Nevertheless, the conversion of neutrons into a quark-gluon plasma in blue giants could lead to supernova explosions.
Stars gain their energy through nuclear fusion, which creates heavier elements each time. When this process reaches the production of iron, fusion can no longer generate any more energy and the gravity towards the center is no longer compensated by the fusion energy. Therefore, the star begins to compress and ejects the excess mass in the form of a flood of neutrinos. In stars with less than 70 solar masses (like the blue giants), the increase in density caused by the gravitational force could transform the neutrons in the center into a quark-gluon plasma. The special thing: In this extreme state, the smallest building blocks of matter, the quarks, are virtually free and unbound, while they normally only occur in pairs or triplets – the latter are called baryons, the best known are protons and neutrons. In this case, the energy gained by the phase transition (from baryonic matter to quark-gluon plasma) would be high enough to trigger a supernova explosion that would emit a second wave of neutrinos. The result of this second explosion would be a neutron star and not a black hole, which would have formed without the formation of unbound quark matter.
Should such an event occur in our galaxy, it could be experimentally detected. As a result of the double neutrino emission, the neutrino detectors on Earth would register two different signals that would be one second apart.
Quiz
- How many scientists are currently researching at the cluster of excellence PRISMA+?
a. more than 50
b. more than 150
c. more than 300 - What is the current theory model of Particle Physics?
a. world formula
b. Standard Model
c. quark scenario
Precision plays an important role in our everyday life and in many professions. In research and technology, ever greater precision has repeatedly advanced our knowledge of the world in a decisive way. And yet every measurement, every calculation is always subject to an uncertainty – an error.
But that’s not all: Because there are different types of errors or precision. In this module, we use a dartboard to illustrate the difference between statistical and systematic errors. The latter are the real hard bread. Getting to the bottom of them is often not as easy as you can test in detail in the exhibition using seemingly normal dice.
Scientists are aware that there are always errors and uncertainties in their experiments and calculations. That is why they invest a lot of time in identifying and minimizing sources of error. This often involves much more work than the actual measurement. The reward: By minimizing errors, science can now achieve incredible precision in many areas. This is especially true for our research at PRISMA+ – as researchers report in an entertaining way in this module.
Get to know two of our PRISMA+ Minds of Mainz here:
Further Information:
Systematic errors
In the exhibition, we take a close look at systematic errors in physics in particular. Systematic errors not only play a role in the experiments of physicists, but also in your everyday life.
Would you like an example?
In some people, the so-called “white coat effect” occurs when measuring blood pressure: If you know that the blood pressure is currently being measured by the person in the white coat, it is guaranteed to rise – the presence of the doctor falsifies the measurement.
Frequency measurement as the basis of many PRISMA+ experiments
“Never measure anything other than frequencies” is often said in research. And that’s a good thing, because frequencies can be measured extremely accurately in physics these days. Many experiments at PRISMA+ also rely on the most precise frequency measurement possible – for example, hydrogen Spectroscopy, the “Project 8” experiment to determine the neutrino mass, various laboratory experiments to search for dark matter, or the most precise measurement possible of certain properties of elementary particles – above all the so-called anomalous magnetic moment of the muon.
In the following, you will find detailed information on the above-mentioned experiments, all of which are based on the most accurate measurement of frequencies.
Hydrogen Spectroscopy: A look inside the hydrogen atom
The precision Spectroscopy of hydrogen serves to test the quantum electrodynamics (QED) of bound states, the search for “new physics” beyond the Standard Model and the Bestimmung of fundamental natural constants such as the Rydberg constant. An amazing precision is achieved here: “We have determined the 1S-2S transition in atomic hydrogen and deuterium in the work group of Nobel laureate Theodor W. Hänsch at the MPI for Quantum Optics in Garching near Munich with a relative accuracy of a few 10-15,” explains Randolf Pohl, Professor of experimental atomic physics at the cluster of excellence PRISMA+.
more about the research of the AG Pohl (in English)
Project 8: Neutrinos on the scales
The “Project 8” experiment aims to observe a non-vanishing neutrino mass for the first time using a newly developed experimental Technics, the so-called Cyclotron Radiation Emission Spectroscopy. The aim is to measure the energy spectrum of the electrons additionally produced in the beta decay of tritium with the highest possible precision in order to find deviations due to a possibly existing neutrino mass. The energy measurement is carried out via the high-precision measurement of the orbital frequency of the electrons in a magnetic field.
In order for the experiment to work, hydrogen molecules – and later (tritium) hydrogen molecules – must first be split into atoms. The Mainz work group is a leader in the development of such atomic sources and operates a test stand for this purpose in Mainz.
more about Project 8 at PRISMA+ (in English)
Frequency measurement in the search for dark matter
Some of the most promising candidates for dark matter are extremely light bosonic particles such as axions, axion-like particles or even dark photons. PRISMA+ and HIM research groups around Dmitry Budker are currently developing numerous experiments to search for these very light particles using precise frequency measurements.
more about the research of the AG Budker (in English)
The Muon g-2 experiment: The Standard Model on the test bench
An extremely precise frequency measurement is also the basis of the Muon g-2 experiment.
Quiz
- A 20-kilogram metal sphere is weighed ten times in a row with the same scale; the scale shows 23 kilograms each time. Do the measured values show
a. a small spread and a small deviation
b. a small spread, but a large deviation
c. a large spread, but a small deviation
d. a large spread and a large deviation - How can statistical errors be minimized?
a. by measuring frequently
b. by thoroughly checking the measuring instruments
Who doesn’t know it: You did something wrong and still learned something from it. Or doubted something that everyone took for granted and thereby achieved progress. Even in science, deviations and strange measurement results are the salt in the soup. Initially bizarre-seeming contradictions between theory and experiment have repeatedly advanced physics in a decisive way – the module “That’s funny!” is dedicated to such game changers.
PRISMA+ scientists are looking for such inconsistencies and oddities in connection with the Standard Model with high-precision experiments and calculations, no matter how small they may be. The measurement of the proton is one such oddity – depending on the measurement method, the proton is of different sizes. We mainly present hydrogen Spectroscopy as one of the methods used – and show how you can look inside an atom with a laser. Is the proton radius puzzle the key to new physics?
Further Information:
Famous game changers in physics
End of ether
Just as sound waves propagate through the air and water waves on a surface, science firmly assumed that there must also be such a Träger medium for light waves – an omnipresent ether. Until well into the 19th century, people were convinced of the existence of this ether. How else should the light move? The most elaborate experiments, especially the famous Michelson/Morley experiment, did not provide any Hinweise of an ether of any kind – and clearly showed the problems of this assumption.
Albert Einstein came, saw and thought: He threw the ether overboard. It is not needed if, yes if one accepts one thing that seems difficult to accept: The speed of light in a vacuum is always the same, for all observers, and nothing can be faster than light! More info
Who ordered that? – The discovery of muons
In the mid-1930s, the world of the smallest particles was still small and manageable. With protons, neutrons and
Electrons, physics could very well describe what was observed. When Carl D. Anderson and Seth Neddermeyer discovered a particle in 1936 while studying cosmic radiation that behaved like an electron but was about 200 times heavier – obviously not an electron – confusion was great.
“Who ordered that?”, the physicist Isidor Isaac Rabi is said to have exclaimed, because the new particle, the muon, did not fit into the existing model at all. But that was only the beginning of the discovery of a veritable particle zoo, into which Murray Gell-Mann brought order again: His sorting of all particles finally led to the Standard Model of Particle Physics, which is still valid today.
The whole particle adventure to read
Mrs. Wu breaks physics
In 1956, the physicist Chien-Shiung Wu refuted with her experiment the assumption that a certain fundamental symmetry applies in nature – the space mirror symmetry, also known as parity (P). Her results show that the so-called “weak interaction” within the atoms violates parity.
The P-violation was only the beginning, later more comprehensive and combined symmetries were also refuted. For the most comprehensive symmetry, the CPT theorem (charge, parity, time) on the other hand, it is true that it is always preserved, and also quantum electron dynamics (QED) only works under this premise. But who knows …?? More info
The measurement of the proton
All known atomic nuclei consist of protons and neutrons – and yet many properties of these ubiquitous nucleons are not yet understood. In particular, the radius of the proton has been a mystery for several years: In 2010, a new measurement of the proton radius using laser Spectroscopy of muonic hydrogen caused a great stir. In this “special” hydrogen, the electron in the shell of the atom is replaced by its heavy relative, the muon: This allows the accuracy of the measurement to be increased considerably.
The researchers determined a significantly smaller value than was known from corresponding measurements on “normal” electronic hydrogen and the Bestimmung of the proton radius from electron-proton scattering experiments. Can building blocks of a new physics beyond the Standard Model be found in the observed discrepancy? Or are they merely systematic uncertainties of the various measurement methods? PRISMA+ scientists are approaching the solution of the proton radius puzzle from many sides: Their goal is to carry out even more accurate experiments, and additionally to shed light on the darkness with the help of theoretical calculations – as Randolf Pohl explains in the public lecture series “Physics in the Theater”.
The minds behind the PRISMA+ research
Quiz
- What is the proton?
a. a component of the atomic nucleus
b. the heavy relative of the electron
c. an elementary particle - In what order of magnitude does the radius of the proton move?
a. Femtometer
b. Picometer
c. Nanometer
When you flip a coin, it sometimes stays on one side and sometimes on the other. Very rarely, however, it can also happen that it remains standing on the edge. But that is very, very unlikely. But how unlikely exactly and can the coin not stand on the edge? To find out, only one thing helps: You have to try it very, very often!
In this sense, precision can also mean repeating the same measurement extremely often – according to the motto of this module “A lot helps a lot”. The new particle accelerator MESA, which is currently being built on the Gutenberg campus, enables such measurements: The particle beam is not only extremely intense, but also extremely precisely focused on a tiny area in a target. In this way, MESA will be able to track down very subtle and rare events. This applies in particular to the search for dark matter – one of the most exciting challenges of modern Particle Physics.
In the “More is More” module, you can try out the coin experiment described above yourself and join a research team that is searching for Dark Photons with the new MESA accelerator and the MAGIX experiment planned there. We also approach the unknown and mysterious Dark Matter with an artistic comparison.
Further Information:
Particle Accelerators at JGU
MAMI (Mainzer Mikrotron) is a particle accelerator for electron beams, operated by the Institute for nuclear physics. The accelerator has been available for experiments since 1979 and has been continuously expanded since then.
It is very well suited for conducting precision studies on the structure of matter in the subatomic realm. Four experimental work groups are based at the institute.
MAMI’s beam diameter is only a few tenths of a millimeter, and the average energy remains precisely stable to within a few millionths of the target value. The beam’s position is also kept constant to less than 0.2 millimeters.
With these values, MAMI holds a top position among linear accelerators worldwide.
MESA – MAINZ ENERGY RECOVERING SUPERCONDUCTING ACCELERATOR
The linear accelerator MESA (Mainz Energy recovering Superconducting Accelerator) is currently being built on the Gutenberg Campus. With its novel energy-recovering operating mode (Energy Recovery Linac, ERL), MESA will operate very energy-efficiently. This allows the accelerator to achieve an extremely high beam intensity, which would otherwise only be possible with immense energy expenditure: A large number of particles are focused onto a tiny area of the target. Consequently, many particle collisions occur in a short time. This enables the search for very rare events, such as the decay of Dark Photons or other, hitherto unknown particles.
In addition, MESA generates an extremely stable and sharply defined (focused) beam that can be kept stable to within a few micrometers. MESA will also exhibit very high beam quality: All electrons in the accelerator receive exactly the same kinetic energy of 155 MeV. These are optimal conditions for important precision experiments.
Quiz
- How many operating hours has the MAMI accelerator accumulated since 1979?
a. approx. 19,200
b. approx. 192,000
c. approx. 1,920 - What is the name of JGU’s new particle accelerator?
a. MESA
b. MEGA
c. MARS - What is the proportion of Dark Matter in the total matter in the universe?
a. 4%
b. 24%
c. more than 80%
For their experiments, researchers at PRISMA+ often have to create extremely precise or clean conditions. For certain measurements, it is crucial to shield interference signals or eliminate impurities. Only then can the extremely weak effect being sought be detected. For our exhibition, we have come up with an analogy: Gradually turn off various disturbing noises – what remains will surprise you!
All this applies par excellence to neutrino research, an important focus at PRISMA+. Neutrinos are true ghost particles: Billions of them penetrate our bodies every second without us noticing. However, in large experiments with multi-ton detectors, we can detect and study them. Then they have much to tell us: as messengers from the sun’s fire, from the Earth’s interior, or from distant galaxies.
In the Borexino experiment, for example, Mainz scientists work in an environment that is extremely free of radioactivity to detect neutrinos from the sun. For this purpose, the experiment is located deep beneath the mountains of Northern Italy in the Gran Sasso massif. You can get an impression of this with a plastic model and look into a mysterious sphere deep inside the mountain.
Join us on a ghost hunt!
Further Information:
Neutrino Research Around the Globe
BOREXINO EXPERIMENT IN ITALY
The Borexino Experiment collected valuable data on solar neutrinos from 2007 to 2021, which will be analyzed for many years to come. It is located in the world’s largest underground laboratory, the Laboratori Nazionali del Gran Sasso in Italy. The core of the Borexino detector is an extremely thin-walled, spherical nylon balloon containing 280 tons of a special scintillator liquid. Only a few hundred times a day does a neutrino interact with the detector material. This creates tiny flashes of light, which are detected by around 2,000 extremely sensitive photosensors. The Mainz group at PRISMA+ develops sophisticated analysis techniques to suppress unwanted background events.
This video is also worth watching: Solar Neutrinos on their Journey into the Borexino Detector (in Italian with English subtitles)
NEUTRINO TELESCOPE ICECUBE AT THE SOUTH POLE
IceCube is the world’s largest particle detector. It uses a cubic kilometer of ice as a detection medium and is located near the Amundsen-Scott Station at the geographic South Pole. IceCube has been collecting data on neutrinos since 2010. In 2013, IceCube discovered extremely high-energy neutrinos for the first time, which most likely originate from cosmic accelerators in space. Another highlight of IceCube research occurred on September 22, 2017: The detectors reported a high-energy neutrino that most likely came from a galaxy 3 billion light-years away in the constellation Orion. The Mainz group at PRISMA+ is significantly involved in the further development of the neutrino telescope. In the coming years, it is to undergo extensive expansion. Above all, the researchers want to install even more light sensors.
JUNO EXPERIMENT IN CHINA
The Jiangmen Underground Neutrino Observatory (JUNO) aims to precisely measure the oscillations of neutrinos and thus investigate one of the most current questions in neutrino physics: the ordering or hierarchy of neutrino masses. The experiment, currently under construction, is approximately 100 times larger than the Borexino detector and uses neutrinos from two reactor complexes on the South China coast: At least 100,000 neutrino reactions will be necessary to obtain answers to the question of the order of neutrino masses. At the same time, JUNO will be able to measure the energy of neutrinos with record resolution. The Mainz group at PRISMA+ is responsible for several detector subsystems at the experimental site in Jiangmen.
Neutrinos have also been the topic several times in the “Physics in the Theater” series:
Low Background Physics
To achieve precision and measure only the relevant events, scientists try to exclude all background events that could interfere, in various ways. For this, they use a mixture of shielding, cleaning, cutting out, and sorting out:
- They experiment underground to shield cosmic radiation.
- They install buffer layers (e.g., made of oil or water) around the actual detector to shield natural radioactivity.
- They clean their detector materials using elaborate procedures and only evaluate signals from the inner part of the detector, as this is particularly clean.
- They analyze their data precisely and computationally sort out incorrect events.
This principle is called “Low Background Physics” and also applies to other experiments at PRISMA+: for example, the Dark Matter Experiment XENON, in which Mainz scientists are also involved.
Quiz
- Which particles are the scientists looking for in the Borexino Experiment?
a. Electrons
b. Photons
c. Neutrinos - How many sensors is the Borexino detector equipped with?
a. approx. 500
b. approx. 2,000
c. approx. 5,000 - Where is the JUNO experiment being built?
a. in China
b. in Chile
c. at the South Pole
In everyday life, we constantly encounter numbers, values, and measurements: There is an average life expectancy and an average height of people in Germany. All these figures have one thing in common: There is a mean value, but the actual values of individuals, for example, their body heights, are distributed very differently – they vary.
A very typical form of distribution around a mean value is the “normal distribution.” Measurement values from an often-repeated
experiment also follow it. In the “Everything Varies” module, you can understand how such a distribution comes about using a “Galton board.”
But it goes even further: Physicists use the expected value and the standard deviation “sigma” of a normal distribution to classify their results.
Because if the value determined from many individual measurements deviates by more than five sigma from the expected, it can no longer be a coincidence!
Ultimately, this is about extremely small probabilities, which we want to illustrate with 1.7 million grains of rice.
A prime example in this context is the Muon g-2 Experiment, which we present in detail in this module. Initial results caused a stir in 2021, as a “real” – and not merely “random” – deviation between theory and experiment is becoming increasingly likely. Does the muon open the door to hitherto unknown particles or forces?
Further Information:
Muon Fact Sheet
Muon g-2 Experiment
The Muon g-2 experiment at Fermilab near Chicago was designed to measure the magnetic properties of the muon more precisely than ever before.
For this purpose, a muon beam is guided into a ring-shaped magnet. The muons orbit in this until they decay. This allows conclusions to be drawn about their so-called anomalous magnetic moment.
In April 2021, the Muon g-2 collaboration published initial results that caused a stir. With the new result, evidence for new physics beyond the Standard Model, and thus for the existence of hitherto unknown particles or forces, is accumulating. Not only is the global physics community in turmoil, but headlines are also overflowing. The Neue Zürcher Zeitung, for example, writes: “Two weeks ago, the Standard Model of Particle Physics got its feet wet. Now the water is up to its neck.”
Prof. Dr. Martin Fertl and his work group at PRISMA+ focus particularly on the extremely precise measurement of the magnetic field in the muon storage ring over the entire multi-year measurement period.
Quiz
- Where is the Muon g-2 Experiment located?
a. in Italy
b. in the USA
c. in Switzerland - Muons are measured in the Muon g-2 experiment. They are
a. 200 times heavier than an electron
b. just as heavy as an electron
c. 200 times lighter than an electron
Have you ever seen the ultrasound waves that bats use to orient themselves in their surroundings? Or felt a magnetic field that aligns a compass needle as if by magic? Measuring devices and detectors can make such “invisible things,” for which we have no sensory organ, visible. They are more objective than our senses, because they cannot be deceived. They can not only subjectively feel temperatures, but objectively measure them. They
have better resolution because they can concentrate on a very specific measuring range. We, on the other hand, have to find our way in the world with all its diverse impressions using our senses.
Detectors are, so to speak, the high-tech eyes of Particle Physics. We dedicate the final module of our exhibition to them. Detectors extend and “refine” our senses. They overcome the limits of human vision and can make visible the smallest structures invisible to the human eye. They are unimaginably precise, unimaginably large, unimaginably fast, and unimaginably thin. They are true wonders of the Technics Department, and in them, the entire beauty of Particle Physics is revealed.
In this module, we present the Mu3e Experiment as an example, which is currently being set up at the Swiss Paul Scherrer Institute, and show using a simple example what high spatial and temporal resolution mean and why both are so important.
And since detectors are often found in the most extreme places around the globe, we conclude by taking you on a multimedia world tour with them!
Further Information:
Extreme Detectors
ATLAS DETECTOR AT CERN IN SWITZERLAND
What happened in the early universe?
Five stories tall, weighing 7,000 tons. ATLAS at CERN in Geneva is the largest particle detector ever built at an accelerator. In 2012, the Higgs particle was experimentally detected here for the first time. This scientific sensation opened a new window to unravel the great mysteries of the universe.
ICECUBE DETECTOR AT THE SOUTH POLE
What do neutrinos from the depths of space tell us?
5,160 glass spheres with highly sensitive detectors, submerged up to two and a half kilometers deep in the Antarctic ice: Located directly at the South Pole, IceCube is one of the most spectacular physics experiments worldwide.
XENON DETECTOR IN THE GRAN SASSO UNDERGROUND LABORATORY IN ITALY
How can we finally “see” Dark Matter?
1,400 meters underground, in the Italian Gran Sasso Laboratory, the XENON Experiment is searching for WIMPs, promising candidates for Dark Matter. Its core is the inner detector – a cylindrical two-phase time projection chamber filled with several tons of liquid xenon.
Quiz
- What is the circumference of the LHC particle accelerator at CERN?
a. 400 meters
b. 27,000 meters
c. 2,100 meters - How many scientists work on the ATLAS detector?
a. 500
b. 1,300
c. more than 3,200 - How deep underground is the XENON Experiment located?
a. 100 meters
b. 10 meters
c. 1,400 meters - Which detection medium does the IceCube Experiment use?
a. Glacial ice in Antarctica
b. Liquid xenon
c. Oil
Why so precise?
- How many scientists are currently conducting research at the cluster of excellence PRISMA+?
a. more than 50
b. more than 150
c. more than 300 - What is the current theoretical model of Particle Physics called?
a. Theory of Everything
b. Standard Model
c. Quark Scenario
What does precise mean?
- A 20-kilogram metal sphere is weighed ten times in a row with the same scale; the scale shows 23 kilograms each time. Do the measured values show
a. a small spread and a small deviation
b. a small spread, but a large deviation
c. a large spread, but a small deviation
d. a large spread and a large deviation - How can statistical errors be minimized?
a. through frequent measurements
b. through thorough checking of measuring instruments
That’s funny!
- What is the proton?
a. a component of the atomic nucleus
b. the heavy relative of the electron
c. an elementary particle - What is the order of magnitude of the proton’s radius?
a. Femtometers
b. Picometers
c. Nanometers
A lot helps a lot
- How many operating hours has the MAMI accelerator accumulated since 1979?
a. approximately 19,200
b. approximately 192,000
c. approximately 1,920 - What is the name of the JGU’s new particle accelerator?
a. MESA
b. MEGA
c. MARS - What is the proportion of Dark Matter in the total matter of the universe?
a. 4 percent
b. 24 percent
c. more than 80 percent
Please do not disturb!
- Which particles are scientists looking for in the Borexino Experiment?
a. Electrons
b. Photons
c. Neutrinos - How many sensors is the Borexino detector equipped with?
a. approximately 500
b. approximately 2,000
c. approximately 5,000 - Where is the JUNO experiment being set up?
a. in China
b. in Chile
c. at the South Pole
Everything scatters
- Where is the Muon g-2 experiment located?
a. in Italy
b. in the USA
c. in Switzerland - Muons are measured in the Muon g-2 experiment. They are
a. 200 times heavier than an electron
b. as heavy as an electron
c. 200 times lighter than an electron
I measure something you don’t see
- What is the circumference of the LHC particle accelerator at CERN?
a. 400 meters
b. 27,000 meters
c. 2,100 meters - How many scientists work on the ATLAS detector?
a. 500
b. 1,300
c. more than 3,200 - How deep underground is the XENON experiment located?
a. 100 meters
b. 10 meters
c. 1,400 meters - What detection medium does the IceCube experiment use?
a. Glacial ice in Antarctica
b. Liquid xenon
c. Oil
