10,267 research outputs found
Vector Boson Pair Production and Trilinear Gauge Boson Couplings - Results From the Tevatron
Direct measurements of vector boson pair production processes and trilinear
gauge boson couplings have been conducted by the CDF and DO Collaborations.
Preliminary results from searches for anomalous WW/WZ->muon-neutrino-jet-jet
and WZ->e-e-e-neutrino production are presented. 95% CL anomalous coupling
limits from previously published DO results are -0.20 < lambda < 0.20 (Delta
kappa=0) and -0.30 < Delta kappa < 0.43 (lambda=0) for Lambda=2000 GeV where
the WWgamma couplings are assumed to equal the WWZ couplings. Combined DO + LEP
experiment anomalous coupling limits are presented for the first time. 95% CL
limits are -0.16<lambda(gamma)< 0.10 (Delta kappa=0) and -0.15 < Delta
kappa(gamma) < 0.41 (lambda=0) under the assumption that the couplings are
related by the ``HISZ'' constraints. 95% CL anomalous ZZg and Zgg coupling
limits from DO are |h(30)^Z|<0.36 (h(40)^Z=0) and |h(40)^Z|<0.05 (h(30)^Z=0)
for Lambda=750 GeV. CDF reports the first observation of a ZZ event. Prospects
for Run II are discussed.Comment: Submitted to the proceedings of ICHEP 98 XXIX International
Conference on High Energy Physics, UBC, Vancouver, B.C., Canada, July 23-29,
1998. 6 page
Exclusive electroproduction and off-diagonal parton distributions
Off-diagonal parton distributions occur in several hard exclusive reactions.
They extend the study of hadron structure beyond what can be learned from
ordinary distributions and have a particularly rich spin structure. The hard
scattering subprocesses in electroproduction of mesons and of real photons
satisfy helicity selection rules, which provide powerful tools to test
leading-twist dominance at a given value of the hard scale.Comment: 7 pages, 3 figures, LaTeX2e. Talk given at the Fourth Workshop on
Quantum Chromodynamics, Paris, France, 1-6 June 199
Exclusive hadronization in gamma* gamma -> pi pi
We perform a QCD analysis of exclusive two-meson production in gamma* gamma
collisions in the kinematical domain of large photon virtuality Q^2 and small
hadronic invariant mass W^2. In these kinematics the amplitude factorizes into
a perturbative subprocess gamma* gamma -> q qbar and a two-meson distribution
amplitude. This opens the way to study new hadronic matrix elements related
with the physics of hadronization and confinement.Comment: 5 pages, 1 figure. Talk given at PHOTON 99, Freiburg, Germany, 23-27
May 1999. Eq. (8) correcte
Polarisation in deeply virtual meson production
We discuss two aspects of polarisation in hard exclusive meson production:
the leading-twist selection rule for the meson helicity, and the different
partial waves of a (pi pi)-pair which may or may not be due to the decay of a
rho.Comment: 9 pages, 1 figure. Talk given at the Workshop on Exclusive and
Semiexclusive Processes at High Momentum Transfer, Jefferson Lab, May 1999.
Remark added on the transition from two gluons to a pion pai
Massive Field-Theory Approach to Surface Critical Behavior in Three-Dimensional Systems
The massive field-theory approach for studying critical behavior in fixed
space dimensions is extended to systems with surfaces.This enables one to
study surface critical behavior directly in dimensions without having to
resort to the expansion. The approach is elaborated for the
representative case of the semi-infinite |\bbox{\phi}|^4 -vector model
with a boundary term {1/2} c_0\int_{\partial V}\bbox{\phi}^2 in the action.
To make the theory uv finite in bulk dimensions , a renormalization
of the surface enhancement is required in addition to the standard mass
renormalization. Adequate normalization conditions for the renormalized theory
are given. This theory involves two mass parameter: the usual bulk `mass'
(inverse correlation length) , and the renormalized surface enhancement .
Thus the surface renormalization factors depend on the renormalized coupling
constant and the ratio . The special and ordinary surface transitions
correspond to the limits with and ,
respectively. It is shown that the surface-enhancement renormalization turns
into an additive renormalization in the limit . The
renormalization factors and exponent functions with and
that are needed to determine the surface critical exponents of the special and
ordinary transitions are calculated to two-loop order. The associated series
expansions are analyzed by Pad\'e-Borel summation techniques. The resulting
numerical estimates for the surface critical exponents are in good agreement
with recent Monte Carlo simulations. This also holds for the surface crossover
exponent .Comment: Revtex, 40 pages, 3 figures, and 8 pictograms (included in equations
Boundary critical behavior at m-axial Lifshitz points for a boundary plane parallel to the modulation axes
The critical behavior of semi-infinite -dimensional systems with
-component order parameter and short-range interactions is
investigated at an -axial bulk Lifshitz point whose wave-vector instability
is isotropic in an -dimensional subspace of . The associated
modulation axes are presumed to be parallel to the surface, where . An appropriate semi-infinite model representing the
corresponding universality classes of surface critical behavior is introduced.
It is shown that the usual O(n) symmetric boundary term
of the Hamiltonian must be supplemented by one of the form involving a
dimensionless (renormalized) coupling constant . The implied boundary
conditions are given, and the general form of the field-theoretic
renormalization of the model below the upper critical dimension
is clarified. Fixed points describing the ordinary, special,
and extraordinary transitions are identified and shown to be located at a
nontrivial value if . The surface
critical exponents of the ordinary transition are determined to second order in
. Extrapolations of these expansions yield values of these
exponents for in good agreement with recent Monte Carlo results for the
case of a uniaxial () Lifshitz point. The scaling dimension of the surface
energy density is shown to be given exactly by , where
is the anisotropy exponent.Comment: revtex4, 31 pages with eps-files for figures, uses texdraw to
generate some graphs; to appear in PRB; v2: some references and additional
remarks added, labeling in figure 1 and some typos correcte
The Al Gamma-ray Line from Massive-Star Regions
The measurement of gamma rays from the diffuse afterglow of radioactivity
originating in massive-star nucleosynthesis is considered a laboratory for
testing models, when specific stellar groups are investigated, at known
distance and with well-constrained stellar population. Regions which have been
exploited for such studies include Cygnus, Carina, Orion, and
Scorpius-Centaurus. The Orion region hosts the Orion OB1 association and its
subgroups at about 450~pc distance. We report the detection of Al gamma
rays from this region with INTEGRAL/SPI.Comment: Contribution to Symposium "Nuclei in the Cosmos XIV", Niigata, Japan,
Jun 2016; 3 pages, 2 figures; accepted for publication in JPS (Japan Physical
Society) Conference Proceedings http://jpscp.jps.jp
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