Structure functions and low x physics

Capella, A.; Kaǐdalov, A. B.; Merino, C.; Vân, J. Trân Thanh

doi:10.1016/0370-2693(94)90988-1

Cited by 213 publications

(308 citation statements)

References 19 publications

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“…5. For F p 2 (x, Q 2 ) the parameterization of Capella et al [36] in terms of Pomeron and Reggeon exchanges has been taken. The slope parameter Λ is given by…”

Section: W -Dependencementioning

confidence: 99%

Exclusive leptoproduction of $\rho^0$ mesons from hydrogen at intermediate virtual photon energies

2000

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Abstract. Measurements of the cross section for exclusive virtual-photoproduction of ρ 0 mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum Q 2 of the virtual photon varies from 0.7 to 5.0 GeV 2 . The present data together with most of the previous data in the intermediate W -domain are well described by a model that infers the W -dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the ρ 0 production cross section for Q 2 > 2 GeV 2 .2

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“…5. For F p 2 (x, Q 2 ) the parameterization of Capella et al [36] in terms of Pomeron and Reggeon exchanges has been taken. The slope parameter Λ is given by…”

Section: W -Dependencementioning

confidence: 99%

Exclusive leptoproduction of $\rho^0$ mesons from hydrogen at intermediate virtual photon energies

2000

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“…In this way e, f and F P become independent of t. All the parameters in F d 2 are given in ref. [6]. In particular B = B u + B d = 1.2.…”

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confidence: 95%

“…Note that in order to perform the QCD evolution we have to know the gluon distribution function. In the proton case, the normalization of this distribution was obtained [6] using the energy-momentum conservation sum rule. In the Pomeron case, σ tot γ * P is not an ordinary cross-section (see the discussion following eq.…”

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confidence: 99%

Diffractive dissociation in deep inelastic scattering at HERA

et al. 1995

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The diffraction dissociation of virtual photons is considered in the framework of conventional Regge theory. It is shown that the recent HERA data on large rapidity gap events can be successfully described in terms of the Pomeron structure function. Using Regge factorization, the latter can be related to the deuteron structure function. The parameters which relate these two structure functions are determined from soft hadronic diffraction data. The size of the shadowing corrections at low x and large Q 2 is also obtained. LPTHE Orsay 94-42May 1994 + Permanent address : ITEP, B. Cheremushkinskaya 25, Moscow, Russia. * Laboratoire associé au Centre National de la Recherche Scientifique -URA 63. 2Experiments at HERA provide new possibilities to study diffractive processes and the properties of the Pomeron. Recently, spectacular large rapidity gap events in deep inelastic scattering at very small x have been observed by Zeus [1] and H1 [2] collaborations at HERA. On the other hand, diffractive production has been studied for many years in high energy hadronic interactions and a large amount of information on these reactions has been obtained (see for example reviews [3−5] ). A new unexplored region of diffraction production by highly virtual photons is now accessible at HERA.Here we shall consider the process of diffractive dissociation of highly virtual photons in the framework of Reggeon theory, which is the basis for the description of diffractive processes in hadronic interactions. We shall demonstrate that the characteristic features of the data on large rapidity gaps events can be understood using the Regge based description of structure functions, introduced in a previous work [6] , together with our knowledge of diffractive production in high-energy soft hadronic collisions.The amplitude of the single diffractive production of a hadronic state X is described by the Pomeron exchange diagram shown in Fig. 1. The initial particle i in this figure can be either a hadron or a photon (real or virtual). This diagram corresponds to single diffractive production without dissociation of the initial proton, while double diffraction corresponds to dissociation of both projectile and target. At high energies s >> m 2 , when the total rapidity interval ξ = ℓn s m 2 is large, these diagrams describe kinematical configurations of final particles in which large rapidity gaps (∆y) are present.Consider first the single diffraction dissociation of a real particle i (Fig. 1). In the pole approximation for Pomeron exchange the cross section of this process is given by (see e.g. [3] )where s 1 ≡ M 2 is the square of the invariant mass of the hadronic system X, t = (p ′ − p) 2 3 is the invariant momentum transfer to the final proton and g P pp (t) is the vertex describing the Pomeron coupling to a proton. The Feynman-x of the Pomeron is defined by x P = s 1 s , and ξ ′ = ℓn s/s 1 ≈ ∆y. The last term in eq. (1) is the total Pomeron-particle crosssection [7] . It is obtained by summation over all final states X and over thei...

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“…The numerical values (11)- (12) are extracted just by plugging in (10) the masses and the spins of ρ 1 (770) and ρ 3 (1690) resonances. Remarkably enough, the same α(0) value (11) is compatible with the ∆σ data for the total cross-section differences…”

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confidence: 99%

A possible two-component structure of the non-perturbative Pomeron

Gauron

Nicolescu

2000

Physics Letters B

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We propose a QCD-inspired two-component Pomeron form which gives an excellent description of the pp, πp, Kp, γp and γγ total cross-sections. Our fit has a better χ 2 /dof for a smaller number of parameters as compared with the PDG fit. Our 2-Pomeron form is fully compatible with weak Regge exchange-degeneracy, universality, Regge factorization and the generalized vector dominance model. LPNHE 00-02April 2000 * Unité de Recherche des Universités Paris 6 et Paris 7, Associée au CNRS 1 40 years after its introduction [1] and in spite of very important advances in QCD, the Pomeron remains an open problem. In particular, the nonperturbative structure of the Pomeron is still controversial.The most popular model of the non-perturbative Pomeron is, of course, the Donnachie-Landshoff (DL) model [2]. The total cross-sections for pp and pp scattering are parametrized in terms of five parameters :whereandα P (0) is the Pomeron-intercept, α R (0) is the effective non-leading exchangedegenerate Regge intercept and X, Y the corresponding Regge residues. An overall scale factor s 0 = 1 GeV 2 is implicitely present in eqs.(1)-(2). The key-parameters ε and α R (0) have the following values :and α R (0) = 0.5475.The pp data are well reproduced. It was therefore tempting to use the DL form to the simultaneous study of all existing total cross-sections. It is precisely what was done by PDG in the last edition of the "Review of Particle Physics" [3], [4]. The total cross-sections σ are parametrized in refs. 3 and 4 in the variant of a non-exchange-degenerate DL form :whereα R + (0) and α R − (0) being the Regge intercepts of the non-leading Regge trajectory R + in the even-under-crossing amplitude and R − in the odd-undercrossing amplitude respectively. X, Y 1 , Y 2 are the corresponding Regge 2 residues. There are 16 parameters for fitting 271 experimental points involving 8 reactions :pp, pp, π ± p, K ± p, γp and γγ. The overall χ 2 is excellent : χ 2 /dof = 0.93 1 . The key-parameter ε has now the value 0.0900. The problem with the form of refs. 3 and 4 is the bad violation of the weak exchange-degeneracy (i.e. α R + (0) = α R − (0)), namelyHowever, the masses of the resonances, as published in the "Review of Particle Physics" [5], clearly indicate that the weak exchange-degeneracy is respected. As seen from fig. 1a) the 10 resonances belonging to the 4 different I G (J P C ) families ρ−ω−f 2 −a 2 are compatible with a unique linear exchangedegenerate Regge trajectorywithandThe numerical values (11)-(12) are extracted just by plugging in (10) the masses and the spins of ρ 1 (770) and ρ 3 (1690) resonances. Remarkably enough, the same α(0) value (11) is compatible with the ∆σ data for the total cross-section differencesThe ∆σ data for pp, Kp and πp and √ s > ∼ 6 GeV [6] shown in the log-log plot of fig. 1b) are all compatible with the straight lines of eq. 14 , the slopes of which are precisely given by the α R − (0) value of eq. (11).These indications in favour of the weak exchange-degeneracy, coming both from the resonanc...

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Structure functions and low x physics

Cited by 213 publications

References 19 publications

Exclusive leptoproduction of $\rho^0$ mesons from hydrogen at intermediate virtual photon energies

Exclusive leptoproduction of $\rho^0$ mesons from hydrogen at intermediate virtual photon energies

Diffractive dissociation in deep inelastic scattering at HERA

A possible two-component structure of the non-perturbative Pomeron

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