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1.
A measurement is presented of dijet and 3-jet cross sections in low- diffractive deep-inelastic scattering interactions of the type , where the system X is separated by a large rapidity gap from a low-mass baryonic system Y. Data taken with the H1 detector at HERA, corresponding to an integrated luminosity of 18.0 pb, are used to measure hadron level single and double differential cross sections for and . The energy flow not attributed to jets is also investigated. The measurements are consistent with a factorising diffractive exchange with trajectory intercept close to 1.2 and tightly constrain the dominating diffractive gluon distribution. Viewed in terms of the diffractive scattering of partonic fluctuations of the photon, the data require the dominance of over states. Soft colour neutralisation models in their present form cannot simultaneously reproduce the shapes and the normalisations of the differential cross sections. Models based on 2-gluon exchange are able to reproduce the shapes of the cross sections at low values. Received: 21 December 2000 / Published online: 6 April 2001  相似文献   

2.
We calculate the cross section of diffractive charge-parity neutral meson production in virtual photon proton collision at high energies. Due to the opposite -parities of photon and meson () this process probes the -channel odderon exchange which is described here as noninteracting three–gluon exchange. Estimates for the cross section of inelastic diffractive process are presented. The total cross section of diffractive meson photoproduction is found to be 47 pb. The cross sections for the diffractive production of light mesons () in collisions are of the same order if the photon virtuality is . Received: 30 July 1997  相似文献   

3.
We study the diffractive production of jets with large transverse momenta in the region of large diffractive masses (small ). Cross sections for transverse and longitudinal photons are obtained in the leading log and log approximation, keeping all powers in log . 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. Received: 11 March 1999 / Published online: 14 October 1999  相似文献   

4.
We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading-order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant Q2 dependence. We give numerical predictions for single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor.  相似文献   

5.
We discuss diffractive production in the context of two-component models. After defining the class of models that we consider and discussing their general properties, we develop integral equations for the generating functions of diffractive processes. We consider single and double diffraction and two fireball production. We investigate the behavior of the partial cross sections for n-particle production in all three cases and obtain a successful fit to recent data.  相似文献   

6.
We calculate the nuclear inclusive and diffractive cross sections for heavy quark photoproduction within a phenomenological saturation approach. The nuclear cross section is obtained by the extension of the saturation model through the Glauber-Gribov formalism. We predict large nuclear heavy quark cross sections at LHC energies.Received: 6 May 2003, Revised: 1 July 2003, Published online: 5 September 2003  相似文献   

7.
The model-dependence of the relation between the inelastic and various minimum-bias proton-proton cross sections is analyzed, paying a special attention to the sensitivity of minimum-bias triggers to diffractive collisions. Concentrating on the trigger selections of the ATLAS experiment, the measured cross sections are compared to predictions of a number of hadronic Monte Carlo models used in the cosmic ray field. It is demonstrated that the ATLAS results are able to discriminate between different models and between certain theoretical approaches for soft multi-particle production. On the other hand, the strong model-dependence of the selection efficiency of the minimum-bias triggers prevents one from inferring high mass diffraction rate from the discussed data. Moreover, the measured cross sections prove to be insensitive to the production of low mass diffractive states in proton-proton collisions. Consequently, a reliable determination of the total inelastic cross section requires forward proton tracking by a dedicated experiment.  相似文献   

8.
Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q2<0.01 GeV2) and deep-inelastic scattering processes (DIS, 4<Q2<80 GeV2). The event topology is given by ep→eXY, in which the system X, containing at least two jets, is separated from a leading low-mass baryonic system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction in photoproduction is a factor 0.5±0.1 smaller than the same ratio in DIS. This suppression is the first clear observation of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model fails in both kinematic regions.  相似文献   

9.
We have calculated the diffractive dijet cross section in low-Q 2 ep scattering in the HERA regime. The results of the calculation in LO and NLO are compared to recent experimental data of the H1 Collaboration. We find that in LO the calculated cross sections are in reasonable agreement with the experimental results. In NLO, however, some of the cross sections disagree, showing that factorization breaking occurs in that order. By suppressing the resolved contribution by a factor of approximately three, good agreement with all the data is found. The size of the factorization breaking effects in diffractive dijet photoproduction agrees well with absorptive model predictions.Received: 18 August 2004, Published online: 28 October 2004  相似文献   

10.
The single diffractive component in hadronhadron interactions is studied in the two-component Dual Parton Model. We distinguish high mass single diffraction represented by a triple-Pomeron exchange and low mass single diffraction described via a two channel eikonal method. The calculated single diffractive cross sections, and the distributions agree quite well with data from collider and fixed target experiments. The fit of the model parameters to cross section data gives a extrapolation of the total, elastic, and single diffractive cross sections to supercollider energies which depends on the parton structure functions used for the minijet component.  相似文献   

11.
Single diffractive hadron-nucleus interactions are studied within the framework of the dual parton model. Introducing a diffractive component into the Monte-Carlo event generator DTUNUC we investigate particle production and the dependence of the diffractive cross section on the atomic number of the target nucleus. A comparison of the numerical results with recent experimental data is presented. We furthermore introduce hadronic cross section fluctuations and discuss their influence on diffractive proton-nucleus cross sections.  相似文献   

12.
Using three sets of Pomeron structure functions, the cross sections of J/ψ and γ associated productionvia resolved photon and proton diffractive scatting in ep collision are investigated. It is found that the cross sectionscalculated with various gluon distribution functions of Pomeron are different. The discrepancy is about 1.8 times fordifferential cross sections and 1.7 times for total cross sections. The experimental studies of the process could give valuableinsight in the diffractive production mechanism and test the color-octet mechanism for heavy quarkonium production ina new environment.  相似文献   

13.
A critical comparison is made between recent predictions of the cross sections for diffractive Higgs production at the Tevatron and the LHC. We show that the huge spread of the predictions arises either because different diffractive processes are studied or because important effects are overlooked. Exclusive production offers a reliable, viable Higgs signal at the LHC provided that proton taggers are installed. Received: 13 August 2002 / Revised version: 24 September 2002 / Published online: 18 October 2002  相似文献   

14.
彭宏安  泰克诚  何祯民 《中国物理 C》1994,18(12):1078-1085
讨论从ISR到SSC能区p+p(p)→p+J/ψ(Υ)+X过程.假定Pomeron(p)的结构以胶子为主且在小x处有的行为后,在QCD最低阶计算了两个主要子过程的硬衍射截面和作为背景项的Drell-Yan模式的相应截面.与背景项在高能时随Ins增加不同,硬衍射项基本上随(InS)2增加,因而在TeV能区以上时后者将大大超过前者.这种性质对其它硬衍射过程具有普适性.因此如果关于P的上述假定正确,在准确地测定P的结构后,选择适当的硬衍射过程,可能在超高能时提供探测物理粒子的新实验方法.  相似文献   

15.
As shown in previous papers, Reggeon “Field” Theory is actually a Markov process describing the evolution of wee partons during a boost. In the present paper, the physical interpretation of scattering amplitudes and cross sections is discussed, both for the uncut (unlabelled) and cut (labelled) version. Elastic amplitudes and total cross sections, inclusive cross sections, fully diffractive events, and inelastic diffraction are all shown to have simple interpretations in the parton model. Finally, the connection with models for evolution of hard partons in QCD is discussed.  相似文献   

16.
Analysis of diffractive production on nuclei implied cross sections of the diffractively produced system on nucleons which are smaller than the corresponding projectile nucleon cross sections. We provide a natural explanation for this feature in the Good-Walker coherent production formalism. A specific realization of the Good-Walker formalism stated in terms of quarks and connecting electric flux tubes and some ensuing consequences are also discussed briefly.  相似文献   

17.
We extend the standard analysis of the QCD planar ladder diagrams to the nonforward direction. Results are used for calculating exclusive and semiinclusive cross sections of diffractive photoproduction in the small-x region ofep-collisions. As an example we estimate the event rate for diffractive photoproduction of the neutral vector boson at Hera energies.  相似文献   

18.
D S Narayan 《Pramana》1974,2(5):252-258
Topological cross sections for diffractive and nondiffractive components in pp collisions are deduced on the basis of a dynamical model proposed earlier to explain the multiplicity distribution of charged particles. The model has an important prediction for the angular and momentum distributions of charged particles in diffractive events.  相似文献   

19.
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   

20.
We show that the enhancement of the saturation scale in large nuclei relative to the proton is significantly influenced by the effects of quantum evolution and the impact parameter dependence of dipole cross sections in high energy QCD. We demonstrate that there is a strong A dependence in diffractive deeply inelastic scattering and discuss its sensitivity to the measurement of the recoil nucleus.  相似文献   

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