arXiv subjects

Evgueni Goudzovski

Publications and source records attributed to Evgueni Goudzovski.

At least 19 recordsLinked to original sources

arXiv2025

Kaon Physics: A Cornerstone for Future Discoveries

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

hep-ph↗

arXiv2025

Proposal of the KOTO II experiment

The KOTO II experiment is proposed to measure the branching ratio of the decay $K_L\toπ^0ν\barν$ at J-PARC. With a beamline to extract long-lived neutral kaons at 5 degrees from a production target, the single event sensitivity of the decay is $8.5\times 10^{-13}$, which is much smaller than the Standard Model prediction $3\times 10^{-11}$. This allows searches for new physics beyond the Standard Model and the first discovery of the decay with a significance exceeding $5σ$. As the only experiment proposed in the world dedicated to rare kaon decays, KOTO II will be indispensable in the quest for a complete understanding of flavor dynamics in the quark sector. Moreover, by combining efforts from the kaon community worldwide, we plan to develop the KOTO II detector further and expand the physics reach of the experiment to include measurements of the branching ratio of the $K_L\toπ^0\ell^+\ell^-$ decays, studies of other $K_L$ decays, and searches for dark photons, axions, and axion-like particles. KOTO II will therefore obtain a comprehensive understanding of $K_L$ decays, providing further constraints on new physics scenarios with existing $K^+$ results.

hep-ex↗

arXiv2023

New Physics Searches at Kaon and Hyperon Factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

hep-ph↗

arXiv2022

Weak Decays of Strange and Light Quarks

The present report of the RF2 Topical Group to Snowmass 2021 describes the physics case for the studies of weak decays of strange and light quarks. Ongoing and proposed precision measurements of kaon, hyperon, pion and $η^{(\prime)}$ meson decays allow for unique tests of the Standard Model (SM). This includes precision measurements of the elements of the CKM quark-mixing matrix leading to stringent unitarity tests; precision symmetry tests including lepton flavor and lepton number conservation; and precision lepton flavor universality tests. In the context of models beyond the SM description, strange and light quark decay experiments provide sensitivity to new physics up to the PeV mass scale, as well as leading sensitivities to scenarios involving feebly interacting hidden sectors below the GeV mass scale.

hep-ex↗

arXiv2022

The Present and Future Status of Heavy Neutral Leptons

The existence of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs). In this white paper we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding on key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.

hep-ph↗

arXiv2022

Feebly-Interacting Particles:FIPs 2020 Workshop Report

With the establishment and maturation of the experimental programs searching for new physics with sizeable couplings at the LHC, there is an increasing interest in the broader particle and astrophysics community for exploring the physics of light and feebly-interacting particles as a paradigm complementary to a New Physics sector at the TeV scale and beyond. FIPs 2020 has been the first workshop fully dedicated to the physics of feebly-interacting particles and was held virtually from 31 August to 4 September 2020. The workshop has gathered together experts from collider, beam dump, fixed target experiments, as well as from astrophysics, axions/ALPs searches, current/future neutrino experiments, and dark matter direct detection communities to discuss progress in experimental searches and underlying theory models for FIPs physics, and to enhance the cross-fertilisation across different fields. FIPs 2020 has been complemented by the topical workshop "Physics Beyond Colliders meets theory", held at CERN from 7 June to 9 June 2020. This document presents the summary of the talks presented at the workshops and the outcome of the subsequent discussions held immediately after. It aims to provide a clear picture of this blooming field and proposes a few recommendations for the next round of experimental results.

hep-ph↗

arXiv2021

Projected NA62 sensitivity to heavy neutral lepton production in $K^+ \to π^0 e^+ N$ decays

Heavy neutral leptons (HNLs) appear in many extensions of the Standard Model of particle physics. In this study, we investigate to which extent the NA62 experiment at CERN could improve the existing bounds on the HNL mixing angle $|U_e|^2$ by performing a missing mass search in $K^+ \to π^0 e^+ N$ decays in flight. We show that the limit $|U_e|^2 \simeq 2\times 10^{-6}$ can be reached with the currently available data in the mass range 125 -- 144 MeV, which is currently not well covered by production searches. Future data, together with a dedicated trigger and/or improvements in rejection of out-of-acceptance photons, can improve this limit by another order of magnitude.

hep-ph↗

arXiv2019

Precise determination of the branching ratio of the neutral-pion Dalitz decay

We provide a new value for the ratio $R={Γ(π^0\to e^+e^-γ(γ))}/{Γ(π^0\toγγ)}=11.978(6)\times10^{-3}$, which is by two orders of magnitude more precise than the current Particle Data Group average. It is obtained using the complete set of the next-to-leading-order radiative corrections in the QED sector, and incorporates up-to-date values of the $π^0$-transition-form-factor slope. The ratio $R$ translates into the branching ratios of the two main $π^0$ decay modes: $\mathcal{B}(π^0\toγγ)=98.8131(6)\,\%$ and $\mathcal{B}(π^0\to e^+e^-γ(γ))=1.1836(6)\,\%$.

hep-ph↗

arXiv2017

Neutral pion form factor measurement at NA62

The NA62 experiment at CERN collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. The kaon beam represents a source of tagged neutral pion decays in vacuum. A measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like region from $1.05\times10^6$ fully reconstructed $π^0$ Dalitz decay is presented. The limits on dark photon production in $π^0$ decays from the earlier kaon experiment at CERN, NA48/2, are also reported.

hep-ex↗

arXiv2016

Kaon experiments at CERN: recent results and prospects

The NA48/2 and NA62-$R_K$ experiments at the CERN SPS collected large samples of charged kaon decays in flight in 2003--07. The data analysis is still on-going (with over 20 publications produced so far); the recent results from these experiments are presented. A new upper limit on the rate of a lepton number violating decay $K^\pm\toπ^\mpμ^\pmμ^\pm$ is reported: $\mathcal{B} < 8.6\times 10^{-11}$ at 90\% CL. Searches for heavy sterile neutrino $N_4$ and neutral scalar resonances ($χ$) in $K^\pm\toπμμ$ decays are reported. Upper limits on the products $\mathcal{B}(K^\pm\toμ^\pm N_4)\mathcal{B}(N_4\toπ^\mpμ^\pm)$ and $\mathcal{B}(K^\pm\toπ^\pm χ)\mathcal{B}(χ\toμ^+μ^-)$ are set in the range $10^{-10}$ to $10^{-9}$ for resonance lifetimes up to 100~ps. A preliminary measurement of the electromagnetic transition form factor slope of the $π^0$ from $1.05\times 10^6$ fully reconstructed $π^0\toγe^+e^-$ decays is presented: the obtained result $a = (3.70 \pm 0.53_\text{stat} \pm 0.36_\text{syst})\times 10^{-2}$ represents the first observation of a non-zero slope in the time-like region of momentum transfer.

hep-ex↗

arXiv2015

Search for the dark photon in $π^0$ decays

A sample of $1.69\times 10^7$ fully reconstructed $π^0\toγe^+e^-$ decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is analysed to search for the dark photon ($A'$) production in the $π^0\toγA'$ decay followed by the prompt $A'\to e^+e^-$ decay. No signal is observed, and an exclusion region in the plane of the dark photon mass $m_{A'}$ and mixing parameter $\varepsilon^2$ is established. The obtained upper limits on $\varepsilon^2$ are more stringent than the previous limits in the mass range $9~{\rm MeV}/c^2<m_{A'}<70~{\rm MeV}/c^2$. The prospects of the dark photon search in the $K^\pm\toπ^\pm A'$ decay are also discussed.

hep-ex↗

arXiv2015

Development of the kaon tagging system for the NA62 experiment at CERN

The NA62 experiment at CERN aims to make a precision measurement of the ultra-rare decay $K^{+} \rightarrow π^{+}ν\overlineν$, and relies on a differential Cherenkov detector (KTAG) to identify charged kaons at an average rate of 50 MHz in a 750 MHz unseparated hadron beam. The experimental sensitivity of NA62 to K-decay branching ratios (BR) of $10^{-11}$ requires a time resolution for the KTAG of better than 100 ps, an efficiency better than 95% and a contamination of the kaon sample that is smaller than $10^{-4}$. A prototype version of the detector was tested in 2012, during the first NA62 technical run, in which the required resolution of 100 ps was achieved and the necessary functionality of the light collection system and electronics was demonstrated.

physics.ins-det↗

arXiv2014

Search for the dark photon in $π^0$ decays by the NA48/2 experiment at CERN

A sample of $4.687\times 10^6$ fully reconstructed $K^\pm\toπ^\pmπ^0_D$, $π^0_D\toγe^+e^-$ decay candidates in the kinematic range $m_{ee}>10~{\rm MeV}/c^2$ with a negligible background contamination collected by the NA48/2 experiment at CERN in 2003-04 is analysed to search for the dark photon ($A'$) via the decay chain $K^\pm\toπ^\pmπ^0$, $π^0\toγA'$, $A'\to e^+e^-$. No signal is observed, and preliminary exclusion limits on space of dark photon mass $m_A'$ and mixing parameter $\varepsilon^2$ are reported.

hep-ex↗

arXiv2013

Rare kaon decays (NA48/2 and NA62)

The rare decay $K^\pm\toπ^\pmγγ$ has been recently measured from data samples collected by the NA48/2 and NA62 experiments at CERN. These measurements are presented, including model-independent spectrum measurements and fits to the Chiral Perturbation Theory description.

hep-ex↗

arXiv2013

Rare Kaon Decay Experiments at CERN

The NA62 experiment at the CERN SPS aims to measure the branching ratio of the rare decay $K^+\toπ^+ν\barν$ with a relative precision of $\sim10%$. To achieve that goal, it is designed to be exposed to $1.2\times 10^{13}$ $K^+$ decays in its fiducial volume. The unprecedented $K^+$ flux will lead to record sensitivities to rare and forbidden decays of $K^+$ and $π^0$, including those that violate lepton flavour or lepton number conservation. The expected NA62 performances for lepton flavour conservation and lepton universality tests are discussed. Relevant on-going or recently completed measurements from the $K^\pm$ decay data sets collected by earlier kaon experiments at CERN (NA48/2 and NA62-$R_K$) are also presented.

hep-ex↗

arXiv2012

Kaon experiments at CERN: recent results and prospects

Recent results from the NA48/2 and NA62 kaon decay-in-flight experiments at CERN are presented. A precision measurement of the helicity-suppressed ratio RK of the K+- to e+- nu and K+- to mu+- nu decay rates has been performed using the full dedicated data set collected by the NA62 experiment (RK phase); the result is in agreement with the Standard Model expectation. New measurements of the K+- to pi+- gamma gamma decay at the NA48/2 and NA62 experiments provide further tests of the Chiral Perturbation Theory. A planned measurement of the branching ratio of the ultra-rare K+ to pi+ nu anti-nu decay at 10% precision is expected to represent a powerful test of the Standard Model.

hep-ex↗

arXiv2011

Kaon experiments at CERN: NA48 and NA62

Searches for violation of lepton flavour universality and lepton number conservation in kaon decays by the NA62 and NA48/2 experiments at CERN, status and future plans of the CERN kaon programme are presented. A precision measurement of the helicity-suppressed ratio $R_K$ of the $K^\pm\to e^\pmν$ and $K^\pm\toμ^\pmν$ decay rates has been performed using the full data set collected by the NA62 experiment in 2007--2008. The result is $R_K=(2.488\pm0.010)\times10^{-5}$, in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating $K^\pm\toπ^\mpμ^\pmμ^\pm$ decay from the NA48/2 experiment (2003--2004 data set) is presented. Finally, the NA62 project aiming at a measurement of the branching ratio of the ultra-rare decay $K^+\toπ^+ν\barν$ at 10% precision is discussed.

hep-ex↗

arXiv2011

Kaon programme at CERN: recent results

Searches for lepton flavour and lepton number violation in kaon decays by the NA48/2 and NA62 experiments at CERN are presented. A precision measurement of the helicity-suppressed ratio RK of the K --> e nu and K --> mu nu decay rates has been performed using the full data set collected by the NA62 collaboration in 2007. The data sample amounted to 145,958 reconstructed K --> e nu candidates with 11.0% background contamination. The result is RK = (2.488 +- 0.010) X 10^{-5}, which is in agreement with the Standard Model expectation. An improved upper limit on the lepton number violating K+- --> pi-+ mu+- mu+- decay rate is also presented.

hep-ex↗