Inclusive and differential cross section measurements of single top quark production in association with a Z boson in proton-proton collisions at √s = 13 TeV

Inclusive and differential cross sections of single top quark production in association with a Z boson are measured in proton-proton collisions at a center-of-mass energy of 13 TeV with a data sample corresponding to an integrated luminosity of 138 fb−1 recorded by the CMS experiment. Events are selected based on the presence of three leptons, electrons or muons, associated with leptonic Z boson and top quark decays. The measurement yields an inclusive cross section of 87.9 +7.5 −7.3 (stat)+7.3 −6.0 (syst) fb for a dilepton invariant mass greater than 30 GeV, in agreement with standard model (SM) calculations and represents the most precise determination to date. The ratio between the cross sections for the top quark and the top antiquark production in association with a Z boson is measured as 2.37+0.56 −0.42 (stat)+0.27 −0.13 (syst). Differential measurements at parton and particle levels are performed for the first time. Several kinematic observables are considered to study the modeling of the process. Results are compared to theoretical predictions with different assumptions on the source of the initial-state b quark and found to be in agreement, within the uncertainties. Additionally, the spin asymmetry, which is sensitive to the top quark polarization, is determined from the differential distribution of the polarization angle at parton level to be 0.54±0.16 (stat)±0.06 (syst), in agreement with SM prediction

Global investigation of the ionospheric irregularities during the severe geomagnetic storm on September 7–8, 2017

In this study, the global effects of the severe geomagnetic storm on the Earth's ionosphere on September 5–9, 2017 with Coronal Mass Ejections (CMEs) associated with X-9.3 flares on September 6, 2017 were investigated by the Rate of Total Electron Content (TEC) Index (ROTI). ROTI was used as a criterion of ionospheric irregularities that took place during the storm. This study was conducted with TEC values obtained from fifty stations connected to the International GNSS System (IGS)-GPS network for five different latitude regions. As a result, it was observed that the irregularities in the high latitude regions of the southern hemisphere were greater in number in comparison with those at the high latitude regions of the northern hemisphere during the storm. It was observed that these irregularities generally occurred during the main and recovery phases of the storm at all latitudes. The weak and moderate ionospheric irregularities that developed at high latitudes during the storm were more in the southern hemisphere. Especially, moderate ionospheric irregularities in high latitudes of both hemispheres took place in eastern longitudes (18oE-160oE). However, ionospheric irregularities in the mid-latitude regions were observed in more stations at the northern hemisphere than at the southern hemisphere. Generally, ionospheric irregularities during the storm developed at eastern longitudes in all sectors. © 2019 The Author

Updating Conductivity Tensor of Cold and Warm Plasma for Equatorial Ionosphere F2-Region in The Northern Hemisphere

We compared the conductivity tensor becoming important parameter of ionospheric plasma using the real geometry of Earth’s magnetic field in the Northern hemisphere for both cold and warm ionospheric plasma for equinox days. It could be that the conductivity tensor certainly depends on the vector of wave propagation (k) and the adiabatic sound speed (U e ) in warm ionospheric plasma and it is possible to say that the adiabatic sound speed for electron generally decreases the magnitudes of conductivity tensor components with respect to the cold ionosphere plasma except for ?23R?(U e  ? 0) = ? 23 R (U e  = 0), ?33R?(U e  ? 0) = ? 33 R (U e  = 0), ?13S?(U e  ? 0) = ? 13 S (U e  = 0) and ?33S?(U e  ? 0) = ? 33 S (U e  = 0). In this sense, the resistivity and reactance increase in ionospheric plasma. In this context, according to the accepted conditions, the change of conductivity with local time is similar to change of electron density with local time for both (cold and warm) conditions in ionospheric plasma as trend. © 2017, Shiraz University

The Relation Between the Refractive Index of the Equatorial Ionospheric F2 Region and Long-Term Solar Indices

Ionospheric refractive index is especially important in the reflection and propagation of HF (3–30 MHz) waves from the ionosphere. For this reason, in this study, the relation between the real parts (?02, ?x2 and ?p2) of the refractive index computed as based on the direction of the Earth’s magnetic field for 300 km altitude in the equatorial ionospheric F2 region and the long-term solar indices (Sunspot Number-R12, Solar Flux at 10.7 cm -F10.7, Coronal Mass Ejection-CME) has been examined by using the multiple regression model. As a result of the examinations, it has been determined that there is a very strong relation between the three refractive index values and solar indices. While it was determined that the R12 and F10.7 indices have a very strong relation, it was also determined that CME did not have a statistically significant relation. This insignificant situation may only be explained with the magnetic field of the Earth acting like a shield. © 2018, Springer Science+Business Media, LLC, part of Springer Nature

The effect of QBO on foE

In the present work, the relationship with QBO of difference (?foE = foE mea  ? foE IRI ) between critical frequency (foE) values of ionospheric E-region, measured at Darwin and Casos Island stations and calculated by IRI-2012 ionospheric model, is statistically investigated. A multiple regression model is used as statistical tool. The “Dummy” variables (“DummyWest” and “DummyEast” represent westerly QBO values and easterly QBO values, respectively) are added to model in order to see the effect of westerly and easterly QBO. In the result of calculations, it is observed that the changes in ?foE about 50–52% can be explained by QBO at both stations. The relationship between QBO and ?foE is negative at both stations. The change of 1 ms ?1 in whole set of QBO leads to a decrease of 0.008 MHz at Casos Island station and 0.017 MHz at Darwin station in ?foE. Directions of QBO have an effect on ?foE at the Darwin station, but they've not any effect on ?foE at Casos Island station. It is thought that the difference values in the foE are due to not to be included in the IRI-model of all parameters affecting the critical frequency value. Thus, QBO which is not included to IRI-model can have an effect on foE and more accurate results can be obtained by IRI model if the QBO is included in this model calculations. © 2016 COSPA

Lower İonospheric Electron Density Changes Following Lightning Discharges

The effect of lightning-induced electromagnetic (EM) waves on electron density (Ne) of the lower ionosphere is calculated by using the four-component Glukhov–Pasko–Inan (GPI) model which is modified by including two-body attachment reactions and associative detachment with negative ions of active species (namely, O and N atoms). As a result of the calculations, it is seen that three-body attachment reactions take place at about 50–73 km altitudes, associative detachment takes place at approximately 73–85 km altitudes and two-body attachment reactions take place at approximately 85–95 km altitudes on the electron density. While the effect on electron density of electric field of lightning-induced EM wave is weak at altitudes where associative detachment is effective, it is strong at altitudes where two-body attachment reactions are effective. Also, it is shown that the electron density increases up to approximately 5.5 times when compared with the background density values due to electrons occurring as a result of associative detachment with negative ions of active species. © 2018, Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences

The effect of solar and geomagnetic parameters on total electron content over Ankara, Turkey

In this study, the relationship between total electron content (TEC) and solar and geomagnetic parameters for Ankara station (39.7 N, 32.76 E), Turkey located in the mid-latitude ionosphere is investigated. In this context, F10.7 solar flux and Interplanetary Magnetic Fields (IMF) from solar parameters and Kp and Dst indices from geomagnetic parameters affecting on TEC are considered. The relationship between the variables is investigated by means of the statistical multiple regression model at the universal time (UT) (Local Time = UT + 2 h) 1200 and 2400 in the years when the 24th solar cycle was minimum (2007–2009) and maximum (2015). As a result, it is found that explainable rates by solar and geomagnetic parameters of TEC changes in 2007–2009 are lower than in 2015 at daytime, while the explainable rates in the solar minimum years are higher than those the maximum year at nighttime. To be higher than the solar maximum of explainable rate in the solar minimum years at nighttime may be related to the fact that the dynamics of the ionosphere is significantly different than expected in this deep minimum period. As expected in 2015, the relationship between TEC and independent parameters is greater at daytime than at nighttime. © 2019 COSPA

The effect of the stratospheric QBO on the neutral density of the D region

A multiple regression model, which defines relationship between two variables, is used to perform a statistical analysis of the relationship between the stratospheric QBO and the neutral density of the D region (NnD) at altitudes of 75 km and 90 km for Singapore station. While performing the analysis, the solar maxima and solar minima epochs of the sun for 21st, 22nd and 23rd solar cycles (SCs) are taken into account. Before applying the model for the statistical analysis of the relationship, the stationary of the variables is investigated by using the unit root test. The relationship between the variables is also investigated by using the co-integration test. The relationship between NnD measured at 75 km altitude and QBO obtained at altitude of 10 hPa is observed that it is positive for solar maximum epoch at 21st and 23rd SCs and for solar minimum epoch at 21st SC and is negative at the other epochs. The relationship between NnD measured at 90 km altitude and QBO is observed to be negative at both the solar maxima expect for solar maximum of 23rd SC and the solar minima epochs. The relationship between variables is positive for both phases (east and west) of QBO. Thus, QBO leads to a statistical change in the NnD. It may also give rise to changes on the ion chemistry of the D region. . © 2015 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved

Measurement of the Drell-Yan forward-backward asymmetry at high dilepton masses in proton-proton collisions at root s=13 TeV

WOS:000838673900001A measurement of the forward-backward asymmetry of pairs of oppositely charged leptons (dimuons and dielectrons) produced by the Drell-Yan process in proton-proton collisions is presented. The data sample corresponds to an integrated luminosity of 138 fb(-1) collected with the CMS detector at the LHC at a center-of-mass energy of 13 TeV. The asymmetry is measured as a function of lepton pair mass for masses larger than 170 GeV and compared with standard model predictions. An inclusive measurement across both channels and the full mass range yields an asymmetry of 0.612 +/- 0.005 (stat) +/- 0.007 (syst). As a test of lepton flavor universality, the difference between the dimuon and dielectron asymmetries is measured as well. No statistically significant deviations from standard model predictions are observed. The measurements are used to set limits on the presence of additional gauge bosons. For a Z' boson in the sequential standard model the observed (expected) 95% confidence level lower limit on the Z' mass is 4.4 TeV (3.7 TeV)

Search for long-lived heavy neutral leptons with displaced vertices in proton-proton collisions at root s=13 TeV

WOS:000826915800001A search for heavy neutral leptons (HNLs), the right-handed Dirac or Majorana neutrinos, is performed in final states with three charged leptons (electrons or muons) using proton-proton collision data collected by the CMS experiment at root s = 13 TeV at the CERN LHC. The data correspond to an integrated luminosity of 138 fb(-1). The HNLs could be produced through mixing with standard model neutrinos v. For small values of the HNL mass (<20 GeV) and the square of the HNL-v mixing parameter (10(-7)-10(-2)), the decay length of these particles can be large enough so that the secondary vertex of the HNL decay can be resolved with the CMS silicon tracker. The selected final state consists of one lepton emerging from the primary proton-proton collision vertex, and two leptons forming a displaced, secondary vertex. No significant deviations from the standard model expectations are observed, and constraints are obtained on the HNL mass and coupling strength parameters, excluding previously unexplored regions of parameter space in the mass range 1-20 GeV and squared mixing parameter values as low as 10(-7)