arXiv subjects

J. Bartels

Publications and source records attributed to J. Bartels.

90 records · Page 5Linked to original sources

arXiv1999

Quark-Antiquark-Gluon Jets in DIS Diffractive Dissociation

We study the diffractive production of $q\bar{q}g$ jets with large transverse momenta in the region of large diffractive masses (small $β$). Cross sections for transverse and longitudinal photons are obtained in the leading log $1/x_{\fP}$ and log $1/β$ approximation, keeping all powers in log $k_t^2/Q^2$. We perform a numerical study and illustrate the angular distribution of the three jets. We also estimate the integrated diffractive three jet cross section and compare with the dijet cross section obtained before.

hep-ph↗

arXiv1998

On the 2nd Order Corrections to the Hard Pomeron and the Running Coupling Constant

It is shown that solutions to the 2nd order BFKL eigenvalue equation exist for arbitrary large real values of the complex angular momentum $j$. This corresponds to a cut in the complex $j$ plane along the whole real axis, and it makes the use of the complex angular momentum variable for the calculation of the high-energy behavior somewhat questionable. The eigenfunctions contain non-perturbative pieces which behave as $\exp(-1/α_s b)$ and have no counterpart in the leading-log BFKL equation. The high-energy behavior of the 2nd order BFKL Green function as found by other authors, is reproduced by excluding these non-perturbative pieces of the eigenfunctions.

hep-ph↗

arXiv1998

An Analysis of Diffraction in Deep-Inelastic Scattering

We propose a simple parametrization for the deep-inelastic diffractive cross section. It contains the contribution of $q\bar{q}$ production to both the longitudinal and the transverse diffractive structure functions, and of the production of $q\bar{q}g$ final states from transverse photons. We start from the hard region and perform a suitable extrapolation into the soft region. We test our model on the 1994 ZEUS and H1 data, and confront it with the H1 conjecture of a singular gluon distribution.

hep-ph↗

arXiv1997

The gamma* gamma* Total Cross Section and the BFKL Pomeron at the 500 GeV e+e- Collider

We present a numerical estimate of the $γ^* γ^*$ total cross section at the designed 500 GeV $e^+e^-$ Linear Collider, based upon the BFKL Pomeron. We find that the event rate is substantial provided electrons scattered under small angles can be detected, and a measurement of this cross section provides an excellent test of the BFKL Pomeron.

hep-ph↗

arXiv1996

The Space-Time Picture of the Wee Partons and the AGK Cutting Rules in Perturbative QCD

We discuss the space-time picture of scattering amplitudes with single and double ladder exchange in perturbative QCD. Particular emphasis is given to the Abramovsky Gribov Kanchelli (AGK) rules which describe the relative contributions of the diffractive dissociation and processes with other multiplicities to the elastic scattering amplitude. Inside the Pomeron Pomeron interaction vertices we find a new matrix which describes the transition from one s-cut to another and which goes beyond the original the AGK rules.

hep-ph↗

arXiv1996

Azimuthal Dependence of Forward-Jet Production in DIS in the High-Energy Limit

As a signal for the BFKL Pomeron in small-x deep inelastic $ep$ scattering, we calculate the azimuthal dependence of the inclusive cross section of forward jets relative to the outgoing electron. For not very large differences in rapidity between the current jet and the forward jet the cross section peaks at $π/2$. For increasing rapidity BFKL dynamics predicts a decorrelation in the azimuthal dependence between the electron and the forward jet.

hep-ph↗

arXiv1996

The $γ^γ^$ Total Cross Section and the BFKL Pomeron at $e^{+}e^{-}$ Collider

We present a numerical estimate of the $γ^* γ^*$ total cross section at LEP and at the designed $e^+e^-$ Next Linear Collider (NLC), based upon the BFKL Pomeron. We find for the linear collider that the event rate is substantial provided electrons scattered under small angles can be detected, and a measurement of this cross section provides an excellent test of the BFKL Pomeron. For LEP, although the number of events is substantially smaller, an initial study of this process is feasible.

hep-ph↗

arXiv1996

Azimuthal Distribution of Quark-Antiquark Jets in DIS Diffractive Dissociation

We investigate the azimuthal distribution of quark-antiquark jets in DIS diffractive dissociation with large transverse momentum. In this kinematical region the matrix element is expressed in terms of the gluon structure function. For the transverse part of the cross section we find a $\cos(2 ϕ)$-distribution with the maximum at $ϕ= \pm π/2$, i.e.\ the jets prefer a direction perpendicular to the electron plane. This is in contrast to boson gluon fusion where the $q\bar{q}$ jet cross section for transversely polarized bosons peaks at $ϕ=0$ and $ϕ=π$. We discuss the origin of this striking difference and present numerical results relevant for the diffractive dissociation at HERA.

hep-ph↗

arXiv1996

Working Group Report on the Structure of the Proton

We summarize the developments on the structure of the proton that were studied at the Workshop on "HERA Physics" that was held in Durham in September 1995. We survey the latest structure function data; we overview the QCD interpretations of the measurements of the structure functions and of final state processes; we discuss charm production and the spin properties of the proton.

hep-ph↗

arXiv1996

Associated Jet Production at HERA

We compare the BFKL prediction for the associated production of forward jets at HERA with fixed-order matrix element calculations taking into account the kinematical cuts imposed by experimental conditions. Comparison with H1 data of the 1993 run favours the BFKL prediction. As a further signal of BFKL dynamics, we propose to look for the azimuthal dependence of the forward jets.

hep-ph↗

arXiv1996

Flavor Singlet Contribution to the Structure Function $g_1$ at Small-x

The singlet contribution to the $g_1(x,Q^2)$ structure function is calculated in the double-logarithmic approximation of perturbative QCD in the region $x \ll 1$. Double logarithmic contributions of the type $(α_s \ln ^2 (1/x))^k$ which are not included in the GLAP evolution equations are shown to give a power-like rise at small-x which is much stronger than the extrapolation of the GLAP expressions. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the region $x \ll 1$. The two main reasons why the small-x behavior of the double logarithmic approximation is so much stronger than the usual GLAP evolution are: the larger kinematical region of integration (in particular, no ordering in transverse momentum) and the contributions from non-ladder diagrams.

hep-ph↗

arXiv1996

Quark-Antiquark Production in DIS Diffractive Dissociation

We calculate the cross section for the production of two jets with large transverse momenta $\kf^2$ in DIS diffractive dissociation for both transverse and longitudinally polarized photons. The scale which defines the hardness of the pomeron is found to be $\kf^2\frac{Q^2+M^2}{M^2}$. We present analytic expressions and discuss numerical results relevant for the diffractive dissociation at HERA.

hep-ph↗

arXiv1996

A Numerical Estimate of the Small-$k_T$ Region in the BFKL Pomeron

A computer study is performed to estimate the influence of the small-$k_T$ region in the BFKL evolution equation. We consider the small-x region of the deep inelastic structure function $F_2$ and show that the magnitude of the small-$k_T$ region depends on $Q^2$ and $x_B$. We suggest that the width of the $\log k_T^2$-distribution in the final state may serve as an additional footprint of BFKL dynamics. For diffractive dissociation it is shown that the contribution of the infrared region is large - even for large $Q^2$. This contribution becomes smaller only if restrictions on the final state are imposed.

hep-ph↗

arXiv1996

Diffractive Production of Vector Mesons at Large t

The cross section for elastic vector meson production in photon-proton interactions at large $t$ is considered using the exact analytic solution of the BFKL equation in the azimuthally symmetric $n=0$ limit. We use a non-relativistic model for the vector meson production and find a small shrinkage in the $t$-distribution with increasing energy.

hep-ph↗

arXiv1995

Conformal Invariance of the Transition Vertex $2 \to 4$ gluons

We show that the transition vertex: two reggeized gluons $\to$ four reggeized gluons is invariant under Möbius transformations. This provides an important step in defining a conformally invariant effective field theory for QCD in the Regge limit.

hep-ph↗

arXiv1995

Nonsinglet Contributions to the Structure Function g1 at Small-x

Nonsinglet contributions to the $g_1(x,Q^2)$ structure function are calculated in the double-logarithmic approximation of perturbative QCD in the region $x \ll 1$. Double logarithmic contributions of the type $(α_s \ln ^2 (1/x))^k$ which are not included in the GLAP evolution equations are shown to give a stronger rise at small-x than the extrapolation of the GLAP expressions. Further enhancement in the small-x region is due to non-ladder Feynman graphs which in the DLA of the unpolarized structure functions do not contribute. Compared to the conventional GLAP method (where neither the whole kinematical region which gives the double logs nor the non-ladder graphs are taken into account) our results lead to a growth at small-x which, for HERA parameters, can be larger by up to factor of 10 or more.

hep-ph↗

arXiv1995

The BFKL-Pomeron In Deep Inelastic Diffractive Dissociation near t=0

The small-$t$ behaviour of the deep inelastic diffractive dissociation cross section in the triple Regge region is investigated, using the BFKL approximation in perturbative QCD. We show that the cross section is finite at $t=0$, but the diffusion in $\ln{k_t^2}$ leads to a large contribution of small momenta at the triple Pomeron vertex. We study the dependence upon the total energy and the invariant mass. At $t=0$, there is a decoupling of the three BFKL singularities which is a consequence of the conservation of the conformal dimension. For large invariant masses, the four gluon state in the upper t-channel plays an important role and cannot be neglected.

hep-ph↗

arXiv1995

How does the BFKL-Pomeron couple to quarks ?

We investigate the coupling of the BFKL-Pomeron to quarks and to colorless states. Special emphasis is given to the effective quark-quark scattering amplitude of Mueller and Tang.

hep-ph↗