Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

The reactionspp → e + e − and e + e − →pp are analyzed in the near-threshold region. Specific emphasis is put on the role played by the interaction in the initial-or final antinucleon-nucleon (NN) state which is taken into account rigorously. For that purpose a recently publishedNN potential derived within chiral effective field theory and fitted to results of a new partial-wave analysis ofpp scattering data is employed. Our results provide strong support for the conjecture that the pronounced energy dependence of the e + e − ↔pp cross section, seen in pertinent experiments, is primarily due to thepp interaction. Predictions for the proton electromagnetic form factors G E and G M in the timelike region, close to theNN threshold, and for spin-dependent observables are presented. The steep rise of the effective form factor for energies close to thepp threshold is explained solely in terms of thepp interaction. The corresponding experimental information is quantitatively described by our calculation.

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“…In the helicity basis, the amplitudes for the reaction e + e − →pp for one-photon exchange are given by [46,47] …”

Section: Formalismmentioning

confidence: 99%

The electromagnetic form factors of the proton in the timelike region

2014

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“…The resulting polarization seems to be insufficient for the requirements of studies relating to transversity [1] and to the evaluation of time-like electromagnetic form factors [17]. The resulting polarization seems to be insufficient for the requirements of studies relating to transversity [1] and to the evaluation of time-like electromagnetic form factors [17].…”

Section: Asymmetrymentioning

confidence: 99%

Overview of Processes Involved in Spin Transfer Collisions

Barber¹,

Buttimore²,

Chattopadhyay³

et al. 2008

AIP Conference Proceedings

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Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions AIP Conf.Abstract. An outline is provided of methods for polarizing antiprotons that include the possible use of channelling in a bent crystal and also the technique of scattering off leptons or protons at a suitably small angle. In the method of channelling it is suggested that the angular dependence of the analysing power of the incident particle is cubic in the angle for single scattering in the crystal when this takes place within the region of electromagnetic hadronic interference as is most likely for channelled particles. Polarization transfer in the scattering of antiprotons off leptons or protons is discussed in addition where emphasis is laid on the angular integrals over spin observables appropriate for spin filtering.

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“…However, e − e + → pp is dominated by the one-photon intermediate state in the s-channel. For this mechanism, in the more general case of the B 1 B 1 → B 2 B 2 reaction, the non-vanishing helicity amplitudes read (see, e.g., [103] for a recent compilation)…”

Section: Special Casesmentioning

confidence: 99%

Spin observables and spin structure functions: inequalities and dynamics

Artru,

Elchikh,

Richard

et al. 2008

Preprint

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Model-independent identities and inequalities which relate the various spin observables of collisions in nuclear and particle physics are reviewed in a unified formalism. Their physical interpretation and their implications for dynamical models are also discussed. These constraints between observables can be obtained in several ways: from the explicit expression of the observables in terms of a set of helicity or transversity amplitudes, a non-trivial algebraic exercise which can be preceded by numerical simulation with randomly chosen amplitudes, from anticommutation relations, or from the requirement that any polarisation vector is less than unity. The most powerful tool is the positivity of the density matrices describing the spins in the initial or final state of the reaction or its crossed channels. The inequalities resulting from positivity need to be projected to single out correlations between two or three observables. The quantum aspects of the information carried by spins, in particular entanglement, are considered when deriving and discussing the constraints Several examples are given, with a comparison with experimental data in some cases. For the exclusive reactions, the cases of the strangeness-exchange proton-antiproton scattering and the photoproduction of pseudoscalar mesons are treated in some detail: all triples of observables are constrained, and new results are presented for the allowed domains. The positivity constraints for total cross-sections and for the simplest observables of single-particle inclusive reactions are reviewed. They also apply to spin-dependent structure functions and parton distributions, both integrated or transverse-momentum dependent. The corresponding inequalities are shown to be preserved by the evolution equations of quantum chromodynamics.

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Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

Cited by 7 publications

References 16 publications

The electromagnetic form factors of the proton in the timelike region

The electromagnetic form factors of the proton in the timelike region

Overview of Processes Involved in Spin Transfer Collisions

Spin observables and spin structure functions: inequalities and dynamics

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