Search results for "DIPOLE"
showing 10 items of 982 documents
Dispersive analysis of the γγ⁎ → ππ process
2019
Abstract We present a theoretical study of the γ γ ⁎ → π + π − , π 0 π 0 processes from the threshold through the f 2 ( 1270 ) region in the ππ invariant mass. We adopt the Omnes representation in order to account for rescattering effects in both s- and d-partial waves. For the description of the f 0 ( 980 ) resonance, we implement a coupled-channel unitarity. The constructed amplitudes serve as an essential framework to interpret the current experimental two-photon fusion program at BESIII. They also provide an important input for the dispersive analyses of the hadronic light-by-light scattering contribution to the muon's anomalous magnetic moment.
Search for CP violation in ZmF ττ
1992
Abstract Using the 18.8 pb−1 of data accumulated at LEP in 1990 and 1991 with the ALEPH detector, a direct test of neutral current CP-invariance is performed by a search for CP-odd correlations in Z decays to τ pairs where both τ decay modes are identified. No evidence for CP-violation is observed. The weak dipole moment of the τ has been measured to be dτ(mZ) = (1.3 ± 1.4 ± 0.1) × 10−17 e·cm which results in an upper limit on the weak dipole moment of |dτ(mZ)| ⩽ 3.7 × 10−17 e·cm with 95% confidence level.
IMPROVED BOUNDS ON THE TAU MAGNETIC MOMENTS
2001
New limits on the tau magnetic couplings to the photon, the Z and the W bosons are obtained from the most general effective Lagrangian. Model independent bounds are set using data for tau pair production and W decay into tau leptons at LEP1, LEP2, SLD and hadron colliders. For the anomalous magnetic moment the bounds are, for the first time, of the order of magnitude of the standard model prediction.
Quasielastic neutrino (antineutrino) reactions in nuclei and the axial-vector form factor of the nucleon
1992
Abstract Quasielastic neutrino and antineutrino reactions in nuclei are studied to investigate the effect of the nuclear medium on the determination of axial dipole mass M A in nuclei. The calculations are done in the local density approximation and various nuclear effects like Pauli blocking, Fermi motion of nucleons and strong renormalization effects in the spin-isospin channel are taken into account. The nuclear effects are found to be quite large at low q 2 , but the data in this region are too meagre to influence the determination of M A . The experimental data on differential and total cross sections are found to be consistent with M A as determined from deuterium experiments and no c…
Leptonic universality breaking in Upsilon decays as a probe of new physics
2003
In this work we examine the possible existence of new physics beyond the standard model which could modify the branching fractions of the leptonic (mainly tauonic) decays of bottomonium vector resonances below the $B\bar{B}$ threshold. The decay width is factorized as the product of two pieces: a) the probability of an intermediate pseudoscalar color-singlet $b\bar{b}$ state (coupling to the dominant Fock state of the Upsilon via a magnetic dipole transition) and a soft (undetected) photon; b) the annihilation width of the $b\bar{b}$ pair into two leptons, mediated by a non-standard CP-odd Higgs boson of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in the partial…
Study of the discovery potential for hidden photon emission at future electron scattering fixed target experiments
2013
Electron scattering fixed target experiments are a versatile tool to explore various physics phenomena. Recently these experiments came into focus to search for $U(1)$ extensions of the Standard Model of particle physics at low energies. These extensions are motivated from anomalies in astrophysical observations as well as from deviations from Standard Model predictions, such as the discrepancy between the experimental and theoretical determination of the anomalous magnetic moment of the muon. They also arise naturally when the Standard Model is embedded into a more general theory. In the considered $U(1)$ extensions a new, light messenger particle $\gamma^\prime$, the hidden photon, couple…
Searching for new physics in leptonic decays of bottomonium
2002
New Physics can show up in various well-known processes already studied in the Standard Model, in particular by modifying decay rates to some extent. In this work, I examine leptonic decays of $\Upsilon$ vector resonances of bottomonium below $B\bar{B}$ production, subsequent to a magnetic dipole radiative structural transition of the vector resonance yielding a pseudoscalar continuum state, searching for the existence of a light Higgs-like neutral boson that would imply a slight but experimentally measurable breaking of lepton universality.
Electric dipole moments from flavor-changing supersymmetric soft terms
2008
The standard model predictions for the hadronic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics (effects. Especially, within a minimal supersymmetric standard model framework with flavor-changing (but not necessarily CP-violating) soft terms, large and potentially visible effects to the EDMs are typically expected. In this paper we point out that, beyond-leading-order effects, so far neglected in the literature, dominate over the leading-order effects in large regions of the parameter space; hence, their inclusion in the evaluation of the hadronic EDMs is unavoidable.
A potential test of the CP properties and Majorana nature of neutrinos
1999
The scattering of solar neutrinos on electrons may reveal their CP properties, which are particularly sensitive to their Majorana nature. The cross section is sensitive to the neutrino dipole moments through an interference of electro-magnetic and weak amplitudes. We show how future solar neutrino experiments with good angular resolution and low energy threshold, such as Hellaz, can be sensitive to the resulting azimuthal asymmetries in event number, and could therefore provide valuable information on the CP properties and the nature of the neutrinos, provided the solar magnetic field direction is fixed.
Gluon spectrum in the glasma from JIMWLK evolution
2011
The JIMWLK equation with a "daughter dipole" running coupling is solved numerically starting from an initial condition given by the McLerran-Venugopalan model. The resulting Wilson line configurations are then used to compute the spectrum of gluons comprising the glasma inital state of a high energy heavy ion collision. The development of a geometrical scaling region makes the spectrum of produced gluons harder. Thus the ratio of the mean gluon transverse momentum to the saturation scale grows with energy. Also the total gluon multiplicity increases with energy slightly faster than the saturation scale squared.