# Diffractive electroproduction of ρ and ϕ mesons at HERA

H1 Collaboration; Egli, S; Hildebrandt, M; Horisberger, R; Del Degan, M; Grab, C; Leibenguth, G; Sauter, M; Zimmermann, T; Müller, K; Nowak, K; Robmann, P; Straumann, U; Truöl, P; Perez, E (2010). Diffractive electroproduction of ρ and ϕ mesons at HERA. Journal of High Energy Physics, (5):1-111.

## Abstract

Diffractive electroproduction of ρ and ϕ mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb−1. About 10500 ρ and 2000 φ events are analysed in the kinematic range of squared photon virtuality 2.5 ≤ Q 2 ≤ 60 GeV2, photon-proton centre of mass energy 35 ≤ W ≤ 180 GeV and squared four-momentum transfer to the proton |t| ≤ 3 GeV2. The total, longitudinal and transverse cross sections are measured as a function of Q 2, W and |t|. The measurements show a transition to a dominantly “hard” behaviour, typical of high gluon densities and small $$q\overline q$$ dipoles, for Q 2 larger than 10 to 20 GeV2. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (Q 2+M 2 V )/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections.

Diffractive electroproduction of ρ and ϕ mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb−1. About 10500 ρ and 2000 φ events are analysed in the kinematic range of squared photon virtuality 2.5 ≤ Q 2 ≤ 60 GeV2, photon-proton centre of mass energy 35 ≤ W ≤ 180 GeV and squared four-momentum transfer to the proton |t| ≤ 3 GeV2. The total, longitudinal and transverse cross sections are measured as a function of Q 2, W and |t|. The measurements show a transition to a dominantly “hard” behaviour, typical of high gluon densities and small $$q\overline q$$ dipoles, for Q 2 larger than 10 to 20 GeV2. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (Q 2+M 2 V )/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections.

## Citations

26 citations in Web of Science®
27 citations in Scopus®

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Physics Institute 530 Physics English 7 May 2010 20 Jan 2011 09:50 05 Apr 2016 14:36 Springer 1029-8479 Related URL. An embargo period may apply. 10.1007/JHEP05(2010)032 http://arxiv.org/abs/0910.5831v3
Permanent URL: http://doi.org/10.5167/uzh-42695

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