The future of physics

The construction of the machine that will take us into this realm, the tera-electron-volt or TeV region, the ring Large Hadron Collider (LHC) at the European Laboratory for Particle Physics, CERN, is now nearing completion

By Graham P. Collins

Editors' introduction

The scientists call this field of energies the tera-electron-volt field or the TeV field. This is the realm of physics that appears before our eyes when two elementary particles collide with each other with a total energy of a billion electron-volts (10eV), or one tera-electron-volt. Building the machine that will take us to this realm, The Large Hadron Collider (LHC) The ring at the European Laboratory for Particle Physics, CERN, is now nearing its end.

When we climb the energy scales, from single electron volts to the TeV range, we are actually traveling from the known world through a chain of distinct landscapes: from the realms of solid state electronics and chemistry (a few electron volts) through the world of nuclear reactions (millions of electron volts) to The territory that particle physicists have been exploring for half a century, billions of electron volts.

What awaits us somewhere in the TeV field? no one knows

But we are pretty much guaranteed that new and revolutionary phenomena of some kind will soon take place. Scientists hope to identify long-sought particles that could help complete our understanding of the nature of matter. Stranger discoveries, such as signs of extra dimensions, may also emerge from the darkness.

At the end of this "journey" to the TeV field and beyond, we will know for the first time what we are made of and how the place where our lives pass so quickly, deep in its infrastructure, works. Like the LHC itself when completed, we will have come full circle.

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The discovery machine

A global collaboration of scientists plans to launch the largest particle physics experiment in history.

You can think of it as the largest and most powerful microscope in the history of science. The Large Hadron Collider (LHC), now under construction under a land of fields and villages a short drive from Geneva, will peer into the physics of the shortest distances (down to the nanometer) and the highest energies ever explored. For ten years or more, particle physicists have been eagerly awaiting the opportunity to enter this realm, sometimes called the TeV domain because of the energy ranges involved: one billion electron volts, or one tera electron volt (TeV). Significant new physics is expected to appear at these energies, such as the elusive Higgs particle (which is said to be responsible for giving mass to other particles) and the particle that makes up dark matter, which is what makes up most of the matter in the universe.

This Nephilim machine, which has been under construction for nine years, is designed (without the evil eye) to start producing its particle beams at the end of 2008. According to the plan, the operational process will begin with one beam, continue with two beams and reach colliding beams; from low energies to the TeV range; from weaker test intensities to stronger intensities suitable for generating a useful amount of data, but more difficult to control. Each step along the way will raise challenges for the more than 5,000 scientists, engineers and students collaborating on this massive effort. When I visited the project in the fall of 2007 to see with my own eyes the preparations for the investigation of the high energy limit, I found that everyone I spoke to expressed confidence in the success of the project, despite the schedule being repeatedly delayed. The particle physicist community is eagerly awaiting the first results of the LHC. Many will find an echo of their feelings in the words of Frank Wilchek from the Massachusetts Institute of Technology (MIT), who describes the chances of the LHC to bring in its wings a "golden age of physics".

A machine of records

In order to break into this new territory, the TeV range, the LHC's baseline data must exceed those of all previous accelerators in almost every respect. For starters, it is necessary to produce proton beams at much higher energies than ever before. The LHC has almost 7,000 magnets, cooled in liquid helium to temperatures below two degrees Kelvin so that they become superconductors. These magnets will guide and focus two beams of protons moving at a speed close to the speed of light by only a millionth of a percent. Each proton will have an energy of about TeV7 7,000 times more than the energy inherent in the mass of a proton at rest, calculated courtesy of Einstein's equation E = mc2. This energy is about seven times higher than that provided by today's undisputed accelerator record, the twatron at the US Fermi National Accelerator Laboratory in Batavia, Illinois. Equally important, the machine is designed to produce beams whose power, or brightness, is 40 times greater than that of the Twatron. When the accelerator will be fully charged and its energy will be maximum, all the particles rotating inside it will carry energy roughly equivalent to the kinetic energy of about 900 cars traveling at a speed of 100 km/h, or enough energy to heat water for almost 2,000 liters of coffee.

The protons will move in a structure of almost 3,000 bunches, scattered at intervals around the 27 kilometer circumference of the accelerator. Each bundle will contain up to 100 billion protons and will be the size of a needle, only a few centimeters long and compressed to a diameter of 16 microns (about the thinnest human hair) at the collision points. At four locations around the ring, these needles will pass each other, producing more than 600 million particle collisions every second. The collisions, or events, if we use the terminology used by the physicists, will actually occur between the particles that make up the protons - quarks and gluons. The most destructive crashes will release about one-seventh of the available energy in the mother's protons, about 2 TeV. (This is why the capabilities of the tevatron fall roughly five times short of what is needed to study TeV physics, even though its protons and antiprotons have an energy of one teraelectronvolt.)

Four huge detectors - the largest of which can fill up to half of the Notre Dame Cathedral in Paris, and the heaviest contains more steel than the Eiffel Tower - will measure and track the thousands of particles that will be emitted from each of the collisions taking place in their center. Despite the enormous size of the detectors, some of their components must be located with an accuracy of 50 microns.

The data flowing in the nearly 100 million channels coming out of the two largest detectors could fill 100,000 disks per second, enough to create a stack that reaches the moon in six months. Instead of trying to record everything, the experimenters will therefore have what are called "trigger systems" and data collection, which act like huge spam filters, immediately discarding almost all information and sending only the data from the 100 most promising events every second to the central computer system of LHC at CERN, the European Laboratory for Particle Physics and home of the accelerator, for archiving and further analysis.

A farm of several thousand computers at CERN will turn the filtered raw information into more compressed data sets, organized and ready for physicists to scan. The researchers will analyze the data in a lattice network consisting of tens of thousands of personal computers in institutions all over the world, all connected to a core of twelve large centers on three continents, connected to CERN via dedicated optical cables.

A journey of a thousand steps

In the coming months, all eyes will be focused on the accelerator. The final connections between adjacent magnets in the ring were made at the beginning of November 2007 and when the writing of the article was completed in mid-December 2007, one of the eight sections was cooled almost to the freezing temperature necessary for its operation, and they began to cool the other. One cut had already been cooled, run and then returned to room temperature earlier in 2007. After the operation of the cuts is tested, at first individually and then as an integrated system, a proton beam will be injected into one of the pair of tubes that carry it around the 27 kilometers of the machine.

A series of smaller accelerators feeding the beam to the LHC's main ring, which has already been tested, brought protons with an energy of 0.45 TeV, the "threshold" through which they would be injected into the LHC's core. The first injection of the beam will be a critical step, and LHC scientists will start with a low-power beam to minimize the danger of damaging the LHC's hardware. Only after carefully evaluating how these "experimental" beams react inside the accelerator and introducing subtle corrections to the magnetic fields that steer them will they continue on to higher intensities. In the first run at the planned energy of 7 TeV, only one bunch of protons will spin in each direction instead of nearly 3,000, the number they aim to eventually reach.

There is no doubt that problems will arise as the accelerator progresses in measured steps towards full operation. The big question is how long it will take engineers and scientists to overcome each and every challenge. If a cut needs to be returned to room temperature for repairs, months will be added to the process.

The four experiments - ATLAS, ALICE, CMS and LHCb, are also facing a long process of completion, and they must be shut down before the beam starts operating. Some incredibly fragile units are still in the process of being installed, such as the detector known as the "vortex finder" (vortex detector) installed at LHCb in mid-November 2007. Many years ago I studied for an advanced degree in physics, specializing in the theoretical rather than the experimental side, so during my visits I was deeply impressed by The solid streams of thousands of cables required to carry all the information channels from the detectors - each cable is labeled as its own and is adjusted with meticulous port work to the appropriate socket and tested by students.

Although the beams will collide in just months, some of the students and postdocs have already got their hands on real data, courtesy of the cosmic rays seeping down through the Franco-Swiss rocks and passing through their detectors at random. Observing the response of the detectors to these trespassers provides an important situational assessment showing that everything is working together as required - from the power supplies and detector components to the circuits of the output devices and the data collection software that integrates the millions of discrete signals into a coherent description of an "event".

And now they are all together

And when everything does work in coordination, including the colliding beams at the center of each detector, the detectors and the data processing systems will face a tremendous task. At the designed luminosity, up to 20 events will occur each time the needle-like bunches of protons pass through each other, which happens every 25 nanoseconds on average (sometimes there are longer intervals). Every time the beams pass through each other, particles created as a result of the collisions will be scattered and pass through the detector. When the beams pass through each other the next time, the particles from the previous encounter will still continue to move through the outer layers of the detector. Different components in each of the detector layers will therefore react when a particle of the appropriate type passes through them. The millions of data channels flowing from the detector will produce about a megabyte of data from each event: a petabyte, that is, a billion megabytes every two seconds.

The filtering systems that will reduce this deluge of data to manageable sizes have several levels. The first level receives and analyzes data coming from only a subset of all the detector components, from which it can glean promising events based on isolated factors, such as whether an energetic muon flying at a large angle from the beam axis has been detected. Such filtering, at level 1, will be managed by hundreds of dedicated computer boards whose logic is baked into the hardware. The panels will select 10,000 sets of data per second for a more rigorous analysis to be conducted in the next step, with a higher level of filtering.

The high-level filtering systems, on the other hand, will receive data from all of the detector's millions of channels. Their software will run in the computer farm, and thanks to the time interval of 10 microseconds on average between each group approved by the level 1 filtering systems, they will have enough time to "reconstruct" each and every event. In other words, they will draw traces leading to common starting points and thus build a coordinated data system: the energy, momentum, trajectory and other data of the particles created in each event.

The high-level filtering passes about 100 events per second into the heart of the LHC's computing array. A lattice network combines the processing power of a network of computer centers and makes it accessible to users who wish to access it from their home institutions [see "Limitless Computing", by Ian Foster, Scientific American Israel, August-September 2003].

The LHC lattice is organized in tiers. Tier 0 is located at CERN and consists mostly of thousands of commercial computer processors, both boxes that resemble a personal computer and, more recently, "blade" systems that are the size of a pizza box but in stylish black, stored in rows of shelves. Even now computers are still being purchased and added to the system. Those responsible for the system, similar to the home user, are looking for the most cost-effective winning combination, which is never silent, and therefore avoid buying the newest and most powerful models and prefer more economical options.

The data passing to stack 0 by the four data collection systems of the LHC experiments will be recorded on magnetic tape. This may sound old-fashioned and primitive in this age of DVD-RAM discs and flash drives, but Francois Gray of CERN's computing center says it turned out to be the most secure and cost-effective approach.

Tier 0 will distribute the data to 12 tier 1 centers, located at CERN itself and 11 other important institutions around the world, including Permilab and the US National Laboratory in Brookhaven, as well as centers in Europe, Asia and Canada. This way the unprocessed information will be kept in two copies, one at CERN and the other scattered around the world. Each of the Tier 1 centers will also hold a complete set of data in a centralized structure, allowing scientists to conduct many physical analyses.

The full LHC computing array also has Tier 2 centers, which are smaller computing centers at universities and research institutes. The computers in these centers will provide distributed processing power to the entire grid for data analysis.

obstacle course

Given all the innovative technologies that are in the midst of getting ready for operation, it's no surprise that the LHC has encountered some hiccups – and some more serious bumps – along the way. One of the magnets of the type designed to focus the proton beams just before the point of collision (the so-called quadrupole magnet) suffered a "serious failure" in March 2007 while testing its ability to withstand the strong forces that might appear if, for example, the magnet's coils lose their superconducting property during The movement of the beam (a malfunction known as shutdown, or collapse). Some of the magnet struts collapsed under the pressure of the test, there was a loud bang as if something exploded and helium gas was released. (By the way, when workers or visiting journalists enter the tunnel, they carry a small emergency breathing apparatus, as a precaution.)

These magnets are built in groups of three, first to compress the beam side to side, then vertically and finally side to side again. This series of actions brings the beam into sharp focus. The LHC uses 24 such magnets, one trio on each side of the four interaction points. At first, the scientists did not know if it would be necessary to remove all 24 magnets from the machine and bring them to the ground for renovation, a time-consuming process that could add weeks to the schedule. The problem was a flaw in the design: the magnet designers (researchers at Paralab) did not take into account all the types of forces that the magnets have to withstand. The researchers from CERN and Permilab worked feverishly, identified the problem and thought of a strategy to repair the undamaged magnets without removing them from the accelerator tunnel. (The trio that was damaged in the test was brought to the surface for repairs.)

CERN Director General Robert Eimer announced in June 2007 that due to the failure of the magnet, which was accompanied by a collection of minor problems, he was forced to postpone the planned start-up date of the accelerator from November 2007 to spring 2008. The beam energy must gain momentum faster, to try to meet the schedule and " to do physics" in July 2008.

Although several of the detector workers have hinted to me that they would be happy to have a little more time, there is cause for concern with the repeatedly delayed opening date, because the longer it takes for the LHC to produce decent amounts of data, the more opportunities the Tevatron – which is still operating – will have to steal its lead. the glory The Tevatron could find evidence for the existence of a Higgs boson or something equally exciting, if nature played a cruel trick and gave it enough mass to cause it to appear right now in the growing mountain of Permilab data.

The delays can also cause personal distress due to the price some of the scientists and students pay when their career progress is stalled while they wait for the data.

Another, potentially serious, problem arose in September 2007, when engineers discovered that sliding copper fingers inside the beam tubes, called removable modules, crumpled after a section of the accelerator was cooled to the freezing temperatures needed for operation and then warmed back to room temperature.

Initially the extent of the problem was not clear. In each section where the test cooling was conducted, there are 366 removable modules, and if it was necessary to open each and every one of them to check and possibly repair, it would be terrible and terrible. Instead, the team dealing with the problem managed a trick: they inserted a ball slightly smaller than a ping-pong ball into the beam tube - small enough to fit into the tube and be pushed inside with compressed air and large enough to be stopped by a twisted module. The ball transmitted radio waves at a frequency of 40 MHz - the same frequency at which the proton bundles will travel along the tube when the accelerator is operating at full capacity - and thus it was possible to track its progress with the help of the beam sensors installed at 50 meter intervals. To everyone's relief, this exercise showed that only six of the sector's modules were malfunctioning, so opening and repairing them could be tackled.

When the final connection between the accelerator magnets was made in November 2007, the connection that completed the circuit and paved the way for the cooling of all sectors to begin, project manager Lynn Evans said: "For such a complex machine, things are going incredibly smoothly, and we all look forward to starting doing physics with the LHC in the summer the nearest.”

Editor's note - is a revolution in physics expected?

"The Next Revolutions in Particle Physics" by Chris Quigg and "The Machine of Discovery" by Graham P. Collins are the two articles we are publishing in this issue ahead of the revolutionary event in the history of particle physics: the activation of the Large Hadron Collider (LHC) whose construction is being completed at CERN, the European Center for Nuclear Physics in Geneva. It seems that no scientific event in recent years has aroused as much interest, anticipation and excitement as the upcoming activation of the LHC. The expectations are skyrocketing, and they are not only the lot of physicists, they are also of everyone who is interested in the development of science and wants to take part in the persistent and constant journey that may bring us to a better understanding of the world in which we live and the worlds around us.

Thousands of physicists and engineers from all over the world participate in the design and construction of the large accelerator. The LHC has two main tasks: one, building a subatomic particle accelerator (hadrons) to a speed close to the speed of light with an energy of about 7 teraelectron volts (TeV7). The collision of the particles at this speed will have a double energy of TeV 14, or 14 million million electron volts, an energy equivalent to a mass 14,000 times greater than the mass of the proton. This is therefore an energy range that has never been tried. The researchers predict that a collision of protons at such energies will produce a "rain" of particles, some of which are known, which are also obtained at lower collision energies, and some of which have not yet been observed and which should not be "missed". Discoveries of the unknown particles should provide answers to questions that will determine the fate of tomorrow's physics, such as the puzzle of the origin of mass. Hence the great importance of the second task: designing and building detectors that can discover these particles and measure their properties. One of the facilities, ATLAS, is the largest array of detectors of its kind, and its dimensions are unprecedented: it is about 25 meters in diameter, about 46 meters long and weighs about 7,000 tons. The inherent combination of technology, engineering and science in the development of the LHC actually reflects the interdependence of theoretical science and technological innovations on each other. Thousands of physicists and engineers from many countries, including Israel, participated in its planning and the planning of the experiments to be carried out.

This is an international enterprise in the full sense of the word and the Israeli scientists have an important part in planning the experiments that will be carried out at the LHC and in their analysis. Professor Giura Mickenberg from the Weizmann Institute of Science heads the Israeli project, and as part of it, a huge neutron detector was built (at the Weizmann Institute), designed to determine when a collision has a chance to create the "interesting" particles, and it must be stored in the database. Other partners in the project are Dr. Lauren Levinson, Dr. Daniel Leloche and professors Elam Gross (responsible for the statistical analysis of the data in the Atlas detector) and Ehud Duchovni from the Weizmann Institute, Shlomit Terem and Yoram Rosen from the Technion and Erez Etzion from Tel Aviv University. The Israeli scientists are participating in the planning of the experiments that will mainly focus on the discovery of the Higgs boson (which is responsible for the mechanism of imparting mass and is the only particle that has not yet been discovered within the standard model), as well as in physics beyond the standard model: supersymmetric particles and black holes.

Indeed, expectations are high, will the LHC make it possible to finally confirm the standard model and discover the "missing" particles that the model predicts, such as Higgs bosons? But the activation of the "discovery machine", as Graham Collins calls the LHC, may also provide answers to basic questions about the universe, such as what the dark matter is made of, which makes up about 96% of the universe, are there new symmetries of nature that link matter, energy, space and time? Why nature prefers matter rather than antimatter, and how matter evolved in the first moments of the universe. These are just some of the intriguing questions that the LHC may answer, questions that are formulated and the attempts to solve them form the basis for the constant development of science.