155 research outputs found
Accessing quark helicity in and SIDIS via dihadron correlations
The correlation between the longitudinal polarization of a fragmenting quark
and the transverse momenta of the produced hadrons was predicted over two
decades ago. Nevertheless, experimental searches in the electron-positron
annihilation process, both through the so-called jet handedness measurements by
the {\tt SLD} Collaboration and more recently via the measurements of the
azimuthal asymmetry containing the helicity-dependent dihadron fragmentation
function (DiFF) by the Collaboration, did not yield a signal.
We will first discuss our recent explanation of the zero result at
, and the two new methods for accessing the helicity-dependent
DiFFs both in the electron-positron annihilation experiments, and in the
semi-inclusive deep inelastic scattering (SIDIS) experiments with a
longitudinally polarized target. We will also for the first time describe yet
another, new method for accessing the helicity-dependent DiFFs in SIDIS using
polarized beam asymmetry. Finally, we will present a new Monte Carlo
calculation of the specific Fourier moments of the helicity-dependent DiFF
entering in to the new asymmetries, performed within the extended quark-jet
model, and compare the results to those for the interference DiFF.Comment: 5 pages, 1 figure. To appear in PoS DIS201
1/Nc Expansion in QCD: Double-Line Counting Rules and the Undeservingly Discarded U(1) Ghost
The 1/Nc expansion is one of the very few methods we have for generating a
systematic expansion of QCD at the energy scale relevant to hadron structure.
The present formulation of this theory relies on the double-line notation for
calculating the leading order of a diagram in the 1/Nc expansion, where the
local SU(Nc) gauge symmetry is substituted by a U(Nc) symmetry and the
associated U(1) ghost field is ignored. In the current work we demonstrate the
insufficiency of this formulation for describing certain non-planar diagrams.
We derive a more complete set of Feynman rules that include the U(1) ghost
field and provide a useful tool for calculating both color factors and 1/Nc
orders of all color-singlet diagrams
Dihadron Fragmentation Functions in the NJL-jet model
The NJL-jet model provides a framework for calculating fragmentation
functions without introducing ad hoc parameters. Here the NJL-jet model is
extended to investigate dihadron fragmentation functions.Comment: 4 pages, 5 figures, Proceedings of 8th Circum-Pan-Pacific Symposium
on High Energy Spin Physic
Studies of Azimuthal Modulations in Two Hadron Fragmentation of a Transversely Polarised Quark
We study the azimuthal modulations of dihadron fragmentation functions
(DiFFs) of a transversely polarised quark using an NJL-jet based model that
incorporates the Collins effect for single hadron emission. The DiFFs are
extracted as Monte Carlo (MC) averages of corresponding multiplicities using
their probabilistic interpretation. To simplify the model and highlight the
possible mechanisms that create this modulation, we choose the elementary
Collins function to be proportional to the elementary unpolarised fragmentation
and a constant probability () for the quark to flip its spin after a
single hadron emission. Moreover, as a leading order calculation, only one of
the produced hadrons in the decay chain of the quark is produced with
elementary Collins modulation. We calculate the dependence of the polarised
DiFFs on various angles such as the azimuthal angle of the single hadron and
the angle of the two hadron production plane for several values of
. We observe that the polarised DiFFs for oppositely charged pion pairs
exhibit a modulation. This effect is induced purely via the
elementary Collins effect and persists even when the quark completely
depolarises after a single hadron emission (). Moreover, similar
sine modulations are present in the distribution of pion pairs with respect to
the azimuthal angle of their total transverse momentum, .Comment: 10 pages, 12 figures - small updates and added references, to comply
with the version to be published in PL
Monte-Carlo Approach to Calculating the Fragmentation Functions in NJL-Jet Model
Recent studies of the fragmentation functions using the Nambu--Jona-Lasinio
(NJL) - Jet model have been successful in describing the quark fragmentation
functions to pions and kaons. The NJL-Jet model employs the integral equation
approach to solve for the fragmentation functions in quark-cascade description
of the hadron emission process, where one assumes that the initial quark has
infinite momentum and emits an infinite number of hadrons. Here we introduce a
Monte Carlo (MC) simulation method to solve for the fragmentation functions,,
that allows us to relax the above mentioned approximations. We demonstrate that
the results of MC simulations closely reproduce the solutions of the integral
equations in the limit where a large number of hadrons are emitted in the quark
cascade. The MC approach provides a strong foundation for the further
development of the NJL-Jet model that might include many more hadronic emission
channels with decays of the possible produced resonances, as well as inclusion
of the transverse momentum dependence (TMD), all of which are of considerable
importance to the experimental studies of the transverse structure of hadrons.Comment: 5 pages, 3 figures, Proceedings of "TROPICAL QCD II Workshop
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