Search results for "Baryon"
showing 10 items of 759 documents
Search for the supersymmetric partner of the top quark inpp¯collisions ats=1.96 TeV
2010
We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy root s = 1: 96 TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb(-1) collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence …
Standard Model CP-violation and Baryon asymmetry
1993
Simply based on CP arguments, we argue against a Standard Model explanation of the baryon asymmetry of the universe in the presence of a first order phase transition. A CP-asymmetry is found in the reflection coefficients of quarks hitting the phase boundary created during the electroweak transition. The problem is analyzed both in an academic zero temperature case and in the realistic finite temperature one. The building blocks are similar in both cases: Kobayashi-Maskawa CP-violation, CP-even phases in the reflection coefficients of quarks, and physical transitions due to fermion self-energies. In both cases an effect is present at order $\alpha_W^2$ in rate. A standard GIM behaviour is f…
Measurement of the electric charge of the top quark intt¯events
2014
We present a measurement of the electric charge of top quarks using t (t) over bar events produced in p (p) over bar collisions at the Tevatron. The analysis is based on fully reconstructed t (t) over bar pairs in lepton + jets final states. Using data corresponding to 5.3 fb(-1) of integrated luminosity, we exclude the hypothesis that the top quark has a charge of Q = -4/3e at a significance greater than 5 standard deviations. We also place an upper limit of 0.46 on the fraction of such quarks that can be present in an admixture with the standard model top quarks (Q = +2/3e) at a 95% confidence level.
Chiral quark cluster model approach to the baryon spectra and the NN interaction
2000
Pion-Quark Interaction and Baryon Mass Splitting
1985
Heavy Quark Symmetries: Molecular Partners of the X(3872) and $Z_{b}(10610)/Z_{b}'(10650)$
2013
In this work, we have used an Effective Field Theory (EFT) framework based on Heavy Quark Spin (HQSS), Heavy Flavour (HFS) and Heavy Antiquark-Diquark symmetries (HADS). Using a standard lagrangian for the heavy meson-heavy antimeson system, we fit the counter-terms of the model to predict some promising experimental data that can be interpreted as heavy meson-heavy antimeson molecules, that is, the X(3872) and the $Z_{b}(10610)/Z'_{b}(10650)$. Next, and, taking advantage of HADS, we use the same lagrangian to explore the consequences for heavy meson-doubly heavy baryon molecules, which can also be interpreted as triply heavy pentaquarks.
Symmetry Violations and Quark Flavour Physics
2020
AbstractOne of the surprising facts in our present understanding of the development of the Universe is the complete absence of “primordial” antimatter from the Big Bang about 13.7 billion years ago. The detection of charged cosmic-ray particles by magnetic spectrometers borne by balloons, satellites, and the space shuttle has shown no evidence for such primordial (high-energy) antibaryons; nor has the search for gamma rays from antimatter–matter annihilation yielded any such observation. In the early phases of the expanding Universe, a hot (1032 K) and dense plasma of quarks, antiquarks, leptons, antileptons and photons coexisted in equilibrium. This plasma expanded and cooled down, and mat…
Molecular $\Omega_c$ states generated from coupled meson-baryon channels
2018
We have investigated $\Omega_c$ states that are dynamically generated from the meson-baryon interaction. We use an extension of the local hidden gauge to obtain the interaction from the exchange of vector mesons. We show that the dominant terms come from the exchange of light vectors, where the heavy quarks are spectators. This has as a consequence that heavy quark symmetry is preserved for the dominant terms in the $(1/m_Q)$ counting, and also that the interaction in this case can be obtained from the $\textrm{SU(3)}$ chiral Lagrangians. We show that for a standard value for the cutoff regulating the loop, we obtain two states with $J^{P}={1/2}^{-}$ and two more with $J^{P}={3/2}^{-}$, thr…
Exotic dynamically generated baryons with C=-1
2010
We follow a model based on the SU(8) symmetry for the interaction of mesons with baryons. The model treats on an equal footing the pseudo-scalars and the vector mesons, as required by heavy quark symmetry. The T-matrix calculated within an unitary scheme in coupled channels has poles which are interpreted as baryonic resonances.
The effect of hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons
2010
We consider the role played by hyperfine mixing in electromagnetic and semileptonic decays of doubly heavy baryons, which give rise to large corrections to the decay widths in both cases.