Tau magnetic moment González-Sprinberg, G. A.; Vidal, J.
Journal of physics. Conference series,
10/2017, Letnik:
912, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The τ lepton magnetic moment theoretical predictions and measurements are reviewed. While it is believed that such a high mass particle is a good candidate to show up new physics, this is not the ...case up to now. The magnetic moment of elementary fermions, and in particular the anomalous magnetic moment of the electron, had an historical impact both in relativistic quantum mechanics and in quantum field theories. Besides, many new physics models were discarded when confronted with these magnitudes. More recently, the discrepancy of the experiments and the theoretical predictions for the muon anomalous magnetic moment is still an open issue. For the τ lepton, instead, while the theoretical prediction is well known for the standard model and some new physics models, the data are very far of determining even its sign or the first figure. We will discuss the most important theoretical aspects of the τ magnetic moment, and also the current accepted measurements and future perspectives, in particular related to B-factories.
The proposed high-luminosity B/flavor factories offer new opportunities for the improved determination of the fundamental physical parameters of standard heavy leptons. Compared to the electron or ...the muon case, the magnetic properties of the
τ lepton are largely unexplored. We show that the electromagnetic properties of the
τ, and in particular its magnetic form factor, may be measured competitively in these facilities, using unpolarized or polarized electron beams. Various observables of the
τ's produced on top of the
ϒ resonances, such as cross-section and normal polarization for unpolarized electrons or longitudinal and transverse asymmetries for polarized beams, can be combined in order to increase the sensitivity on the magnetic moment form factor. In the case of polarized electrons, we identify a special combination of transverse and longitudinal
τ polarizations able to disentangle this anomalous magnetic form factor from both the charge form factor and the interference with the
Z-mediating amplitude. For an integrated luminosity of
15
×
10
18
b
−1
one could achieve a sensitivity of about 10
−6, which is several orders of magnitude below any other existing high- or low-energy bound on the magnetic moment. Thus one may obtain a QED test of this fundamental quantity to a few % precision.
Radiation treatment of cancer has evolved to include massive particle beams, instead of traditional irradiation procedures. Thus, patient doses and worker radiological protection have become issues ...of constant concern in the use of these new technologies, especially for proton- and heavy-ion-therapy. In the beam energies of interest of heavy-ion-therapy, secondary particle radiation comes from proton, neutron, and neutral and charged pions produced in the nuclear collisions of the beam with human tissue atoms. This work, for the first time, offers the upper bound of meson radiation dose in organic tissues due to secondary meson radiation in heavy-ion therapy. A model based on intranuclear collision has been used to follow in time the nuclear reaction and to determine the secondary radiation due to the meson yield produced in the beam interaction with nuclei in the tissue-equivalent media and water. The multiplicity, energy spectrum, and angular distribution of these pions, as well as their decay products, have been calculated in different scenarios for the nuclear reaction mechanism. The results of the produced secondary meson particles has been used to estimate the energy deposited in tissue using a cylindrical phantom by a transport Monte Carlo simulation and we have concluded that these mesons contribute at most 0.1% of the total prescribed dose.
The new proposals for high luminosity B/Flavor factories, near and on top of the
ϒ resonances, allow for a detailed investigation of CP-violation in the
τ-pair production. In particular, bounds on ...the tau electric dipole moment can be obtained of genuine CP-odd observables related to the
τ-pair production. We perform an independent analysis from low energy (10 GeV) data by means of linear spin observables. We show that for a longitudinally polarized electron beam a CP-odd asymmetry, associated to the normal polarization term, can be measured at these low energy facilities both at resonant and non-resonant energies. In this way stringent and independent bounds to the tau electric dipole moment, which are orders of magnitude below other high or low energy previous bounds, can be obtained.
FCNC top quark decays in extra dimensions González-Sprinberg, G.A.; Martínez, R.; Rodriguez, J.-A.
The European physical journal. C, Particles and fields,
8/2007, Letnik:
51, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The flavor changing neutral top quark decay t→cX is computed, where X is a neutral standard model particle, in an extended model with a single extra dimension. The cases for the photon, X=γ, and a ...standard model Higgs boson, X=H, are analyzed in detail in a non-linear Rξ gauge. We find that the branching ratios can be enhanced by the dynamics originating in the extra dimension. In the limit where 1/R≫mt, we have found Br(t→cγ)≃10-10 for 1/R = 0.5 TeV. For the decay t→cH, we have found Br(t→cH)≃10-10 for a low Higgs mass value. The branching ratios go to zero when 1/R→∞.
Purpose:
To optimize the dose in bladder and rectum and show the different shapes of the isodose volumes in Co60-HDR brachytherapy, considering different utero and vaginal sources dwell ratio times ...(TU:TV).
Methods:
Besides Ir192-HDR, new Co60-HDR sources are being incorporated. We considered different TU:TV times and computed the dosis in bladder, rectum and at the reference points of the Manchester system. Also, we calculated the isodose volume and shape in each case. We used a EZAG-BEBIG Co0.A86 model with TPS HDRplus3.0.4. and LCT42-7, LCT42-2(R,L) applicators. A reference dose RA= 1.00 Gy was given to the A-right point. We considered the TU:TV dwell time ratios 1:0.25, 1:0.33, 1:0.5, 1:1, 1:2, 1:3, and 1:4. Given TU:TV, the stop time at each dwell position is fixed for each applicator.
Results:
Increasing TU:TV systematically results in a decreasing of the dose in bladder and rectum, e.g. 9% and 27% reduction were found in 1:0.25 with respect to 1:1, while 12% and 34% increase were found in 1:4 with respect to 1:1. Also, the isodose volume parameters height (h), width (w), thickness (t) and volume (hwt) increased from the 1:0.25 case to the 1:4 value: hwt is 25% lower and 31% higher than the 1:1 reference volume in these cases. Also w decreased for higher TU:TV and may compromise the tumoral volume coverage, decreasing 17% in the 1:0.25 case compared to the 1:1 case. The shape of the isodose volume was obtained for the different TU:TV considered.
Conclusion:
We obtained the shape of isodose volumes for different TU:TV values in gynecological Co60-HDR. We studied the dose reduction in bladder and rectum for different TU:TV ratios. The volume parameters and hwt are strongly dependent on this ratio. This information is useful for a quantitative check of the TPS and as a starting point towards optimization.
In this study, three holders were designed, constructed and characterized to perform quality assurance on the source position and transit time in remote afterloading systems with Co-60 sources for ...high dose rate brachytherapy. The holders design focused on achieving accuracy, low cost, and a time efficient tool for use in clinical settings. Sensitivities greater than 0.6%/mm and maximum precisions better than 0.14 mm for the source position were obtained. The transit time was determined for the holders with a relative precision better than 19%.
•Quality assurance in HDR brachytherapy strongly depends on system parameters.•Check of the dwell positions and transit time in an afterloader with a Co-60 source.•Three holders constructed for quality assurance on Co-60 HDR afterloader.•Design focused on accuracy, low cost, and a time efficiency for clinical settings.
Precise measurements of magnetic and electric dipole moments are important tests of the Standard Model and beyond Standard Model physics, particularly for the electron and the muon. However, the ...situation presents distinctive challenges when dealing with the tau lepton due to its very short lifetime and relatively high mass. Here, we review the theoretical predictions and experimental measurements of both the anomalous magnetic and electric dipole moments of the tau lepton. Note: Contribution to the proceedings of the 17th International Workshop on Tau Lepton Physics, Louisville, USA, 4-8 December 2023
CP violation at low energy is investigated at the
τ electromagnetic vertex. High statistics at B-factories, and on top of the
ϒ resonances, allows a detailed investigation of CP-odd observables ...related to the
τ-pair production. The contribution of the tau electric dipole moment is considered in detail. We perform an analysis independent from the high energy data by means of correlation and linear spin observables at low energy. We show that different CP-odd asymmetries, associated to the normal–transverse and normal–longitudinal correlation terms can be measured at low energy accelerators, both at resonant and non-resonant energies. These observables allow to put stringent and independent bounds to the tau electric dipole moment that are competitive with other high or low energy results.
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