Search results for "dipole"
showing 10 items of 982 documents
Bounds on the Tau Magnetic Moments: Standard Model and Beyond
2001
We obtain new bounds for the magnetic dipole moments of the tau lepton. These limits on the magnetic couplings of the tau to the electroweak gauge bosons (gamma, W, Z) are set in a model independent way using the most general effective Lagrangian with the SU(2)_L x U(1)_Y symmetry. Comparison with data from the most precise experiments at high energies shows that the present limits are more stringent than the previous published ones. For the anomalous magnetic moment the bounds are, for the first time, within one order of magnitude of the standard model prediction.
Search for dark photons from neutral meson decays inp+pandd+Aucollisions atsNN=200 GeV
2015
The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g−2)μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a “dark photon,” an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π0,η→γe+e− decays and obtained upper limits of O(2×10−6) on U−γ mixing at 90% C.L. for the mass range 30<mU<90 MeV/c2. Combined with other experimental limits, the remaining region in the U−γ mixing parameter space that can explain the (g−2)μ deviation from its SM…
Two-loop gluino contributions to the neutron electric dipole moment in theCP-violating minimal supersymmetric standard model
2005
We analyze two-loop gluino corrections to the neutron electric dipole moment (EDM) in the minimal supersymmetry extension of the standard model (MSSM). The dependence of two-loop corrections on the relevant CP violating phases differs from that of the one-loop contributions, and there is a region in the parameter space where the two-loop contributions are comparable with the one-loop contributions. Our numerical results show that the two-loop corrections can be as large as 30% of the one-loop results.
Electric Dipole Moments in Two-Higgs-Doublet Models
2014
Electric dipole moments are extremely sensitive probes for additional sources of CP violation in new physics models. Specifically, they have been argued in the past to exclude new CP-violating phases in two-Higgs-doublet models. Since recently models including such phases have been discussed widely, we revisit the available constraints in the presence of mechanisms which are typically invoked to evade flavour-changing neutral currents. To that aim, we start by assessing the necessary calculations on the hadronic, nuclear and atomic/molecular level, deriving expressions with conservative error estimates. Their phenomenological analysis in the context of two-Higgs-doublet models yields strong…
Electric dipole moments from flavoredCPviolation in supersymmetry
2008
The so-called supersymmetric flavor and $CP$ problems are deeply related to the origin of flavor and hence to the origin of the standard model Yukawa couplings themselves. We show that realistic $SU(3)$ flavor symmetries with spontaneous $CP$ violation reproducing correctly the standard model Yukawa matrices can simultaneously solve both problems without ad hoc modifications of the supersymmetric model. We analyze the leptonic electric dipole moments and lepton flavor violation processes in these models. We show that the electron electric dipole moment and the decay $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ are naturally within reach of the proposed experiments if the s…
Vector-like leptons: Higgs decays and collider phenomenology
2013
We study the impact of heavy vector-like leptons on several observables in collider and low-energy physics. These states, present in many well-motivated extensions of the Standard Model, can induce lepton flavour violation and non-standard Higgs decays. We study these effects in an effective model inspired by the composite Higgs scenario. After deriving bounds on the mass and production cross-section of the vector-like states using recent LHC data on multilepton searches, we discuss the modification of the Higgs decays to dilepton, diphoton and $Z\gamma$ final states as well as low-energy observables like radiative lepton decays, the anomalous magnetic moment of the muon and the electric di…
Status of the g-2 experiment at BNL
1999
The muon g-2 experiment at Brookhaven has successfully completed two exploratory runs using pion injection and direct muon injection for checkout and initial data taking. The main components of the experiment, which include the pion beam line, the superconducting storage ring and inflector magnets, the muon kicker and the lead-scintillating fiber calorimeters have been satisfactorily commissioned. First results on the anomalous magnetic moment of the positive muon from pion injection are in good agreement with previous experimental results for a(mu+) and a(mu-) from CERN and of comparable accuracy (13 ppm). Analysis of the 1998 muon injection run is in progress and expected to improve the p…
Nuclear modification of forward J/ψ production in proton-nucleus collisions at the LHC
2016
We re-evaluate the nuclear suppression of forward J/ψ production at high energy in the Color Glass Condensate framework. We use the collinear approximation for the projectile proton probed at large x and an up to date dipole cross section fitted to HERA data to describe the target in proton-proton collisions. We show that using the Glauber approach to generalize the proton dipole cross section to the case of a nucleus target leads to a nuclear modification factor much closer to LHC data than previous estimates using the same framework.
Centrality dependence of forward J/ψ suppression in high energy proton–nucleus collisions
2015
The production of forward $J/\psi$ mesons in proton-nucleus collisions can provide important information on gluon saturation. In a previous work we studied this process in the Color Glass Condensate framework, describing the target using a dipole cross section fitted to HERA inclusive data and extrapolated to the case of a nuclear target using the optical Glauber model. In this work we study the centrality dependence of the nuclear suppression in this model and compare our results with recent LHC data for this observable.
Model independent bounds on the tau lepton electromagnetic and weak magnetic moments
2000
Using LEP1, SLD and LEP2 data, for tau lepton production, and data from CDF, D0 and LEP2, for W decays into tau leptons, we set model independent limits on non-standard electromagnetic and weak magnetic moments of the tau lepton. The most general effective Lagrangian giving rise to tau moments is used without further assumptions. Precise bounds ($2\sigma$) on the non-standard model contributions to tau electromagnetic ($-0.007<a_\gamma< 0.005$), tau Z-magnetic ($-0.0024 <a_Z< 0.0025$) and tau W-magnetic ($-0.003 < \kappa^W < 0.004$) dipole moments are set from the analysis.