共查询到20条相似文献,搜索用时 31 毫秒
1.
《Nuclear Physics A》1999,646(3):343-363
We develop a method for constructing the heavy baryon chiral perturbation theory (HBChPT) Lagrangian, to a given chiral order, within HBChPT. We work within SU(2) theory, with only the pion field interacting with the nucleon. The main difficulties, which are solved, are to develop techniques for implementing charge conjugation invariance, and for taking the nucleon on shell, both within the non-relativistic formalism. We obtain complete lists of independent terms in LHBChPT through O(q3) for off-shell nucleons. Then, eliminating equation-of-motion (e.o.m.) terms at the relativistic and non-relativistic level (both within HBChPT), we obtain LHBChPT for on-shell nucleons, through O(q3). The extension of the method (to obtain on-shell LHBChPT within HBChPT) to higher orders is also discussed. 相似文献
2.
《Zeitschrift fur Physik C Particles and Fields》1997,75(2):215-228
The reaction γ p → J/ψ p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/ψ photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q 2 of 5 × 10?5 GeV2. The photoproduction cross section, σγp→ J/ψp, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter δ in the form σγp→ J/ψp α W δ yields the value δ = 0.92±0.14±0.10. The differential cross section dσ/d ¦t¦is presented over the range ¦t¦< 1.0 GeV2 where t is the square of the four-momentum exchanged at the proton vertex. dσ/d ¦t¦falls exponentially with a slope parameter of $4.6pm 0.4_{-0.6}^{+0.4} {? GeV}^{-2}$. The measured decay angular distributions are consistent with s-channel helicity conservation. 相似文献
3.
We calculate the contribution from nucleon binding to the coefficient Re B0 in the optical potential of pionic atoms. The relevant Feynman graphs are deduced for nuclear matter. They depend on off-shell values for pion-nucleon scattering lengths aπN and for the nucleon-binding potential VNA. Off-shell effects are found to be very important: A pole model for aπN, extrapolated off-shell, increases binding effects by a factor of three over the use of on-shell values. Two simple models are proposed for the off-shell continuation of VNA. One leads to attractive, the other to repulsive contributions to Re B0. 相似文献
4.
Carl B. Dover 《Annals of Physics》1973,79(2):441-479
The second order terms in a density expansion of the pion optical potential Vopt are evaluated quantitatively. The coefficients of these terms are proportional to various combinations of on- and off-shell nucleon-nucleon T-matrices, averaged over the distribution of two nucleon relative momenta in the Fermi sea. The on-shell contributions can be obtained directly from experimental phase shifts, but the calculation of the off-shell-parts requires a model for the nucleon-nucleon potential. We consider a number of realistic local and nonlocal, separable potentials which fit nucleon-nucleon phase shifts, in order to study the variations in Vopt which arise from differences in the off-shell behavior of T. We find absorptive (imaginary) and dispersive (real) contributions to Vopt which are of comparable magnitude. The dispersive part, which leads to a real energy shift associated with the two nucleon absorptive process, has not been previously estimated quantitatively. We compare our results to empirical potentials obtained by fitting energy level shifts and widths in pi-mesic atoms, as well as theoretical estimates based on threshold cross sections for the processes π + N + N ? N + N. 相似文献
5.
A unified model for spacelike and timelike hadron form factors within light-front dynamics successfully applied to the pion is extended to the nucleon to study the role of valence and nonvalence vertex functions. Preliminary results for ?10(GeV/c)2 ≤ q 2 ≤ 10(GeV/c)2 are presented. 相似文献
6.
7.
Vertex functions for composite fields are defined in a model field theory both on and off mass shell. Light-cone dominance at large momentum transfer is shown to hold, by the compositeness assumption, for the off-shell vertex function. On the other hand, it is in general untrue that the elastic form factor probes light-like distances between the constituents inside the nucleon. The relevant light-cone singularity (in the relative space-time separation x) is less important in this case than the large x0 behaviour of the wave function at fixed x2. It is found however that, under some conditions, the light-cone singularity determines the large x0 behaviour of the wave function, and therefore the large q2 behaviour of the form factor. For composite particles described by a Bethe-Salpeter equation, this result is equivalent to the known fact that at large q2 the form factor depends on the binding interaction at small distances. A relation similar to that of Drell-Yan-West is finally established between the asymptotic behaviour of the elastic form factor and the threshold behaviour of the absorptive part of the vertex scaling function. 相似文献
8.
A. Del Guerra A. Giazotto M.A. Giorgi A. Stefanini D.R. Botterill H.E. Montgomery P.R. Norton G. Matone 《Nuclear Physics B》1976,107(1):65-81
Threshold π+ electroproduction has been measured at momentum transfers 6k26 of 0.45, 0.58 and 0.88 (GeV/c)2, extending the range of earlier measurements. Using PCAC and current algebra-based models we have deduced the axial vector form factor of the nucleon GA(k2), and find that the dipole parametrisation is favoured over the monopole. The value of MA in the dipole parametrisation is, in a weak PCAC model, 0.96 ± 0.03 GeV, in excellent agreement with neutrino measurements. The threshold cross section is also in excellent agreement with the predictions of a fixed-t dispersion relation model. 相似文献
9.
H. Muirhead J.R. Fry H. Rohringer E. Simopoulou A. Apostolakis P. Papailas H. Rozaki M Spyropoulou G. Vassiliades T.A. Filippas G. Grammatikakis P. Tsilimigras A. Yayaki D. Dollmans P. Girtler M. Markytan 《Nuclear Physics B》1975,99(3):376-396
Aspects of the process K?p → Λ + pions for K? mesons of momentum 8.25 GeV/c are examined. It is shown that the hypercharge annihilation process can be effectively separated into off-shell baryon (B?B) and strangeness (K?K) annihilation. Both annihilation regions have many features in common and show strong similarities to on-shell annihilation processes; some differences are also noted. 相似文献
10.
11.
V. V. Dubinina N. P. Egorenkova V. I. Krotkova E. A. Pozharova V. A. Smirnitskii 《JETP Letters》2005,82(1):14-16
The azimuthal anisotropy of the emission of α particles in collisions of the 22Ne, 24Mg, 56Fe, and 197Au nuclei with photoemulsion nuclei has been measured at projectile energies Epr = 1.88–10.6 GeV/nucleon. The results are compared with similar measurements for protons. It has been found that the ratio of the azimuthal anisotropy coefficients v2 for α particles and protons is equal to 6 ± 2 at low energies Epr ≈ 2 GeV/nucleon, whereas these coefficients coincide with each other for energies Epr ≥ 4 GeV/nucleon. This difference may indicate that, at low projectile energies, α particles are formed predominantly at the early stage of a collective flow. Formation of α particles for Epr ≥ 4 GeV/nucleon likely occurs at the stage of nuclear matter scattering. 相似文献
12.
Relativistic study of the reaction pp → dπ: Formalism and comparison with experiment at Tp = 578 MeV
A detailed relativistic calculation of pp → πd is presented. The leading graph is the exchange of a nucleon and a pion. The πN amplitudes, including off-shell information, are input, together with relativistic dpn and πNN vertex functions. The dominant nucleon spectator term is calculated without uncontrolled approximations, and the relativistic pion antiparticle contribution is evaluated. The single nucleon exchange diagram is added. Higher order rescattering is treated by initial and final state distortion factors. All amplitudes and spin observables are calculated and a detailed comparison with the measured data at 578 MeV is made. The remaining observed discrepancies are traced to the pp spin-triplet waves. 相似文献
13.
We have extended the dispersion relation calculation of the πNN vertex function to include off-shell terms in the πN scattering matrix. These off-shell terms are constrained by the current algebra and PCAC results, and contribute to the s-wave. As such, they add to the kinematic off-shell effects which Durso, Jackson and VerWest found in the p-terms. The off-shell terms increase the calculated Goldberger-Treiman discrepancy from 0.02 to 0.03, bringing it into agreement with the field theory value of Jones and Scadron (0.035). The calculated discrepancy remains smaller than the experimental value of 0.06±0.01. 相似文献
14.
G. Benfatto 《Nuclear Physics B》1972,50(1):205-221
We discuss the implications of gauge invariance in the problem of the on-shell extrapolation of the electroproduction low-energy theorems. We show that there is an invariant amplitude which can be evaluated at the Breit threshold either using gauge invariance and on-shell dispersion relations or following the Fubini and Furlan [5] extrapolation method starting from the current-algebra low-energy value of the amplitude. Comparing the two expressions, we find a relation between the electromagnetic pion form factor, Fπ (k2), and the axial-vector nucleon form factors, gA (k2) and hA (k2). 相似文献
15.
M. Barth C. De Clercq E. De Wolf J. J. Dumont D. P. Johnson J. Lemonne P. Peeters R. Contri H. Drevermann L. Gerdyukov Y. Goldschmidt-Clermont G. Harigel J. Joensuu C. Milstene J. P. Porte R. T. Ross M. Spyropoulou-Stassinaki C. Caso F. Fontanelli R. Monge S. Squarcia U. Trevisan J. F. Baland J. Beaufays F. Grard J. Hanton P. A. Van der Poel L. Gatignon W. Kittel W. J. Metzger D. J. Schotanus A. Stergiou R. T. Van de Walle Y. Belokopitov V. Brizgalov P. Chliapnikov A. Fenuyk V. Kubic E. Krytchenko S. Lugovsky V. Nikolaenko J. Petrovikh V. Ronjin O. Tchikilev V. Yarba V. Zjigunov 《Zeitschrift fur Physik C Particles and Fields》1981,7(2):89-96
The inclusive inelastic processesK + p→pX + andK + p→Δ ++ X 0 are studied at an incident momentum of 70 GeV/c. The data comes from the Big European Bubble Chamber BEBC filled with hydrogen, exposed to an rf reparatedK + beam at the CERN SPS accelerator. The inclusive cross section for protons with laboratory momentump LAB≦1.2 GeV/c is equal to (6.1±0.1) mb. InclusiveΔ ++-production is studied for |t p, Δ|<1.0(GeV/c)2. Comparisons are made with otherK + p data and withpp data at 69 GeV/c. Evidence is found for Pomeron exchange at the beam vertex both for slow proton andΔ ++-production as well as for absorptive pion exchange at the (p,Δ ++) vertex. 相似文献
16.
P.U. Sauer 《Annals of Physics》1973,80(2):242-283
The 1S0 two-nucleon transition matrix T is constructed from the symmetric part σ of its half-shell elements. The on-shell component of σ is given by the phase shift, while a wide class of parametrizations is suggested for the off-shell part. Restrictions on the off-shell part of σ arising from the short range and the proper one-pion-exchange tail of the nucleon-nucleon interaction are investigated. Using σ in the 1S0 and the Reid soft-core potential in the other partial waves, the binding energy per particle in nuclear matter and 16O and the 18O shell-model spectrum are computed. The sensitivity of these nuclear-structure results is tested with respect to (i) smooth off-shell changes in σ, (ii) various assumptions on the high-energy phase shift, (iii) the charge dependence of the phase shift, and (iv) experimental uncertainties in the phase shift. 相似文献
17.
J. Badier M. Bardadin-Otwinowska C. Bemporad U. Berthon H. Bienvenu J. Boucrot J. Bourotte G. Burgun O. Callot Ph. Charpentier A. M. Cnops M. Cohen F. Constantini M. Crozon D. Décamp P. Delpierre J. F. Detoeuf P. Espigat B. Gandois G. R. Giannini V. Hajjar M. Hansroul Y. Karyotakis P. Lariccia P. Le D? J. Mas A. Michelini G. C. Moneti M. Moniez E. Paré G. Rahal-Callot M. Rumpf O. Runolfsson A. Tilquin S. Weisz NA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1986,31(3):341-347
Direct photon production has been studied by an experiment performed with the NA3 spectrometer at CERN, using incident negative and positive beams at 200 GeV/c interacting with an isoscalar Carbon target. Two different triggers have been used; one of them requires the photon conversion. The experiment is sensitive to direct photons produced with 3.0≦P T ≦6 GeV/c and center-of-mass rapidity ?0.4≦y *≦1.2. Inclusive cross sections are given for incident π± and protons, and compared with second order QCD predictions; finally an estimation of the gluon structure function of the nucleon is given. 相似文献
18.
P. U. Sauer 《Annals of Physics》1973,80(2)
The 1S0 two-nucleon transition matrix T is constructed from the symmetric part σ of its half-shell elements. The on-shell component of σ is given by the phase shift, while a wide class of parametrizations is suggested for the off-shell part. Restrictions on the off-shell part of σ arising from the short range and the proper one-pion-exchange tail of the nucleon-nucleon interaction are investigated. Using σ in the 1S0 and the Reid soft-core potential in the other partial waves, the binding energy per particle in nuclear matter and 16O and the 18O shell-model spectrum are computed. The sensitivity of these nuclear-structure results is tested with respect to (i) smooth off-shell changes in σ, (ii) various assumptions on the high-energy phase shift, (iii) the charge dependence of the phase shift, and (iv) experimental uncertainties in the phase shift. 相似文献
19.
V. V. Dubinina N. P. Egorenkova V. I. Krotkova E. A. Pozharova V. A. Smirnitsky 《Physics of Atomic Nuclei》2007,70(2):319-325
The azimuthal asymmetry is measured for the emission of Z ≥ 2 particles from the interaction of 22Ne, 24Mg, 32S, 56Fe, 197Au, and 207Pb nuclei with photoemulsion nuclei that is induced by semicentral collisions characterized by projectile energies in the range E pr = 1.88–200 GeV per nucleon and by impact-parameter (b) values in the range 0.12 ≤ b/b max ≤ 0.70. The results of these measurements are compared with the results of similar measurements for protons. It is found that, at a low energy of E pr ≈ 2 GeV per nucleon, the ratio of the azimuthal-anisotropy coefficients v 2 for Z ≥ 2 particles and protons is 6 ± 2, but that, for energies in the region E pr ≥ 4 GeV per nucleon, the coefficients in question agree with each other. This may suggest that, at low energies, Z ≥ 2 particles are predominantly formed at an early stage of the development of a collective flow. For E pr ≥ 4 GeV per nucleon, these particles are presumably formed at the stage of nuclear-matter expansion. Other possible explanations for the results of the observation of an elliptic flux of Z ≥ 2 particles are discussed. 相似文献
20.
R. Albrecht T. C. Awes C. Baktash P. Beckmann G. Claesson F. Berger R. Bock L. Dragon R. L. Ferguson A. Franz S. Garpman R. Glasow H. ?. Gustafsson H. H. Gutbrod K. H. Kampert B. W. Kolb P. Kristiansson I. Y. Lee H. L?hner I. Lund F. E. Obenshain A. Oskarsson I. Otterlund T. Peitzmann S. Persson F. Plasil A. M. Poskanzer M. Purschke H. G. Ritter R. Santo H. R. Schmidt T. Siemiarczuk S. P. Sorensen E. Stenlund G. R. Young WA Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,38(1):109-115
Target remnants withZ<3 from proton-nucleus and16O-nucleus reactions at 60 and 200 GeV/nucleon were measured in the angular range from 30° to 160° (?1.7<η<1.3) employing the Plastic Ball detector. The excitation energy of the target spectator matter in central oxygen-induced collisions is found to be high enough to allow for complete disintegration of the target nucleus into fragments withZ<3. The average longitudinal momentum transfer per proton to the target in central collisions is considerably higher in the case of16O-induced reactions (≈300 MeV/c) than in proton-induced reactions (≈130 MeV/c). The baryon rapidity distributions are roughly in agreement with one-fluid hydrodynamical calculations at 60 GeV/nucleon16O+Au but are in disagreement at 200 GeV/nucleon, indicating the higher degree of transparency at the higher bombarding energy. Both, the transverse momenta of target spectators and the entropy produced in the target fragmentation region are compared to those attained in head-on collisions of two heavy nuclei at Bevalac energies. They are found to be comparable or do even exceed the values for the participant matter at beam energies of about 1–2 GeV/nucleon. 相似文献