Search results for "Vector"
showing 10 items of 2660 documents
Charm quark mass with calibrated uncertainty
2016
We determine the charm quark mass ${\hat m}_c({\hat m}_c)$ from QCD sum rules of moments of the vector current correlator calculated in perturbative QCD. Only experimental data for the charm resonances below the continuum threshold are needed in our approach, while the continuum contribution is determined by requiring self-consistency between various sum rules, including the one for the zeroth moment. Existing data from the continuum region can then be used to bound the theoretical error. Our result is ${\hat m}_c({\hat m}_c) = 1272 \pm 8$ MeV for $\hat\alpha_s(M_Z) = 0.1182$. Special attention is given to the question how to quantify and justify the uncertainty.
Tevatron constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quark pairs.
2015
et al.
Charmed Mesons in Nuclei with Heavy-Quark Spin Symmetry
2012
We study the properties of charmed pseudoscalar and vector mesons in dense matter within a unitary meson-baryon coupled-channel model which incorporates heavy-quark spin symmetry. This is accomplished by extending the SU(3) Weinberg-Tomozawa Lagrangian to SU(8) spin-flavor symmetry and implementing a suitable flavor symmetry breaking. Several resonances with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with $1/2^+$ and $3/2^+$ baryons. Those states are then compared to experimental data as well as theoretical models. Next, Pauli-blocking effects and meson self-energies are introduced in a self-consistent manner to obtai…
Consistent measurements of alpha(s) from precise oriented event shape distributions
2000
An updated analysis using about 1.5 million events recorded at $\sqrt{s} = M_Z$ with the DELPHI detector in 1994 is presented. Eighteen infrared and collinear safe event shape observables are measured as a function of the polar angle of the thrust axis. The data are compared to theoretical calculations in ${\cal O} (\alpha_s^2)$ including the event orientation. A combined fit of $\alpha_s$ and of the renormalization scale $x_{\mu}$ in $\cal O(\alpha_s^2$) yields an excellent description of the high statistics data. The weighted average from 18 observables including quark mass effects and correlations is $\alpha_s(M_Z^2) = 0.1174 \pm 0.0026$. The final result, derived from the jet cone energ…
Search for the Associated Production of the Standard-Model Higgs Boson in the All-Hadronic Channel
2009
We report on a search for the standard-model Higgs boson in pp collisions at s=1.96 TeV using an integrated luminosity of 2.0 fb(-1). We look for production of the Higgs boson decaying to a pair of bottom quarks in association with a vector boson V (W or Z) decaying to quarks, resulting in a four-jet final state. Two of the jets are required to have secondary vertices consistent with B-hadron decays. We set the first 95% confidence level upper limit on the VH production cross section with V(-> qq/qq('))H(-> bb) decay for Higgs boson masses of 100-150 GeV/c(2) using data from run II at the Fermilab Tevatron. For m(H)=120 GeV/c(2), we exclude cross sections larger than 38 times the standard-m…
The phi NN coupling from chiral loops
2002
Starting from effective Lagrangians which combine a gauge formulation of Vector Meson Dominance with Chiral Lagrangians, the coupling of the phi to the nucleon, which is zero at tree level due to the OZI rule, is calculated perturbatively considering loop contributions to the electric and magnetic form factors. We obtain reasonably smaller values for both form factors than those for rho NN and consistent with the expected order of magnitude of the OZI rule violation.
New Angle on the Strong CP and Chiral Symmetry Problems from a Rotating Mass Matrix
2007
It is shown that when the mass matrix changes in orientation (i.e. rotates) in generation space for a changing energy scale, the masses of the lower generations are not given just by its eigenvalues. In particular, these masses need not be zero even when the eigenvalues are zero. In that case, the strong CP problem can be avoided by removing the unwanted theta term by a chiral transformation not in contradiction with the nonvanishing quark masses experimentally observed. Similarly, a rotating mass matrix may shed new light on the problem of chhiral symmetry breaking. That the fermion mass matrix may so rotate with the scale has been suggested before as a possible explanation for up-down fer…
Long-distance structure of the X(3872)
2014
We investigate heavy quark symmetries for heavy meson hadronic molecules, and explore the consequences of assuming the X(3872) and $Z_b(10610)$ as an isoscalar $D\bar D^*$ and an isovector $B\bar B^*$ hadronic molecules, respectively. The symmetry allows to predict new hadronic molecules, in particular we find an isoscalar $1^{++}$ $B\bar B^*$ bound state with a mass about 10580 MeV and the isovector charmonium partners of the $Z_b(10610)$ and the $Z_b(10650)$ states. Next, we study the $X(3872) \to D^0 \bar D^0\pi^0$ three body decay. This decay mode is more sensitive to the long-distance structure of the X(3872) resonance than its $J/\psi\pi\pi$ and $J/\psi3\pi$ decays, which are mainly c…
Dirac operator spectrum in the linear σ model
2003
Abstract The spectrum of the Dirac operator for the linear σ Model with quarks in the large Nc approximation is presented. The spectral density can be related to the chiral condensate which is obtained using renormalization group flow equations. For small eigenvalues, the Banks-Casher relation and the vanishing linear correaction are recovered. The spectrum beyond the low energy regime is discussed.
The $Z$ boson in the Framed Standard Model
2018
The framed standard model (FSM), constructed initially for explaining the existence of three fermion generations and the hierarchical mass and mixing patterns of quarks and leptons, suggests also a "hidden sector" of particles including some dark matter candidates. It predicts in addition a new vector boson $G$, with mass of order TeV, which mixes with the $\gamma$ and $Z$ of the standard model yielding deviations from the standard mixing scheme, all calculable in terms of a single unknown parameter $m_G$. Given that standard mixing has been tested already to great accuracy by experiment, this could lead to contradictions, but it is shown here that for the three crucial and testable cases s…