Search results for "kaon physics"
showing 10 items of 14 documents
Searches for lepton number violation and resonances in K± → πμμ decays
2017
The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003–2004. A new upper limit on the rate of the lepton number violating decay K±→π∓μ±μ± is reported: B(K±→π∓μ±μ±)<8.6×10−11 at 90% CL. Searches for two-body resonances X in K±→πμμ decays (such as heavy neutral leptons N4 and inflatons χ ) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K±→μ±N4)B(N4→πμ) and B(K±→π±X)B(X→μ+μ−) for ranges of assumed resonance masses and lifetimes. The limits are in the (10−11,10−9) range for resonance lifetimes below 100 ps.
Probing the chiral weak Hamiltonian at finite volumes
2006
Non-leptonic kaon decays are often described through an effective chiral weak Hamiltonian, whose couplings ("low-energy constants") encode all non-perturbative QCD physics. It has recently been suggested that these low-energy constants could be determined at finite volumes by matching the non-perturbatively measured three-point correlation functions between the weak Hamiltonian and two left-handed flavour currents, to analytic predictions following from chiral perturbation theory. Here we complete the analytic side in two respects: by inspecting how small ("epsilon-regime") and intermediate or large ("p-regime") quark masses connect to each other, and by including in the discussion the two …
Searches for lepton number violating $K^+$ decays
2019
The NA62 experiment at CERN reports a search for the lepton number violating decays K+ -> pi(-)e(+)e(+) and K+ -> pi(-)mu(+)mu(+) using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2 x 10(-10) and 4.2 x 10(-11) are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.
Light quark masses and pseudoscalar decay constants from N(f)=2 Lattice QCD with twisted mass fermions
2007
We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non-perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +- 9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +- 3.1 MeV and the …
Search for heavy neutral lepton production in K+ decays to positrons
2020
A search for heavy neutral lepton ($N$) production in $K^+\to e^+N$ decays using the data sample collected by the NA62 experiment at CERN in 2017--2018 is reported. Upper limits of the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the level of $10^{-9}$ over most of the accessible heavy neutral lepton mass range 144--462 MeV/$c^2$, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The $|U_{e4}|^2$ range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/$c^2$.
Improved $K_{e3}$ radiative corrections sharpen the $K_{\mu 2}$--$K_{l3}$ discrepancy
2021
The measurements of $V_{us}$ in leptonic $(K_{\mu 2})$ and semileptonic $(K_{l3})$ kaon decays exhibit a $3\sigma$ disagreement, which could originate either from physics beyond the Standard Model or some large unidentified Standard Model systematic effects. Clarifying this issue requires a careful examination of all existing Standard Model inputs. Making use of a newly-proposed computational framework and the most recent lattice QCD results, we perform a comprehensive re-analysis of the electroweak radiative corrections to the $K_{e3}$ decay rates that achieves an unprecedented level of precision of $10^{-4}$, which improves the current best results by almost an order of magnitude. No larg…
A strategy to study the role of the charm quark in explaining the Delta{I}=1/2 rule
2004
We present a strategy designed to separate several possible origins of the well-known enhancement of the Delta{I}=1/2 amplitude in non-leptonic kaon decays. In particular, we seek to disentangle the contribution of physics at the typical QCD scale (soft-gluon exchange) from the effects at the scale of the charm quark mass. This is achieved by considering QCD with an unphysically light charm quark, so that the theory possesses an approximate SU(4)_L x SU(4)_R chiral symmetry. By computing the relevant operator matrix elements and monitoring their values as the charm quark mass departs from the SU(4)-symmetric situation, the role of the charm quark can be assessed. We study the influence of t…
Determination of the ΔS=1 weak Hamiltonian of the SU(4) chiral limit through topological zero-mode wave functions
2008
38 pages, 9 figures.-- Published in: JHEP05(2008)043, available at: http://dx.doi.org/10.1088/1126-6708/2008/05/043 (open-acess).
K°- K°, - D° and B° - B° oscillations in the Standard Model and beyond from unquenched Twisted Mass Lattice QCD
2013
El análisis del triángulo de unitariedad y la búsqueda de cotas restrictivas sobre las escala de nueva física requiere medidas precisas de las amplitudes de mezcla de las oscilaciones de mesones. El retículo proporciona una óptima herramienta no perturbativa para el cálculo de dichos elementos de matriz con incertidumbres del 1% y errores sistemáticos bajo control. La tesis se centra en el cálculo de los parámetros B, que controlan las oscilaciones de mesones, la masa del quark b y las constantes de desintegración fB y fBs a partir de QCD simulada en el retículo con fermiones Twisted Mass e incluyendo los efectos cuánticos de quarks dinámicos en el mar. A lo largo de esta tesis, a partir de…
Orderp6chiral couplings from the scalarK form factor
2004
15 páginas, 2 tablas.-- arXiv:hep-ph/0401080v2