762 research outputs found
Decays of W Bosons to Charginos and Neutralinos
The region of the supersymmetry parameter space, in which charginos decay
predominantly into sneutrinos and leptons: chi+ -> \tilde{\nu} + l+, is not
excluded experimentally for small mass differences between charginos and
sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories
since they are either the lightest supersymmetric particles or they decay
primarily into the channel: neutrino + lightest neutralino. If the energy of
the decay leptons is so small that they escape detection, chargino events e+e-
-> chi+chi- in e+e- collisions remain invisible, eroding the excluded chargino
mass range at LEP. This region of the supersymmetry parameter space can partly
be covered by searching for single W events in e+e- -> W+W-$, with one W boson
decaying to leptons or quark jets, but the second W boson decaying to
(undetected) charginos and neutralinos.Comment: 11 pages, 3 figures, uses epsfig.st
Soil organisms in organic and conventional cropping systems.
Apesar do crescente interesse pela agricultura orgânica, são poucas as informações de pesquisa disponíveis sobre o assunto. Assim, num Argissolo Vermelho-Amarelo distrófico foram comparados os efeitos de sistemas de cultivo orgânico e convencional, para as culturas do tomate (Lycopersicum esculentum) e do milho (Zea mays), sobre a comunidade de organismos do solo e suas atividades. As populações de fungos,bactérias e actinomicetos, determinadas pela contagem de colônias em meio de cultura, foram semelhantes para os dois sistemas de produção. A atividade microbiana, avaliada pela evolução de CO2, manteve-se superior no sistema orgânico, sendo que em determinadas avaliações foi o dobro da evolução verificada no sistema convencional. O número de espécimes de minhoca foi praticamente dez vezes maior no sistema orgânico. Não foi observada diferença na taxa de decomposição de matéria orgânica entre os dois sistemas. De modo geral, o número de indivíduos de microartrópodos foi superior no sistema orgânico do que no sistema convencional, refletindo no maior índice de diversidade de Shannon. As maiores populações de insetos foram as da ordem Collembola, enquanto para os ácaros a maior população foi a da superfamília Oribatuloidea. Indivíduos dos grupos Aranae, Chilopoda, Dyplopoda, Pauropoda, Protura e Symphyla foram ocasionalmente coletados e de forma similar entre os sistemas
The Neutralino Sector in the U(1)-Extended Supersymmetric Standard Model
Motivated by grand unified theories and string theories we analyze the
general structure of the neutralino sector in the USSM, an extension of the
Minimal Supersymmetric Standard Model that involves a broken extra U(1) gauge
symmetry. This supersymmetric U(1)-extended model includes an Abelian gauge
superfield and a Higgs singlet superfield in addition to the standard gauge and
Higgs superfields of the MSSM. The interactions between the MSSM fields and the
new fields are in general weak and the mixing is small, so that the coupling of
the two subsystems can be treated perturbatively. As a result, the mass
spectrum and mixing matrix in the neutralino sector can be analyzed
analytically and the structure of this 6-state system is under good theoretical
control. We describe the decay modes of the new states and the impact of this
extension on decays of the original MSSM neutralinos, including radiative
transitions in cross-over zones. Production channels in cascade decays at the
LHC and pair production at colliders are also discussed.Comment: 50 pages, 9 figures, equations.sty include
The gauge-string duality and heavy ion collisions
I review at a non-technical level the use of the gauge-string duality to
study aspects of heavy ion collisions, with special emphasis on the trailing
string calculation of heavy quark energy loss. I include some brief
speculations on how variants of the trailing string construction could provide
a toy model of black hole formation and evaporation. This essay is an invited
contribution to "Forty Years of String Theory" and is aimed at philosophers and
historians of science as well as physicists.Comment: 21 page
Genuine Correlations of Like-Sign Particles in Hadronic Z0 Decays
Correlations among hadrons with the same electric charge produced in Z0
decays are studied using the high statistics data collected from 1991 through
1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth
order are used to measure genuine particle correlations as a function of the
size of phase space domains in rapidity, azimuthal angle and transverse
momentum. Both all-charge and like-sign particle combinations show strong
positive genuine correlations. One-dimensional cumulants initially increase
rapidly with decreasing size of the phase space cells but saturate quickly. In
contrast, cumulants in two- and three-dimensional domains continue to increase.
The strong rise of the cumulants for all-charge multiplets is increasingly
driven by that of like-sign multiplets. This points to the likely influence of
Bose-Einstein correlations. Some of the recently proposed algorithms to
simulate Bose-Einstein effects, implemented in the Monte Carlo model PYTHIA,
are found to reproduce reasonably well the measured second- and higher-order
correlations between particles with the same charge as well as those in
all-charge particle multiplets.Comment: 26 pages, 6 figures, Submitted to Phys. Lett.
The influence of a hot environment on physiological stress responses in exercise until exhaustion
Exhaustive exercise in a hot environment can impair performance. Higher epinephrine plasma levels occur during exercise in heat, indicating greater sympathetic activity. This study examined the influence of exercise in the heat on stress levels. Nine young healthy men performed a maximal progressive test on a cycle ergometer at two different environmental conditions: hot (40 degrees C) and normal (22 degrees C), both between 40% and 50% relative humidity. Venous blood and saliva samples were collected pre-test and post-test. Before exercise there were no significant changes in salivary biomarkers (salivary IgA: p = 0.12; alpha-amylase: p = 0.66; cortisol: p = 0.95; nitric oxide: p = 0.13; total proteins: p = 0.07) or blood lactate (p = 0.14) between the two thermal environments. Following exercise, there were significant increases in all variables (salivary IgA 22 degrees C: p = 0.04, 40 degrees C: p = 0.0002; alpha-amylase 22 degrees C: p = 0.0002, 40 degrees C: p = 0.0002; cortisol 22 degrees C: p = 0.02, 40 degrees C: p = 0.0002; nitric oxide 22 degrees C: p = 0.0005, 40 degrees C: p = 0.0003, total proteins 22 degrees C: p<0.0001, 40 degrees C: p<0.0001 and; blood lactate 22 degrees C: p<0.0001, 40 degrees C: p<0.0001) both at 22 degrees C and 40 degrees C. There was no significant adjustment regarding IgA levels between the two thermal environments (p = 0.74), however the levels of alpha-amylase (p = 0.02), cortisol (p<0.0001), nitric oxide (p = 0.02) and total proteins (p = 0.01) in saliva were higher in the hotter conditions. Blood lactate was lower under the hot environment (p = 0.01). In conclusion, enduring hot temperature intensified stressful responses elicited by exercise. This study advocates that hot temperature deteriorates exercise performance under exhaustive stress and effort conditions
Measurement of the B0 Lifetime and Oscillation Frequency using B0->D*+l-v decays
The lifetime and oscillation frequency of the B0 meson has been measured
using B0->D*+l-v decays recorded on the Z0 peak with the OPAL detector at LEP.
The D*+ -> D0pi+ decays were reconstructed using an inclusive technique and the
production flavour of the B0 mesons was determined using a combination of tags
from the rest of the event. The results t_B0 = 1.541 +- 0.028 +- 0.023 ps, Dm_d
= 0.497 +- 0.024 +- 0.025 ps-1 were obtained, where in each case the first
error is statistical and the second systematic.Comment: 17 pages, 4 figures, submitted to Phys. Lett.
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