Search

The apparent tensions emerging from the comparison of experimental data of the anomalous magnetic moments of the muon and electron to the Standard Model predictions ( $$\Delta a_{\mu ,e}$$ Δ a μ , e ) could be interpreted as a potential signal of New Physics. Models encompassing a light vector boson have been known to offer a satisfactory explanation to $$\Delta a_{\mu }$$ Δ a μ , albeit subject to stringent experimental constraints. Here we explore a minimal extension of the Standard Model via a leptophilic vector boson $$Z^\prime $$ Z ′ , under the hypothesis of strictly flavour-violating couplings of the latter to leptons. The most constraining observables to this ad-hoc construction emerge from lepton flavour universality violation (in Z and $$\tau $$ τ decays) and from rare charged lepton flavour violating transitions. Once these are accommodated, one can saturate the tensions in $$\Delta a_{\mu }$$ Δ a μ , but $$\Delta a_{e}$$ Δ a e is predicted to be Standard Model-like. We infer prospects for several observables, including leptonic Z decays and several charged lepton flavour violating processes. We also discuss potential signatures of the considered $$Z^\prime $$ Z ′ at a future muon collider, emphasising the role of the $$\mu ^+\mu ^- \rightarrow \tau ^+\tau ^- $$ μ + μ - → τ + τ - forward-backward asymmetry as a key probe of the model.

The apparent tensions emerging from the comparison of experimental data of the anomalous magnetic moments of the muon and electron to the Standard Model predictions ($Δa_{μ,e}$) could be interpreted as a potential signal of New Physics. Models encompassing a light vector boson have been known to offer a satisfactory explanation to $Δa_μ$, albeit subject to stringent experimental constraints. Here we explore a minimal extension of the Standard Model via a leptophilic vector boson $Z^\prime$, under the hypothesis of strictly flavour-violating couplings of the latter to leptons. The most constraining observables to this ad-hoc construction emerge from lepton flavour universality violation (in $Z$ and $τ$ decays) and from rare charged lepton flavour violating transitions. Once these are accommodated, one can saturate the tensions in $Δa_μ$, but $Δa_{e}$ is predicted to be Standard Model-like. We infer prospects for several observables, including leptonic $Z$ decays and several charged lepton flavour violating processes. We also discuss potential signatures of the considered $Z^\prime$ at a future muon collider, emphasising the role of the $μ^+μ^- \toτ^+τ^- $ forward-backward asymmetry as a key probe of the model., 36 pages, 15 figures, v3: minor changes, few clarifications added, results and conclusions unchanged, matches version published in EPJC

International audience; In this paper, we investigated the origins of the Ce positive influence on the radiation response of Yb/Er-doped phosphosilicate optical fibers. To this purpose, we carried out during γ-irradiations an online characterization on active optical fiber prototypes, made with different Ce concentrations and integrated in optical amplifiers. The hardening effect of Ce-codoping is highlighted, as well as some aspects related to the radiation response of the phosphosilicate host glass of the active optical fibers.

We investigated the radiation hardening of optical fiber amplifiers operating in space environments. Through a real-time analysis in active configuration, we evaluated the role of Ce in the improvement of the amplifier performance against ionizing radiations. Ce-codoping is an efficient hardening solution, acting both in the limitation of defects in the host glass matrix of RE-doped optical fibers and in the stabilization of lasing properties of the Er3+-ions. On the one hand, in the nearinfrared region, radiation induced attenuation measurements show the absence of radiation induced P-related defect species in host glass matrix of the Ce-codoped active fibers; on the other hand, in the Ce-free fiber, the higher lifetime variation shows stronger local modifications around the Er3+-ions with the absence of Ce.

National audience; Cette étude vise à comprendre les effets d'une irradiation Ȗ sur les propriétés optiques et structurales des fibres dopées aux Terres Rares en vue de leur utilisation dans des amplificateurs à fibre réalisés pour des applications spatiales. L'enjeu majeur de durcissement de ces composants est abordé via des techniques telles que le chargement en hydrogène et/ou le co-dopage au Cérium du cœur des fibres optiques. L'identification des centres responsables de l'atténuation induite par irradiation et la compréhension des mécanismes de dégradation mis en jeu sont des étapes indispensables au développement de ces fibres.

National audience; Cette étude porte sur les effets des rayonnements ionisants sur les propriétés optiques et structurales des fibres phosphosilicates dopées aux Terres Rares en vue de leur emploi comme amplificateurs optiques pour des applications spatiales. L'action durcissante due au codopage au Cérium est analysée, à travers l'interaction de ce dernier avec la matrice phosphosilicate hôte. L'identification et la limitation des mécanismes responsables de la dégradation sous rayonnements ionisants de la performance des amplificateurs optiques est une étape essentielle pour leur développement technologique.

Heavy neutral leptons are motivated by several extensions of the Standard Model and their presence induces modifications in the lepton mixing matrix, including new Dirac and Majorana CP violating phases. It has been recently shown that these phases play an important role in lepton number and lepton flavour violating decays and transitions, with a striking impact for the predicted rates of certain observables. In this work, we now consider the potential role of the heavy neutral fermions and of the new CP violating phases in Higgs and $Z$-boson lepton flavour violating decays $H,Z\to \ell_\alpha^\pm\ell_\beta^\mp$, as well as in the corresponding CP asymmetries. In order to allow for a thorough analysis, we derive the full analytical expressions of the latter observables, taking into account the effect of the (final state) charged lepton masses. A comprehensive exploration of lepton flavour violating $Z$ and Higgs decays confirms that these are very sensitive to the presence of the additional heavy neutral leptons. Moreover, the new CPV phases have a clear impact on the decay rates, leading to both destructive and constructive interferences. Interestingly, in the $\mu\tau$ sector, the $Z\to \ell_\alpha^\pm\ell_\beta^\mp$ rates are within reach of FCC-ee, with associated CP asymmetries that can potentially reach up to $20\% - 30\%$., Comment: 36 pages, 12 figures

International audience; We present an approach coupling a limited experimental number of tests with numerical simulations regarding the design of radiation-hardened (RH) rare earth (RE)-doped fiber amplifiers. Radiation tests are done on RE-doped fiber samples in order to measure and assess the values of the principal input parameters requested by the simulation tool based on particle swarm optimization (PSO) approach. The proposed simulation procedure is validated by comparing the calculation results with the measured degradations of two amplifiers made with standard and RH RE-doped optical fibers, respectively. After validation, the numerical code is used to theoretically investigate the influence of some amplifier design parameters on its sensitivity to radiations. Simulations show that the RE-doped fiber length used in the amplifier needs to be adjusted to optimize the amplifier performance over the whole space mission profile rather than to obtain the maximal amplification efficiency before its integration in the harsh environment. By combining this coupled approach with the newly-developed RH RE-doped fibers, fiber-based amplifiers nearly insensitive to space environment may be designed in the future.

Er/Yb doped fibers and amplifiers have been shown to be very radiation sensitive, limiting their integration in space. We present an approach including successive hardening techniques to enhance their radiation tolerance. The efficiency of our approach is demonstrated by comparing the radiation responses of optical amplifiers made with same lengths of different rare-earth doped fibers and exposed to gamma-rays. Previous studies indicated that such amplifiers suffered significant degradation for doses exceeding 10 krad. Applying our techniques significantly enhances the amplifier radiation resistance, resulting in a very limited degradation up to 50 krad. Our optimization techniques concern the fiber composition, some possible pre-treatments and the interest of simulation tools used to harden by design the amplifiers. We showed that adding cerium inside the fiber phosphosilicate-based core strongly decreases the fiber radiation sensitivity compared to the standard fiber. For both fibers, a pre-treatment with hydrogen permits to enhance again the fiber resistance. Furthermore, simulations tools can also be used to improve the tolerance of the fiber amplifier by helping identifying the best amplifier configuration for operation in the radiative environment.