Kovalenko, Sergey

The Search for Hidden Particles (SHiP) Collaboration has shown that the CERN SPS accelerator with its 400 GeV c proton beam offers a unique opportunity to explore the Hidden Sector [1–3]. The proposed experiment is an intensity frontier experiment which is capable of searching for hidden particles through both visible decays and through scattering signatures from recoil of electrons or nuclei. The high-intensity experimental facility developed by the SHiP Collaboration is based on a number of key features and developments which provide the possibility of probing a large part of the parameter space for a wide range of models with light long-lived superweakly interacting particles with masses up to O¹10º GeV c2 in an environment of extremely clean background conditions. This paper describes the proposal for the experimental facility together with the most important feasibility studies. The paper focuses on the challenging new ideas behind the beam extraction and beam delivery, the proton beam dump, and the suppression of beam-induced background.

We found a new important tree-level contribution to muon–electron nuclear conversion from neutrino exchange between two quarks in the same nucleon and demonstrated that this process, contrary to common belief, can be observed in the near future experiments if there exists a mixed sterile-active neutrino state νh heavier than the quark confinement scale Λc ∼ 1 GeV. From the present non-observation of muon–electron conversion we derive new experimental constraints on νh − νe,µ mixing

We propose a Majoron-like extension of the Standard Model with an extra global -symmetry where neutrino masses are generated through an inverse seesaw mechanism at the 1-loop level. In contrast to the tree-level inverse seesaw, our framework contains dark matter (DM) candidates stabilized by a residual -symmetry surviving spontaneous breaking of the -group. We explore the case in which the DM is a Majorana fermion. Furthermore, we provide parameter space regions allowed by current experimental constraints coming from the dark matter relic abundance, (in)direct detection, and charged lepton flavor violation.

AbstractWe report the results of a search for a new vector boson ($$ A'$$ A ′ ) decaying into two dark matter particles $$\chi _1 \chi _2$$ χ 1 χ 2 of different mass. The heavier $$\chi _2$$ χ 2 particle subsequently decays to $$\chi _1$$ χ 1 and an off-shell Dark Photon $$ A'^* \rightarrow e^+e^-$$ A ′ ∗ → e + e - . For a sufficiently large mass splitting, this model can explain in terms of new physics the recently confirmed discrepancy observed in the muon anomalous magnetic moment at Fermilab. Remarkably, it also predicts the observed yield of thermal dark matter relic abundance. A detailed Monte-Carlo simulation was used to determine the signal yield and detection efficiency for this channel in the NA64 setup. The results were obtained re-analyzing the previous NA64 searches for an invisible decay $$A'\rightarrow \chi \overline{\chi }$$ A ′ → χ χ ¯ and axion-like or pseudo-scalar particles $$a \rightarrow \gamma \gamma $$ a → γ γ . With this method, we exclude a significant portion of the parameter space justifying the muon g-2 anomaly and being compatible with the observed dark matter relic density for $$A'$$ A ′ masses from 2$$m_e$$ m e up to 390 MeV and mixing parameter $$\varepsilon $$ ε between $$3\times 10^{-5}$$ 3 × 10 - 5 and $$2\times 10^{-2}$$ 2 × 10 - 2 .

We study nuclear µ−–e− conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the Standard Model (SM) responsible for lepton flavor violation (L/f ). We show that vector meson exchange between lepton and nucleon currents plays an important role in this process. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the φ meson. This allows us to extract new limits on the L/f lepton–quark effective couplings from the existing experimental data.

Recently it has been demonstrated that QCD corrections are numerically important for short-range mechanisms (SRM) of neutrinoless double beta decay (0νββ) mediated by heavy particle exchange. This is due to the effect of color mismatch for certain effective operators, which leads to mixing between different operators with vastly different nuclear matrix elements (NMEs). In this note we analyze the QCD corrections for long-range mechanisms (LRM), due to diagrams with light-neutrino exchange between a Standard Model (V-A)×(V-A) and a beyond the SM lepton number violating vertex. We argue that in contrast to the SRM in the LRM case, there is no operator mixing from color-mismatched operators. This is due to a combined effect of the nuclear short-range correlations and color invariance. As a result, the QCD corrections to the LRM amount to an effect no more than 60%, depending on the operator in question. Although less crucial, taken into account QCD running makes theoretical predictions for 0νββ-decay more robust also for LRM diagrams. We derive the current experimental constraints on the Wilson coefficients for all LRM effective operators.

The Standard Model has no Flavor-Changing Neutral Current (FCNC) processes at the tree level. Therefore, processes featuring FCNC in new physics are tightly constrained by data. Typically, the lower bounds on the scale of new physics obtained from or mixing lie well above 10 TeV, surpassing the reach of current and future colliders. In this paper, we demonstrate, using a specific model that features flavor-changing interactions, that such limits can be severely weakened by specific choices of the quark mixing matrices with no prejudice while maintaining the CKM matrix in agreement with the data. We highlight the valuable role of the often-overlooked mixing in deriving robust FCNC limits and show that the LHC and HL-LHC are promising probes for flavor-changing interactions mediated by a boson.

We propose a low-scale renormalizable trinification theory that successfully explains the flavor hierarchies and neutrino puzzle in the Standard Model (SM), as well as provides a dark matter candidate and also contains the necessary means for efficient leptogenesis. The proposed theory is based on the trinification SUð3ÞC × SUð3ÞL × SUð3ÞR gauge symmetry, which is supplemented with an additional flavor symmetry Uð1ÞX × Zð1Þ 2 × Zð2Þ 2 . In the proposed model the top quark and the exotic fermions acquire tree-level masses, whereas the lighter SM charged fermions gain masses radiatively at one-loop level. In addition, the light active neutrino masses arise from a combination of radiative and type-I seesaw mechanisms, with the Dirac neutrino mass matrix generated at one-loop level

AbstractThe SHiP-charm project was proposed to measure the associated charm production induced by 400 GeV/c protons in a thick target, including the contribution from cascade production. An optimisation run was performed in July 2018 at CERN SPS using a hybrid setup. The high resolution of nuclear emulsions acting as vertex detector was complemented by electronic detectors for kinematic measurements and muon identification. Here we present first results on the analysis of nuclear emulsions exposed in the 2018 run, which prove the capability of reconstructing proton interaction vertices in a harsh environment, where the signal is largely dominated by secondary particles produced in hadronic and electromagnetic showers within the lead target.

Abstract We propose a class of models providing an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe via leptogenesis and offering viable dark matter candidates. In these models the Majorana masses of the active neutrino are generated by the inverse seesaw mechanism with the lepton number violating right-handed Majorana neutrino masses μ arising at three loops. The latter is ensured by the preserved discrete symmetries, which also guarantee the stability of the dark matter candidate. We focus on one of these models and perform a detailed analysis of the phenomenology of its leptonic sector. The model can successfully accommodate baryogenesis through leptogenesis in both weak and strong washout regimes. The lightest heavy fermion turns out to be a viable dark matter candidate, provided that the entries of the Majorana submatrix μ are in the keV to MeV range. The solutions are consistent with the experimental constraints, accommodating both mass orderings for active neutrinos, in particular charged-lepton flavor violating decays μ → eγ, μ → eee, and the electron-muon conversion processes get sizable rates within future sensitivity reach.