Measurement of spin observables in the quasifree np→{pp}_{s}π^{−} reaction at 353 MeV (original) (raw)
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Perturbative QCD results on pion production in pp, pA and AA collisions
We summarize new pQCD results on pion production in protonproton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation introduces intrinsic parton transverse momentum (k T ) and is performed effectively at next-to-leading order (NLO), applying a K factor extracted for jet events. Two different factorization scales, Q = p T,jet /2 and p T,jet are used. Experimental data in pA collisions imply a preference for the latter choice at NLO level. We display our results at CERN SPS for AA collisions.
Novel approach to pi\pipi and eta\etaeta production in proton-proton collisions
1999
We evaluate the threshold matrix-element for the reaction pptopppi0pp \to pp\pi^0pptopppi0 in a fully relativistic Feynman diagrammatic approach. We employ a simple effective range approximation to take care of the S-wave pppppp final-state interaction. The experimental value for the threshold amplitude calA=(2.7−i0.3){\cal A} = (2.7 - i 0.3)calA=(2.7−i0.3) fm$^4$ can be reproduced by contributions from tree level chiral (long--range) pion exchange and short-range effects related to heavy meson exchanges, with these two very different contributions of roughly the same size. Pion loop effects appear to be small. We stress that the commonly used heavy baryon formalism is not applicable in the NN-system above the pion production threshold due to the large external momentum, ∣vecp∣simeqrespectively.Wefurthermoreinvestigatethereaction|\vec p | \simeq respectively. We furthermore investigate the reaction ∣vecp∣simeqrespectively.Wefurthermoreinvestigatethereactionpp\to p n \pi^+$ near threshold within the same approach. We extract from the data the triplet threshold amplitude, calB=(3.9−i2.1){\cal B}= (3.9 -i 2.1)calB=(3.9−i2.1) fm$^4$, which comes out too small by a factor o...
Pion-nucleon interaction in a covariant hadron-exchange model
Physical Review C, 2000
We develop a relativistic covariant and unitary description of the pion-nucleon interaction in a hadron-exchange model. The model is based on the solution of a dimensionally reduced (quasipotential) Bethe-Salpeter equation for the partial-wave off-shell πN scattering amplitudes with the potential consisting of the field-theoretical s-and u-channel nucleon, Roper, Delta, D 13 , S 11 exchanges, and the t-channel ρ and σ meson exchanges. The contributions of the spin-3/2 Delta and D 13 resonances are treated within the Rarita-Schwinger formalism and different forms of the πN ∆ vertex are investigated. The free parameters of the model are fitted to the πN phase-shift data of the KH80 and SM95 partial-wave analyses in the region up to 600 MeV pion kinetic energy. The resulting on-shell solution provides a good description of the πN scattering lengths, as well as the energy behavior of the S, P, and D partial waves. The sensitivity of the phase shifts on various model-dependent effects is examined.
Pion production in pion-nucleon collisions in the Chew-Low-Wick formalism
1956
The produc~ion of a single p-wave pion in pion-nucleon collisions has been studied using the Chew-Low-Wick formalism. This theory is a low-energy, static-source theory. The purposes of this study are: to determine the ability of the theory to handle high-energy processes; to determine the effects of high-energy processes upon the low-energy predictions of the theory; a.nd to obtain information on the behavior of the production cross-section. An equation has been derived which, in the one-intermediatemeson approximation, gives the matrix element for meson production in terms of the matrix element for scattering. This equations exhibits a crossing symmetry under a time reversal of one of the outgoing mesons. The angular momentum a.nd isotopic spin dependences have been extracted. This allows one to take advantage of the conservation of the total angular momentum and total isotopic spin, and to use the symmetry of the theory between angular momentum and isotopic spin. The resulting equations have the form of twenty coupled integral equations; they are uncoupled by neglecting integrals containing non-resonant denominators. Solutions have been obtained by including scattering 1n only the T = J = 3/2 state. The resulting production cross-section for ff-incident on protons shows a peak. for an incident energy of 700 Mev. For energies in this region, each outgoing meson can attain the 33-resonant energy relative to the nucleon. The peak is the result of this "two-particle resonance". The one-meson approximation does not maintain the requirements of unitarity. It is found that the production cross-sections violate unitarity in the region of 500 Mev. This is attributable to the inadequacies of the one-meson approximation and to the fact that high-energy scattering effects are important. The equation for the production matrix element shows that the high-energy scattering amplitudes act to damp the production cross-section. The solutions for meson production have been used to examine the two-meson corrections to the equation for the scattering matrix element. These corrections are small relative to the scattering amplitude for the 33-state, but large relative to the amplitudes for the 11-and 13-atates. The equation for the matrix element describing the photoproduction of two p-wave pions has been derived. All quantities involved have been expressed 1n terms of multipoles. The structure of the equation is identical with the equation for meson production, leading to the belief that double photoproduction will show a peak for incident photon energies of about 800 Mev.
Pion-nucleon scattering in chiral perturbation theory (I): Isospin-symmetric case
Nuclear Physics A, 1998
We construct the complete effective chiral pion-nucleon Lagrangian to third order in small momenta based on relativistic chiral perturbation theory. We then perform the so-called heavy baryon limit and construct all terms up-to-and-including order 1/m 2 with fixed and free coefficients. As an application, we discuss in detail pionnucleon scattering. In particular, we show that for this process and to third order, the 1/m expansion of the Born graphs calculated relativistically can be recovered exactly in the heavy baryon approach without any additional momentum-dependent wave function renormalization. We fit various empirical phase shifts for pion laboratory momenta between 50 and 100 MeV. This leads to a satisfactory description of the phase shifts up to momenta of about 200 MeV. We also predict the threshold parameters, which turn out to be in good agreement with the dispersive analysis. In particular, we can sharpen the prediction for the isovector S-wave scattering length, 0.083 M −1 π ≤ a − 0+ ≤ 0.093 M −1 π. We also consider the subthreshold parameters and give a short comparison to other calculations of πN scattering in chiral perturbation theory or modifications thereof.