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We propose analytical forms, in both momentum transfer and impact parameter spaces, for the amplitudes of elastic pp scattering, giving coherent and accurate description of the observables at all energies $sqrt{s}geq 20$ GeV. The real and imaginary parts are separately identified through their roles at small and large t values. The study of the differential cross sections in b-space leads to the understanding of the effective interaction ranges contributing to elastic and inelastic processes.
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The production of $toverline{t}$, $W+boverline{b}$ and $W+coverline{c}$ is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $pm$ 0.02 $mbox{fb}^{-1}$. The $W$ bosons are reconstructed in the decays $Wrightarrowell u$, where $ell$ denotes muon or electron, while the $b$ and $c$ quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.
We present a measurement of the ratio of top quark branching fractions R = B(t -> Wb)/B(t -> Wq), where q can be a d, s or b quark, in the lepton+jets and dilepton ttbar final states. The measurement uses data from 5.4 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure R = 0.90 +/- 0.04, and we extract the CKM matrix element |Vtb| as |Vtb| = 0.95 +/- 0.02, assuming unitarity of the 3x3 CKM matrix.
A method of determination of the real part of the elastic scattering amplitude is examined for high energy proton-proton and proton-nuclei elastic scattering at small momentum transfer. The method allows to decrease the number of model assumptions, to obtain the real parts of the spin non-flip and spin-flip amplitudes in the narrow region of momentum transfer.
The production fractions of $overline{B}_s^0$ and $Lambda_b^0$ hadrons, normalized to the sum of $B^-$ and $overline{B}^0$ fractions, are measured in 13 TeV pp collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of 1.67/fb. These ratios, averaged over the $b$-hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are $0.122 pm 0.006$ for $overline{B}_s^0$, and $0.259 pm 0.018$ for $Lambda_b^0$, where the uncertainties arise from both statistical and systematic sources. The $Lambda_b^0$ ratio depends strongly on transverse momentum, while the $overline{B}_s^0$ ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of $D^+$ to $D^0$ mesons produced in the sum of $overline{B}^0$ and $B^-$ semileptonic decays is determined as $0.359pm0.006pm 0.009$, where the uncertainties are statistical and systematic.
The $text{t}bar{text{t}}text{H}(text{b}bar{text{b}})$ process is an essential channel to reveal the Higgs properties but has an irreducible background from the $text{t}bar{text{t}}text{b}bar{text{b}}$ process, which produces a top quark pair in association with a b quark pair. Therefore, understanding the $text{t}bar{text{t}}text{b}bar{text{b}}$ process is crucial for improving the sensitivity of a search for the $text{t}bar{text{t}}text{H}(text{b}bar{text{b}})$ process. To this end, when measuring the differential cross-section of the $text{t}bar{text{t}}text{b}bar{text{b}}$ process, we need to distinguish the b-jets originated from top quark decays, and additional b-jets originated from gluon splitting. Since there are no simple identification rules, we adopt deep learning methods to learn from data to identify the additional b-jets from the $text{t}bar{text{t}}text{b}bar{text{b}}$ events. Specifically, by exploiting the special structure of the $text{t}bar{text{t}}text{b}bar{text{b}}$ event data, we propose several loss functions that can be minimized to directly increase the matching efficiency, the accuracy of identifying additional b-jets. We discuss the difference between our method and another deep learning-based approach based on binary classification arXiv:1910.14535 using synthetic data. We then verify that additional b-jets can be identified more accurately by increasing matching efficiency directly rather than the binary classification accuracy, using simulated $text{t}bar{text{t}}text{b}bar{text{b}}$ event data in the lepton+jets channel from pp collision at $sqrt{s}$ = 13 TeV.
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