共查询到20条相似文献,搜索用时 31 毫秒
1.
Utilizing very recent deep inelastic scattering measurements, a QCD analysis of proton structure function ${F_{2}^{p} (x,Q^2)}$ is presented. A wide range of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data used in order to extract an updated set of parton distribution functions (PDFs). The HERA ‘combined’ data set on ${\sigma_{r,NC}^\pm (x,Q^2)}$ together with all available published data for heavy quarks ${F_2^{c,b}(x,Q^2)}$ , longitudinal F L (x, Q 2) and also very recent reduced DIS cross section ${\sigma_{r,NC}^\pm (x,Q^2)}$ data from HERA experiments are the input in the present next-to-leading order (NLO) QCD analysis which determines a new set of parton distributions, called ${{\tt KKT11C}}$ . The extracted PDFs in the ‘fixed flavour number scheme’ (FFNS) are in very good agreement with the available theoretical models. 相似文献
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Based on relativistic constituent quark (RCQ) model, the electric
and magnetic form factors are analyzed. The ratio of the two form
factors for the proton $G_{E_p}/G_{M_p}$, which is an image of its
charge and magnetization distributions, is calculated in the
light-front formulism of RCQ model. Recently, this ratio was
measured at the Thomas Jefferson National Accelerator Facility
(JLab) using the polarization technique. The new data presented
span the range 3.5 GeV2<Q2<5.6 GeV2
and are well described by a linear Q2 fit. Also, the ratio
$\sqrt{Q^{2}}F_{2p}/k_{p}F_{1p}$ reaches a constant value while
Q2 becomes larger than 2 (GeV)2. Our calculation results
are presented and appear to be consistent with
the experimental ones. 相似文献
5.
M. Braun 《The European Physical Journal C - Particles and Fields》1999,6(2):343-348
In the hard pomeron model consequences are studied which follow from the recently obtained form of the diffractive amplitude for the double scattering on the nucleus and the related EMC effect at small x. It is shown that at large Q2Q^2 to the double scattering contribution to the latter falls as Q-0.6338Q^{-0.6338} and in all probability dominates the total effect. 相似文献
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In this paper we demonstrate that the selection of events with different multiplicities of produced particles, leads to the violation of the azimuthal angular symmetry, \(\phi \rightarrow \pi - \phi \). We find for LHC and lower energies, that this violation can be so large for the events with multiplicities \(n \ge 2 \bar{n}\), where \(\bar{n}\) is the mean multiplicity, that it leads to almost no suppression of \(v_n\), with odd n. However, this can only occur if the typical size of the dipole in DIS with a nuclear target is small, or \(Q^2 \,>\,Q^2_s\left( A; Y_{\mathrm{min}},b\right) \), where \(Q_s\) is the saturation momentum of the nucleus at \(Y = Y_{\mathrm{min}}\). In the case of large sizes of dipoles, when \(Q^2 \,<\,Q^2_s\left( A; Y_{\mathrm{min}},b\right) \), we show that \(v_n =0\) for odd n. Hadron-nucleus scattering is discussed. 相似文献
8.
We discuss \({(\pi^{0}, \eta, \eta') \to \gamma^{*}\gamma}\) transition form factors using the light-front quark model. Our discussion includes the analysis of the mixing angles for \({\eta-\eta'}\). Our results for \({Q^{2} F_{(\pi^0,\eta,\eta')\to\gamma^*\gamma}(Q^2)}\) show scaling behavior for high Q2 consistent with pQCD predictions. 相似文献
9.
S. S. Agaev N. G. Stefanis 《The European Physical Journal C - Particles and Fields》2004,32(4):507-528
Employing the standard hard-scattering approach (HSA) in conjunction with the running coupling (RC) method, the latter joined with the infrared renormalon calculus, we compute power-suppressed corrections
to the massless
-meson-virtual-gluon transition form factor (FF)
. Contributions to the form factor from the quark and gluon components of the
meson are taken into account. Analytic expressions for the FFs
and
are also presented, as well as Borel transforms
and resummed expressions. It is shown that except for
, the Borel transform contains an infinite number of infrared renormalon poles. It is demonstrated that in the explored range of the total gluon virtuality
, power corrections found with the RC method considerably enhance the FF
relative to results obtained only in the context of the standard HSA with a frozen coupling.Received: 19 May 2003, Revised: 24 October 2003, Published online: 8 December 2003Permanent address: S.S. Agaev: High Energy Physics Lab., Baku State University, Z. Khalilov St. 23, 370148 Baku, Azerbaijan 相似文献
10.
A calculation of the non-singlet part of spin dependent structure function, \(xg_{1}^{NS}(x,Q^{2})\) and associated sum rule, the Bjorken Sum rule up to next-next-to-leading order(NNLO) is presented. We use a unified approach incorporating Regge theory and the theoretical framework of perturbative Quantum Chromodynamics. Using a Regge behaved model with Q 2 dependent intercept as the initial input, we have solved the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equation up to NNLO at small-x for \(xg_{1}^{NS}(x,Q^{2})\) and the solutions are utilised to calculate the polarised Bjorken sum rule(BSR). We have also extracted the higher twist contribution to BSR based on a simple parametrisation. These results for both of \(xg_{1}^{NS}(x,Q^{2})\) and BSR, along with higher twist corrections are observed to be consistent with the available data taken from SMC, E143, HERMES, COMPASS and JLab experiments. In addition, our results are also compared with that of other theoretical and phenomenological analysis based on different models and a very good agreement is also observed in this regard. Further a very good consistency between our calculated results and theoretical QCD predictions of BSR is also achieved. 相似文献
11.
An exact expression for the leading-order (LO) gluon distribution function G(x,Q 2)=xg(x,Q 2) from the DGLAP evolution equation for the proton structure function $F_{2}^{\gamma p}(x,Q^{2})$ for deep inelastic γ * p scattering has recently been obtained (Block et al., Phys. Rev. D 79:014031, 2009) for massless quarks, using Laplace transformation techniques. Here, we develop a fast and accurate numerical inverse Laplace transformation algorithm, required to invert the Laplace transforms needed to evaluate G(x,Q 2), and compare it to the exact solution. We obtain accuracies of less than 1 part in 1000 over the entire x and Q 2 spectrum. Since no analytic Laplace inversion is possible for next-to-leading order (NLO) and higher orders, this numerical algorithm will enable one to obtain accurate NLO (and NNLO) gluon distributions, using only experimental measurements of $F_{2}^{\gamma p}(x,Q^{2})$ . 相似文献
12.
Robert Eckardt Jörg Hansper Manfred F. Gari 《Zeitschrift für Physik A Hadrons and Nuclei》1992,343(4):443-449
In a re-analysis of nucleon form factors in perturbative quantum chromodynamics we examine the
-dependence of the nucleon quark distribution amplitude by means of some model distribution amplitudes. We point out some problems that arise in the determination of the
-evolution of the distribution amplitude. Our suggestions to cure these problems are discussed and resulting nucleon quark distribution amplitudes are presented. These give reasonable agreement with the available data for the form factors.Work is supported by Deutsche Forschungsgemeinschaft (Ga 153-13-1) and partially by NATO (0581/87) 相似文献
13.
We propose an analytical solution for DGLAP evolution equations with polarized splitting functions at the Leading Order (LO) approximation based on the Laplace transform method. It is shown that the DGLAP evolution equations can be decoupled completely into two second order differential equations which then are solved analytically by using the initial conditions \(\delta F^{\mathrm {S}}(x,Q^{2})=\mathcal {F}[\partial \delta F^{\mathrm {S}}_{0}(x), \delta F^{\mathrm {S}}_{0}(x)]\) and \({\delta G}(x,Q^{2})=\mathcal {G}[\partial \delta G_{0}(x), \delta G_{0}(x)]\). We used this method to obtain the polarized structure function of the proton as well as the polarized gluon distribution function inside the proton and compared the numerical results with experimental data of COMPASS, HERMES, and AAC’08 Collaborations. It was found that there is a good agreement between our predictions and the experiments. 相似文献
14.
The spin-Hamiltonian parameters (zero-field splitting D, g-factors g //, g ⊥ and hyperfine structure constants A //, A ⊥) of Cr3+ and Mn4+ ions at the trigonal Ga3+ site of Ca3Ga2Ge3O12 (CGGG) garnet crystals are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, besides the contributions to spin-Hamiltonian parameters from the crystal-field (CF) mechanism in the frequently applied CF theory, those from the charge-transfer (CT) mechanism (which is neglected in CF theory) are taken into account. The calculated results are in reasonable agreement with the experimental values. The defect structures of Cr3+ and Mn4+ impurity centers in CGGG crystals are also obtained from the calculations. The calculations show that the relative importance of CF mechanism (characterized by $ \left| {{{Q^{\text{CT}} } \mathord{\left/ {\vphantom {{Q^{\text{CT}} } {Q^{\text{CF}} }}} \right. \kern-0pt} {Q^{\text{CF}} }}} \right| $ , where $ Q = D,\;\Delta g_{\rm{//}} ,\;\Delta g_{ \bot } ,\;A_{\rm{//}}^{(2)} or\;A_{ \bot }^{(2)} $ ) for Mn4+ center in CGGG is larger than that for Cr3+ center. So, for the high valence state dn ions in crystals, the reasonable calculations of spin-Hamiltonian parameters should consider the contributions due to both the CF and CT mechanisms. 相似文献
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《Zeitschrift fur Physik C Particles and Fields》1997,74(1):49-55
We have studied azimuthal correlations in singly-tagged e+e? → e+e?μ+μ? events at an average Q 2 of 5.2 GeV2. The data were taken with the OPAL detector at LEP at e+e? centre-of-mass energies close to the Z0 mass, with an integrated luminosity of approximately 100 pb?1. The azimuthal correlations are used to extract the ratio $F_{B}^{αmma}/F_{2}^{αmma}$ of the QED structure functions $F_{B}^{αmma}(x,Q^{2})$ and $F_{2}^{αmma}(x,Q^{2})$ of the photon. In leading order and neglecting the muon mass $F_{B}^{αmma}$ is expected to be identical to the longitudinal structure function $F_{L}^{αmma}$. The measurement of $F_{B}^{αmma}/F_{2}^{αmma}$ is found to be significantly different from zero and to be consistent with the QED prediction. 相似文献
17.
G. R. Boroun 《The European Physical Journal A - Hadrons and Nuclei》2009,42(2):251-255
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
18.
Alexander Cardona Catherine Ducourtioux Sylvie Paycha 《Communications in Mathematical Physics》2003,242(1-2):31-65
-regularized traces, resp. super-traces, are defined on a classical pseudo-differential operator A by:
where f.p. refers to the finite part and Q is an (invertible and admissible) elliptic reference operator with positive order. They are commonly used in quantum field theory in spite of the fact that, unlike ordinary traces on matrices, they are neither cyclic nor do they commute with exterior differentiation, thus giving rise to tracial anomalies. The purpose of this article is to show, on two examples, how tracial anomalies can lead to anomalous phenomena in quantum field theory. 相似文献
19.
Carlos A. Ballon-Bayona Henrique Boschi-Filho Nelson R. F. Braga 《Few-Body Systems》2012,52(3-4):243-248
We study Drell-Yan process in proton–proton collisions through the exchange of vector mesons using the holographic hard wall model to describe the dynamics and interactions of vector mesons and baryons. We estimate the angular parameters λ,?μ, ν of the produced dileptons in a region of ${q_{T}^2 << Q^{2}}$ , where the effective coupling of perturbative QCD is large due to logarithm corrections. 相似文献
20.
The hadronic photon structure function
is measured from data taken with the ALEPH detector at LEP. At centre-of-mass energies between
and
an integrated luminosity of
is analyzed in two ranges of Q2 with
GeV2 and 67.2 GeV2. Detector effects and acceptance are corrected for with a Tikhonov unfolding procedure. The results are compared to theoretical predictions and measurements from other experiments.Received: 12 June 2003, Published online: 11 August 2003 相似文献