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119-414: The experiment is a collaboration involving 6,003 members, out of which 3,822 are physicists (last update: June 26, 2022) from 257 institutions in 42 countries. The first cyclotron , an early type of particle accelerator, was built by Ernest O. Lawrence in 1931, with a radius of just a few centimetres and a particle energy of 1 megaelectronvolt (MeV) . Since then, accelerators have grown enormously in

238-455: A ν μ (with T 3 = ⁠+ + 1 / 2 ⁠ ) and a μ (as a right-handed antiparticle, ⁠+ + 1 / 2 ⁠ ). For the development of the electroweak theory, another property, weak hypercharge , was invented, defined as where Y W is the weak hypercharge of a particle with electrical charge Q (in elementary charge units) and weak isospin T 3 . Weak hypercharge

357-504: A W  boson or by absorbing a W  boson. More precisely, the down-type quark becomes a quantum superposition of up-type quarks: that is to say, it has a possibility of becoming any one of the three up-type quarks, with the probabilities given in the CKM matrix tables. Conversely, an up-type quark can emit a W  boson, or absorb a W  boson, and thereby be converted into

476-425: A T 3 of ⁠− + 1 / 2 ⁠ and conversely. In any given strong, electromagnetic, or weak interaction, weak isospin is conserved : The sum of the weak isospin numbers of the particles entering the interaction equals the sum of the weak isospin numbers of the particles exiting that interaction. For example, a (left-handed) π , with a weak isospin of +1 normally decays into

595-700: A master's degree like MSc, MPhil, MPhys or MSci. For research-oriented careers, students work toward a doctoral degree specializing in a particular field. Fields of specialization include experimental and theoretical astrophysics , atomic physics , biological physics , chemical physics , condensed matter physics , cosmology , geophysics , gravitational physics , material science , medical physics , microelectronics , molecular physics , nuclear physics , optics , particle physics , plasma physics , quantum information science , and radiophysics . The three major employers of career physicists are academic institutions, laboratories, and private industries, with

714-535: A neutron is heavier than a proton (its partner nucleon ) and can decay into a proton by changing the flavour (type) of one of its two down quarks to an up quark. Neither the strong interaction nor electromagnetism permit flavour changing, so this can only proceed by weak decay ; without weak decay, quark properties such as strangeness and charm (associated with the strange quark and charm quark, respectively) would also be conserved across all interactions. All mesons are unstable because of weak decay. In

833-448: A quark or a lepton (e.g., an electron or a muon ) emits or absorbs a neutral Z boson . For example: Like the W  bosons, the Z  boson also decays rapidly, for example: Unlike the charged-current interaction, whose selection rules are strictly limited by chirality, electric charge, and / or weak isospin, the neutral-current Z interaction can cause any two fermions in

952-518: A bus architecture cannot keep up with the data requirements of the LHC detectors, all the ATLAS data acquisition systems rely on high-speed point-to-point links and switching networks. Even with advanced electronics for data reading and storage, the ATLAS detector generates too much raw data to read out or store everything: about 25 MB per raw event, multiplied by 40 million beam crossings per second (40 MHz ) in

1071-566: A complex scalar Higgs field doublet. Likewise, there are four massless electroweak vector bosons, each similar to the photon . However, at low energies, this gauge symmetry is spontaneously broken down to the U(1) symmetry of electromagnetism, since one of the Higgs fields acquires a vacuum expectation value . Naïvely, the symmetry-breaking would be expected to produce three massless bosons , but instead those "extra" three Higgs bosons become incorporated into

1190-503: A compound symmetry CP to be conserved. CP combines parity P (switching left to right) with charge conjugation C (switching particles with antiparticles). Physicists were again surprised when in 1964, James Cronin and Val Fitch provided clear evidence in kaon decays that CP symmetry could be broken too, winning them the 1980 Nobel Prize in Physics . In 1973, Makoto Kobayashi and Toshihide Maskawa showed that CP violation in

1309-412: A contact force with no range. In the mid-1950s, Chen-Ning Yang and Tsung-Dao Lee first suggested that the handedness of the spins of particles in weak interaction might violate the conservation law or symmetry. In 1957, Chien Shiung Wu and collaborators confirmed the symmetry violation . In the 1960s, Sheldon Glashow , Abdus Salam and Steven Weinberg unified the electromagnetic force and

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1428-433: A corresponding neutrino (with a charge of 0), where the type ("flavour") of neutrino (electron ν e , muon ν μ , or tau ν τ ) is the same as the type of lepton in the interaction, for example: Similarly, a down-type quark ( d , s , or b , with a charge of ⁠− + 1  / 3 ⁠ ) can be converted into an up-type quark ( u , c , or t , with a charge of ⁠+ + 2  / 3 ⁠ ), by emitting

1547-442: A current pulse (signal) in the wire. The wires with signals create a pattern of 'hit' straws that allow the path of the particle to be determined. Between the straws, materials with widely varying indices of refraction cause ultra-relativistic charged particles to produce transition radiation and leave much stronger signals in some straws. Xenon and argon gas is used to increase the number of straws with strong signals. Since

1666-408: A down-type quark, for example: The W boson is unstable so will rapidly decay, with a very short lifetime. For example: Decay of a W boson to other products can happen, with varying probabilities. In the so-called beta decay of a neutron (see picture, above), a down quark within the neutron emits a virtual W boson and is thereby converted into an up quark, converting

1785-433: A few centimetres from the proton beam axis, extends to a radius of 1.2 metres, and is 6.2 metres in length along the beam pipe. Its basic function is to track charged particles by detecting their interaction with material at discrete points, revealing detailed information about the types of particles and their momentum. The Inner Detector has three parts, which are explained below. The magnetic field surrounding

1904-510: A larger area practical. Each strip measures 80 micrometres by 12 centimetres. The SCT is the most critical part of the inner detector for basic tracking in the plane perpendicular to the beam, since it measures particles over a much larger area than the Pixel Detector, with more sampled points and roughly equal (albeit one-dimensional) accuracy. It is composed of four double layers of silicon strips, and has 6.3 million readout channels and

2023-455: A life of only about 10  seconds. In contrast, a charged pion can only decay through the weak interaction, and so lives about 10  seconds, or a hundred million times longer than a neutral pion. A particularly extreme example is the weak-force decay of a free neutron, which takes about 15 minutes. All particles have a property called weak isospin (symbol T 3 ), which serves as an additive quantum number that restricts how

2142-516: A lifetime of under 10  seconds. The weak interaction has a coupling constant (an indicator of how frequently interactions occur) between 10 and 10 , compared to the electromagnetic coupling constant of about 10 and the strong interaction coupling constant of about 1; consequently the weak interaction is "weak" in terms of intensity. The weak interaction has a very short effective range (around 10 to 10  m (0.01 to 0.1 fm)). At distances around 10  meters (0.001 fm),

2261-452: A minimum, the owner must possess a three-year bachelors or equivalent degree in physics or a related field and an additional minimum of six years' experience in a physics-related activity; or an Honor or equivalent degree in physics or a related field and an additional minimum of five years' experience in a physics-related activity; or master or equivalent degree in physics or a related field and an additional minimum of three years' experience in

2380-471: A neutron (an up quark is changed to a down quark), and an electron neutrino is emitted. Due to the large masses of the W ;bosons, particle transformations or decays (e.g., flavour change) that depend on the weak interaction typically occur much more slowly than transformations or decays that depend only on the strong or electromagnetic forces. For example, a neutral pion decays electromagnetically, and so has

2499-541: A number of predictions, including a prediction of the masses of the Z and W  bosons before their discovery and detection in 1983. On 4 July 2012, the CMS and the ATLAS experimental teams at the Large Hadron Collider independently announced that they had confirmed the formal discovery of a previously unknown boson of mass between 125 and 127 GeV/ c , whose behaviour so far

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2618-505: A physics-related activity; a Doctorate or equivalent degree in Physics or a related field; or training or experience which, in the opinion of the Council, is equivalent to any of the above. Physicists may be a member of a physical society of a country or region. Physical societies commonly publish scientific journals, organize physics conferences and award prizes for contributions to the field of physics. Some examples of physical societies are

2737-416: A professional practice examination must also be passed. An exemption can be granted to a candidate that has practiced physics for at least seven years and provide a detailed description of their professional accomplishments which clearly demonstrate that the exam is not necessary. Work experience will be considered physics-related if it uses physics directly or significantly uses the modes of thought (such as

2856-500: A single, general-purpose particle detector for a new particle accelerator , the Large Hadron Collider . At present, the ATLAS Collaboration involves 6,003 members, out of which 3,822 are physicists (last update: June 26, 2022) from 257 institutions in 42 countries. The design was a combination of two previous projects for LHC, EAGLE and ASCOT, and also benefitted from the detector research and development that had been done for

2975-506: A star. This is because it can convert a proton (hydrogen) into a neutron to form deuterium which is important for the continuation of nuclear fusion to form helium. The accumulation of neutrons facilitates the buildup of heavy nuclei in a star. Most fermions decay by a weak interaction over time. Such decay makes radiocarbon dating possible, as carbon-14 decays through the weak interaction to nitrogen-14 . It can also create radioluminescence , commonly used in tritium luminescence , and in

3094-471: A total area of 12,000 square meters. The ATLAS detector uses two large superconducting magnet systems to bend the trajectory of charged particles, so that their momenta can be measured. This bending is due to the Lorentz force , whose modulus is proportional to the electric charge q {\displaystyle q} of the particle, to its speed v {\displaystyle v} and to

3213-430: A total area of 61 square meters. The Transition Radiation Tracker (TRT), the outermost component of the inner detector, is a combination of a straw tracker and a transition radiation detector . The detecting elements are drift tubes (straws), each four millimetres in diameter and up to 144 centimetres long. The uncertainty of track position measurements (position resolution) is about 200 micrometres. This

3332-470: A weak isospin value of either ⁠+ + 1 / 2 ⁠ or ⁠− + 1 / 2 ⁠ ; all right-handed fermions have 0 isospin. For example, the up quark has T 3 = ⁠+ + 1 / 2 ⁠ and the down quark has T 3 = ⁠− + 1 / 2 ⁠ . A quark never decays through the weak interaction into a quark of the same T 3 : Quarks with a T 3 of ⁠+ + 1 / 2 ⁠ only decay into quarks with

3451-742: A wide range of research fields , spanning all length scales: from sub-atomic and particle physics , through biological physics , to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of natural phenomena and the development and analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena. Physicists can apply their knowledge towards solving practical problems or to developing new technologies (also known as applied physics or engineering physics ). The study and practice of physics

3570-434: Is a pixel (50 by 400 micrometres); there are roughly 47,000 pixels per module. The minute pixel size is designed for extremely precise tracking very close to the interaction point. In total, the Pixel Detector has over 92 million readout channels, which is about 50% of the total readout channels of the whole detector. Having such a large count created a considerable design and engineering challenge. Another challenge

3689-431: Is an extremely large tracking system, consisting of three parts: The extent of this sub-detector starts at a radius of 4.25 m close to the calorimeters out to the full radius of the detector (11 m). Its tremendous size is required to accurately measure the momentum of muons, which first go through all the other elements of the detector before reaching the muon spectrometer. It was designed to measure, standalone,

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3808-688: Is based on an intellectual ladder of discoveries and insights from ancient times to the present. Many mathematical and physical ideas used today found their earliest expression in the work of ancient civilizations, such as the Babylonian astronomers and Egyptian engineers , the Greek philosophers of science and mathematicians such as Thales of Miletus , Euclid in Ptolemaic Egypt , Archimedes of Syracuse and Aristarchus of Samos . Roots also emerged in ancient Asian cultures such as India and China, and particularly

3927-502: Is designed to detect these particles, namely their masses, momentum , energies , lifetime, charges, and nuclear spins . Experiments at earlier colliders, such as the Tevatron and Large Electron–Positron Collider , were also designed for general-purpose detection. However, the beam energy and extremely high rate of collisions require ATLAS to be significantly larger and more complex than previous experiments, presenting unique challenges of

4046-416: Is large and comprises a huge amount of construction material: the main part of the calorimeter – the tile calorimeter – is 8 metres in diameter and covers 12 metres along the beam axis. The far-forward sections of the hadronic calorimeter are contained within the forward EM calorimeter's cryostat, and use liquid argon as well, while copper and tungsten are used as absorbers. The Muon Spectrometer

4165-408: Is nonzero. The second type is called the " neutral-current interaction " because the weakly interacting fermions form a current with total electric charge of zero. It is responsible for the (rare) deflection of neutrinos . The two types of interaction follow different selection rules . This naming convention is often misunderstood to label the electric charge of the W and Z bosons , however

4284-399: Is not as precise as those for the other two detectors, but it was necessary to reduce the cost of covering a larger volume and to have transition radiation detection capability. Each straw is filled with gas that becomes ionized when a charged particle passes through. The straws are held at about −1,500 V, driving the negative ions to a fine wire down the centre of each straw, producing

4403-421: Is not uniform, because a solenoid magnet of sufficient size would be prohibitively expensive to build. It varies between 2 and 8 Teslameters. The ATLAS detector is complemented by a set of four sub-detectors in the forward region to measure particles at very small angles. Earlier particle detector read-out and event detection systems were based on parallel shared buses such as VMEbus or FASTBUS . Since such

4522-589: Is the Nobel Prize in Physics , awarded since 1901 by the Royal Swedish Academy of Sciences . National physical societies have many prizes and awards for professional recognition. In the case of the American Physical Society , as of 2023, there are 25 separate prizes and 33 separate awards in the field. Chartered Physicist (CPhys) is a chartered status and a professional qualification awarded by

4641-482: Is the generator of the U(1) component of the electroweak gauge group ; whereas some particles have a weak isospin of zero, all known spin- ⁠ 1 / 2 ⁠ particles have a non-zero weak hypercharge. There are two types of weak interaction (called vertices ). The first type is called the " charged-current interaction " because the weakly interacting fermions form a current with total electric charge that

4760-437: Is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms: The weak interaction participates in nuclear fission and nuclear fusion . The theory describing its behaviour and effects is sometimes called quantum flavordynamics ( QFD ); however, the term QFD is rarely used, because the weak force is better understood by electroweak theory (EWT). The effective range of

4879-494: Is then close to zero, so these mostly interact with the Z  boson through the axial coupling. The Standard Model of particle physics describes the electromagnetic interaction and the weak interaction as two different aspects of a single electroweak interaction. This theory was developed around 1968 by Sheldon Glashow , Abdus Salam , and Steven Weinberg , and they were awarded the 1979 Nobel Prize in Physics for their work. The Higgs mechanism provides an explanation for

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4998-596: Is typically several orders of magnitude less than that of the electromagnetic force, which itself is further orders of magnitude less than the strong nuclear force. The weak interaction is the only fundamental interaction that breaks parity symmetry , and similarly, but far more rarely, the only interaction to break charge–parity symmetry . Quarks , which make up composite particles like neutrons and protons, come in six "flavours" – up, down, charm, strange, top and bottom – which give those composite particles their properties. The weak interaction

5117-433: Is unique in that it allows quarks to swap their flavour for another. The swapping of those properties is mediated by the force carrier bosons. For example, during beta-minus decay , a down quark within a neutron is changed into an up quark, thus converting the neutron to a proton and resulting in the emission of an electron and an electron antineutrino. Weak interaction is important in the fusion of hydrogen into helium in

5236-523: The American Physical Society , the Institute of Physics , with the oldest physical society being the German Physical Society . Weak interaction In nuclear physics and particle physics , the weak interaction , also called the weak force , is one of the four known fundamental interactions , with the others being electromagnetism , the strong interaction , and gravitation . It

5355-598: The Grand Unified Theories (GUTs) including Supersymmetry (SUSY), predicts the existence of new particles with masses greater than those of Standard Model . Most of the currently proposed theories predict new higher-mass particles, some of which may be light enough to be observed by ATLAS. Models of supersymmetry involve new, highly massive particles. In many cases these decay into high-energy quarks and stable heavy particles that are very unlikely to interact with ordinary matter. The stable particles would escape

5474-683: The Institute of Physics . It is denoted by the postnominals "CPhys". Achieving chartered status in any profession denotes to the wider community a high level of specialised subject knowledge and professional competence. According to the Institute of Physics, holders of the award of the Chartered Physicist (CPhys) demonstrate the "highest standards of professionalism, up-to-date expertise, quality and safety" along with "the capacity to undertake independent practice and exercise leadership" as well as "commitment to keep pace with advancing knowledge and with

5593-539: The Islamic medieval period , which saw the development of scientific methodology emphasising experimentation , such as the work of Ibn al-Haytham (Alhazen) in the 11th century. The modern scientific worldview and the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of astronomer Nicolaus Copernicus leading to the physics of Galileo Galilei and Johannes Kepler in

5712-443: The Lorentz force is equal to where p = γ m v {\displaystyle p=\gamma \,m\,v} is the relativistic momentum of the particle. As a result, high-momentum particles curve very little (large r {\displaystyle r} ), while low-momentum particles curve significantly (small r {\displaystyle r} ). The amount of curvature can be quantified and

5831-483: The Standard Model at lower energies, but dramatically different above symmetry breaking. The laws of nature were long thought to remain the same under mirror reflection . The results of an experiment viewed via a mirror were expected to be identical to the results of a separately constructed, mirror-reflected copy of the experimental apparatus watched through the mirror. This so-called law of parity conservation

5950-452: The Standard model is believed to be theoretically self-consistent and has demonstrated huge successes in providing experimental predictions , it leaves some phenomena unexplained and falls short of being a complete theory of fundamental interactions . It does not fully explain baryon asymmetry , incorporate the full theory of gravitation as described by general relativity , or account for

6069-417: The Standard model . The Standard model of particle physics is the theory describing three of the four known fundamental forces (the electromagnetic , weak , and strong interactions, while omitting gravity ) in the universe , as well as classifying all known elementary particles . It was developed in stages throughout the latter half of the 20th century, through the work of many scientists around

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6188-526: The Superconducting Super Collider , a US project interrupted in 1993. The ATLAS experiment was proposed in its current form in 1994, and officially funded by the CERN member countries in 1995. Additional countries, universities , and laboratories have joined in subsequent years. Construction work began at individual institutions, with detector components then being shipped to CERN and assembled in

6307-902: The W and Z bosons mass while leaving the photon massless. On July 4, 2012, ATLAS — together with CMS, its sister experiment at the LHC — reported evidence for the existence of a particle consistent with the Higgs boson at a confidence level of 5 sigma , with a mass around 125 GeV, or 133 times the proton mass. This new "Higgs-like" particle was detected by its decay into two photons ( H → γ γ {\displaystyle H\rightarrow \gamma \gamma } ) and its decay to four leptons ( H → Z Z ∗ → 4 l {\displaystyle H\rightarrow ZZ^{*}\rightarrow 4l} and H → W W ∗ → e ν μ ν {\displaystyle H\rightarrow WW^{*}\rightarrow e\nu \mu \nu } ). In March 2013, in

6426-521: The accelerating expansion of the universe as possibly described by dark energy . The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology . It also does not incorporate neutrino oscillations and their non-zero masses. With the important exception of the Higgs boson , detected by the ATLAS and the CMS experiments in 2012, all of

6545-444: The center of mass of the collision. Since then, the LHC energy has been increasing: 1.8 TeV at the end of 2009, 7 TeV for the whole of 2010 and 2011, then 8 TeV in 2012. The first data-taking period performed between 2010 and 2012 is referred to as Run I. After a long shutdown (LS1) in 2013 and 2014, in 2015 ATLAS saw 13 TeV collisions. The second data-taking period, Run II, was completed, always at 13 TeV energy, at

6664-436: The photon . Instead, neutrinos have mass . In 1998 research results at detector Super-Kamiokande determined that neutrinos can oscillate from one flavor to another, which dictates that they have a mass other than zero. For these and other reasons, many particle physicists believe it is possible that the Standard Model will break down at energies at the teraelectronvolt (TeV) scale or higher. Most alternative theories,

6783-502: The pseudorapidity ) and its angle within the perpendicular plane are both measured to within roughly 0.025  radians . The barrel EM calorimeter has accordion shaped electrodes and the energy-absorbing materials are lead and stainless steel , with liquid argon as the sampling material, and a cryostat is required around the EM calorimeter to keep it sufficiently cool. The hadron calorimeter absorbs energy from particles that pass through

6902-579: The 19th century. Many physicists contributed to the development of quantum mechanics in the early-to-mid 20th century. New knowledge in the early 21st century includes a large increase in understanding physical cosmology . The broad and general study of nature, natural philosophy , was divided into several fields in the 19th century, when the concept of "science" received its modern shape. Specific categories emerged, such as "biology" and "biologist", "physics" and "physicist", "chemistry" and "chemist", among other technical fields and titles. The term physicist

7021-424: The ATLAS experiment pit starting in 2003. Construction was completed in 2008 and the experiment detected its first single proton beam events on 10 September of that year. Data-taking was then interrupted for over a year due to an LHC magnet quench incident . On 23 November 2009, the first proton–proton collisions occurred at the LHC and were recorded by ATLAS, at a relatively low injection energy of 900 GeV in

7140-403: The EM calorimeter, but do interact via the strong force ; these particles are primarily hadrons. It is less precise, both in energy magnitude and in the localization (within about 0.1 radians only). The energy-absorbing material is steel, with scintillating tiles that sample the energy deposited. Many of the features of the calorimeter are chosen for their cost-effectiveness; the instrument

7259-577: The Inner Detector, with muons curving so that their momentum can be measured, albeit with a different magnetic field configuration, lower spatial precision, and a much larger volume. It also serves the function of simply identifying muons – very few particles of other types are expected to pass through the calorimeters and subsequently leave signals in the Muon Spectrometer. It has roughly one million readout channels, and its layers of detectors have

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7378-415: The LHC collide. Maintaining detector performance in the high radiation areas immediately surrounding the proton beams is a significant engineering challenge. The detector can be divided into four major systems: Each of these is in turn made of multiple layers. The detectors are complementary: the Inner Detector tracks particles precisely, the calorimeters measure the energy of easily stopped particles, and

7497-536: The Large Hadron Collider. In order to identify all particles produced at the interaction point where the particle beams collide, the detector is designed in layers made up of detectors of different types, each of which is designed to observe specific types of particles. The different traces that particles leave in each layer of the detector allow for effective particle identification and accurate measurements of energy and momentum. (The role of each layer in

7616-612: The Standard Model in equal numbers and leaving an unequivocal signature in the ATLAS detector. The ATLAS detector is 46 metres long, 25 metres in diameter, and weighs about 7,000 tonnes; it contains some 3,000 km of cable. At 27 km in circumference , the Large Hadron Collider (LHC) at CERN collides two beams of protons together, with each proton carrying up to 6.8  TeV of energy – enough to produce particles with masses significantly greater than any particles currently known, if these particles exist. When

7735-468: The amount of transition radiation is greatest for highly relativistic particles (those with a speed very near the speed of light ), and because particles of a particular energy have a higher speed the lighter they are, particle paths with many very strong signals can be identified as belonging to the lightest charged particles: electrons and their antiparticles, positrons . The TRT has about 298,000 straws in total. The calorimeters are situated outside

7854-399: The approach to problem-solving) developed in your education or experience as a physicist, in all cases regardless of whether the experience is in academia, industry, government, or elsewhere. Management of physics-related work qualifies, and so does appropriate graduate student work. The South African Institute of Physics also delivers a certification of Professional Physicist (Pr.Phys). At

7973-494: The behavior of matter and antimatter , known as CP violation , is also being investigated. Recent experiments dedicated to measurements of CP violation, such as BaBar and Belle , have not detected sufficient CP violation in the Standard Model to explain the lack of detectable antimatter in the universe. It is possible that new models of physics will introduce additional CP violation, shedding light on this problem. Evidence supporting these models might either be detected directly by

8092-452: The center of the detector. This produces a total of 1 petabyte of raw data per second. By avoiding to write empty segments of each event (zero suppression), which do not contain physical information, the average size of an event is reduced to 1.6 MB , for a total of 64 terabyte of data per second. The trigger system uses fast event reconstruction to identify, in real time, the most interesting events to retain for detailed analysis. In

8211-449: The decay of a hadron with a bottom quark (see b-tagging ). The Pixel Detector, the innermost part of the detector, contains four concentric layers and three disks on each end-cap, with a total of 1,744  modules , each measuring 2 centimetres by 6 centimetres. The detecting material is 250 μm thick silicon . Each module contains 16 readout chips and other electronic components. The smallest unit that can be read out

8330-441: The deepest levels, all weak interactions ultimately are between elementary particles . In the weak interaction, fermions can exchange three types of force carriers, namely W , W , and Z  bosons . The masses of these bosons are far greater than the mass of a proton or neutron, which is consistent with the short range of the weak force. In fact, the force is termed weak because its field strength over any set distance

8449-517: The designation of Professional Engineer (P. Eng.). This designation was unveiled at the CAP congress in 1999 and already more than 200 people carry this distinction. To get the certification, at minimum proof of honours bachelor or higher degree in physics or a closely related discipline must be provided. Also, the physicist must have completed, or be about to complete, three years of recent physics-related work experience after graduation. And, unless exempted,

8568-428: The details of the Standard Model, with the possibility of revealing inconsistencies that point to new physics. While the Standard Model predicts that quarks , leptons and neutrinos should exist, it does not explain why the masses of these particles are so different (they differ by orders of magnitude ). Furthermore, the mass of the neutrinos should be, according to the Standard Model , exactly zero as that of

8687-419: The detector is discussed below .) As the energy of the particles produced by the accelerator increases, the detectors attached to it must grow to effectively measure and stop higher-energy particles. As of 2022, the ATLAS detector is the largest ever built at a particle collider. The ATLAS detector consists of a series of ever-larger concentric cylinders around the interaction point where the proton beams from

8806-553: The detector must be " hermetic ", meaning it must detect all non-neutrinos produced, with no blind spots. The installation of all the above detector systems was finished in August 2008. The detectors collected millions of cosmic rays during the magnet repairs which took place between fall 2008 and fall 2009, prior to the first proton collisions. The detector operated with close to 100% efficiency and provided performance characteristics very close to its design values. The Inner Detector begins

8925-511: The detector, leaving as a signal one or more high-energy quark jets and a large amount of "missing" momentum . Other hypothetical massive particles, like those in the Kaluza–Klein theory , might leave a similar signature. The data collected up to the end of LHC Run II do not show evidence of supersymmetric or unexpected particles, the research of which will continue in the data that will be collected from Run III onwards. The asymmetry between

9044-455: The early 1600s. The work on mechanics , along with a mathematical treatment of physical systems, was further developed by Christiaan Huygens and culminated in Newton's laws of motion and Newton's law of universal gravitation by the end of the 17th century. The experimental discoveries of Faraday and the theory of Maxwell's equations of electromagnetism were developmental high points during

9163-449: The end of 2018 with a recorded integrated luminosity of nearly 140 fb (inverse femtobarn ). A second long shutdown (LS2) in 2019-22 with upgrades to the ATLAS detector was followed by Run III, which started in July 2022. The ATLAS Collaboration is currently led by Spokesperson Andreas Hoecker and Deputy Spokespersons Marumi Kado and Manuella Vincter . Former Spokespersons have been: In

9282-417: The energy of the original particle from this measurement. The electromagnetic (EM) calorimeter absorbs energy from particles that interact electromagnetically , which include charged particles and photons. It has high precision, both in the amount of energy absorbed and in the precise location of the energy deposited. The angle between the particle's trajectory and the detector's beam axis (or more precisely

9401-416: The entire inner detector causes charged particles to curve; the direction of the curve reveals a particle's charge and the degree of curvature reveals its momentum. The starting points of the tracks yield useful information for identifying particles ; for example, if a group of tracks seem to originate from a point other than the original proton–proton collision, this may be a sign that the particles came from

9520-565: The field and most likely not be measured; however, this energy is very small compared to the several TeV of energy released in each proton collision. The outer toroidal magnetic field is produced by eight very large air-core superconducting barrel loops and two smaller end-caps air toroidal magnets, for a total of 24 barrel loops all situated outside the calorimeters and within the muon system. This magnetic field extends in an area 26 metres long and 20 metres in diameter, and it stores 1.6  gigajoules of energy. Its magnetic field

9639-491: The field of particle physics , ATLAS studies different types of processes detected or detectable in energetic collisions at the Large Hadron Collider (LHC). For the processes already known, it is a matter of measuring more and more accurately the properties of known particles or finding quantitative confirmations of the Standard model . Processes not observed so far would allow, if detected, to discover new particles or to have confirmation of physical theories that go beyond

9758-735: The increasing expectations and requirements for which any profession must take responsibility". Chartered Physicist is considered to be equal in status to Chartered Engineer, which the IoP also awards as a member of the Engineering Council UK, and other chartered statuses in the UK. It is also considered a "regulated profession" under the European professional qualification directives. The Canadian Association of Physicists can appoint an official designation called Professional Physicist ( P. Phys. ), similar to

9877-505: The intensity B {\displaystyle B} of the magnetic field: Since all particles produced in the LHC's proton collisions are traveling at very close to the speed of light in vacuum ( v ≃ c ) {\displaystyle (v\simeq c)} , the Lorentz force is about the same for all the particles with same electric charge q {\displaystyle q} : The radius of curvature r {\displaystyle r} due to

9996-1172: The largest employer being the last. Physicists in academia or government labs tend to have titles such as Assistants, Professors , Sr./Jr. Scientist, or postdocs . As per the American Institute of Physics , some 20% of new physics Ph.D.s holds jobs in engineering development programs, while 14% turn to computer software and about 11% are in business/education. A majority of physicists employed apply their skills and training to interdisciplinary sectors (e.g. finance ). Job titles for graduate physicists include Agricultural Scientist , Air Traffic Controller , Biophysicist , Computer Programmer , Electrical Engineer , Environmental Analyst , Geophysicist , Medical Physicist , Meteorologist , Oceanographer , Physics Teacher / Professor / Researcher , Research Scientist , Reactor Physicist , Engineering Physicist , Satellite Missions Analyst, Science Writer , Stratigrapher , Software Engineer , Systems Engineer , Microelectronics Engineer , Radar Developer, Technical Consultant, etc. The majority of Physics terminal bachelor's degree holders are employed in

10115-474: The light of the updated ATLAS and CMS results, CERN announced that the new particle was indeed a Higgs boson. The experiments were also able to show that the properties of the particle as well as the ways it interacts with other particles were well-matched with those of a Higgs boson, which is expected to have spin 0 and positive parity . Analysis of more properties of the particle and data collected in 2015 and 2016 confirmed this further. In October 2013, two of

10234-436: The mass [(80,370±19) MeV ] of the W boson , one of the two mediators of the weak interaction , with a measurement uncertainty of ±2.4 ‰ . One of the most important goals of ATLAS was to investigate a missing piece of the Standard Model, the Higgs boson . The Higgs mechanism , which includes the Higgs boson, gives mass to elementary particles, leading to differences between the weak force and electromagnetism by giving

10353-521: The momentum difference (called " running ") between the particles involved. Hence since by convention ⁠ sgn ⁡ T 3 ≡ sgn ⁡ Q {\displaystyle \operatorname {sgn} T_{3}\equiv \operatorname {sgn} Q} ⁠ , and for all fermions involved in the weak interaction ⁠ T 3 = ± 1 2 {\displaystyle T_{3}=\pm {\tfrac {1}{2}}} ⁠ . The weak charge of charged leptons

10472-406: The momentum of 100 GeV muons with 3% accuracy and of 1 TeV muons with 10% accuracy. It was vital to go to the lengths of putting together such a large piece of equipment because a number of interesting physical processes can only be observed if one or more muons are detected, and because the total energy of particles in an event could not be measured if the muons were ignored. It functions similarly to

10591-430: The muon system makes additional measurements of highly penetrating muons. The two magnet systems bend charged particles in the Inner Detector and the Muon Spectrometer, allowing their electric charges and momenta to be measured. The only established stable particles that cannot be detected directly are neutrinos ; their presence is inferred by measuring a momentum imbalance among detected particles. For this to work,

10710-420: The naming convention predates the concept of the mediator bosons, and clearly (at least in name) labels the charge of the current (formed from the fermions), not necessarily the bosons. In one type of charged current interaction, a charged lepton (such as an electron or a muon , having a charge of −1) can absorb a W  boson (a particle with a charge of +1) and be thereby converted into

10829-436: The neutron into a proton. Because of the limited energy involved in the process (i.e., the mass difference between the down quark and the up quark), the virtual W boson can only carry sufficient energy to produce an electron and an electron-antineutrino – the two lowest-possible masses among its prospective decay products. At the quark level, the process can be represented as: In neutral current interactions,

10948-468: The particle momentum can be determined from this value. The inner solenoid produces a two tesla magnetic field surrounding the Inner Detector. This high magnetic field allows even very energetic particles to curve enough for their momentum to be determined, and its nearly uniform direction and strength allow measurements to be made very precisely. Particles with momenta below roughly 400 MeV will be curved so strongly that they will loop repeatedly in

11067-415: The particle can interact with the W of the weak force. Weak isospin plays the same role in the weak interaction with W as electric charge does in electromagnetism , and color charge in the strong interaction ; a different number with a similar name, weak charge , discussed below , is used for interactions with the Z . All left-handed fermions have

11186-429: The particles predicted by the Standard Model had been observed by previous experiments. In this field, in addition to the discovery of the Higgs boson , the experimental work of ATLAS has focused on precision measurements, aimed at determining with ever greater accuracy the many physical parameters of theory. In particular for ATLAS measures: For example, the data collected by ATLAS made it possible in 2018 to measure

11305-437: The presence of three massive gauge bosons ( W , W , Z , the three carriers of the weak interaction), and the photon ( γ , the massless gauge boson that carries the electromagnetic interaction). According to the electroweak theory, at very high energies, the universe has four components of the Higgs field whose interactions are carried by four massless scalar bosons forming

11424-433: The private sector. Other fields are academia, government and military service, nonprofit entities, labs and teaching. Typical duties of physicists with master's and doctoral degrees working in their domain involve research, observation and analysis, data preparation, instrumentation, design and development of industrial or medical equipment, computing and software development, etc. The highest honor awarded to physicists

11543-413: The process known as beta decay , a down quark in the neutron can change into an up quark by emitting a virtual W  boson, which then decays into an electron and an electron antineutrino . Another example is electron capture  – a common variant of radioactive decay  – wherein a proton and an electron within an atom interact and are changed to

11662-472: The production of new particles, or indirectly by measurements of the properties of B- and D- mesons . LHCb , an LHC experiment dedicated to B-mesons, is likely to be better suited to the latter. Some hypotheses, based on the ADD model , involve large extra dimensions and predict that micro black holes could be formed by the LHC. These would decay immediately by means of Hawking radiation , producing all particles in

11781-522: The proton beams produced by the Large Hadron Collider interact in the center of the detector, a variety of different particles with a broad range of energies are produced. The ATLAS detector is designed to be general-purpose. Rather than focusing on a particular physical process, ATLAS is designed to measure the broadest possible range of signals. This is intended to ensure that whatever form any new physical processes or particles might take, ATLAS will be able to detect them and measure their properties. ATLAS

11900-532: The quest to produce new particles of greater and greater mass . As accelerators have grown, so too has the list of known particles that they might be used to investigate. The ATLAS Collaboration, the international group of physicists belonging to different universities and research centres who built and run the detector, was formed in 1992 when the proposed EAGLE (Experiment for Accurate Gamma, Lepton and Energy Measurements) and ASCOT (Apparatus with Super Conducting Toroids) collaborations merged their efforts to build

12019-428: The related field of betavoltaics (but not similar radium luminescence ). The electroweak force is believed to have separated into the electromagnetic and weak forces during the quark epoch of the early universe . In 1933, Enrico Fermi proposed the first theory of the weak interaction, known as Fermi's interaction . He suggested that beta decay could be explained by a four- fermion interaction, involving

12138-459: The second data-taking period of the LHC, Run-2, there were two distinct trigger levels: Physicist A physicist is a scientist who specializes in the field of physics , which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena , and usually frame their understanding in mathematical terms. They work across

12257-411: The solenoidal magnet that surrounds the Inner Detector. Their purpose is to measure the energy from particles by absorbing it. There are two basic calorimeter systems: an inner electromagnetic calorimeter and an outer hadronic calorimeter. Both are sampling calorimeters ; that is, they absorb energy in high-density metal and periodically sample the shape of the resulting particle shower , inferring

12376-419: The standard model to deflect: Either particles or anti-particles, with any electric charge, and both left- and right-chirality, although the strength of the interaction differs. The quantum number weak charge ( Q W ) serves the same role in the neutral current interaction with the Z that electric charge ( Q , with no subscript) does in the electromagnetic interaction : It quantifies

12495-601: The theoretical physicists who predicted the existence of the Standard Model Higgs boson, Peter Higgs and François Englert , were awarded the Nobel Prize in Physics . The properties of the top quark , discovered at Fermilab in 1995, had been measured approximately. With much greater energy and greater collision rates, the LHC produces a tremendous number of top quarks, allowing ATLAS to make much more precise measurements of its mass and interactions with other particles. These measurements provide indirect information on

12614-409: The three weak bosons, which then acquire mass through the Higgs mechanism . These three composite bosons are the W , W , and Z  bosons actually observed in the weak interaction. The fourth electroweak gauge boson is the photon ( γ ) of electromagnetism, which does not couple to any of the Higgs fields and so remains massless. This theory has made

12733-550: The vector part of the interaction. Its value is given by: Since the weak mixing angle ⁠ θ w ≈ 29 ∘ {\displaystyle \theta _{\mathsf {w}}\approx 29^{\circ }} ⁠ , the parenthetic expression ⁠ ( 1 − 4 sin 2 ⁡ θ w ) ≈ 0.060 {\displaystyle (1-4\,\sin ^{2}\theta _{\mathsf {w}})\approx 0.060} ⁠ , with its value varying slightly with

12852-541: The weak force is limited to subatomic distances and is less than the diameter of a proton. The Standard Model of particle physics provides a uniform framework for understanding electromagnetic, weak, and strong interactions. An interaction occurs when two particles (typically, but not necessarily, half-integer spin fermions ) exchange integer-spin, force-carrying bosons . The fermions involved in such exchanges can be either elementary (e.g. electrons or quarks ) or composite (e.g. protons or neutrons ), although at

12971-465: The weak interaction acts only on left-handed particles (and right-handed antiparticles). Since the mirror reflection of a left-handed particle is right-handed, this explains the maximal violation of parity. The V − A theory was developed before the discovery of the Z ;boson, so it did not include the right-handed fields that enter in the neutral current interaction. However, this theory allowed

13090-420: The weak interaction by showing them to be two aspects of a single force, now termed the electroweak force. The existence of the W and Z  bosons was not directly confirmed until 1983. The electrically charged weak interaction is unique in a number of respects: Due to their large mass (approximately 90 GeV/ c ) these carrier particles, called the W and Z  bosons, are short-lived with

13209-460: The weak interaction has an intensity of a similar magnitude to the electromagnetic force, but this starts to decrease exponentially with increasing distance. Scaled up by just one and a half orders of magnitude, at distances of around 3 × 10  m, the weak interaction becomes 10,000 times weaker. The weak interaction affects all the fermions of the Standard Model , as well as the Higgs boson ; neutrinos interact only through gravity and

13328-401: The weak interaction required more than two generations of particles, effectively predicting the existence of a then unknown third generation. This discovery earned them half of the 2008 Nobel Prize in Physics. Unlike parity violation, CP  violation occurs only in rare circumstances. Despite its limited occurrence under present conditions, it is widely believed to be the reason that there

13447-404: The weak interaction was once described by Fermi's theory , the discovery of parity violation and renormalization theory suggested that a new approach was needed. In 1957, Robert Marshak and George Sudarshan and, somewhat later, Richard Feynman and Murray Gell-Mann proposed a V − A ( vector minus axial vector or left-handed) Lagrangian for weak interactions. In this theory,

13566-469: The weak interaction. The weak interaction does not produce bound states , nor does it involve binding energy  – something that gravity does on an astronomical scale , the electromagnetic force does at the molecular and atomic levels, and the strong nuclear force does only at the subatomic level, inside of nuclei . Its most noticeable effect is due to its first unique feature: The charged weak interaction causes flavour change . For example,

13685-445: The world, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks . Since then, confirmation of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard model . In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy. Although

13804-522: Was "consistent with" a Higgs boson, while adding a cautious note that further data and analysis were needed before positively identifying the new boson as being a Higgs boson of some type. By 14 March 2013, a Higgs boson was tentatively confirmed to exist. In a speculative case where the electroweak symmetry breaking scale were lowered, the unbroken SU(2) interaction would eventually become confining . Alternative models where SU(2) becomes confining above that scale appear quantitatively similar to

13923-738: Was coined by William Whewell (also the originator of the term "scientist") in his 1840 book The Philosophy of the Inductive Sciences . A standard undergraduate physics curriculum consists of classical mechanics , electricity and magnetism , non-relativistic quantum mechanics , optics , statistical mechanics and thermodynamics , and laboratory experience. Physics students also need training in mathematics ( calculus , differential equations , linear algebra , complex analysis , etc.), and in computer science . Any physics-oriented career position requires at least an undergraduate degree in physics or applied physics, while career options widen with

14042-430: Was known to be respected by classical gravitation , electromagnetism and the strong interaction ; it was assumed to be a universal law. However, in the mid-1950s Chen-Ning Yang and Tsung-Dao Lee suggested that the weak interaction might violate this law. Chien Shiung Wu and collaborators in 1957 discovered that the weak interaction violates parity, earning Yang and Lee the 1957 Nobel Prize in Physics . Although

14161-440: Was the radiation to which the Pixel Detector is exposed because of its proximity to the interaction point, requiring that all components be radiation hardened in order to continue operating after significant exposures. The Semi-Conductor Tracker (SCT) is the middle component of the inner detector. It is similar in concept and function to the Pixel Detector but with long, narrow strips rather than small pixels, making coverage of

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