B.K. Jain

Study of the p(p, n)Δ++ reaction in nuclei

Abstract The p(p, n) Δ ++ reaction has been studied theoretically from threshold to 5.5 GeV/ c beam momenta. A formalism has been written which includes the effect of various channels in the pp scattering on the pp→ n Δ ++ channel through the use of complex potentials in the continuum states. The scattering wave functions for them are written directly in terms of the scattering amplitudes. Calculations have been done for various differential and total cross-sections for the pp → n Δ ++ reaction. The calculated results using the one-pion-exchange transition potential with Λ π ≈ 1 GeV/ c agree remarkably well with all the available experimental data in the energy region considered. The “distortion” is found to essentially weaken the transition potential in the large momentum domain. The effect of rho-exchange is also calculated.

η production in proton-proton collisions

We have studied η production in proton-proton collisions from threshold to 6 GeV beam energy. We have used the resonance model taking only the S11(1535) (N∗) resonance, and distorted wave approximation to take into account the initial and final state interactions. We find that the measured total cross-section in pp → ppη channel can be understood in this model taking a sum of the one-pion, one-eta, one-rho and one-omega exchange potential for the pp → pN∗ transition. The dominant contribution, however, comes from the rho exchange. We have tried to understand the reason for this dominance. The effect of distortion in the entrance and exit channels is to reduce the cross section. However, the effect is different for different potentials. We have also calculated the mass distribution and t distribution for pp → pN∗ reaction.

Off-shell effects in the (α, 2α) reaction

Abstract The half-off-shell factor relevant to the factorized impulse-approximation treatment of the (α, 2α) reaction from 60 to 140 MeV are calculated for four phenomenological phase-shift equivalent potentials. It is found that the behaviour of the, off-shell factor is similar for all the four potentials. The off-shell effect itself is large below 140 MeV. In comparing the half-shell prescription with the various on-shell prescriptions it is found that the “final energy prescription” is consistently closer to the half-shell values.

Strong absorption model for the (α, 2α) reaction

Abstract The (α, 2α) reaction has been studied in the “diffraction model” for 16O, 29Mg, 40Ca and 66Zn nuclei at 90 MeV incident energy. Using R c = 1.15(A 1 3 +4 1 3 ) fm for the strong absorption radius and Δ = 0.06Rc for the diffuseness of the absorbing surface the spectroscopic factors are extracted. These spectroscopic factors are in excellent agreement with the theoretical values. The positions of the minima and second maxima are also reproduced.

Study of the (π, nn) reaction on 12C

Abstract Simplified expressions for the transition strength of the (π−, nn) reaction on even-mass 4nuclei and for the back-to-back emission of neutrons are presented. These expressions are then used to study the effect of various factors on the transition strength and to analyse the recent available data on the 12C(π−, nn) reaction. A good agreement with the experimental data is found.

INCLUSIVE (3He, t) REACTION IN DELTA EXCITATION REGION

Using the one step reaction mechanism, calculations are presented for the overall features of the inclusive (3He, t) reaction on various target nuclei in the delta excitation region. The interaction for the elementary pp→nΔ++ process is given by one-pion-exchange, and is written in the covariant relativistic form. The values of the parameters in the interaction are chosen such that the interaction successfully describes the spin averaged experimental elementary cross-sections. The distortion in the entrance and exit channels is described in the eikonal approximation, and the nuclear response is described in the “distorted wave Fermi gas model”. The cross-sections for the triton energy spectrum, angular distribution, and the total events at 0° on several nuclei, are calculated and compared with the corresponding experimental data. The main features of the measured cross-sections are reproduced.

Pion-induced knock-out reactions

Abstract A strong absorption model for pion-induced knock-out reactions is proposed. The distortion of the incoming and outgoing pions has been included by (i) computing the pion wave number in a nuclear medium (dispersive effect) and (ii) excluding the central region of the nucleus where the real pion absorption is dominant (absorption effect). In order to study the dependence of the ( π + , π + p) reaction on the off-shell pion-nucleon t -matrix, different off-shell extrapolations are used. The magnitude of the cross sections seems to be sensitive to the type of off-shell extrapolation; their shapes, however, are similar. The theoretical results are compared with experimental data. The agreement between the theoretical results for separable off-shell extrapolation and the data is good.

Pion absorption in 3He

Abstract A formalism for the reactions 3 He + π − → n + d and 3 He + π → n + n + p is given in the two-nucleon absorption model, employing a partial-wave description. Final-state interactions, anti-symmetrization in the entrance and exit channel and the absorption of pions on both n-p and p-p pairs are included. Detailed results for different kinematical conditions have been computed and compared with available experimental data. It is found that FSI for the n + n + p channel changes the results considerably and brings them into better agreement with experiment.

Pion absorption and the structure of 6Li

Abstract The available data on the 6 Li(π − , nn) reaction are analysed using the two-nucleon model for pion absorption, distorted waves for the outgoing neutrons, a Seki-Cromer wave function for the 1S pion and the modified α-d cluster-model wave function of Jain etal . for 6 Li. The computed results are not in good agreement with the experimental data. Possible ways of improvement are pointed out. The sensitivity of the recoil momentum distribution to the radial inter-cluster wave function is studied.

Delta production in 3He-proton collisions

Abstract The cross section for the p( 3 He, t)Δ ++ reaction in the incident energy range 2–8.2 GeV has been calculated in the distorted-wave Born approximation, including coherently the excitation of both the projectile and target nucleons to δ ++ . The transition interaction is described by the exchange of one pion plus one rho with monopole form factors at coupling vertices. The length parameter. Λ, for the form factors is taken to be 1.2 GeV/ c for pion and 2 GeV for rho. The calculated results agree well with the experimental data. Unlike earlier conclusions in the literature we find that the contribution due to excitation of the projectile nucleon to Δ ++ is large at all the energies. Reasons for this large contribution are investigated. The contribution of rho-exchange is found to be large at higher energies. At lower energies this contribution is not significant.