Large Hadron Collider

from Wikipedia, the free encyclopedia
Large Hadron Collider (LHC) Arrangement of the various accelerators and detectors of the LHC
Arrangement of the various accelerators and detectors of the LHC
Detectors
 Partly built up:
Pre-accelerator

The Large Hadron Collider ( LHC, German name Großer Hadronen -Speicherring ) is a particle accelerator at the European Nuclear Research Center CERN near Geneva . In terms of energy and frequency of particle collisions, the LHC is the most powerful particle accelerator in the world. Over 10,000 scientists and technicians from over 100 countries were involved in the planning and construction; hundreds of university chairs and research institutes cooperated. The key component is a synchrotron in a 26.7 km long underground circular tunnel in which protons or lead - cores in opposite directions to nearly the speed of light are accelerated and made to collide. The experiments at the LHC are therefore colliding beam experiments .

Research objectives at the LHC are the generation and precise investigation of known and still unknown elementary particles and states of matter. The starting point is the review of the current Standard Model of particle physics . Special attention is therefore paid to the Higgs boson , the last particle of the Standard Model that was not yet experimentally proven at the start of operation. In addition, the LHC is intended to search for physics beyond the Standard Model in order to possibly find answers to open questions. Four large and two smaller detectors register the traces of the particles created during the collisions. The large number of collisions per second that can be achieved (high luminosity ) results in enormous amounts of data. These are pre-sorted with the help of a sophisticated IT infrastructure. Only a small part of the data is forwarded to the participating institutes for analysis by means of a specially constructed, global computer network.

Starting in 2010, a previously unattainable energy range was opened up in the experiments. An essential result of the previous experiments (as of March 2019) is an extraordinarily good confirmation of the standard model. Several new hadrons were found, a quark-gluon plasma could be generated and the first time was at the B s 0 - Meson the CP violation in its decay into kaons and pions observed and be extremely rare decay into two muons . A CP violation was also found in the D 0 meson. The experimental proof of the Higgs boson is regarded as the greatest success to date. This led to the award of the Nobel Prize in Physics 2013 to François Englert and Peter Higgs .

history

Location and size of the LHC with the smaller ring of the PLC
CERN's accelerator complex
List of the current
particle accelerators at CERN
Linac 2 Accelerates protons
Linac 3 Accelerates ions
Linac 4 Accelerates negative hydrogen ions
AD Brakes antiprotons
LHC Collides protons or heavy ions
LEIR Accelerates lead ions
PSB Accelerates protons or ions
PS Mainly accelerates protons
PLC Accelerates protons, among other things

The direct forerunner of the LHC was the Large Electron-Positron Collider (LEP) , which operated until 2000 . The ring tunnel, in which the LHC is located today, was built for him in the 1980s. The possibility of continuing to use the tunnel, which had already been taken into account in the conception of the LEP, was decisive for the location of the LHC. The detailed planning for the LHC began while the LEP was still under construction. In the LEP, electrons and positrons , which belong to the group of leptons , were brought to collision. In the LHC, on the other hand, protons or atomic nuclei, which belong to the hadrons , collide . Hence the name Large Hadron Collider comes from .

In a ten-year planning and preparation phase it was clarified which specific questions should be investigated with the LHC and whether an accelerator based on superconductivity is technically feasible at all. On December 16, 1994, the CERN Council finally gave the go-ahead for construction. Initially, the energy with which the protons collide should be 10 T eV and later increased to 14 TeV. After India and Canada had also declared non-member states of CERN to participate in the financing and development of the LHC and thus in its subsequent use, it was decided in December 1996 to forego the intermediate step of 10 TeV and to tackle 14 TeV directly to take. Cooperation agreements with other countries followed. In 1997 the Italian Istituto Nazionale di Fisica Nucleare delivered the first prototype of the dipole magnets, and the first successful test took place the following year. In that year, the official Swiss and French authorities also gave their approval for the construction work required for the new caverns of the largest detectors. The tunnel expansion began at the end of 2000 and was completed in 2003. Within a year, 40,000 tons of material were removed from the tunnel.

In the years 1998 to 2008, tests were continuously carried out on individual components and orders for industrial production were subsequently awarded. At the same time, the detector systems were put together and the connection to existing accelerators such as the SPS established. The components came from all over the world, for example the wire chambers for the ATLAS muon detector were manufactured in more than half a dozen countries. The brass supplied by Russia for the CMS detector comes from an armaments conversion agreement . In 2006 the production of all superconducting main magnets was completed, in February 2008 the last components of the ATLAS were at their destination.

The preparatory work on data processing led to the start of the European DataGrid Project in 2001 . Two years later, a record was set for data transfer via the Internet. Within an hour, a data volume of one terabyte was sent from CERN to California. After two more years, the group of participants in the LHC Computing Grid had grown to over 100 data centers in over 30 countries.

The official start of accelerator operation at the LHC was September 10, 2008, when a proton packet circled the entire ring for the first time. However, a technical defect led to a year-long standstill after just nine days: the weld seam of a superconducting connection could not withstand the load and destroyed a helium tank in the cooling system, the explosion of which in turn displaced one of the 30-tonne magnets by half a meter. During this “quenching” six tons of liquid helium were lost, the affected magnets heated up very quickly by about 100 K. After restarting on November 20, 2009, the first proton-proton collisions took place in the particle detectors three days later , another six days later the proton beam reached 1.05 TeV, the energy of the Tevatron , the most powerful particle accelerator to date. During the winter of 2009/10, improvements were made to the particle accelerator that allowed 3.5 TeV per beam, i.e. a center- of- mass energy of 7 TeV. On March 30, 2010, collisions with this energy took place for the first time. All those responsible showed great satisfaction, including CERN General Director Rolf-Dieter Heuer :

“It's a great day to be a particle physicist. A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends. "

“Today is a big day for particle physicists. Many people have waited a long time for this moment, but now their patience and commitment are starting to pay off. "

- Rolf Heuer, General Director of CERN

For the following year and a half, interrupted only by a scheduled maintenance break in winter 2010/11, the detectors were able to investigate proton-proton collisions at 7 TeV center of mass energy. The originally planned number of collisions was exceeded thanks to continuously improved beam focusing. Operation in proton mode was interrupted on October 30, 2011, in order to insert a short phase with collisions of lead nuclei until the next maintenance shutdown in winter 2011/12.

Originally, after around two years of operation, the LHC was supposed to go into a longer conversion phase of 15 to 18 months at the end of 2011 in order to exchange the existing connections between the magnets and to prepare the accelerator for 7 TeV (main energy 14 TeV). In January 2011, however, it was decided to extend the runtime by one year before the upgrade phase until the end of 2012. This date was later postponed to the beginning of 2013. The reason for the decision was the excellent performance of the accelerator in the first year of operation, so that signs of novel particles were to be expected after three years of operation, which was confirmed with the discovery of a new elementary particle, the Higgs boson .

From April 5, 2012 to December 17, 2012, proton-proton collisions were examined again. The focus energy could be increased to 8 TeV. This was followed by further collisions of lead nuclei and additional collisions between lead nuclei and protons.

From February 2013 to April 2015, the LHC was in the first long conversion phase, during which the accelerator was prepared for a collision energy of 13 TeV. Some of the superconducting magnets were replaced and more than 10,000 electrical connections and the magnets were better protected against possible faults. The higher collision energy was first reached on May 20, 2015. The proton packets now contain fewer protons than in 2012, but follow one another at half the distance. Until the beginning of November 2015, protons were collided with lead nuclei again at the end of November and beginning of December, also with a higher energy than before. In proton-proton collisions in 2016, the design luminosity and thus the planned collision rate were achieved for the first time. In the last four weeks of operation in 2016, protons collided with lead nuclei.

The LHC was also repaired for 17 weeks in winter 2016/17. One of the superconducting coils was replaced (for which the helium used for cooling had to be drained off), and the Super Proton Synchrotron pre-accelerator was also modified. One of the goals for the new operating year was a further increase in luminosity. From May to November 2017, data was collected again. the collision rate could be increased to double the design value. The last measurement campaign ran from April 28, 2018, again with lead cores since the beginning of November, before the accelerator was switched off on December 10, 2018 until spring 2021 for modifications to further increase the luminosity.

Structure, operation and functionality

Tunnel of the LHC before installing the magnets
LHC tunnel in finished condition
Prototype of a dipole magnet

Accelerator ring

The LHC was built in the existing ring tunnel of the European nuclear research facility CERN, in which the Large Electron-Positron Collider was previously installed until it was decommissioned in 2000. In addition to the tunnel, two detector chambers of the LEP could continue to be used, only the chambers for the ATLAS and CMS detectors had to be rebuilt. The tunnel has a diameter of about 3.80 meters and a circumference of 26.659 kilometers and is located at a depth of 50 to 175 meters with a slight incline of 1.4%. The accelerator ring is not exactly circular, but consists of eight arcs and eight straight sections. The largest experimental facilities and the pre-accelerators are located in Meyrin in French-speaking Switzerland , the control station is in France. Large parts of the accelerator rings and some underground experimental sites are located on French territory.

The LHC tunnel contains two adjacent beamlines in which two hadron beams circulate in opposite directions. For reasons of space, both radiant tubes had to be accommodated in a common tube with the magnets and the cooling devices. To enable the particles to collide, the beam pipes cross at four points on the ring. With the predecessor, the LEP, this happened in eight places. There is an ultra-high vacuum in the jet pipes so that an accelerated particle collides with a gas molecule in the remaining air as rarely as possible. To this end, 178 turbo-molecular pumps and 780 ion getter pumps are installed along the ring . The residual pressure of the vacuum is 10 −14 to 10 −13  bar , which roughly corresponds to the measurable atmospheric pressure on the moon. The magnets and the helium supply lines are also surrounded by a vacuum for insulation in order to keep the heat flow as small as possible. The insulating vacuum of the magnets has a volume of around 9,000 cubic meters.

The limiting factor for the achievable energy is the field strength of the magnets that cause the deflection. In order to have to bring about less pronounced changes in direction, less straight sections and instead longer, less curved arc sections in the ring would have been better. For cost reasons, however, the tunnel was not converted. In the LHC, the high-energy particles are held on their path by 1232 superconducting dipole magnets made of niobium and titanium , which generate a magnetic flux density of up to 8.33  Tesla using currents of 11,850  amperes . The strength of the magnetic field in the dipoles and the frequency of the electric field in the accelerating cavity resonators are constantly adapted to the increasing energy of the particles. To keep the particle beams focused and to increase the collision rate when the two beams cross, 392 superconducting quadrupole magnets are also used. The magnets are cooled down in two steps to their operating temperature of 1.9  Kelvin (−271.25 ° C), close to absolute zero . In the first step, they are pre-cooled to 80 K (−193.2 ° C) with 10,080 tons of liquid nitrogen , and in the second step they are brought to their final temperature using 100 tons of liquid helium. To keep the magnets at their operating temperature, they are constantly surrounded by around 60 tons of liquid helium in a superfluid state. In this state, helium has particularly good thermal conductivity. A total of 140 tons of helium are stored at the LHC for cooling purposes. The LHC is therefore the largest cryostat that has been built to date (as of 2018).

When operating the accelerator facility, in addition to the tidal forces , which change the circumference of the ring by around 1 mm, the water level of Lake Geneva and other external disturbances must be taken into account.

Proton mode

For the proton mode in the LHC, a center of mass energy of 14  TeV was planned; this corresponds to 99.9999991% of the speed of light. So far, 13 TeV have been achieved. In order to achieve such energies, the protons are accelerated one after the other through a series of systems. First, the protons are brought to an energy of 50 MeV in a linear accelerator. Then they are accelerated to 450 GeV by means of the rings of the Proton Synchrotron Booster , the Proton Synchrotron and the Super Proton Synchrotron, which existed before the construction of the LHC , until they are finally threaded into the main ring of the LHC and there reach their desired energy. The acceleration of the protons takes place according to the synchrotron principle by means of a high-frequency alternating electric field and takes about 20 minutes.

The protons are bundled into packets in the beam tubes. The length of these packages is a few centimeters, the diameter about 1 mm. In the vicinity of the collision zone, the beam is compressed to a width of about 16 µm. Each packet contains over 100 billion protons. In full operation, the LHC should be filled with around 2800 packets that circulate at a frequency of 11 kHz, i.e. 11,000 times per second. In normal operation, a proton packet remains in the beam tube for up to a day.

When the beams crossed, two packets of protons penetrated each other every 50 nanoseconds in the collision zone until the retrofit between 2013 and 2014. Since 2015 the interval between the collisions is only 25 nanoseconds. In normal operation, around 20 to 40 protons from both packets actually collide, which is up to 800 million collisions per second. The design luminosity of 10 34  cm −2 s −1 was first achieved in June 2016, and the collision rate was doubled in the course of 2017.

Lead mode

To produce a beam of lead atomic nuclei, isotopically pure lead ( 208 Pb) is first heated in a microoven and the resulting lead vapor is ionized in an electron-cyclotron-resonance ion source (ECRIS). The most frequently occurring 208 Pb 29+ ions are selected from the different charge states generated and accelerated to 4.2 MeV per nucleon . A carbon foil then serves as a “stripper”, which means that the lead ions lose further electrons when they pass through the foil. Most of them lose 25 electrons and are now in the form of Pb 54+ ions. These lead ions are accelerated in the Low Energy Ion Ring (LEIR) to 72 MeV per nucleon, then in the Proton Synchrotron (PS) to 5.9 GeV per nucleon. When flying through a second stripper film, the lead nuclei lose all of the electrons that have remained; it is now completely ionized Pb 82+ . Finally, these nuclei are accelerated to 117 GeV per nucleon in the Super Proton Synchrotron (SPS) and fed into the LHC, which brings them to 2.76 TeV per nucleon. Overall, the collision of lead nuclei will - each with 208 nucleons - thus at a center of mass energy of 1148 TeV (0.2  mJ ) instead, which is about the energy of motion of a fly in flight.

LHC versus LEP and Tevatron

In the Tevatron , the other large ring accelerator with beams running in opposite directions, particles with opposite charges circulated in opposite directions in the two beam pipes. The LHC predecessor LEP worked according to the same principle . All particles move on their orbit through an equally directed magnetic field. Due to the relativistic Lorentz force , they experience the necessary inward deflection and are thus kept on their annular path. In the LHC, however, the opposing protons or lead ions carry the same charge. The magnetic field in the two beam pipes must therefore point in opposite directions in order to deflect all particles inwards. According to the concept of John Blewett (1971), this is achieved by an approximately ring-shaped magnetic field, which penetrates one beam pipe from top to bottom and the other from bottom to top.

While in the LEP electrons and positrons , i.e. the antiparticles to each other, were brought to collision, at the LHC, depending on the operating mode, protons or lead nuclei are accelerated and brought to collision. Due to the much larger mass of the hadrons, they lose less energy through synchrotron radiation and can thus achieve a much greater energy. The higher center of gravity energy compared to the previous experiments enables research into new energy areas. By opting for protons instead of antiprotons in the second beam, such as at the Tevatron, a higher luminosity could also be achieved. The high particle density at the points of interaction leads to the desired high event rates in the particle detectors and enables larger amounts of data to be collected in a shorter time.

Safety measures

The total energy of the rays circulating in the tunnels is up to 500 megajoules in proton  mode , an increase to 600 MJ is planned. This corresponds to the kinetic energy of two ICE trains traveling at 150 km / h and would be enough to melt around half a ton of copper. In the event of an uncontrolled loss of the beam, the accelerator facility would be severely damaged. Lyn Evans , the LHC project manager from 1994, speaks of an amount of energy as contained in 80 kg of TNT . The system is therefore designed in such a way that, within three revolutions, i.e. less than 300  microseconds , an unstable beam is registered and directed into a special branch of the tunnel by special magnets. There is a special jet stopper, which is made up of a number of graphite plates of different densities and can intercept the jet. The energy stored in the dipole magnets is significantly higher at 11 GJ. If necessary, the current in the magnet coils is passed through connected resistors and the energy is converted into heat. The damage in the accident that occurred in 2008 when the accelerator started operating (see the history section ) was caused by this energy stored in the magnets.

Both the particle beam on its curved path and the collisions inevitably generate radiation . It is not possible to stay in the tunnel and the detectors' caverns during beam times. Maintenance work is accompanied by active and passive radiation protection measures. The soil above the tunnel effectively holds back the scattered radiation during operation and the residual radioactivity. The air from the accelerator tunnel is filtered with the aim of keeping the radioactivity released for the residents below the value of 10  μSv per year.

Detectors

Simulated detection of particles after proton collision in the CMS detector

The collision of the protons by crossing the two proton beams takes place in four underground chambers along the accelerator ring. The four large particle detectors ATLAS , CMS , LHCb and ALICE are located in the chambers . The TOTEM and LHCf detectors are much smaller and are located in the chambers of the CMS and ATLAS experiments. They only examine particles that brush against each other during the collisions instead of colliding with one another. In addition, other special experiments with associated detector units are planned, such as MoEDAL for the search for magnetic monopoles and relics of microscopic black holes and supersymmetrical particles . The FASER detector searches for long-lived hypothetical particles, for example dark photons , and measures neutrino interactions at high energies.

The aim of the four large detector systems can be summarized as follows:

detector description
ATLAS Search for the Higgs boson, supersymmetry and possible substructures of leptons and quarks , study of the collisions of heavy ions. Around 2,700 researchers from over 200 institutes worldwide are taking part in the ATLAS experiment.
CMS Search for the Higgs boson, supersymmetry and possible substructures of leptons and quarks , study of the collisions of heavy ions. The CMS group comprises around 3500 people from 200 scientific institutes.
ALICE Investigation of the extremely dense and high-energy quark-gluon plasma , the state of matter immediately after the Big Bang . Over 1000 employees.
LHCb Among other things, specialized in the investigation of decays of hadrons that contain a bottom or charm quark , precision measurements of CP violation or rare decays as sensitive tests of the standard model . About 800 employees.

The complex internal structure of the protons means that collisions often produce many different particles. This leads to high demands on the detector systems, which should record these particles and their properties as completely as possible. Since the resulting particles are very diverse in their properties, different detector components are required that are specifically suitable for certain questions. The only exception are the neutrinos that are produced and cannot be detected directly. The determination of the original location of the respective collision products is of crucial importance: This does not have to coincide with the collision point of the protons, since some of the short-lived products decay during the flight through the detector.

The basic structure of the detectors consists of a series of different detector parts of different types and operating principles, which, according to the onion skin principle, surround the collision point as completely as possible. Strong magnetic fields from superconducting magnets cause the charged particles to be deflected. The specific charge and momentum of charged particles can be determined from the curvature of the path. The innermost layer is the so-called track detector, a semiconductor detector with fine spatial resolution. It is surrounded by an electromagnetic and a hadronic calorimeter and a spectrometer for muons.

The ATLAS detector with a length of 45 m and a diameter of 22 m

The lead nuclei are mainly brought to collision in the ALICE detector, which was specially built to measure these collisions. To a lesser extent, ATLAS and CMS are also investigating such heavy ion collisions. In addition, lead nuclei can be made to collide with protons, which is investigated by all four large detectors.

Data analysis

The amount of data that is generated during operation through recorded detector signals or computer simulations is estimated at 30  petabytes per year. It would be considerably greater if sophisticated hardware and software triggers did not discard a large part of the measurement signals before processing or permanent storage. The amount of data from the CMS detector alone is comparable to that of a 70 megapixel camera, which takes 40 million images per second. Without a trigger, such data volumes would not be manageable with current technology. In the first trigger stage on the ATLAS detector, around 75,000 of the data from the 40 million beam crossings per second are selected. Of these, fewer than 1000 pass the second trigger stage, and only these events are fully analyzed. Ultimately, around 200 events per second are stored permanently.

“The flood of data in the detectors will be so enormous during the collisions that it will outstrip the flow of information in all of the world's communication networks combined. There is no data memory that could hold them, which is why the computers sift through the digital tsunami in the first few nanoseconds and sort out 99.9 percent of it, according to criteria that are based on the very theories that the LHC is actually supposed to examine. It cannot be ruled out that the super machine will simply delete the really revolutionary data. "

- Tobias Hürter, Max Rauner : Fascination Cosmos: Planets, Stars, Black Holes (2008)

In order to process this reduced amount of data, the computing power required is still so great that around 170 computer clusters distributed around the world are used. These are connected to a computer network, the LHC Computing Grid .

To simulate the particle trajectories in the accelerator ring, computer owners are involved in the LHC @ Home project, who make the computing power of their private computers available according to the principle of distributed computing .

Power supply

Haupteinspeisepunkt for the supply of the CERN electrical power is the 400 kV - substation Prevessin, which is a short stub with the 400 kV substation Bois-Toillot in conjunction. A further feed is made with 130 kV in the Meyrin station. From these feed points, 66 kV and 18 kV underground cables lead to the larger transformer points, where they are converted to the operating voltage of the terminal equipment (18 kV, 3.3 kV and 400 V). In the event of a power failure, emergency power generators with outputs of 275  kVA and 750 kVA are installed in the experiment stations ; an uninterruptible power supply is guaranteed for particularly sensitive devices .

The storage ring requires an electrical output of 120  MW . Together with the cooling system and the experiments, this results in a power requirement of around 170 MW. Because of the higher electricity costs, the LHC is partially switched off in winter, which then reduces the required output to 35 MW. The maximum annual energy consumption of the LHC is given as 700–800  GWh . For comparison: that is just under 10% of consumption in the canton of Geneva . Thanks to the use of superconducting magnets, the energy consumption of the LHC is lower than that of previous experiments such as the LEP .

costs

The immediate cost of the LHC project, excluding the detectors, is about 3 billion euros. When the construction was approved in 1995, a budget of 2.6 billion Swiss francs (at that time corresponding to 1.6 billion euros) was estimated for the construction of the LHC and the underground halls for the detectors. However, in 2001 additional costs of 480 million Swiss francs (around 300 million euros) were estimated for the accelerator, of which 180 million Swiss francs (120 million euros) went to the superconducting magnets. Further cost increases resulted from technical difficulties in the construction of the underground hall for the Compact Muon Solenoid , partly due to defective parts that had been made available by the partner laboratories Argonne National Laboratory , Fermilab and KEK .

During the first, longer conversion phase (February 2013 to April 2015), work directly on the LHC resulted in costs of around 100 million Swiss francs.

Concerns about commissioning in 2008

In physics beyond the Standard Model, there are theoretical models according to which it is possible that microscopic black holes or strange matter could be generated at the LHC . There are isolated warnings that the LHC could destroy the earth. A group around the biochemist Otto Rössler filed a lawsuit against the commissioning of the LHC at the European Court of Human Rights . The related urgent application was rejected by the court in August 2008. The German Federal Constitutional Court refused to accept a constitutional complaint in February 2010 due to a lack of fundamental significance and a lack of prospect of success. Scientists have repeatedly stated that the LHC and other particle accelerators pose no danger. The main arguments are that, first, the theoretically possible, microscopic black holes would directly annihilate instead of absorbing more and more mass or energy from the environment, as feared, and that, second, natural cosmic rays constantly hit the earth's atmosphere with even higher energy than in the LHC and hits other celestial bodies without causing disaster.

Research objectives and previous results

Basic research

The scientists hope that the experiments at the LHC will answer fundamental questions about the basic forces of nature , the structure of space and time, and the relationship between quantum physics and the theory of relativity . The experiments at the LHC will either confirm the standard model of elementary particle physics or show that corrections to the physical worldview are necessary.

The high collision energy of the LHC means that it is not the protons as a whole, but their individual components, quarks and gluons , that collide independently of one another. In most cases, only a single quark or gluon of each of the two protons is involved in the collision. Although the energy of the protons has a precisely defined value before the collision, the energy and momentum of individual quarks or gluons can vary over a wide range according to the Parton distribution functions , so that the collision energy of the two actually relevant collision partners cannot be precisely determined. Because of this, it is possible, on the one hand, to search for newly generated particles in a large energy range despite the constant energy of the protons, which is why the LHC is referred to as a "discovery machine". On the other hand, the possibility of precisely measuring certain properties of these new particles is restricted. For this reason, a successor to the LHC is already being considered. In the International Linear Collider , as previously in the LEP, electrons and positrons will again be brought to collision. Their energy can be precisely adjusted and, in contrast to protons, they have no - at least no known - substructure.

The Higgs boson

Feynman diagram of vector boson fusion, a prominent process for the generation of Higgs bosons

One of the main tasks of the LHC was the search for the Higgs boson , the last particle of the Standard Model of particle physics that has not yet been finally proven . On July 4, 2012, the research groups at the ATLAS and CMS detectors reported that they had found a new boson; further measurements confirmed that the particle behaved as expected from the Higgs boson. The Higgs boson confirms theories by means of which the masses of the elementary particles are introduced into the Standard Model or into the Glashow-Weinberg-Salam theory of the electroweak interaction . In other words, the Higgs boson confirms the existence of the so-called Higgs field and the underlying Higgs mechanism ; this field is omnipresent in the universe and, through interaction with the elementary particles, leads to their mass .

For the related theory, published in 1964, François Englert and Peter Higgs were awarded the Nobel Prize in Physics in 2013 .

Quark-Gluon Plasma

The operating mode of the collision of lead nuclei, which is less used than proton collisions, serves to briefly generate a very high-energy plasma of quasi-free quarks and gluons, a so-called quark-gluon plasma . In this way, the conditions that prevailed shortly after the Big Bang according to the Big Bang model are simulated and examined at the ALICE detector .

Specification of standard model parameters

Compared to previous accelerators, the LHC has a higher energy range and a higher data rate. It is therefore suitable for determining the properties of elementary particles of the standard model that have already been verified more precisely than was possible in previous experiments. In the previous experiment, Tevatron, the heaviest of the elementary particles known to date, the top quark , could indeed be detected, but its properties could only be determined very imprecisely due to the small number of particles produced and the resulting poor statistics . At the LHC, on the other hand, top quarks are generated in large numbers, which enables a more detailed study of the properties of this particle. This makes it the first so-called “t-factory”. In addition, several new hadrons were found at the LHC , for example the χb (3P) meson or the Ξcc baryon .

Another important field of research is the matter-antimatter asymmetry in the universe, which is not explained by the common big bang theories. Asymmetry is understood to mean the fact that the visible universe is made up exclusively of matter and not of equal parts of matter and antimatter. The study of B physics , with a focus on the LHCb experiment, should help to measure the CKM matrix more precisely. This matrix contains a CP-violating part, which is an important building block for the explanation of the matter-antimatter asymmetry. However, the size of the CP violation predicted by the Standard Model cannot explain the observed asymmetry, so that the measurements are also used to look for deviations from the Standard Model. The LHCb collaboration was able to prove CP violation in B s mesons for the first time.

The tests of the Standard Model also exploring one of the rare decay of B s 0 - meson into two muons , which was first observed at the LHC. The prediction that about three out of one billion B s 0 mesons decay in this way was confirmed in the LHCb detector and then by CMS. Without this decay, such a measurement result would otherwise only be possible with a probability of less than 0.001%.

Physics beyond the standard model

Process in a supersymmetric model: a gluon g and a down quark transform into their respective super partners. These break down into the lightest super partners , which can be registered indirectly due to the lack of overall impulse.

On the review of the standard model and the precise measurement of its parameters is also intense at the LHC for clues to physics beyond the Standard Model ( English Physics beyond the standard model ) sought. By far the greatest effort is devoted to finding indications of supersymmetry . Since the supersymmetric extension of the standard model is very complex, the LHC mainly tests certain supersymmetric models, such as the minimum supersymmetric standard model (MSSM). Some of the new particles appearing in these models, for example the lightest supersymmetric particle , represent a possible particle-physical explanation for the dark matter postulated in astrophysics . Furthermore, supersymmetry is part of most models that combine the three interactions of the Standard Model - so-called large unified theories . It is also necessary for the super string theory . In expert circles it is assumed that many super partners have a mass in the range of approximately 100 GeV to 1 TeV and can therefore be generated and measured in principle at the LHC. A typical signal for supersymmetry would be the creation of electrically neutral super partners. Although these possible particles of dark matter cannot be registered directly by the detector, they are noticeable during the reconstruction of the entire collision process via special decay signatures with a high lack of momentum . Many of the model variants tested are already considered to be excluded based on the results of the LHC experiments. The most recent searches for supersymmetric particles (status 05/2019) were also unsuccessful.

Another research object within physics beyond the standard model is, due to their small size, previously undiscovered spatial dimensions. These extra dimensions could become noticeable through increased interaction with gravitons , through the detection of small Kaluza particles or through the creation of short-lived microscopic black holes .

future

The LHC is expected to Template: future / in 5 yearsend in 2035 . However, there are various plans up to this point. Up to and including 2018, the main priority was to increase the luminosity, the second major renovation break in 2019 and 2020 should increase this even further. The pre-accelerators are also being improved. In addition, the collision energy should increase to 14 TeV. In addition, the internal detectors of ALICE, CMS and LHCb will be replaced in order to obtain a higher resolution and to reduce radiation damage in the detectors. Recommissioning is planned for spring 2021.

Further improvements are expected from 2024, the exact implementation of which will also depend on the discoveries made up to that point. It is planned to prepare the accelerator and the experiments for an even higher luminosity ( High Luminosity LHC , HL-LHC). To do this, the number of particles in circulation must be increased further. In addition, new quadrupoles are used to better focus the particle beam. In addition, special cavities , so-called crab cavities , are planned, which rotate the elongated particle packages shortly before the point of interaction so that they collide as centrally as possible and thus penetrate each other better.

For the more distant future, there are several ideas how the accelerator can continue to be used. One concept provides for the conversion of the LHC to even higher energies ( High Energy LHC ). For this it would be necessary to increase the field strength of all dipole magnets from the current 8.3  Tesla to 20 Tesla and to use new types of quadrupoles, whereby energies of 16.5 TeV (center of gravity energy 33 TeV) could be achieved. The luminosity would then suffer as a result, since only half as many particle packets could be accelerated. Retrofitting to a Hadron Electron Collider ( LHeC ) would also be possible.

Web links

Commons : Large Hadron Collider  - Album with pictures, videos and audio files
 Wikinews: Large Hadron Collider  - in the news

literature

  • Oliver Sim Brüning (Ed.) U. a .: LHC design report. Volume I: The LHC main ring. CERN, Geneva 2004, ISBN 92-9083-224-0 . On-line. (PDF; 39.7 MB).
  • CERN Communication group: Destination Universe. The incredible journey of a proton in the Large Hadron Collider. CERN, Geneva 2008, ISBN 978-92-9083-316-1 . On-line. (PDF; 155 MB).
  • CERN communication group (translation by Th. Naumann): LHC - a guide. CERN, 2009 (PDF; 26 MB). Retrieved July 30, 2013.

Individual evidence

  1. ↑ LHC - The Great Hadron Storage Ring. (PDF; 1 MB) CERN - European Organization for Nuclear Research, June 2006, accessed on August 3, 2013 .
  2. ^ A b Nobelprize.org: The Nobel Prize in Physics 2013. Accessed October 8, 2013.
  3. ↑ a b c d e f g h i Lyndon Evans, Philip Bryant: LHC Machine . In: Journal of Instrumentation . tape 3 , no. 8 , 2008, p. 1–2 , doi : 10.1088 / 1748-0221 / 3/08 / S08001 .
  4. ^ LHC milestones. DSU - Communication Group, 2008, accessed on July 30, 2013 .
  5. ↑ a b c lhc-facts.ch: History of the LHC. Chronology of the LHC 1980 to 2008. Retrieved September 7, 2013.
  6. ^ Anna Di Ciaccio: The ATLAS Muon Spectrometer. (PDF; 1.3 MB), 7th Intern. Conference on Advanced Technology and Particle Physics, October 2001. Retrieved September 14, 2013.
  7. ↑ Lucas Taylor: Using Russian navy shells. November 23, 2011, accessed September 14, 2013 .
  8. ↑ Ulrich Ellwanger: From the universe to the elementary particles. A first introduction to cosmology and the fundamental interactions . 2nd Edition. Springer, 2011, ISBN 978-3-642-15798-1 , pp. 108 .
  9. ^ Anaïs Schaeffer: Please use the emergency exit. CERN Bulletin, May 6, 2013, accessed July 30, 2013 .
  10. ↑ CERN Press Office: CERN releases analysis of LHC incident. October 16, 2008, accessed January 15, 2016 .
  11. ↑ Particle accelerator triples energy record. Spiegel Online, March 19, 2010, accessed July 30, 2013 .
  12. ↑ CERN Press Office: LHC sets new record - accelerates beam to 3.5 TeV. March 19, 2010, accessed July 30, 2013 .
  13. ↑ CERN Press Office: LHC research program gets underway. March 30, 2010, accessed January 15, 2016 .
  14. ↑ CERN Press Office: LHC proton run for 2011 reaches successful conclusion. October 31, 2011, accessed January 15, 2016 .
  15. ↑ CERN Press Office: CERN announces LHC to run in 2012. January 31, 2011, accessed on January 15, 2016 (English).
  16. ↑ 2013 LHC & Injector Schedule. (PDF; 257 kB) (No longer available online.) July 31, 2012, archived from the original on March 15, 2013 ; accessed on November 25, 2012 (English). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / espace.cern.ch
  17. ↑ CERN Press Office: The first LHC protons run ends with new milestone. December 17, 2012, accessed July 30, 2013 .
  18. ↑ Restart at Cern: The world machine is running again. Spiegel Online, April 5, 2015, accessed April 5, 2015 .
  19. ^ A b First images of collisions at 13 TeV. May 21, 2015, accessed May 21, 2015 .
  20. ↑ a b LHC progresses towards higher intensities. August 24, 2015, accessed September 21, 2015 .
  21. ↑ 2016: an exceptional year for the LHC. December 6, 2016, accessed May 1, 2017 .
  22. ↑ Kick-off for the 2017 LHC physics season. May 23, 2017, accessed May 25, 2017 .
  23. ↑ a b Record luminosity: well done LHC . November 15, 2017. Retrieved December 2, 2017. 
  24. ↑ The 2018 data-taking run at the LHC has begun. April 30, 2018, accessed June 10, 2018 .
  25. ^ Key plans for the next two years of the LHC. December 10, 2018, accessed October 11, 2019 .
  26. ↑ a b c d e CERN communication group: LHC - a guide. CERN 2009 (PDF; 26 MB), accessed on July 30, 2013, p. 20.
  27. ↑ lhc-facts.ch: LHC - vacuum technology. Retrieved September 7, 2013 .
  28. ↑ weltmaschine.de: LHC - numbers and facts. Retrieved July 30, 2013 .
  29. ^ Lyndon Evans, Philip Bryant: LHC Machine . In: Journal of Instrumentation . tape 3 , no. 8 , 2008, p. 88-89 , doi : 10.1088 / 1748-0221 / 3/08 / S08001 .
  30. ↑ K. Barth, V. Benda, S. Claudet, M. Pezzetti, O. Pirotte, B. Vullierme: Upgrade of the Liquid Helium Storage for the Large Hadron Collider. (PDF; 314 kB). 24th International Cryogenic Materials Conference, Fukoaka, Japan 2012 (CERN-ATS-2013-002).
  31. ↑ iter.org: Cryogenics
  32. ^ Philipp Gramlich: The LHC: Large Hadron Collider
  33. ↑ Cryostat Design: Case Studies, Principles and Engineering, Chapter 3
  34. ↑ Ulrich Schnabel: Spook in the ring. Retrieved September 7, 2019 .
  35. ↑ Oliver Sim Brüning a. a. (Ed.): LHC design report. Volume I: The LHC main ring. (PDF; 38.7 MB). CERN, Geneva 2004, p. 21.
  36. ↑ LHC morning meeting: June 27, 2016. ( Memento of the original from June 27, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. P. 14.  @1@ 2Template: Webachiv / IABot / indico.cern.ch
  37. ↑ CERN communication group: LHC - a guide. (PDF; 26 MB). CERN, 2009, accessed July 30, 2013, p. 13.
  38. ↑ Michael Krause: CERN - In the cathedrals of technology: Encounters at CERN . John Wiley & Sons, August 12, 2013, ISBN 978-3-527-67009-3 , pp. 111 ff. (Accessed September 22, 2013).
  39. ↑ L. Coull et al. a .: LHC Magnet Quench Protection System. (PDF; 3 MB) Retrieved September 22, 2013 .
  40. ↑ lhc-facts.ch: Radioactivity. Dangers and Risks of the LHC. Retrieved September 22, 2013.
  41. ↑ FIBER: CERN approves new experiment to look for long-lived, exotic particles. Retrieved January 1, 2020 .
  42. ↑ FASER's new detector expected to catch first collider neutrino. Retrieved January 1, 2020 .
  43. ↑ Computing. CERN, 2016, accessed May 25, 2016 .
  44. ↑ data processing. In: lhc-facts.ch. Adrian Schmitz, accessed August 6, 2013 .
  45. ↑ Tobias Hürter, Max Rauner: A Big Bang on Earth. In: Andreas Sentker (Ed.): Fascination Cosmos: Planets, Stars, Black Holes. Spektrum Akademischer Verlag, 2008, ISBN 978-3-8274-2001-5 .
  46. ↑ Worldwide LHC Computing Grid (WLCG) - Welcome. 2015, accessed on January 15, 2016 (English, the figure given is the sum of the 12 tier 1 and ≈ 140 tier 2 clusters).
  47. ^ CERN EN / EL Group: CERN Electrical Network short description. Retrieved July 30, 2013 .
  48. ↑ lhc-facts.ch: LHC parameters and data. Retrieved July 30, 2013.
  49. ↑ weltderphysik.de: What is the energy consumption of the LHC? Retrieved July 30, 2013.
  50. ↑ Florian Freistetter: The coldest place in the universe ... ScienceBlogs, July 1, 2008, accessed on July 30, 2013.
  51. ↑ Luciano Maiani: LHC Cost Review to Completion . CERN. October 16, 2001. Archived from the original on June 17, 2004. Retrieved June 17, 2004.
  52. ↑ Toni Feder: CERN Grapples with LHC Cost Hike . In: Physics Today . 54, No. 12, December 2001, p. 21. doi : 10.1063 / 1.1445534 . Retrieved on July 30, 2013.  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / physicstoday.org  
  53. ↑ LHC Season 2: facts & figures.
  54. ^ Adrian Kent: A Critical Look at Risk Assessments for Global Catastrophes . In: Risk Analysis . tape 24 , no. 1 , 2004, p. 157–168 , doi : 10.1111 / j.0272-4332.2004.00419.x , arxiv : hep-ph / 0009204 .
  55. ^ Rainer Plaga: On the potential catastrophic risk from metastable quantum-black holes produced at particle colliders. August 10, 2008. arxiv : 0808.1415 .
  56. ↑ Felix Knoke: Fear of the end of the world - Americans complain against particle accelerators. In: Spiegel Online. March 31, 2008, accessed August 23, 2011 .
  57. ↑ Holger Dambeck: court rejects urgent application against super accelerator. In: Spiegel Online. Retrieved August 23, 2011 .
  58. ↑ Federal Constitutional Court : BVerfG rejects measures against super accelerators. 2 BvR 2502/08 of January 18, 2010, accessed on July 31, 2013.
  59. ↑ J.-P. Blaizot et al. a .: Study of potentially dangerous events during heavy-ion collisions at the LHC. (PDF; 176 kB), CERN Theoretical Physics Division, February 28, 2003, accessed on July 31, 2013.
  60. ^ Arnon Dar, Alvaro De Rújula, Ulrich Heinz: Will relativistic heavy-ion colliders destroy our planet? Phys. Lett. B 470, 1999, pp. 142-148. arxiv : hep-ph / 9910471 .
  61. ↑ W. Busza et al. a .: Review of speculative "disaster scenarios" at RHIC. Rev. Mod. Phys. 72, 2000, pp. 1125-1140.
  62. ↑ SB Giddings: Astrophysical implications of hypothetical stable TeV-scale black holes. In: Proceedings of APS / DPF / DPB Summer Study on the Future of Particle Physics. Snowmass, Colorado, 2001, p. P328, arxiv : hep-ph / 0110127 .
  63. ^ Opinion on the assertions of Prof. Rössler. (PDF; 82 kB), Committee for Elementary Particle Physics (KET), July 30, 2008, accessed on July 31, 2013.
  64. ^ J. Ellis , GF Giudice , ML Mangano, I. Tkachev, U. Wiedemann: Review of the Safety of LHC Collisions. In: Journal of Physics G : Nuclear and Particle Physics. Vol. 35, 115004 (2008). arxiv : 0806.3414 .
  65. ↑ G. Weiglein et al. a .: Physics interplay of the LHC and the ILC . In: Physics Reports . tape 426 , no. 2-6 , 2006, pp. 47-358; here pp. 1–10 , doi : 10.1016 / j.physrep.2005.12.003 , arxiv : hep-ph / 0410364 .
  66. ↑ M. Spira, A. Djouadi, D. Graudenz, RM Zerwas: Higgs boson production at the LHC . In: Nuclear Physics B . tape 453 , no. 1-2 , 1995, pp. 17-82 , doi : 10.1016 / 0550-3213 (95) 00379-7 , arxiv : hep-ph / 9504378 .
  67. ↑ CERN Press Office: CERN experiments observe particle consistent with long-sought Higgs boson. July 4, 2012, accessed July 30, 2013 .
  68. ↑ Ker Than: Densest Matter Created in Big-Bang Machine. National Geographic News, May 24, 2012; accessed July 30, 2013.
  69. ^ W. Bernreuther: Top-quark physics at the LHC . In: Journal of Physics G: Nuclear and Particle Physics . tape 35 , no. 8 , 2008, p. 083001 , doi : 10.1088 / 0954-3899 / 35/8/083001 , arxiv : 0805.1333 .
  70. ↑ ATLAS Collaboration: Observation of a new chi_b state in radiative transitions to Upsilon (1S) and Upsilon (2S) at ATLAS . December 21, 2011, arxiv : 1112.5154v1 .
  71. ^ LHCb Collaboration: Observation of excited Lambda b0 baryons . October 27, 2012, arxiv : 1205.3452 .
  72. ^ CMS Collaboration: Observation of a new Xi (b) baryon . June 21, 2012, arxiv : 1204.5955 .
  73. ↑ P. Ball and a .: B Decays at the LHC. CERN, March 25, 2000, arxiv : hep-ph / 0003238v3 , p. 105.
  74. ↑ CERN Press Office: LHCb experiment observes new matter-antimatter difference. April 24, 2013. Retrieved July 21, 2013 .
  75. ↑ CERN Press Office: CERN experiments put Standard Model to stringent test. July 19, 2013. Retrieved July 21, 2013 .
  76. ↑ CMS Collaboration: Measurement of the B s → µµ branching fraction and search for B 0 → µµ with the CMS Experiment . July 21, 2013, arxiv : 1307.5025v1 .
  77. ^ I. Hinchliffe, FE Paige, MD Shapiro, J. Söderqvist, W. Yao: Precision SUSY measurements at CERN LHC . In: Physical Review D . tape 55 , no. 9 , 1997, pp. 5520-5540 , doi : 10.1103 / PhysRevD.55.5520 , arxiv : hep-ph / 9610544 .
  78. ↑ ATLAS Supersymmetry (SUSY) searches . Retrieved September 14, 2013.
  79. ↑ ATLAS surveys new supersymmetry territory - New studies from the ATLAS collaboration search for hypothetical “supersymmetric” particles around uncharted corners (23 May 2019) . Retrieved September 5, 2019.
  80. ↑ Gouranga C Nayak: Graviton and Radion Production at LHC: From pp and PbPb Collisions . In: High Energy Physics - Phenomenology . 2002, arxiv : hep-ph / 0211395 .
  81. ↑ Savas Dimopoulos, Greg Landsberg: Black Holes at the Large Hadron Collider . In: Physical Review Letters . tape 87 , no. 16 , 2001, p. 161602 , doi : 10.1103 / PhysRevLett.87.161602 , arxiv : hep-ph / 0106295 .
  82. ^ Frédérick Bordry: LHC Status and Outlook. EPS 2017.
  83. ^ Anaïs Schaeffer: The LHC and its successors. CERN Bulletin, March 19, 2012, accessed August 15, 2013 .
This article was added to the list of excellent articles on September 15, 2013 in this version .

Coordinates: 46 ° 14 ′ 0 ″  N , 6 ° 3 ′ 0 ″  E ; CH1903:  492881  /  121160