Search results for "Invariant"
showing 10 items of 783 documents
Quark–lepton mass relation in a realistic A4 extension of the Standard Model
2013
We propose a realistic A4A4 extension of the Standard Model involving a particular quark–lepton mass relation, namely that the ratio of the third family mass to the geometric mean of the first and second family masses are equal for down-type quarks and charged leptons. This relation, which is approximately renormalization group invariant, is usually regarded as arising from the Georgi–Jarlskog relations, but in the present model there is no unification group or supersymmetry. In the neutrino sector we propose a simple modification of the so-called Zee–Wolfenstein mass matrix pattern which allows an acceptable reactor angle along with a deviation of the atmospheric and solar angles from thei…
Four-quark spectroscopy within the hyperspherical formalism
2006
We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ …
Study of exclusive semileptonic and nonleptonic decays ofBc−in a nonrelativistic quark model
2006
We present results for different observables measured in semileptonic and non-leptonic decays of the $B_c^-$ meson. The calculations have been done within the framework of a nonrelativistic constituent quark model. In order to check the sensitivity of all our results against the inter-quark interaction we use five different quark--quark potentials. We obtain form factors, decay widths and asymmetry parameters for semileptonic $B_c^-\to c\bar c$ and $B_c^-\to \bar B$ decays. In the limit of infinite heavy quark mass our model reproduces the constraints of heavy quark spin symmetry. For the actual heavy quark masses we find nonetheless large corrections to that limiting situation for some for…
A new state of hadronic matter at high density
1997
We propose in this article that if the chemical potential exceeds a critical value in dense hadronic medium, a first-order phase transition to a new state of matter with Lorentz symmetry spontaneously broken (in addition to the explicit breaking) takes place. As a consequence, light vector mesons get excited as ``almost'' Goldstone bosons. Since the light vector mesons dominantly couple to photons, the presence of these new vector mesons could lead to an enhancement in the dilepton production from dense medium at an invariant mass lower than the free-space vector-meson mass. We provide a low-energy quark model which demonstrates that the above scenario is a generic case for quark theories w…
Parton showers from the dipole formalism
2007
We present an implementation of a parton shower algorithm for hadron colliders and electron-positron colliders based on the dipole factorisation formulae. The algorithm treats initial-state partons on equal footing with final-state partons. We implemented the algorithm for massless and massive partons.
The CP-Conserving Direction
1998
A symmetry transformation is well defined in the case of an invariant theory, being the corresponding operator undetermined otherwise. However, we show that, even with CP violation, it is possible to determine the CP transformation by separating the Lagrangian of the Standard Model in a CP-conserving and a CP-violating part, in a unique way, making use of the empirically known quark mixing hierarchy. To order \lambda^3 for the Bd-system, the CP-conserving direction matches one of the sides of the (bd) unitarity triangle. We use this determination to calculate the rephasing invariant parameter \epsilon, which measures CP-mixing in the B0-B0bar system.
Measurement of the Branching Fractions ofB¯→D**ℓ−ν¯ℓDecays in Events Tagged by a Fully ReconstructedBMeson
2008
We report a measurement of the branching fractions of D**- decays based on 417 fb-1 of data collected at the (4S) resonance with the BABAR detector at the PEP-II e+e- storage rings. Events are selected by fully reconstructing one of the B mesons in a hadronic decay mode. A fit to the invariant mass differences m(D(*))-m(D(*)) is performed to extract the signal yields of the different D** states. We observe the D**- decay modes corresponding to the four D** states predicted by heavy quark symmetry with a significance greater than 5 standard deviations including systematic uncertainties.
Measurement of the Effective Weak Mixing Angle inpp¯→Z/γ*→e+e−Events
2015
We present a measurement of the fundamental parameter of the standard model, the weak mixing angle, in $p\bar{p}\rightarrow Z/\gamma^{*}\rightarrow e^{+}e^{-}$ events at a center of mass energy of 1.96 TeV, using data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron. The effective weak mixing angle is extracted from the forward-backward charge asymmetry as a function of the invariant mass around the Z boson pole. The measured value of $\sin^2\theta_{\text{eff}}^{\text{$\ell$}}=0.23146 \pm 0.00047$ is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.
The Bc → J/ΨKD weak decay and its relation with the D*s0(2317) resonance
2016
We study the influence of the D * s 0 (2317) + resonance in the decay B c → J/ψKD . In this process, we consider that the B c meson decays first into J/ψ and the quark pair cs , and then the quark pair hadronizes into DK or D s η components. The final state interaction, generating the D * s 0 (2317) + resonance, is described by the chiral heavy meson unitary approach. With the parameters chosen in order to match the pole position of the D * s 0 (2317) + , we obtain the DK invariant mass distribution of the decay B c → J/ψDK , and also the rate for B c → J/ψD * s 0 (2317). We predict the ratio of these two magnitudes. This decay mechanism has not been measured yet, and it would provide insig…
SU(3) Analysis of $$p\overline p$$ Decays into Two Mesons
1985
The process \(p\overline p \to MM'\) is analyzed in terms of 8 SU(3) invariant amplitudes with definite charge conjugation properties. The amplitudes are constructed such that they either correspond to quark annihilation or rearrangement diagrams. For the C’-odd case the process \(p\overline p \to PS + PS\) is examined, whereas for the C’-even case the decay \(p\overline p \to PS + V\) is analyzed. It will be shown that for C’-odd both annihilation and rearrangement contribute, whereas rearrangement is dominant in the C’-even case.