7,074 research outputs found
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
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
Transverse momentum dependent parton distributions in a light-cone quark model
The leading twist transverse momentum dependent parton distributions (TMDs)
are studied in a light-cone description of the nucleon where the Fock expansion
is truncated to consider only valence quarks. General analytic expressions are
derived in terms of the six amplitudes needed to describe the three-quark
sector of the nucleon light-cone wave function. Numerical calculations for the
T-even TMDs are presented in a light-cone constituent quark model, and the role
of the so-called pretzelosity is investigated to produce a nonspherical shape
of the nucleon.Comment: references added and typos corrected; version to appear in Phys. Rev.
Specific Heat of Disordered Superfluid He
The specific heat of superfluid He, disordered by a silica aerogel, is
found to have a sharp discontinuity marking the thermodynamic transition to
superfluidity at a temperature reduced from that of bulk He. The
magnitude of the discontinuity is also suppressed. This disorder effect can be
understood from the Ginzburg-Landau theory which takes into account elastic
quasiparticle scattering suppressing both the transition temperature and the
amplitude of the order parameter. We infer that the limiting temperature
dependence of the specific heat is linear at low temperatures in the disordered
superfluid state, consistent with predictions of gapless excitations everywhere
on the Fermi surface.Comment: accpeted for publication in Physical Review Letter
Bounds on transverse momentum dependent distribution and fragmentation functions
We give bounds on the distribution and fragmentation functions that appear at
leading order in deep inelastic 1-particle inclusive leptoproduction or in
Drell-Yan processes. These bounds simply follow from positivity of the defining
matrix elements and are an important guidance in estimating the magnitude of
the azimuthal and spin asymmetries in these processes.Comment: 5 pages, Revtex, 3 Postscript figures, version with minor changes, to
be published in Physical Review Letter
Generalized universality of higher transverse moments of quark transverse momentum dependent correlators
The color gauge-invariant transverse momentum dependent (TMD) quark
correlators contain process dependent gauge links in the bilocal matrix
elements. In this paper, we split these process dependent correlators into
universal TMD correlators, which in turn can be parametrized in universal TMD
distribution functions. The process dependence is contained in gluonic pole
factors, of which the value is determined by the gauge link. The operator
structures of the universal TMD correlators are identified using transverse
moments. In this paper, specific results for double transverse weighting of
quark TMDs are given. In particular, we show that for a spin 1/2 target one has
three universal time-reversal even leading `pretzelocity distributions', two of
which involve double gluonic pole matrix elements and come with process
dependent gluonic pole factors. We generalize the results for single and double
weighting to TMD correlators of any specific rank, illustrating it for
unpolarized, spin 1/2 and spin 1 targets.Comment: 15 pages, minor corrections and updated reference
Dihyperon in Chiral Colour Dielectric Model
The mass of dihyperon with spin, parity and isospin
is calculated in the framework of Chiral colour dielectric model. The wave
function of the dihyperon is expressed as a product of two colour-singlet
baryon clusters. Thus the quark wave functions within the cluster are
antisymmetric. Appropriate operators are then used to antisymmetrize
inter-cluster quark wave functions. The radial part of the quark wavefunctions
are obtained by solving the the quark and dielectric field equations of motion
obtained in the Colour dielectric model. The mass of the dihyperon is computed
by including the colour magnetic energy as well as the energy due to meson
interaction. The recoil correction to the dihyperon mass is incorporated by
Peierls-Yoccoz technique. We find that the mass of the dihyperon is smaller
than the threshold by over 100 MeV. The implications of our
results on the present day relativistic heavy ion experiments is discussed.Comment: LaTeX, 13 page
- …