789 research outputs found
Experimental study of direct photon emission in K- --> pi- pi0 gamma decay using ISTRA+ detector
The branching ratio in the charged-pion kinetic energy region of 55 to 90 MeV
for the direct photon emission in the K- --> pi- pi0 gamma decay has been
measured using in-flight decays detected with the ISTRA+ setup operating in the
25 GeV/c negative secondary beam of the U-70 PS. The value
Br(DE)=[0.37+-0.39(stat)+-0.10(syst)]*10^(-5) obtained from the analysis of 930
completely reconstructed events is consistent with the average value of two
stopped-kaon experiments, but it differs by 2.5 standard deviations from the
average value of three in-flight-kaon experiments. The result is also compared
with recent theoretical predictions.Comment: 13 pages, 8 figure
B Physics at the Tevatron: Run II and Beyond
This report provides a comprehensive overview of the prospects for B physics
at the Tevatron. The work was carried out during a series of workshops starting
in September 1999. There were four working groups: 1) CP Violation, 2) Rare and
Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and
Spectroscopy. The report also includes introductory chapters on theoretical and
experimental tools emphasizing aspects of B physics specific to hadron
colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a
Summary.Comment: 583 pages. Further information on the workshops, including
transparencies, can be found at the workshop's homepage:
http://www-theory.lbl.gov/Brun2/. The report is also available in 2-up
http://www-theory.lbl.gov/Brun2/report/report2.ps.gz or chapter-by-chapter
http://www-theory.lbl.gov/Brun2/report
Особенности действия брассиностероидов на растения в условиях солевого стресса
The dependence of the protective effect of brassinosteroids (BS) in a wide range of concentrations on the growth of the root system of fiber flax (Linum usitatissimum L.) and spring barley (Hordeum vulgare L.) seedlings under salt stress was studied. A narrow range of BS concentrations was revealed, in which they cause a weakening of the inhibitory effect of salinity on the root system of seedlings. An almost complete coincidence of the BS concentration ranges was noted, in which the maximum stress-protective effect of phytohormones was observed for the both crops (6,9 ⋅ 10–7–5,9 ⋅ 10–8 М for fiber flax and 2,8 ⋅ 10–7–2,4 ⋅ 10–8 М for spring barley). In the experiment with winter wheat (Triticum aestivum L.), which lasted 19 days, already on the 6th day before the seedlings were placed under stress conditions, the elongation of the seedlings treated with exogenous brassinosteroids was noted. By the end of the experiment (in the second leaf unfolding phase), all brassinosteroids showed a pronounced protective-stimulating effect under the salinity conditions that depended on the chemical structure of the hormone and changed in the brassinolide > homobrassinolide > homocastasterone > epibrassinolide series.Исследована зависимость протекторного действия брассиностероидов (БС) в широком диапазоне концентраций на рост корневой системы проростков льна-долгунца (Linum usitatissimum L.) и ярового ячменя (Hordeum vulgare L.) в условиях солевого стресса. Выявлены узкие диапазоны концентраций БС (6,9 ⋅ 10–7–5,9 ⋅ 10–8 М для льна-долгунца и 2,8 ⋅ 10–7–2,4 ⋅ 10–8 М для ярового ячменя), в которых они вызывают ослабление ингибирующего эффекта засоления на корневую систему проростков. Отмечено практически полное совпадение диапазонов концентраций БС, в которых наблюдалось максимальное стресс-протекторное действие фитогормонов для обеих культур. В опыте с озимой пшеницей (Triticum aestivum L.), длившемся 19 суток, уже на 6-е сутки, до помещения растений в стрессовые условия, было отмечено удлинение проростков, обработанных экзогенными брассиностероидами, а к концу эксперимента (в фазу развертывания второго листа) все брассиностероиды показали выраженный защитностимулирующий эффект в условиях засоления, зависящий от химической структуры гормона и изменяющийся в ряду брассинолид > гомобрассинолид > гомокастастерон > эпибрассинолид.
A Precise Measurement of the Muon Neutrino-Nucleon Inclusive Charged Current Cross-Section off an Isoscalar Target in the Energy Range 2.5 < E_\nu < 40 GeV by NOMAD
We present a measurement of the muon neutrino-nucleon inclusive charged
current cross-section, off an isoscalar target, in the neutrino energy range
GeV. The significance of this measurement is its
precision, % in GeV, and % in GeV regions, where significant uncertainties in previous
experiments still exist, and its importance to the current and proposed long
baseline neutrino oscillation experiments.Comment: 14 pages, 3 figures, submitted to Phys.Lett.
Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV
We have measured the polarizations of \jpsi and \psiprime mesons as
functions of their transverse momentum \pt when they are produced promptly in
the rapidity range with \pt \geq 5 \pgev. The analysis is performed
using a data sample with an integrated luminosity of about 800 \ipb collected
by the CDF II detector. For both vector mesons, we find that the polarizations
become increasingly longitudinal as \pt increases from 5 to 30 \pgev. These
results are compared to the predictions of nonrelativistic quantum
chromodynamics and other contemporary models. The effective polarizations of
\jpsi and \psiprime mesons from -hadron decays are also reported.Comment: 8 pages, 7 figures, published in Physical Review Letter
Searches for Direct Pair Production of Supersymmetric Top and Supersymmetric Bottom Quarks in p-pbar Collisions at sqrt(s)=1.96 TeV
We search for direct pair production of supersymmetric top quarks and
supersymmetric bottom quarks in proton-antiproton collisions at sqrt(s)=1.96
TeV, using 295 pb^-1 of data recorded by the Collider Detector at Fermilab (CDF
II) experiment. The supersymmetric top (supersymmetric bottom) quarks are
selected by reconstructing their decay into a charm (bottom) quark and a
neutralino, which is assumed to be the lightest supersymmetric particle. The
signature of such processes is two energetic heavy-flavor jets and missing
transverse energy. The number of events that pass our selection for each search
process is consistent with the expected standard model background. By comparing
our results to the theoretical production cross sections of the supersymmetric
top and supersymmetric bottom quarks in the minimal supersymmetric standard
model, we exclude, at a 95% confidence level in the frame of that model, a
supersymmetric top quark mass up to 132 GeV/c^2 for a neutralino mass of 48
GeV/c^2, and a supersymmetric bottom quark mass up to 193 GeV/c^2 for a
neutralino mass of 40 GeV/c^2.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
Observation and Mass Measurement of the Baryon
We report the observation and measurement of the mass of the bottom, strange
baryon through the decay chain , where
, , and .
Evidence for observation is based on a signal whose probability of arising from
the estimated background is 6.6 x 10^{-15}, or 7.7 Gaussian standard
deviations. The mass is measured to be (stat.) (syst.) MeV/.Comment: Minor text changes for the second version. Accepted by Phys. Rev.
Let
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a measurement of the top quark pair production cross section in
ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with
the Collider Detector at Fermilab. We select ttbar decays into the final states
e nu + jets and mu nu + jets, in which at least one b quark from the t-quark
decays is identified using a secondary vertex-finding algorithm. Assuming a top
quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat)
+1.1-0.9 (syst) pb. We also report the first observation of ttbar with
significance greater than 5 sigma in the subsample in which both b quarks are
identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3
(syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page
Search for Third Generation Vector Leptoquarks in p anti-p Collisions at sqrt(s) = 1.96 TeV
We describe a search for a third generation vector leptoquark (VLQ3) that
decays to a b quark and tau lepton using the CDF II detector and 322 pb^(-1) of
integrated luminosity from the Fermilab Tevatron. Vector leptoquarks have been
proposed in many extensions of the standard model (SM). Observing a number of
events in agreement with SM expectations, assuming Yang-Mills (minimal)
couplings, we obtain the most stringent upper limit on the VLQ3 pair production
cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317
GeV/c^2 (251 GeV/c^2) at 95% C.L.Comment: 7 pages, 2 figures, submitted to PR
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