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Transverse Momentum Distributions
In high energy particle physics, specifically in hadron-beam scattering experiments, transverse momentum distributions (TMDs) are the distributions of the hadron's quark or gluon momenta that are perpendicular to the momentum transfer between the beam and the hadron. Specifically, they are probability distributions to find inside the hadron a parton with a transverse momentum and longitudinal momentum fraction . TMDs provide information on the confined motion of quarks and gluons inside the hadron and complement the information on the hadron structure provided by parton distribution functions (PDFs) and generalized parton distributions (GPDs). In all, TMDs and PDFs provide the information of the momentum distribution (transverse and longitudinal, respectively) of the quarks (or gluons), and the GPDs, the information on their spatial distribution. Description, interpretation and usefulness TMDs are an extension of the concept of parton distribution functions (PDFs) and structu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Particle Physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, but 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, 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lattice QCD
Lattice QCD is a well-established non-perturbative approach to solving the quantum chromodynamics (QCD) theory of quarks and gluons. It is a lattice gauge theory formulated on a grid or lattice of points in space and time. When the size of the lattice is taken infinitely large and its sites infinitesimally close to each other, the continuum QCD is recovered. Analytic or perturbative solutions in low-energy QCD are hard or impossible to obtain due to the highly nonlinear nature of the strong force and the large coupling constant at low energies. This formulation of QCD in discrete rather than continuous spacetime naturally introduces a momentum cut-off at the order 1/''a'', where ''a'' is the lattice spacing, which regularizes the theory. As a result, lattice QCD is mathematically well-defined. Most importantly, lattice QCD provides a framework for investigation of non-perturbative phenomena such as confinement and quark–gluon plasma formation, which are intractable by means ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quantum Chromodynamics
In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of quantum field theory called a non-abelian gauge theory, with symmetry group SU(3). The QCD analog of electric charge is a property called ''color''. Gluons are the force carriers of the theory, just as photons are for the electromagnetic force in quantum electrodynamics. The theory is an important part of the Standard Model of particle physics. A large body of experimental evidence for QCD has been gathered over the years. QCD exhibits three salient properties: * Color confinement. Due to the force between two color charges remaining constant as they are separated, the energy grows until a quark–antiquark pair is spontaneously produced, turning the initial hadron into a pair of hadrons instead of isolating a color charge. Although ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron–ion Collider
An electron–ion collider (EIC) is a type of particle accelerator collider designed to collide spin-polarized beams of electrons and ions, in order to study the properties of nuclear matter in detail via deep inelastic scattering. In 2012, a whitepaperA. Accardi et al., "Electron Ion Collider: The Next QCD Frontier – Understanding the glue that binds us all" 2012. was published, proposing the developing and building of an EIC accelerator, and in 2015, the Nuclear Science Advisory Committee (NSAC) named the construction of an electron–ion collider one of the top ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Jefferson Lab
Thomas Jefferson National Accelerator Facility (TJNAF), commonly called Jefferson Lab or JLab, is a US National Laboratory located in Newport News, Virginia. Its stated mission is "to provide forefront scientific facilities, opportunities and leadership essential for discovering the fundamental structure of nuclear matter; to partner in industry to apply its advanced technology; and to serve the nation and its communities through education and public outreach." Since June 1, 2006, it has been operated by Jefferson Science Associates, LLC, a limited liability company created by Southeastern Universities Research Association and PAE Applied Technologies. Until 1996 it was known as the Continuous Electron Beam Accelerator Facility (CEBAF); commonly, this name is still used for the main accelerator. Founded in 1984, Jefferson Lab employs more than 750 people, and more than 2,000 scientists from around the world have conducted research using the facility. History The facility w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
COMPASS Experiment
The NA58 experiment, or COMPASS (standing for "Common Muon and Proton Apparatus for Structure and Spectroscopy") is a 60-metre-long fixed-target experiment at the M2 beam line of the SPS at CERN. The experimental hall is located at the CERN North Area, close to the French village of Prévessin-Moëns. The experiment is a two-staged spectrometer with numerous tracking detectors, particle identification and calorimetry. The physics results are extracted by recording and analysing the final states of the scattering processes. The versatile set-up, the use of different targets and particle beams allow the investigation of various processes. The main physics goals are the investigation of the nucleon spin structure and hadron spectroscopy. The collaboration consists of 220 physicists from 13 different countries, involving 28 universities and research institutes. History and physics goals The COMPASS experiment was proposed in 1996 and approved by the CERN research committee. Betwee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CERN
The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Geneva, on the France–Switzerland border. It comprises 23 member states, and Israel (admitted in 2013) is currently the only non-European country holding full membership. CERN is an official United Nations General Assembly observer. The acronym CERN is also used to refer to the laboratory; in 2019, it had 2,660 scientific, technical, and administrative staff members, and hosted about 12,400 users from institutions in more than 70 countries. In 2016, CERN generated 49 petabytes of data. CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research — consequently, numerous experiments have been constructed at CERN through international collaborations. CERN is the site of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HERMES Experiment
HERMES was an experiment conducted using the HERA particle accelerator located at the German national laboratory DESY in Hamburg. The experiment's goal was to investigate the quark-gluon structure of matter by examining how a nucleon's constituents affect its spin. It later developed into a pioneering experiment for measuring generalised parton parton distributions and a general-purpose experiment for the study of QCD processes. HERMES completed its first run between 1995 and 2000, and a second run began in 2001 and ended during the summer of 2007. HERMES was conducted by scientists from more than 13 countries. Method Polarized electrons are fired at polarized gas targets. The virtual photon emitted by the electron was also polarized and sought out quarks of spin in the opposite direction as the photon. The asymmetry of ejected quarks was determined to deduce the net polarisation of the quarks. UGFS The unpolarized gas feed system (UGFS) was used for non polarized "end of fil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DESY
The Deutsches Elektronen-Synchrotron (English ''German Electron Synchrotron''), commonly referred to by the abbreviation DESY, is a national research center in Germany. It operates particle accelerators used to investigate the structure of matter, and conducts a broad spectrum of inter-disciplinary scientific research in three main areas: particle and high energy physics; photon science, and the development, construction and operation of particle accelerators. Its name refers to its first project, an electron synchrotron. DESY is publicly financed by the Federal Republic of Germany, the States of Germany, and the German Research Foundation (DFG). DESY is a member of the Helmholtz Association and operates at sites in Hamburg and Zeuthen. Functions DESY's function is to conduct fundamental research. It specializes in particle accelerator development, construction and operation, particle physics research to explore the fundamental characteristics of matter and forces, including ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fragmentation Function
In a sufficiently hard interaction between particles, the cross section can be factorized into parton distribution functions (PDFs), the hard scattering part, and fragmentation functions. The fragmentation functions, as are the PDFs, are non-perturbative functions describing the production of a given observed final state. In a leading order picture, it can be interpreted as the probability that the observed final state originates from a given quark or gluon. See also *Proton structure function The structure function (also known as the proton structure function), like the fragmentation function, is a probability density function in physics. It is somewhat analogous to the structure factor in solid-state physics, and the form factor (quant ... References Functions related to probability distributions {{particle-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scattering Cross-section
In physics, the cross section is a measure of the probability that a specific process will take place when some kind of radiant excitation (e.g. a particle beam, sound wave, light, or an X-ray) intersects a localized phenomenon (e.g. a particle or density fluctuation). For example, the Rutherford cross-section is a measure of probability that an alpha particle will be deflected by a given angle during an interaction with an atomic nucleus. Cross section is typically denoted ( sigma) and is expressed in units of area, more specifically in barns. In a way, it can be thought of as the size of the object that the excitation must hit in order for the process to occur, but more exactly, it is a parameter of a stochastic process. In classical physics, this probability often converges to a deterministic proportion of excitation energy involved in the process, so that, for example, with light scattering off of a particle, the cross section specifies the amount of optical power scattered ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hadronization
Hadronization (or hadronisation) is the process of the formation of hadrons out of quarks and gluons. There are two main branches of hadronization: quark-gluon plasma (QGP) transformation and colour string decay into hadrons. The transformation of quark-gluon plasma into hadrons is studied in lattice QCD numerical simulations, which are explored in relativistic heavy-ion experiments. Quark-gluon plasma hadronization occurred shortly after the Big Bang when the quark–gluon plasma cooled down to the Hagedorn temperature (about 150 MeV) when free quarks and gluons cannot exist. In string breaking new hadrons are forming out of quarks, antiquarks and sometimes gluons, spontaneously created from the vacuum. Statistical hadronization A highly successful description of QGP hadronization is based on statistical phase space weighting according to the Fermi–Pomeranchuk model of particle production. This approach was developed, since 1950, initially as a qualitative descriptio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
