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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.
4.
We determined the saturation exponent of the gluon distribution using the solution of the QCD nonlinear Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (NLDGLAP) evolution equation at small x . The very small-x behavior of the gluon distribution is obtained by solving the Gribov, Levin, Ryskin, Mueller and Qiu (GLR-MQ) evolution equation with the nonlinear shadowing term incorporated. The form of the initial condition for the equation is determined. We find, with decreasing x , the emergence of a singular behavior and the eventual taming (at R = 5 GeV^-1) and the essential taming (at R = 2 GeV^-1) of this singular behavior by the shadowing term. The nonlinear gluon density functions are calculated and compared with the results for the integrated gluon density from the Balitsky-Kovchegov (BK) equation for the different values of Q2. It is shown that the results for the gluon density function are comparable with the results obtained from the BK equation solution. Also we show that for each x , the Q2-dependence of the data is well described by gluon shadowing corrections to the GLR-MQ equation. The resulting analytic expression allows us to predict the logarithmic derivative \( {\frac{{\partial F^{s}_{2} (x,Q^{2})}}{{\partial \ln Q^{2}}}}\) and to compare the results with H1 data and a QCD analysis fit.  相似文献   

5.
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   

6.
The gluon and sea distributions of the pion are uniquely determined by the requirement of avalence-like structure of the input parton distributions at some low resolution scale. These (dynamical) results are obtained with practically no free parameters, just using the experimentally determined pionic valence distribution combined with the constraints for the pionic gluon distribution provided by direct-γ data. Simple parametrizations of the resulting parton distributions are presented in the range 10?5?x<1 and 0.3?Q 2?108 GeV2 as obtained from the leading-and higher-order evolution equations.  相似文献   

7.
The gluon and antiquark distributions of the nucleon are generated radiatively using the assumption that at some low resolution scale the nucleon consists entirely of valence quarks and valence-like gluons. The agreement between the uniquely predicted gluon and sea distributions and the available data on deep inelastic structure functions (including also recent low-Q 2 measurements) and direct-photon production is demonstrated and discussed in detail. Simple parametrizations of the resulting (positive definite!) parton distributions are presented in the range 10?4?x≦1 and 0.2?Q 2?106 GeV2 as obtained according to the leading- and higher-order renormalization group evolution equations.  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.
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   

10.
M.K. Chase 《Nuclear Physics B》1980,174(1):109-122
We calculate the Q2 evolution of the quark-antiquark and gluon-gluon components of helicity-zero, flavour and colour singlet wave functions by summing diagrams to all orders in axial gauge QCD perturbation theory in the leading logarithm approximation. We find that Gegenbauer moments of these components have exactly the same scale-breaking behaviour as moments of singlet quark and gluon distribution functions in leptoproduction. The resulting singlet wave function is used to calculate the amplitudes for quark-antiquark and gluon-gluon jet production in off-shell photon-photon collisions.  相似文献   

11.
The solutions of Lipatov-Fadin-Kuraev equation (LFK) within LLX approximation for gluon distributions are studied. The results are based on the semiphenomenological boundary conditions taken from LLQ2 analysis. We find, that pure theoretical LLX approach can reproduce the form of singular small-x behaviour of gluon and sea-quark distributions obtained within LLQ2A with singular input parametrizations. Some remarks about shadowing corrections are presented.  相似文献   

12.
U. Jamil  J. K. Sarma 《Pramana》2008,71(3):509-519
Evolution of gluon distribution function from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equation in next-to-leading order (NLO) at low-x is presented assuming the Regge behaviour of quark and gluon at this limit. We compare our results of gluon distribution function with MRST2004, GRV98LO and GRV98NLO parametrizations and show the compatibility of Regge behaviour of quark and gluon distribution functions with perturbative quantum chromodynamics (PQCD) at low-x.   相似文献   

13.
U. Jamil  J. K. Sarma 《Pramana》2007,69(2):167-180
In this paper, t and x-evolutions of gluon distribution function from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equation in leading order (LO) at low-x are presented assuming the Regge behaviour of quarks and gluons at this limit. We compare our results of gluon distribution function with MRST 2001, MRST 2004 and GRV 1998 parametrizations and show the compatibility of Regge behaviour of quark and gluon distribution functions with perturbative quantum chromodynamics (PQCD) at low-x. We also discuss the limitations of Taylor series expansion method used earlier to solve DGLAP evolution equations in the Regge behaviour of distribution functions.   相似文献   

14.
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   

15.
We show that it is possible to use hard-Pomeron behavior to the gluon distribution and singlet structure function at low x. We derive a second-order independent differential equation for the gluon distribution and the singlet structure function. In this approach, both singlet quarks and gluons have the same high-energy behavior at small x. These equations are derived from the next-to-leading order DGLAP evolution equations. All results can be consistently described in the framework of perturbative QCD, which shows an increase of gluon distribution and singlet structure functions as x decreases.  相似文献   

16.
We present a set of independent formulas to extract the gluon distribution and the singlet structure function from its derivatives with respect to lnQ 2 in the next-to-leading order of perturbation theory at low x based on a hard Pomeron exchange. In this approach, both singlet quarks and gluons have the same high-energy behavior at small x. This approach requires the QCD input parameterizations for independent DGLAP evolutions, which we calculated numerically and compared with the MRST, GRV, and DL models. The Pomeron has a hard nature. Its evolution gives a good fit to the experimental data. The values obtained are in the range 10−4x ≤ 10−2 at Q 2 = 20 GeV2. The text was submitted by the author in English.  相似文献   

17.
The aim of the present paper is to calculate longitudinal structure function F L from QCD (Quantum Chromodynamics) evolution equation in next-to-next-to-leading order (NNLO) at small-x. The calculation of F L is important for the phenomenological study of gluon distribution function inside the nucleon. Here we use Taylor Series Expansion method to solve the evolution equation for small-x and thus obtain t-evolution of F L structure function. The calculated results are compared with H1 and ZEUS data and results of Block and Donnachie-Landshoff (DL) models.  相似文献   

18.
19.
We consider influence of gluon shadowing effects on the proton structure function in the smallx interval. These effects are noticeable in the HERA kinematical region. The explicit form of the gluon distribution in the proton depend 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   

20.
Recent experimental results on the EMC effect are presented. The ratios of structure functions for nuclei and deuterium measured by the two muon experiments at CERN show a clear enhancement of a few percent forx<0.25. Atx below 0.05 substantial shadowing with littleQ 2 dependence has been observed by a dedicated low angle experiment of the EMC. No significant nuclear mass dependence ofRLT has been seen in the SLAC experiment E 140. There are several indications that theQ 2 evolution of nuclear structure functions deviates from the expectations of perturbative QCD and that the gluon distribution in nuclei is harder than in free nucleons. This is possibly caused by nucleon-nucleon correlations on the quark-gluon level. Many aspects of the EMC effect are presently being investigated by the high energy muon experiment of the NMC collaboration at CERN and a Drell-Yan experiment at FNAL. First results can be expected soon. They will help to develop a better understanding of nuclear effects in quark and gluon distributions.  相似文献   

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