Double π0\pi^0 Photoproduction off the Proton at Threshold

The reaction $\gamma p \to \pi^0 \pi^0 p$ has been measured using the TAPS BaF$_2$ calorimeter at the tagged photon facility of the Mainz Microtron accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold this channel is significantly enhanced compared to double pion final states with charged pions. In contrast to other reaction channels, the lower order tree terms are strongly suppressed in 2$\pi^0$ photoproduction. The consequence is the dominance of pion loops in the 2$\pi^0$ channel close to threshold - a result that opens new prospects for the test of ChPT and in particular its inherent loop terms. The present measurement is the first which is sensitive enough for a conclusive comparison with the ChPT calculation and is in agreement with its prediction. The data also show good agreement with a calculation in the unitary chiral approach.Comment: Submitted to PL

Improved depth sensitivity by separation of excitation and detection coils

A laparoscopic probe for magnetic sentinel node biopsy has been developed. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as a tracer. They are selectively detected by Differential Magnetometry (DiffMag). Excitation and detection coils are separated. To make this possible, we developed active compensation, which removes influence of the excitation field. Separation of coils leads to improved depth sensitivity, from 20 mm with our handheld probe to 80 mm with our novel laparoscopic probe. As stated by Biot-Savart law, we win a factor distance to the third power by separating the excitation and detection part of the system

Separation of excitation and detection coils for in vivo detection of superparamagnetic iron oxide nanoparticles

A novel probe for laparoscopic in vivo detection of superparamagnetic iron oxide nanoparticles (SPIONs) has been developed. The main application for in vivo detection of SPIONs our research group aims at is sentinel node biopsy. This is a method to determine if a tumor has spread through the body, which helps to improve cancer patient care. The method we use to selectively detect SPIONs is Differential Magnetometry (DiffMag). DiffMag makes use of small magnetic field strengths in the mT range. For DiffMag, a handheld probe is used that contains excitation and detection coils. However, depth sensitivity of a handheld probe is restricted by the diameter of the coils. Therefore, excitation and detection coils are separated in our novel probe. As a result, excitation coils can be made large and placed underneath a patient to generate a sufficiently large volume for the excitation field. Detection coils are made small enough to be used in laparoscopic surgery. The main challenge of this setup is movement of detection coils with respect to excitation coils. Consequently, the detector signal is obscured by the excitation field, making it impossible to measure the tiny magnetic signature from SPIONs. To measure SPIONs, active compensation is used, which is a way to cancel the excitation field seen by the detection coils. SPIONs were measured in various amounts and at various distances from the excitation coils. Furthermore, SPIONs were measured in proximity to a surgical steel retractor, and 3 L water. It is shown that small amounts of SPIONs (down to 25 μg Fe) can be measured, and SPIONs can be measured up to 20 cm from the top of the excitation coil. Also, surgical steel, and diamagnetism of water – and thus of tissue – have minor influence on DiffMag measurements. In conclusion, these results make this novel probe geometry combined with DiffMag promising for laparoscopic sentinel node biopsy

Differential magnetometry to detect sentinel lymph nodes in laparoscopic procedures

Differential Magnetometry to detect sentinel lymph nodes in laparoscopic procedure

The Semileptonic Decays D→π(ρ)eνD\to \pi(\rho) e \nu and B→π(ρ)eνB\to \pi (\rho) e \nu from QCD Sum Rules

We investigate the semileptonic decays of B and D mesons into $\pi$ and $\rho$ mesons, respectively, by means of QCD sum rules. We find that for the vector formfactors involved the pole dominance hypothesis is valid to good accuracy with pole masses in the expected range. Pole dominance, however, does not apply to the axial formfactors which results in specific predictions for the predominant polarization of the $\rho$ meson and the shape of the lepton spectrum. For the total decay rates we find $\Gamma (\bar B^0 \to \pi^+ e^- \bar\nu) = (5.1\pm 1.1)\,|V_{ub}|^2\, 10^{12}\,{\rm s^{-1}}$, $\Gamma ( D^0 \to \pi^- e^+ \nu) = (8.0\pm 1.7)\,|V_{cd}|^2\, 10^{10}\,{\rm s^{-1}}$, $\Gamma (\bar B^0 \to \rho^+ e^- \bar\nu) = (1.2\pm 0.4\,)\,|V_{ub}|^2\, 10^{13}\,{\rm s^{-1}}$ and $\Gamma (D^0 \to \rho^- e^+\nu) = (2.4\pm 0.7)\,|V_{cd}|^2\, 10^{9}\,{\rm s^{-1}}$.Comment: 23 pages, 12 figures included as uu-encoded file, needs REVTEX, TUM--T31--39/9

Polarized photons in radiative muon capture

We discuss the measurement of polarized photons arising from radiative muon capture. The spectrum of left circularly polarized photons or equivalently the circular polarization of the photons emitted in radiative muon capture on hydrogen is quite sensitive to the strength of the induced pseudoscalar coupling constant $g_P$. A measurement of either of these quantities, although very difficult, might be sufficient to resolve the present puzzle resulting from the disagreement between the theoretical prediction for $g_P$ and the results of a recent experiment. This sensitivity results from the absence of left-handed radiation from the muon line and from the fact that the leading parts of the radiation from the hadronic lines, as determined from the chiral power counting rules of heavy-baryon chiral perturbation theory, all contain pion poles.Comment: 10 pages, 6 figure