31 research outputs found
Polarized 3 parton production in inclusive DIS at small x
Azimuthal angular correlations between produced hadrons/jets in high energy
collisions are a sensitive probe of the dynamics of QCD at small x. Here we
derive the triple differential cross section for inclusive production of 3
polarized partons in DIS at small x using the spinor helicity formalism. The
target proton or nucleus is described using the Color Glass Condensate (CGC)
formalism. The resulting expressions are used to study azimuthal angular
correlations between produced partons in order to probe the gluon structure of
the target hadron or nucleus. Our analytic expressions can also be used to
calculate the real part of the Next to Leading Order (NLO) corrections to
di-hadron production in DIS by integrating out one of the three final state
partons.Comment: 5 pages, 6 figures; version accepted for publication in Physics
Letters
Feynman parametrization and Mellin summation at finite temperature
We show that the Mellin summation technique (MST) is a well defined and
useful tool to compute loop integrals at finite temperature in the
imaginary-time formulation of thermal field theory, especially when interested
in the infrared limit of such integrals. The method makes use of the Feynman
parametrization which has been claimed to have problems when the analytical
continuation from discrete to arbitrary complex values of the Matsubara
frequency is performed. We show that without the use of the MST, such problems
are not intrinsic to the Feynman parametrization but instead, they arise as a
result of (a) not implementing the periodicity brought about by the possible
values taken by the discrete Matsubara frequencies before the analytical
continuation is made and (b) to the changing of the original domain of the
Feynman parameter integration, which seemingly simplifies the expression but in
practice introduces a spurious endpoint singularity. Using the MST, there are
no problems related to the implementation of the periodicity but instead, care
has to be taken when the sum of denominators of the original amplitude
vanishes. We apply the method to the computation of loop integrals appearing
when the effects of external weak magnetic fields on the propagation of scalar
particles is considered.Comment: 16 pages, 1 figure. Discussion expanded. References added. Published
versio
Vacuum Polarization and Dynamical Chiral Symmetry Breaking: Phase Diagram of QED with Four-Fermion Contact Interaction
We study chiral symmetry breaking for fundamental charged fermions coupled
electromagnetically to photons with the inclusion of four-fermion contact
self-interaction term. We employ multiplicatively renormalizable models for the
photon dressing function and the electron-photon vertex which minimally ensures
mass anomalous dimension = 1. Vacuum polarization screens the interaction
strength. Consequently, the pattern of dynamical mass generation for fermions
is characterized by a critical number of massless fermion flavors above which
chiral symmetry is restored. This effect is in diametrical opposition to the
existence of criticality for the minimum interaction strength necessary to
break chiral symmetry dynamically. The presence of virtual fermions dictates
the nature of phase transition. Miransky scaling laws for the electromagnetic
interaction strength and the four-fermion coupling, observed for quenched QED,
are replaced by a mean-field power law behavior corresponding to a second order
phase transition. These results are derived analytically by employing the
bifurcation analysis, and are later confirmed numerically by solving the
original non-linearized gap equation. A three dimensional critical surface is
drawn to clearly depict the interplay of the relative strengths of interactions
and number of flavors to separate the two phases. We also compute the
beta-function and observe that it has ultraviolet fixed point. The power law
part of the momentum dependence, describing the mass function, reproduces the
quenched limit trivially. We also comment on the continuum limit and the
triviality of QED.Comment: 9 pages, 10 figure
A beam-beam monitoring detector for the MPD experiment at NICA
The Multi-Purpose Detector (MPD) is to be installed at the Nuclotron Ion
Collider fAcility (NICA) of the Joint Institute for Nuclear Research (JINR).
Its main goal is to study the phase diagram of the strongly interacting matter
produced in heavy-ion collisions. These studies, while providing insight into
the physics of heavy-ion collisions, are relevant for improving our
understanding of the evolution of the early Universe and the formation of
neutron stars. In order to extend the MPD trigger capabilities, we propose to
include a high granularity beam-beam monitoring detector (BE-BE) to provide a
level-0 trigger signal with an expected time resolution of 30 ps. This new
detector will improve the determination of the reaction plane by the MPD
experiment, a key measurement for flow studies that provides physics insight
into the early stages of the reaction. In this work, we use simulated Au+Au
collisions at NICA energies to show the potential of such a detector to
determine the event plane resolution, providing further redundancy to the
detectors originally considered for this purpose namely, the Fast Forward
Detector (FFD) and the Hadron Calorimeter (HCAL). We also show our results for
the time resolution studies of two prototype cells carried out at the T10 beam
line at the CERN PS complex.Comment: 16 pages, 12 figures. Updated to published version with added
comments and correction