Search results for "Elementary Particle"
showing 10 items of 659 documents
τ EDM at low energies
2002
Low energy tau pair production, at B factories and on top of the $\Upsilon$ resonances, allows for a detailed investigation on the CP violation at the electromagnetic tau pair production vertex. High statistic available at low energies offers the opportunity for an independent analysis of CP-violation in the $\tau$ lepton physics. We show that stringent and independent bounds on the $\tau$ electric dipole moment, competitive with the high energy measurements, can be established in low energies experiments.
Flavor violation in supersymmetric SU(5) GUT at large tan beta
2001
We study flavor violation in the general SUSY SU(5) GUT assuming all the third generation Yukawa couplings to be due to the renormalizable physics above GUT scale. At large tan beta, as suggested by Yukawa unification in SU(5), sizable flavor violation in the left (right) slepton (down squark) sector can be induced in nonminimal models due to renormalization effects of down type Yukawa couplings between GUT and Planck scales, in addition to the flavor violation in the right slepton sector. The new flavor physics contribution to K-(K) over bar, B-(B) over bar mixing is small but might be of phenomenological interest in the case of b --> s gamma. The sign of the latter contribution is the sam…
Chiral approach to the two pion decay of the Roper
2003
Abstract The analysis of Manley and collaborators [1] of the decay of the Roper into two pions requires the introduction of an effective scalar-isosclar ϵ or σ meson in order to describe the s-wave ππ interaction. Here we try to understand at a more fundamental level the origin of this effective channel. In our model the two pions are produced in single pion-baryon-baryon vertices and their re-scattering in the L=0, I=0 channel is explicitly evaluated. For that purpose we use unitarized chiral perturbation theory to obtain the Bethe-Salpeter amplitude for the two pion re-scattering in the appropriate channel. Our model produces invariant mass distributions in agreement with the ones obtaine…
Tau polarization at the Z peak from the acollinearity between both τ-decay products
1992
21 páginas, 4 figuras, 6 tablas.
Invisible Higgs decays and neutrino physics
1993
Abstract A wide class of neutrino physics motivated models are characterized by the spontaneous violation of a global U(1) lepton number symmetry at or below the electroweak scale by an SU(2)⊗U(1) singlet vacuum expectation value 〈 σ 〉 ≲ O(1) TeV. In all these models the main Higgs decay channel is likely to be “invisible”, e.g. h → JJ, where J denotes the associated weakly interacting pseudoscalar Goldstone boson — the majoron. This leads to events with large missing energy that could be observable at LEP and affect the Higgs mass bounds obtained, as well as lead to novel ways to search for Higgs bosons and high-energy supercolliders such as the LHC/SSC.
Combined Tevatron upper limit ongg→H→W+W−and constraints on the Higgs boson mass in fourth-generation fermion models
2010
We combine results from searches by the CDF and D0 collaborations for a standard model Higgs boson (H) in the process gg -> H -> W+W- in p (p) over bar collisions at the Fermilab Tevatron Collider at root s = 1.96 TeV. With 4.8 fb(-1) of integrated luminosity analyzed at CDF and 5.4 fb(-1) at D0, the 95% confidence level upper limit on sigma(gg -> H) x B(H -> W+W-) is 1.75 pb at m(H) = 120 GeV, 0.38 pb at m(H) = 165 GeV, and 0.83 pb at m(H) = 200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% confidence level a standard-model-like Higgs boson with a mass between 131 and 204 GeV.
Search forWWandWZResonances Decaying to Electron, MissingET, and Two Jets inpp¯Collisions ats=1.96 TeV.
2009
We present a search for WW and WZ production in final states that contain a charged lepton (electron or muon) and at least two jets, produced in {radical}(s)=1.96 TeV pp collisions at the Fermilab Tevatron, using data corresponding to 1.2 fb{sup -1} of integrated luminosity collected with the CDF II detector. Diboson production in this decay channel has yet to be observed at hadron colliders due to the large single W plus jets background. An artificial neural network has been developed to increase signal sensitivity, as compared with an event selection based on conventional cuts. We set a 95% confidence level upper limit of {sigma}{sub WW}xBR(W{yields}l{nu}{sub l},W{yields}jets)+{sigma}{sub…
Lepton flavour nonconservation in H0 decays
1992
Abstract We calculate the off-diagonal lepton-lepton-Higgs boson vertex induced by one-loop electroweak corrections, in the context of the standard model in which one right-handed neutrino for each family has been introduced. We find that in the presence of very heavy Majorana neutrinos the lepton-flavour-violating decays of the H0 boson can be significantly enhanced yielding observable signals at high energy collider machines.
Revealing the Majorana nature of heavy neutrinos via a heavy Higgs boson
1992
Abstract Analyzing several recently proposed models, based on simple extensions of the standard model (SM), with heavy Majorana neutrinos, it is shown that the change of detecting lepton number violation through their production and subsequent decays may be significantly enhanced, if a heavy Higgs boson with mass within a reasonably broad range is present.
Search for neutral Higgs bosons from supersymmetry in Z decays
1990
The light scalar Higgs boson h and the pseudoscalar Higgs boson A of the minimal supersymmetric standard model have been searched for in the processes e+e−→hff and e+e−→hA using data collected by ALEPH at the LEP e+e− collider, with center of mass energies at and near the Z peak. Using a variety of signatures adapted to various mass ranges for h and A, we have excluded a large domain in the parameter space. For large values of ν2ν1, the ratio of the vacuum expectation values of the two Higgs fields, the whole range from 0 to 38.8 GeV is excluded for Mh and MA at 95% CL.