Showing papers on "Parton published in 2002"
TL;DR: In this paper, a new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented, using a recently developed eigenvector-basis approach to the hessian method, which provides the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions.
Abstract: A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work signiflcantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errorsforbothnewandolddata sets; (ii) asystematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the hessian method. The new gluon distribution is considerably harder than that of previous standard flts. A numberofphysicsissues,particularlyrelatingtothebehaviorofthegluondistribution,are addressedinmorequantitativetermsthanbefore. Extensiveresultsontheuncertaintiesof parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, basedoncurrentknowledgeofthepartondistributions. Inparticular, theuncertaintieson the production cross sections of the W, Z at the Tevatron and the LHC are estimated to be§4% and§5%, respectively, and that of a light Higgs at the LHC to be§5%.
4,427 citations
TL;DR: In this paper, it was shown that the Sivers asymmetry vanishes due to the path-ordered exponential of the gluon field in the operator definition of parton densities.
696 citations
TL;DR: In this paper, the dipole subtraction method for calculating next-to-leading order corrections in QCD was extended to include massive partons, namely quarks, squarks and gluinos.
574 citations
01 Oct 2002
TL;DR: In this article, a new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented, using a recently developed eigenvector-basis approach to the hessian method, which provides the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions.
Abstract: A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work signiflcantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errorsforbothnewandolddata sets; (ii) asystematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the hessian method. The new gluon distribution is considerably harder than that of previous standard flts. A numberofphysicsissues,particularlyrelatingtothebehaviorofthegluondistribution,are addressedinmorequantitativetermsthanbefore. Extensiveresultsontheuncertaintiesof parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, basedoncurrentknowledgeofthepartondistributions. Inparticular, theuncertaintieson the production cross sections of the W, Z at the Tevatron and the LHC are estimated to be§4% and§5%, respectively, and that of a light Higgs at the LHC to be§5%.
441 citations
TL;DR: In this paper, the authors used all the available new precise data for deep inelastic and related hard scattering processes to perform NLO global parton analyses and found a somewhat smaller gluon at low x than previous determinations.
Abstract: We use all the available new precise data for deep inelastic and related hard scattering processes to perform NLO global parton analyses. These new data allow an improved determination of partons and, in particular, the inclusion of the recent measurements of the structure functions at HERA and of the inclusive jets at the Tevatron help to determine the gluon distribution and $\alpha_S$
better than ever before. We find a somewhat smaller gluon at low x than previous determinations and that $\alpha_S (M_Z^2) = 0.119 \pm 0.002 (\rm expt.) \pm 0.003 (\rm theory)$
.
407 citations
TL;DR: In this article, a NNLO (and a LO) global parton analysis was performed for the Tevatron high-ET jet data, and the results showed that the partons are changed by up to 10% at Q 2 = 10 GeV 2, in particular in the x < 0.01 regime.
339 citations
TL;DR: In this article, the Fourier transform of generalized parton distribution functions at xi = 0 describes the distribution of partons in the transverse plane, and the physical significance of these impact parameter dependent parton distributions is discussed.
Abstract: The Fourier transform of generalized parton distribution functions at xi=0 describes the distribution of partons in the transverse plane. The physical significance of these impact parameter dependent parton distribution functions is discussed. In particular, it is shown that they satisfy positivity constraints which justify their physical interpretation as a probability density. The generalized parton distribution H is related to the impact parameter distribution of unpolarized quarks for an unpolarized nucleon, H-tilde is related to the distribution of longitudinally polarized quarks in a longitudinally polarized nucleon, and $E$ is related to the distortion of the unpolarized quark distribution in the transverse plane when the nucleon has transverse polarization.
330 citations
TL;DR: In this paper, a new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented, which significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; and (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the Hessian method.
Abstract: A new generation of parton distribution functions with increased precision and quantitative estimates of uncertainties is presented. This work significantly extends previous CTEQ and other global analyses on two fronts: (i) a full treatment of available experimental correlated systematic errors for both new and old data sets; (ii) a systematic and pragmatic treatment of uncertainties of the parton distributions and their physical predictions, using a recently developed eigenvector-basis approach to the Hessian method. The new gluon distribution is considerably harder than that of previous standard fits. A number of physics issues, particularly relating to the behavior of the gluon distribution, are addressed in more quantitative terms than before. Extensive results on the uncertainties of parton distributions at various scales, and on parton luminosity functions at the Tevatron RunII and the LHC, are presented. The latter provide the means to quickly estimate the uncertainties of a wide range of physical processes at these high-energy hadron colliders, based on current knowledge of the parton distributions. In particular, the uncertainties on the production cross sections of the $W,Z$ at the Tevatron and the LHC are estimated to be $\pm 4%$ and $\pm 5%$ respectively, and that of a light Higgs at the LHC to be $\pm 5%$.
321 citations
TL;DR: In this article, the cross section for leptoproduction of the real photon off the nucleon, which is sensitive to the deeply virtual Compton scattering amplitude with power accuracy, is computed.
310 citations
Posted Content•
06 Apr 2002
TL;DR: In this article, a systematic error in the extraction of W$ from nuclear deep inelastic scattering of neutrinos and antineutrinos arises from higher-twist effects arising from nuclear shadowing.
Abstract: A systematic error in the extraction of $\sin^2 \theta_W$ from nuclear deep inelastic scattering of neutrinos and antineutrinos arises from higher-twist effects arising from nuclear shadowing. We explain that these effects cause a correction to the results of the recently reported significant deviation from the Standard Model that is potentially as large as the deviation claimed, and of a sign that cannot be determined without an extremely careful study of the data set used to model the input parton distribution functions.
307 citations
TL;DR: In this paper, a tree level QCD matrix elements for the production of multi jet final states and the parton shower in hadronic interactions is proposed. But this method is not suitable for the case of e+e− annihilations.
Abstract: A method is suggested to combine tree level QCD matrix elements for the production of multi jet final states and the parton shower in hadronic interactions. The method follows closely an algorithm developed recently for the case of e+e− annihilations \cite{Catani:2001cc}.
TL;DR: In this article, generalized parton distributions in the impact parameter representation, including the case of nonzero skewness, were investigated in which way they simultaneously describe longitudinal and transverse structure of a fast moving hadron.
Abstract: We study generalized parton distributions in the impact parameter representation, including the case of nonzero skewness $\xi$
. Using Lorentz invariance, and expressing parton distributions in terms of impact parameter dependent wave functions, we investigate in which way they simultaneously describe longitudinal and transverse structure of a fast moving hadron. We compare this information with the one in elastic form factors, in ordinary and in kT-dependent parton distributions.
TL;DR: In this article, it was shown that the final-state interaction effects in the single target spin asymmetry discovered by Brodsky et al. can be reproduced by either a standard light-cone gauge definition of the parton distributions with a prescription for the lightcone singularities consistent with the light cone gauge link, or a modified lightcone gauge defined with a gauge link involving the gauge potential at the spatial infinity.
TL;DR: In this article, the authors studied the production of hadronic collisions with W gauge bosons, heavy quark pairs, and n extra jets, with n up to 4 jets.
TL;DR: In this article, the MPC parton cascade technique was used to obtain a consistent numerical solution of the ultrarelativistic Boltzmann equation for the particle spectra and elliptic flow.
TL;DR: In this paper, the cross section of single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime was calculated, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear.
Abstract: We calculate the cross section of single inclusive gluon production in deep inelastic scattering at very high energies in the saturation regime, where the parton densities inside hadrons and nuclei are large and the evolution of structure functions with energy is nonlinear. The expression we obtain for the inclusive gluon production cross section is generated by this nonlinear evolution. We analyze the rapidity distribution of the produced gluons as well as their transverse momentum spectrum given by the derived expression for the inclusive cross section. We propose an ansatz for the multiplicity distribution of gluons produced in nuclear collisions which includes the effects of nonlinear evolution in both colliding nuclei.
TL;DR: In this paper, the authors studied the elliptic flow in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) in a multiphase transport model by converting the strings in the high energy density regions into partons.
Abstract: The elliptic flow in heavy ion collisions at the Relativistic Heavy Ion Collider is studied in a multiphase transport model By converting the strings in the high energy density regions into partons, we find that the final elliptic flow is sensitive to the parton scattering cross section To reproduce the large elliptic flow observed in Au+Au collisions at $\sqrt{s}=130 A\mathrm{GeV}$ requires a parton scattering cross section of about 6 mb We also study the dependence of the elliptic flow on the particle multiplicity, transverse momentum, and particle mass
TL;DR: In this article, it was shown that if parton saturation sets in at sufficiently small energy, then in nucleus-nucleus collisions at RHIC and LHC energies the cross sections of semi-hard processes should scale approximately with the number of participants.
Abstract: We argue that the suppression of high p_t hadrons discovered recently in heavy ion collisions at RHIC may be a consequence of saturation in the Color Glass Condensate. We qualitatively and semi-quantitatively describe the data, in particular, the dependence upon the number of nucleon participants. We show that if parton saturation sets in at sufficiently small energy, then in nucleus-nucleus collisions at RHIC and LHC energies the cross sections of semi-hard processes should scale approximately with the number of participants, N_{part}. Our results provide a possible explanation of both the absence of apparent jet quenching at SPS energies and its presence at RHIC. Under the same assumption we predict that in semi--central and central pA (dA) collisions at collider energies the dependence of semi--hard processes on the number of participating nucleons of the nucleus will change to \sim (N_{part}^A)^{1/2}. The forthcoming data on dA collisions will provide a crucial test of this description.
TL;DR: In this paper, a QCD analysis of the world data on polarized deep-inelastic scattering is presented in leading and next-to-leading order, where new parameterizations are derived for the quark and gluon distributions for the kinematic range x∈[10 −9,1],Q 2 ∈[1,10 6 ] GeV 2.
CERN1
TL;DR: A scaling law is established which relates medium effects in a collision of arbitrary dynamical expansion to that in an equivalent static scenario, and is calculated for typical kinematical values of the RHIC and LHC heavy ion programming medium-modified fragmentation functions for collisions with realistic dynamical Expansion.
Abstract: Medium modifications of parton fragmentation provide a novel tomographic tool for the study of the hot and dense matter created in ultrarelativistic nucleus-nucleus collisions. Their quantitative analysis, however, is complicated by the strong dynamical expansion of the collision region. Here we establish for the multiple scattering induced gluon radiation spectrum a scaling law which relates medium effects in a collision of arbitrary dynamical expansion to that in an equivalent static scenario. Based on this scaling, we calculate for typical kinematical values of the RHIC and LHC heavy ion programming medium-modified fragmentation functions for collisions with realistic dynamical expansion.
TL;DR: In this paper, a QCD analysis of the world data on polarized deep inelastic scattering is presented in leading and next-to-leading order, where new parameterizations are derived for the quark and gluon distributions for the kinematic range.
Abstract: A QCD analysis of the world data on polarized deep inelastic scattering is presented in leading and next-to-leading order. New parameterizations are derived for the quark and gluon distributions for the kinematic range $x \epsilon [10^{-9},1], Q^2 \epsilon [1,10^6] \GeV^2$. The extrapolation far outside the domain of the current measurements is given both to allow for applications at higher values of $Q^2$ and to be able to calculate integral properties of the present distributions. The values of $\Lambda_{\rm QCD}$ and $\alpha_s(M_z)$ are determined. Emphasis is put on the derivation of the fully correlated $1\sigma$ error bands for these distributions, which are also given in terms of parameterizations and are directly applicable to determine experimental errors of other polarized observables. The impact of the variation of both the renormalization and factorization scales on the value of $\alpha_s$ is studied. Finally we perform a factorization--scheme invariant QCD analysis based on the observables $g_1(x,Q^2)$ and $d g_1(x,Q^2)/d \log(Q^2)$ in next-to-leading order, which is compared to the standard analysis. A series of low moments of parton densities, accounting for error correlation, are given to allow for comparison with results from lattice simulations.
TL;DR: In this paper, it was shown that gluon exchange between the fast, outgoing partons and target spectators, which is usually assumed to be an irrelevant gauge artifact, affects the leading twist structure functions in a profound way.
Abstract: The common view that structure functions measured in deep inelastic lepton scattering are determined by the probability of finding quarks and gluons in the target is not correct in gauge theory. We show that gluon exchange between the fast, outgoing partons and target spectators, which is usually assumed to be an irrelevant gauge artifact, affects the leading twist structure functions in a profound way. This observation removes the apparent contradiction between the projectile (eikonal) and target (parton model) views of diffractive and small x_{Bjorken} phenomena. The diffractive scattering of the fast outgoing quarks on spectators in the target causes shadowing in the DIS cross section. Thus the depletion of the nuclear structure functions is not intrinsic to the wave function of the nucleus, but is a coherent effect arising from the destructive interference of diffractive channels induced by final state interactions. This is consistent with the Glauber-Gribov interpretation of shadowing as a rescattering effect.
TL;DR: In this article, the PHOBOS experiment has measured the charged particle multiplicity at midrapidity in Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of the collision centrality.
Abstract: The PHOBOS experiment has measured the charged particle multiplicity at mid-rapidity in Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of the collision centrality. Results on dN/deta(eta , are presented as a function of . As was found from similar data at sqrt(s_NN) = 130 GeV, the data can be equally well described by parton saturation models and two-component fits which include contributions that scale as Npart and the number of binary collisions, Ncoll. We compare the data at the two energies by means of the ratio R(200/130) of the charged particle multiplicity for the two different energies as a function of . For events with >100$, we find that this ratio is consistent with a constant value of 1.14+-0.01(stat.)+-0.05(syst.).
TL;DR: In this paper, the results for the differential distributions of jets from non-leptonic decays of polarized top quarks within the Standard Model, including QCD radiative corrections, were presented.
TL;DR: Using a multiphase transport model that includes both initial partonic and final hadronic interactions, the pion interferometry at the Relativistic Heavy-Ion Collider is studied and it is found that the two-pion correlation function is sensitive to the magnitude of the parton-scattering cross section.
Abstract: Using a multiphase transport model that includes both initial partonic and final hadronic interactions, we study the pion interferometry at the Relativistic Heavy-Ion Collider. We find that the two-pion correlation function is sensitive to the magnitude of the parton-scattering cross section, which controls the parton density at which the transition from the partonic to hadronic matter occurs. Also, the emission source of pions is non-Gaussian, leading to source radii that can be more than twice larger than the radius parameters extracted from a Gaussian fit to the correlation function.
TL;DR: In this article, the exclusive photoproduction of a heavy timelike photon which decays into a lepton pair was investigated, and the authors argued that the two processes are complementary for studying generalized parton distributions in the nucleon.
Abstract: We investigate the exclusive photoproduction of a heavy timelike photon which decays into a lepton pair, $\gamma p\to \ell^+\!\ell^- p$
. This can be seen as the analog of deeply virtual Compton scattering, and we argue that the two processes are complementary for studying generalized parton distributions in the nucleon. In an unpolarized experiment the angular distribution of the leptons readily provides access to the real part of the Compton amplitude. We estimate the possible size of this effect in kinematics where the Compton process should be dominated by quark exchange.
01 May 2002
TL;DR: In this article, a pedagogical introduction to the perturbative and non-perturbative aspects of quantum chromodynamics (QCD) is provided, along with a review of the historical development of the subject, covering pre-QCD ideas such as the quark and parton models, the notion of colours and the S-matrix approach.
Abstract: This book provides a pedagogical introduction to the perturbative and non-perturbative aspects of quantum chromodynamics (QCD). Introducing the basic theory and recent advances in QCD, it also reviews the historical development of the subject, covering pre-QCD ideas of strong interactions such as the quark and parton models, the notion of colours and the S-matrix approach. The author then discusses gauge theory, techniques of dimensional regularization and renormalization, deep inelastic scattering and hard processes in hadron collisions, hadron jets and e+e– annihilations. Other topics include power corrections and the technologies of the Shifman-Vainshtein-Zakharov operating product expansion. The final parts of the book are devoted to modern non-perturbative approaches to QCD and the phenomenological aspects of QCD spectral sum rules. The book will be a valuable reference for graduate students and researchers in high-energy particle and nuclear physics, both theoretical and experimental.
TL;DR: In this paper, the authors present a fully analytic calculation of the Higgs boson transverse momentum and rapidity distributions, for nonzero Higgs p⊥, at next-to-leading order in the infinite-top-mass approximation.
Abstract: We present a fully analytic calculation of the Higgs boson transverse momentum and rapidity distributions, for nonzero Higgs p⊥, at next-to-leading order in the infinite-top-mass approximation. We separate the cross section into a part that contains the dominant soft, virtual, collinear, and small-p⊥-enhanced contributions, and the remainder, which is organized by the contributions due to different parton helicities. We use this cross section to investigate analytically the small-p⊥ limit and compare with the expectation from the resummation of large logarithms of the type ln mH/p⊥. We also compute numerically the cross section at moderate p⊥ where a fixed-order calculation is reliable. We find a K-factor that varies from ≈ 1.6−1.8, and a reduction in the scale dependence, as compared to leading order. Our analysis suggests that the contribution of current parton distributions to the total uncertainty on this cross section at the LHC is probably less than that due to uncalculated higher orders.
TL;DR: In this article, the hard contribution from mini-jets is evaluated using the latest parameterization of partondistributions and nuclear shadowing, and the energy dependence of the experimental data from RHIC requires a strong nuclear shadows of the gluon distribution in this model.