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Register a new userMeasurement of Inverse Pion Photoproduction at Energies Spanning the N(1440) Resonance
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Differential cross sections for the process pi^- p -> gamma n have been measured at Brookhaven National Laboratorys Alternating Gradient Synchrotron with the Crystal Ball multiphoton spectrometer. Measurements were made at 18 pion momenta from 238 to 748 MeV/c, corresponding to E_gamma for the inverse reaction from 285 to 769 MeV. The data have been used to evaluate the gamma n multipoles in the vicinity of the N(1440) resonance. We compare our data and multipoles to previous determinations. A new three-parameter SAID fit yields 36 +/- 7 (GeV)^-1/2 X 10^-3 for the A^n_1/2 amplitude of the P_11.
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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 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.
Neutrons produced by the carbon fusion reaction 12C(12C,n)23Mg play an important role in stellar nucleosynthesis. However, past studies have shown large discrepancies between experimental data and theory, leading to an uncertain cross section extrapolation at astrophysical energies. We present the first direct measurement that extends deep into the astrophysical energy range along with a new and improved extrapolation technique based on experimental data from the mirror reaction 12C(12C,p)23Na. The new reaction rate has been determined with a well-defined uncertainty that exceeds the precision required by astrophysics models. Using our constrained rate, we find that 12C(12C,n)23Mg is crucial to the production of Na and Al in Pop-III Pair Instability Supernovae. It also plays a non-negligible role in the production of weak s-process elements as well as in the production of the important galactic gamma-ray emitter 60Fe.
We present measurements of $rho^0$, $omega$ and K$^{*0}$ spectra in $pi^{-} + $C production interactions at 158 GeV/c and $rho^0$ spectra at 350 GeV/c using the NA61/SHINE spectrometer at the CERN SPS. Spectra are presented as a function of the Feynmans variable $x_text{F}$ in the range $0 < x_text{F} < 1$ and $0 < x_text{F} < 0.5$ for 158 GeV/c and 350 GeV/c respectively. Furthermore, we show comparisons with previous measurements and predictions of several hadronic interaction models. These measurements are essential for a better understanding of hadronic shower development and for improving the modeling of cosmic ray air showers.
The excitation of the Roper resonance $N^*(1440)$ in $NN$ collisions leading to single and double pion production exhibits a structure in the energy dependence of the total cross section, which does not correspond to the usual opening of the $N^*(1440)$ production channel, but rather to the formation of dibaryon states with $I(J^P) = 0(1^+)$ and $1(0^+)$ at the $N^*(1440)N$ threshold. This is very similar to the situation at the $Delta(1232)N$ threshold, where meanwhile a number of dibaryonic resonances have been found.
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