Search results for "ODN"
showing 10 items of 2772 documents
Search at the Mainz Microtron for light massive gauge bosons relevant for the muon g-2 anomaly.
2014
A massive, but light, Abelian U(1) gauge boson is a well-motivated possible signature of physics beyond the standard model of particle physics. In this Letter, the search for the signal of such a U(1) gauge boson in electron-positron pair production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron is described. Exclusion limits in the mass range of 40 MeV/c^{2} to 300 MeV/c^{2}, with a sensitivity in the squared mixing parameter of as little as ε^{2}=8×10^{-7} are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous magnetic moment of the muon with theory might be explained by an additional U(1) gauge …
Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics
2019
We present measurements of the polarization-transfer components in the H2(e→,e′p→) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, pmiss, up to 220MeV/c, and Q2=0.65 (GeV/c)2. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components Px and Pz and their ratio agree with the theoretical calculations, which use free-proton form factor…
Nuclear symmetry energy and neutron skins derived from pygmy dipole resonances
2007
By exploiting Coulomb dissociation of high-energy radioactive beams of the neutron-rich nuclei $^{129\ensuremath{-}132}\mathrm{Sn}$ and $^{133,134}\mathrm{Sb}$, their dipole-strength distributions have been measured. A sizable fraction of ``pygmy'' dipole strength, energetically located below the giant dipole resonance, is observed in all of these nuclei. A comparison with available pygmy resonance data in stable nuclei ($^{208}\mathrm{Pb}$ and $N=82$ isotones) indicates a trend of strength increasing with the proton-to-neutron asymmetry. On theoretical grounds, employing the RQRPA approach, a one-to-one correlation is found between the pygmy strength and parameters describing the density d…
Goodness-of-fit tests in many dimensions
2004
A method is presented to construct goodness-of-fit statistics in many dimensions for which the distribution of all possible test results in the limit of an infinite number of data becomes Gaussian if also the number of dimensions becomes infinite. Furthermore, an explicit example is presented, for which this distribution as good as only depends on the expectation value and the variance of the statistic for any dimension larger than one.
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
2001
We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with …
Polarization-transfer measurement to a large-virtuality bound proton in the deuteron
2017
Possible differences between free and bound protons may be observed in the ratio of polarization-transfer components, $P'_x/P'_z$. We report the measurement of $P'_x/P'_z$, in the $^2\textrm{H}(\vec{e},e^{\prime}\vec{p})n$ reaction at low and high missing momenta. Observed increasing deviation of $P'_x/P'_z$ from that of a free proton as a function of the virtuality, similar to that observed in \hefour, indicates that the effect in nuclei is due to the virtuality of the knock-out proton and not due to the average nuclear density. The measured differences from calculations assuming free-proton form factors ($\sim10\%$), may indicate in-medium modifications.
New Insight in the $Q^2$-Dependence of Proton Generalized Polarizabilities
2019
Virtual Compton scattering on the proton has been investigated at three yet unexplored values of the four-momentum transfer $Q^2$: 0.10, 0.20 and 0.45 GeV$^2$, at the Mainz Microtron. Fits performed using either the low-energy theorem or dispersion relations allowed the extraction of the structure functions $P_{LL} -P_{TT} / \epsilon$ and $P_{LT}$, as well as the electric and magnetic generalized polarizabilities $\alpha_{E1}(Q^2)$ and $\beta_{M1}(Q^2)$. These new results show a smooth and rapid fall-off of $\alpha_{E1}(Q^2)$, in contrast to previous measurements at $Q^2$ = 0.33 GeV$^2$, and provide for the first time a precise mapping of $\beta_{M1}(Q^2)$ in the low-$Q^2$ region.
Level structure of 99Nb
1998
The β decay of 97Sr to 97Y has been investigated using ion-guide on-line mass separation and a 10 Ge-detector array to record γ−γ coincidences to a detection limit well below that of former studies. Similarities are found in the β-decay patterns of 99Zr and of its isotone 97Sr and also in the γ-ray decay rates and branchings of the corresponding levels in their respective daughters 99Nb and 97Y. This indicates a persisting influence of the d5/2 neutron shell closure for 99Nb. The level structure of 99Nb and the β-feeding pattern are discussed in the frame of the interacting boson-fermion plus broken pair model and the microscopic quasiparticle phonon model.
Level structure of ^100Nb
2000
Levels in the odd-odd nucleus ${}^{100}\mathrm{Nb}$ situated at the edge of a region of especially fast shape transitions have been calculated in the framework of the interacting boson fermion fermion model. Levels observed in decay studies can be interpreted in a spherical basis. Low-lying ${I}^{\ensuremath{\pi}}{=8}^{+}$ and ${10}^{\ensuremath{-}}$ states are predicted. Their relationship with the unplaced levels populated with a $12 \ensuremath{\mu}\mathrm{s}$ delay after fission is discussed.
Taisnīgums Platona dialogā "Valsts"
2018
Platona dialogs Valsts ir viens no nozīmīgākajiem antīkajiem filozofiskajiem darbiem, kurā izteiktās domas tiek apspriestas ļoti aktīvi vēl līdz mūsdienām. Veicot oriģinālteksta leksikas analīzi, kas izmantota taisnīguma jēdziena paskaidrošanā, bakalaura darbs pievēršas Platona izpratnei par taisnīgumu un tam, kā taisnīgums izpaužas gan cilvēkā, gan valstiskā veidojumā. Darbs veltīts Platona skatījumam uz valstī esošo kārtu – ražotāju, sargu un likumdevēju – dabisko izveidošanos, aplūkota to nozīme un vieta valstiskajā sistēmā un katras kārtas sava dabas noteiktā darba darīšana, nejaucoties svešos darbos. Šīs sistēmas saglabāšana ir atslēga taisnīguma nodrošināšanai valstī. Līdzīgi arī noti…