Matching in $$ pp\to t\overline{t}W/Z/h+ $$ jet SMEFT studies

In this paper, we explore the impact of extra radiation on predictions of $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z} $$ pp → t t ¯ X , X = h / W ± / Z processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower and merged. While a matched/merged leading-order calculation for $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$ t t ¯ X is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values, $$ {\sigma}_{\mathrm{SM}\mathrm{EFT}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)/{\sigma}_{\mathrm{SM}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)\equiv \mu $$ σ SMEFT t t ¯ X + j / σ SM t t ¯ X + j ≡ μ . Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator $$ \left({\varphi}^{\dagger }i{\overleftrightarrow{D}}_{\mu}\varphi \right)\left(\overline{t}{\gamma}^{\mu }t\right) $$ φ † i D ↔ μ φ t ¯ γ μ t on $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{h} $$ t t ¯ h and $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{W} $$ t t ¯ W , for which the relative cross section prediction increases by more than 10% — significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching and merging. Being leading order at heart, matching and merging can be applied to all operators and processes relevant to $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z}+\mathrm{jet} $$ pp → t t ¯ X , X = h / W ± / Z + jet , is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$ t t ¯ X + jet studies where complete next-to-leading order results are currently unavailable or unwieldy.

Measurements of Electron Impact K-shell Ionization Cross Sections of Cr21+ Ions

We present relative cross section measurements of the inner-shell ionization of highly charged chromium ions by high-energy (7-30 keV) electrons. The measurements use a technique based on high-resolution x-ray spectroscopy, which correlates ionization events with K∝ decay x rays. Moreover, the measurements show that inner-shell ionization only affects the strength of the heliumlike 1s2s 3S1 -> 1s2 1S0 forbidden line. The cross sections inferred for Li-like Cr21+ agree well with distorted wave calculations.

Engineering assessment of minimum fatigue life for given probability of its non-exceedance

Object and purpose of research. This paper discusses structural materials under cyclic load. The purpose is to determine the minimum fatigue life corresponding to a certain non-exceedance probability of this value. Materials and methods. The study was performed on three structural materials: steel 15ХМ, steel 08Kh18N10Т and titanium alloy PТ-7М. Initial estimate of fatigue life distribution parameters relied on the data about guaranteed maximum and minimum values of temporary resistance and relative cross-section tapering. The assessment was performed as per a common curve “conditionally elastic stress amplitude versus number of cycles to failure” taking into account the mechanical prop-erties of given material. The values of minimum fatigue life were obtained as per two different methods: statistical simulation of the random values following the Weibull distribution law and the analytical expression for probability density of the lows for given distribution function of random value and fixed scope of sampling. Main results. The lows yielded by statistical simulation are more conservative than those yielded by the analytical formula. The margin in terms of the number of cycles to failure stipulated as 10 in several regulatory documents seems to be somewhat unsubstantiated. This margin is too great in the low-cycle domain and too small in the high-cycle one. Conclusion. This paper postulates the existence of guaranteed maximum and minimum values for mechanical properties of structural materials, namely temporary resistance and relative cross-section tapering. These values were applied to well-known analytical curves of fatigue, which finally yielded possible variation ranges for fatigue life at various amplitudes of conditionally elastic reduced stresses, assuming the existence of a certain shift in the sensitivity limit of fatigue life distribution. These data were further used to establish standard deviations and mathematical expectations for the number of cycles to failure.

Charge Transfer, Complexes Formation and Furan Fragmentation Induced by Collisions with Low-Energy Helium Cations

The present work focuses on unraveling the collisional processes leading to the fragmentation of the gas-phase furan molecules under the He+ and He2+ cations impact in the energy range 5–2000 eV. The presence of different mechanisms was identified by the analysis of the optical fragmentation spectra measured using the collision-induced emission spectroscopy (CIES) in conjunction with the ab initio calculations. The measurements of the fragmentation spectra of furan were performed at the different kinetic energies of both cations. In consequence, several excited products were identified by their luminescence. Among them, the emission of helium atoms excited to the 1s4d 1D2, 3D1,2,3 states was recorded. The structure of the furan molecule lacks an He atom. Therefore, observation of its emission lines is spectroscopic evidence of an impact reaction occurring via relocation of the electronic charge between interacting entities. Moreover, the recorded spectra revealed significant variations of relative band intensities of the products along with the change of the projectile charge and its velocity. In particular, at lower velocities of He+, the relative cross-sections of dissociation products have prominent resonance-like maxima. In order to elucidate the experimental results, the calculations have been performed by using a high level of quantum chemistry methods. The calculations showed that in both impact systems two collisional processes preceded fragmentation. The first one is an electron transfer from furan molecules to cations that leads to the neutralization and further excitation of the cations. The second mechanism starts from the formation of the He−C4H4O+/2+ temporary clusters before decomposition, and it is responsible for the appearance of the narrow resonances in the relative cross-section curves.

Determination of the fast-neutron-induced fission cross-section of 242Pu at nELBE

The fast-neutron-induced fission cross section of 242Pu was determined in the energy range of 0.5 MeV to 10MeV at the neutron time-of-flight facility nELBE. Using a parallel-plate fission ionization chamber this quantity was measured relative to 235U(n,f). The number of target nuclei was thereby calculated by means of measuring the spontaneous fission rate of 242Pu. An MCNP 6 neutron transport simulation was used to correct the relative cross section for neutron scattering. The determined results are in good agreement with current experimental and evaluated data sets.

The use of probiotics versus psyllium husk as a bowel preparation for prostate radiotherapy: a retrospective analysis

IntroductionThe use of bowel preparation strategies to reduce the degree of rectal distension during prostate radiotherapy is well documented. This retrospective pilot study analysed and compared a probiotic agent against a psyllium-supplemented diet to establish the feasibility of probiotics as a bowel preparation for patients receiving radical radiotherapy for prostate cancer.MethodA retrospective chart review of five patients taking probiotics and five taking psyllium husk (psyllium) during their course of radiotherapy treatment was conducted. On treatment, cone beam computed tomography (CBCT) scans were compared with planning CTs to quantify inter-fractional variation in rectal volume and distension.ResultsForty-five CBCT scans were available in both the psyllium and probiotics groups for analysis. Variation in mean difference in rectal volume from planning (ΔRV), mean rectal cross-section area (CSA) and mean relative cross-section area (CSArel) was significantly increased for the probiotics group compared with the psyllium group (p=0·001, 0·008 and 0·007, respectively). No statistically significant differences in mean ΔRV, CSA and CSArel were detected between the two groups.ConclusionThis retrospective analysis suggests that a probiotics-based bowel preparation that utilises Lactobacillus acidophilus and Bifidobacterium lactis may result in increased rectal volume and CSA variation throughout treatment in comparison with a psyllium-supplemented diet.