An experimental procedure is proposed to perform measurements of differential cross sections for vector boson production which can be compared to fixed-order QCD predictions with improved accuracy. ...The procedure relies on applying theoretical acceptance corrections computed as a function of the transverse momentum of the
W
/
Z
boson,
p
T
, to the experimental measurement, rather than comparing data directly against fiducial fixed-order predictions. It is demonstrated that, contrary to standard fiducial computations, these acceptance factors vary little at low
p
T
, so they can be reliably computed using fixed-order perturbation theory. An example analysis is performed using the ATLAS measurement of the
Z
-boson production cross section at center-of-mass energy of 8 TeV. The resulting full phase space measurement of the cross section differential in the boson rapidity is compared to theoretical predictions computed with next-to-next-to leading-order accuracy in QCD. Further extensions of the approach which include different types of measurements and improved theoretical predictions are discussed.
The results of numerical simulation of an ogee spillway with a step on the crest are described. Quantitative estimates confirming the efficiency of the crest step are given. It is concluded that it ...is necessary to study in detail the operation of such spillways by numerical and physical simulation.
Charged lepton pairs are produced copiously in high-energy hadron collisions via electroweak gauge boson exchange, and are one of the most precisely measured final states in proton-proton collisions ...at the Large Hadron Collider (LHC). We propose that measurements of lepton angular distributions can be used to improve the accuracy of theoretical predictions for Higgs boson production cross sections at the LHC. To this end, we exploit the sensitivity of the lepton angular coefficient associated with the longitudinal Z-boson polarization to the parton density function (PDF) for gluons resolved from the incoming protons, in order to constrain the Higgs boson cross section from gluon fusion processes. By a detailed numerical analysis using the open-source platform xFitter, we find that high-statistics determinations of the longitudinally polarized angular coefficient at the LHC Run III and high-luminosity HL-LHC improve the PDF systematic uncertainties of the Higgs boson cross section predictions by 50% over a broad range of Higgs boson rapidities.
Small RNAs derived from snoRNAs Taft, Ryan J; Glazov, Evgeny A; Lassmann, Timo ...
RNA (Cambridge),
07/2009, Letnik:
15, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Small nucleolar RNAs (snoRNAs) guide RNA modification and are localized in nucleoli and Cajal bodies in eukaryotic cells. Components of the RNA silencing pathway associate with these structures, and ...two recent reports have revealed that a human and a protozoan snoRNA can be processed into miRNA-like RNAs. Here we show that small RNAs with evolutionary conservation of size and position are derived from the vast majority of snoRNA loci in animals (human, mouse, chicken, fruit fly), Arabidopsis, and fission yeast. In animals, sno-derived RNAs (sdRNAs) from H/ACA snoRNAs are predominantly 20-24 nucleotides (nt) in length and originate from the 3' end. Those derived from C/D snoRNAs show a bimodal size distribution at approximately 17-19 nt and >27 nt and predominantly originate from the 5' end. SdRNAs are associated with AGO7 in Arabidopsis and Ago1 in fission yeast with characteristic 5' nucleotide biases and show altered expression patterns in fly loquacious and Dicer-2 and mouse Dicer1 and Dgcr8 mutants. These findings indicate that there is interplay between the RNA silencing and snoRNA-mediated RNA processing systems, and that sdRNAs comprise a novel and ancient class of small RNAs in eukaryotes.
An analytical hydraulic method for calculating the flow parameters downstream of an overfall taking into account the characteristic features of a falling jet is described. Design formulas are ...presented. The calculated results are compared with experimental data to validate the method proposed.
The nuclear recoil effect on the g factor of Li-like ions is evaluated. The one-electron recoil contribution is treated within the framework of the rigorous QED approach to the first order in the ...electron-to-nucleus mass ratio m/M and to all orders in the parameter αZ. These calculations are performed in a range Z=3-92. The two-electron recoil term is calculated for low- and middle-Z ions within the Breit approximation using a four-component approach. The results for the two-electron recoil part obtained in the Letter strongly disagree with the previous calculations performed using an effective two-component Hamiltonian. The obtained value for the recoil effect is used to calculate the isotope shift of the g factor of Li-like ^{A}Ca^{17+} with A=40 and A=48 which was recently measured. It is found that the new theoretical value for the isotope shift is closer to the experimental one than the previously obtained value.
The recently established agreement between experiment and theory for the g factors of lithiumlike silicon and calcium ions manifests the most stringent test of the many-electron bound-state quantum ...electrodynamics (QED) effects in the presence of a magnetic field. In this Letter, we present a significant simultaneous improvement of both theoretical gth=2.000 889 894 4 (34) and experimental gexp=2.000 889 888 45 (14) values of the g factor of lithiumlike silicon Si2811+. The theoretical precision now is limited by the many-electron two-loop contributions of the bound-state QED. The experimental value is accurate enough to test these contributions on a few percent level.
We propose a new experimental method to probe the photon parton distribution function inside the proton (photon PDF) at LHC energies. The method is based on the measurement of dilepton production ...from the γp→ℓ+ℓ−+X reaction in proton-lead collisions. These experimental conditions guarantee a clean environment, both in terms of reconstruction of the final state and in terms of possible background. We first calculate the cross sections for this process with collinear photon PDFs, where we identify the optimal choice of the scale, in analogy to deep inelastic scattering kinematics. We then perform calculations including the transverse-momentum dependence of the probed photon. Finally, we estimate rates of the process for the existing LHC data samples.
The magnetic moment μ of a bound electron, generally expressed by the g-factor μ=-g μB s ħ(-1) with μB the Bohr magneton and s the electron's spin, can be calculated by bound-state quantum ...electrodynamics (BS-QED) to very high precision. The recent ultra-precise experiment on hydrogen-like silicon determined this value to eleven significant digits, and thus allowed to rigorously probe the validity of BS-QED. Yet, the investigation of one of the most interesting contribution to the g-factor, the relativistic interaction between electron and nucleus, is limited by our knowledge of BS-QED effects. By comparing the g-factors of two isotopes, it is possible to cancel most of these contributions and sensitively probe nuclear effects. Here, we present calculations and experiments on the isotope dependence of the Zeeman effect in lithium-like calcium ions. The good agreement between the theoretical predicted recoil contribution and the high-precision g-factor measurements paves the way for a new generation of BS-QED tests.
A rigorous QED evaluation of the two-photon exchange corrections to the g factor of lithiumlike ions is presented. The screened self-energy corrections are calculated for the intermediate-Z region, ...and its accuracy for the high-Z region is essentially improved in comparison with that of previous calculations. As a result, the theoretical accuracy of the g factor of lithiumlike ions is significantly increased. The theoretical prediction obtained for the g factor of (28)Si(11+) g(th) = 2.000 889 892(8) is in an excellent agreement with the corresponding experimental value g(exp) = 2.000 889 889 9(21) A. Wagner et al., Phys. Rev. Lett. 110, 033003 (2013).
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