Black Holes in the Lab

English
 
 
Giant machine, tiny particles

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Thousands of physicists from 62 countries will embark in the coming years on one of the most fascinating adventures in the annals of science. Using the world’s largest machine – it weighs in at six times the weight of the Eiffel Tower – they’ll attempt to prove the existence of a tiny, subatomic particle – the Higgs boson. Finding this particle will provide the last piece of a puzzle known as “the standard model” – the most complete and widely accepted theory to date on the structure of all the material in the universe. Failure to find it could shake the world of science like a 9.0 earthquake, necessitating no less than a total rethink of the fundamentals of physics.
 
The machine is a particle accelerator. It’s nestled in a 27-km-long tunnel, dug some 100 meters beneath the border between France and Switzerland, near Geneva. This accelerator is a part of CERN, the European particle physics laboratory. CERN is a world giant in the field of physics: Its scientists came up with, among other things, the computer languages and protocols that became the basis of the World Wide Web, and it has an effect on the European economy similar to that of the American space program in the U.S. Yet for all its accomplishments, the scientists at CERN, with all their complex machinery, haven’t managed to track down this one missing particle. Their best hope yet lies with the new accelerator being built, called the Large Hadron Collider (LHC), which will be able to accelerate bundles of protons to 99.999998% of the speed of light. These bundles will be aimed straight at each other, causing collisions that will release so much energy, the protons themselves will explode. For 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 will be present in the accelerator. 
 
At that first moment, the universe was simple, hot and very energetic. As the seconds ticked by, space expanded, and that energy began to dissipate. The universe cooled, becoming more complex as it did so, until it reached the level of complexity we know today. Inside the collider, the scientists will try to recreate those simpler, primordial conditions – a cosmos in which all particles were simply “different faces” of a small number of elementary particles, and the four fundamental forces that act between those particles were but expressions of a single force. As a first step in reconstructing that primal force, scientists have managed to join two of those forces: the electromagnetic force and the weak nuclear force. (The other two are the strong nuclear force and gravity.) But the existence of this “electro-weak” force presupposes the existence of a particle called a “Higgs” – named after the Scottish physicist Peter Higgs who, along with Robert Brout and Francois Englert, first predicted it. The only fly in the ointment is that since its prediction over 40 years ago, no Higgs particle has yet been detected. 
 
A number of Weizmann Institute physicists have joined in the effort to find the missing Higgs particle. They’re a somewhat multigenerational scientific family – Prof. Giora Mikenberg, who heads the Israeli team, is the teacher and mentor of Prof. Ehud Duchovni, who taught Prof. Eilam Gross. Also working with these three are Dr. Vladimir Smakhtin, Dr. Daniel Lellouch and Dr. Lorne Levinson, all of the Particle Physics Department and the Nella and Leon Benoziyo Center for High Energy Physics.
  
High-Speed Collisions
 
Inside the accelerator, powerful, head-on collisions take place continuously between the protons, resulting in highly energetic particles that wink in and out of existence in a tiny fraction of a second. To obtain proof of their existence, one must identify the traces they leave behind. Thus a number of particle detectors have been created, each designed to trap a different kind of particle. The Weizmann team led by Mikenberg has developed a special detector, constructed at the Institute and other places around the world, which will contribute to detecting the elusive Higgs. “Elusive” may be an understatement: The chances of being able to find a Higgs particle in a single collision are about the same as those of coming up with a specific cell from a specific leaf on a specific plant by plucking one cell at random from all of the plants on the whole planet. 
 

The LHC, equipped with superconducting magnets that work at temperatures of less than 2 degrees above absolute zero (absolute zero is -273° C), will produce something like a billion collisions per second. If protons were people, the collision rate would entail every person on the planet running into every other person on the planet every six seconds. Calculating and analyzing the data from all of these collisions will be akin to listening in on all of the planet’s telephone conversations at once, assuming the entire population is talking simultaneously on 20 phones apiece. 
  
 

Hidden Dimensions and Black Holes

 
In addition to the Higgs particle, the LHC might, at some time in the future, produce millions of very tiny black holes. This surprising idea arises indirectly from string theory, which posits that the particles we know are simply manifestations of one “fundamental constituent,” called a string, and all the forces acting in nature are nothing more than different aspects of one single primeval force. Reality, as suggested by this theory, contains at least eleven dimensions, but seven of them are “curled up” and shrunk so small they can’t be observed. 
 
Another recent model has suggested that the gravitational force can propagate in the additional dimensions, and that the size of the curvature of some of these additional dimensions might not be so small. Under these assumptions gravitational force becomes very strong at short distances, in particular for very energetic (massive) particles. Close to particle collision sites, this can lead to an enormous concentration of gravitational power in a small area. If this happens, a black hole might form. In fact, if calculations are correct, black holes could be created in the LHC at a rate of up to one per second. There’s no need to worry though: The physics of black holes dictates that the smaller the black hole, the higher its temperature. Such tiny black holes will be so hot they’ll vaporize almost as soon as they come into existence.    
  
Prof. Giora Mikenberg’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics. Prof. Mikenberg is the incumbent of the Lady Davis Professorial Chair of Experimental Physics.
 
Prof. Ehud Duchovni’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics.
 
Joint experiment: An Israeli-Pakistani team at the “Atlas” experimental station

 

 

Prof. Ehud Duchovni

 
Prof. Ehud Duchovni
 

Prof. Ehud Duchovni was born in Israel in 1953. In his youth he was an Israeli swimming and target-shooting champion. He served in an elite army unit and was later a target of a terrorist attack. He was awarded a medal for bravery by the Israeli Police, and the Verdienstkreuz am Band by the German President, for his actions in this attack. Later, while on reserve duty, he was wounded in the back. Duchovni is married to Noga and is the father of Inbal, Eynat, Gilead and Avner.

 

Prof. Giora Mikenberg

 
He was born Jorge Mikenberg in Buenos Aires, Argentina, in 1947. When he was just 16, he left his family in South America, changed his name to Giora, and set out for Israel to live on a kibbutz. In Israel, with encouragement from Prof. Yehuda Shadmi, he began to study physics, eventually ending up at the Weizmann Institute of Science. In the army, he served under Sergeant Ehud Duchovni, who would become his pupil. At CERN, Giora is known as George.
 

Prof. Eilam Gross

 
Prof. Eilam Gross
 

Prof. Eilam Gross was born in Tel Aviv. After completing his army service in an elite communications unit, he left for New York to study music. There he came across a cult book, The Tao of Physics, which prompted him to come back to Israel and study physics at the Hebrew University of Jerusalem. His master’s thesis at the Weizmann Institute was written on string theory, after which he “deserted” theortical work for experimental high-energy physics and the team of Prof. Mikenberg. Today, between mathematical formulas and charting particle trajectories, he continues to work on his music, and he dreams of staging a performance that will combine music with insights gained from particle physics. He is the father of two daughters, Nuphar (20) and Yaara (15).

 

 

 
An Israeli-Pakistani team at the “Atlas” experimental station
Space & Physics
English
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Particle Physics
  • Particle detector

First Matter

English

 

The first matter that came into being right after the Big Bang may not have been quite what scientists had expected. This conclusion emerged recently from the large-scale PHENIX experiment carried out in the United States by a team of 460 physicists from 12 countries, including scientists from the Weizmann Institute.

 

Using an accelerator at the Brookhaven National Laboratory on Long Island, New York, the scientists may have recreated what’s believed to have been the primordial matter in the universe, known as the quark-gluon plasma. Two beams of gold ions were accelerated toward each other, causing head-on collisions. The enormous power of the collisions – about 40 trillion electron volts – turned part of the beams’ kinetic energy into various particles (a process described by Einstein’s E=mc2 equation). A number of the particle detectors used in the experiment were designed and built by Prof. Itzhak Tserruya and his team in the Weizmann Institute’s Particle Physics Department.

 

While many of the experimental results fit in with predictions of how particles in the quark-gluon plasma should behave, others have been a surprise. In particular, scientists were amazed to discover that the plasma, created at a heat up to 150,000 times hotter than the center of the sun, behaves not like a super-hot gas, as expected, but more like a liquid! The experiment, now in its fifth year, is scheduled to run for at least five more years and is certain to yield more susprises in the future.

 

Prof. Itzhak Tserruya’s research is supported by the Nella and Leon Benoziyo Center for High Energy Physics and the Center for Scientific Excellence. Prof. Tserruya is the incumbent of the Samuel Sebba Professorial Chair of Pure and Applied Physics.

Space & Physics
English
  • Itzhak Tserruya
  • Particle Physics
  • Quark-gluon plasma

And Energy for All

English
Prof. Yitzhak Maron. Containing fusion
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
An ancient Greek myth relates that Prometheus, son of gods, stole fire from the heavens and gave it to the people on Earth. This gift and all its many applications catapulted humankind from a harsh, primitive existence toward civilization. Today, scientists in many parts of the world seek to perform a Prometheus-like act, granting human civilization a new energy source that will propel it forward once again. They are looking for ways to harness nuclear fusion, the process by which the sun and other stars generate their abundant energy. Formerly this process was used for destructive purposes: to fuel the explosion of the hydrogen bomb. Today’s researchers, however, pursue peaceful applications of nuclear fusion for its greatest potential benefit: a safe and abundant energy source for all humankind.
 
The existence of nuclear fusion was first hypothesized in the 1920s, and in the late 1930s it was described in quantitative terms by Hans Bethe and others. They discovered that light chemical elements appear to act in an “anti-holistic” manner: the whole is somehow smaller than the sum of its parts. For example, the overall mass of the nucleus of helium (which can be created by fusing two hydrogen atoms) is smaller than the joint mass of its components. What happens to the small mass missing from the helium nucleus? It turns out that when the helium nucleus is created by the fusion of its parts, this mass is converted into energy in accordance with Einstein’s famous equation, E=mc2 (energy = mass x the speed of light squared).
 
From this equation, one can see that a very small amount of matter can yield enormous amounts of energy. Indeed, calculations show that the energy released by fusing 25 grams of hydrogen into helium could provide all the energy needs of a person living in the Western world throughout his or her entire lifetime. And hydrogen is the most abundant element in the universe. Fusion for energy production is environmentally friendly, safe and clean: there is substantially less radioactive waste than with nuclear fission and no harmful byproducts such as the carbon dioxide associated with fossil fuels – a significant contributor to global warming. The catch is that building an installation to convert the energy of nuclear fusion into electricity is like trying to harness a raging tiger to a supermarket shopping cart. Nuclear fusion is a tumultuous event with huge, destructive potential; safely controlling the process is the biggest challenge facing fusion researchers today.
 
Nuclear fusion is the result of a sort of atomic train wreck: two stripped-down hydrogen isotopes speed toward each other, accelerating as they go, until they slam into each other with so much force they stick together, releasing “surplus” energy as heat. Because the isotopes – essentially positively charged nuclei – repel each other, their speed must be quite high to overcome the strong forces of electrical repulsion between them.
 

Cooking with plasma

 
For any kind of energy production to be feasible, one must get more energy out of the system than one puts in, over time. Though this may seem self-evident, fusion until now has demanded a colossal amount of energy to achieve the conditions required to get it up and running, and these still fall short of what’s needed to sustain it in a controlled manner: The hydrogen atoms must reach a temperature of at least 100 million degrees centigrade. (In comparison, the temperature at the center of the sun is “only” 15 million degrees centigrade.) This intense heat transforms the hydrogen gas into a plasma of hot, electrically charged ions. (Plasma is the fourth state of matter after solids, liquids and gases.)
 
Unfortunately, hot and dense plasma, the favored medium for fusion, seeks to expand, thereby losing its heat and reducing the chances for atom collision. The energy invested in containing the plasma and creating the right conditions for nuclear fusion has until now been much greater than the energy obtained. Today, intense research efforts are aimed at finding ways to increase the efficiency of the process and enable it to become “profitable.”
 
Several methods have been proposed to this end. For instance, giant, hollow donuts, the size of football fields, employ strong magnetic fields to keep plasma going for about one second. That’s an eternity compared to the life span of the plasma created in a second approach, where much hotter and denser plasma is formed in a mini-scule area, just a few millimeters in size, for only ten billionths of a second. In this method, there’s no need to contain the plasma – it’s so hot and the atoms are so close together, fusion takes place within that tiny instant.
 
One way to create the extremely hot and dense plasma needed for the second method involves compressing the plasma with powerful pulses of magnetic fields produced by strong electrical currents. In the past decade this approach has led to several breakthroughs, most of them achieved at the Sandia National Laboratories in the United States, which has close ties and an open exchange of ideas with the Weizmann Institute. Still, numerous basic questions need to be answered, calling for additional research. That’s where Prof. Yitzhak Maron and his plasma laboratory in the Particle Physics Department enter the picture.

 

Modest facility, international scale research

 
The Weizmann Institute of Science is one of only two research institutions outside the United States involved in the University Excellence Center – a prestigious initiative sponsored by the United States Department of Energy that promotes research into hot and dense plasma. Maron and the scientists who work with him in the relatively small system on the Weizmann Institute campus study the behavior of plasma created using the leading approach in this area, known as Z-pinch. (Z-pinch refers to the vertical, or Z, axis on a three-dimensional grid; in this method, magnetic pulses compress plasma in a vertical tube along the Z axis.) By investigating the behavior of Z-pinched plasma and the different processes by which this plasma’s kinetic energy is converted into heat and radiation, the scientists hope to identify those in which energy will undergo the most efficient conversion. In other words, they are looking for ways to get the most usable radiation energy output for the least input.
 
Capturing processes that take place within nanoseconds at blistering temperatures requires sophisticated methods. Maron’s group uses spectroscopy, the technique scientists employ to study the most remote and violent areas of the universe. Their equipment captures the spectra of radiation emitted from the plasma, translating light intensities and wavelengths into information about plasma components and their properties: temperature, density, electric and magnetic fields, and atomic velocities.
 
Expanding magnetic field in plasma
 
 
Researchers in Maron’s lab, in collaboration with scientists from the University of Jena and the GSI Laboratory in Germany, have recently come up with innovations in spectroscopy, making it possible to obtain better information about dynamic plasma processes. With these innovations, Dr. Eyal Kroupp and his team in the Institute’s plasma labmeasured and tracked very rapid changes in the energies of the plasma ions. A series of spectral images captured at increments of one per nanosecond (one billionth of a second), at ultrahigh spectral resolution, is what allowed them to see more clearly than ever what happens in plasma. The images revealed cases in which most of the compressed plasma energy is converted to radiation. The innovative methods developed by Maron’s team are now being employed in large laboratories in the United States and Europe.
 
In other experiments, Dr. Ramy Doron and a team of researchers in Maron’s laboratory were able to observe plasma phenomena never before seen in a lab, such as ions separating and electrons accelerating at the advancing edge of magnetic fields. Similar phenomena have recently been recorded by research satellites monitoring the plasma and magnetic activity of the sun, and the scientists are currently discovering what laboratory measurements can tell us about events observed from space. Thus out of one relatively modest laboratory comes research that contributes insights into the universe in which we live, as well as those that bring us closer to the use of controlled nuclear fusion for making our own world more livable.

 
Prof. Yitzhak Maron’s research is supported by the Monroe and Marjorie Burk Fund for Alternative Energy Studies; Sandia National Laboratories; and Dr. and Mrs. Robert Zaitlin, Los Angeles, CA. Prof. Maron is the incumbent of the Stephen and Mary Meadow Professorial Chair of Laser Photochemistry.
 

 

Prof. Yitzhak Maron. Creating a hot, dense plasma
Space & Physics
English
  • Alternative Energy
  • Nuclear fusion
  • Particle Physics
  • Spectroscopy
  • Yitzhak Maron

After the Big Bang

English

Kozlov, Fraenkel, Tserruya, Ravinovich and Cherlin. PHENIX rising

In the first millionth of a second after the Big Bang, atoms as we know them today did not yet exist.

 

The jets of blazing matter that dispersed in all directions in those first few fractions of a second contained a mixture of infinitesimal particles (quarks and gluons), called the quark-gluon plasma. This was the first form of matter in the universe. Later on, when the universe cooled down a bit and became less dense, the quarks and gluons organized into various combinations, forming particles such as protons and neutrons. Since then, in fact, quarks and gluons have not existed as free particles in the universe.

 

Scientists have been trying to recreate the quark-gluon plasma in the lab in a joint experiment including 460 physicists from 57 research institutions in 12 countries. Recent results strongly indicate that they they are on the right track.

 

The ongoing project, called PHENIX, is being conducted at the Brookhaven National Laboratory in Long Island, using an accelerator, called RHIC (Relativistic Heavy Ion Collider), built especially for creating the quark-gluon plasma. The Israeli team is led by Prof. Itzhak Tserruya, head of the Weizmann Institute's Particle Physics Department. Tserruya and his colleagues designed and built special particle detectors, called pad chambers, which are a central part of PHENIX's detecting system.

 

The accelerator creates two beams of gold ions and accelerates them toward each other, causing a head-on collision. The power of the collision (about 40 trillion electron volts, the highest level of energy attainable in the lab) turns part of the beams' kinetic energy into heat, while the other part turns into various particles. The first stage in the creation of these new particles, like the first stage in the creation of matter in the Big Bang, is assumed to consist of the quark-gluon plasma.

 

Quark gluon plasma condenses

 

 

Prof. Tserruya's research was supported by the Nella and Leon Benoziyo Center for High Energy Physics. He is the incumbent of the Samuel Sebba Professorial Chair of Pure and Applied Physics.

One of the ways to identify the quark-gluon plasma is by observing its interaction with other particles. When a single quark moves through regular matter, it emits radiation that slows down its progress somewhat. When it enters a very dense medium like quark-gluon plasma, its progress is slowed much more. That's precisely the phenomenon that has recently been observed and analyzed in the PHENIX project. According to physicists taking part in the experiment, these findings are very encouraging and could indicate that they have succeeded in creating the quark-gluon plasma.

 

Other than Tserruya, the Weizmann team participating in the PHENIX experiment included Prof. Zeev Fraenkel, Dr. Ilia Ravinovich, postdoctoral fellow Dr. Wei Xie and graduate students Alexandre Kozlov, Alexander Milov and Alexander Cherlin.

 
(l-r) Graduate student Alexandre Kozlov, Prof. Zeev Fraenkel, Prof. Itzhak Tserruya, Dr. Ilia Ravinovich, and graduate student Alexander Cherlin. An international experiment
Space & Physics
English
  • Itzhak Tserruya
  • PHENIX
  • Particle Physics
  • Particle detector
  • Quark-gluon plasma
  • Zeev Fraenkel

Pulling the Strings

English
Dr. Micha Berkooz. created by vibrations
 
 

 

You'd think physicists would be satisfied. It may have taken them several dozen years, but they did succeed in formulating the Standard Model -  the widely accepted and so far most substan- tiated theory on the structure of matter in the universe. This theory neatly divides particles into several "families,"affected by three forces.

Yet physicists are now striving to show that all forces in nature are different aspects of a single, basic component. If they succeed, they hope to have reconciled the Standard Model with another highly acclaimed theory -  Einstein's General Theory of Relativity, which explains gravity. Currently these two landmark achievements don't get along too well.

Dr. Ofer Aharony
 
The proposed component underpinning all matter and gravity in the universe is called a "string."It's different from the particles described by the Standard Model. For starters, it's much smaller. In fact, a string compares to an atom in the same way that an atom compares to the entire solar system. Second, all the "regular"particles are usually viewed by physicists as points, lacking dimensions such as length, width, or depth. In contrast, a string is believed to have a dimension -  length. It is able to vibrate in different ways, creating a multitude of particles.

Most of these particles, however, can be revealed only under exceedingly high-energy conditions, such as those that existed in the first few moments after the Big Bang. Since it is unlikely that such conditions can be reproduced on Earth, all physicists working on string theory are, unsurprisingly, theoreticians -  like Dr. Ofer Aharony and Dr. Micha Berkooz, who recently joined the Weizmann Institute of Science's Particle Physics Department.

Aharony and Berkooz hope to prove that all particles making up the universe, including a sought-after particle underlying gravity (the graviton), are created by the vibration of strings as they move, unite, and separate. In other words, material reality is determined by the "music"played by these string elements.

In the beginning it seemed that string theory could hold true only in a universe possessing a whopping 26 dimensions. The number of dimensions then dropped to 10, and eventually the theory turned out to require 11 dimensions. (The number depends somewhat on one's definition of "dimension.") This leaves two options: It is either impossible to apply string theory to our four-dimensional universe (three spatial dimensions and one of time) or our universe may indeed consist of 11 dimensions, with seven of them beyond our perception.

Physicists working on string theory have shown that this second option is in fact conceivable as long as one is willing to accept that the extra sevendimensions exist in "folded"form next to the familiar four. According to their calculations, if these additional, folded dimensions are very small, their existence will not contradict the observed picture of material reality.

To understand what is meant by "folded dimensions,"think of an ant crawling along a pipe. When crawling in a straight line along the pipe, the ant is aware of one dimension -  length. If it were to crawl around the pipe's diameter, it would discover an additional dimension. But should the pipe's diameter be very small, much smaller than the ant itself, it would no longer be able to crawl around the pipe and, in effect, would not even be aware of its existence.

String theory physicists propose a picture of the world in which the remaining seven dimensions are so "folded"or "shrunken"that we are unable perceive them. In trying to present our four-dimensional world as a partial view of the string theory universe, scientists are examining how familiar phenomena would appear within the string theory framework.

One such phenomenon isholography, which can be relatively easily shown to occur near black holes and involves the compression of three-dimensional information into the two-dimensional surface of the black hole. Physicists have managed to explain this phenomenon in certain black holes using stringtheory. Aharony and Berkooz are studying additional problems within this system, including the information problem: Can radiation created near a black hole be used to reveal the nature of the matter swallowed up by the hole? For example, if we throw a chair into a black hole, will we be able to describe this chair on the basis of the radiation produced at the site?

Another phenomenon that may occur near black holes is described by the so-called "little string theory."Despite its friendly name, this theory is far more complex than the original string theory: It describes the joint behavior of numerous intertwined strings. Little string theory does not require the existence of a graviton. Aharony and Berkooz are examining whether the strong combination of several strings eliminates the need for this particle.

The "hottest"topic in their research, however, deals with the relationships among strings themselves. What is the relationship between two strings moving in parallel? According to the picture currently painted by string theorists, strings can join or separate after touching each other even for a split second, creating a tiny tunnel that connects them and immediately disappears. Aharony and Berkooz, together with Prof. Eva Silverstein of Stanford University, are now exploring the possibility of an entirely different, less tangible connection between strings, in which strings influence one another without physically converging. The aim, they explain, is to grasp the true nature of such "long-distance relationships."
 

Left: One string divides into two. Right: two strings unite

 

 

 

 

 

 

Dr. Berkooz holds the Recanati Family Career Development Chair in Energy Research.

Dr. Aharony holds the Joseph and Celia Reskin Career Development Chair.

 

 

 
Left: One sting divides into two. Right: two strings unite
Space & Physics
English
  • Micha Berkooz
  • Ofer Aharony
  • Particle Physics
  • Theoretical physics›Theoretical particle physics

The Physics of Bargaining

English
Umansky, Heiblum, Chung and Mahalu. A third the price
 
 

 

We don't expect nature to negotiate. Yet Weizmann Institute scientists have shown recently that nature sometimes has a surprisingly opportunistic streak.

This phenomenon was revealed in an experiment examining the behavior of particles whose electric charge is one-third that of an electron. These particles were first observed several years ago by Prof. Moty Heiblum and members of his team at the Condensed Matter Physics Department.

Until recently, the accepted wisdom was that the charge of an electron, first measured some 80 years ago by American physicist Robert Millikan, was the smallest basic unit of electric charge. However, in 1982, American physicist Robert Laughlin explained certain electronic phenomena by proposing a theory based on the assumption that, under certain conditions, the electric current gives rise to "quasi"particles, each of which carries an electric charge smaller than the basic charge of a single electron (one-third, one-fifth, one-seventh, or even smaller, depending on the circumstances).

The first evidence that Laughlin's theory was correct was supplied some four years ago by the Weizmannscientists, who managed, for the first time, to measure an electric charge one-third that of a single electron. This evidence played an important role in the decision to grant Robert Laughlin, Horst Stoermer, and Daniel Tsui the 1998 Nobel Prize in Physics. However, the properties of quasi particles remained a mystery, and Heiblum's team continued to pursue them.

In one series of experiments, the scientists examined how quasi particles act when they run into an obstacle. They discovered that when particles with one-third the charge of an electron arrive en masse at a tall barrier, they "join forces,"creating partnerships of three (that is, together forming a whole electron). Only then are they able to penetrate the obstacle and reach the other side. This cooperative effort has since become known as one of their basic properties.

However, in a more recent series of experiments, the scientists created a beam in which each quasi particle was separated from the others and thus arrived at the barrier alone. The scientists had predicted that the individual particles would be unable to penetrate the tall barrier, but much to their surprise it turned out that when a single particle ran into the obstacle, it was able to cross to the other side!

This event can be compared to bargaining at a toll booth. Imagine that a highway inspector charges all drivers who arrive en masse a toll of three dollars, but when a particular driver arrives alone with only one dollar, the inspector makes sure nobody is watching and agrees to let him pass through at one-third the price. "One would expect to encounter such a phenomenon, say, in the market, where people bargain over price,"says Heiblum, "but laws of nature are supposed to have more 'integrity.'They are expected to be 'unbiased'and consistent."Heiblum's team included graduatestudent Eyal Comforti, visiting scientist Dr. Yungchul Chung, Dr. Vladimir Umansky, and Dr. Diana Mahalu. The scientists are now searching for a theory to explain the hidden logic allowing nature to bend its own rules.

Prof. Heiblum's research is supported by the Joseph H. and Belle R. Braun Center for Submicron Research; Dan and Hermann Mayer, France; the Wolfson Family Foundation Charitable Trust; Mr. Hugo Ramniceanu, France; Mr. Uzi Zucker, New York, NY; Mr. and Mrs. Harold Simpson, Delray Beach, FL; and Mr. Joe Gurwin, Kings Point, NY. He holds the Alex and Ida Sussman Chair in Submicron Electronics.
 
Dr. Vladimir Umansky, Prof. Moty Heiblum, Dr. Yungchul Chung, and Dr. Diana Mahalu. Negotiating skills
Space & Physics
English
  • Condensed Matter Physics
  • Moty Heiblum›Moty Heiblum
  • Quasiparticle

Re-creating the Big Bang

English
 
Prof. Itzhak Tserruya and team. Colliding heavy ions

In a 2.4-mile-long tunnel built in the shape of a racetrack, scientists plan to race ion beams instead of horses. Two gold ion beams, traveling almost at the speed of light, will cross each other at four junctures, where they will collide head-on. The collision will produce a temperature ten thousand times that of the sun --a trillion degrees. Then, hopefully, as the particles fly out from the area of collision, the objective will be obtained: the re-creation of the big bang.

 
A team from the Weizmann Institute, headed by Prof. Itzhak Tserruya of the Particle Physics Department, is participating in the biggest and most extensive effort yet to answer one of the most fundamental questions of our existence: What happened after the big bang? Walking around the collider complex at the U.S. government's Brookhaven National Laboratory on Long Island with some of the leading scientists in this multi-pronged project (in which 430 scientists from 11 countries are participating), one can feel the almost childlike excitement of these scientists in the days leading up to the initial experiment. Reproducing the big bang is the kind of experience that generations of physicists before them could only dream of.
 
Fulfilling a critical role in the project, the Weizmann Institute scientists have designed and built 16 particle detectors; they will be used in the experiment to detect particles flying out of the collision area. With the highly sensitive and very strong, yet lightweight, detectors installed near the collision site, it will be possible to detect the interactions going on in the site and to identify the particles. The electronic circuitry of these detectors will identify the precise three-dimensional location of the particles as they come flying out from the collision. This information will then be combined with that from other detectors to calculate the energy of the particles and their subatomic identity.
 
Scientists theorize that quarks and gluons are the smallest, most basic building blocks of all matter. Microseconds after the big bang, in conditions of very high temperature and pressure, these quarks and gluons were in a special state of matter called quark-gluon plasma. According to the theory, this plasma state immediately began to cool down and then condensed into the nuclear particles with which we are familiar, protons and neutrons. Gradually, over time, these particles became atoms, which later combined into molecules, from which all forms of life eventually emerged.
 
Reenacting the Big Bang
 
The experimental apparatus at Brookhaven used to re-create the big bang, is called a Relativistic Heavy Ion Collider (RHIC). The RHIC's accelerator is the most powerful in the world for use with heavy gold or lead ions used in nuclear experiments. By colliding two gold nuclei, the temperature will be so high and the pressure so intense, it is believed that the nuclei of the gold ions will go through a rapid transition phase and thus be transformed into the quark-gluon plasma. If this happens, a core component of the big bang theory will finally be proved.
 
The physicists involved in the Brookhaven project are used to being asked about the social value of the basic research they are doing. With obvious passion one of the researchers in the project explains to his visitors, as he leads them through the underground tunnels of RHIC, that pursuing answers to theoretical questions is the lifeblood of science. What motivates him, Tserruya, and others involved in the project is curiosity about the universe we live in. Without that curiosity and the directed energy that comes from it, there would be no Internet, no MRI, no high-speed trains, and no advances in cancer treatment. The applications of scientific discoveries create wealth and generate wonder about the power of technology. Curiosity about basic science, however, is the spark that lights the flame.
 
Space & Physics
English
  • Itzhak Tserruya
  • Particle Physics
  • Particle accelerator
  • Quark-gluon plasma

May the One-and-Only Force Be with You

English

Gross, Mikenberg and Shoa, in the lab

Once upon a time the universe was a simple place. It was composed of a few particles interacting by means of just one basic force. But being a very hot and extremely energetic universe, it existed for only a few seconds following the Big Bang. As the seconds passed, the energy spread out through the expanding space and the universe cooled, exactly like a cup of tea.
 
Its primary particles, able to exist only at very high energy levels, continued to multiply and form complex, highly charged relationships. In this way we progressed, more or less, from a simple primeval universe to our more complex cosmos, where we can recline and sip our tea (though it is cooling as well) while perusing at leisure articles on scientific principles.
 
For most of us, the complex place in which we live is a world filled with visual marvels. But physicists are not content with visible reality; their quest is to get to the root of its forces and to examine whether our visual reality is truly based on the profound-but-lost simplicity of the ancient universe.
 
An important milestone in their scientific research was the unification of electromagnetic and weak forces into a single, more ancient force, known as the electroweak force. The remaining missing link for proving the existence of the electroweak force is a force-carrying particle named the Higgs boson.
 
Weizmann Institute scientists at the Nella and Leon Benoziyo Center for High Energy Physics are participating in an international effort to find the Higgs, which is considered responsible for providing mass to all the particles in the universe. The research is being conducted in the largest particle accelerator in the world, known as LEP, at the European Laboratory for Particle Physics (CERN), near Geneva. This accelerator is located in a circular 16.7-mile (27-km) tunnel, excavated 110 yards (100 meters) below the earth's surface.
 
Weizmann scientists Dr. Daniel Lellouch, Dr. Lorne Levinson, Prof. Eilam Gross, and Prof. Ehud Duchovni, led by Prof. Giora Mikenberg of the Particle Physics Department, Director of the Benoziyo Center, are working in Europe within the framework of scientific cooperation agreements signed between Israel and CERN.
 
In the accelerator, particles moving in opposite directions create numerous collisions. A highly energized system develops in the vicinity of the collision, similar to the conditions that existed among particles during the first moment following the Big Bang. As a result, the particles of matter are converted into energy. This is an illustration of Einstein's famous equation; E=mc2 describes the equivalence between matter and energy. Subsequently, the energy spreads throughout the space and the system cools (just as happened in the developing universe). The energy is reconverted into particles of matter that undergo the same multistage process until they form the particles capable of existing in our familiar reality.
 
Scientists monitoring the various stages of this process are learning about the structure of matter and the development of the universe. But herein lies the rub: These energetic particles exist for only fractions of a second. To detect their very existence, it is necessary to identify the tracks they leave behind -- for which purpose scientists construct particle detectors. For example, in order to detect and identify the Higgs, the Institute's scientists, headed by Prof. Mikenberg, developed the thinnest gas-based particle detector in existence. This detector is capable of identifying tracks left by the passage of charged particles at a rate 50 times greater than that achieved by previous detectors. (Most of these detectors are made at the Weizmann Institute, while some are manufactured in Japan in close collaboration with Institute scientists.)
 
According to Mikenberg, unlocking the mystery of the Higgs depends primarily on its mass. "The heavier it is, the more powerful are the collisions required for its discovery. The current CERN accelerator is capable of producing collisions with an energy of about 200 billion electron volts."
 
What if the Higgs is too heavy for the current accelerator?
 
"In that event, the research will continue with a new accelerator now being installed in the circular tunnel, which will create about one billion collisions per second with energies that will, undoubtedly, trap this elusive particle."
 
The days of the Higgs as a particle-in-theory are numbered. If it ultimately transpires that the mass of the Higgs is close to 100 billion electron volts, it is likely that a supersymmetry will exist between the force-carrying particles and the "worldly" particles of matter.
 
It may also demonstrate the possibility that at the foundation of the material universe there existed a single, two-dimensional particle: a "superstring" -- the ancestor of all other particles.
 
The significance of this activity is the opening of a new and exciting hunting season for a swarm of anonymous particles filling key positions in the complex reality of our world. The real prize upon finding them could be the long-sought proof that at the origin of reality there existed a one-and-only basic force of nature, the descendants of which exist today.
Space & Physics
English
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Particle Physics
  • Particle accelerator

Centers of Excellence: Particle Detectors

English

The Israel Science Foundation has recently initiated the establishment of Centers of Excellence at the country's leading academic institutions. The goal of this program -- to provide recognition and support for the work of outstanding groups of local scientists engaged in research at the highest international level. Ten Centers have been created to date, six of them headed by Weizmann Institute professors. Interface describes the activities of three Weizmann-led Centers of Excellence

Prof. Giora Mikenberg. Preparing for the big event

Solving one of the greatest mysteries of the universe, the origin of mass, is the ultimate goal of research conducted at the Center of Excellence devoted to particle physics and headed by Prof. Giora Mikenberg.


Thanks to their extensive experience in the design of particle detectors, the Center's physicists are key players in one of the most colossal experiments ever performed. Known as ATLAS, the experiment involves some 1,500 physicists from 30 countries intent on tracking down the elusive particle believed to endow matter with mass. The search will be conducted at the Geneva-based European Laboratory for Particle Physics (CERN), where the world's most powerful accelerator -- the Large Hadron Collider (LHC) -- is scheduled for completion in the year 2005.

Institute experts are currently constructing some 8,000 square meters of ultrathin high performance detectors for ATLAS in a special laboratory on the Rehovot campus. The superfast elements are the latest in a series of Weizmann contributions to the mammoth international effort underway at CERN. In 1983, Weizmann physicists developed and constructed detectors that were used to capture the decay products of yet another elementary particle at CERN's existing particle accelerator, the Large Electron Positron Collider.

The new ATLAS experiment will be the most ambitious attempt ever to nab the Higgs boson, the particle believed to be responsible for the fact that all other particles in the universe have mass. Its discovery is expected also to shed light on what happened in the first trillionth of a second after the Big Bang, the giant explosion in which the universe is thought to have been created. Failure to locate the particle may force scientists to modify the Standard Model, the accepted theory about the nature of matter founded on the premise that the Higgs boson does exist.

The quest to unravel the secrets of the universe has its down-to-earth aspects as well. Mikenberg recounts that scientists working in the 27-kilometer-long underground tunnel at CERN have had to take into account such prosaic factors as rain affecting the 100-meter-deep tunnel, the gravitational pull of the moon and even the passing of the TGV, or rapid train, several kilometers away. That's because the slightest interference can distort the ultraprecise measurements of elementary particle collisions.

"We can now calculate whether the Swiss train is on time by a factor of 10 to the minus 20th of a second," quips Mikenberg, one of the scientists who pinpointed the train as the cause of several fumbled experiments.

Mikenberg, a member of the Particle Physics Department, serves on the CERN committee supervising the LHC experimental program and heads one of the five Weizmann research groups in the new Center of Excellence. The other four are led by Profs. Ehud Duchovni and Uri Karshon, and Drs. Eilam Gross and Lorne Levinson, also members of the Particle Physics Department.

Researchers from Tel Aviv University and the Technion-Israel Institute of Technology also participate in the project.
 
Space & Physics
English
  • Ehud Duchovni
  • Eilam Gross
  • Giora Mikenberg
  • Higgs boson
  • Particle Physics
  • Particle detector
  • Uri Karshon

Haim Harari Predicted Existence of Top Quark In 1975

English

Prof. Haim Harari. Presenting the full picture

When physicists at the Fermi National Laboratory in the U.S. observed traces of the top quark -- the remaining undetected member of this most important family of fundamental particles -- this sent waves of excitement throughout the scientific community. News of this discovery, widely covered in the media climaxed an over three-decade-long study of quarks -- the building blocks of matter governed by the strong nuclear force, namely, most of the visible material universe.

Unknown to many outside the field is the fact that one of the first physicists to suggest the existence of top quark and the one who gave it its name is Weizmann Institute President Prof. Haim Harari. In a 1975 paper in Physics Letters, Prof. Harari postulated that apart from the three species of quarks that had already been observed and a fourth one which was just discovered there was a theoretical "need" for two additional heavy quarks with charges of 2/3 and -1/3. He named the two new proposed quarks "top" and "bottom," names that remain in use today.

The original model, presented then by Harari, needed major modifications, but a few months later in his rapporteur lecture at the year's International Conference on particle physics, Harari presented for the first time the full correct picture of the world of quarks and leptons, as we know it today, consisting of six species of quarks and six species of leptons. That picture has become the standard understanding. It was followed by the discovery of the bottom quark in 1977.

Commenting on the new Fermilab data, Harari says that while seeing traces of the top quark was of major importance, physicists were convinced of its existence for the last 19 years. But because the top quark has the largest mass of all quarks, experimental evidence about it could only be gathered with accelerators operating at the cutting edge of high-energy technology, a situation that delayed its detection.

Elementary particle physics has matured considerably since 1975, and it is now known that the experiments around which Harari built his early theory were not correctly interpreted. Nevertheless, subsequently gathered data have provided a firm basis for the presently accepted Standard Model of the material universe, which assumes -- as Harari did -- a six-member family of quarks.

This work, says Harari, is still far from complete. For one, the measurement of the top quark at Fermilab still needs further conformational studies. In addition, the theoretical relationship between the quarks and the second central family of particles, the leptons, still has to be ironed out, several different approaches having already been formulated. Whatever future developments will be, the excitement surrounding particle physics shows no signs of dying down.

Prof. Harari occupies the Annenberg Chair of High Energy Physics.
 

Need for additional quarks

 
Space & Physics
English
  • Haim Harari
  • Particle Physics
  • Theoretical physics›Theoretical particle physics
Yes

Pages