Search results for "Pion"
showing 10 items of 1304 documents
Quasi-deuteron effects at intermediate energies
2008
It has been shown that photon and pion reactions in certain energy regions are dominated by the absorption on correlated (n-p)-pairs. Therefore, calculations based on quasi-deuteron models describe rather well the present experimental results. However, with more accurate data out of the reactions (γ,np),(γ,N), (π,NN) and (π,N) performed so that the complete kinematics is known, the correlation function of nucleon pairs in nuclei can be studied a quantity very important for our understanding of the nuclear many body system. The dominance for absorption on pairs in reactions with a rather big mismatch in energy and momentum in the entrance channel compared with the exit channel of the reactio…
Antiproton-proton annihilation at rest intoπ + π − η ′ andπ + π − η from atomicS andP states
1990
We have measured the branching ratios for\(\bar pp\) annihilation at rest intoπ+π−η andπ+π−η′ in hydrogen gas in two data samples that have different fractions ofS-wave andP-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for\(\bar pp\) annihilations into four charged pions of (49±4)% and the branching ratio intoπ+π−π+π−π0 of (18.7±1.6)%. We find a significant reduction of the branching ratios fromP-states for\(\bar pp \to \pi ^ + \pi ^ - \eta \) andπ+π−η′ in comparison toS-state annihilation. $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta ) = (13.7 \pm 1.46) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta …
The γd → π0 d and γd → pn Reactions in the Δ-Resonance Region
1994
Coherent pion photoproduction on the deuteron and deuteron photodisintegration in the Δ-resonance region is studied treating the final state interaction within a NN−NΔ coupled channel approach.
Deuteron Compton Scattering
1995
We have calculated deuteron Compton scattering below pion production threshold using different realistic NN potential models and explicit meson exchange current contributions. The gauge conditions for the current and two photon operators have been exploited extensively, so that our model fulfills the low energy theorems. Rescattering, meson exchange and nucleon substructure contributions are studied and compared with a previous calculation and recent experimental data.
A method for measuring total cross sections of (γ, π−) reactions at threshold
1981
Abstract A new method for detecting low energy negative pions has been investigated. The negative pions are identified via monoenergetic neutrons produced in the reaction π − + D → 2 n and detected by means of a time of flight spectrometer. The feasibility for measuring D ( γ , π − ) cross sections near threshold is demonstrated; an extension to heavier nuclei seems to be possible. Futher the method is well suited for applications together with tagged photon beams.
Threshold pion photoproduction in a light-cone quark model
1991
Abstract The instantaneous and seagull graphs are calculated for pion photoproduction in a relativistic light-cone model of the nucleon. In both pseudoscalar and pseudovector coupling we find the ratios A (−) : A (0) : A (+) = 1: ( −1 2 μ):( −9 5 μ) in the nonrelativistic limit. These results correspond to the sum of seagull and Z -graph in the nonrelativistic quark model. In pseudovector coupling also the numerical results for realistic-model parameters are close to those values.
Radiative muon capture on 12C and 16O
1979
Abstract We study exclusive radiative muon capture on 12 C(g.s.) leading to 12 B(g.s.), and on 16 O(g.s.) leading to 16 N(0 − , 120 keV). Our investigation, which is based on impulse approximation, puts special emphasis on elementary particle aspects of radiative capture, such as tests of magnitude and momentum transfer dependence of the induced pseudoscalar, and possible contributions of axial currents of second kind (weak electricity). We calculate several correlation observables which are sensitive to the nucleonic currents but depend very little on the structure of the nuclear initial and final states. In particular, it is shown that in capture on 12 C the polarization and alignment of …
Photoproduction of delta and Roper resonances in the cloudy bag model.
1988
The photoproduction of delta and Roper resonances has been calculated within the framework of the cloudy bag model. Two alternative formulations, the original pseudoscalar surface coupling and the pseudovector volume coupling of pions, have been used, and the results are compared. The helicity amplitudes are in fair agreement with experimental data, the prediction for the small ${E}_{1+}$/${M}_{1+}$ ratio for delta production is -1.8% for a bag radius of 1 fm and pseudovector coupling.
Experiments on threshold pion electroproduction
2008
Experimental techniques to access the reactions p(e, e′ p)π0 and d(e, e′ d)π0 at low four momentum transfer and close to threshold are presented. For p(e, e′ p)π0 results at Q 2=0.1 GeV2/c 2 are given and compared to chiral perturbation theory. A new experimental program on d(e, e′ d)π0 is presented.
Large-angle production of charged pions by 3 GeV/c - 12.9 GeV/c protons on beryllium, aluminium and lead targets
2008
Measurements of the double-differential pi(+/-) production cross-section in the range of momentum 100 MeV/c <= p < 800 MeV/c and angle 0.35 rad <= theta < 2.15 rad in proton-beryllium, proton-aluminium and proton-lead collisions are presented. The data were taken with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12.9 GeV/c hitting a target with a thickness of 5% of a nuclear interaction length. The tracking and identification of the produced particles was performed using a small-radius cylindrical time projection chamber (TPC) placed inside a solenoidal magnet. Incident particles were identified by an elabo…