共查询到20条相似文献,搜索用时 46 毫秒
1.
The asymptotic collinear factorisation theorem, which holds for diffractive deep-inelastic scattering, has important modifications in the sub-asymptotic HERA regime. We use perturbative QCD to quantify these modifications. The diffractive parton distributions are shown to satisfy an inhomogeneous evolution equation. We emphasise that it is necessary to include both the gluonic and sea-quark t-channel components of the perturbative pomeron. The corresponding pomeron-to-parton splitting functions are derived in the appendix.Received: 20 April 2005, Published online: 27 July 2005 相似文献
2.
J. Bartels M. A. Braun G. P. Vacca 《The European Physical Journal C - Particles and Fields》2004,33(4):511-521
The rates of inclusive photo- and electroproduction of the
meson:
are calculated in the triple Regge region, integrated over the diffractive mass X. For the Regge exchanges we use the hard pomeron and odderon, both being calculated in the framework of perturbative QCD. The integrated cross section depends upon the coupling of the BFKL pomeron to two C = -1 odderons, and it is found to be of the order of 60 pb for photoproduction and 1.5 pb at Q2 = 25 GeV2.Received: 16 April 2003, Published online: 25 February 2004 相似文献
3.
The idea that the pomeron has partonic structure similar to any other hadron has been given strong support by recent measurements of the diffractive structure function at HERA. We present a detailed theoretical analysis of the diffractive structure function under the assumption that the diffractive cross section can be factorized into a pomeron emission factor and the deep inelastic scattering cross section of the pomeron. We pay particular attention to the kinematic correlations implied by this picture, and suggest the measurement of an angular correlation which should provide a first test of the whole picture. We also present two simple phenomenological models for the quark and gluon structure of the pomeron, which are consistent with various theoretical ideas and which give equally good fits to recent measurements by the H1 collaboration, when combined with the pomeron emission factor of Donnachie and Landshoff. We predict that a large fraction of diffractive deep inelastic events will contain charm, and discuss how improved data will be able to distinguish the models. 相似文献
4.
M. Braun 《The European Physical Journal C - Particles and Fields》1999,6(2):321-330
The amplitude for 4 interacting reggeized gluons is studied in the high-colour limit. The leading order amplitude is explicitly
shown to reduce to a pair of reggeons, i.e to a single BFKL pomeron. The next-to-leading order diffractive amplitude is found
to split into a double pomeron exchange and triple pomeron contribution. The obtained three-pomeron vertex is different from
the originally proposed in [2].
Received: 26 June 1997 / Revised version: 28 February 1998 / Published online: 3 September 1998 相似文献
5.
6.
V. P. Gonçalves M. V. T. Machado 《The European Physical Journal C - Particles and Fields》2004,38(3):319-328
We calculate the nuclear cross section for vector meson exclusive photoproduction within the QCD color dipole picture and in the Regge approach. For the former approach, we have considered the phenomenological saturation model, whereas for the latter we use a model based on the dipole pomeron framework. Theoretical estimates for scattering on both light and heavy nuclei are given over a large range of energy.Received: 17 April 2004, Revised: 21 September 2004, Published online: 18 November 2004 相似文献
7.
J. Kwieciński 《Zeitschrift fur Physik C Particles and Fields》1990,45(3):461-469
The shadowing corrections to gluon and quark distributions in nuclei in the region of small values ofx are discussed. They are related to parton distributions in a pomeron which are in principle measurable in hard diffractive processes on the nucleon target. Multiple scattering corrections to shadowing are considered in a model dependent way. The perturbative QCD evolution of shadowing is also taken into account. Various possibilities of the partonic content of a pomeron are considered. It is shown in particular that the conventional parametrizations of parton distributions in a pomeron which are based on the assumption that it consists mostly of gluons imply substantial nuclear shadowing in gluon distributions in heavy nuclei. Possible phenomenological implications of shadowing corrections in nuclear parton distributions for various semi-hard processes with nuclear targets are briefly discussed. 相似文献
8.
J. Bartels M.G. Ryskin G.P. Vacca 《The European Physical Journal C - Particles and Fields》2003,27(1):101-113
We estimate the size of the triple-pomeron vertex in perturbative QCD and compare with the phenomenological value extracted
from Regge fits to the experimental data. For simplicity, the results of the QCD analysis are taken in the large-Nc limit. We find that the perturbative triple-pomeron coupling is of the same order of magnitude as the observed one. We also
estimate the size of the pomeron self-energy and its contribution to the renormalization of the pomeron intercept. The effect
is very small, in agreement with previous non-perturbative estimates.
Received: 9 October 2002 / Published online: 20 December 2002 相似文献
9.
10.
M.V.T. Machado 《The European Physical Journal C - Particles and Fields》2008,54(3):443-449
We present a study of heavy quarkonium production in hard diffractive processes by pomeron exchange for Tevatron and LHC energies.
The numerical results are computed using a recent experimental determination of the diffractive parton density functions in
the pomeron and these are corrected by unitarity corrections through the gap survival probability factor. We give predictions
for single as well as central diffractive ratios. These processes are sensitive to the gluon content of the pomeron at small
Bjorken variable x and may be particularly useful in studying small-xphysics. They may also be a good place to test the different
available mechanisms for quarkonium production at hadron colliders.
PACS 13.60.Hb; 12.38.Bx; 12.40.Nn; 13.85.Ni; 14.40.Gx 相似文献
11.
J. Ellis G.G. Ross J. Williams 《The European Physical Journal C - Particles and Fields》1999,10(3):443-460
We suggest that the pseudo-rapidity cut dependence of diffractive deep-inelastic scattering events at HERA may provide a
sensitive test of models of diffraction. A comparison with the experimental cross section shows that the Donnachie-Landshoff
model and a simple two-gluon exchange model of the pomeron model are disfavoured. However a model with a direct coupling of
the pomeron to quarks is viable for a harder quark–pomeron form factor, as is a model based on the leading-twist operator
contribution. We also consider a direct-coupling scalar pomeron model. We comment on the implications of these results for
the determination of the partonic structure of the pomeron.
Received: 5 March 1999 / Published online: 3 August 1999 相似文献
12.
Tapobrata Sarkar Rahul Basu 《The European Physical Journal C - Particles and Fields》1998,5(3):493-500
In this paper we check the validity of the ideas of double scaling as given by Ball and Forte in a semi inclusive process
like production at HERA, in different kinematical regions, for low values of the Bjorken variable . In particular, we study production in the inelastic and diffractive (elastic) regimes using the double scaling form of the gluon distribution functions.
We compare these predictions with data (wherever available) and with other standard parameterisations. We find that double
scaling holds in the inelastic regime over a larger kinematic region than that given by the analysis of the proton structure
function . However, in the diffractive region, double scaling seems to suggest an admixture of hard pomeron boundary conditions for
the gluon distribution, while predicting a steeper rise in the cross section than suggested by present data.
Received: 17 December 1997 / Published online: 10 March 1998 相似文献
13.
K. Prytz 《The European Physical Journal C - Particles and Fields》2001,22(2):317-321
The notion of a pomeron structure function arises in a model of electromagnetic diffractive scattering based on Regge factorization.
Due to its small size we expect gluon recombination to occur significantly in the pomeron. The latest data from H1 (1999)
show a evolution in qualitative accordance with the GLR-MQ equations; these are the DGLAP (Altarelli–Parisi) equations corrected
for the effect of gluon recombination.
Received: 9 October 2000 / Revised version: 25 July 2001 / Published online: 5 November 2001 相似文献
14.
E. Gotsman E. Levin U. Maor J. S. Miller 《The European Physical Journal C - Particles and Fields》2008,57(4):689-709
In this paper we develop an approach to soft scattering processes at high energies which is based on two elements: the Good–Walker
mechanism for low mass diffraction and multi-pomeron interactions for high mass diffraction. The principal idea, which allows
us to specify the theory for pomeron interactions, is that the so called soft processes occur at rather short distances (r
2
∝1/〈p
t
〉2
∝
α′ℙ≈0.01 GeV−2), where perturbative QCD is valid. The value of the pomeron slope α′ℙ is obtained from a fit to the experimental data. Using this theoretical approach, we suggest a model that fits all soft data
in the ISR-Tevatron energy range: total, elastic, single and double diffractive cross sections, as well as the t dependence of the differential elastic cross section, and the mass dependence of single diffraction. In this model we calculate
the survival probability of diffractive Higgs production, and we obtain a value for this observable that is smaller than 1%
at the LHC energy range. 相似文献
15.
J. Bartels T. Gehrmann M.G. Ryskin 《The European Physical Journal C - Particles and Fields》1999,11(2):325-333
Using a perturbative model for diffractive interactions, we derive an expression for the polarized diffractive structure
function in the high energy limit. This structure function is given by the interference of diffractive amplitudes with polarized and
unpolarized exchanges. For the polarized exchange we consider both two-gluon and quark-antiquark amplitudes. The polarized
diffractive amplitude receives sizable contributions from non-strongly ordered regions in phase space, resulting in a double
logarithmic enhancement at small x. The resummation of these double logarithmic terms is outlined. We also discuss the transition from our perturbative expression
to the nonperturbative region. A first numerical estimate indicates that the perturbative contribution to the spin asymmetry
is substantially larger than the nonperturbative one.
Received: 7 July 1999 / Published online: 14 October 1999 相似文献
16.
In the perturbative QCD approach single and double inclusive cross-sections for gluon production off the nucleus are studied by the relevant reggeized gluon diagrams. Various terms corresponding to emission of gluons from the triple pomeron vertex are found. Among them the term derived by Kovchegov and Tuchin emerges as a result of the transition from the diffractive to effective high-energy vertex. However it does not exhaust all the vertex contributions to the inclusive cross-section. In the double inclusive cross-section a contribution violating the naive AGK rules is found in which one gluon is emitted from the vertex and the other from one of the two pomerons below the vertex. But then this contribution is subdominant at high energies and taking it into account seems to be questionable.Received: 6 March 2005, Revised: 5 May 2005, Published online: 8 June 2005 相似文献
17.
In the hard pomeron theory with the number of colours the diffractive amplitude obtained in [3] is compared with the results found for in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by
an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially
coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher
order densities in the dipole approach do not involve 1 to k pomeron verteces with but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling.
Received: 11 December 1997 / Revised version: 6 February 1998 / Published online: 7 August 1998 相似文献
18.
N.N. Nikolaev J. Speth V.R. Zoller 《The European Physical Journal C - Particles and Fields》2002,22(4):637-646
High-energy virtual photon–virtual photon scattering can be viewed as an interaction of small size color dipoles from the
beam and target photons, which makes scattering at high energies (LEP, LEP200 and NLC) an indispensable probe of the short distance properties of the QCD pomeron
exchange. Based on the color dipole representation, we investigate the consequences for the scattering of the incorporation of asymptotic freedom into the BFKL equation which makes the QCD pomeron a series of isolated
poles in the angular momentum plane. The emerging color dipole BFKL–Regge factorization allows us to relate in a model-independent
way the contributions of each BFKL pole to scattering and DIS off protons. Numerical predictions based on our early works on the color dipole BFKL phenomenology of
DIS on protons are in good agreement with the experimental data on the photon structure function and the most recent data on the cross section from the OPAL and L3 experiments at LEP200. We discuss the role of non-perturbative dynamics and predict a pronounced effect
of the Regge-factorization breaking due to large unfactorizable non-perturbative corrections to the perturbative vacuum exchange.
We comment on the salient features of the BFKL–Regge expansion for scattering including the issue of the decoupling of subleading BFKL poles and the soft plus rightmost hard BFKL pole dominance.
Received: 9 January 2001 / Revised version: 25 September 2001 / Published online: 7 December 2001 相似文献
19.
20.
We propose to test perturbative QCD(pQCD) in the Regge limit by means of diffractive photon scattering, , at large and very high energies, . The helicity amplitudes of this process were calculated using the Lipatov solution of the BFKL equation for . We found that the perturbatively calculated cross section for this process is comparable in magnitude to the cross section
for photoproduction assuming similar kinematics.
Received: 9 September 1998 / Revised version: 2 October 1998 / Published online: 14 January 1999 相似文献