$K^+\Lambda(1405)$ photoproduction has been studied at the BGOOD experiment
via the all neutral decay, $\Lambda(1405)\rightarrow\Sigma^0\pi^0$. The unique
BGOOD experimental setup allows both the ...cross section and $\Lambda(1405)$
invariant mass distribution (line shape) to be measured over a broad $K^+$
polar angle range, extending to extreme forward $K^+$ angles unattainable at
previous experiments.
Evidence is provided for the role of a triangle singularity driven by the
$N^*(2030)$ resonance, which appears to contribute significantly to
$K^+\Lambda(1405)$ photoproduction. This is observed in both the angular
distributions and the integrated cross section which was determined with
unprecedented energy resolution. The measured line shape is also in agreement
with the previous results of CLAS and ANKE, and is consistent with two poles
derived in $\chi$PT based models.
The differential cross section for the quasi-free photoproduction reaction
$\gamma n\rightarrow K^0\Sigma^0$ was measured at BGOOD at ELSA from threshold
to a centre-of-mass energy of 2400 MeV. Close ...to threshold the results are
consistent with existing data and are in agreement with partial wave analysis
solutions over the full measured energy range, with a large coupling to the
$\Delta$(1900)1/2- evident. This is the first dataset covering the K* threshold
region, where there are model predictions of dynamically generated vector
meson-baryon resonance contributions.
The $\gamma p \rightarrow K^+\Sigma^0$ differential cross section at
extremely forward angles was measured at the BGOOD experiment. A three-quarter
drop in strength over a narrow range in energy and ...a strong dependence on the
polar angle of the $K^+$ in the centre-of-mass of the reaction is observed at a
centre-of-mass energy of 1900\,MeV. Residing close to multiple open and hidden
strangeness thresholds, the structure appears consistent with meson-baryon
threshold effects which may contribute to the reaction mechanism.
Eur. Phys. J. A 57, 80 (2021) $\gamma p \rightarrow K^+ \Lambda$ differential cross sections and recoil
polarisation data from threshold for extremely forward angles are presented.
The measurements ...were performed at the BGOOD experiment at ELSA, utilising the
high angular and momentum resolution forward spectrometer for charged particle
identification. The data discriminates between conflicting results in the world
data set and enable extraction of the cross section as the minimum momentum
transfer to the recoiling hyperon is approached.
The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly ...segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where t-channel exchange mechanisms play an important role. This also allows access to low momentum exchange kinematics where extended, molecular structure may manifest in reaction mechanisms. First key results at low \(t\) indicate a cusp-like structure in \(K^+\Sigma^0\) photoproduction at \(W = 1900\)\,MeV, line shapes and differential cross sections for \(K^+\Lambda\)(1405)\(\rightarrow K^+\Sigma^0\pi^0\), and a peak structure in \(K^0_S\Sigma^0\) photoproduction. The peak in the \(K^0_S\Sigma^0\) channel appears consistent with meson-baryon generated states, where equivalent models have been used to describe the \(P_C\) pentaquark candidates in the heavy charmed quark sector.
The differential cross section for the quasi-free photoproduction reaction \(\gamma n\rightarrow K^0\Sigma^0\) was measured at BGOOD at ELSA from threshold to a centre-of-mass energy of 2400 MeV. ...Close to threshold the results are consistent with existing data and are in agreement with partial wave analysis solutions over the full measured energy range, with a large coupling to the \(\Delta\)(1900)1/2- evident. This is the first dataset covering the K* threshold region, where there are model predictions of dynamically generated vector meson-baryon resonance contributions.
The BGOOD experiment at the ELSA facility in Bonn has been commissioned within the framework of an international collaboration. The experiment pursues a systematic investigation of non-strange and ...strange meson photoproduction, in particular \(t\)-channel processes at low momentum transfer. The setup uniquely combines a central almost \(4\pi\) acceptance BGO crystal calorimeter with a large aperture forward magnetic spectrometer providing excellent detection of both neutral and charged particles, complementary to other setups such as Crystal Barrel, Crystal Ball, LEPS and CLAS.
The effect of short bouts (1 min) of electrically induced ventricular tachycardias (VT) of increasing rates (160-240/min) was studied in 8 anesthetized dogs before and after graded constrictions of ...the left anterior descending (LAD) and the circumflex (CCA) coronary arteries. In the absence of coronary stenosis, paroxysmal VT caused a significant decrease in tension-time index (TTI), coronary blood flow (CBF) and coronary vascular resistance (CVR). Single and combined coronary stenosis caused relatively small alterations of the VT-induced depression of the systemic hemodynamics but reversed the effect of paroxysmal VT on the CVR. In the presence of single 90% LAD stenosis, VT resulted in an increase in CVR-LAD and a decrease in F-LAD associated with a fall in CVR-CCA and a rise in F-CCA. Combination of 90% LAD plus 70% CCA stenosis abolished the compensatory fall of CVR-CCA resulting in a pronounced reduction of F-CCA during VT. The results support the concept that in the presence of severe coronary stenosis brief paroxysmal ventricular tachycardias do increase myocardial nutritional demand but rather decrease nutritional supply.
The effects of short episodes (1 min) of vagally-mediated bradycardia were studied in 9 anesthetized dogs utilizing vagal stimulation and slow atrial pacing (120 and 80 beats/min) before and after ...graded coronary constriction of the left anterior descending (LAD) and the left circumflex (CCA). In the presence of 90% LAD stenosis, bradycardia tended to restore both the elevated total LAD coronary vascular resistance (CVR-LAD) and the reduced, total CVR-CCA towards control levels obtained at corresponding slow rates in the absence of coronary stenosis; as a result, LAD coronary flow (F-LAD) was relatively less reduced and the accessory rise of F-CCA disappeared. In the presence of combination of 90% LAD plus 70% CCA stenosis, the effects of bradycardia on total CVR-LAD and F-LAD were similar to those obtained with single 90% LAD stenosis, but the accessory flow through the CCA was abolished resulting in no significant difference of the rate-dependent alterations of total CVR-CCA and F-CCA as compared with those observed in the absence of coronary stenosis. In the presence of single or combined coronary stenosis, bradycardia restored the depressed aortic pressure and cardiac output towards control values obtained at comparable slow rates before coronary stenosis. The results support the concept that in the presence of 90% LAD stenosis vagally-mediated bradycardia 1) decreases the tension-time index (myocardial nutritional demand) shifting cardiac performance to less expensive "flow work" and 2) facilitates antegrade flow through the highly stenotic LAD thereby inhibiting accessory flow through the nonstenotic CCA.
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