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1.
We consider the influence of shadowing effects on the proton structure function in the small-x interval. The gluon-gluon shadowing are noticeable in the HERA kinematical region while the screening of the quark component of the structure function effects negligibly the gluon distribution. The only noticeable effect is the decreasing of sea quark densities at small-x. The explicit form of the gluon distribution in the proton depends significantly on the form of used boundary condition atQ 2=Q 0 2 . We consider also difference of results obtained with the help of Kuraev-Lipatov-Fadin and Altarelli-Parisi evolution equations.  相似文献   

2.
The differential gluon structure function of the proton, ?(x, Q 2), introduced by Fadin, Kuraev, and Lipatov in 1975 is extensively used in small-x QCD. We report here the first determination of ?(x, Q 2) from experimental data on the small-x proton structure function F 2p (x, Q 2). We give convenient parametrizations for ?(x, Q 2) based partly on the available DGLAP evolution fits (GRV, CTEQ, and MRS) to parton distribution functions and on realistic extrapolations into the soft region. We discuss the impact of soft gluons on various observables. The x dependence of the so-determined ?(x, Q 2) varies strongly with Q 2 and does not exhibit simple Regge properties. Nonetheless, the hard-to-soft diffusion is found to give rise to a viable approximation of the proton structure function F 2p (x, Q 2) by the soft and hard Regge components with intercepts Δsoft=0 and Δhard ~ 0.4.  相似文献   

3.
The BFKL and the unified angular-ordered equations are solved to determine the gluon distribution at smallx. The impact of kinematic constraints is investigated. Predictions are made for observables sensitive to the gluon at smallx. In particular comparison is made with measurements at the HERA electron-proton collider of the proton structure functionF 2(x, Q 2) as a function of lnQ 2, the charm componentF c 2 (X, Q 2) and diffractiveJ/Ψ photoproduction.  相似文献   

4.
The BFKL and the unified angular-ordered equations are solved to determine the gluon distribution at smallx. The impact of kinematic constraints is investigated. Predictions are made for observables sensitive to the gluon at smallx. In particular comparison is made with measurements at the HERA electron-proton collider of the proton structure functionF 2(x, Q 2) as a function of lnQ 2, the charm componentF c 2 (X, Q 2) and diffractiveJ/?? photoproduction.  相似文献   

5.
We have performed a Monte Carlo study of photon-gluon interactions at theep collider HERA. We show that it is possible to determine the fractional momentum carried by the gluon (x g) from hadronic informations alone. In particular, in the photoproduction region, where thex andQ 2 are badly measured, this could be the only global physical variable of interest, together with the hadronic invariant mass. The study of these quantities would allow a direct measurement of the gluon density of the proton in the rangex g=2.5×10?3∶5×10?1.  相似文献   

6.
We consider the interaction of the partonic fluctuation of a scalar photon with an external color field to calculate the leading and next-to-leading order gluon distribution of the proton following the work done by Dosch-Hebecker-Metz-Pirner. We relate these gluon distributions to the short and long distance behavior of the cross section of an adjoint dipole scattering off a proton. The leading order result is a constant, while the next-to-leading order result shows a enhancement at small x. To get numerical results for the gluon distributions at the initial scale Q20 = 1.8 GeV2, we compute the adjoint dipole-proton cross section in the loop-loop correlation model. Quark distributions at the same initial scale are parameterized according to Regge theory. We evolve quark and gluon distributions to higher Q2 values using the DGLAP equation and compute charm and proton structure functions in the small-x region for different Q2 values.Received: 13 September 2003, Revised: 22 November 2003, Published online: 15 January 2003  相似文献   

7.
We derive the Leading-Order (LO) master equation to extract the polarized gluon distribution G(x,Q 2)=xδg(x,Q 2) from polarized proton structure function, gp1(x,Q2)g^{p}_{1}(x,Q^{2}). By using a Laplace-transform technique, we solve the master equation and derive the polarized gluon distribution inside the proton. The test of accuracy which is based in our calculations on two different methods, confirms that we achieve to the correct solution for the polarized gluon distribution. To determine the polarized gluon distribution xδg(x,Q 2) more accurately, we only need to have more experimental data on the polarized structure functions, g1p(x,Q2)g_{1}^{p}(x,Q^{2}). Our result for polarized gluon distribution is in good agreement with some phenomenological models.  相似文献   

8.
We present new parametrisations of the parton distribution functions of the photon including the first parametrisation in next-to-leading order QCD. We take into account some recent theoretical considerations pertaining to the gluon content of the photon,g γ. We argue that if an evolution is started at very lowQ 2 and a fit to allF 2 γ data performed with no constraints on the gluon distribution, then physically unreasonable gluon distributions may result. Our results support recent indications thatQ 0 2 ≤1 GeV2 is too low a value from which to start a perturbative evolution. Starting our evolution atQ 0 2 =5.3 GeV2, we evolve up inQ 2 using a modified version of Rossi's Ansatz. The limited lever arm inQ 2 leads to limited sensitivity to the QCD scale parameter Λ, though there is a preference for low values in the 0.1–0.2 GeV range. We also present new parametrisations of the singular asymptotic quark and gluon distribution functions of the photon which we believe are more accurate than those in current use.  相似文献   

9.
The Lorentz contracted form of the static wave functions is used to calculate the valence parton distributions for mesons and baryons, boosting the rest frame solutions of the path integral Hamiltonian. It is argued that nonperturbative parton densities are due to excitedmultigluon baryon states. A simplemodel is proposed for these states ensuring realistic behavior of valence and sea quarks and gluon parton densities at Q2 = 10 (GeV/c)2. Applying the same model to the proton spin problem one obtains Σ3 = 0.18 for the same Q2.  相似文献   

10.
11.
We propose a two parameter expression for the high momentum transfer behaviour of the ratio of proton form factors GM(Q2)/QE(Q2) based on perturbation theory calculations in Quantum Chromodynamics. A fit to the present experimental data and its consistency with a previous fit to the high Q2 behaviour of the Dirac form factor [1] is also discussed.  相似文献   

12.
Using recent data on deep inelastic lepton-nucleon scattering an attempt is made to extract the gluon distributionG(x, Q 2=4 GeV2) from the observed scaling violations of structure functions. The accuracy of the data allows only for a rough determination of the gluon distribution. In particular it is found that a hard gluon distributionis consistent with present measurements. Implications of the hard gluon distribution for charm production in the gluon fusion model and for the perturbative contributions to σ L T are further discussed. Finally, analytic parametrizations of the QCDx- andQ 2-dependence of quark and gluon distributions are presented facilitating further possible applications.  相似文献   

13.
The screening corrections to gluon distributions in a proton corresponding to the triple gluonic ladder diagram are estimated. They are found to be relatively small: their values does not exceed 10% of the leading order QCD gluon distribution forx?10?4 andQ 2 ?100 GeV2.  相似文献   

14.
It is important to examine the strong-coupling parameter Λ in deep-inelastic scattering, since (e.g.) the proton lifetime in grand-unified theories is quite sensitive to Λ. We show that Λ is not as small in μN scattering as previously reported. Furthermore, Λ extracted from F2(x, Q2) os highly correlated with the parameterization of the gluon distribution. Other problems arise from σL/σT assumptions.  相似文献   

15.
At HERA energies the smallx region (x?10?2) can be explored atQ 2 values large enough that leading twist QCD calculations are valid. We show how measurement of the longitudinal structure function,F L (x,Q 2), can lead to accurate measurement of the gluon structure function at such smallx values. Experimental systematic errors are discussed fully and requirements for the measurement outlined. We conclude that it should be possible to distinguish between the widely varying gluon distributions which are currently allowed.  相似文献   

16.
I present a theoretical discussion of the uncertainties related to the QCD analysis of the proton structure function F 2(x,Q 2) at small x. The role played by the ‘unphysical’ gluon density is pointed out. It is shown how the study of more observables can reduce the theoretical uncertainty and, in particular, an alternative method of analysis, based on the introduction of physical anomalous dimensions, is suggested.  相似文献   

17.
We show that the gluon helicity inside a proton and a photon can be deduced from a knowledge of a special combination of cross sections of the semi-inclusive processese+pe+π+π+... ande ++e ?e ++e ?+π+π+... Such a measurement could thus be used to check the QCD prediction that the gluon helicity increases linearly with lnQ 2.  相似文献   

18.
The gluon distributions in a proton are calculated in the region of smallx (10?4?x?10?2) and largeQ 2 taking into account the corrections which correspond to the sum of the leading powers of log 1/x beyond the leading logQ 2 approximation. It is shown that they become significant for very small values ofx only provided however that the non-leading terms in the limit of smallx are also consistently included. The leading log 1/x approximation gives the gluon distributions which can differ by a factor of 2 from their leading logQ 2 counterpart.  相似文献   

19.
We use perturbative QCD to calculate the cross sections σLT for the diffractive production of open charm (cc) from longitudinally and transversely polarised photons (of virtuality Q2) incident at high energy (√S) on a proton target. We study both the Q 2 and M 2 dependence of the cross sections, where M is the invariant mass of the cc pair. Surprisingly, the result for σT, as well as for σL, is perturbatively stable. We estimate higher-order corrections and find a sizeable enhancement of the cross sections. The cross sections depend on the square of the gluon density g(x, K2), and we show that the observation of open charm at the HERA electron-proton collider can act as a sensitive probe of the gluon distribution for x = (Q 2 + M 2)/s and scale K2 = (M 2c + )(1 + Q 2/M 2) where the average quark transverse momentum squared 〈k 2 t ~ (M 2c . As compared to diffractive J/#x03C8; production, open charm has the advantage that it is independent of the non-perturbative ambiguities arising from the J/#x03C8; wave function. We estimate the fraction of diffractive events that arise from cc¯ production.  相似文献   

20.
We present a detailed study of scaling violations for non-singlet, singlet and glue distribution functions in the framework of several approximation schemes of QCD. Our formalism consists of direct resolution of the Altarelli-Parisi type equations and leads to a simple exponential form for the function q(x, Q2). This form is very suitable for the analysis of experimental data and for the exploration of different evolution schemes. In particular, we examine the implications on the QCD scaling parameter Λ and the gluon parameter nG.  相似文献   

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