Charged particle cross sections in photoproduction and extraction of the gluon density in the photon

Photoproduction data collected with the H1 detector at HERA in 1994 are used to study the cross-sections for inclusive charged particle production and the structure of the photon. The differential cross-sections , for in the HERA laboratory frame, and for GeV/c and GeV/c have been measured. Model calculations of these cross-sections, based on perturbative QCD, indicate that the results are sensitive to the parton densities of the photon as well as to higher order effects, which are phenomenologically treated by multiple interactions. This sensitivity is exploited to determine the leading order distribution of partons in the photon using a new method based on high charged particles. The gluon content of the photon is extracted and found to rise with decreasing . Received: 8 October 1998 / Published online: 8 September 1999     

The QCD generalized parton model and a next-to-leading approximation of the gluon density

Using recent neutrino data, we calculate in the framework of the generalized parton model the modification of the gluon density caused by next-to-leading logarithmic effects. We find that they are of the same order of magnitude as the experimental uncertainties, and that the gluon density tends to be more peaked towards small x.     

The dual parametrization for gluon GPDs

We consider the application of the dual parametrization for the case of gluon GPDs in the nucleon. This provides opportunities for the more flexible modeling of unpolarized gluon GPDs in a nucleon which in particular contain the invaluable information on the fraction of nucleon spin carried by gluons. We perform the generalization of the Abel transform tomography approach for the case of gluons. We also discuss the skewness effect in the framework of the dual parametrization. We strongly suggest to employ the fitting strategies based on the dual parametrization to extract the information on GPDs from the experimental data.     

Saturation of gluon density and soft pp collisions at LHC

We find the relation of the unintegrated gluon distribution at low intrinsic transverse momenta to the inclusive spectrum of the hadrons produced in pp collision at LHC energies in the mid-rapidity region and low hadron transverse momenta. It allows us to study the saturation of the gluon density at low Q ² more carefully and find the saturation scale that does not contradict to both the LHC and HERA data.     

Evolution of the gluon density in x with a running coupling constant

We describe the calculation of the evolution of the gluon density in from an initial value to smaller values, up to in the hard pomeron formalism with a running coupling introduced on the basis of the bootstrap equation. The obtained gluon density is used to calculate the singlet part of the proton structure function. Comparison with experiment and the results following from the fixed coupling evolutio n is made. Received: 10 June 1997 / Revised version: 20 August 1997 / Published online: 24 April 1998     

Measurement of the longitudinal structure function and the smallx gluon density of the proton

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.     

Particle production at high gluon density: from ep to AA

We review the physics of gluon saturation and some of its phenomenological applications.     

剪切波变换在星点提取中的应用

为了实现高精度和高准确性的星图识别和姿态确定,本文对星点提取算法进行了研究,将剪切波变换应用到星点提取技术中。首先,通过利用剪切波变换对星图进行分解,得到不同尺度、不同方向的系数;然后,对剪切系数进行阈值处理并重构得到去噪后的星图,再对重构星图进行顶帽变换和自适应阈值处理,完成星图滤波;最后,通过质心误差补偿法提取星点的坐标,有效地完成星点提取。实验结果表明,采用剪切波变换的星图滤波对噪声去除非常有效;质心误差补偿法的误差在0.003左右,明显优于传统的质心法,基本满足星敏感器的精度高和抗干扰能力强等要求。     

The gluon condensate and the deconfinement transition

The gluon condensate of dimension 4 is shown to stay unchanged through the deconfining phase transition.     

The gluon propagator in the Coulomb gauge

We give the results for all the one-loop propagators, including finite parts, in the Coulomb gauge. In the finite parts we find new non-rational functions in addition to the single logarithms of the Feynman gauge. Of course, the two gauges must agree for any gauge invariant function.Received: 14 November 2003, Revised: 20 July 2004, Published online: 24 September 2004     

Lumped-element technique for the measurement of complex density.

A novel lumped-element technique is employed to measure the complex density of a gas in circular pores. The complex density expresses the geometry-dependent viscous coupling between the gas and the pore walls and is related to the thermoacoustic function f(mu), or equivalently, F(lambdaV). The acoustic impedance of a compliant region coupled to a pore (or pore-array) is measured and the impedance of the compliant region is subtracted to yield the impedance of the pore(s) alone, which is directly related to F(lambdaV). Pores of different lengths are measured in order to eliminate end effects. Working down to very low frequencies achieves a wide range of values for the ratio of the viscous penetration depth to the mean pore size. The results agree very well with analytical solutions for circular pores. The technique is also applied to two porous foam materials. Comparing the results to previous measurements of the complex compressibility, it is shown that two different shape factors (or equivalently, characteristic dimensions) are required to account for the data.     

The color structure of gluon emission

The color structure of an arbitrary QCD diagram is studied. A basis for the color form factors of a generic amplitude is suggested, in which all the coherence effects are automatically and simply accounted for to the leading order in N_c. Some applications of this formalism are given for tree-level amplitudes describing processes with one or two pairs of fermions and radiation of gluons and photons. The different coherence properties of the abelian and non-abelian radiation are exhibited with some analytic and explicit examples, leading to the appearance of string-effect-like correlations for hard non-abelian radiation.     

从流密度的Fourier分量出发民出多极矩表达式

从运动电荷产生的流密度入手，通过Ｆｏｕｒｉｅｒ变换引入各级多极矩的表达式。     

The shape of polarized gluon distributions

The recent high precision SMC data on polarized μp scatterings have again confirmed that very little of the proton spin is carried by quarks. To unravel the mystery of the proton spin structure, it is quite important to know the behavior of the polarized gluon distribution. By using the positivity condition of distribution functions together with the unpolarized and polarized experimental data, we restrict thex dependence of the polarized gluon distribution.     

从流密度的Fourier分量出发导出多极矩表达式

从运动电荷产生的流密度入手,通过Fourier变换引入各级多极矩的表达式.     

Effective-potential model for the self-interacting gluon gas

The thermodynamic behaviour of a pure gluon-plasma is investigated within the context of an effective-interaction model and the relativistic Landau theory of quantum liquids. Agreement is sought withSU (2) andSU (3) lattice computer simulations and asymptotic perturbation theory. For bothSU (2) andSU (3) the available data are fitted rather well by a logarithmically screened Coulomb potential. The difference in critical behaviour ofSU (2) andSU (3) can also be modelled. Contact is made with the Bare Bones bag model, yielding a bag pressure ofB ^1/4≈200 MeV.     

The 3 gluon decay of quarkonium

We discuss the process $$e^ + e^ - \to Q\bar Q \to 3gluons \to 3jets$$ with attention to the kinematics and observability of the jets. We also show how to check the gluon spin through jet or hadron angular distributions. Gluon flavor can be checked by looking for quantum number correlations between opposite jets. We predict that correlations exist off resonance for \(e^ + e^ - \to q\bar q\) , but not on resonance for \(Q\bar Q \to 3g\) .