Search results for "Pseudoscalar"
showing 9 items of 189 documents
Unified QCD determination of all pseudoscalar leptonic decay constants
1992
Leptonic decay constants of all pseudoscalar mesons are determined in QCD by means of a new QCD sum-rule method. In the light meson and heavy quark limit the results are very similar and also agree with the well-known PCAC and scaling predictions respectively. The corrections to light meson pole dominance are generally small while those to the heavy quark limit are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainfπ=132 MeV,fk=161 MeV,fB=128±28 MeV,fD=175±13 MeV,fBs=144±30 MeV andfDs=193±12 MeV.
Finite Volume Scaling of Pseudo Nambu-Goldstone Bosons in QCD
2008
We consider chiral perturbation theory in a finite volume and in a mixed regime of quark masses. We take N_l light quarks near the chiral limit, in the so-called epsilon-regime, while the remaining N_h quarks are heavier and in the standard p-regime. We compute in this new mixed regime the finite-size scaling of the light meson correlators in the scalar, pseudoscalar, vector and axial vector channels.Using the replica method, we easily extend our results to the partially quenched theory. With the help of our results, lattice QCD simulations with 2+1 flavors can safely investigate pion physics with very light up and down quark masses even in the region where the pion's correlation length ove…
B and B-s decay constants from QCD duality at three loops
2004
Using special linear combinations of finite energy sum rules which minimize the contribution of the unknown continuum spectral function, we compute the decay constants of the pseudoscalar mesons B and B_s. In the computation, we employ the recent three loop calculation of the pseudoscalar two-point function expanded in powers of the running bottom quark mass. The sum rules show remarkable stability over a wide range of the upper limit of the finite energy integration. We obtain the following results for the pseudoscalar decay constants: f_B=178 \pm 14 MeV and f_{B_s}=200 \pm 14 MeV. The results are somewhat lower than recent predictions based on Borel transform, lattice computations or HQET…
Beam-Recoil Polarization Measurement of π0 Electroproduction on the Proton in the Region of the Roper Resonance
2017
The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1 GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440 MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in t…
The complete experiment for photoproduction of pseudoscalar mesons in a truncated partial wave analysis
2013
The complete experiment problem in the truncated partial wave analysis of pseudoscalar meson photoproduction with suppressed t-channel exchanges is investigated. The focus is set to ambiguities of the group S observables with the unpolarized differential cross section, $\sigma_0$, and the three single-spin observables, $\Sigma$, $T$ and $P$. For this purpose, the approach and formalism already worked out by Omelaenko in 1981 is revisited in this work. A numerical study using multipoles of the PWA solution MAID2007 shows how only one additional double polarization observable can resolve all ambiguities. Therefore, the possibility emerges to perform a complete experiment with only five observ…
Double β Decay and the Axial Strength
2019
Quenching of the weak axial strength gA is discussed and relations of this quenching to the nuclear matrix elements of double beta decays are highlighted. An analysis of Gamow-Teller transitions in the mass range A = 62 − 142 is presented and its results are compared with those of many previous works. The enhancement of the axial charge is discussed for first-forbidden pseudoscalar β transitions. Higher-forbidden β transitions are introduced and their role in determining the effective value of gA is examined, in particular from the point of view of the β-decay half-lives and the shapes of electron spectra of forbidden non-unique β transitions. peerReviewed
New exclusion limits on scalar and pseudoscalar axionlike particles from light shining through a wall
2015
Physics beyond the Standard Model predicts the possible existence of new particles that can be searched at the low-energy frontier in the sub-eV range. The OSQAR photon regeneration experiment looks for ``light shining through a wall'' from the quantum oscillation of optical photons into ``weakly interacting sub-eV particles,'' such as axion or axionlike particles (ALPs) in a 9 T transverse magnetic field over a length of $2\ifmmode\times\else\texttimes\fi{}14.3\text{ }\text{ }\mathrm{m}$. In 2014, this experiment was run with an outstanding sensitivity, using an 18.5 W continuous wave laser emitting in the green at the single wavelength of 532 nm. No regenerated photons have been detected …
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…
Excess electronic recoil events in XENON1T
2020
We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 t-y and an unprecedentedly low background rate of $76\pm2$ events/(t y keV) between 1 and 30 keV, the data enables sensitive searches for solar axions, an enhanced neutrino magnetic moment, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4$\sigma$ significance, and a 3D 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by $g_{ae}<3.8 \times 10^{-12}$,…