Polarization in diffractive electroproduction of light vector mesons

We outline in detail the properties of generalized parton distributions (GPDs), which contain new information on the structure of hadrons and which enter the description of hard exclusive reactions. We highlight the physics content of the GPDs and discuss the quark GPDs in the large Nc limit and within the context of the chiral quark-soliton model. Guided by this physics, we then present a general parametrization for these GPDs. Subsequently we discuss how these GPDs enter in a wide variety of hard electroproduction processes and how they can be accessed from them. We consider in detail deeply virtual Compton scattering and the hard electroproduction of mesons. We identify a list of key observables which are sensitive to the various hadron structure aspects contained in the GPDs and which can be addressed by present and future experiments.

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“…in Refs. [Bro94,Fra96,Abr97,Mar98b,Iva98,Iva99,Shu99,Cle00] and of DVCS at small x B in Ref. [Fra98b,Fra99a].…”

Section: Introductionmentioning

confidence: 99%

Hard exclusive reactions and the structure of hadrons

Goeke

Polyakov

Vanderhaeghen

2001

Progress in Particle and Nuclear Physics

943

1,354

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“…(H1, 4.46 < |t| < 30 GeV 2 ) . (213) A comparison of the results (212) and (213) shows an importance of the finite mass effects in the t-dependence, see also ′ > |t|/(900(GeV 2 ) + |t|) from H1 collaboration [79]. The theoretical results for the pQCD two-gluon exchange with fixed and running α S and scaling BFKL approximations are from Poludniowski et al [261].…”

Section: The Experimental Results: the T-dependence For A Nucleon Targetmentioning

confidence: 99%

“…From the point of view of the vector meson production, it is important that the transverse and longitudinal γ * and V share the intermediate qq state with λ + λ = 0, which allows the s-channel helicity non-conserving (SCHNC) transitions between the transverse (longitudinal) γ * and longitudinal(transverse) vector meson V [170,212]. This mechanism of SCHNC does not require an applicability of pQCD.…”

Section: The S-channel Helicity Non-conservation (Schnc)mentioning

confidence: 99%

“…The works by D.Ivanov and Kirschner [212] and Kuraev et al [170], in conjunction with B.Zakharov's [211] early pQCD motivated discussion of helicity flip in hadronic scattering, have led to understanding of SCHNC as a generic property of high-energy scattering the origin of which does not require an applicability of pQCD. The emerging phenomenology of spin properties of diffractive vector mesons has been very successful at small t, the SCHNC in high energy small-t diffractive scattering is sill another major discovery at HERA.…”

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confidence: 99%

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Diffractive vector meson production

Enberg

2005

Nuclear Physics A

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“…The interaction cross section for the latter can be, in principle, fully calculated in perturbative QCD. Moreover, for heavy vector mesons, like the J/Ψ or the Υ, perturbative calculations apply even at Q 2 = 0, as the smallness of the dipole is guaranteed by the mass of the quarks.Independently of particular calculations [12,13], in the region dominated by perturbative QCD, the following features are predicted:• the total γ ⋆ p → V p cross section, σ γ ⋆ p→V p , exhibits a steep rise with W , the photon-proton center-of-mass energy, that can be parameterized as σ ∼ W δ , with δ increasing with Q 2 ;• the Q 2 dependence, which for a longitudinally polarized photon is expected to behave like Q −6 , becomes milder, more like Q −4 , due to the sharp increase of the gluon density with Q 2 ;• the distribution of t, the four momentum transfer squared at the proton vertex, becomes universal, with little or no dependence on W or Q 2 ;All these features have been observed at HERA [14][15][16][17] in the exclusive production of ρ 0 , φ, ω and J/Ψ mesons. However, the agreement between measurements and theory is far from perfect.…”

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confidence: 99%

Exclusive vector meson production at HERA

Szuba¹

2013

AIP Conference Proceedings

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Abstract.An extended study of exclusive vector meson production in ep interactions has been performed by the H1 and the ZEUS collaborations at the HERA collider. Recent measurements are reported and discussed within the framework of the dipole model and pQCD. I INTRODUCTIONThe sharp rise of the electromagnetic proton structure function, F 2 , toward low values of Bjorken x, discovered at HERA [1,2], and the observation of a large fraction of diffractive-like events [3,4] are attributed to a large gluon density in the proton at very low x values, typically x < 0.01. The rise of F 2 with decreasing x can be accommodated by the QCD, DGLAP evolution equations [5] in NLO down to momentum transfer squared Q 2 ≃ 1 GeV 2 [6,7]. This suggests that perturbative effects set in at relatively low values of the interaction scale. However, the validity of the DGLAP evolution equation is established through fits to data which involve many unknown parameters and therefore it may be doubtful. Exclusive vector meson (V) production at high Q 2 has been proposed as an alternative method to infer the gluon content of the proton [8].High energy elastic V production in Deep Inelastic Scattering (DIS) may be described, in the rest frame of the proton, by the fallowing sequence of happenings [9]. The incoming lepton emits a virtual photon, which subsequently fluctuates into a qq pair. The life time of such a quark pair fluctuation is long enough so that it is the pair that elastically scatters off the proton and evolves, long after the interaction, into a V state. The character of the interaction of the qq pair with the proton depends on the transverse momenta of the pair. If the transverse momentum is large, the spatial transverse separation between the quarks is small and it forms a color dipole, whose interaction with the proton may be calculated perturbatively [10]. The leading process is two gluon exchange. If the transverse momentum is small, the color dipole is large and perturbative calculations do not apply. In this case the interaction looks similar to hadron-hadron elastic scattering and the process should proceed through Pomeron exchange as expected from Regge phenomenology [11].The qq wave function of the virtual photon depends on the polarization of the virtual photon. For longitudinally polarized photons, small transverse size qq dominate. The opposite is true for transversely polarized photons. The attractive features of elastic V production is that, at high Q 2 , the longitudinal component of the virtual photon dominates. The interaction cross section for the latter can be, in principle, fully calculated in perturbative QCD. Moreover, for heavy vector mesons, like the J/Ψ or the Υ, perturbative calculations apply even at Q 2 = 0, as the smallness of the dipole is guaranteed by the mass of the quarks.Independently of particular calculations [12,13], in the region dominated by perturbative QCD, the following features are predicted:• the total γ ⋆ p → V p cross section, σ γ ⋆ p→V p , exhibits a steep rise with W , the photo...

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Polarization in diffractive electroproduction of light vector mesons

Cited by 54 publications

References 9 publications

Hard exclusive reactions and the structure of hadrons

Hard exclusive reactions and the structure of hadrons

Diffractive vector meson production

Exclusive vector meson production at HERA

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