345 research outputs found
Transverse momentum dependence in gluon distribution and fragmentation functions
We investigate the twist two gluon distribution functions for spin 1/2
hadrons, emphasizing intrinsic transverse momentum of the gluons. These
functions are relevant in leading order in the inverse hard scale in scattering
processes such as inclusive leptoproduction or Drell-Yan scattering, or more
general in hard processes in which at least two hadrons are involved. They show
up in azimuthal asymmetries. For future estimates of such observables, we
discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure
Accessing Transversity in Double-Spin Asymmetries at the BNL-RHIC
We give upper bounds for transverse double-spin asymmetries in polarized
proton-proton collisions by saturating the positivity constraint for the
transversity densities at a low hadronic resolution scale. We consider prompt
photon, jet, pion, and heavy flavor production at the BNL Relativistic Heavy
Ion Collider (RHIC). Estimates of the expected statistical accuracy for such
measurements are presented, taking into account the acceptance of the RHIC
detectors.Comment: 15 pages, LaTeX, 2 figures as eps file
Investigating the origins of transverse spin asymmetries at RHIC
We discuss possible origins of transverse spin asymmetries in hadron-hadron
collisions and propose an explanation in terms of a chiral-odd T-odd
distribution function with intrinsic transverse momentum dependence, which
would signal a correlation between the transverse spin and the transverse
momentum of quarks inside an unpolarized hadron. We will argue that despite its
conceptual problems, it can account for single spin asymmetries, for example in
p + p(transversely polarized) -> pion + X, and at the same time for the large
cos(2 phi) asymmetry in the unpolarized Drell-Yan cross section, which still
lacks understanding. We use the latter asymmetry to arrive at a crude model for
this function and show explicitly how it relates unpolarized and polarized
observables in the Drell-Yan process, as could be measured with the
proton-proton collisions at RHIC. Moreover, it would provide an alternative
method of accessing the transversity distribution function h_1. For future
reference we also list the complete set of azimuthal asymmetries in the
unpolarized and polarized Drell-Yan process at leading order involving T-odd
distribution functions with intrinsic transverse momentum dependence.Comment: 14 pages, Revtex, 4 Postscript figures, uses aps.sty, epsf.sty, Minor
mistakes in cross sections corrected, Conclusions are unaffecte
Today's View on Strangeness
There are several different experimental indications, such as the
pion-nucleon sigma term and polarized deep-inelastic scattering, which suggest
that the nucleon wave function contains a hidden s bar s component. This is
expected in chiral soliton models, which also predicted the existence of new
exotic baryons that may recently have been observed. Another hint of hidden
strangeness in the nucleon is provided by copious phi production in various N
bar N annihilation channels, which may be due to evasions of the
Okubo-Zweig-Iizuka rule. One way to probe the possible polarization of hidden s
bar s pairs in the nucleon may be via Lambda polarization in deep-inelastic
scattering.Comment: 8 pages LaTeX, 10 figures, to appear in the Proceedings of the
International Conference on Parity Violation and Hadronic Structure,
Grenoble, June 200
A tetragonal-to-monoclinic phase transition in a ferroelectric perovskite: the structure of PbZr(0.52)Ti(0.48)O3
The perovskite-like ferroelectric system PbZr(1-x)Ti(x)O3 (PZT) has a nearly
vertical morphotropic phase boundary (MPB) around x=0.45-0.50. Recent
synchrotron x-ray powder diffraction measurements by Noheda et al. [Appl. Phys.
Lett. 74, 2059 (1999)] have revealed a new monoclinic phase between the
previously-established tetragonal and rhombohedral regions. In the present work
we describe a Rietveld analysis of the detailed structure of the tetragonal and
monoclinic PZT phases on a sample with x= 0.48 for which the lattice parameters
are respectively: at= 4.044 A, ct= 4.138 A, at 325 K, and am= 5.721 A, bm=
5.708 A, cm= 4.138 A, beta= 90.496 deg., at 20K. In the tetragonal phase the
shifts of the atoms along the polar [001] direction are similar to those in
PbTiO3 but the refinement indicates that there are, in addition, local
disordered shifts of the Pb atoms of ~0.2 A perpendicular to the polar axis..
The monoclinic structure can be viewed as a condensation along one of the
directions of the local displacements present in the tetragonal phase. It
equally well corresponds to a freezing-out of the local displacements along one
of the directions recently reported by Corker et al.[J. Phys. Condens.
Matter 10, 6251 (1998)] for rhombohedral PZT. The monoclinic structure
therefore provides a microscopic picture of the MPB region in which one of the
"locally" monoclinic phases in the "average" rhombohedral or tetragonal
structures freezes out, and thus represents a bridge between these two phases.Comment: REVTeX, 7 figures. Modifications after referee's suggestion: new
figure (figure 5), comments in 2nd para. (Sect.III) and in 2nd & 3rd para.
(Sect. IV-a), in the abstract: "...of ~0.2 A perpendicular to the polar
axis.
Confirmation of a pi_1^0 Exotic Meson in the \eta \pi^0 System
The exclusive reaction , at 18 GeV has been studied with a partial wave analysis on a sample
of 23~492 events from BNL experiment E852. A mass-dependent fit
is consistent with a resonant hypothesis for the wave, thus providing
evidence for a neutral exotic meson with , a mass of MeV, and a width of MeV. New
interpretations of the meson exotics in neutral system observed in
E852 and Crystal Barrel experiments are discussed.Comment: p3, rewording the paragraph (at the bottom) about the phase
variations. p4, rewording paragrath "The second method ..." . p4, at the
bottom of paragrath "The third method ..." added consistent with the results
of methods 1 and 2
A Raman Study of Morphotropic Phase Boundary in PbZr1-xTixO3 at low temperatures
Raman spectra of PbZr1-xTixO3 ceramics with titanium concentration varying
between 0.40 and 0.60 were measured at 7 K. By observing the
concentration-frequency dependence of vibrational modes, we identified the
boundaries among rhombohedral, monoclinic, and tetragonal ferroelectric phases.
The analysis of the spectra was made in the view of theory group analysis
making possible the assignment of some modes for the monoclinic phase.Comment: 5 pages, 4 figure
Studies on Desi and Kabuli Chickpea (Cicer arietinum L.) Cultivars.The Levels of Amylase Inhibitots, Levels of Oligosaccharides and In Vitro Starch Digestibility
Amylase inhibitor activity (AIA) of chickpea extracts was investigated
usmg pancreatic and salivary amylases. The extracts showed
higher inhibitor activity towards pancreatic amylase than salivary
amylase..Mean values indicated slightly higher inhibitory activity in
desi than kabuli cultivars, though clear-cut differences were..not
observed among- the cultivars. While in vitro starch digestibility of
meal samples indicated no large differences among desi and kabuli
types of chickpea, the mean values of digestibility of- isolated
starches of kabuli -types wasp higher than those -of desi types: The
mean values of stachyose were higher in desi cultivars. When desi
and kabuli types were considered together, stachyose- and raffmose
contents were not found significantly related to the concentrations
of total soluble sugars while stachyose showed a significant correlation
with raftinose
Stability of the monoclinic phase in the ferroelectric perovskite PbZr(1-x)TixO3
Recent structural studies of ferroelectric PbZr(1-x)TixO3 (PZT) with x= 0.48,
have revealed a new monoclinic phase in the vicinity of the morphotropic phase
boundary (MPB), previously regarded as the the boundary separating the
rhombohedral and tetragonal regions of the PZT phase diagram. In the present
paper, the stability region of all three phases has been established from high
resolution synchrotron x-ray powder diffraction measurements on a series of
highly homogeneous samples with 0.42 <=x<= 0.52. At 20K the monoclinic phase is
stable in the range 0.46 <=x<= 0.51, and this range narrows as the temperature
is increased. A first-order phase transition from tetragonal to rhombohedral
symmetry is observed only for x= 0.45. The MPB, therefore, corresponds not to
the tetragonal-rhombohedral phase boundary, but instead to the boundary between
the tetragonal and monoclinic phases for 0.46 <=x<= 0.51. This result provides
important insight into the close relationship between the monoclinic phase and
the striking piezoelectric properties of PZT; in particular, investigations of
poled samples have shown that the monoclinic distortion is the origin of the
unusually high piezoelectric response of PZT.Comment: REVTeX file, 7 figures embedde
Exotic Meson Production in the System observed in the Reaction at 18 GeV/c
This letter reports results from the partial wave analysis of the
final state in collisions at 18GeV/c.
Strong evidence is observed for production of two mesons with exotic quantum
numbers of spin, parity and charge conjugation, in the decay
channel . The mass MeV/c^2 and
width MeV/c^2 of the first state are consistent
with the parameters of the previously observed . The second
resonance with mass MeV/c^2 and width MeV/c^2 agrees very well with predictions from theoretical
models. In addition, the presence of is confirmed with mass MeV/c^2 and width MeV/c^2
and a new state, , is observed with mass
MeV/c^2 and width MeV/c^2. The decay properties of
these last two states are consistent with flux tube model predictions for
hybrid mesons with non-exotic quantum numbers
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