Double Meson Production Research Articles

Dipole model for double meson production in two-photon interactions at high energies

In this work double vector meson production in two-photon interactions at high energies is investigated considering saturation physics. We extend the color dipole picture for this process and study the energy and virtuality dependence of the forward differential cross section. A comparison with previous results is presented, and the contribution of the different photon polarizations is estimated.

Vector meson production in ultraperipheral heavy ion collisions

Ultraperipheral heavy ion collisions (UPCs) are an important alternative for studying QCD dynamics until the next generation of e+e−/ep/eA colliders becomes a reality. Due to the coherent action of all the protons in the nucleus, the electromagnetic field is very strong and the resulting flux of equivalent photons is large, which allows us to study two-photon as well as photonuclear interactions at high energies. In this paper we present a brief review of the vector meson production in UPCs at high energies using the QCD colour dipole approach to describe their photonuclear production and the perturbative QCD Pomeron (BFKL dynamics) to describe the double meson production in photon–photon processes. Predictions for rates and integrated cross sections are presented for energies of RHIC and LHC.

Double meson production in ultraperipheral heavy-ion collisions

The double meson production in ultraperipheral heavy ions collisions is addressed, focusing on the particular case of rho-J/Psi from two-photon reactions. The cross section at photon level is obtained using distinct parameterizations for the gluon distribution on the light meson. The resulting estimates for the nuclear case are presented and discussed. As a by product, we estimate the double rho production cross section using the Pomeron-exchange factorization relations.

Probing Chiral Symmetry of Nucleons by Threshold Production

Double meson production of eta and pi mesons in the threshold region is investigated in order to determine chiral properties of the nucleon. The eta can be used as a probe for the negative parity nucleon N* ≡N*(1535), produced in the intermediate state. The coupling of the low energy pion in the final state is then used to extract the sign of the Yukawa coupling, gπN*N*, which distinguishes the two realizations of chiral symmetry, naive and mirror, for the nucleon.

Particle ratios in double-meson production by baryon's fragmentation

The double-meson inclusive reaction in the fragmentation region of incident baryons is studied with the sequential decay mechanism of excited hadrons, which has successfully explained the variety of the longitudinal-momentum dependence of the single-particle inclusive cross sections. The production ratios of two charged pions with the opposite sign to those with the same sign by incident proton are reproduced with the values of the parameters obtained previously.

Multiple Meson Production by Photons in Hydrogen

The analysis of 235 events of double meson production by photons with energy up to 1.1 Bev (reaction $\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) observed in a ${\mathrm{H}}_{2}$ diffusion cloud chamber has produced the following results. The cross section rises rapidly at about 500 Mev to a value of approximately 70 \ensuremath{\mu}b. The angular, momentum, and $Q$ distributions of the reaction products cannot be satisfactorily accounted for either by a pure statistical model, or by a pure isobaric state model, or by a model assuming interaction of the incoming photon with the meson cloud of the proton, leading to $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ interaction. The observation of 14 cases of the reactions $\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}$ and $\ensuremath{\gamma}+p\ensuremath{\rightarrow}n+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$ suggests that the combined cross section for these reactions is about 10 \ensuremath{\mu}b between 700 and 1000 Mev.

Proton-deuteron interactions at 970 MeV

A high-pressure diffusion cloud chamber has been used to study the interactions of 970 MeV protons from the Birmingham synchrotron with deuterium. Analysis of the 569 collisions observed indicates that at this energy the deuteron behaves as if it were composed of two free nucleons. The properties of proton-proton and proton-neutron scattering have been determined on this assumption. An estimate is made of the extent of the ‘shadowing’ of each nucleon in the deuteron by the other. The partial cross-sections for p-p and p-n elastic scattering have been determined, as have also the values for the five possible single meson production processes. They have the following ‘best’ values: (1) ( p + p-> p + p ) = 25.9 + 1.7 mb, (2) ( p + n-> p + n ) = 16.2 + 3.5 mb, (3) ( p + p-> p + p + 7T 0 ) = 5.4 + 1.0 mb, (4) ( p + p -> n + p + 7T + ) = 15.6 + 1.7 mb, (5) ( p + n-> p + n + n 0 ) = 14.3 + 3.5 mb, (6) ( p + n-+ p + p + 7T - ) = 2.7 + 0.6mb, (7) ( p + n-> n + n + 7T + ) = 4.3 + 1.1 mb. Double meson production and reactions involving secondary deuterons are not important. The cross-sections (1), (2), (3), (4) and (5) are consistent with values extrapolated from data at energies below 660 MeV by Russian workers. Knowledge of the other cross-sections (6) and (7) makes possible a test of the validity of the charge independence of nuclear forces. The present results are not in good agreement with this. The results for inelastic scattering indicate that, assuming charge independence, the formation of excited nucleons of isotopic spin 3/2 does not dominate the process of pion production. This is also true for the Russian data. Twelve cases of double meson production were observed. The angular distribution of proton-neutron elastic scattering has the form expected from lower energy data.

Multiple Meson Production by Photons in Hydrogen

Pictures of a ${\mathrm{H}}_{2}$ diffusion cloud chamber with magnetic field taken at the 1.1-Bev Cornell synchrotron have been analyzed to study multiple meson production by photons on protons. They have yielded 108 cases of double charged meson production ($\ensuremath{\gamma}+p\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$) and 4 cases of triple meson production.For each event of double meson production, the energy of the incoming photon and the angles and momenta of the emitted particles could be determined. The most significant results are the following.The cross section for double charged meson production rises rapidly around 500 Mev to approximately 70 microbarns, a value of the same order as the total cross section for single meson production.In the reaction leading to a charged meson pair, ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ play dissimilar roles, as evidenced by the marked dissimilarities in their center-of-mass angular and momentum distributions. The $Q$-distributions suggest the interpretation that the predominant mode of pair production in the energy range from 500 to 700 Mev is ${N}^{*}+{\ensuremath{\pi}}^{\ensuremath{-}}$, ${N}^{*}\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{+}$, where ${N}^{*}$ likely is the resonant $\frac{3}{2}$, $\frac{3}{2}$ excited state of the proton. The fact that the angular distributions for the protons and the ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons are asymmetric about 90\ifmmode^\circ\else\textdegree\fi{} indicates that the reaction does not derive from a single state, but from a mixture of at least two interfering states of different parity.

Totalp−pand "p−n" Cross Sections at Cosmotron Energies

The total proton-proton cross section (excluding Coulomb scattering) has been measured at energies from 410 Mev up to 2.6 Bev, using external beams from the Cosmotron. Fast counting equipment was used to measure the attenuation of the beams through polyethylene, carbon, and liquid ${\mathrm{H}}_{2}$ absorbers. At each energy $E$, ${\ensuremath{\sigma}}_{p\ensuremath{-}p}(E, \ensuremath{\Omega})$ was measured as a function of the solid angle $\ensuremath{\Omega}$ subtended by the rear counter at the center of the absorber. The total cross section ${\ensuremath{\sigma}}_{p\ensuremath{-}p}$ was obtained by a least squares straight line extrapolation to $\ensuremath{\Omega}=0$. The measured ${\ensuremath{\sigma}}_{p\ensuremath{-}p}$ as a function of energy rises sharply from 26.5 mb at 410 Mev to 47.8 mb at 830 Mev and then remains approximately constant out to 1.4 Bev, above which energy it decreases gradually to about 42 mb at 2.6 Bev.Using the same equipment and procedure, we have also measured the ${\mathrm{D}}_{2}$O-${\mathrm{H}}_{2}$O difference cross section, called "${\ensuremath{\sigma}}_{p\ensuremath{-}n}$," for protons over the same energy range. From a comparison of "${\ensuremath{\sigma}}_{p\ensuremath{-}n}$," and ${\ensuremath{\sigma}}_{p\ensuremath{-}p}$, with the $n\ensuremath{-}p$ and $n\ensuremath{-}d$ measurements of Coor et al. at 1.4 Bev, it is apparent that one nucleon is "shielded" by the other in the deuteron. This effect is not present at energies below 410 Mev.Comparing the measured $p\ensuremath{-}p$ and "$p\ensuremath{-}n$" (corrected) cross sections with the results of other high-energy experiments, one may infer the following conclusions: (1) The sharp rise in ${\ensuremath{\sigma}}_{p\ensuremath{-}p}$ from 400 to 800 Mev results from increasing single pion production, which may proceed through the $T=\frac{3}{2}$, $J=\frac{3}{2}$ excited nucleon state. (2) Above 1 Bev the inelastic (meson production) $p\ensuremath{-}p$ cross section appears to be approximately saturated at 27-29 mb. (3) The rise in cross section for $n\ensuremath{-}p$ interaction in the $T=0$ state, associated with the rise in double pion production, implies that double meson production also proceeds through the $T=\frac{3}{2}$ nucleon state. (4) The probable equality of ${\ensuremath{\sigma}}_{p\ensuremath{-}d}$ and ${\ensuremath{\sigma}}_{n\ensuremath{-}d}$ at 1.4 Bev implies the validity of charge symmetry at this energy.

Meson Production in Nucleon-Nucleon Collisions at High Energies

Calculations based on a statistical model have yielded results concerning the relative probabilities for the different multiplicities and charge distribution of mesons produced in nucleon-nucleon collisions. In deviating from a pure statistical model the important effects of final state interactions and various selection rules have been included, using results of meson-nucleon scattering experiments. Notably in the results the suppression of some one-meson final states by consideration of the Pauli principle and conservation of angular momentum and parity, along with the enhancement of two-meson states due to resonance effects, have brought about results which are in closer agreement with experiment than predictions of a pure statistical nature. Account was taken of the final state interactions by considering separately the nucleon-nucleon and meson-nucleon interactions, a separation made plausible by consideration of the small amount of kinetic energy taken away by the more massive particles. Meson-meson interactions were neglected. The nucleon-nucleon interaction was taken care of by introducing in the statistical weight a factor which is the square of the wave function for the scattering of two nucleons evaluated at the origin of their interaction. The meson-nucleon final state scattering was treated by the method discussed by Chew, modified for the case of a meson scattering off two stationary and superposed nucleons. Multiplicities up to two mesons were considered. On comparing with experimental results, at 1.7-Bev bombarding energy of neutrons on protons the ratio of the probability of occurrence of the final states $(np+\ensuremath{-}):(pp\ensuremath{-}0):(pp\ensuremath{-})$ is calculated to be 3.0:1.0:0.9, while experiment gives 3.3:1:0.8. The ratio of the total probability for double meson production to that for single meson production at this energy is 1.2, while a modified result of observations gives 1.4. Results on proton-proton collisions do not yield good agreement with present observations.

Double Meson Production in the Intermediate-Coupling Theory, I

The intermediate-coupling theory is applied to the problem of the meson production in meson­ nucleon collisions. For simplicity, the model used is a charged scalar meson field interacting with a fixed nucleon. The amplitudes of the ordinary scattering and the meson production are obtained in the The intermediate-coupling theory has been formulated to exhibit its validity in a region of moderate coupling strength. The essential point of this theory consists in the distinc­ tion of meson configurations between bound and unbound ones. Mesons in bound configura· tion are bound to the nucleon and make the so-called meson cloud around the nucleon. The various states of the meson cloud correspond to the various isobar levels of the nucleon. Mesons in unbound configurations, which are called s·mesons , move in the outer space. When a meson collides with the nucleon, there arise the resonance-like interactions between the incident s-meson and the meson cloud. Actually in this case the one-level is allowed; that is, only one nucleon level is excited in the course of the collision process. In the scattering problems hitherto treated the presence of more than one s-meson can be neglected. It seems that the one level approximation is closely connected with the neglect of two or more s·meson configurations and therefore the process of the double meson production cannot be treated in this approximation. 1l

Meson Production inn−pCollisions at Cosmotron Energies

154 analyzable three-prong events were observed in collisions between Cosmotron-produced neutrons, with energies up to 2.2 Bev, and protons in a hydrogen-filled diffusion cloud chamber. These events were classified as a result of the reactions $n+p\ensuremath{\rightarrow}p+p+{\ensuremath{\pi}}^{\ensuremath{-}}$, $p+p+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}$, and $p+n+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$ with frequencies in the ratio (0.8\ifmmode\pm\else\textpm\fi{}0.3): (1\ifmmode\pm\else\textpm\fi{}0.35): (3.2\ifmmode\pm\else\textpm\fi{}0.7), respectively. The observed ratio of the probability for double meson production to that for single meson production is more than 20 times higher than the ratio predicted from Fermi's statistical model. No triple meson production is observed, in agreement with the statistical model. The momentum distributions of the observed mesons are also in rough agreement with the theory. In the center-of-mass system, in the reaction $n+p+{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$, protons and ${\ensuremath{\pi}}^{+}$ show a tendency to be emitted backward, while neutrons and ${\ensuremath{\pi}}^{\ensuremath{-}}$ tend towards forward emission. However, the data suggest that protons and ${\ensuremath{\pi}}^{+}$, and also neutrons and ${\ensuremath{\pi}}^{\ensuremath{-}}$, tend to be emitted more frequently in opposite directions than protons and ${\ensuremath{\pi}}^{\ensuremath{-}}$ or neutrons and ${\ensuremath{\pi}}^{+}$. All of these results may be qualitatively in agreement with a meson production model where each nucleon is excited separately to an intermediate, possibly resonant, state which subsequently decays by emission of a meson.

Pseudoscalar Mesons with Applications to Meson-Nucleon Scattering and Photoproduction

The scattering of ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ mesons by protons and the production of ${\ensuremath{\pi}}^{+}$ mesons by gamma-rays incident on protons are studied with the quantized theory of pseudoscalar mesons with pseudoscalar coupling. The Dyson transformation is applied to the Hamiltonian to yield a new representation in which the velocity-independent aspects of the nucleon dynamics are more readily identified. A large term appears in the meson-nucleon interaction in this representation and is incorporated into the zero-order Hamiltonian. The remaining interaction terms are treated perturbation-wise or according to the Heitler damping procedure. It is found that even after separating out the large core term, this method of approach fails to give agreement between theory and experiment. It does, however, improve on the results of the straight perturbation approximation and brings the theory in closer accord with the observations. It is suggested that a direct test of the role of the term is possible in the process of double meson production by gamma-rays incident on protons.