A Donnachie, P V Landshoff
Exclusive vector meson production from real and virtual photons is, for the most part, described well by soft pomeron exchange. However, there are some unsolved normalisation problems, and just a hint that an additional contribution from hard pomeron exchange may be needed.
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Some important recent results on subnuclear diffractive phenomena obtained at HERA are reviewed and new issues in nucleon tomography are discussed.
We describe new QCD fits to diffractive proton structure functions measured at HERA, and we use these parton densities to predict the shape of the dijet mass fraction at the Tevatron and look for the existence of exclusive events in the dijet channel.
Exclusive vector meson production and deeply virtual Compton scattering are ideally suited reactions for studying the structure of the proton and the transition from soft to hard processes. The main experimental data obtained at HERA are summarised and presented in the light of QCD approaches.
Recent results obtained at HERA on deeply virtual Compton scattering and exclusive vector meson production are reviewed, with the emphasis on the transition from soft to hard diffraction and on spin dynamics.
Exclusive photoproduction of heavy quarkonia at HERA is analyzed in the framework of the Regge-eikonal approach together with the nonrelativistic bound state formalism. Total and differential cross-sections for the process $γ+p\to (Q\bar{Q})_{1S}+p$ are calculated. The model predicts cross-sections of Exclusive Double Diffractive Events (EDDE) at TeVatron and LHC.
The amplitude for photoproduction gamma p -> Υp is calculated in a pQCD k_\perp-factorization approach. The total cross section for diffractive Υ's is compared to recent HERA data. The amplitude is used to predict the cross section for exclusive ppbar \to ppbar Υ(1S,2S) process in hadronic reactions at Tevatron energies. We also included absorption effects.
The forward photoproduction amplitude for gamma p to Upsilon p is calculated in a pQCD k_t-factorization approach with an unintegrated gluon distribution constrained by inclusive deep-inelastic structure functions. The total cross section for diffractive Upsilons is compared with a recent HERA data. We also discuss the 2S/1S ratio in diffractive Upsilon-production. The amplitude is used to predict the cross section for exclusive Upsilon production in hadronic reactions. Differential distributions for the exclusive p pbar to p Upsilon pbar process are calculated for Tevatron energies. We also s…
A detailed analysis of semi-exclusive diffractive processes in e-p DIS at HERA, with the diffractive final states in the forward direction is presented. The contributions of the subleading f_2, ω, a_2, ρreggeons and the pion exchanges to the diffractive structure function with the forward proton or neutron are estimated. It is found that the (a_2,ρ) reggeons are entirely responsible for the forward neutron production at x_P < 10^{-3}. The πN production in the forward region is estimated using the Deck mechanism. The significance of this reaction for the processes measured at HERA, especially w…
Following recent predictions that the geometric scaling properties of deep inelastic scattering data in inclusive gamma*-p collisions are expected also in exclusive diffractive processes, we investigate the diffractive production of vector mesons. Using analytic results in the framework of the BK equation at non-zero momentum transfer, we extend to the non-forward amplitude a QCD-inspired forward saturation model including charm, following the theoretical predictions for the momentum transfer dependence of the saturation scale. We obtain a good fit to the available HERA data and make predictio…
We calculate cross sections for the exclusive diffractive leptoproduction of $ρ$-mesons, $γ^*~p~\to~ρ~p$, within the framework of high-energy factorization. Cross sections for longitudinally and transversally polarized mesons are shown. We employ a wide variety of unintegrated gluon distributions available in the literature and compare to HERA data. The resulting cross sections strongly depend on the choice of unintegrated gluon distribution. We also present predictions for the proton target in the kinematics of the Brookhaven EIC.
A review is presented of diffractive vector meson production at HERA, with stress on the investigation of ``hard'' features and comparisons with theoretical predictions based on perturbative QCD approaches.
We study the feasibility of measuring semi-exclusive photon production γ+ p \to γ+ Y at HERA. The cross section of photons produced at large transverse momenta, recoiling off an inclusive system Y of limited mass, can without photon isolation cuts be simply expressed in terms of hard pQCD subprocesses and standard target parton distributions. With the help of event generators we identify the kinematic region where quark and gluon fragmentation processes can be neglected. The cross section in this semi-exclusive region is large enough to be measured with an upgraded HERA luminosity of L = 100/p…
Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic QCD are reviewed with an emphasis on the BFKL color dipole and kt-factorization approaches.
We present a simultaneous analysis, within an impact parameter dependent saturated dipole model, of exclusive diffractive vector meson (J/psi, phi and rho) production, deeply virtual Compton scattering and the total gamma* p cross section data measured at HERA. Various cross sections measured as a function of the kinematic variables Q^2, W and t are well described, with little sensitivity to the details of the vector meson wave functions. We determine the properties of the gluon density in the proton in both longitudinal and transverse dimensions, including the impact parameter dependent satur…
QED radiative corrections to the cross section of diffractive electro- and photoproduction of vector mesons is calculated at HERA energies. Both semi-analytical and Monte Carlo approaches are discussed and compared.
I show that a lowest-order pQCD calculation of elastic vector-meson production does reproduce all the features of experimental measurements at HERA, for all Q^2 and all mesons, at fixed energy.
The rich experimental landscape of exclusive vector meson production at the high energy electron-proton collider HERA is reviewed, with emphasis on the transition from soft to hard diffraction and QCD interpretations.
In the framework of the vector dominance model (VDM) new contribution into the cross-section of $D^*$-meson photoproduction at HERA has been estimated. This contribution is due to the interaction of the virtual vector $c\bar c$-mesons from photon with the proton. It has been shown that the mechanism under discussion plays the essential role for all values of transverse momentum of $D^*$-mesons at HERA. Taking into account for the contribution of this mechanism improves the description of the experimental cross section distribution.
We demonstrate another success of the AdS/QCD correspondence by showing that an AdS/QCD holographic light-front wavefunction for the $ρ$ meson generates predictions for the cross-sections of diffractive $ρ$ production that are in agreement with data collected at the HERA electron-proton collider.
We extract the light-cone wavefunctions of the rho meson using the HERA data on diffractive rho photoproduction. We find good agreement with predictions for the distribution amplitude based on QCD sum rules and from the lattice. We also find that the data prefer a transverse wavefunction with enhanced end-point contributions.
Results on elastic vector meson production at HERA are presented in the framework of perturbative QCD. The energy dependence of the cross section for J/Psi photoproduction and for rho electroproduction is studied. A full polarisation analysis, including the measurement of the 15 elements of the spin density matrix and of R=sigma_L/sigma_T, is presented for rho electroproduction. Finally heavier vector mesons (Psi' and Upsilon) production is discussed.
We explore QCD calculations for the process gamma p -> V X where V is a vector meson, in the region s >> -t and -t >> Lambda_QCD^2. We compare our calculations for the J/psi, phi and rho mesons with data from the ZEUS Collaboration at HERA and demonstrate that the BFKL approach is consistent with the data even for light mesons, whereas the two-gluon exchange approach is inadequate. We also predict the differential cross-sections for the Upsilon and omega for which no data are currently available.
The anomalous value of the tensor form factor in the kaon decay K -> pi e nu and the destructive interference in pion decay pi -> e nu gamma can be simultaneously described by admixture of a tensor interaction in the standard V-A one. It is shown that the same tensor interaction can describe recent HERA data at very large Q^2.
Recent $HERA$ data on the photoproduction of vector mesons are analysed within a "soft", dipole pomeron model. We argued that the data on $σ^{γ\rightarrow J/ψ}_{el}$ is consistent with a soft pomeron, the apparent rapid increase resulting from the non-asymptotic effects due to the delayed asymptotics of $σ_{el}$ with respect to $σ_{tot}$.
A successful interpretation of the cross sections for elastic and inelastic vector meson production can be made if one assumes the underlying dynamics to be governed by hard partonic subprocesses. Extending these partonic approaches to longitudinally polarized electron-proton collisions, we estimate the expected production asymmetries at the HERA collider. The anticipated statistical errors on these asymmetries mostly turn out to be larger than the asymmetries themselves, such that an experimental observation of these asymmetries at HERA looks not feasible.
A Reggeometric (Regge+Geometry) model, based on the observed proportionality between the forward slope of the differential cross section and the interaction radius, the latter depending on virtuality Q2 of the incoming virtual photon and on the mass M 2 of the produced particle, is constructed. The objective of this study is the dependence of the Regge-pole amplitude on the virtuality Q2 and masses of the external particles, which remains an open problem for the theory. The present analysis is based on the HERA data on Deeply Virtual Compton Scattering (DVCS) and exclusive diffractive Vector M…
Exclusive diffractive photoproduction of heavy vector mesons (V=phi, J/psi and Upsilon) at HERA is studied in a model employing a dipole Pomeron exchange (P) with an inelastic gamma-P-V vertex. The model is fitted to the data on dsigma/dt, B and elastic sigma for Q^2=0 and beyond the threshold region. The elastic cross sections for both phi and J/psi photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (little or no shrinkage) for J/psi is not correlated with the slope of the Pomeron trajectory. Estimates for Upsilon photoproduction at HERA a…
Decay widths, branching ratios and production dynamics of some recently discovered $J^{PC} = 1^{-+}, 0^{-+}$,$1^{--}$ and $2^{-+}$ mesons are found to be in remarkable agreement with the predicted properties of hybrid mesons. We propose tests for this new dynamics, emphasise the critical role of $πb_1$ or $πh_1$ decay channels in discriminating hybrids from conventional states, and suggest that photoproduction may offer special opportunities for isolation and confirmation of hybrids.
Selected recent results from the H1 and ZEUS experiments are reviewed, illustrating some of the many facets of ``meson physics'' at the HERA ep collider. The results cover exclusive elastic and proton-dissociative diffractive vector meson production and comparisons with recent theoretical calculations show that perturbative QCD models are successful in describing these processes when at least one of the involved scales have large values. Furthermore a search for odderon induced exclusive photoproduction of pseudoscalar and tensor mesons is described; upper limits for the cross sections are bel…
We studied the $ep\rightarrow ep+2jets$ diffractive cross section with ZEUS phase space. Neglecting the $t$-channel momentum in the Born and gluon dipole impact factors, we calculated the corresponding contributions to the cross section differential in $β=\frac{Q^{2}}{Q^{2}+M_{2jets}^{2}}$ and the angle $ϕ$ between the leptonic and hadronic planes. The gluon dipole contribution was obtained in the exclusive $k_{t}$-algorithm with the exclusive cut $y_{cut}=0.15$ in the small $y_{cut}$ approximation. In the collinear approximation we canceled singularities between real and virtual contributions…
Imaging constituent quark shape of proton with exclusive vector meson production at HERA
本文基于质子热点图像，通过计算HERA上的专属矢量介子产生截面，发现上夸克比下夸克更宽且周围胶子更多，验证了该方法与模型细节及介子种类无关。
We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic scattering. The dependence of the slopes on the mass of the vector meson is reproduced as well. We examine the lower-energy data, and find that the energy dependence of the cross section does not depend on Q2, but may depend on the vector-meson mass.
Exclusive diffractive dijets at HERA and EIC using GTMDs
本研究利用GTMDs计算ep反应中遍举衍射双喷注的微分分布，对比HERA实验数据发现计算截面仅为测量值的一小部分，同时指出喷注横动量截断产生的方位角关联易被误判为椭圆GTMD的效应。
We use an anti-de Sitter/Quantum Chromodynamics (AdS/QCD) holographic light-front wavefunction for the $ρ$ and $ϕ$ mesons, in conjunction with the Color Glass Condensate (CGC) dipole cross-section whose parameters are fitted to the most recent 2015 high precision HERA data on inclusive Deep Inelastic Scattering (DIS), in order to predict the cross-sections for diffractive $ρ$ and $ϕ$ electroproduction. Our results suggest that the holographic meson light-front wavefunction is able to give a simultaneous description of the $ρ$ and $ϕ$ production data provided we use a set of light quark masses …
Elastic production of vector mesons $γ^{*} N\to V N$ is the pomeron-exchange dominated diffractive reaction with much potential of probing the BFKL pomeron. The BFKL pomeron can conveniently be described in terms of the dipole cross section which is a solution of the generalized BFKL equation. In this paper we discuss, how the energy and $Q^{2}$ dependence of elastic production of vector mesons at HERA will allow scanning the dipole cross section as a function of dipole size $r$. We show that determinaton of the intercept of the BFKL pomeron requires measuring the $ρ^{0}$ and $J/Ψ$ production …
I review recent theory developments for hard exclusive and semi-exclusive production of mesons, emphasising the variety of physics issues that can be studied in these processes.
The B_c photoproduction at HERA has been considered in the frame work of the pQCD. The estimated value of the total production cross section of Bc+, Bc*+, Bc- and Bc*- mesons is about 5 pb. Higher excitations yield about 30% to the total cross section. Thus for integrated HERA luminosity 1 fb-1 about 7000 Bc mesons will be produced.
We demonstrate that perturbative QCD allows one to calculate the absolute cross section of diffractive exclusive production of photons at large $Q^2$ at HERA, while the aligned jet model allows one to estimate the cross section for intermediate $Q^2 \sim 2 GeV^2$. Furthermore, we find that the imaginary part of the amplitude for the production of real photons is larger than the imaginary part of the corresponding DIS amplitude by about a factor of 2, leading to the prediction of a significant counting rate for the current generation of experiments at HERA. We also find a large azimuthal angle …
Within the color dipole gBFKL dynamics applied to the diffraction slope we predict an anomalous t dependence of the differential cross section as a function of energy and Q^2 for production of radially excited V'(2S) light vector mesons in contradiction with a well known standard monotonous t- behaviour for V(1S) mesons. The origin of this phenomenon is based on the interplay of the nodal structure of V'(2S) radial wave function with the energy and dipole size dependence of the color dipole cross section and of the diffraction slope. We present how a different position of the node in V'(2S) wa…
We compare recent experimental results for one-particle-inclusive processes in deeply inelastic scattering at HERA with theoretical predictions in next-to-leading-order QCD perturbation theory, and study the factorization scale dependence of cross sections and charged multiplicities. In the future, for the HERA machine running at design luminosity, scaling violations of fragmentation functions permit the measurement of the strong coupling constant. We estimate the size of the statistical error of $α_s$ that can be achieved, and study the theoretical error due to the various parton density para…
We present a detailed analysis of exclusive semileptonic decays of Bc meson involving pseudoscalar and vector mesons in the BSW framework, by investigating the effects of the flavor dependence on the average transverse quark momentum inside a meson. Branching ratios of exclusive semileptonic decays of Bc meson are predicted.
HERA data on soft hadron production are discussed. The measured inclusive and exclusive hadron cross sections show a simple scaling behaviour.
We suggest a method of determination of the pion structure function down to x \simeq 10^{-4} based on semi-exclusive deep inelastic scattering off protons. The idea is to exploit the nonperturbative πN$ and πΔFock components of the nucleon, which contribute significantly to deep inelastic scattering and dominate the fragmentation of protons into fast neutrons and deltas. The intrinsic factorization properties of the semi-exclusive cross section give a good test for the validity of this approach.
We present the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*} N\to V(V') N$ of vector mesons ($V(1S) = ϕ^0, ω^0, ρ^0, J/Ψ, Υ$) and their radial excitations ($V'(2S) = ϕ', ω', ρ', Ψ', Υ'$). The main emphasis is related to light vector mesons. We discuss how the energy dependence of the color dipole cross section in conjuction with the node of the radial wave function of the $2S$ states can lead to an anomalous $Q^2$ and energy dependence of diffractive production of $V'(2S)$ vector mesons. The color dipole model predictions for $V(1S)$ light vector meson productio…
The perturbative QCD formalism for exclusive heavy meson decays, especially the three-scale factorization theorem for nonleptonic modes is reviewed and compared to the conventional Bauer-Stech-Wirbel model.
We discuss two different models for the impact parameter dependent dipole cross section: one based on DGLAP evolution and the other inspired by the Balitsky-Kovchegov equation. The parameters are determined from fits to data on the total gamma* p cross section measured at HERA. The impact parameter dependent saturation scale is extracted. Predictions are then confronted with HERA data on exclusive diffractive vector meson production and deeply virtual Compton scattering. Finally, predictions are given for the cross sections of exclusive photoproduced J/psi and Upsilon mesons, and Z^0 bosons, e…
I discuss mechanisms of exclusive production of mesons at high energies. Some illustrative examples for the FNAL Tevatron and CERN LHC as well as for lower energies are shown.
We report on numerical studies of the NLO corrections to exclusive meson electroproduction, both in collider and fixed-target kinematics. Corrections are found to be huge at small xB and sizeable at intermediate or large xB.
The spin and flavor symmetries of the heavy quark effective theory are employed to discuss the exclusive cross sections for pair production of heavy mesons in photon-photon collision. The ratios of the exclusive cross sections for heavy mesons are obtained explicitly and the validity of results is discussed.
We present a short review of anomalous properties in diffractive photo- and electroproduction of radially excited V'(2S) vector mesons. Using the color dipole gBFKL phenomenology we analyze anomalous Q^{2} and energy dependence of the production cross section, V'(2S)/V(1S) production ratio, the diffraction slope and anomalous t behaviour of the differential cross section dσ/dt. The origin of these anomalies is based on the interplay of the nodal structure of V'(2S) radial wave function with the energy and dipole size dependence of the dipole cross section and the diffraction slope. We analyze …
Theory and phenomenology of the eta_c photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The η_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction …
I review recent progress on exclusive $B$ meson decays made in the perturbative QCD approach, concentrating on the evolution of the $B$ meson wave function in $k_T$ factorization, radiative decays, polarizations in $VV$ modes, and new physics effect in $B\to ϕK_S$.
It is shown that the universality of the initial and final state interactions responsible for the transition between the on-- and off--mass shell states leads to the energy independence of the ratio of exclusive $ρ$ electroproduction cross section to the total cross section. It is demonstrated that the above universality and explicit mass dependence of the exponent in the power--like energy behavior of the cross-section obtained in the approach based on unitarity is in a quantitative agreement with the high--energy HERA experimental data. We discuss also HERA results on angular distributions o…
We compare results of our recent studies on vector meson production within the QCD factorization at next-to-leading order with HERA data.
Protons and antiprotons at collider energies are a source of high energy Weizsaecker--Williams photons. This opens up a possibility to study at the LHC exclusive photoproduction of heavy vector mesons at energies much larger than possible at the HERA accelerator. We present selected results of our detailed studies of various distributions for the production of heavy quarkonia (e.g. rapidity, transverse momenta, azimuthal angles). We give predictions for LHC energies. Our calculations are based on modelling the photoproduction amplitudes in a k_\perp-factorisation approach which is checked agai…
By using a Regge-pole model for vector meson production (VMP), successfully describing the HERA data, we analyse the correlation between VMP cross sections in photon-induced reactions at HERA and those in ultra-peripheral collisions at the Large Hadron Collider (LHC). Predictions for future experiments on production of $J/ψ$ and $ψ(2S)$ are presented.
We point out that hard exclusive production of tensor mesons $f_2(1270)$ with helicity $λ=\pm 2$ is dominated by the gluon component in the meson wave function and can be used to determine gluon admixture in tensor mesons in a theoretically clean manner. We present a detailed analysis of the tensor meson distribution amplitudes and calculate the transition form factor $γ+γ^*\to f_2(1270)$ for one real and one virtual photon.
The paper is devoted to investigation of $K$ mesons production in exclusive $B_{c}$ decays $B_{c} \to ψ^{(')}K^{+}K^{-}π^{+}$ and $B_{c} \to ψ^{(')}K^{+}π^{+}π^{-}$. In the framework of resonance approximation we obtain theoretical predictions for branching fractions of these decays and present distributions over different kinematical variables.
Exclusive semileptonic B meson decays to orbitally excited D mesons are investigated in the infinitely heavy quark limit in the framework of the relativistic quark model based on the quasipotential approach. The B\to D^{**}eνIsgur-Wise functions τ_{3/2}(w) and τ_{1/2}(w) are determined. It is found that the relativistic transformation of the meson wave functions (Wigner rotation of the light quark spin) contribute already at the leading order of the heavy quark expansion.
Phenomenological studies of exclusive heavy-quarkonium electroproduction at NLO
本文在次领头阶下研究了重夸克onium的电产生现象，比较了与HERA数据的截面结果，并为EIC测量提供了预测，同时讨论了重新求和对数增强贡献的必要性。
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