共查询到20条相似文献,搜索用时 0 毫秒
1.
The perturbative properties of parton distributions generated radiatively from a valence-like input at some low resolution scale are discussed with the aim of explaining the physical aspects underlying the reliability of the predicted distributions in the small-x region. Aspects of higher-twist (shadowing) effects as well as small-x resummations are discussed. Utilizing recent improved data atx?10?2 and a factorization scheme in which the heavy quarksc, b, ..., arenot entailed among the intrinsic (massless) parton distributions, we readjust our valencelike input and provide parametrizations of the slightly modified dynamical LO and NLO $(\overline {MS} ,DIS)$ predictions for parton distributions. 相似文献
2.
Several theoretical aspects in leading (1-loop) and higher (2-loop) order as well as various approaches of extracting leading
twist-2 parton distributions from structure function measurements are discussed and summarized. Their implications for the
small-x region (x⩽10−2) are analyzed and compared with alternative approaches where higher twist contributions (‘fans’) are added to the twist-2
LO terms in the evolution equations. The second part of these lectures deals with longitudinally polarized parton distributions
related to the structure functiong
1, in particular with various scenarios to explain the total spin structure of nucleons, including the gluon anomaly as well.
Specific (realistic) tests for discriminating between these alternatives are discussed as well asx-dependent expectations, in particular for neutron targets in connection with the Bjorken sum rule. Furthermore, various theoretical
expectations and sum rules for the transverse (chiral-even) structure functiong
2 are presented and very recent developments of transverse chiral-odd (‘transversity’) distributions are briefly discussed. 相似文献
3.
4.
5.
Dynamical parton densities, generated radiatively from valence-like inputs at some low resolution scale, are confronted with
recent small-x data on deep inelastic and other hard scattering processes. It is shown that within theoretical uncertainties our previous
(1994) dynamical/radiative parton distributions are compatible with most recent data and still applicable within the restricted
accuracy margins of the presently available next-to-leading order calculations. Due to recent high precision measurements
we also present an updated, more accurate, version of our (valence-like) dynamical input distributions. Furthermore, our perturbatively
stable parameter-free dynamical predictions are extended to the extremely small-x region, , relevant to questions concerning ultra-high-energy cosmic ray and neutrino astronomy.
Received: 22 June 1998 / Published online: 21 August 1998 相似文献
6.
C.-W. Kao 《Few-Body Systems》2008,44(1-4):107-110
Using heavy-baryon chiral perturbation theory (HBChPT), we study the leading chiral corrections to the complete set of nucleon generalized parton distributions (GPDs). 相似文献
7.
M. Diehl A. Manashov A. Schäfer 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):315-326
We analyze the moments of the isosinglet generalized parton distributions H, E,
,
of the nucleon in one-loop order of heavy-baryon chiral perturbation theory. We discuss in detail the construction of the
operators in the effective theory that are required to obtain all corrections to a given order in the chiral power counting.
The results will serve to improve the extrapolation of lattice results to the chiral limit. 相似文献
8.
M. Diehl Th Feldmann R. Jakob P. Kroll 《The European Physical Journal C - Particles and Fields》2005,39(1):1-39
We present a simple empirical parameterization of the x- and t-dependence of generalized parton distributions at zero skewness, using forward parton distributions as input. A fit to experimental data for the Dirac, Pauli and axial form factors of the nucleon allows us to discuss quantitatively the interplay between longitudinal and transverse partonic degrees of freedom in the nucleon (nucleon tomography). In particular we obtain the transverse distribution of valence quarks at given momentum fraction x. We calculate various moments of the distributions, including the form factors that appear in the handbag approximation to wide-angle Compton scattering. This allows us to estimate the minimal momentum transfer required for reliable predictions in that approach to be around
. We also evaluate the valence contributions to the energy-momentum form factors entering Jis sum rule.Received: 16 September 2004, Revised: 15 October 2004, Published online: 17 December 2004 相似文献
9.
H.L. Lai J. Huston S. Kuhlmann J. Morfin F. Olness J.F. Owens J. Pumplin W.K. Tung 《The European Physical Journal C - Particles and Fields》2000,12(3):375-392
An up-to-date global QCD analysis of high energy lepton-hadron and hadron-hadron interactions is performed to better determine
the gluon and quark parton distributions in the nucleon. Improved experimental data on inclusive jet production, in conjunction
with precise deep inelastic scattering data, place good constraints on the gluon over a wide range of x; while new data on asymmetries in Drell-Yan processes contribute to better determine the d/u ratio. Comparisons with results of other recent global analyses are made, and the differences are described. Open issues
and the general problem of determining the uncertainties of parton distributions are discussed.
Received: 7 April 1999 / Published online: 21 December 1999 相似文献
10.
Hägler P Negele JW Renner DB Schroers W Lippert T Schilling K;LHPC SESAM Collaboration 《Physical review letters》2004,93(11):112001
This work presents the first calculation in lattice QCD of three moments of spin-averaged and spin-polarized generalized parton distributions in the proton. It is shown that the slope of the associated generalized form factors decreases significantly as the moment increases, indicating that the transverse size of the light-cone quark distribution decreases as the momentum fraction of the struck parton increases. 相似文献
11.
M. Diehl A. Manashov A. Schäfer 《The European Physical Journal A - Hadrons and Nuclei》2007,31(3):335-355
We complete the analysis of twist-two generalized parton distributions of the nucleon in one-loop order of heavy-baryon chiral
perturbation theory. Extending our previous study of the chiral-even isosinglet sector, we give results for chiral-even isotriplet
distributions and for the chiral-odd sector. We also calculate the one-loop corrections for the chiral-odd generalized parton
distributions of the pion. 相似文献
12.
We analyze the recently measured first moment Г p (Q 2) of the structure functiong 1 p (x,Q 2) obtained in deep inelastic scattering of polarized electrons from polarized protons. It is shown that the recent experimental result Г p (〈Q 2〉?10 GeV2)? 0.113 implies a polarized strange quark sea whose total polarization Δs(μ2)??0.22 is comparable to Δμ(μ2)?0.74 and Δd(μ2)??0.50 already at a typically hadronic scale μ=0(1 GeV). Most remarkably, the total polarization due to quark distributions Δμ(μ2)+Δd(μ2)+Δs(μ2) practically vanishes which implies that the spin of the proton is carried by the gluons, ΔG(μ2), and/or the angular momentum of the partons. This surprising conjecture can be experimentally tested with heavy quark production in longitudinally polarized lepton-nucleon scattering. In particular the (real) photon-gluon fusion process γg→Q \(\bar Q\) provides a rather unique measure of ΔG(x,Q 2). 相似文献
13.
Using the dynamical assumption that at low resolution-energies hadrons consist of valence quarks only, we calculate uniquely nucleonic as well as pionic parton and gluon distributions within the framework of QCD, and give analytic expressions for their x- and Q2-dependence. Applications to dilepton and W-boson Drell-Yan production in pN and πN reactions are illustrated and possible applications to high-pT processes are discussed. 相似文献
14.
Determination of proton parton distribution functions is presented under the dynamical parton model assumption by applying DGLAP equations with GLR-MQ-ZRS corrections.We provide two data sets,referred to as IMParton16,which are from two different nonperturbative inputs.One is the naive input of three valence quarks and the other is the input of three valence quarks with flavor-asymmetric sea components.Basically,both data sets are compatible with the experimental measurements at high scale(Q~2 2 GeV~2).Furthermore,our analysis shows that the input with flavor-asymmetric sea components better reproduces the structure functions at high Q~2.Generally,the parton distribution functions obtained,especially the gluon distribution function,are good options for inputs to simulations of high energy scattering processes.The analysis is performed under the fixed-flavor number scheme for nf = 3,4,5.Both data sets start from very low scales,around 0.07 GeV~2,where the nonperturbative input is directly connected to the simple picture of the quark model.These results may shed some lights on the origin of the parton distributions observed at high Q~2. 相似文献
15.
16.
Considering the nucleon as consisting entirely of its valence quarks confined independently in a scalar-vector harmonic potential;
unpolarized structure functions F
1(x, μ
2) and F
2(x, μ
2) are derived in the Bjorken limit under certain simplifying assumptions; from which valence quark distribution functions
u
v(x, μ
2) and d
v(x, μ
2) are appropriately extracted satisfying the normalization constraints. QCD-evolution of these input distributions from a
model scale of μ
2=0.07 GeV2 to a higher Q
2 scale of Q
0
2
=15 GeV2 yields xu
v(x, Q
0
2
) and xd
v(x, Q
0
2
) in good agreement with experimental data. The gluon and sea-quark distributions such as G(x, Q
0
2
) and q
s(x, Q
0
2
) are dynamically generated with a reasonable qualitative agreement with the available data; using the leading order renormalization
group equations with appropriate valence-quark distributions as the input. 相似文献
17.
A. H. Mueller 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):527-530
The idea of parton saturation is reviewed. The use of saturation in describing HERA data is discussed in the context of the McLerran-Venugopalan and Golec-Biernat Wüsthoff models. Applications of saturation ideas to RHIC data are reviewed and a comparison between applications at HERA and at RHIC is given.Received: 30 September 2002, Published online: 22 October 2003PACS:
11.10.-z Field theory 相似文献
18.
P. N. Harriman 《Zeitschrift fur Physik C Particles and Fields》1992,55(3):449-453
We show that knowledge of thex 1 andx 2 dependence of the ratio of Drell-Yan cross-sections measured on heavy nuclei and deuterium can give us information about the origin of the EMC effect. Conversely, we show that an understanding of the EMC effect, together with (non-ratio) Drell-Yan data, can provide us with a way of discriminating between candidates for nucleon parton distributions. 相似文献
19.
A selected review of topics at the border of hard and soft physics is given. Particular emphasis is placed on diffraction
dissociation at Fermilab and HERA. Recently, significant differences between diffraction dissociation at HERA and at Fermilab
have become apparent. This may suggest that one already is reaching nonlinear (unitarity) effects which are extending from
the soft physics region into the semihard regime of QCD.
Received: 3 November 1997 相似文献
20.
We study the effects of light gluinos with
GeV on the nucleon parton densities and the running of
S
. It is shown that from the available high-statistics DIS data no lower bound on the gluino mass can be derived. Also in the new kinematical region accessible at HERA the influence of such light gluinos on structure functions is found to be very small and difficult to detect. For use in more direct searches involving final state signatures we present a radiative estimate of the gluino distribution in the nucleon.Work supported by the German Federal Ministry for Research and Technology under contract No. 05 6MU93P 相似文献