Research with real photons at the MAMI 1.6 GeV electron accelerator

The A2-CB Collaboration at Mainz is studying the structure of hadrons by meson photoproduction using unpolarised, linearly polarised and circularly polarised photons with energies up to 1.6 GeV. Photons are energy-tagged using the Glasgow-Mainz tagged photon spectrometer and a new high-energy end-point tagger which allows η’ reactions to be studied. Reaction products are detected in a ~4π detector consisting of the Crystal Ball detector and TAPS forward wall. Transverse or longitudinally polarised proton targets are available and new techniques have been developed to measure the polarisation of recoiling protons. These facilities have allowed an extensive programme of double-polarisation meson-photoproduction experiments to be carried out to search for so-called “missing baryon resonances” on proton and deuteron targets. Searches have also been carried out to investigate narrow resonances in the η-photoproduction channel at invariant masses around 1680 MeV. Coherent π0 production measurements have been used to estimate the neutron skin thickness in 208Pb. This paper presents selected highlights from the A2-CB collaboration research programme at MAMI

Hurricane Impact on Emergency Services and Use of Telehealth to Support Prehospital Care

The impact of hurricanes on emergency services is well-known. Recent history demonstrates the need for prehospital and emergency department coordination to serve communities during evacuation, storm duration, and cleanup. The use of telehealth applications may enhance this coordination while lessening the impact on health-care systems. These applications can address triage, stabilization, and diversion and may be provided in collaboration with state and local emergency management operations through various shelters, as well as during other emergency medical responses

Quasi-free Compton Scattering and the Polarizabilities of the Neutron

Differential cross sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48 cm $\oslash$ $\times$ 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at $\theta^{LAB}_\gamma=136.2^\circ$. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction $p(\gamma,\pi^+ n)$. The "free" proton Compton scattering cross sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross section for free scattering from quasi-free data. Differential cross sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron have been obtained to be $\alpha-\beta= 9.8\pm 3.6(stat){}^{2.1}_1.1(syst)\pm 2.2(model)$ in units $10^{-4}fm^3$. In combination with the polarizability sum $\alpha +\beta=15.2\pm 0.5$ deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, $\alpha_n=12.5\pm 1.8(stat){}^{+1.1}_{-0.6}\pm 1.1(model)$ and $\beta_n=2.7\mp 1.8(stat){}^{+0.6}_{-1.1}(syst)\mp 1.1(model)$ are obtained. The backward spin polarizability of the neutron was determined to be $\gamma^{(n)}_\pi=(58.6\pm 4.0)\times 10^{-4}fm^4$

Ancient Yersinia pestis and Salmonella enterica genomes from Bronze Age Crete

During the late 3rd millennium BCE, the Eastern Mediterranean and Near East witnessed societal changes in many regions, which are usually explained with a combination of social and climatic factors.1, 2, 3, 4 However, recent archaeogenetic research forces us to rethink models regarding the role of infectious diseases in past societal trajectories.5 The plague bacterium Yersinia pestis, which was involved in some of the most destructive historical pandemics,5, 6, 7, 8 circulated across Eurasia at least from the onset of the 3rd millennium BCE,9, 10, 11, 12, 13 but the challenging preservation of ancient DNA in warmer climates has restricted the identification of Y. pestis from this period to temperate climatic regions. As such, evidence from culturally prominent regions such as the Eastern Mediterranean is currently lacking. Here, we present genetic evidence for the presence of Y. pestis and Salmonella enterica, the causative agent of typhoid/enteric fever, from this period of transformation in Crete, detected at the cave site Hagios Charalambos. We reconstructed one Y. pestis genome that forms part of a now-extinct lineage of Y. pestis strains from the Late Neolithic and Bronze Age that were likely not yet adapted for transmission via fleas. Furthermore, we reconstructed two ancient S. enterica genomes from the Para C lineage, which cluster with contemporary strains that were likely not yet fully host adapted to humans. The occurrence of these two virulent pathogens at the end of the Early Minoan period in Crete emphasizes the necessity to re-introduce infectious diseases as an additional factor possibly contributing to the transformation of early complex societies in the Aegean and beyond.Results and discussion STAR★Method

In-medium modifications of the ππ\pi\pi interaction in photon-induced reactions

Differential cross sections of the reactions $(\gamma,\pi^\circ\pi^\circ)$ and $(\gamma,\pi^\circ\pi^++\pi^\circ\pi^-)$ have been measured for several nuclei ($^1$H,$^{12}$C, and $^{\rm nat}$Pb) at an incident-photon energy of $E_{\gamma}$=400-460 MeV at the tagged-photon facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the $\pi\pi$ invariant-mass distribution is found in the $\pi^\circ\pi^\circ$ channel. This dependence is not observed in the $\pi^\circ\pi^{+/-}$ channel and is consistent with an in-medium modification of the $\pi\pi$ interaction in the $I$=$J$=0 channel. The data are compared to $\pi$-induced measurements and to calculations within a chiral-unitary approach

The reaction γp→π∘γ′p\gamma p \to \pi^\circ \gamma^\prime p and the magnetic dipole moment of the Δ+(1232)\Delta^+(1232) resonance

The reaction $\gamma p \to \pi^\circ \gamma^\prime p$ has been measured with the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for energies between $\sqrt{s}$ = 1221--1331 MeV. Cross sections differential in angle and energy have been determined for all particles in the final state in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the $\Delta^{+}(1232)$ resonance and, for the first time, a value of $\mu_{\Delta^+} = (2.7_{-1.3}^{+1.0}(stat.) \pm 1.5 (syst.) \pm 3(theo.)) \mu_N$ has been extracted

Photoproduction of eta-mesic 3He

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma+3He->eta+X has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonance-like structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasi-bound state. This is supported by studies of a competing decay channel of such a quasi-bound eta-mesic nucleus into pi^0+p+X. A binding energy of (-4.4+-4.2) MeV and a width of (25.6+-6.1) MeV is deduced for the quasi-bound eta-mesic state in 3He.Comment: v1: 4 pages, 4 figures, submitted to PRL; v2: minor revisions and corrections, new figure added, 4 pages, 5 figs; v3: minor change

Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C

The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it can be used with the 1500 MeV electron beam now available from the Mainz microtron MAMI-C. The changes made and the resulting properties of the spectrometer are discussed.Comment: 20 pages, 12 figure

Deuteron photodisintegration cross-sections 50-155 MeV

The study of the photodisintegration of the deuteron should be a rewarding area over the next few years both as a result of the increased sophistication of recent theoretical treatments and also because of the potential, which has only just begun to be realised, of much more accurate and reliable photoreaction data

Quasi-free π0\pi^0 Photoproduction from the Bound Nucleon

Differential cross-sections for quasi-free $\pi^0$ photoproduction from the proton and neutron bound in the deuteron have been measured for $E_\gamma= 200 - 400$ MeV at $\theta^{\rm lab}_\gamma = 136.2^\circ$ usind the Glasgow photon tagger at MAMI, the Mainz 48 cm $\varnothing$ $\times$ 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA recoil detector. For the proton measurements made with both liquid deuterium and liquid hydrogen targets allow direct comparison of "free" $\pi^0$ photoproduction cross-sections as extracted from the bound proton data with experimental free cross sections which are found to be in reasonable agreement below 320 MeV. At higher energies the "free" cross sections extracted from quasifree data are significantly smaller than the experimental free cross sections and theoretical predictions based on multipole analysis. For the first time, "free" neutron cross sections have been extracted in the $\Delta$-region. They are also in agreement with the predictions from multipole analysis up to 320 MeV and significantly smaller at higher photon energies