Unconventional decay law for excited states in closed many-body systems

We study the time evolution of an initially excited many-body state in a finite system of interacting Fermi-particles in the situation when the interaction gives rise to the ``chaotic'' structure of compound states. This situation is generic for highly excited many-particle states in quantum systems, such as heavy nuclei, complex atoms, quantum dots, spin systems, and quantum computers. For a strong interaction the leading term for the return probability $W(t)$ has the form $W(t)\simeq \exp (-\Delta_E^2t^2)$ with $\Delta_E^2$ as the variance of the strength function. The conventional exponential linear dependence $W(t)=C\exp (-\Gamma t)$ formally arises for a very large time. However, the prefactor $C$ turns out to be exponentially large, thus resulting in a strong difference from the conventional estimate for $W(t)$.Comment: RevTex, 4 pages including 1 eps-figur

Search for the associated production of the Higgs boson with a top-quark pair

A search for the standard model Higgs boson produced in association with a top-quark pair t t ¯ H (tt¯H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb −1 and 19.7 fb −1 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed t t ¯ H tt¯H signal strength relative to the standard model cross section, μ = σ/σ SM ,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is μ = 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV

Measurement of prompt Jψ\psi pair production in pp collisions at \sqrt s = 7 Tev

Production of prompt J/ ψ meson pairs in proton-proton collisions at s s√ = 7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 fb −1 . The two J/ ψ mesons are fully reconstructed via their decays into μ + μ − pairs. This observation provides for the first time access to the high-transverse-momentum region of J/ ψ pair production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/ ψ transverse momentum ( p T J/ ψ ) and rapidity (| y J/ ψ |): | y J/ ψ | 6.5 GeV/ c ; 1.2 4.5 GeV/ c . The total cross section, assuming unpolarized prompt J/ ψ pair production is 1.49 ± 0.07 (stat) ±0.13 (syst) nb. Different assumptions about the J/ ψ polarization imply modifications to the cross section ranging from −31% to +27%

Measurements of the t(t)Overbar charge asymmetry using the dilepton decay channel in pp collisions at root s=7 TeV

The tt¯ charge asymmetry in proton-proton collisions at s√ = 7 TeV is measured using the dilepton decay channel (ee, e μ , or μμ ). The data correspond to a total integrated luminosity of 5.0 fb −1 , collected by the CMS experiment at the LHC. The tt and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be A C = −0 . 010 ± 0 . 017 (stat . ) ± 0 . 008 (syst . ) and AlepC = 0 . 009 ± 0 . 010 (stat . ) ± 0 . 006 (syst . ). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the tt¯ system. All measurements are consistent with the expectations of the standard model

Long Term Productivity Benefits of Soil Conservation

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Long term productivity benefits of soil conservation

Many studies have documented that erosion reduces crop yields (Langdale and Shrader, 1982; Follet and Stewart, 1985; Am. Soc. Ag. Engr., 1985). Few of those studies have incorporated the effect on yield of changes in technology (Young, 1984) and only one, to our knowledge, has considered the effect of yield-enhancing agricultural technical progress on erosion damage assessment (Walker and Young, 1986). Lost yield potential is the major on-site effect of erosion. Off-site effects in the form of sedimentation and impaired water quality are also important but are not discussed here. A conservation practice that reduces erosion and yield damage produces a benefit from conservation. This potential benefit, in the form of yield damage avoided, is the objective of soil conservation research and conservation adoption. Understanding the cost of erosion damage and the benefits from erosion control are essential for developing long range policies for conserving soil resources. The tri-state STEEP multidisciplinary research program is dedicated to finding solutions to the erosion problems in the Pacific Northwest. STEEP research results concerning the long term productivity impacts of erosion are the focus of this paper. This paper describes the different types of erosion damage and presents concepts for correctly measuring that damage or the potential benefits from erosion control. STEEP research is presented to show the effect of erosion on the soil resource and on crop productivity. The potential for restoring productivity on eroded soils is discussed. The paper also describes how to separate the effects of technology and yield damage and presents empirical estimates of conservation benefits. A first classification of erosion damage distinguishes between current damage and long-term damage. Current erosion damage is due primarily to seedbed erosion, reduced tillering, and plant suffocation by sediment, all of which reduce stand density. Current damage is yield loss this year due to erosion this year. These erosional effects do not carry over into subsequent years. Long-term erosion damage occurs when erosion this year reduces yield in future years. This yield loss is due to the loss of nutrient-rich topsoil, to degradation of soil structure and to reduction of plant-available water-holding capacity of eroded soil. Long-term damage is of great concern because its effects are enduring, even irreversible in large part. Estimates of the long-term productivity benefits of soil conservation are formulated in terms of long-term erosion damage avoided by conservation