Molecules Tip Their Hands

English
(l-r) Profs. Zeev Vager and Dirk Schwalm and Dr. Oded Heber
     

 

 
 
To understand the new finding arising from a recent collaboration between scientists at the Weizmann Institute and researchers in Germany, one must go back in time. First, one needs to go back to 1847, the year Louis Pasteur discovered that tartaric acid crystals come in two different forms – mirror images that, like hands, appear in “left” and “right” versions that cannot be superimposed on one another. Those molecules – known as chiral molecules – presaged a headache for drug manufacturers and the chemical industry in general, who soon found that the right- and left-handed forms could react very differently, especially in drug compounds. While researchers working in the field of stereochemistry, which deals specifically with the chemistry of chiral molecules, have made some progress in purifying compounds to contain just one form or the other, separating the two remains a problem in many cases.

Next, one needs to look back some 30 years, to the work being done in a Weizmann Institute lab. That’s when Prof. Zeev Vager of the then Nuclear Physics Department, together with the Institute’s Prof. Ron Naaman and researchers from the Argonne National Laboratory, Illinois, developed an innovative method of imaging molecules. Called Coulomb explosion imaging, it consists of accelerating molecular ions to a significant fraction of the velocity of light and shooting them onto a very thin sheet of carbon. As the molecules speed through this foil, their electrons are stripped away while the positively charged nuclei spread out in formation as they race toward a detector. The detector not only records the landing points of the nuclei but also times their touchdown, presenting a magnified, accurate, three-dimensional image of the molecule.

Vager continued to work on the Coulomb explosion technique for many years; he and Prof. Daniel Zajfman introduced it to the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, while Vager was on a sabbatical in the mid-1990s. While the method proved most effective for imaging very small molecules, Vager at some point thought it could also be used for identifying left- and right-handed chiral molecules, even though they tend to be larger and more complex. As he was searching for a feasible chiral species, another Weizmann Institute scientist, the late Prof. Emanuel Gil-Av, whose research dealt with various aspects of chirality, suggested a molecule called oxirane as a test object. Vager discussed this proposal with Prof. Volker Schurig (a former postdoc of Gil-Av’s) and with one of Schurig’s students, Oliver Trapp, at the Institute for Organic Chemistry of the University of Tübingen. Though the molecule was borderline as far as the Coulomb explosion technique was concerned, a more serious obstacle was the difficulty in producing the relatively large amounts of chiral oxirane (up to a gram) needed for these experiments. Thus the intriguing prospect of being the first to determine the spatial structure of a chiral molecule in its gas phase had to be put on ice.  
 
Coulomb explosion method
 
 
Fast forward to this past year: A group of physicists and chemists from the Weizmann Institute and Germany finally managed to systematically overcome the various hurdles to imaging chiral oxirane molecules with the Coulomb explosion method. Oliver Trapp, now a professor at the Institute of Organic Chemistry at Heidelberg University, together with his PhD student Kersten Zawatzky and his former mentor Schurig, devised and succeeded in carrying out a sophisticated, multi-step process to synthesize grams of isotope-labeled oxirane with a well-defined chirality. Dr. Holger Kreckel of the Max Planck Institute for Nuclear Physics and his PhD student Philipp Herwig, together with his institute colleagues Prof. Dr. Dirk Schwalm (see below) and Prof. Dr. Andreas Wolf, as well as Vager and Dr. Oded Heber of the Weizmann institute, rejuvenated and modified the Coulomb explosion imaging setup at the Max Planck Institute to cope with the special requirements imposed on the detection system by the atomic break-up products of oxirane. After several test runs with non-chiral oxirane molecules, the team could finally perform the imaging measurements with chiral oxirane; its handedness was kept secret by the chemists until the final analyses of the experiment had been performed by the physicists. “Fortunately,” jokes Vager, “we got the right answer.”
 
The results appeared recently in Science. This was the first time that the spatial structure of isolated chiral molecules could be directly imaged. The method could prove highly useful to researchers and drug developers who need to unambiguously determine the handedness of their compounds.
 

Back to his roots

 
 
Prof. Dirk Schwalm
 
“I agreed to come to the Weizmann Institute for a year,” says Prof. Dirk Schwalm, “and I have already been here for seven.” Schwalm is a former director of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, where he worked on the ion storage ring – an evacuated tube about 56 m in circumference used for physics experiments. Among other things, this ring enables scientists to mimic atomic and molecular processes that occur in the emptiest stretches of outer space. That facility is what drew the Weizmann Institute’s Prof. Daniel Zajfman, a physicist who researches these processes, to frequently visit the Max Planck Institute.
 
In 2005, when Schwalm retired, Zajfman took over the directorship, spending part of his time in Heidelberg and part in his Weizmann Institute lab. But the next year, when Zajfman was appointed President of the Weizmann Institute, he resigned his position at the Max Planck Institute. He did not, however, give up his friendship with Schwalm and, indeed asked Schwalm to join the Weizmann Institute as a visiting scientist. Schwalm now spends more than half of each year helping lead Zajfman’s research group, thus enabling Prof. Zajfman to invest more time and energy in his presidential duties.
 
Schwalm says that he is very happy to be at the Weizmann Institute. He especially enjoys the fact that the experimental tools and the research groups are comparatively small, which enables him to get involved again in hands-on physics. “I have the chance to know every screw in the equipment,” he says. “This is a fantastic opportunity to go back to my ‘physics roots.’”
 
(l-r) Profs. Zeev Vager and Dirk Schwalm and Dr. Oded Heber
Space & Physics
English
  • Chiral
  • Daniel Zajfman
  • Nuclear physics
  • Particle Physics and Astrophysics
  • Ron Naaman
  • Zeev Vager

Visitors from across the Universe

English

Detectors for high-energy cosmic neutrinos are buried under the Antarctic ice

 

 

 
When we change our point of view, we can often see things not previously apparent. Something similar holds true at the subatomic level: Getting our sights on particles we have not previously been able to “see” can expose us to a new and different “world view.” So, for instance, most of our observations of the Universe are based on the absorption of light waves in different lengths (some visible and some outside the visible range). But looking for tiny particles called neutrinos that come from outer space can provide unusual insights about the cosmos.

That has already been the case with neutrinos detected from relatively close sources: a supernova in a neighboring galaxy and our own Sun. In the first, the neutrinos emitted from the explosion confirmed that the star underwent a gravitational collapse, transforming it into a neutron star. And neutrinos measured from our Sun helped reveal the energy-production mechanisms at the Sun’s core, as well as enabling researchers to determine that neutrinos are not massless. The fact that neutrinos almost never interact with matter makes studying them a challenge, but it presents new possibilities as well: They are emitted from deep inside the core of such bodies as the Sun, where even photons can’t escape.   
 
Prof. Eli Waxman
 

 

Theoretical studies have hinted that these two examples are just the tip of the iceberg: Neutrinos are thought to arrive at Earth from far across the Universe, bringing with them new insights that are not possible to attain with mere light-based observations. And that point of view could present us with a completely new sort of astronomy. For example, the Universe contains natural particle accelerators hundreds of millions of times more powerful than the biggest accelerator on Earth. We know these accelerators exist because we see their byproducts: When the accelerated particles hit the upper atmosphere with great force, they generate a shower of other particles that move down through the atmosphere, where they can be measured with earthly instruments. This finding has raised a host of questions: Where, exactly, are these accelerators located? What particles do they accelerate – protons or heavy nuclei, for instance? How do the particles attain their extreme velocities?

Prof. Eli Waxman of the Particle Physics and Astrophysics Department believes that these distant accelerators exist near young black holes approximately the mass of our Sun. These, he has proposed, are also the source of certain mysterious, high-energy gamma-ray bursts. Waxman and the late Prof. John Bahcall of the Institute for Advanced Study, Princeton, had developed a model that predicted how the particle acceleration process would produce energetic neutrinos.
 
 
Neutrinos are not the easiest particles to capture and measure: They have no charge, barely any mass, and they rarely interact with other matter. As they zip through the Universe, they pass though anything in their way – including Earth and its inhabitants – and keep going off toward their unknown destinations. And, if that did not make things difficult enough, Waxman and Bahcall, in another collaborative study, added an upper limit to possible neutrino numbers: One neutrino passing through a square kilometer of Earth per second. At that rate, with a billion-ton detector on Earth, one could record, over the course of a year, no more than a dozen or so energetic neutrinos arriving from the far reaches of the cosmos.
Neutrino detection: on the left, of a cosmic particle that has passed through the atmosphere, while that recorded on the right was produced in the atmosphere and passed through the Earth
 
The detector that was eventually built, of course, was not a billion-ton device. Rather, its designers made use of a natural structure: the Antarctic ice cap. This detector is made up of many smaller detectors buried deep under the ice. Though this giant experiment, called IceCube, began recording before the setup was completed, it is the data from the last two years – around and after the end of its construction – that have yielded interesting results. A few dozen neutrinos were detected in that time – a number close to the upper limit set by Waxman and Bahcall. This suggests that these neutrinos are, indeed, coming from the far-off reaches of the Universe, and that the model is valid. Among the model’s assumptions that are supported by the experiment’s findings: The still unknown accelerators are equally distributed across the Universe; the particles accelerated are protons, in a process that generates neutrinos; the different types of neutrinos reaching the Earth are equally represented; and the pace of acceleration increases with distance. The last point implies that the more ancient the accelerator (i.e., the more distant from us), either the more particles it produces or the accelerators were closer together in the ancient Universe. In any case, it is clear that a large part of the accelerators’ energy goes into neutrino production.

Waxman expects that the data that will be collected from the Antarctic detector in the coming years will help clarify the nature of these neutrinos and may even help point to their still unknown source. “We hope the unique properties of these high-energy neutrinos, like those we detected from nearby sources, will enable us to draw valuable conclusions,” he says. “In particular, neutrinos produced close to the black holes – the most likely candidates for being the accelerators – in a region from which photons may not reach us, carry unique information on the workings of these objects.”  Among other things, he says, the findings will provide new tools and data sets for developing the new astrophysics. These could, for instance, be used to test the theory of relativity with much more precise methods than those used today. It all depends, as they say, on one’s point of view.
 
neutrino infographic
 
 
 

Prof. Eli Waxman heads the Benoziyo Center for Astrophysics; his research is supported by the Friends of the Weizmann Institute in memory of Richard Kronstein. Prof. Waxman is the incumbent of the Max Planck Professorial Chair of Quantum Physics.
 

 
 
Detectors for high-energy cosmic neutrinos are buried under the Antarctic ice
Space & Physics
English
  • Black hole
  • Eli Waxman
  • Gamma ray
  • Neutrino
  • Particle Physics and Astrophysics
  • Particle detector

Materials on the Edge

English
 
 
(l-r) Yoav Lahini, Mor Verbin, Yaacov Kraus, Oded Zilberberg and Zohar Ringel
 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
The story begins in two separate locations in the Institute’s physics buildings. In one of those – the lab of Prof. Yaron Silberberg – research students Yoav Lahini and Mor Verbin were experimenting with a quasicrystalline optical system. Quasicrystals, discovered 30 years ago by Prof. Dan Schechtman of the Technion, are unique in the arrangement of their atoms: Like regular crystals, they are arranged in an orderly fashion but, unlike most crystals, that arrangement is not periodic. Quasicrystals represent a new type of matter; recognition of this fact changed the face of materials science and forced scientists to redefine the meaning of the term “crystal.” Schechtman received the 2011 Nobel Prize in Chemistry for his discovery, which garnered interest among crystallographers, chemists, physicists and mathematicians alike. Yoav and Mor, who were studying a new type of optical quasicrystals developed in the lab, had noticed some strange, inexplicable phenomena taking place at their crystals’ edges. They measured, but could not explain, these phenomena.

In another part of the physics buildings, research students Oded Zilberberg in the group of Prof. Yuval Gefen, Yaacov Kraus in the group of Prof. Adi Stern and Zohar Ringel in the group of Prof. Ehud Altman were becoming interested in the new field of topological materials. These materials, discovered in 2007, are mostly normal, periodic crystals, but they have unusual electrical properties: The interior of the material acts as an insulator, but its surface conducts electricity just as if it were coated with metal. Like the discovery of quasicrystals, these new materials forced scientists to rethink accepted views – in this case, that a material was either an insulator (in which electrons don’t move) or a conductor (in which electrons can easily flow). Since then, scientists have been searching for additional topological materials, both with a view to possible applications and to investigate their unique properties.
 
 
A SEM figure of the etched waveguides composing the optical quasicrystal
 
These three students asked themselves whether quasicrystals might have topological properties. A certain overlap among various studies hinted that the answer might, at least partly be positive: Topological materials and quasicrystals can both be described, in some sense, as “projections” of higher dimensional systems. Yet the models of quasicrystals they worked with did not reveal topological phenomena.
 
The first meeting of these two ideas occurred far from the Weizmann campus. Yoav and Oded ran into each other by chance on a fine Saturday afternoon in Tel Aviv. While chatting, the two realized that their respective research efforts could be complementary, and a meeting was soon set up between the theoretical group and the experimental one.

Working together, the five students succeeded in showing – in theoretical work and in experimental measurement – that quasicrystals do, indeed, have topological properties. In some ways these newly-discovered properties are similar to those of “regular” topological materials, but in other ways they are very different.

In experiments conducted in Silberberg’s lab, the students built a quasicrystal using an array of coupled thin optical fibers etched with a powerful laser beam into a single glass cube. The parallel fibers were arranged at quasiperiodic (non-repeating) distances. When light was shined into a central fiber in this system, it “hopped” to the other fibers, emerging from all the fibers at the other side. But when the light was introduced at one of the far edges of the array, it remained confined to that side. In other words, the quasicrystal setup showed an “edge state” with different properties than the states found in the middle of the array. Just as electrons in topological materials flow only on the surface and do not penetrate the interior, the light shined through the outer edge of the optical quasicrystal setup stayed in that plane. This finding was a surprise, as scientists had believed such topological behavior to be impossible in a one-dimensional system.
 
An adiabatic light pump: (l) The setup: The spacing between the optic fibers is slowly varied to induce light pumping. (r) Measurements of the intensity distribution as the light moves down the quasicrystal show it crossing from right to left
 

 

 
In an additional experiment, the team varied the distances between the optic fibers, so that they were no longer parallel along their entire length. When they got the arrangement just right, light going into a fiber at one edge hopped across the entire array, exiting from the fiber at the opposite edge. Though somewhat unexpected, this phenomenon, called an “adiabatic pump,” supplied further proof that the quasicrystal system had topological properties.

Adiabatic pumps are known from a different kind of topological system called a quantum Hall system, in which electrons are exposed to directional magnetic fields. The model the students developed to explain this behavior enabled them to envision the optical quasicrystal setup as a sort of one-dimensional cross section of a two-dimensional quantum Hall system. That cross section, to the team’s surprise, preserves the topological properties of the two-dimensional system. In other words, one-dimensional quasicrystals “inherit” their topological properties from higher-dimensional “ancestors,” which are periodic crystals.

These findings were recently published in Physical Review Letters, and they were highlighted in Science and other scientific journals. Now, among other things, the team is checking whether their results are applicable to other dimensions. For instance, the theory they developed suggests that topological properties in three-dimensional quasicrystals can be linked to topological systems existing in six dimensions.
 
Dr. Ehud Altman's research is supported by the Yeda-Sela Center for Basic Research; and the estate of Ernst and Anni Deutsch.

 
Prof.Yuval Gefen is the incumbent of the Isabelle and Samuel Friedman Professorial Chair of Theoretical Physics.
 
Prof. Yaron Silberberg's research is supported by the Crown Photonics Center, which he heads; the Cymerman - Jakubskind Prize; and the European  Research Council. Prof. Silberberg is the incumbent of the Harry Weinrebe Professorial Chair of Laser Physics.


 
 
 
(l-r) Yoav Lahini, Mor Verbin, Yaacov Kraus, Oded Zilberberg and Zohar Ringel
Space & Physics
English
  • Adi Stern
  • Condensed Matter Physics
  • Ehud Altman
  • Optics
  • Physics of Complex Systems
  • Topological material
  • Yaron Silberberg
  • Yuval Gefen

A New Particle Has Been Discovered – Chances Are, It Is the Higgs Boson

English
 
The Higgs boson is the final building block that has been missing from the “Standard Model,” which describes the structure of matter in the universe. The Higgs boson combines two forces of nature and shows that they are, in fact, different aspects of a more fundamental force. The particle is also responsible for the existence of mass in the elementary particles.

Weizmann Institute scientists have been prominent participants in this research from its onset. Prof. Giora Mikenberg was for many years head of the research group that searched for the Higgs boson in CERN’s OPAL experiment. He was then leader of the ATLAS Muon Project – one of the two experiments that eventually revealed the particle. Prof. Ehud Duchovni heads the Weizmann Institute team that examines other key questions at CERN. Prof. Eilam Gross is currently the ATLAS Higgs physics group convener. In the Weizmann team three scientific “generations” are represented: Mikenberg was Duchovni’s supervisor, who were both, in turn, Gross’s supervisor.

Gross: “This is the biggest day of my life. I have been searching for the Higgs since I was a student in the 1980’s. Even after 25 years, it still came as a surprise. No matter what you call it – we are no longer searching for the Higgs but measuring its properties. Though I believed it would be found, I never dreamed it would happen while I was holding a senior position in the global research team.”

Most of us experience the world as a diverse and complex place. But the physicists among us are not content with visible reality. They are striving to get to the bottom of that reality and to see whether it is, as they think, based on the absolute simplicity displayed by the early universe. They expect to observe a range of particles that are different “ensembles” of a handful of elementary particles. The scientists are hoping to see a unification of the four fundamental forces of nature that act on these particles (the weak force responsible for radioactivity, electromagnetic force, the strong force responsible for the existence of protons and neutrons, and gravitation).

The first step in the journey to unify the forces was completed with the almost certain discovery of the Higgs particle: The union of two elementary forces – the electromagnetic and weak force, to become the electroweak force.

One aspect of the Higgs boson, named after the Scottish physicist Peter Higgs, manifests itself in the giving of mass to the weak force carriers – the “W” and “Z” particles. (The electromagnetic force carrier, the photon, remains massless.)
 


The Largest Machine in the World


In the effort to discover the Higgs boson, unify the fundamental forces and understand the origin of mass in the universe, scientists built the world's largest machine: a particle accelerator nestled in a 27-km-long circular tunnel, 100 meters beneath the border between France and Switzerland, in the European particle physics laboratory, CERN, near Geneva.

This accelerator, called LHC (Large Hadron Collider), accelerates beams of protons up to 99.999998% the speed of light. According to the theory of relativity, this increases their mass by 7,500 times that of their normal resting mass. The accelerator aims the beams straight at each other, causing collisions that release so much energy, the protons themselves explode. For much less than the blink of an eye, conditions similar to those that existed in the universe in the first fraction of a second after the Big Bang are present in the accelerator.

As a result, particles of matter are turned into energy, in accordance with Albert Einstein’s famous equation describing the conversion of matter into energy: E=mc2. The energy then propagates through space and the system cools. (Something similar happened in the early evolution of the universe.) Consequently, energy turns back into particles of matter and the process is repeated until particles that can exist in reality as we know it are formed.

The collisions produce energetic particles, some of which exist for extremely short periods of time. The only way to discern their existence is to identify the footprints they leave behind. For this purpose, a variety of particle detectors were developed, each optimized for capturing particular types of particles.
 
 


Statistics


The likelihood of creating the Higgs boson in a single collision is similar to that of randomly extracting a specific living cell from the leaf of a plant, out of all the plants growing on Earth. To cope with this task, Weizmann Institute scientists, headed by Prof. Mikenberg, developed unique particle detectors, which were manufactured at the Institute, and in Japan and China. These detectors have been adapted to detect muon particles. In some of the very rare collisions that produce Higgs particles, the footprint of the Higgs particle – that which is recorded in the detectors – is four energetic muons. Thus, the detection of such muons provides circumstantial evidence for the existence of the Higgs particle.

The scientists analyzed data from a thousand trillion proton collisions; in these Higgs bosons are created along with many other similar particles. Evidence to suggest the existence of the Higgs arises through searches for anomalies in the collected data (in comparison with the expected data if such a particle does not exist). This search focuses on the estimated mass of the particle: 126 trillion electron volts (Gev). When the scientists do manage to find such anomalies, they must then rule out the possibility that it is due to statistical fluctuation.

The calculations carried out by scientists in recent weeks, in which Prof. Gross played a central role, have revealed, with a high degree of statistical significance, a new particle with a mass similar to the expected mass of the Higgs. The wording is purposely cautious, leaving room for the possibility that a new particle other than the Higgs can be found within this mass range. The probability that this is, indeed, a new particle, is quite low. (But if it were, in truth, a different particle, say some physicists, things will start to get "really interesting.")
 
 

CERN


CERN scientists invented and developed the computer language and basic concepts that later served as the basis for the establishment of the Internet. In fact, the first server of the “World Wide Web” was activated in CERN to facilitate communication between scientists from around the globe participating in experiments carried out locally. The organization also served as a model for the establishment of the European Union, and its influence on Europe’s technology and economy is reminiscent of the American space program.

The LHC particle accelerator is based on superconducting electromagnets working at very low temperatures: less than two degrees above absolute zero (minus 271° Celsius). It generates about one billion particle collisions per second: If they were people, it would be as if each person on the planet meets every one of the six billion inhabitants of the world every six seconds. Calculating and analyzing data from these collisions is like trying to understand what all the inhabitants of the world are saying, while each is holding 20 telephone conversations at once.

This experimental system includes the world’s largest superconducting electromagnets, built in conjunction with Israeli companies. The entire structure includes 10,000 radiation detectors spaced just one millimeter apart, has a volume of 25,000 cubic meters and features half a million electronic channels. Most of the muon radiation detectors were built from components produced in Israel. A unique laser system tracks the exact location of the detectors with an accuracy of 25 microns (half the thickness of a human hair).
 
 
Illustration depicting particle collisions
 

 

 


CRASH - The race for the Higgs boson 
 
 
The Mexico Building, which houses the Laboratory for Development & Construction of Particle Detectors at the Weizmann Institute is funded by:
 
Lazaro Becker
Mauricio Gerson
Abraham and Rebeca Itzkovich
Armando and Maria Jinich
Abraham and Elena Kahn
Robert Kazdan
Benito Lasky
Ramon and Rebecca Marcos
Stella and Rafael Rayek
The late Leon Schidlow and Lily Schidlow
Luis and Miriam Stillmann


Prof. Ehud Duchovni’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein; the Nella and Leon Benoziyo Center for High Energy Physics; and the Yeda-Sela Center for Basic Research. Prof. Duchovni is the incumbent of the Professor Wolfgang Gentner Professorial Chair of Nuclear Physics.
 
Prof. Eilam Gross’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein.

Prof. Giora Mikenberg’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics, which he heads. Prof. Mikenberg is the incumbent of the Lady Davis Professorial Chair of Experimental Physics.
 
Illustration depicting particle collisions
Space & Physics
English
  • CERN
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Particle Physics and Astrophysics
  • Particle accelerator
  • Particle detector

Workplace: On the Ice

English
 
 
Dr. Hagar Landsman at the geographical South Pole
 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Dr. Hagar Landsman (Peles) smiles when she talks about Antarctica – the featureless landscape, the - 40°C temperatures in summer, the relentless midnight sun. “It’s a very special place,” she says. Landsman has already made two trips to the South Pole, and she hopes to go again in the next southern summer – sometime between November and February.

Landsman is a member of the international “IceCube” research team – IceCube being a unique sort of telescope, one that tracks particles called neutrinos, rather than light. Though quite common, neutrinos are almost impossible to detect. They are nearly without mass and carry no charge, and they very rarely interact with normal matter. The only way to detect them is to look for signs of those rare interactions.

In recent years, science has revealed much about these elusive little particles – for instance, the fact that they can change from one type to another as they zip through space – but many mysteries remain. One of those mysteries is the source of certain high-energy neutrinos connected with cosmic phenomena known as gamma ray bursts. Observing neutrinos from these bursts might help researchers understand their origins and how they are produced. Neutrinos are also believed to be connected to mysterious cosmic rays and could shed light on puzzling phenomena that have been observed in these rays. In addition, neutrinos might yield clues to the unseen side of the universe – dark matter. “People have been using photons (light) to observe the universe since the dawn of history,” says Landsman. “In IceCube we use neutrinos for astronomy, which gives us a fresh and exciting view.”
 
 
at the pole
Landsman has been working on IceCube for the past eight years – since receiving her Ph.D. in physics from the Technion, Haifa, and going on to postdoctoral research at the University of Wisconsin. Her main responsibility has been calibrating and testing, and ensuring that all of the 5,000 detectors now buried under the Antarctic ice function properly.

Completed just last year, IceCube is an enormous array of light detectors, one cubic kilometer in size, buried at a depth of 2.5 km below the polar ice. At this depth, there is total darkness. Yet rare bursts of light occur in those infrequent cases in which a neutrino interacts with the million tons of ice. Down there, the ice is crystal clear, and a burst of light can travel hundreds of meters, reaching a number of IceCube’s light detectors.
 

 

arrival
 
Each basketball-sized detector, says Landsman, undergoes several months of rigorous testing and calibration. Once it is encased in ice, there is no moving or repairing it. Yet it is expected to function for the next decade. At the South Pole, Landsman retests and readjusts the detectors one last time before sending them down the boreholes into place.

Trips last a month – three weeks “on the ice” and another week in transit – though the Antarctic’s unpredictable weather can extend travel time by days. In those three weeks, Landsman works nearly around the clock, not just because it is light 24 hours a day, but because she feels the need to accomplish as much as possible in the short time she has there. “All of the 150 or so people at the South Pole Station – researchers, engineers and support staff – work this way. The cost of bringing a person there is so high that only truly necessary people are allowed. Housekeeping chores – from cleaning toilets to washing dishes – are shared by all.”
 
 
into the Borehole
 
Most of Landsman’s work is outdoors. At an elevation of 2,800 m, altitude sickness is a problem, and the extremely dry air is even more troublesome than the cold. The conditions slow the work down: “If you forget a screwdriver, it can take two hours to go back and get it,” she says. Indoors, the station is kept cool to save on heating, and showers are limited to two minutes twice a week. “One gets used to it all,” says Landsman. And once in a while, the work stops for entertainment – for instance, the Christmastime “race around the world”:  a circumpolar run accompanied by snow vehicles fitted out as parade floats by the station’s engineers.


A change of scenery


Landsman’s most recent work trip was much closer to home – to Italy. At the Weizmann Institute, Landsman is a member of the Particle Physics and Astrophysics Department in the group of Profs. Ehud Duchovni, Eilam Gross and Amos Breskin. Specifically, she is a key member of the Weizmann team participating in the XENON project, which is attempting to find evidence for dark matter particles with a detector deep underground in Italy’s San Grasso National Lab. The team is now building a new detector that will hold a ton of liquid Xenon. Landsman is involved both in data analysis and in planning the new device.
 
 
 
She is also involved in planning and installing the next neutrino project at the South Pole. Known by the acronym ARA, the new project will eventually be 100 km. sq, with detectors spaced a kilometer apart. The new detectors work with radio waves, rather than light waves, and can thus be placed under just 200 m of ice. Landsman describes ARA as “a really big net, designed to catch the biggest fish” – in this case the highest-energy neutrinos.

Hagar is married to Adi, who is also on the IceCube team. Because he is involved with the administrative side of the project, work takes him to Wisconsin, rather than Antarctica. But he is pleased that the $300 million dollar project was completed on time, and slightly under budget. The couple has a daughter and a son, who, according to Hagar, don’t quite understand what their mother does on her trips. “When she was younger, my daughter told everyone her mother was going to Antarctica to feed neutrinos to the penguins.”
 
IceCube research station
 

 

 

Waiting for a particle


Earth’s atmosphere is under a constant barrage of extremely high energy cosmic rays – exceeding a hundred million gigavolts. (That’s a million times the energy of the most energetic particle created in a lab.) The source of these particles and their means of production are still unknown. The Weizmann Institute’s Prof. Eli Waxman and the late Prof. John Bahcall proposed that these particles are produced near young black holes with masses similar to that of the sun, and that such black holes are also responsible for the production of strong gamma ray bursts. One of the central aims of the giant IceCube project in Antarctica is to test this theory, by searching for high-energy neutrinos that are predicted to be produced alongside the cosmic rays and gamma rays. As yet, the detector has not found these high-energy neutrinos, but according to the model proposed by Waxman and Bahcall, the number of neutrinos this detector is likely to record is relatively tiny, so that data will need to be collected over a period of five to ten years before any conclusions can be drawn.
 
 
landsman
 
Prof. Amos Breskin’s research is supported by Erica A. Drake and Robert Drake; the Nella and Leon Benoziyo Center for High Energy Physics; the estate of David Turner; and the Friends of Weizmann Institute in memory of Richard Kronstein. Prof. Breskin is the incumbent of the Walter P. Reuther Chair of Research in Peaceful Uses of Atomic Energy.
 
Prof. Ehud Duchovni’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein; the Nella and Leon Benoziyo Center for High Energy Physics; and the Yeda-Sela Center for Basic Research. Prof. Duchovni is the incumbent of the Professor Wolfgang Gentner Professorial Chair of Nuclear Physics.

Prof. Eilam Gross’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein.
 
Prof. Eli Waxman heads the Benoziyo Center for Astrophysics. Prof. Waxman is the incumbent of the Max Planck Professorial Chair of Quantum Physics

 
 

 
 


 

Dr. Hagar Landsman at the geographical South Pole
Space & Physics
English
  • Amos Breskin
  • Ehud Duchovni
  • Eilam Gross
  • Eli Waxman
  • Hagar Landsman
  • Neutrino
  • Particle Physics and Astrophysics
  • Particle detector

Searching for a Particle

English
 
In mid-December, as the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN), near Geneva, was winding up for the year, two of its groups, ATLAS and CMS, made an announcement. After a long search for the Higgs boson, both teams had discovered some anomalies in their data that may be traces of the elusive Higgs. While the results were not proof positive, the scientists involved in the project believe they are a very encouraging sign, raising hopes for more conclusive findings in the 2012 LHC run, set to begin in April.
Results of a collision that could represent a Higgs boson from the ATLAS experiment

 
Members of the Weizmann Institute’s Particle Physics and Astrophysics Department have been prominent participants in ATLAS. Prof. Giora Mikenberg was the ATLAS Muon Project leader for many years and now heads the Israeli LHC team. Prof. Ehud Duchovni heads the Weizmann ATLAS group as well as a small group looking for SUSY signals. And Prof. Eilam Gross is currently an ATLAS Higgs physics group convener. These three have been part of the effort to find the Higgs since 1987.

The Higgs boson is thought to be the particle that gives all the other elementary particles their mass. Predicted by the Standard Model of Particle Physics – a framework for all of the subatomic particles in nature – the Higgs is the one piece of the model that has not yet been proven to exist.

In 2011 the LHC particle accelerator in Geneva collided over 300 trillion (a million million) protons. Seven billion electron volts went into the effort to produce the Higgs boson. But in each collision, other, similar, particles are created. Gross: “There was no way to foresee what we would find. The chances of a collision producing a Higgs boson are so small that only about a hundred are expected to be observed in a year.”

The ATLAS results suggest that there could be a Higgs boson with a mass of around 126 GeV.
 
Prof. Ehud Duchovni’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein; the Nella and Leon Benoziyo Center for High Energy Physics; and the Yeda-Sela Center for Basic Research. Prof. Duchovni is the incumbent of the Professor Wolfgang Gentner Professorial Chair of Nuclear Physics.

Prof. Eilam Gross’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein.

Prof. Giora Mikenberg’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics, which he heads. Prof. Mikenberg is the incumbent of the Lady Davis Professorial Chair of Experimental Physics.



 
 
Results of a collision that could represent a Higgs boson from the ATLAS experiment
Space & Physics
English
  • CERN
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Large Hadron Collider
  • Particle Physics and Astrophysics

Weizmann Institute Scientists Make Significant Contributions to LHC Findings

English
 
Today’s announcement from the Large Hadron Collider (LHC) at CERN points to promising signs for the existence of the Higgs boson. Weizmann Institute scientists have been prominent participants in ATLAS, one of the two experiments to produce results in the search for this elementary particle. Prof. Giora Mikenberg was the ATLAS Muon Project leader for many years and now heads the Israeli LHC team. Prof. Ehud Duchovni heads the Weizmann ATLAS group as well as a small group looking for SUSY signals. Prof Eilam Gross is currently the ATLAS Higgs physics group convener. All are members of the Weizmann Institute’s Particle Physics and Astrophysics Department, and they have been part of the effort to find the Higgs since 1987.

ATLAS and its sister experiment in the LHC, CMS, have been searching for the Higgs boson, thought to be the particle that gives all the other elementary particles their mass. The Higgs is predicted by the Standard Model of Particle Physics, which provides a framework for all of the subatomic particles in nature. The Higgs is the one piece of the Standard Model that has not been proven to exist, and some scientists believe that the model will have to be rethought if the Higgs is not found.

Gross: “In 2011 the LHC particle accelerator in Geneva collided over 300 trillion (a million million) protons. All of that enormous energy (7 trillion electron volts) went into the effort to produce the Higgs boson. But in each collision, other similar particles are created and there is no way to foresee what we will find. The chances of a collision producing a Higgs boson are so small that only about a hundred are expected to be observed over the course of a year.”

Finding possible signs of a Higgs involved looking for statistical anomalies in the data (compared to what the results would look like if there were no Higgs) in the expected mass range. The problem is that once these anomalies appear, the scientists had to rule out statistical flukes. But several weeks ago, it was noticed that “extra” events in the probable Higgs range had accumulated in the experimental results during 2011. Gross: “We couldn’t believe our eyes -- we looked at the screen for ages before we started to digest what we were seeing. In the past three weeks, the entire Higgs search team in the ATLAS experiment have checked and rechecked the results from every possible angle. We checked for errors… for bugs in the program.”
 
The ATLAS results suggest that there could be a Higgs boson with a mass of around 126 GeV, and that there is just a 1 in 5000 chance that the extra events they observed in this particular mass are the result of a statistical fluke and not the creation of a Higgs boson. Such fluctuations might still disappear, so  the proof is still not at all conclusive, but scientists believe that it bodes well for the next round of LHC collisions, set to begin in April 2012.
 

Results of a collision that could represent a Higgs boson from the ATLAS experiment

 

Prof. Ehud Duchovni’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein; the Nella and Leon Benoziyo Center for High Energy Physics; andthe Yeda-Sela Center for Basic Research. Prof. Duchovni is the incumbent of the Professor Wolfgang Gentner Chair of Nuclear Physics.

Prof. Eilam Gross’s research is supported by the Friends of Weizmann Institute in memory of Richard Kronstein.

Prof. Giora Mikenberg’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics, which he heads. Prof. Mikenberg is the incumbent of the Lady Davis Chair of Experimental Physics.
 

 

 


Crash: The race for the Higgs boson

 


 
Results of a collision that could represent a Higgs boson from the ATLAS experiment
Space & Physics
English
  • CERN
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Large Hadron Collider
  • Particle Physics and Astrophysics

Still at Large: WIMPs

English

 

XENON100 dark matter detector
 
 
 
 
 
 
 
 
 

 

The existence of particles known as WIMPs is still up in the air. The WIMP, or Weakly Interacting Massive Particle, is one candidate for the mysterious dark matter thought to make up much of our universe. Such a particle would hardly ever interact with regular, everyday matter and thus should be extremely hard to detect.

 
Weizmann Institute scientists have been participating in an experiment to look for traces of WIMPs. The experiment consists of 161 kilos of liquid xenon buried deep underground in Italy’s Gran Sasso National Lab. Besides the 1400 meters of rock, layers of copper, water, lead and polyethylene shield the experiment from cosmic and background radiation, so that any rare WIMP signals can be recorded. Working with 60 physicists from around the globe, Profs. Eilam Gross, Ehud Duchovni and Amos Breskin of the Institute’s Particle Physics and Astrophysics Department were instrumental in increasing both the search sensitivity of the experiment and the possibility of discovering the particles.
 
(l-r) Ofer Vitells, and Profs. Amos Breskin, Eilam Gross and Ehud Duchovni. Waiting for dark matter
 

After 100 days of operation, three candidate events were recorded, but these could well have been rare background radiation events within the xenon tank. Because XENON100 was the most sensitive of the WIMP searches conducted in various labs around the world, it has narrowed the possible range for this particle. Now the scientists are working on a new version of the detector that will contain 1000 kilos of liquid xenon and be a hundred times more sensitive.

 

Prof. Amos Breskin's research is supported by the Nella and Leon Benoziyo Center for High Energy Physics; and the estate of Richard Kronstein. Prof. Breskin is the incumbent of the Walter P. Reuther Chair of Research in Peaceful Uses of Atomic Energy.
 
 
Prof. Ehud Duchovni's research is supported by the Nella and Leon Benoziyo Center for High Energy Physics; and the Yeda-Sela Center for Basic Research.
 
Prof. Eilam Gross's research is supported by the estate of Richard Kronstein.
 
 
 
(l-r) Ofer Vitells, and Profs. Amos Breskin, Eilam Gross and Ehud Duchovni. Waiting for dark matter
Space & Physics
English
  • Amos Breskin
  • Dark matter
  • Ehud Duchovni
  • Eilam Gross
  • Particle Physics
  • Particle detector

New Data from XENON100 Narrows the Possible Range for Dark Matter

English
 
An International team of scientists in the XENON collaboration, including several from the Weizmann Institute, announced on Thursday the results of their search for the elusive component of our universe known as dark matter. This search was conducted with greater sensitivity than ever before. After one hundred days of data collection in the XENON100 experiment, carried out deep underground at the Gran Sasso National Laboratory of the INFN, in Italy, they found no evidence for the existence of Weakly Interacting Massive Particles – or WIMPs – the leading candidates for the mysterious dark matter. The three candidate events they observed were consistent with two they expected to see from background radiation. These new results reveal the highest sensitivity reported as yet by any dark matter experiment, while placing the strongest constraints on new physics models for particles of dark matter. Weizmann Institute professors Eilam Gross, Ehud Duchovni and Amos Breskin, and research student Ofer Vitells, made significant contributions to the findings by introducing a new statistical method that both increases the search sensitivity and enables new discovery.
 
Any direct observation of WIMP activity would link the largest observed structures in the Universe with the world of subatomic particle physics. While such detection cannot be claimed as yet, the level of sensitivity achieved by the XENON100 experiment could be high enough to allow an actual detection in the near future. What sets XENON100 apart from competing experiments is its significantly lower background radiation, which is 100 times lower, greatly reducing the potential obscuring of any dark matter signal. The XENON100 detector, which uses 62 kg of liquid xenon as its WIMP target, and which measures tiny charges and light signals produced by predicted rare collisions between WIMPs and xenon atoms, continues its search for WIMPs. New data from the 2011 run, as well as the plan to build a much larger experiment in the coming years, promise an exciting decade in the search for the solution to one of nature's most fundamental mysteries.
 
Cosmological observations consistently point to a picture of our universe in which the ordinary matter we know makes up only 17% of all matter; the rest – 83% – is in an as yet unobserved form – so-called dark matter. This complies with predictions of the smallest scales; necessary extensions of the Standard Model of particle physics suggest that exotic new particles exist, and these are perfect dark matter candidates. Weakly Interacting Massive Particles (WIMPs) are thus implied in both cosmology and particle physics. An additional hint for their existence lies in the fact that the calculated abundance of such particles arising from the Big Bang matches the required amount of dark matter. The search for WIMPs is thus well-founded; a direct detection of such particles would provide the central missing piece needed to confirm this new picture of our Universe.
 
The properties of dark matter have been addressed through a variety of approaches and methods; these have provided the scientists with indirect hints of what to search for. WIMPs are expected to have a mass comparable to that of atomic nuclei, with a very low probability that they will interact with normal matter. Such particles are thought be distributed in an enormous cloud surrounding the visible disk of the Milky Way. Earth is moving through this cloud, along with the Sun, on its journey around the Galaxy center. This movement results in a 'WIMP wind,' which may occasionally scatter off atomic nuclei in an Earth-bound detector, releasing a tiny amount of energy which can then be detected with ultra-sensitive devices.
 
In the XENON100 experiment, 62 kg of liquid xenon acts as a WIMP target. The liquid, at a temperature of about -90° C, is contained in a stainless steel cryostat equipped with a cryo-cooler to maintain highly stable operating conditions. The experiment is located in the Gran Sasso Underground Laboratory (LNGS) in Italy where it is shielded from cosmic radiation by 1400 meters of rock. Further shielding from radioactivity in the detector itself and its surroundings is provided by layers of active and passive absorbers surrounding the target. These include 100 kg of active liquid xenon scintillator, 2 tons of ultra-pure copper, 1.6 tons of polyethylene and 34 tons of lead and water. The radio-pure materials used to produce the detector components assure an ultra-low background radiation environment.
 
Particles interacting within the active liquid xenon space excite and ionize atoms. This results in light emission in the deep ultraviolet. As electrons drift across the liquid xenon, they create a delayed, luminescent signal on the top of the detector, due to the experiment’s strong electric field. Both primary and secondary scintillation light signals are detected via two arrays of photosensors – one located in the liquid xenon at the bottom, and one in the gas above the liquid. The simultaneous measurement of these two light signals enables the researchers to infer both the energy and the spatial coordinates of the particles’ interaction, while providing information on their nature. This analysis of ratio of the two light signals and their precise localization in space is an extremely accurate method of distinguishing WIMP signals from background events.
 
Many of technologies and methods used in the XENON100 experiment have been built on the research and development efforts of the XENON Dark Matter Search program, which produced, in 2006, the XENON10 prototype. For XENON100, a ten-fold increase in fiducial target mass, combined with 100-fold reduction in background, translates into a substantial improvement in sensitivity to WIMP-nucleon elastic scattering. An extensive calibration using various sources of gammas and neutrons was performed to demonstrate that XENON100 reached its goals for sensitivity and for low background radiation.
 
Results from a preliminary analysis from 11.2 days worth of data, taken during the experiment’s commissioning phase in October and November 2009, have already set new upper limits on the interaction rate of WIMPs – the world's best for WIMP masses below about 80 times the mass of a proton (Physical Review Letters 105 (2010) 131302).
 
A new dark matter search was performed between January and June, 2010, and 100 days worth of data from this run have been analyzed. Three candidate events were found within the pre-defined parameters in which the WIMP signal is expected to appear. However, these events, while coming from true particle interactions in the detector, are consistent with predictions of two such events resulting from radioactive backgrounds. Thus evidence for dark matter cannot be claimed, but a new upper limit for the strength of its interaction with normal matter could be calculated. These results represent the best limits to date. They narrow the possibilities open to supersymmetric particle physics theories that predict the nature of dark matter.
 
XENON100 has achieved the lowest background among all dark matter experiments worldwide (Physical Review D (2011); arXiv:1101.3866). Since the data presented here were collected, the intrinsic background from radioactive krypton in the xenon filling XENON100 has been reduced to an unprecedented low level and the detectors’ performance has been improved as well. Even as new data are being collected in these improved conditions, the scientific team is preparing a next-generation dark-matter search experiment featuring a detector that will contain more than 1000 kg of liquid xenon as a fiducial WIMP target. With further reduction in overall background radiation, XENON1T promises to be a hundred times more sensitive than XENON100.
 
The XENON collaboration consists of 60 scientists from 14 institutions in the USA (Columbia University New York, University of California Los Angeles, Rice University Houston), China (Shanghai Jiao Tong University), France (Subatech Nantes), Germany (Max-Planck-Institut Heidelberg, Johannes Gutenberg University Mainz, Willhelms Universität Münster), Israel (Weizmann Institute of Science), Italy (Laboratori Nazionali del Gran Sasso, INFN e Università di Bologna), Netherlands (Nikhef Amsterdam), Portugal (Universidade de Coimbra) and Switzerland (Universität Zürich).
 
XENON100 is supported by the collaborating institutions and by the National Science Foundation and the Department of Energy in the USA, by the Swiss National Foundation in Switzerland, by l'Institut national de physique des particules et de physique nucléaire and La Région des Pays de la Loire in France, by the Max-Planck-Society and by Deutsche Forschungsgemeinschaft in Germany, by the Weizmann Institute of Science, by FOM in the Netherlands, by the Fundação para a Ciência e Tecnologia in Portugal, by the Instituto Nazionale di FIsica Nucleare in Italy and by STCSM in China.
 
Contact:
Professor Elena Aprile (Spokesperson)
Columbia University, Physics Department
Tel.: +1 212-854-3258 ; +1 914-591-2878
Email: age@astro.columbia.edu
 
 
WIMP detection principle in the XENON100 experiment
 
 
 
Prof. Amos Breskin’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics; and the estate of Richard Kronstein. Prof. Breskin is the incumbent of the Walter P. Reuther Chair of Research in Peaceful Uses of Atomic Energy.

Prof. Ehud Duchovni’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics; and the Yeda-Sela Center for Basic Research. Prof. Duchovni is the incumbent of the Professor Wolfgang Gentner Chair of Nuclear Physics.

Prof. Eilam Gross’ research is supported by the estate of Richard Kronstein.
 
WIMP detection principle in the XENON100 experiment
Space & Physics
English
  • Amos Breskin
  • Dark matter
  • Ehud Duchovni
  • Eilam Gross
  • Particle Physics
  • Particle detector

Where Does Mass Come From?

English
W particle produced in a collision in the ATLAS experiment, triggered by Weizmann-made detectors (red lines). Image: the ATLAS Experiment at CERN
 
 

Understanding how particles – say, electrons – get their mass is a challenge for physicists. The Standard Model says that all fundamental particles – for instance, the electron or the “W” and “Z” particles that carry the electroweak force – owe their mass to another particle called the “Higgs boson.” Only, no such particle has yet been discovered in any experiment. Another mystery: Most of the mass in the Universe comes, not from the particles we know about, but from some strange, invisible material that has been dubbed “dark matter.”


Scientists in the Institute’s Faculty of Physics are key players in the global effort to solve the riddle of the source of mass. Prof. Ehud Duchovni participated in the experiments in which the W and Z particles were discovered. He and others have now joined in the search for the Higgs boson in the gigantic LHC particle accelerator at CERN. Prof. Giora Mikenberg, who heads the Israeli research team at CERN, developed, together with his team at the Institute, a unique particle detector that is now installed in the LHC. This detector is specially tuned to find evidence that Higgs bosons have been created in the experiments. Prof. Eilam Gross is responsible for the statistical methods used to interpret the data collected in the ATLAS research station.

Dr. Gilad Perez investigates the possibility that our universe has extra dimensions, and suggests ways to find them through the LHC experiments. The existence of such extra dimensions might solve the riddle of mass in the Universe. Prof. Yosef Nir researches the “family tree” of mass through three “generations” of quarks with different masses. He also works on the theory of supersymmetry, which explains, among other things, the existence and unique properties of the Higgs particle, as well as the source of dark matter.
 
(l-r) Dr. Gilad Perez, Profs. Ehud Duchovni, Yosef Nir, Eilam Gross and Giora Mikenberg
 
 

 

Prof. Eilam Gross’s research is supported by the Rosa and Emilio Segre Research Award.

Prof. Giora Mikenberg is Head of the Nella and Leon Benoziyo Center for High Energy Physics; his research is supported by the Rosa and Emilio Segre Research Award. Prof. Mikenberg is the incumbent of the Lady Davis Chair of Experimental Physics.

Prof. Yosef Nir is Head of the Center for Experimental Physics. Prof. Nir is the incumbent of the Amos de-Shalit Chair of Theoretical Physics.

Dr. Gilad Perez’s research is supported by the Peter and Patricia Gruber Award. Dr. Perez is the incumbent of the Shlomo and Michla Tomarin Career Development Chair.
 
 
W particle produced in a collision in the ATLAS experiment, triggered by Weizmann-made detectors (red lines). Image: the ATLAS Experiment at CERN
Space & Physics
English
  • Annual Report 2010
  • Dark matter
  • Ehud Duchovni
  • Eilam Gross
  • Gilad Perez
  • Giora Mikenberg
  • Higgs boson
  • Particle Physics
  • Particle accelerator

Pages