1,116 research outputs found
Testing J/psi Production and Decay Properties in Hadronic Collisions
The polar and azimuthal angular distributions for the lepton pair arising
from the decay of a J/psi meson produced at transverse momentum p_T balanced by
a photon [or gluon] in hadronic collisions are calculated in the color singlet
model (CSM). It is shown that the general structure of the decay lepton
distribution is controlled by four invariant structure functions, which are
functions of the transverse momentum and the rapidity of the J/psi. We found
that two of these structure functions [the longitudinal and transverse
interference structure functions] are identical in the CSM. Analytical and
numerical results are given in the Collins-Soper and in the Gottfried-Jackson
frame. We present a Monte Carlo study of the effect of acceptance cuts applied
to the leptons and the photon for J/psi+ gamma production at the Tevatron.Comment: 22 pages (LaTeX) plus 11 postscript figures, MAD/PH/822, YUMS94-11.
Figures are available from the authors or as a compressed tar file via
anonymous ftp at phenom.physics.wisc.edu in directory
{}~pub/preprints/madph-94-822-figs.tar.
Large Hadroproduction of as a Probe of Gluon Distribution inside Proton
The transverse momentum distribution of single vector boson production at
hadron colliders provides useful ways of testing the Standard Model and
searching new physics beyond the Standard Model. We study large
hadroproduction of -boson as a probe of gluon distributions inside proton.
We investigate how to get initial gluon-involving contributions, or how to
subtract quark-quark (or -antiquark) contributions from total cross section. We
also investigated the simultaneous measurement of the rapidity and the
transverse momentum of the produced boson, to obtain momentum fractions of
initial partons. And we extracted relevant uncertainties involving in
experimental and theoretical analyses. This large hadroproduction of
can be used as constraints on analyses of global parton (gluon and quarks)
distribution functions inside proton.Comment: (a) 13 pages(LaTeX) + 1 figure ps file(3 pages):compressed, uuencoded
(b) accepted by Phys.Lett.B. (c) some figures are combined and one is
omitted. (d) conclusion part is included into abstrac
Virtual photon fragmentation functions
We introduce operator definitions for virtual photon fragmentation functions,
which are needed for reliable calculations of Drell-Yan transverse momentum
() distributions when is much larger than the invariant mass . We
derive the evolution equations for these fragmentation functions. We calculate
the leading order evolution kernels for partons to fragment into a unpolarized
as well as a polarized virtual photon. We find that fragmentation functions to
a longitudinally polarized virtual photon are most important at small , and
the fragmentation functions to a transversely polarized virtual photon dominate
the large region. We discuss the implications of this finding to the
J/ mesons' polarization at large transverse momentum.Comment: Latex, 19 pages including 6 figures. An error in the first version
has been corrected, and references update
J/Psi Decay Lepton Distribution in Hadronic Collisions
We propose the measurement of the decay angular distribution of leptons from
J/Psi's produced at high transverse momentum balanced by a photon [or gluon] in
hadronic collisions. The polar and azimuthal angular distribution are
calculated in the color singlet model (CSM). It is shown that the general
structure of the decay lepton distribution is controlled by four invariant
structure functions, which are functions of the transverse momentum and the
rapidity of the J/Psi. We found that two of these structure functions [the
longitudinal and transverse interference structure functions] are identical in
the CSM. We present analytical and numerical results in the Collins-Soper and
in the Gottfried-Jackson frame.Comment: 8 pages, RevTex, 2 figures
Initial-State Interactions in the Unpolarized Drell-Yan Process
We show that initial-state interactions contribute to the
distribution in unpolarized Drell-Yan lepton pair production and , without suppression. The asymmetry is expressed as a
product of chiral-odd distributions , where the quark-transversity function
is the transverse momentum dependent, light-cone
momentum distribution of transversely polarized quarks in an {\it unpolarized}
proton. We compute this (naive) -odd and chiral-odd distribution function
and the resulting asymmetry explicitly in a quark-scalar diquark
model for the proton with initial-state gluon interaction. In this model the
function equals the -odd (chiral-even) Sivers
effect function . This suggests that the
single-spin asymmetries in the SIDIS and the Drell-Yan process are closely
related to the asymmetry of the unpolarized Drell-Yan process,
since all can arise from the same underlying mechanism. This provides new
insight regarding the role of quark and gluon orbital angular momentum as well
as that of initial- and final-state gluon exchange interactions in hard QCD
processes.Comment: 22 pages, 6 figure
Supersymmetric effects in top quark decay into polarized W-boson
We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak
(SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal
or transverse W-boson. The corrections are presented in terms of the
longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio
\Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both
SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1%
in magnitude and they tend to have opposite signs. The corrections to the total
width \Gamma(t-->W b) are also presented for comparison with the existing
results in the literature. We find that our SUSY-EW corrections to the total
width differ significantly from previous studies: the previous studies give a
large correction of more than 10% in magnitude for a large part of the
parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added
Higher twists in the pion structure function
We calculate the QCD moments of the pion structure function using Drell-Yan
data on the quark distributions in the pion and a phenomenological model for
the resonance region. The extracted higher twist corrections are found to be
larger than those for the nucleon, contributing around 50% of the lowest moment
at Q^2=1 GeV^2.Comment: 8 pages, 3 figures, to appear in Phys. Rev.
Cage transplant experiment shows weak transport effect on relative abundance of fish community composition as revealed by eDNA metabarcoding
Protection of freshwater fish diversity is a global conservation priority in face of its alarming decline in the last decades. A crucial step to protect freshwater fish diversity is the production of prompt and precise evaluation of community composition and spatial distribution. Metabarcoding of environmental DNA (eDNA metabarcoding) generally surpasses traditional methods for documenting diversity and community composition in aquatic environments. Nevertheless, empirical evidence evaluating how eDNA transportation in water affect community composition and structure via eDNA metabarcoding data remains scarce. Using a brown trout (Salmo trutta) cage transplant experiment in the St. Lawrence River (Canada), a large fluvial system, we tested the detection and relative abundance of species’ eDNA along 15 sampling locations. We detected brown trout eDNA in five localities up to 5,000 m from the cage, but only one sampling location situated 10 m downstream and in the direct line of the cage was affected at the community composition level. This locality showed a relative abundance of brown trout eDNA of 13.1%, while the four others showed a relative abundance under 1.0%. K-means cluster analysis confirmed the impact of brown trout eDNA on community composition by separating this locality from all others. Based on species loading of a redundancy analysis, we showed that this different k-means group was associated with the high relative abundance of brown trout. No evidence of transport effect of brown trout eDNA on fish community composition was observed in any other sampling locations. Together, our results support the view that eDNA metabarcoding can be both a conveyor belt of biodiversity information and a precise tool to study the composition and structure of fish communities in river
Aspects of Two-Photon Physics at Linear e+e- Colliders
We discuss various reactions at future e+e- and gamma-gamma colliders
involving real (beamstrahlung or backscattered laser) or quasi--real
(bremsstrahlung) photons in the initial state and hadrons in the final state.
The production of two central jets with large pT is described in some detail;
we give distributions for the rapidity and pT of the jets as well as the
di--jet invariant mass, and discuss the relative importance of various initial
state configurations and the uncertainties in our predictions. We also present
results for `mono--jet' production where one jet goes down a beam pipe, for the
production of charm, bottom and top quarks, and for single production of W and
Z bosons. Where appropriate, the two--photon processes are compared with
annihilation reactions leading to similar final states. We also argue that the
behaviour of the total inelastic gamma-gamma cross section at high energies
will probably have little impact on the severity of background problems caused
by soft and semi--hard (`minijet') two--photon reactions. We find very large
differences in cross sections for all two--photon processes between existing
designs for future e+e- colliders, due to the different beamstrahlung spectra;
in particular, both designs with >1 events per bunch crossing exist.Comment: 51 pages, 13 figures(not included
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