arXiv subjects

Karim Massri

Publications and source records attributed to Karim Massri.

9 recordsLinked to original sources

arXiv2026

NO LESS: Novel Opportunities for Light Exotic Searches at the SPS

A powerful way to test models with feebly interacting particles in the MeV to GeV mass range is through proton beam-dump experiments. In this paper, we compare the current sensitivity of CERN's NA62 experiment running in beam-dump mode with that of a hypothetical experiment using the same detectors in a future CERN ECN3 beam-dump facility. When optimising such an experiment, the geometric setup is particularly relevant for the specific new-physics scenario under study, since different production mechanisms can generate different angular distributions of new particles. We show that even the most minimalistic reconfiguration of the existing NA62 experiment's detectors can already provide a very competitive sensitivity and collect data immediately after the beam is available.

hep-ex↗

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↗

arXiv2019

Rare B, D and K decays, radiative and electroweak penguin decays, including constraints on $V_{td}/V_{ts}$ and $ε'/ε$: Summary of CKM 2018 working group 3

Rare $B$, $D$ and $K$ decays provide interesting probes of the Standard Model (SM), with a potential sensitivity to New Physics (NP) higher than other, more common, decays. Their experimental measurement is challenging, and their theoretical interpretation requires a precise knowledge of QCD at low energies, in the non-perturbative (hadronic) regime. The various $b$, $c$, $s$ decays provide different types of tests of the Standard Model, which can be performed in different experimental settings and which may exhibit correlated deviations in models of New Physics.

hep-ex↗

arXiv2017

New limits on heavy neutrinos from Kaon experiments at CERN

The NA48/2 and NA62-$R_K$ experiments at CERN collected large samples of charged kaon decays in 2003--2004 and 2007, respectively. These samples, collected with different trigger conditions, allow to search for both short and long-living heavy neutrinos produced in $K^{\pm}\toμ^{\pm}N_4$ decays. The results of these complementary searches are presented in this letter. In the absence of observed signal, the limits obtained on $\mathcal{B}(K^{\pm}\toπ^{\mp}μ^{\pm}μ^{\pm})$, $\mathcal{B}(K^{\pm}\to μ^{\pm} N_4)\mathcal{B}(N_4\to πμ)$, $\mathcal{B}(K^{+}\toμ^{+}N_4)$ and on the mixing matrix element $|U_{\mu4}|^2$ are reported.

hep-ex↗

arXiv2016

Searches for Lepton Number Violation and resonances in the $K^{\pm}\rightarrow πμμ$ decays at the NA48/2 experiment

The NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay $K^{\pm}\toπ^{\mp}μ^{\pm}μ^{\pm}$ obtained from this sample is reported: $\mathcal{B}(K^{\pm}\toπ^{\mp}μ^{\pm}μ^{\pm})<8.6 \times 10^{-11}$ at 90\% CL. Searches for two-body resonances in the $K^{\pm}\toπμμ$ decays (including heavy neutral leptons~$N_4$ and inflatons~$χ$) in the accessible range of masses and lifetimes are also presented. In the absence of a signal, upper limits are set on the products of branching ratios~$\mathcal{B}(K^{\pm}\toμ^{\pm}N_4)\mathcal{B}(N_4\toπμ)$ and $\mathcal{B}(K^{\pm}\toπ^{\pm}χ)\mathcal{B}(χ\toμ^+μ^-)$ as functions of the resonance mass and lifetime. These limits are in the $10^{-10}-10^{-9}$ range for resonance lifetimes below 100~ps.

hep-ex↗

arXiv2016

The Kaon identification system at the NA62 experiment at CERN

The NA62 experiment at CERN SPS aims to measure the branching ratio of the ultra-rare kaon decay $K^+\toπ^+ν\barν$ with 10\% precision, collecting $\sim 100$ events, assuming the Standard Model~(SM) branching ratio of $8.4 \times 10^{-11}$, starting in 2016. The NA62 experiment uses a kaon decay-in-flight technique and is exposed to a 750~MHz high-energy unseparated charged hadron beam, in which kaons are a minor component (6\%). Kaon identification is therefore mandatory to reduce the interference of the dominant non-kaon component with the experimental measurements. The NA62 kaon identification system and its performances are presented.

physics.ins-det↗

arXiv2016

Searches for Lepton Number Violation and resonances in the $K^{\pm} \to πμμ$ decays at the NA48/2 experiment

The NA48/2 experiment at CERN collected a large sample of charged kaon decays into final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay $K^{\pm} \to π^{\mp} μ^{\pm} μ^{\pm}$ obtained from this sample is reported: $\mathcal{B}(K^{\pm} \to π^{\mp} μ^{\pm} μ^{\pm})<8.6 \times 10^{-11}$ at 90\% CL. Searches for two-body resonances in the $K^{\pm} \to πμμ$ decays (including heavy neutral leptons~$N_4$ and inflatons~$χ$) in the accessible range of masses and lifetimes are also presented. In the absence of a signal, upper limits are set on the products of branching ratios~$\mathcal{B}(K^{\pm} \to μ^{\pm} N_{4})\mathcal{B}(N_{4} \to π^{\mp}μ^{\pm})$ and $\mathcal{B}(K^{\pm} \to π^{\pm} χ)\mathcal{B}(χ\to μ^{+}μ^{-})$ as functions of the resonance mass and lifetime. These limits are in the $10^{-10}-10^{-9}$ range for resonance lifetimes below 100~ps.

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↗