The NA48/2 and NA62-RK 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± →π∓μ±μ± is reported: B< 8.6×10−11 at 90% CL. Searches for heavy sterile neutrino N4 and neutral scalar resonances (χ) in K± → πμμ decays are reported. Upper limits on the products B(K± → μ±N4)B(N4 → π∓μ±) and B(K± → π±χ)B(χ → μ+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 π0 from 1.05 × 106 fully reconstructed π0 → γe+e− decays is presented: the obtained result a = (3:70 ± 0:53stat ± 0:36syst) × 10−2 represents the first observation of a non-zero slope in the time-like region of momentum transfer.
A sample of 4.687 × 106 fully reconstructed K± → π±π0D, π0D → γe+e- decay candidates in the kinematic range mee > 10 MeV/c2 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± → π±π0, π0 → γA′, A′ → e+e-. No signal is observed, and preliminary exclusion limits on space of dark photon mass m′A and mixing parameter ε2 are reported.
We provide a new value for the ratio R=Γ(π^{0}→e^{+}e^{-}γ(γ))/Γ(π^{0}→γγ)=11.978(6)×10^{-3}, which is by 2 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: B(π^{0}→γγ)=98.8131(6)% and B(π^{0}→e^{+}e^{-}γ(γ))=1.1836(6)%.
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 |Ue|2 by performing a missing mass search in K+ → π0 e+ N decays in flight. We show that the limit | Ue |2 ≃ 2 × 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.
A sample of 4.687 x 10 super(6) fully reconstructed (ProQuest: Formulae and/or non-USASCII text omitted), (ProQuest: Formulae and/or non-USASCII text omitted) decay candidates in the kinematic range ...m sub(e)e> 10 MeV/c super(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 super(+ or -) arrow right pi super(+ or -), pi super(0) arrow right gamma A', A' arrow right e super(+)e super(-). No signal is observed, and preliminary exclusion limits on space of dark photon mass m' sub(A) and mixing parameter varepsilon super(2) are reported.
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.
Abstract
The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model 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 of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.
Shedding light on X17: community report Alves, Daniele S. M.; Barducci, Daniele; Cavoto, Gianluca ...
The European physical journal. C, Particles and fields,
03/2023, Letnik:
83, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The workshop “Shedding light on X17” brings together scientists looking for the existence of a possible new light particle, often referred to as X17. This hypothetical particle can explain the ...resonant structure observed at
∼
17 MeV in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as
8
Be
and
4
He
by means of proton beams at the Atomki Laboratory in Debrecen. The purpose of the workshop is to discuss implications of this anomaly, in particular theoretical interpretations as well as present and future experiments aiming at confirming the result and/or at providing experimental evidence for its interpretation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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