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Register a new userFirst measurement of coherent $phi$-meson photoproduction on deuteron at low energies
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The cross section and decay angular distributions for the coherent phi meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t =(p_{gamma}-p_{phi})^2 =-2 GeV^2/c^2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are compared with predictions from a re-scattering model. In a framework of vector meson dominance, the data are consistent with the total phi-N cross section sigma_{phi N} at about 10 mb. If vector meson dominance is violated, a larger sigma_{phi N} is possible by introducing larger t-slope for the phi N to phi N process than that for the gamma N to phi N process. The decay angular distributions of the phi are consistent with helicity conservation.
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The differential cross sections and decay angular distributions for coherent $phi$-meson photoproduction from helium-4 have been measured for the first time at forward angles with linearly polarized photons in the energy range $E_{gamma} = text{1.685-2.385 GeV}$. Thanks to the target with spin-parity $J^{P} = 0^{+}$, unnatural-parity exchanges are prohibited, and thus natural-parity exchanges can be investigated clearly. The decay asymmetry with respect to photon polarization is shown to be very close to the maximal value. This ensures the dominance ($> 94%$) of natural-parity exchanges in this reaction. To evaluate the contribution from natural-parity exchanges to the forward cross section ($theta = 0^circ$) for the $gamma p rightarrow phi p$ reaction near the threshold, the energy dependence of the forward cross section ($theta = 0^circ$) for the $gamma {^{4}text{He}} rightarrow phi {^{4}text{He}}$ reaction was analyzed. The comparison to $gamma p rightarrow phi p$ data suggests that enhancement of the forward cross section arising from natural-parity exchanges, and/or destructive interference between natural-parity and unnatural-parity exchanges is needed in the $gamma p rightarrow phi p$ reaction near the threshold.
The total cross sections were measured for coherent double neutral-pion photoproduction on the deuteron at incident energies below 0.9 GeV for the first time. No clear resonance-like behavior is observed in the excitation function for $W_{gamma d}=2.38$--2.61 GeV, where the $d^*(2380)$ dibaryon resonance observed at COSY is expected to appear. The measured excitation function is consistent with the existing theoretical calculation for this reaction. The upper limit of the total cross section is found to be $0.034$~$mu$b for the dibaryon resonance at $W_{gamma d}=2.37$~GeV (90% confidence level) in the $gamma d to pi^0pi^0 d$ reaction.
The scarce data systematics and complexity of deuteron interactions demand the update of both the experimental database and theoretical frame of deuteron activation cross sections. Various reactions induced by neutrons and protons following the deuteron breakup (BU) should be also taken into account. On the other hand, deuteron reaction cross sections recommended recently for high-priority elements are still based on data fit without predictive power. Purpose: Accurate new measurements of low-energy deuteron-induced reaction cross sections for monoisotopic (55Mn) natural manganese target enhance the related database as well as the opportunity of an unitary and consistent account of the related reaction mechanisms. Method: Activation cross sections of 54,56Mn, and 51Cr nuclei by deuterons on $^{55}$Mn were measured at energies <20 MeV by the stacked-foil technique and high resolution gamma spectrometry at the U-120M cyclotron of CANAM, NPI CAS. Then all available data for deuterons on 55Mn up to 50 MeV are analyzed paying particular attention to BU and direct reaction (DR) mechanisms. Results: Newly measured activation cross sections strengthen the deuteron database at low energies, at once with a consistent account for the first time of all available data. Conclusions: Due account of deuteron-induced reactions on 55Mn, including particularly the new experimental data at low energies, is provided by a suitable BU and DR assessment.
Photoproduction of $phi$-meson on protons was studied by means of linearly polarized photons at forward angles in the low-energy region from threshold to $E_{gamma}$= 2.37 GeV. The differential cross sections at $t = -|t|_{min}$ do not increase smoothly as $E_{gamma}$ increases, but show a local maximum at around 2.0 GeV. The angular distributions demonstrate that $phi$-mesons are photo-produced predominantly by helicity-conserving processes, and the local maximum is not likely due to unnatural-parity processes.
We present measurements of differential cross sections and the analyzing powers A_y, iT11, T20, T21, and T22 at E_c.m.=431.3 keV. In addition, an excitation function of iT11(theta_c.m.=87.8 degrees) for 431.3 <= E_c.m. <= 2000 keV is presented. These data are compared to calculations employing realistic nucleon-nucleon interactions, both with and without three-nucleon forces. Excellent agreement with the tensor analyzing powers and cross section is found, while the Ay and iT11 data are found to be underpredicted by the calculations.
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