Double polarization experiments at intermediate energy

At modern electron accelerators with highly polarized, intense, high duty factor beams double polarization coincidence experiments became feasible with good statistical accuracy. The strong potential towards the precise determination of small nucleon structure quantities is illustrated by two recent examples from MAMI. The measurement of $G_E^n$ in the quasifree reaction $D(\vec e, e'\vec n)p$ lead to a new parametrization of $G_E^n$ which is significantly above the previously preferred one from elastic $e-D$ scattering. A $p(\vec e, e'\vec p)\pi^0$ experiment at the energy of the $\Delta$ resonance yields preliminary results for the longitudinal quadrupole mixing. Both experimental errors and model uncertainties are complementary to unpolarized measurements.Comment: 8 pages, 6 figures, plenary talk given at PANIC'9

Proton Polarization in the p(e⃗,e′p⃗)π0p(\vec e,e'\vec p)\pi^0 Reaction and the Measurement of Quadrupole Components in the N to Δ\Delta Transition

The recoil proton polarization in the $\pi^0$ production off the proton with longitudinally polarized electron beam has been studied as a means to measure quadrupole components in the N to $\Delta$ transition. On top of the $\Delta$ resonance a high sensitivity to a possible Coulomb quadrupole excitation is found in parallel kinematics. The ratio of $S_{1+}/M_{1+}$ multipole amplitudes can be determined from the ratio of the two in-scattering-plane recoil proton polarization components. Avoiding the absolute measurement of the polarizations, such a ratio allows small experimental uncertainties. Furthermore, the electron helicity independent proton polarization component enables the characterization of resonant and non-resonant pieces.Comment: 14 pages, 2 figures, LateX. Submitted to Z.Phys.

Polarization degrees of freedom in near-threshold photoproduction of omega mesons in the pi^0 gamma decay channel

We study polarization variables in the photoproduction of omega-mesons with subsequent omega to gamma pi^0 decay. Single and double polarization observables are calculated as a function of different final-state angles. Reaction models include pomeron (natural parity) and pi^0 (unnatural parity) exchange in the t-channel. In addition, the contribution of s-channel resonances is considered. The sensitivity of the polarization observables to the reaction dynamics is discussed.Comment: 10 pages, 10 figures, explicit reference to sign of decay asymmetry adde

Aspects of the gauge hierarchy of the standard model

The standard model (SM) is a huge success, being able to explain particle physics phenomenology up to the energy scales accessible nowadays (up to 13 TeV). Albeit this huge feat, the SM is not considered to provide an ultimate description of nature. Many extensions of the standard model have been motivated by the so-called hierarchy problem. While this does not characterize an incosistency of the standard model, it rather refers to the aesthetics of the theory, or its naturalness. This issue is often paraphrased as: How can the Higgs mass stay small compared to an UV cutoff while it receives radiative corrections which are naively of order cutoff squared? In this work functional renormalization group techinques are employed to provide a new perspective on the gauge hierarchy of various toy models mimicking parts of the standard model. First a Z2-symmetric toy model containing one real scalar field and one Dirac fermion is studied, especially focussing on the dependence of the scale separation on the IR observables top mass and Higgs mass. Then a model containing Nf = 6 Fermions transforming in the fundamental representation of SU(3), gauge bosons, and one scalar SU(2) doublet is investigated. The strong interaction forces spontaneous chiral symmetry breaking which will be accounted for by partial bosonization of the theory, in addition to the the usual electroweak symmetry breaking in the scalar sector. The hierarchy of the emerging scales is studied, namely the UV cutoff, the electroweak scale and in the latter model also the QCD scale for different values of the parameters of the models. The goal is to study the phase transition or crossover of this standard-model-like system from a “deeply-Higgsed” into a pure QCD-type phase. From the renormalization group perspective, the rapidness of this transition is quantitatively related to the severity of the naturalness problem

Pi0 electroproduction in the Delta(1232) region at MAMI

The extraction of the Coulomb quadrupole to magnetic dipole ratio from a p(e_pol,e'p_pol)pi^0 measurement is discussed. Preliminary results from further asymmetry measurements with polarized and unpolarized electron beam indicate that the imaginary background is well under control in the MAID2000 parameterization, but not the real (Born-) amplitudes.Comment: Invited talk given at NSTAR2001 (Mainz, Germany), 8 pages, 6 figure

Flow around wings accompanied by separation of vortices

The flow around wings computed by the usual method leads in the case of a finite trailing edge to a stagnation point in the trailing edge due to the Kutta-Joukowsky condition of flow governing this region. As a result, the theoretical pressure distribution differs substantially from the experimental values in the vicinity of the trailing edge. The present report describes an alternative method of calculation in which the rear stagnation point no longer appears. The stream leaves the trailing edge tangentially on the pressure side and a similar tangential separation occurs on the suction side of the profile at a point slightly in front of the trailing edge

The Global Network of Cavities to Search for Gravitational Waves (GravNet): A novel scheme to hunt gravitational waves signatures from the early universe

The idea of searching for gravitational waves using cavities in strong magnetic fields has recently received significant attention. Specifically, discussions focus on cavities with relatively small volumes, which are currently employed in the search for axions. In this context, we propose a novel experimental scheme that enables the detection of gravitational waves in the GHz regime, which could originate, for example, from primordial black hole mergers. The scheme is based on synchronous measurements of cavity signals from multiple devices operating in magnetic fields at distant locations. While gravitational wave signatures might be detectable in individual cavities, distinguishing them from noise is highly challenging. By analyzing the correlation among signals from several, possibly geographically separated cavities, it is not only possible to significantly enhance the signal-to-noise ratio but also to investigate the source of those gravitational wave signatures. In the context of this proposal, a first demonstration experiment with one superconducting cavity is currently conducted, which is the basis of the proposed data-analysis approaches. On this basis the prospects of GravNet (Global Network of Cavities to Search for Gravitational Waves) are outlined in the paper.Comment: 9 page

Searching for Gravitational Waves with CMS

The idea of searching for gravitational waves using cavities in strong magnetic fields has recently received significant attention. Most concepts foresee moderate magnetic fields in rather small volumes, similar to those which are currently employed for axion-like particle searches. We propose to use the magnet system of the Compact Muon Solenoid (CMS) experiment after the high luminosity phase of the LHC as a key component for a future detector for gravitational waves in the MHz frequency range. In this paper we briefly discuss a possible cavity concept which can be integrated into CMS and additionally provide a first estimation of its possible sensitivity.Comment: 4 pages, 2 figure

Interplay of Chiral Transitions in the Standard Model

We investigate nonperturbative aspects of the interplay of chiral transitions in the standard model in the course of the renormalization flow. We focus on the chiral symmetry breaking mechanisms provided by the QCD and the electroweak sectors, the latter of which we model by a Higgs-top-bottom Yukawa theory. The interplay becomes quantitatively accessible by accounting for the fluctuation-induced mixing of the electroweak Higgs field with the mesonic composite fields of QCD. In fact, our approach uses dynamical bosonization and treats these scalar fields on the same footing. Varying the QCD scale relative to the Fermi scale we quantify the mutual impact of the symmetry-breaking mechanisms, specifically the departure from the second order quantum phase transition of the pure Yukawa sector in favor of a crossover upon the inclusion of the gauge interactions. This allows to discuss the ``naturalness'' of the standard model in terms of a pseudo-critical exponent which we determine as a function of the ratio of the QCD and the Fermi scale. We also estimate the minimum value of the $W$ boson mass in absence of the Higgs mechanism.Comment: 25 pages, 13 figure