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Register a new userSearching for New Physics with multilepton events at PADME
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The PADME experiment is searching for the Dark Photon $A$ in the $e^{+}e^{-} to gamma A$ process, assuming a $A$ decay into invisible particles. In extended Dark Sector models, a Dark Higgs $h$ can be produced alongside $A$ in the process $e^{+}e^{-} to h A$. If the $h$ mass is greater than twice the $A$ mass the final state will be composed by three $e^{+}e^{-}$ pairs. Such extremely rare process is explorable by the PADME experiment, which could get a first measure and impose limits on models of physics beyond the Standard Model.
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In recent years, intriguing hints for the violation of Lepton Flavour Universality (LFU) have been accumulated in semileptonic $B$ decays, both in the neutral-current transitions $bto sell^+ell^-$ (i.e., $R_K$ and $R_{K^*}$) and the charged-current transitions $bto cell^-bar u_ell$ (i.e., $R_D$, $R_{D^*}$ and $R_{J/psi}$). LHCb has reported deviations from the Standard Model (SM) expectations in $bto smu^+mu^-$ processes as well as in the ratios $R_K$ and $R_{K^*}$, which together point at New Physics (NP) affecting muons with a high significance. Furthermore, hints for LFU violation in $R_{D^{(*)}}$ and $R_{J/psi}$ point at large deviations from the SM in processes involving tau leptons. Together, these hints for NP motivate the possibility of huge LFU-violating effects in $bto stau^+tau^-$ transitions. In this article we predict the branching ratios of $Bto Ktau^+tau^-$, $Bto K^{*}tau^+tau^-$ and $B_sto phi tau^+tau^-$ taking into account NP effects in the Wilson coefficients $C_{9()}^{tautau}$ and $C_{10()}^{tautau}$. Assuming a common NP explanation of $R_{D^{}}$ , $R_{D^{(*)}}$ and $R_{J/psi}$, we show that a very large enhancement of $bto stau^+tau^-$ processes, of around three orders of magnitude compared to the SM, can be expected under fairly general assumptions. We find that the branching ratios of $B_sto tau^+tau^-$, $B_sto phi tau^+tau^-$ and $Bto K^{(*)}tau^+tau^-$ under these assumptions are in the observable range for LHCb and Belle II.
We explore the sensitivity to new physics of the recently proposed vIOLETA experiment: a 10 kg Skipper Charged Coupled Device detector deployed 12 meters away from a commercial nuclear reactor core. We investigate two broad classes of models which benefit from the very low energy recoil threshold of these detectors, namely neutrino magnetic moments and light mediators coupled to neutrinos and quarks or electrons. We find that this experimental setup is very sensitive to light, weakly coupled new physics, and in particular that it could probe potential explanations of the event excess observed in XENON1T. We also provide a detailed study on the dependence of the sensitivity on the experimental setup assumptions and on the neutrino flux systematic uncertainties.
We explore the decays of $Bto V_1V_2$ ($V_{1,2}= (rho, omega,K^*, phi)$ and $B= (B^0, B^+,B_s)$) with transverse polarizations. We explicitly evaluate the eigenstates of T-odd scalar operators involving spins for the first time, which offer physical insight among the T violating observables. Based on the helicity suppression of tree operators for transverse polarizations in the standard model (SM), we deduce that $Delta phi_p = phi_parallel - phi_perp=0$ with $phi_{perp,parallel}$ the complex phases of the transverse amplitudes. In contrast, the experiments show that $Delta phi _p (B^0 to K^{*0} omega)= -0.84pm 0.54$, which would be a signal of new physics. There is also a discrepancy between our result in the SM and the experimental data for the transverse polarized branching ratio in $B^0 to K^{*0} omega$. In addition, by counting the helicity flips, we obtain that $sin(phi_p ) approx 0$ in $Bto V_1T_2$ with $T_2$ an arbitrary spin-$n$ meson ($nge1$).
In this talk, I review the status and prospects of several low energy flavor observables that are highly sensitive to New Physics effects. In particular I discuss the implications for possible New Physics in b --> s transitions coming from the recent experimental results on the B_s mixing phase, the branching ratio of the rare decay B_s --> mu+mu-, and angular observables in the B --> K* mu+mu- decay. Also the recent evidence for direct CP violation in singly Cabibbo suppressed charm decays and its interpretation in the context of New Physics models is briefly discussed.
In this work we investigate the usefulness of nuSTORM as a probe of two new-physics scenarios which are sterile neutrinos and non-unitarity of the neutrino mixing matrix. For the sterile neutrino we show the importance of the neutral current events when combined with the charged current events to constrain the effective mixing angle, $theta_{mu mu}$, and the sterile mixing angles $theta_{14}$ and $theta_{24}$. We also study the role nuSTORM will play in the study of neutrino oscillation physics if the three generation neutrino mixing matrix is non-unitary. In this context we elucidate the role of nuSTORM, considering both charged current and neutral current events, in constraining the various non-unitarity parameters such as $alpha_{11}$, $|alpha_{21}|$ and $alpha_{22}$.
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