Topic
Parton
About: Parton is a research topic. Over the lifetime, 13484 publications have been published within this topic receiving 368877 citations.
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TL;DR: Though decreasing asymptotically as T/E with the parton energy, the relative reduction is found to be important for intermediate energies.
Abstract: Stimulated gluon emission and thermal absorption, in addition to induced radiation, are considered for an energetic parton propagating inside a quark-gluon plasma. In the presence of thermal gluons, stimulated emission reduces, while absorption increases, the parton's energy. The net effect is a reduction of the parton energy loss. Though decreasing asymptotically as $T/E$ with the parton energy, the relative reduction is found to be important for intermediate energies. The modified energy dependence of the energy loss will affect the shape of suppression of moderately high ${p}_{T}$ hadrons due to jet quenching in high-energy heavy-ion collisions.
101 citations
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TL;DR: The first combination of NLO QCD matrix elements for di-Higgs production, retaining the full top quark mass dependence, with a parton shower was presented in this paper.
Abstract: We present the first combination of NLO QCD matrix elements for di-Higgs production, retaining the full top quark mass dependence, with a parton shower. Results are provided within both the POWHEG-BOX and MadGraph5_aMC@NLO Monte Carlo frameworks. We assess in detail the theoretical uncertainties and provide differential results. We find that, as expected, the shower effects are relatively large for observables like the transverse momentum of the Higgs boson pair, which are sensitive to extra radiation. However, these shower effects are still much smaller than the differences between the Born-improved HEFT approximation and the full NLO calculation in the tails of the distributions.
101 citations
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TL;DR: In this paper, an algorithm for numerical calculation of one-loop QCD amplitudes is presented, which consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of oneloop amplitudes and a method to deform the integration contour for the loop integration into the complex space.
Abstract: We present an algorithm for the numerical calculation of one-loop QCD amplitudes. The algorithm consists of subtraction terms, approximating the soft, collinear and ultraviolet divergences of one-loop amplitudes and a method to deform the integration contour for the loop integration into the complex space. The algorithm is formulated at the amplitude level and does not rely on Feynman graphs. Therefore all required ingredients can be calculated efficiently using recurrence relations. The algorithm applies to massless partons as well as to massive partons.
101 citations
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TL;DR: In this article, the multiplicity and elliptic flow of charged particles produced in Pb-Pb collisions at center of mass energy 2.76$ TeV from the Large Hadron Collider are studied in a multiphase transport (AMPT) model.
Abstract: The multiplicity and elliptic flow of charged particles produced in Pb-Pb collisions at center of mass energy $\sqrt{{s}_{\mathit{NN}}}=2.76$ TeV from the Large Hadron Collider are studied in a multiphase transport (AMPT) model. With the standard parameters in the HIJING model, which is used as initial conditions for subsequent partonic and hadronic scatterings in the AMPT model, the resulting multiplicity of final charged particles at mid-pseudorapidity is consistent with the experimental data measured by the ALICE Collaboration. This value is, however, increased by about $25%$ if the final-state partonic and hadronic scatterings are turned off. Because of final-state scatterings, particularly those among partons, the final elliptic flow of charged hadrons is also consistent with the ALICE data if a smaller but more isotropic parton scattering cross section than previously used in the AMPT model for describing the charged hadron elliptic flow in heavy ion collisions at the Relativistic Heavy Ion Collider is used. The resulting transverse momentum spectra of charged particles as well as the centrality dependence of their multiplicity density and the elliptic flow are also in reasonable agreement with the ALICE data. Furthermore, the multiplicities, transverse momentum spectra, and elliptic flows of identified hadrons such as protons, kaons, and pions are predicted.
101 citations
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TL;DR: In this article, the authors describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation.
Abstract: We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed quarks carry all the meson's momentum at a characteristic hadronic scale and vanish as $(1\ensuremath{-}x{)}^{2}$ when Bjorken-$x\ensuremath{\rightarrow}1$. Comparing such distributions within the pion and kaon, it is apparent that the size of $SU(3)$-flavor symmetry breaking in meson parton distribution functions is modulated by the flavor dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulas may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two thirds of the pion's light-front momentum is carried by valence dressed quarks at a characteristic hadronic scale; this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of $u$-quark distributions that is in agreement with the single existing data set, and predicts a $u$-quark distribution within the pion that agrees with a modern reappraisal of $\ensuremath{\pi}N$ Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.
100 citations