Double pomeron exchange in the reaction pp → ppπ+π−

We compute the cross section for pp → ppπ⁺π^? in the kinematical region for which two-pomeron exchange is important, assuming dominance of the pion-exchange pole. We include effects due to absorption, final-state interaction, and interference between the two contributing Feynman diagrams. These effects have been ignored in previous calculations. Consequently, our predicted cross section is smaller than previous predictions by a factor of ～ 3, and is consistent with experimental indications. We calculate the background cross section in the double pomeron exchange region, and find that it is sizable even at s ～ 3000 GeV². We discuss the two-particle inclusive process pp → ppX.     

Experimental tests of the factorisation of Regge trajectories in the proton fragmentation region

We present double differential cross sections for the reactions K^? + p → π^± + anything at 8.25 GeV/c. Using published data for reactions K⁺ + p→ π^? + anything and p + p → π⁺ anything we predict the differential cross sections for γ + p → π^? + anything, π^? + p → π^? + anything and π^? + p → π⁺ + anything in the target fragmentation region based on factorisation of the pomeron and Regge trajectories. Our predictions agree with the experimental data and support the hypothesis of factorisation of the Regge trajectories in the target fragmentation region.     

Dual properties of inclusive spectra

The dual properties of the inclusive reaction π^?p → pX are studied over a wide energy range by exploiting the scaling behaviour. Semi-local duality is found to be well satisfied. An energy-dependent triple-Regge analysis reveals a strong triple-pomeron coupling. There is some evidence of an abnormal component in which diffractively produced resonances are dual to pomeron exchange. Combining duality with factorization leads to relations between production cross sections of meson and baryon resonances in πp and pp collisions, which are compatible with existing experimental data.     

Inclusive and semi-inclusive ϱ0 production in π−p interactions at 15 GeV/c

We have done an inclusive study of ?⁰ production in π^?p interactions at 15 GeV/c. Evidence for two different production mechanisms, in addition to the known quasi two-body processes, is presented: production of ?⁰'s in the central region of rapidity similar to the “pionization” region seen in the inclusive studies of pions; and forward production in the beam dissociation region of rapidity. Cross sections and rapidity distributions for the ?⁰ are given inclusively and by topology, and the results are compared with similar studies at other energies and with other incident particles. Results are also presented for the semi-inclusive reaction π^?p → p?⁰ + X^? and the exclusive final state pπ^??⁰.     

Study of π−π− scattering in π−n interactions at high energies

We have measured the inclusive cross section for the reaction π^?n→pX^?? at 21, 205 and 360 GeV/c in the kinematic region |t_np|<1.0 (GeV/c)². The differential cross sections can be described qualitatively by the reggeized one-pion-exchange amplitude at all momenta studied; however, there is evidence for the contribution of other amplitudes. The extracted π^?π^? total cross section for 4?s_ππ?340 GeV² is of the order of 10–12 mb. The average number of charged particles and dispersion of the charged particle multiplicity distributions for various s_ππ intervals are compatible with results observed in hadron-proton interactions.     

Elastic and charge exchange scattering of pions on3He in the (3,3)-resonance region

The elastic scattering of pions from³He and the single charge exchange reaction³He(π ^?,π ⁰)³H are calculated in the energy domain of the (3,3)-resonance within the framework of Glauber's theory, including spin and isospin degrees of freedom in all orders. It is pointed out that, from the first minimum on, the differential cross section strongly depends on the parametrization of theπN amplitude, especially on its continuation into the unphysical region of momentum transfer. Single and double spin flip contributions prove to be very important in the charge exchange reaction. Within a modified version of Glauber's formalism, directly usingπN phase shifts rather than amplitudes, the³He charge exchange scattering is reexamined. Whereas the shape of the angle-integrated cross section as a function of pion energy is confirmed, the magnitude is still uncertain within a factor of 2.     

Study of double pomeron exchange in pp collisions at √s=31GeV

The reaction pp→ppπ⁺π^? at √s=31GeV was studied at the Split Field Magnet Facility of the CERN-ISR. Selecting events with two leading protons of x>0.9 and a rapidity gap Δy>2 between the protons and both pions a sample of 720 events is obtained representing a cross section of 25±10μb. The mass distribution of the dipion system, x and p_T distributions for the protons are presented and analyzed for the presence of double pomeron exchange.     

Search for glue balls in a pomeron pomeron scattering experiment

The exclusive reactionpp→ppπ⁺ π^? has been studied using the SFM spectrometer at ISR energies of \(\sqrt s = 24\) and 63 GeV. The cross section in the double pomeron exchange region defined by |x _p |>0.9, |y _π |<1 is 28±6, 23(+13, ?6) and 29(+29, ?10)μb, respectively. The ππ mass spectrum is dominated by an 1/m _ππ ² part, as expected for pomeron pomeron scattering. In addition, thef(1, 270) resonance is clearly distinguished. There are no further resonance signals, which could be assigned to glueball candidates expected in the 1,000 MeV region. Compared to photon photon scattering, the ratio of continuum tof-resonance production cross sections is significantly larger in pomeron pomeron scattering.     

Double Regge exchange phenomenology

We construct a double Regge exchange amplitude which has the proper analytic structure and which is phenomenologically viable. The various couplings involved can be estimated using pole extrapolation techniques which are successful in two-body scattering. We explicitly calculate the double Regge exchange contributions to the well-measured, and related, processes K^±p → K⁰π^±p and π^?p → K^?K⁰p. In this way the observed features of the dimeson partial-wave production amplitudes are used to text the double-exchange approach.     

Duality for the reggeon-reggeon amplitude: A study through quasi-three-body reactions

We consider reactions of the type ab→cdR in the double-Regge region. The cross sections are proportional to the reggeon-reggeon forward amplitude in the resonance region. Using semi-local duality the cross sections can be written in terms of the relevant triple-Regge couplings which are already known from reggeon-particle scattering, i.e. from analysing data on reactions of the type ab→cR. We compare the predictions of pp→pp (?, f) π^?p→π^?p (?, f) with data at 12, 24 and 205 GeV/c and find encouraging results. We suggest a series of cross sections, the measurement of which will provide a definite test of the duality hypothesis for reggeon-reggeon scattering.     

Analysis of the reaction pp → p(ππ)0 p,and the question of double pomeron exchange in high-energy production processes

A low-mass S-wave (ππ)⁰ enhancement is observed in the reaction pp → p (ππ)⁰ p at 12 and 24 GeV/c incident momentum. The mechanism for producing these low-mass pion pairs is investigated, and it is shown that double pomeron exchange can contribute at most 5% to their production cross section at 24 GeV/c.     

Applications of Mueller theory of two-particle inclusive processes

Assuming factorization, and extracting inclusive Reggeon vertices from one-particle inclusive data, we predict Regge corrections to scaling for several two-particle inclusive processes. The data on p + P → π^? + π^? + X, K⁺ + p → π^? + π^? + X, K^? + p → π⁺ + π^? + X, and π⁺ + p → π^? + π^? + X agree with our predictions.     

The reactions K−p→π∓Σ±(1385) at 4.2 GeV/c

The reactions K^?p→π^?Σ⁺(1385) and K^?p→π⁺Σ^?(1385) are studied at 4.2 GeVc incident momentum using data from a high statistics bubble chamber experiment corresponding to ～80 events/μb. The total and differential cross sections are presented. Amplitude analyses are performed and the complete Σ^±(1385) helicity spin density matrices are extracted. The results are compared with the predictions of the additive quark model and exchange degeneracy. A substantial cross section is observed for the reaction K^?p→π⁺Σ^?(1385) in the forward direction, which implies exotic meson quantum numbers in the t-channel. One possible interpretation of this process provides an explanation for the small but significant violations of the additive quark model predictions observed in the reaction K^?p→π^?Σ⁺(1385) at low four-momentum transfer. In the backward direction unnatural parity exchange is shown to give a larger contribution to K^?p→Σ^?(1385)π⁺ than natural parity exchange.     

The inclusive proton spectrum for\bar pd \to 3\pi p at rest re-examined

We re-analyze the spectator proton distribution for ¯pd→π ⁺ π^? π^? p. For this channel previous calculations underestimated the cross section for proton momenta of 300 to 600 MeV/c by about a factor 7 while the channels with higher pion multiplicities and the ¯pd→K¯ Kmπp reactions were well explained. By using detailed experimental information on ¯pn and ¯pp annihilation, meson rescattering can in fact explain the cross section also for the 3π case. The¯ pp annihilation followed by charge exchange pion rescattering is much larger than in the 5π case. Vector meson exchange is small but not negligible at high spectator momenta.     

Pion and nucleon dissociation in π−p→π−π+π−p at 205 GeV/c

In a 48 000-picture exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeV/cπ^?beam, we have measured 169 events of the reaction, π^?p→π^?π⁺π^?p, with a cross section of 635 ± 61 μb. This reaction proceeds almost entirely via low mass π^? → 3π and p → pππ dissociation. Factorization is satisfied for p → pππ dissociation in πp and pp interactions.     

s-and t-channel helicity conservation of pion induced nucleon diffraction dissociation at 3.9 GeV/c and the implications of a two-component model

A study of schannel and t-channel helicity conservation has been carried out on a prism plot separated sample of 3.9 GeV/cπ^±p → π (Nπ)_dd diffraction dissociation events. s-channel helicity conservation is found to be strongly violated while t-channel helicity conservation is found to be mildly violated. These results are similar to that found at 11.7 GeV/c. We explain these violations on the basis of a “two-component model” of which the first component is a single exchange amplitude. We postulate that this amplitude is the generalization of the pomeron exchange amplitude which may conserve s-channel helicity. The second component of the model is a double exchange mechanism which strongly violates s-channel helicity. The predictions of this model agree with the experimental data.     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

Study of process e + e − → π+π−π0π0 at energies √s < 1 GeV with the spherical neutral detector

The cross section for the process e ⁺ e ^? → π⁺π^?π⁰π⁰ has been measured in an experiment with a spherical neutral detector, with the cross section at energies √s < 920 MeV having been measured for the first time. The model of vector dominance describes well the data obtained if the ρ, ρ′, and ρ″ resonances are taken into account. The probability of the decay ρ → π⁺π^?π⁰π⁰ is B(ρ → π⁺π^?π⁰π⁰) = (1.60 ± 0.74 ± 0.18) × 10^?5. The upper limit for the decay ω → π⁺π^?π⁰π⁰ has been improved by two orders of magnitude compared to previous measurements and is B(ω → π⁺π^?π⁰π⁰) < 2 × 10^?4 at a 90% confidence level.     

Measurement of the cross sections for reaction π−p → Xo n in the momentum range up to 50 GeVc

The cross sections for the reaction π^?p → X^on, X^o → 2_λ are measured at 32.5 and $\text{48}\text{GeV}\text{c}$ momenta. The cross spectrometer of γ-quanta is used to select events of reaction, whose cross section is only about 0.05 μbarn. The cross section energy dependence has the power form ($\text{≈ p}{}^{\mathrm{?1.11\pm 0.12}}$. conclusion on U(6) symmetry of quark model is made when comparing the differential cross sections at zero angle for the reactions π^?p → X^o and π^?p → η^o. The angle of octet-singlet mixing for pseudo-scalar mesons β = ?(20.6 ± 2.2)° is defined.