Misplaced Pages

#134865

62-411: In particle physics , B mesons are mesons composed of a bottom antiquark and either an up ( B ), down ( B ), strange ( B s ) or charm quark ( B c ). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark

124-487: A Hilbert space , which is also treated in quantum field theory . Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles. Ordinary matter is made from first- generation quarks ( up , down ) and leptons ( electron , electron neutrino ). Collectively, quarks and leptons are called fermions , because they have

186-402: A microsecond . They occur after collisions between particles made of quarks, such as fast-moving protons and neutrons in cosmic rays . Mesons are also produced in cyclotrons or other particle accelerators . Particles have corresponding antiparticles with the same mass but with opposite electric charges . For example, the antiparticle of the electron is the positron . The electron has

248-498: A quantum spin of half-integers (−1/2, 1/2, 3/2, etc.). This causes the fermions to obey the Pauli exclusion principle , where no two particles may occupy the same quantum state . Quarks have fractional elementary electric charge (−1/3 or 2/3) and leptons have whole-numbered electric charge (0 or 1). Quarks also have color charge , which is labeled arbitrarily with no correlation to actual light color as red, green and blue. Because

310-1055: A " Theory of Everything ", or "TOE". There are also other areas of work in theoretical particle physics ranging from particle cosmology to loop quantum gravity . In principle, all physics (and practical applications developed therefrom) can be derived from the study of fundamental particles. In practice, even if "particle physics" is taken to mean only "high-energy atom smashers", many technologies have been developed during these pioneering investigations that later find wide uses in society. Particle accelerators are used to produce medical isotopes for research and treatment (for example, isotopes used in PET imaging ), or used directly in external beam radiotherapy . The development of superconductors has been pushed forward by their use in particle physics. The World Wide Web and touchscreen technology were initially developed at CERN . Additional applications are found in medicine, national security, industry, computing, science, and workforce development, illustrating

372-446: A collision energy of 7 TeV. In 2012, about 2 fb was collected at an energy of 8 TeV. During 2015–2018 (Run 2 of the LHC), about 6 fb was collected at a center-of-mass energy of 13 TeV. In addition, small samples were collected in proton-lead, lead-lead, and xenon-xenon collisions. The LHCb design also allowed the study of collisions of particle beams with a gas (helium or neon) injected inside

434-452: A fourth generation of fermions does not exist. Bosons are the mediators or carriers of fundamental interactions, such as electromagnetism , the weak interaction , and the strong interaction . Electromagnetism is mediated by the photon , the quanta of light . The weak interaction is mediated by the W and Z bosons . The strong interaction is mediated by the gluon , which can link quarks together to form composite particles. Due to

496-558: A given decay to happen, was found to be 0.846 − 0.041 + 0.044 {\displaystyle 0.846_{-0.041}^{+0.044}} while the Standard Model predicts it to be very close to unity. In December 2022 improved measurements discarded this anomaly. In August 2023 joined searches in leptonic decays b → s ℓ + ℓ − {\displaystyle b\rightarrow s\ell ^{+}\ell ^{-}} by

558-764: A long and growing list of beneficial practical applications with contributions from particle physics. Major efforts to look for physics beyond the Standard Model include the Future Circular Collider proposed for CERN and the Particle Physics Project Prioritization Panel (P5) in the US that will update the 2014 P5 study that recommended the Deep Underground Neutrino Experiment , among other experiments. LHCb The LHCb ( Large Hadron Collider beauty ) experiment

620-430: A negative electric charge, the positron has a positive charge. These antiparticles can theoretically form a corresponding form of matter called antimatter . Some particles, such as the photon , are their own antiparticle. These elementary particles are excitations of the quantum fields that also govern their interactions. The dominant theory explaining these fundamental particles and fields, along with their dynamics,

682-533: A period of about three years. The detector operates in vacuum and is cooled to approximately −25 °C (−13 °F) using a biphase CO 2 system. The data of the VELO detector are amplified and read out by the Beetle ASIC . The RICH-1 detector ( Ring imaging Cherenkov detector ) is located directly after the vertex detector. It is used for particle identification of low- momentum tracks. The main tracking system

SECTION 10

#1732851191135

744-423: A statistical significance of 5 σ . Particle physics Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation . The field also studies combinations of elementary particles up to the scale of protons and neutrons , while the study of combination of protons and neutrons is called nuclear physics . The fundamental particles in

806-435: A wide range of exotic particles . All particles and their interactions observed to date can be described almost entirely by the Standard Model. Dynamics of particles are also governed by quantum mechanics ; they exhibit wave–particle duality , displaying particle-like behaviour under certain experimental conditions and wave -like behaviour in others. In more technical terms, they are described by quantum state vectors in

868-644: Is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN . LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b- hadrons (heavy particles containing a bottom quark ). Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in

930-425: Is a particle physics theory suggesting that systems with higher energy have a smaller number of dimensions. A third major effort in theoretical particle physics is string theory . String theorists attempt to construct a unified description of quantum mechanics and general relativity by building a theory based on small strings, and branes rather than particles. If the theory is successful, it may be considered

992-515: Is called flavor oscillation . The existence of neutral B meson oscillations is a fundamental prediction of the Standard Model of particle physics . It has been measured in the B – B system to be about 0.496 / picoseconds , and in the B s – B s system to be Δ m s = 17.77 ± 0.10 (stat) ± 0.07 (syst) / picosecond measured by CDF experiment at Fermilab . A first estimation of

1054-419: Is called the Standard Model . The reconciliation of gravity to the current particle physics theory is not solved; many theories have addressed this problem, such as loop quantum gravity , string theory and supersymmetry theory . Practical particle physics is the study of these particles in radioactive processes and in particle accelerators such as the Large Hadron Collider . Theoretical particle physics

1116-597: Is determined by a large dipole magnet with the main field component in the vertical direction. [REDACTED] The Vertex Locator (VELO) is built around the proton interaction region. It is used to measure the particle trajectories close to the interaction point in order to precisely separate primary and secondary vertices. The detector operates at 7 millimetres (0.28 in) from the LHC beam. This implies an enormous flux of particles; VELO has been designed to withstand integrated fluences of more than 10  p/cm per year for

1178-532: Is explained by the Standard Model , which gained widespread acceptance in the mid-1970s after experimental confirmation of the existence of quarks . It describes the strong , weak , and electromagnetic fundamental interactions , using mediating gauge bosons . The species of gauge bosons are eight gluons , W , W and Z bosons , and the photon . The Standard Model also contains 24 fundamental fermions (12 particles and their associated anti-particles), which are

1240-591: Is in model building where model builders develop ideas for what physics may lie beyond the Standard Model (at higher energies or smaller distances). This work is often motivated by the hierarchy problem and is constrained by existing experimental data. It may involve work on supersymmetry , alternatives to the Higgs mechanism , extra spatial dimensions (such as the Randall–Sundrum models ), Preon theory, combinations of these, or other ideas. Vanishing-dimensions theory

1302-454: Is not a B meson, but rather bottomonium , which is something else entirely. Each B meson has an antiparticle that is composed of a bottom quark and an up ( B ), down ( B ), strange ( B s ) or charm ( B c ) antiquark respectively. The neutral B mesons, B and B s , spontaneously transform into their own antiparticles and back. This phenomenon

SECTION 20

#1732851191135

1364-497: Is placed before and after the dipole magnet. It is used to reconstruct the trajectories of charged particles and to measure their momenta. The tracker consists of three subdetectors: Following the tracking system is RICH-2. It allows the identification of the particle type of high-momentum tracks. The electromagnetic and hadronic calorimeters provide measurements of the energy of electrons , photons , and hadrons . These measurements are used at trigger level to identify

1426-482: Is the first time CP violation is seen in decays of particles other than kaons or B mesons. The rate of the observed CP asymmetry is at the upper edge of existing theoretical predictions, which triggered some interest among particle theorists regarding possible impact of physics beyond the Standard Model. In 2020, LHCb announced discovery of time-dependent CP violation in decays of B s mesons. The oscillation frequency of B s mesons to its antiparticle and vice versa

1488-579: Is the primary design goal of the LHCb experiment. As of 2021, LHCb measurements confirm with a remarkable precision the picture described by the CKM unitarity triangle . The angle γ ( α 3 ) {\displaystyle \gamma \,\,(\alpha _{3})} of the unitarity triangle is now known to about 4°, and is in agreement with indirect determinations. In 2019, LHCb announced discovery of CP violation in decays of charm mesons. This

1550-471: Is the study of these particles in the context of cosmology and quantum theory . The two are closely interrelated: the Higgs boson was postulated by theoretical particle physicists and its presence confirmed by practical experiments. The idea that all matter is fundamentally composed of elementary particles dates from at least the 6th century BC. In the 19th century, John Dalton , through his work on stoichiometry , concluded that each element of nature

1612-600: Is used to extract the parameters of the Standard Model with less uncertainty. This work probes the limits of the Standard Model and therefore expands scientific understanding of nature's building blocks. Those efforts are made challenging by the difficulty of calculating high precision quantities in quantum chromodynamics . Some theorists working in this area use the tools of perturbative quantum field theory and effective field theory , referring to themselves as phenomenologists . Others make use of lattice field theory and call themselves lattice theorists . Another major effort

1674-544: The atomic nuclei are baryons – the neutron is composed of two down quarks and one up quark, and the proton is composed of two up quarks and one down quark. A baryon is composed of three quarks, and a meson is composed of two quarks (one normal, one anti). Baryons and mesons are collectively called hadrons . Quarks inside hadrons are governed by the strong interaction, thus are subjected to quantum chromodynamics (color charges). The bounded quarks must have their color charge to be neutral, or "white" for analogy with mixing

1736-468: The universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons , and electrons and electron neutrinos . The three fundamental interactions known to be mediated by bosons are electromagnetism ,

1798-401: The weak interaction , and the strong interaction . Quarks cannot exist on their own but form hadrons . Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons . Two baryons, the proton and the neutron , make up most of the mass of ordinary matter. Mesons are unstable and the longest-lived last for only a few hundredths of

1860-514: The "doubly charmed" baryon Ξ c c + + {\displaystyle \Xi _{\rm {cc}}^{++}} in 2017, being a first known baryon with two heavy quarks; and of the fully-charmed tetraquark T c c c c {\displaystyle \mathrm {T} _{\rm {cccc}}} in 2020, made of two charm quarks and two charm antiquarks. Studies of charge-parity (CP) violation in B-meson decays

1922-459: The B ;mesons are sensitive to physics processes outside the standard model . Measuring these rare branching fractions sets limits on new particles. The LHCb experiment has observed and searched for several of these decays such as B s → μ μ. On 21 February 2017, the LHCb collaboration announced that the rare decay of a neutral B meson into two oppositely charged kaons had been observed to

B meson - Misplaced Pages Continue

1984-532: The Fermi National Accelerator Laboratory reported that the oscillations decayed into matter 1% more often than into antimatter, which may help explain the abundance of matter over antimatter in the observed Universe. However, more recent results at LHCb with larger data samples have suggested no significant deviation from the Standard Model. B mesons are an important probe for exploring quantum chromodynamics . Various uncommon decay paths of

2046-408: The Standard Model during the 1970s, physicists clarified the origin of the particle zoo. The large number of particles was explained as combinations of a (relatively) small number of more fundamental particles and framed in the context of quantum field theories . This reclassification marked the beginning of modern particle physics. The current state of the classification of all elementary particles

2108-410: The VELO volume, making it similar to a fixed-target experiment; this setup is usually referred to as "SMOG". These datasets allow the collaboration to carry out the physics programme of precision Standard Model tests with many additional measurements. As of 2021, LHCb has published more than 500 scientific papers. LHCb is designed to study beauty and charm hadrons . In addition to precision studies of

2170-571: The aforementioned color confinement, gluons are never observed independently. The Higgs boson gives mass to the W and Z bosons via the Higgs mechanism – the gluon and photon are expected to be massless . All bosons have an integer quantum spin (0 and 1) and can have the same quantum state . Most aforementioned particles have corresponding antiparticles , which compose antimatter . Normal particles have positive lepton or baryon number , and antiparticles have these numbers negative. Most properties of corresponding antiparticles and particles are

2232-403: The border from Geneva . The (small) MoEDAL experiment shares the same cavern. The experiment has wide physics program covering many important aspects of heavy flavour (both beauty and charm), electroweak and quantum chromodynamics (QCD) physics. Six key measurements have been identified involving B mesons. These are described in a roadmap document that formed the core physics programme for

2294-402: The bottom (1977) and top (1995) quarks were discovered. Surprisingly, the bizarre behavior of the B s (pronounced "B sub s") mesons is actually predicted by the Standard Model of fundamental particles and forces. The discovery of this oscillatory behavior is thus another reinforcement of the Standard Model's durability ... CDF physicists have previously measured the rate of

2356-584: The constituents of all matter . Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson . On 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson. The Standard Model, as currently formulated, has 61 elementary particles. Those elementary particles can combine to form composite particles, accounting for

2418-949: The decays in question are very rare, a larger dataset needs to be analysed in order to make definitive conclusions. In March 2021, LHCb announced that the anomaly in lepton universality crossed the "3 sigma " statistical significance threshold, which translates to a p-value of 0.1%. The measured value of R K = B ( B + → K + μ + μ − ) B ( B + → K + e + e − ) {\displaystyle R_{\rm {K}}={\frac {{\mathcal {B}}(\mathrm {B} ^{+}\to \mathrm {K} ^{+}\mu ^{+}\mu ^{-})}{{\mathcal {B}}(\mathrm {B} ^{+}\to \mathrm {K} ^{+}\mathrm {e} ^{+}\mathrm {e} ^{-})}}} , where symbol B {\displaystyle {\mathcal {B}}} denotes probability of

2480-447: The development of nuclear weapons . Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the " particle zoo ". Important discoveries such as the CP violation by James Cronin and Val Fitch brought new questions to matter-antimatter imbalance . After the formulation of

2542-478: The first experimental deviations from the Standard Model, since neutrinos do not have mass in the Standard Model. Modern particle physics research is focused on subatomic particles , including atomic constituents, such as electrons , protons , and neutrons (protons and neutrons are composite particles called baryons , made of quarks ), that are produced by radioactive and scattering processes; such particles are photons , neutrinos , and muons , as well as

B meson - Misplaced Pages Continue

2604-432: The first high energy LHC running in 2010–2012. They include: The fact that the two b-hadrons are predominantly produced in the same forward cone is exploited in the layout of the LHCb detector. The LHCb detector is a single arm forward spectrometer with a polar angular coverage from 10 to 300 milliradians (mrad) in the horizontal and 250 mrad in the vertical plane. The asymmetry between the horizontal and vertical plane

2666-430: The forward region. The LHCb collaborators, who built, operate and analyse data from the experiment, are composed of approximately 1650 people from 98 scientific institutes, representing 22 countries. Vincenzo Vagnoni succeeded on July 1, 2023 as spokesperson for the collaboration from Chris Parkes (spokesperson 2020–2023). The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire , France just over

2728-538: The gravitational interaction, but it has not been detected or completely reconciled with current theories. Many other hypothetical particles have been proposed to address the limitations of the Standard Model. Notably, supersymmetric particles aim to solve the hierarchy problem , axions address the strong CP problem , and various other particles are proposed to explain the origins of dark matter and dark energy . The world's major particle physics laboratories are: Theoretical particle physics attempts to develop

2790-424: The hundreds of other species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature and that a more fundamental theory awaits discovery (See Theory of Everything ). In recent years, measurements of neutrino mass have provided

2852-433: The interactions between the quarks store energy which can convert to other particles when the quarks are far apart enough, quarks cannot be observed independently. This is called color confinement . There are three known generations of quarks (up and down, strange and charm , top and bottom ) and leptons (electron and its neutrino, muon and its neutrino , tau and its neutrino ), with strong indirect evidence that

2914-468: The known particles such as mysterious X(3872) , a number of new hadrons have been discovered by the experiment. As of 2021, all four LHC experiments have discovered about 60 new hadrons in total, vast majority of which by LHCb. In 2015, analysis of the decay of bottom lambda baryons (Λ b ) in the LHCb experiment revealed the apparent existence of pentaquarks , in what was described as an "accidental" discovery. Other notable discoveries are those of

2976-402: The latter have sizeable uncertainties. In the Standard Model, couplings of charged leptons (electron, muon and tau lepton) to the gauge bosons are expected to be identical, with the only difference emerging from the lepton masses. This postulate is referred to as "lepton flavour universality". As a consequence, in decays of b hadrons, electrons and muons should be produced at similar rates, and

3038-496: The lower and upper limit of the B s – B s system value have been made by the DØ experiment also at Fermilab . On 25 September 2006, Fermilab announced that they had claimed discovery of previously-only-theorized B s meson oscillation. According to Fermilab's press release: This first major discovery of Run 2 continues the tradition of particle physics discoveries at Fermilab, where

3100-471: The matter-antimatter transitions for the B s meson, which consists of the heavy bottom quark bound by the strong nuclear interaction to a strange antiquark. Now they have achieved the standard for a discovery in the field of particle physics, where the probability for a false observation must be proven to be less than about 5 in 10 million ( ⁠ 5 / 10 000 000 ⁠ = ⁠ 1 / 2 000 000 ⁠ ). For CDF's result

3162-497: The models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments (see also theoretical physics ). There are several major interrelated efforts being made in theoretical particle physics today. One important branch attempts to better understand the Standard Model and its tests. Theorists make quantitative predictions of observables at collider and astronomical experiments, which along with experimental measurements

SECTION 50

#1732851191135

3224-527: The particles with large transverse momentum (high-Pt particles). The muon system is used to identify and trigger on muons in the events. At the end of 2018, the LHC was shut down for upgrades, with a restart currently planned for early 2022. For the LHCb detector, almost all subdetectors are to be modernised or replaced. It will get a fully new tracking system composed of a modernised vertex locator, upstream tracker (UT) and scintillator fibre tracker (SciFi). The RICH detectors will also be updated, as well as

3286-483: The photon or gluon, have no antiparticles. Quarks and gluons additionally have color charges, which influences the strong interaction. Quark's color charges are called red, green and blue (though the particle itself have no physical color), and in antiquarks are called antired, antigreen and antiblue. The gluon can have eight color charges , which are the result of quarks' interactions to form composite particles (gauge symmetry SU(3) ). The neutrons and protons in

3348-426: The primary colors . More exotic hadrons can have other types, arrangement or number of quarks ( tetraquark , pentaquark ). An atom is made from protons, neutrons and electrons. By modifying the particles inside a normal atom, exotic atoms can be formed. A simple example would be the hydrogen-4.1 , which has one of its electrons replaced with a muon. The graviton is a hypothetical particle that can mediate

3410-464: The probability is even smaller, at 8 in 100 million ( ⁠ 8 / 100 000 000 ⁠ = ⁠ 1 / 12 500 000 ⁠ ). Ronald Kotulak, writing for the Chicago Tribune , called the particle "bizarre" and stated that the meson "may open the door to a new era of physics" with its proven interactions with the "spooky realm of antimatter". On 14 May 2010, physicists at

3472-444: The same, with a few gets reversed; the electron's antiparticle, positron, has an opposite charge. To differentiate between antiparticles and particles, a plus or negative sign is added in superscript . For example, the electron and the positron are denoted e and e . When a particle and an antiparticle interact with each other, they are annihilated and convert to other particles. Some particles, such as

3534-634: The small difference due to the lepton masses is precisely calculable. LHCb has found deviations from this predictions by comparing the rate of the decay B + → K + μ + μ − {\displaystyle \mathrm {B} ^{+}\to \mathrm {K} ^{+}\mu ^{+}\mu ^{-}} to that of B + → K + e + e − {\displaystyle \mathrm {B} ^{+}\to \mathrm {K} ^{+}\mathrm {e} ^{+}\mathrm {e} ^{-}} , and in similar processes. However, as

3596-412: The whole detector electronics. However, the most important change is the switch to the fully software trigger of the experiment, which means that every recorded collision will be analysed by sophisticated software programmes without an intermediate hardware filtering step (which was found to be a bottleneck in the past). During the 2011 proton-proton run, LHCb recorded an integrated luminosity of 1 fb at

3658-678: Was composed of a single, unique type of particle. The word atom , after the Greek word atomos meaning "indivisible", has since then denoted the smallest particle of a chemical element , but physicists later discovered that atoms are not, in fact, the fundamental particles of nature, but are conglomerates of even smaller particles, such as the electron . The early 20th century explorations of nuclear physics and quantum physics led to proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn ), and nuclear fusion by Hans Bethe in that same year; both discoveries also led to

3720-516: Was found close to the Standard Model predictions. This measurement has harshly limited the possible parameter space of supersymmetry theories, which have predicted a large enhancement in rate. Since then, LHCb has published several papers with more precise measurements in this decay mode. Anomalies were found in several rare decays of B mesons. The most famous example in the so-called P 5 ′ {\displaystyle \mathrm {P} _{5}^{'}} angular observable

3782-428: Was found in the decay B 0 → K ∗ 0 μ + μ − {\displaystyle \mathrm {B} ^{0}\to \mathrm {K} ^{*0}\mu ^{+}\mu ^{-}} , where the deviation between the data and theoretical prediction has persisted for years. The decay rates of several rare decays also differ from the theoretical predictions, though

SECTION 60

#1732851191135

3844-582: Was measured to a great precision in 2021. Rare decays are the decay modes harshly suppressed in the Standard Model, which makes them sensitive to potential effects from yet unknown physics mechanisms. In 2014, LHCb and CMS experiments published a joint paper in Nature announcing the discovery of the very rare decay B s 0 → μ + μ − {\displaystyle \mathrm {B} _{\rm {s}}^{0}\to \mu ^{+}\mu ^{-}} , rate of which

#134865