Search results for "Quark"
showing 10 items of 2905 documents
Evaluation of the flavor-changing vertexb→s+Husing the Breitenlohner-Maison-'t Hooft-Veltmanγ5scheme
1990
We reevaluate the one-loop-induced flavor-changing vertex {ital b}(bottom){r arrow}{ital s}(strange)+{ital H}(Higgs boson) using the Breitenlohner--Maison--'t Hooft--Veltman {gamma}{sub 5} scheme. Our result agrees with the result of previous calculations that employed a naive anticommuting {gamma}{sub 5} if one consistently employs left-chiral fermion fields in the perturbation expansion.
Probing nucleons with photons at the quark level
2014
The description of electromagnetic interactions with hadrons from the quark level requires knowledge of the underlying quark-gluon ingredients. I discuss some properties of the quark-photon vertex and quark Compton vertex, along with the role of electromagnetic gauge invariance and vector-meson dominance. A simple parametrization for the quark-photon vertex is given.
Searches for heavy neutrinos from Z decays
1992
We have searched for possible fourth family heavy neutrinos, pair produced in Z0 decays, in a sample of about 112 000 hadronic Z0 final states collected with the DELPHI detector. For all mixing matrix elements we exclude a new Dirac neutrino lighter than 44.5 GeV at a 95% confidence level, if the neutrino couples to the electron or muon family, and lighter than 44.0 GeV, if the neutrino couples to the tau family. Depending on the values of the mixing element and to which lepton family the neutrino couples, we obtain mass limits up to 46.2 GeV. For all mixing matrix elements we exclude a new Majorana neutrino lighter than 39.0 GeV, if it couples to the electron or the muon family, and lighte…
A SU(4) circle times O(3) scheme for nonstrange baryons
2007
4 pages, 3 tables.-- PACS nrs.: 12.39.Jh, 14.20.-c, 14.20.Gk.-- ISI Article Identifier: 000245667300027.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0610257
The two-photon decay of X(6900) from light-by-light scattering at the LHC
2022
The LHCb Collaboration has recently discovered a structure around 6.9 GeV in the double-$J/\psi$ mass distribution, possibly a first fully-charmed tetraquark state $X(6900)$. Based on vector-meson dominance (VMD) such a state should have a significant branching ratio for decaying into two photons. We show that the recorded LHC data for the light-by-light scattering may indeed accommodate for such a state, with a $\gamma \gamma$ branching ratio of order of $10^{-4}$, which is larger even than the value inferred by the VMD. The spin-parity assignment $0^{-+}$ is in better agreement with the VMD prediction than $0^{++}$, albeit not significantly at the current precision. Further light-by-light…
ATLAS Inner Detector alignment and analysis of the Wtb vertex structure with single top quarks
2018
Esta tesis puede ser dividida en dos partes diferentes: La primera trata sobre el alineamiento del detector interno de ATLAS, y la segunda sobre el estudio de la estructura del vértice Wtb mediante el uso de quarks top producidos en solitario. La primera parte presenta las técnicas utilizadas para alinear el detector interno de ATLAS, así como las mejoras implementadas en algoritmo de alineamiento durante el Run-II del LHC. Durante la toma de datos, tienen lugar en el detector interno diversos movimientos y deformaciones dinámicos que comprometen la calidad de los datos recogidos. Los dos más relevantes son un movimiento vertical del detector de Píxeles, y el combado del IBL. En el alineami…
Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector
2018
Physics letters / B 784, 173 - 191 (2018). doi:10.1016/j.physletb.2018.07.035
Search for weakly decaying b -flavored pentaquarks
2018
Investigations of the existence of pentaquark states containing a single $b$ (anti)quark decaying weakly into four specific final states J/$\psi K^+\pi^- p$, J/$\psi K^- \pi^- p$, J/$\psi K^- \pi^+ p$, and $J/\psi \phi (1020) p$ are reported. The data sample corresponds to an integrated luminosity of 3.0/fb in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the $\Lambda_b$.
B-meson hadroproduction in the SACOT-mT scheme
2023
We apply the SACOT-mT general-mass variable flavour number scheme (GM-VFNS) to the inclusive B-meson production in hadronic collisions at next-to-leading order in perturbative Quantum Chromodynamics. In the GM-VFNS approach one matches the fixed-order heavy-quark production cross sections, accurate at low transverse momentum (pT), with the zero-mass cross sections, accurate at high pT. The physics idea of the SACOT-mT scheme is to do this by accounting for the finite momentum transfer required to create a heavy quark-antiquark pair throughout the calculation. We compare our results with the latest LHC data from proton-proton and proton-lead collisions finding a very good agreement within th…
Temperature dependence of η / s of strongly interacting matter: Effects of the equation of state and the parametric form of ( η / s ) ( T )
2020
We investigate the temperature dependence of the shear viscosity to entropy density ratio η/s using a piecewise linear parametrization. To determine the optimal values of the parameters and the associated uncertainties, we perform a global Bayesian model-to-data comparison on Au+Au collisions at √sNN=200 GeV and Pb+Pb collisions at 2.76 TeV and 5.02 TeV, using a 2+1D hydrodynamical model with the Eskola-Kajantie-Ruuskanen-Tuominen (EKRT) initial state. We provide three new parametrizations of the equation of state (EoS) based on contemporary lattice results and hadron resonance gas, and use them and the widely used s95p parametrization to explore the uncertainty in the analysis due to the c…