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DGLAP
The Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution equations are equations in QCD describing the variation of parton distribution functions with varying energy scales. Experimentally observed scaling violation in deep inelastic scattering is important evidence for the correctness of the equations and of QCD in general. The equations were first published in the western world by Guido Altarelli and Giorgio Parisi in 1977, and so are still sometimes called the Altarelli–Parisi equations. Only later did it become known that an equivalent formula had been published in Russia by in 1977, and by Vladimir Gribov and Lev Lipatov in 1972.V. N. Gribov, L. N. Lipatov. ''Sov. J. Nucl. Phys.'' 15:438 (1972). The DGLAP QCD evolution equations are widely used in global determinations of parton distributions, like those from the CTEQ or NNPDF collaborations. See also * Jet (particle physics) * HERA In ancient Greek religion, Hera (; grc-gre, Ἥρα, Hḗrā; gr ...
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Lev Lipatov
Lev Nikolaevich Lipatov (russian: Лев Никола́евич Липа́тов; 2 May 1940, Leningrad – 4 September 2017, Dubna) was a Russian physicist, well known for his contributions to nuclear physics and particle physics. He has been the head of Theoretical Physics Division at St. Petersburg's Nuclear Physics Institute of Russian Academy of Sciences in Gatchina and an Academician of the Russian Academy of Sciences. For the long period he worked with Vladimir Gribov, laying a basis for a field theory description of deep inelastic scattering and annihilation (Gribov-Lipatov evolution equations, later known as DGLAP, 1972). He wrote significant papers of the Pomeranchuk singularity in Quantum chromodynamics (1977) what resulted in deriving the BFKL evolution equation (Balitsky- Fadin- Kuraev-Lipatov), contributed to the study of critical phenomena (semiclassical Lipatov's approximation), the theory of tunnelling and renormalon contribution to effective couplings. He dis ...
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APFEL (Software)
APFEL is an opensource software able to perform Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (DGLAP) evolution up to next to next to leading order (NNLO) in quantum chromodynamics (QCD) and to leading order (LO) in quantum electrodynamics (QED), both with pole and minimal subtraction scheme (MSbar) masses. The coupled DGLAP QCD+QED evolution equations are solved in x-space by means of higher order interpolations and Runge-Kutta techniques, and allow the exploration of different options for the treatment of subleading terms. Main features See also *NNPDF NNPDF is the acronym used to identify the parton distribution functions from the NNPDF Collaboration. NNPDF parton densities are extracted from global fits to data based on a combination of a Monte Carlo method Monte Carlo methods, or Monte C ... References {{Reflist External links APFEL website Physics software ...
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Guido Altarelli
Guido Altarelli (12 July 1941 – 30 September 2015) was an Italian theoretical physicist. Biography Altarelli graduated in Physics from the Sapienza University of Rome in 1963 with Raoul Gatto whom he followed to the University of Florence (1965–68). He held positions at New York University (1968–69), the Rockefeller University (New York, 1969–70), the École Normale Superieure in Paris (1976–77, 81) and Boston University (1985–86). In 1970-92 he held a faculty position at the Sapienza University of Rome (full professor of theoretical physics since 1980). He was Director of the Rome Section of the INFN (1985–87). In 1992 he moved to the newly established University of Roma Tre. In 1987-2006 he was a Senior Staff Physicist at the Theory Division of CERN, and was Theory Division Leader from 2000-04. At CERN he had a leading role in the interpretation of SppS results, in the preparation of LEP and the LHC and in the theoretical analysis of the experimental resul ...
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Giorgio Parisi
Giorgio Parisi (born 4 August 1948) is an Italian theoretical physicist, whose research has focused on quantum field theory, statistical mechanics and complex systems. His best known contributions are the QCD evolution equations for parton densities, obtained with Guido Altarelli, known as the Altarelli–Parisi or DGLAP equations, the exact solution of the Sherrington–Kirkpatrick model of spin glasses, the Kardar–Parisi–Zhang equation describing dynamic scaling of growing interfaces, and the study of whirling flocks of birds. He was awarded the 2021 Nobel Prize in Physics jointly with Klaus Hasselmann and Syukuro Manabe for groundbreaking contributions to theory of complex systems, in particular "for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales." Career Giorgio Parisi received his degree from the University of Rome La Sapienza in 1970 under the supervision of Nicola Cabibbo. He was a researcher a ...
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Vladimir Gribov
Vladimir Naumovich Gribov (Russian Влади́мир Нау́мович Гри́бов; March 25, 1930, LeningradAugust 13, 1997, Budapest) was a prominent Russian theoretical physicist, who worked on high-energy physics, quantum field theory and the Regge theory of the strong interactions. His best known contributions are the pomeron, the DGLAP equations, and the Gribov copies. Life Gribov was born in Leningrad in 1930 to a Jewish family. His father died in 1938 as a result of disease. His mother, a theater worker, not an actress, brought him up alone with his younger sister. In 1941 the family was evacuated deep into the USSR and returned in 1945. In 1947, he finished school and dreamed of becoming an actor, particularly a cinema actor. He had to accept, however, his awkwardness in such things and so chose another direction: physics. In 1947, Gribov enrolled in the Physical Faculty of Leningrad University, graduating in 1952 with diploma cum laude. Despite his ability, th ...
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Parton Distribution Function
In particle physics, the parton model is a model of hadrons, such as protons and neutrons, proposed by Richard Feynman. It is useful for interpreting the cascades of radiation (a parton shower) produced from quantum chromodynamics (QCD) processes and interactions in high-energy particle collisions. Model Parton showers are simulated extensively in Monte Carlo event generators, in order to calibrate and interpret (and thus understand) processes in collider experiments. As such, the name is also used to refer to algorithms that approximate or simulate the process. Motivation The parton model was proposed by Richard Feynman in 1969 as a way to analyze high-energy hadron collisions. Any hadron (for example, a proton) can be considered as a composition of a number of point-like constituents, termed "partons". The parton model was immediately applied to electron- proton deep inelastic scattering by Bjorken and Paschos. Component particles A hadron is composed of a number of p ...
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Parton (particle Physics)
In particle physics, the parton model is a model of hadrons, such as protons and neutrons, proposed by Richard Feynman. It is useful for interpreting the cascades of radiation (a parton shower) produced from quantum chromodynamics (QCD) processes and interactions in high-energy particle collisions. Model Parton showers are simulated extensively in Monte Carlo event generators, in order to calibrate and interpret (and thus understand) processes in collider experiments. As such, the name is also used to refer to algorithms that approximate or simulate the process. Motivation The parton model was proposed by Richard Feynman in 1969 as a way to analyze high-energy hadron collisions. Any hadron (for example, a proton) can be considered as a composition of a number of point-like constituents, termed "partons". The parton model was immediately applied to electron- proton deep inelastic scattering by Bjorken and Paschos. Component particles A hadron is composed of a number of p ...
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Parton (particle Physics)
In particle physics, the parton model is a model of hadrons, such as protons and neutrons, proposed by Richard Feynman. It is useful for interpreting the cascades of radiation (a parton shower) produced from quantum chromodynamics (QCD) processes and interactions in high-energy particle collisions. Model Parton showers are simulated extensively in Monte Carlo event generators, in order to calibrate and interpret (and thus understand) processes in collider experiments. As such, the name is also used to refer to algorithms that approximate or simulate the process. Motivation The parton model was proposed by Richard Feynman in 1969 as a way to analyze high-energy hadron collisions. Any hadron (for example, a proton) can be considered as a composition of a number of point-like constituents, termed "partons". The parton model was immediately applied to electron- proton deep inelastic scattering by Bjorken and Paschos. Component particles A hadron is composed of a number of p ...
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NNPDF
NNPDF is the acronym used to identify the parton distribution functions from the NNPDF Collaboration. NNPDF parton densities are extracted from global fits to data based on a combination of a Monte Carlo method Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be determi ... for uncertainty estimation and the use of neural networks as basic interpolating functions. Methodology The NNPDF approach can be divided into four main steps: * The generation of a large sample of Monte Carlo replicas of the original experimental data, in a way that central values, errors and correlations are reproduced with enough accuracy. * The training (minimization of the \chi^2) of a set of PDFs parametrized by neural networks on each of the above MC replicas of the data. PDFs are parametrized at the initial e ...
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Jet (particle Physics)
A jet is a narrow cone of hadrons and other particles produced by the hadronization of a quark or gluon in a particle physics or heavy ion experiment. Particles carrying a color charge, such as quarks, cannot exist in free form because of quantum chromodynamics (QCD) confinement which only allows for colorless states. When an object containing color charge fragments, each fragment carries away some of the color charge. In order to obey confinement, these fragments create other colored objects around them to form colorless objects. The ensemble of these objects is called a jet, since the fragments all tend to travel in the same direction, forming a narrow "jet" of particles. Jets are measured in particle detectors and studied in order to determine the properties of the original quarks. A jet definition includes a jet algorithm and a recombination scheme. The former defines how some inputs, e.g. particles or detector objects, are grouped into jets, while the latter specifies how ...
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Deep Inelastic Scattering
Deep inelastic scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons, muons and neutrinos. It provided the first convincing evidence of the reality of quarks, which up until that point had been considered by many to be a purely mathematical phenomenon. It is a relatively new process, first attempted in the 1960s and 1970s. It is an extension of Rutherford scattering to much higher energies of the scattering particle and thus to much finer resolution of the components of the nuclei. Henry Way Kendall, Jerome Isaac Friedman and Richard E. Taylor were joint recipients of the Nobel Prize of 1990 "for their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics." Description To explain each part of the terminology, "scattering" refers t ...
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HERA
In ancient Greek religion, Hera (; grc-gre, Ἥρα, Hḗrā; grc, Ἥρη, Hḗrē, label=none in Ionic and Homeric Greek) is the goddess of marriage, women and family, and the protector of women during childbirth. In Greek mythology, she is queen of the twelve Olympians and Mount Olympus, sister and wife of Zeus, and daughter of the Titans Cronus and Rhea. One of her defining characteristics in myth is her jealous and vengeful nature in dealing with any who offend her, especially Zeus' numerous adulterous lovers and illegitimate offspring. Her iconography usually presents her as a dignified, matronly figure, upright or enthroned, crowned with a '' polos'' or diadem, sometimes veiled as a married woman. She is the patron goddess of lawful marriage. She presides over weddings, blesses and legalises marital unions, and protects women from harm during childbirth. Her sacred animals include the cow, cuckoo and the peacock. She is sometimes shown holding a pomegranate, ...
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