Search results for "Particle physics"
showing 10 items of 6826 documents
Ruling out some predictions of deeply-bound light-heavy tetraquarks using lattice QCD
2022
We discuss our lattice QCD calculations of a number of tetraquark channels with at least one heavy quark where some phenomenological models, already fully constrained by fits to the ordinary meson and baryon spectrum, predict deep binding. We find no evidence of deeply-bound tetraquarks, except in previously established strong-interaction stable $I=0$, $J^P=1^+$, $ud\bar{b}\bar{b}$ and $I=1/2$, $J^P=1^+$ $\ell s\bar{b}\bar{b}$ (where $\ell=u/d$) channels, allowing us to rule out models predicting deep binding. Preliminary results from an updated analysis of doubly-bottom tetraquarks are also presented.
VBFNLO: A parton level Monte Carlo for processes with electroweak bosons
2009
VBFNLO is a fully flexible parton level Monte Carlo program for the simulation of vector boson fusion, double and triple vector boson production in hadronic collisions at next-to-leading order in the strong Coupling constant. VBFNLO includes Higgs and vector boson decays with full spin correlations and all off-shell effects. In addition, VBFNLO implements CP-even and CP-odd Higgs boson via gluon fusion, associated with two jets, at the leading-order one-loop level with the full top- and bottom-quark mass dependence in a generic two-Higgs-doublet model. A variety of effects arising from beyond the Standard Model physics are implemented for selected processes. This includes anomalous coupling…
Measurement of Wγ and Zγ production in proton-proton collisions at √s =7 TeV with the ATLAS detector
2011
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM
The energy spectrum of atmospheric neutrinos between 2 and 200 TeV with the AMANDA-II detector
2010
The muon and anti-muon neutrino energy spectrum is determined from 2000-2003 AMANDA telescope data using regularised unfolding. This is the first measurement of atmospheric neutrinos in the energy range 2 - 200 TeV. The result is compared to different atmospheric neutrino models and it is compatible with the atmospheric neutrinos from pion and kaon decays. No significant contribution from charm hadron decays or extraterrestrial neutrinos is detected. The capabilities to improve the measurement of the neutrino spectrum with the successor experiment IceCube are discussed.
Search for pair production of heavy objects in 4-jet events at sqrt {s}$=130-136 GeV
1996
Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, hA or H$^+$H$^-$, using a data sample of $5.9\,$pb$^{-1}$ of $e^+ e^-$ collisions at $\sqrt{s}=130$-$136\,{\mathrm {GeV}}$ collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on $b$-tagging finds no hA candidate with high mass. A study optimized to search for H$^+$H$^-$ events with mass in the 40-50$\,{\mathrm{GeV}}/c^2$ range also finds no candidate. Finally a comparison is made with a recent ALEPH a…
Search for Higgs bosons decaying to WW in e(+)e(-) stope collisions at LEP
2006
A search for Higgs bosons produced in association with a fermion pair, and decaying to WW, is performed with the data collected by the ALEPH detector at centre-of-mass energies ranging from 191 to 209 GeV. The data correspond to an integrated luminosity of 453.2 pb^-1. Thirteen exclusive selections are developed according to the different final state topologies. No statistically significant evidence for a Higgs boson decaying into a WW pair has been found. An upper limit is derived, as a function of the Higgs boson mass, on the product of the e+e- -> Hff cross section and the H -> WW branching ratio. The data on the search for H -> WW are combined with previously published ALEPH re…
Inclusive semileptonic branching ratios of b hadrons produced in Z decays
2001
A measurement of the inclusive semileptonic branching ratios of b hadrons produced in Z decay is presented, using four million hadronic events collected by the ALEPH detector from 1991 to 1995. Electrons and muons are selected opposite to b-tagged hemispheres. Two different methods are explored to distinguish the contributions from direct $\bl$ and cascade $\bcl$ decays to the total lepton yield. One is based on the lepton transverse momentum spectrum, the other makes use of the correlation between the charge of the lepton and charge estimators built from tracks in the opposite hemisphere of the event. The latter method reduces the dependence on the modelling of semileptonic b decays. The r…
Precision calculations of dark matter relic abundance
2019
The dark matter annihilation channels sometimes involve sharp resonances. In such cases the usual momentum averaged approximations for computing the DM abundance may not be accurate. We develop an easily accessible momentum dependent framework for computing the DM abundance accurately and efficiently near such features. We apply the method to the case of a singlet scalar dark matter $s$ interacting with SM through higgs portal $\lambda_{\rm hs}s^2 h^2$ and compare the results with different momentum averaged methods. The accuracy of the latter depend strongly on the strength of the elastic interactions and corrections are large if WIMP has negligible interactions beyond the main annihilatio…
Quantum walks as simulators of neutrino oscillations in a vacuum and matter
2016
We analyze the simulation of Dirac neutrino oscillations using quantum walks, both in vacuum and in matter. We show that this simulation, in the continuum limit, reproduces a set of coupled Dirac equations that describe neutrino flavor oscillations, and we make use of this to establish a connection with neutrino phenomenology, thus allowing to fix the parameters of the simulation for a given neutrino experiment. We also analyze how matter effects for neutrino propagation can be simulated in the quantum walk. In this way, important features, such as the MSW effect, can be incorporated. Thus, the simulation of neutrino oscillations with the help of quantum walks might be useful to explore the…
Theoretical estimates of supernova-neutrino cross sections for the stable even-even lead isotopes: Charged-current reactions
2016
A detailed study of the charged-current supernova electron neutrino and electron antineutrino scattering off the stable even-mass lead isotopes $A=204$, 206, and 208 is reported in this work. The proton-neutron quasiparticle random-phase approximation (pnQRPA) is adopted to construct the nuclear final and initial states. Three different Skyrme interactions are tested for their isospin and spin-isospin properties and then applied to produce (anti)neutrino-nucleus scattering cross sections for (anti)neutrino energies below 80 MeV. Realistic estimates of the nuclear responses to supernova (anti)neutrinos are computed by folding the computed cross sections with a two-parameter Fermi-Dirac distr…