Flavour changing neutral currents and CP violating processes in generalized supersymmetric theories

We consider supersymmetric extensions of the standard model with general non-universal soft breaking terms. We analyse in a model-independent way the constraints on these terms at the electroweak energy scale coming from gluino mediated flavour (F) changing neutral current and CP-violating processes. We have computed the complete $\Delta F=1$ and $\Delta F=2$ effective hamiltonian for gluino mediated processes, including for the first time the effect of box diagrams in the evaluation of $\epsilon^{\prime}/\epsilon$. We present numerical results for the constraints on these non-universal soft breaking terms for different values of the parameters, extending the analysis also to the leptonic sector. A comparison with previous results in the literature is given.Comment: LaTeX, 17 pages, 3 uuencoded figure

Non-Universal Soft SUSY Breaking and Dark Matter

An analysis is given of the effects of non-universal soft SUSY breaking masses in the Higgs sector and in the third generation squark sector, and it is shown that they are highly coupled. Analytic expressions are obtained for their effects on the parameters $\mu,m_A$ and on the third generation squark masses. Non-universality effects on dark matter event rates in neutralino-nucleus scattering are analysed. It is found that the effects are maximal in the range $m_{\tilde\chi_1}\leq 65$~GeV where the relic density is governed by the Z and Higgs poles. In this range the minimum event rates can be increased or decreased by factors of O(10) depending on the sign of non-universality. Above this range Landau pole effects arising from the heavy top mass tend to suppress the non-universality effects. The effect of more precise measurements of cosmological parameters on event rates, which is expected to occur in the next round of COBE like sattelite experiments, is also investigated. Implications for the analysis for dark matter searches are discussed.Comment: 28 pages, latex, and 7 fig

Measurement of the transverse target and beam-target asymmetries in η\eta meson photoproduction at MAMI

We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $\vec \gamma \vec p\to\eta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $\eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.Comment: 5 pages, 3 figures, accepted for publication in PR

T and F asymmetries in π0 photoproduction on the proton

The γp→π0p reaction was studied at laboratory photon energies from 425 to 1445 MeV with a transversely polarized target and a longitudinally polarized beam. The beam-target asymmetry F was measured for the first time and new high precision data for the target asymmetry T were obtained. The experiment was performed at the photon tagging facility of the Mainz Microtron (MAMI) using the Crystal Ball and TAPS photon spectrometers. The polarized cross sections were expanded in terms of associated Legendre functions and compared to recent predictions from several partial-wave analyses. The impact of the new data on our understanding of the underlying partial-wave amplitudes and baryon resonance contributions is discussed

K+ΛK^+\Lambda and K+Σ0K^+\Sigma^0 photoproduction with fine center-of-mass energy resolution

Measurements of $\gamma p \rightarrow K^{+} \Lambda$ and $\gamma p \rightarrow K^{+} \Sigma^0$ cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel $K^+$ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ($W$) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. The new analyses disfavor a strong role for quark-diquark dynamics in the nucleon.Comment: 7 pages, 8 figure

Neutron skin of 208^{208}Pb from Coherent Pion Photoproduction

Information on the size and shape of the neutron skin on $^{208}$Pb has been extracted from coherent pion photoproduction cross sections measured using the Crystal Ball together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be 6.70$\pm 0.03(stat)$ fm and 0.55$\pm 0.01(stat)$$^{+0.02}_{-0.03}(sys)$ fm respectively, corresponding to a neutron skin thickness $\Delta r_{np}$=0.15$\pm 0.03(stat)$$^{+0.01}_{-0.03}(sys)$ fm. The results give the first successful extraction of a neutron skin with an electromagnetic probe and indicate the skin of $^{208}$Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.Comment: 4 figures 5 pages. Version submitted to journal. Includes additional studies of systematic effects in the extracted diffuseness, which led to a small increase in the quoted systematic error. These additional studies are discussed in the revised manuscript. Also includes minor editorial improvements to the tex

A new measurement of the neutron detection efficiency for the NaI Crystal Ball detector

We report on a measurement of the neutron detection efficiency in NaI crystals in the Crystal Ball detector obtained from a study of single p0 photoproduction on deuterium using the tagged photon beam at the Mainz Microtron. The results were obtained up to a neutron energy of 400 MeV. They are compared to previous measurements made more than 15 years ago at the pion beam at the BNL AGS

Measurement of pi^0 photoproduction on the proton at MAMI C

Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy and angular binning, increase the existing quantity of pi^0 photoproduction data by ~47%. Owing to the unprecedented statistical accuracy and the full angular coverage, the results are sensitive to high partial-wave amplitudes. This is demonstrated by the decomposition of the differential cross sections in terms of Legendre polynomials and by further comparison to model predictions. A new solution of the SAID partial-wave analysis obtained after adding the new data into the fit is presented.Comment: 13 pages, 12 figures, 1 tabl

Determination of the Dalitz plot parameter alpha for the decay eta->3pi^0 with the Crystal Ball at MAMI-B

A precise measurement of the Dalitz plot parameter, alpha, for the eta->3pi^0 decay is presented. The experiment was performed with the Crystal Ball and TAPS large acceptance photon detectors at the tagged photon beam facility of the MAMI-B electron accelerator in Mainz. High statistics of 1.8*10^6 eta->3pi^0 events were obtained, giving the result alpha = -0.032 +/- 0.002(stat) +/- 0.002(syst).Comment: 9 pages, 6 figures, published in the online-first section of EPJ A, included changes referees asked for, added DO