94 research outputs found
Enkele aspecten van vegetatie en bodem der duinen van Goeree, in het bijzonder de contactgordels tussen zout en zoet milieu
RIVON onderzoek zout zoet vegetati
The effects of changing wind regimes on the development of blowouts in the coastal dunes of The Netherlands
Physics Opportunities with the 12 GeV Upgrade at Jefferson Lab
This white paper summarizes the scientific opportunities for utilization of
the upgraded 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and
associated experimental equipment at Jefferson Lab. It is based on the 52
proposals recommended for approval by the Jefferson Lab Program Advisory
Committee.The upgraded facility will enable a new experimental program with
substantial discovery potential to address important topics in nuclear,
hadronic, and electroweak physics.Comment: 64 page
TESTING SUPERSYMMETRY AT THE NEXT LINEAR COLLIDER
Up to now, almost all discussion of supersymmetry at future colliders has
been concerned with particle searches. However, if candidates for
supersymmetric particles are found, there is much more that we will want to
know about them. Supersymmetry predicts quantitative relations among the
couplings and masses of supersymmetric particles. We discuss the prospects for
testing such relations at a future linear collider, using measurements
that exploit the availability of polarized beams. Precision tests from chargino
production are investigated in two representative cases, and sfermion and
neutralino processes are also discussed.Comment: 26pp, Revtex, 7 figures available upon request (text and figures
available as ps at ftp://preprint.slac.stanford.edu/preprints/hep-ph/9502/
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Determination of Fundamental Supersymmetry Parameters from Chargino Production at Lepii
If accessible at LEP II, chargino production is likely to be one of the few
available supersymmetric signals for many years. We consider the prospects for
the determination of fundamental supersymmetry parameters in such a scenario.
The study is complicated by the dependence of observables on a large number of
these parameters. We propose a straightforward procedure for disentangling
these dependences and demonstrate its effectiveness by presenting a number of
case studies at representative points in parameter space. Working in the
context of the minimal supersymmetric standard model, we find that chargino
production by itself is a fairly sensitive probe of the supersymmetry-breaking
sector. For significant regions of parameter space, it is possible to test the
gaugino mass unification hypothesis and to measure the gaugino contents of the
charginos and neutralinos, thereby testing the predictions of grand unification
and the viability of the lightest supersymmetric particle as a dark matter
candidate. For much of the parameter space, it is also possible to set limits
on the mass of the electron sneutrino, which provide a valuable guide for
future particle searches.Comment: 52pp, Revtex, 30 figures available upon request, SLAC-PUB-6497,
RU-94-67 (text and figures available in ps form by anonymous ftp from
preprint.slac.stanford.edu, directory pub/preprints/hep-ph/9408
Search for Associated Production of Massive States Decaying into Two Photonsin e+e- Annihilations at sqrt(s) = 88-209 GeV
A search is performed for production of short-lived particles in e+e- -> XY,
with X -> gamma gamma and Y -> ffbar, for scalar X and scalar or vector Y.
Model-independent limits in the range of 25-60 femtobarns are presented on
sigma (e+e- -> XY) x B(X -> ffbar) for centre-of-mass energies in the range
205-207 GeV. The data from all LEP centre-of-mass energies 88-209 GeV are also
interpreted in the context of fermiophobic Higgs boson models, for which a
lower mass limit of 105.5 GeV is obtained for a "benchmark" fermiophobic Higgs
boson.Comment: 17 pages, 4 figure
Physics with the KLOE-2 experiment at the upgraded DANE
Investigation at a --factory can shed light on several debated issues
in particle physics. We discuss: i) recent theoretical development and
experimental progress in kaon physics relevant for the Standard Model tests in
the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum
Mechanics from time evolution of entangled kaon states, iii) the interest for
improving on the present measurements of non-leptonic and radiative decays of
kaons and eta/eta mesons, iv) the contribution to understand the
nature of light scalar mesons, and v) the opportunity to search for narrow
di-lepton resonances suggested by recent models proposing a hidden dark-matter
sector. We also report on the physics in the continuum with the
measurements of (multi)hadronic cross sections and the study of gamma gamma
processes.Comment: 60 pages, 41 figures; added affiliation for one of the authors; added
reference to section
Updated precision measurement of the average lifetime of B hadrons
The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.
Pulsar Wind Nebulae with Bow Shocks: Non-thermal Radiation and Cosmic Ray Leptons
Pulsars with high spin-down power produce relativistic winds radiating a non-negligible fraction of this power over the whole electromagnetic range from radio to gamma-rays in the pulsar wind nebulae (PWNe). The rest of the power is dissipated in the interactions of the PWNe with the ambient interstellar medium (ISM). Some of the PWNe are moving relative to the ambient ISM with supersonic speeds producing bow shocks. In this case, the ultrarelativistic particles accelerated at the termination surface of the pulsar wind may undergo reacceleration in the converging flow system formed by the plasma outflowing from the wind termination shock and the plasma inflowing from the bow shock. The presence of magnetic perturbations in the flow, produced by instabilities induced by the accelerated particles themselves, is essential for the process to work. A generic outcome of this type of reacceleration is the creation of particle distributions with very hard spectra, such as are indeed required to explain the observed spectra of synchrotron radiation with photon indices Γ≲ 1.5. The presence of this hard spectral component is specific to PWNe with bow shocks (BSPWNe). The accelerated particles, mainly electrons and positrons, may end up containing a substantial fraction of the shock ram pressure. In addition, for typical ISM and pulsar parameters, the e+ released by these systems in the Galaxy are numerous enough to contribute a substantial fraction of the positrons detected as cosmic ray (CR) particles above few tens of GeV and up to several hundred GeV. The escape of ultrarelativistic particles from a BSPWN—and hence, its appearance in the far-UV and X-ray bands—is determined by the relative directions of the interstellar magnetic field, the velocity of the astrosphere and the pulsar rotation axis. In this respect we review the observed appearance and multiwavelength spectra of three different types of BSPWNe: PSR J0437-4715, the Guitar and Lighthouse nebulae, and Vela-like objects. We argue that high resolution imaging of such objects provides unique information both on pulsar winds and on the ISM. We discuss the interpretation of imaging observations in the context of the model outlined above and estimate the BSPWN contribution to the positron flux observed at the Earth
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