A comparison between pp and pp diffractive peaks at and beyond ISR energies

Although a substantial difference between pp differential cross section at ISR energies and $\text{p}\text{p}$ differential cross section at SPS energy has been reported, we demonstrate that both differential cross sections, at least up to |t| ～ 1.2 GeV², can be satisfactory accounted for within the usual eikonal model in which the diffractive component is crossing even. Thus at a given ultra high energy, there is no suggestive evidence for a difference between pp and $\text{p}\text{p}$ diffractive peaks.     

Tests of QCD factorisation in the diffractive production of dijets in deep-inelastic scattering and photoproduction at HERA

Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q²<0.01 GeV²) and deep-inelastic scattering processes (DIS, 4<Q²<80 GeV²). The event topology is given by ep→eXY, in which the system X, containing at least two jets, is separated from a leading low-mass baryonic system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction in photoproduction is a factor 0.5±0.1 smaller than the same ratio in DIS. This suppression is the first clear observation of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model fails in both kinematic regions.     

Proton dissociative ρ and elastic φ electroproduction at HERA

The electroproduction of ρ mesons with proton diffractive dissociation for Q ² > 7 GeV² and the elastic electroproduction of φ mesons for Q ² > 6 GeV² are studied in e ⁺ p collisions at HERA with the H1 detector, for an integrated luminosity of 2.8 pb^-1. The dependence of the cross sections on P _t ² and Q ² is measured, and the vector meson polarisation obtained. The cross section ratio between proton dissociative and elastic production of ρ mesons is measured and discussed in the framework of the factorisation hypothesis of diffractive vertices. The ratio of the elastic cross section for φ and ρ meson production is investigated as a function of Q ².     

Diffractive open charm production in deep-inelastic scattering and photoproduction at HERA

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D^*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.     

Scale breaking at smallx: Charm production

Scale breaking at smallx is duscussed in the context of Generalised Vector Dominance models. It is shown to be naturally described by such models for allQ ², provided that both charm production, and the diffractive rise of the real photoabsorption cross section, are taken into account.     

The88Sr(d,n∼p)88Sr reaction

The⁸⁸Sr(d, n～p)⁸⁸Sr cross section has been measured at 170 ° for deuteron energies from 7.5 to 10.0 MeV, and the total⁸⁸Sr(d, n～p) cross section obtained. The total cross section is compared with results of coupled-channel Born approximation calculations using both empirical and shell-model-reaction-theory form factors to describe the decaying isobaric analog state. It is shown also that the new data and calculations are consistent with earlier⁸⁸Sr(d, p)⁸⁹Sr data.     

The diffractive component of multihadron production processes at high energies

Multihadron production at high energies proceeds through two mechanisms: A nondiffractive mechanism of a general multiperipheral nature and a diffractive mechanism. Assuming that the diffractive mechanism is dominated at present energies (s < 3000 BeV²) by single diffraction excitation we explore its theoretical and phenomenological implications. In particular we study the question of the rising total cross section. We show that “high mass diffraction excitation” leads to the formation of a central plateau in the inclusive single pion distribution and that the height of this plateau rises with energy and obeys scaling when normalized by the total cross section. We compute the multiplicity distribution for the diffractive component, and deduce the properties of the average multiplicity, its moments, and the statistical mechanics analogue of the “diffractive” Feynman gas. Two-particle correlations are computed and shown to be of a long range nature. Finally we outline an “improved” two component model into which some of the detailed features of the diffractive part are incorporated.     

Inclusive single and double diffractive dissociations inK + p interactions at 32 GeV/c

We study single and double inclusive diffractive production in a 32 GeV/c K ⁺ p experiment in MIRABELLE at the Serpukhov accelerator. From reactionsK ⁺ p→K ⁺+X ⁺ andK ⁺ p→X ⁺+p we determine the total proton and kaon single diffractive dissociation cross sections \(\sigma (p\xrightarrow{{K^ + }}p_D ) = 0.90 \pm 0.12 mb\) and \(\sigma (K^ + \xrightarrow{p}K_D^ + ) = 0\) . 90±0.17 mb, respectively. In either case the only notable contributions come from dissociations into 1 and 3 charged particles. Kaon dissociation exhibits a pronounced slope-mass correlation. The search for double diffractive production in reactionsK ⁺ p→(K ⁺π^?π⁺)+X ⁺ andK ⁺ p→(pπ ⁺ π ^?)+X ⁺ leads in either case to an estimated total double diffractive cross section σ(K ⁺p→K _D ⁺ p_D) of ?220 μb. The double dissociation differential cross section exhibits a large slope of ?10GeV^?2 in the nearthreshold mass region, rapidly decreasing to ?4 GeV^?2 with increasing excitation mass. At our c.m. energy \((\sqrt s \simeq 8 GeV)\) the ratio σ_{inel dif}/σ_el is 0.85±0.10, the total diffractive cross section σ_dif≡σ_el+σ_{inel dif}=4.41±0.24 mb and the fraction σ_dif(K ⁺ p)/σ_tot(K ⁺ p) is 25±2%. TheK ⁺ andK ^? diffractive excitation mass spectra, differential cross sections and total diffractive cross sections are very similar for both single and double dissociations.     

Roles of survival probability and barrier reduction in heavy ion fusion induced by break up

Shadowing effects in deep-inelastic lepton-nucleus scattering probe the mass spectrum of diffractive leptoproduction from individual nucleons. We explore this relationship using current experimental information on both processes. In recent data from the NMC and E665 collaboration, taken at small x ? 0.1 and Q ² ? 1 GeV ², shadowing is dominated by the diffractive excitation and coherent interaction of low mass vector mesons. If shadowing is explored at small x ? 0.1 but large Q ² ? 1 GeV ² as discussed at HERA, the situation is different. Here dominant contributions come from the coherent interaction of diffractively produced heavy mass states. Furthermore we observe that the energy dependence of shadowing is directly related to the mass dependence of the diffractive production cross section for free nucleon targets.     

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.     

Elastic photoproduction of ϱ0 mesons at HERA

The cross section for the elastic photoproduction of ϱ⁰ mesons (γp → ϱ⁰p) has been measured with the H1 detector at HERA for two average photon-proton centre-of-mass energies of 55 and 187 GeV. The lower energy point was measured by observing directly the ϱ⁰ decay giving a cross section of 9.1 ± 0.9 (stat.) ± 2.5 (syst.) μb. The logarithmic slope parameter of the differential cross section, dσ/dt, is found to be 10.9 ± 2.4 (stat.) ± 1.1 (syst.) GeV⁻². The ϱ⁰ decay polar angular distribution is found to be consistent with s-channel helicity conservation. The higher energy cross section was determined from analysis of the lower part of the hadronic invariant mass spectrum of diffractive photoproduction and found to be 13.6 ± 0.8 (stat.) ± 2.4 (syst.) μb.     

D meson production in deep-inelastic diffractive interactions at HERA

A measurement is presented of the cross section for D^*± meson production in diffractive deep-inelastic scattering for the first time at HERA. The cross section is given for the process ep→eXY, where the system X contains at least one D^*± meson and is separated by a large rapidity gap from a low mass proton remnant system Y. The cross section is presented in the diffractive deep-inelastic region defined by 2<Q²<100 GeV², 0.05<y<0.7, , M_Y<1.6 GeV and |t|<1 GeV². The D^*± mesons are restricted to the range p_T,D^*>2 GeV and |η_D^*|<1.5. The cross section is found to be 246±54±56 pb and forms about 6% of the corresponding inclusive D^*± cross section. The cross section is presented as a function of various kinematic variables, including which is an estimate of the fraction of the momentum of the diffractive exchange carried by the parton entering the hard-subprocess. The data show a large component of the cross section at low where the contribution of the boson–gluon-fusion process is expected to dominate. The data are compared with several QCD-based calculations.     

Diffractive proteon fragmentation in 16, 32, and 110 GeV/cK − p interactions and the diffractive production of heavy quarks(s\bar s,c\bar c)

The inclusive proton diffraction dissociation cross sections in 16, 32, and 110 GeV/cK ^? p interactions are determined from the spike nearx=1 in the inclusive negative particle spectra and are compared to those obtained inK?p interactions using other selection methods at various energies. The same procedure is applied to events containing aV ⁰ in order to obtain the cross section for diffractive \(s\bar s\) production. While the total cross section for proton diffraction is found to be approximately constant in the energy range studied here, proton diffraction yielding an \(s\bar s - pair\) is found to increase significantly. In particular it is almost constant at 85 μb forΛ ⁰ and Σ production but for \(NK\bar K\) it rises from zero at 16 GeV.c to about 200 μb at 110 GeV/c. From the result for \(s\bar s\) diffractive production an estimate for the \(c\bar c\) diffractive production cross section of approximately 1–10 μb at 110 GeV/c is obtained.     

Open charm production in diffractive ep collisions

The cross section for the diffractive reactionγ + p → cc + p with a real or virtual photon is calculated in the nonperturbative two-gluon exchange model of Landshoff and Nachtmann. Numerical predictions are given for cross sections and spectra at typical HERA values of c.m. energy and photon virtuality. The contribution of charm to the diffractive structure function is evaluated and found to be rather small in the model, and the ratio between the production rates for bb and cc is tiny.     

Deuteron structure and diffractive deuteron-nucleus interaction

A nonrelativistic deuteron wave function involving the D-wave state and having a correct asymptotic behavior is constructed on the basis of the experimentally measured deuteron charge form factor G _C(q) and deuteron structure function A(q). The differential cross section for elastic deuteron-nucleus scattering is calculated by using this wave function and is found to agree with experimental data at an energy of 110 MeV. Integrated cross sections for various processes involving deuteron-nucleus interactions are also calculated. The distribution in the emission angle of the center of mass of the neutron-proton system produced in the diffractive dissociation of 110-MeV deuterons in the field of ²⁰⁸Pb nuclei is obtained.     

The triple regge limit of diffractive dissociation in deep inelastic scattering

We derive, within perturbative QCD, a formula for the inclusive cross section of the diffractive dissociation of the deep inelastic photon γ^*+q→X+q in the triple Regge limits?M ²?Q ²?Λ ². We use the leading ln(s/M ², ln(M ²/Q ²) approximation and derive an, expression for the triple Pomeron vertex. The Pomeron above this vertex is found to be of higher order than the BFKL Pomeron. The resulting formula for the cross section is infrared finite. We show that the Abramovsky-Gribov-Kanchelli cutting rules are satisfied, and we discuss implications for the Pomeron structure function.     

Theoretical considerations on the extraction of pp cross sections from cosmic ray absorption data

It has been suggested, based on the application of Glauber theory to proton-air collisions, that a proton-proton total cross section which rises with energy as 1n²s is consistent with cosmic ray data. We show that if instead of a constant width, one uses a pp diffractive width which decreases consistent with present data, the cosmic ray data continue to rule out constant σ_pp^T. However, the size of the derived pp cross section is somewhat sensitive to the width, and in the relevant energy range 15% uncertainty in σ_pp^T is the maximum consequence of uncertainties in the width. Repetition of these experiments on different nuclei is not a particularly useful way to resolve these width-dependent effects.     

Investigation of anomalous four-boson couplings in photon-photon collisions at high energies

Anomalous four-boson couplings can be studied in the production of two or three bosons in γγ collisions at high energies. The dependence of the cross section for W ⁺ W ^? production on three anomalous couplings is studied at the TESLA energies (√s～1 TeV). A comprehensive analysis of anomalous contributions to the cross section and angular distributions for the process under consideration is presented.     

Color dipole phenomenology of diffractive electroproduction of light vector mesons at HERA

We develop the color dipole phenomenology of diffractive photo- and electroproduction γ* N → V(V′)N of light vector mesons (V(1S) = ?⁰, ω⁰, ρ⁰) and their radial excitations (V′(2S) ?′, ω′, ρ′). The node of the radial wave function of the 2S states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different Q ² and ν dependence of diffractive production of the V(1S) and V′(2S) vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of Q ² + m _V ² . The color dipole model predictions for the ρ ⁰ and ? ⁰ production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data.     

Measurement of coherent elastic and inelastic deuteron-proton scattering at s = 2800 GeV2

Data on coherent elastic and inelastic deuteron-proton scattering are presented. The measurements were made at the CERN ISR with a single arm spectrometer, at s = 2800 GeV² and momentum transfer squared (?t) in the range 0.15 to 0.42 GeV².The data are compared with elastic and inelastic diffractive proton-proton scattering data taken with the same apparatus at the same s and t values. The t dependence of the elastic dp → dp differential cross section is compared to simple predictions based on Glauber theory. The differential cross sections for pp → pX and dp → dX are also compared for M_X² → 280 GeV², where M_X denotes the mass of system X recoiling against the measured proton and deuteron.