8,808 research outputs found
Perspectives in Polarized Leptoproduction
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
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
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 -widths of TMDs
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 -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 -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
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
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
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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