784 research outputs found
Bounds on QCD Instantons from HERA
Signals for processes induced by QCD instantons are searched for in HERA data
on the hadronic final state in deep-inelastic scattering. The maximally allowed
fraction of instanton induced events is found at 95% confidence level to be on
the percent level in the kinematic domain 0.0001<x<0.01 and 5 < Q-squared < 100
GeV-squared. The most stringent limits are obtained from the multiplicity
distributions.Comment: 14 pages, latex, 9 figures as ps/ep
Bounds on R-parity Violation from Resonant Slepton Production at the LHC
We consider the ATLAS and CMS searches for dijet resonances, as well as the
ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center of mass
energy. We interpret their exclusions in terms of bounds on the supersymmetric
R-parity violating parameter space. For this we focus on resonant slepton
production followed by the corresponding decay.Comment: 17 pages, 11 figures, 3 table
Soft Photoproduction Physics
Several topics of interest in soft photoproduction physics are discussed.
These include jet universality issues (particle flavour composition), the
subdivision into event classes, the buildup of the total photoproduction cross
section and the effects of multiple interactions.Comment: 10 pages, LaTeX2e, no figures, to appear in the proceedings of the
Durham Workshop on HERA Physics, ``Proton, Photon and Pomeron Structure'',
17--23 September 1995, Durham, U.
On the analytical approximation to the GLAP evolution at small x and moderate Q^2
Comparing the numerically evaluated solution to the leading order GLAP
equations with its analytical small-x approximation we have found that in the
domain covered by a large fraction of the HERA data the analytic approximation
has to be augmented by the formally non-leading term which has been usually
neglected. The corrected formula fits the data much better and provides a
natural explanation of some of the deviations from the scaling
observed in the HERA kinematical range.Comment: LaTeX, 13 pages including 6 figures, figure 5 replaced, to appear in
Phys. Lett.
Implications of Hadron Collider Observables on Parton Distribution Function Uncertainties
Standard parton distribution function sets do not have rigorously quantified
uncertainties. In recent years it has become apparent that these uncertainties
play an important role in the interpretation of hadron collider data. In this
paper, using the framework of statistical inference, we illustrate a technique
that can be used to efficiently propagate the uncertainties to new observables,
assess the compatibility of new data with an initial fit, and, in case the
compatibility is good, include the new data in the fit.Comment: 22 pages, 5 figure
Interference in Exclusive Vector Meson Production in Heavy Ion Collisions
Photons emitted from the electromagnetic fields of relativistic heavy ions
can fluctuate into quark anti-quark pairs and scatter from a target nucleus,
emerging as vector mesons. These coherent interactions are identifiable by
final states consisting of the two nuclei and a vector meson with a small
transverse momentum. The emitters and targets can switch roles, and the two
possibilities are indistinguishable, so interference may occur. Vector mesons
are negative parity so the amplitudes have opposite signs. When the meson
transverse wavelength is larger than the impact parameter, the interference is
large and destructive.
The short-lived vector mesons decay before amplitudes from the two sources
can overlap, and so cannot interfere directly. However, the decay products are
emitted in an entangled state, and the interference depends on observing the
complete final state. The non-local wave function is an example of the
Einstein-Podolsky-Rosen paradox.Comment: 13 pages with 3 figures; submitted to Physical Review Letter
A characteristic plot of pomeron-exchanged processes in diffractive DIS
The dependence of the fractal behaviors of the pomeron induced system in deep
inelastic lepton-nucleon scattering upon the diffractive kinematic variables is
found rather robust and not sensitive to the distinct parameterization of the
pomeron flux factor and structure function. A feasible experimental test of the
phenomenological pomeron-exchanged model based on the fractal measurement in
DESY collider HERA is proposed.Comment: 14 pages, 2 Postscript figure
Diffractive Phenomena and Shadowing in Deep-Inelastic Scattering
Shadowing effects in deep-inelastic lepton-nucleus scattering probe the mass
spectrum of diffractive leptoproduction from individual nucleons. We explore
this relationship using current experimental information on both processes. In
recent data from the NMC and E665 collaboration, taken at small x << 0.1 and
Q^2 < 1 GeV^2, shadowing is dominated by the diffractive excitation and
coherent interaction of low mass vector mesons. If shadowing is explored at
small x > 1 GeV^2 as discussed at HERA, the situation is
different. Here dominant contributions come from the coherent interaction of
diffractively produced heavy mass states. Furthermore we observe that the
energy dependence of shadowing is directly related to the mass dependence of
the diffractive production cross section for free nucleon targets.Comment: 12 pages Latex, 8 figure
Photoproduction off Nuclei and Point-like Photon Interactions Part I: Cross Sections and Nuclear Shadowing
High energy photoproduction off nuclear targets is studied within the
Glauber-Gribov approximation. The photon is assumed to interact as a
-system according to the Generalized Vector Dominance Model and as a
``bare photon'' in direct scattering processes with target nucleons. We
calculate total cross sections for interactions of photons with nuclei taking
into account coherence length effects and point-like interactions of the
photon. Results are compared to data on photon-nucleus cross sections, nuclear
shadowing, and quasi- elastic -production. Extrapolations of cross
sections and of the shadowing behaviour to high energies are given.Comment: 15 pages, 12 figure
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