8,549 research outputs found

    Perspectives in Polarized Leptoproduction

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    We discuss specific observables that can be measured in deep inelastic leptoproduction in the case of 1-particle inclusive measurements, namely azimuthal asymmetries and power-suppressed (higher twist) corrections. These quantities contain information on the intrinsic transverse momentum of partons, with close connection to the gluon dynamics in hadrons.Comment: 10 pages with figures, LaTex, uses espcrc1.sty and epsfig.sty. Invited talk at the workshop on The Structure of the Nucleon (NUCLEON99), Frascati, June 7-9, 199

    Color entanglement for azimuthal asymmetries in the Drell-Yan process

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    In the resummation of collinear gluons emitted together with active partons from the hadrons in the Drell-Yan process (DY) effects of color entanglement become important when the transverse directions are taken into account. It is then no longer possible to write the cross section as the convolution of two soft correlators and a hard part. We show that the color entanglement introduces additional color factors that must be taken into account in the extraction of transverse momentum dependent parton distribution functions (TMD PDFs) from azimuthal asymmetries. Examples where such effects matter are the extraction of the double Sivers and double Boer-Mulders asymmetries. Furthermore, we will argue why this color entanglement is a basic ingredient already in the tree-level description of azimuthal asymmetries.Comment: 5 pages, minor corrections and updated reference

    Measurement of the W boson mass and width in DELPHI at LEP

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    A measurement of the W boson mass and width has been performed by the DELPHI collaboration. During the years 1997-1999 DELPHI collected data with an integrated luminosity of 435 pb-1 at center-of-mass energies ranging from 183 to 202 GeV. LEP is currently running at energies up to 208 GeV. The DELPHI analysis and preliminary numbers presented at ICHEP 2000, Osaka, are discussed and an overview is given of improvements in statistical sensitivity and determination of systematic errors to be expected for the final analysis of the total LEP2 data sample. (5 refs)

    Operator analysis of pTp_T-widths of TMDs

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    Transverse momentum dependent (TMD) parton distribution functions (PDFs), TMDs for short, are defined as the Fourier transform of matrix elements of nonlocal combinations of quark and gluon fields. The nonlocality is bridged by gauge links, which for TMDs have characteristic paths (future or past pointing), giving rise to a process dependence that breaks universality. It is possible, however, to construct sets of universal TMDs of which in a given process particular combinations are needed with calculable, process-dependent, coefficients. This occurs for both T-odd and T-even TMDs, including also the {\it unpolarized} quark and gluon TMDs. This extends the by now well-known example of T-odd TMDs that appear with opposite sign in single-spin azimuthal asymmetries in semi-inclusive deep inelastic scattering or in the Drell-Yan process. In this paper we analyze the cases where TMDs enter multiplied by products of two transverse momenta, which includes besides the pTp_T-broadening observable, also instances with rank two structures. To experimentally demonstrate the process dependence of the latter cases requires measurements of second harmonic azimuthal asymmetries, while the pTp_T-broadening will require measurements of processes beyond semi-inclusive deep inelastic scattering or the Drell-Yan process. Furthermore, we propose specific quantities that will allow for theoretical studies of the process dependence of TMDs using lattice QCD calculations.Comment: 10 pages, no figures; expanded discussions, matches version accepted by JHE

    Universality of TMD distribution functions of definite rank

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    Transverse momentum dependent (TMD) distribution and fragmentation functions are described as Fourier transforms of matrix elementscontaining nonlocal combinations of quark and gluon fields. These matrix elements also contain a gauge link operator with a process dependent path, of which the process dependence that can be traced back to the color flow in the process. Expanding into irreducible tensors built from the transverse momenta p_\st, we can define a universal set of TMD correlators of definite rank with a well-defined operator structure.Comment: 6 pages, to be published in proceedings of the Third Worshop on the QCD Structure of the Nucleon (QCD N'12), Bilbao, Spain, 22-26 October 201

    Universality of TMD correlators

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    In a high-energy scattering process with hadrons in the initial state, color is involved. Transverse momentum dependent distribution functions (TMDs) describe the quark and gluon distributions in these hadrons in momentum space with the inclusion of transverse directions. Apart from the (anti)-quarks and gluons that are involved in the hard scattering process, additional gluon emissions by the hadrons have to be taken into account as well, giving rise to Wilson lines or gauge links. The TMDs involved are sensitive to the process under consideration and hence potentially nonuniversal due to these Wilson line interactions with the hard process; different hard processes give rise to different Wilson line structures. We will show that in practice only a finite number of universal TMDs have to be considered, which come in different linear combinations depending on the hard process under consideration, ensuring a generalized universality. For quarks this gives rise to three Pretzelocity functions, whereas for gluons a richer structure of functions arises.Comment: 6 pages, presented by the first author at the 4th International Workshop on Transverse Polarization Phenomena in Hard Processes (Transversity 2014), June 9-13, 2014, Chia, Italy. To appear in EPJ Web of Conference

    The Off-forward Quark-Quark Correlation Function

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    The properties of the non-forward quark-quark correlation function are examined. We derive constraints on the correlation function from the transformation properties of the fundamental fields of QCD occurring in its definition. We further develop a method to construct an ansatz for this correlator. We present the complete leading order set of generalized parton distributions in terms of the amplitudes of the ansatz. Finally we conclude that the number of independent generalized parton helicity changing distributions is four.Comment: Accepted for publication in Physical Review
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