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The Bloch Equation for Spin Dynamics in Electron Storage Rings: Computational and Theoretical Apects
No full textIn this paper, we describe our work on spin polarization in high-energy electron storage rings which we base on the Full Bloch equation (FBE) for the polarization density and which aims towards the e−− e+ option of the proposed Future Circular Collider (FCC-ee) and the proposed Circular Electron Positron Collider (CEPC). The FBE takes into account non spin-flip and spin-flip effects due to synchrotron radiation including the spin-diffusion effects and the Sokolov–Ternov effect with its Baier–Katkov generalization as well as the kinetic-polarization effect. This mathematical model is an alternative to the standard mathematical model based on the Derbenev–Kondratenko formulas. For our numerical and analytical studies of the FBE, we develop an approximation to the latter to obtain an effective FBE. This is accomplished by finding a third mathematical model based on a system of stochastic differential equations (SDEs) underlying the FBE and by approximating that system via the method of averaging from perturbative ODE theory. We also give an overview of our algorithm for numerically integrating the effective FBE. This discretizes the phase space using spectral methods and discretizes time via the additive Runge–Kutta (ARK) method which is a high-order semi-implicit method. We also discuss the relevance of the third mathematical model for spin tracking
Chiral anomaly, Schwinger effect, Euler-Heisenberg Lagrangian and application to axion inflation
No full textParticle production in strong electromagnetic fields is a recurring theme in solid state physics, heavy ion collisions, early universe cosmology and formal quantum field theory. In this paper we discuss the Dirac equation in a background of parallel electric and magnetic fields. We review the Schwinger particle production rate, clarify the emergence of the chiral anomaly equation and compute the induced current of charged fermions. We distinguish the contributions from non-perturbative particle production, from the running of the gauge coupling constant and from non-linearities in the effective QED Lagrangian, and clarify how these contributions arise within a single framework. We apply these results to axion inflation. A Chern-Simons coupling between the pseudoscalar particle driving cosmic inflaton and an abelian gauge group induces a dual production of gauge fields and charged fermions. We show that the resulting scalar and gravitational wave power spectra strongly depend on the fermion mass
Remarks on strange-quark simulations with Wilson fermions
No full textIn the simulation of QCD with 2+1 flavors of Wilson fermions, the positivity of the fermion determinant is generally assumed. We present evidence that this assumption is in general not justified and discuss the consequences of this finding
Breakdown of frustrated absorption in x-ray sequential multiphoton ionization
No full textWe investigate the frustrated absorption phenomenon of atomic systems driven by x-ray pulses of extremely high intensity. When an atom is exposed to intense x-ray pulses generated by x-ray free-electron lasers (XFELs), it undergoes complex ionization dynamics characterized by sequential multiphoton multiple ionization. Counterintuitively, as the pulse duration becomes shorter so that the intensity increases, the ionization becomes suppressed because of hollow-atom formation and the reduction of cross section. This is called frustrated absorption. However, as we report here, the paradigm of frustrated absorption can break down at extremely high intensity. By using a state-of-the-art theoretical tool, we examine the pulse-duration dependence of x-ray multiphoton ionization dynamics of heavy atoms, revealing that the reduced ionization for shorter pulses is due to the suppression of Auger decays, rather than the frustration of photoabsorption. Moreover, we predict a situation where ionization is, in fact, enhanced as the pulse duration is decreased and explain the mechanism why this happens. The present results demonstrate that the breakdown of frustrated absorption will emerge at the highest fluence currently available at XFEL facilities and will play an important role when terawatt-attosecond x-ray pulses come into realization
Subleading Logarithmic QED Initial State Corrections to to
No full textUsing the method of massive operator matrix elements, we calculate the subleading QED initial state radiative corrections to the process for the first three logarithmic contributions from to and compare their effects to the leading contribution and one more subleading term . The calculation is performed in the limit of large center of mass energies squared . These terms supplement the known corrections to , which were completed recently. Given the high precision at future colliders operating at very large luminosity, these corrections are important for concise theoretical predictions. The present calculation needs the calculation of one more two--loop massive operator matrix element in QED. The radiators are obtained as solutions of the associated Callen--Symanzik equations in the massive case. The radiators can be expressed in terms of harmonic polylogarithms to weight {\sf w = 6} of argument and and in Mellin space by generalized harmonic sums. Numerical results are presented on the position of the peak and corrections to the width, . The corrections calculated result into a final theoretical accuracy for and which is estimated to be of O(30 keV) at an anticipated systematic accuracy at the FCC\_ee of \sim 100 keV. This precision cannot be reached, however, by including only the corrections up to
production in pp collisions with a new fragmentation function
No full textWe study inclusive -baryon production in collisions in the general-mass variable-flavor number scheme and compare with data from the LHCb, ALICE and CMS collaborations. We perform a new fit of the fragmentation function combining data from OPAL and Belle. The agreement with LHC data is slightly worse compared with a calculation using an older fragmentation function, and the tension between different determinations of production cross sections from the LHC experimental collaborations is not resolved. The ratio of data for -baryon and -meson production seems to violate the universality of -charm quark to -hadron fragmentation
Setting the photoelectron clock through molecular alignment
No full textThe interaction of strong laser fields with matter intrinsically provides a powerful tool for imaging transient dynamics with an extremely high spatiotemporal resolution. Here, we study strong-field ionisation of laser-aligned molecules, and show a full real-time picture of the photoelectron dynamics in the combined action of the laser field and the molecular interaction. We demonstrate that the molecule has a dramatic impact on the overall strong-field dynamics: it sets the clock for the emission of electrons with a given rescattering kinetic energy. This result represents a benchmark for the seminal statements of molecular-frame strong-field physics and has strong impact on the interpretation of self-diffraction experiments. Furthermore, the resulting encoding of the time-energy relation in molecular-frame photoelectron momentum distributions shows the way of probing the molecular potential in real-time, and accessing a deeper understanding of electron transport during strong-field interactions
A multi-dimensional search for new heavy resonances decaying to boosted WW, WZ, or ZZ boson pairs in the dijet final state at 13 TeV
No full textA search in an all-jet final state for new massive resonances decaying to , , or boson pairs using a novel analysis method is presented. The analysis is performed on data corresponding to an integrated luminosity of 77.3 recorded with the CMS experiment at the LHC at a centre-of-mass energy of 13 . The search is focussed on potential narrow-width resonances with masses above 1.2 , where the decay products of each or boson are expected to be collimated into a single, large-radius jet. The signal is extracted using a three-dimensional maximum likelihood fit of the two jet masses and the dijet invariant mass, yielding an improvement in sensitivity of up to 30% relative to previous search methods. No excess is observed above the estimated standard model background. In a heavy vector triplet model, spin-1 and resonances with masses below 3.5 and 3.8 , respectively, are excluded at 95% confidence level. In a bulk graviton model, upper limits on cross sections are set between 27 and 0.2 for resonance masses between 1.2 and 5.2 , respectively. The limits presented in this paper are the best to date in the dijet final state
Application of Different Diffraction Peak Profile Analysis Methods to Study the Structure Evolution of Cold-Rolled Hexagonal α-Titanium
No full textThis paper presents a comparison between the “classical” and the modified Williamson–Hall and Warren–Averabach methods applied to an analysis of the microstructure of -titanium. The microstructural parameters of cold-rolled titanium specimens were retrieved from analysis of the X-ray diffraction (XRD) peaks. The high-quality XRD patterns were received at the P07 beamline (The High Energy Materials Science) at the German electron synchrotron. The dependence of the crystallite size, the inhomogeneous microstrains, the average dislocation density, the dislocation cut-off radius and some other parameters on the plastic strain were estimated. The results clearly indicate that, due to the consideration of the dislocation contrast effect, the modified models are a much better fit to the experimental data in comparison with the “classical” models. The results of hardness and corrosion resistance measurements of Ti samples can be explained based on the results obtained from the XRD analysis
Search for new neutral Higgs bosons through the H ZA process in pp collisions at 13 TeV
No full textThis paper reports on a search for an extension to the scalar sector of the standard model, where a new CP-even (odd) boson decays to a Z boson and a lighter CP-odd (even) boson, and the latter further decays to a b quark pair. The Z boson is reconstructed via its decays to electron or muon pairs. The analysed data were recorded in proton-proton collisions at a center-of-mass energy = 13 TeV, collected by the CMS experiment at the LHC during 2016, corresponding to an integrated luminosity of 35.9 fb. Data and predictions from the standard model are in agreement within the uncertainties. Upper limits at 95% confidence level are set on the production cross section times branching fraction, with masses of the new bosons up to 1000 GeV. The results are interpreted in the context of the two-Higgs-doublet model.[graphic not available: see fulltext