The problem of kinematic effects in the gluon and color dipole cascades is addressed in the large N_c limit of SU(N_c) Yang--Mills theory. We investigate the tree level multi-gluon components of the gluon light cone wave functions in the light cone gauge keeping the exact kinematics of the gluon emissions. We focus on the components with all helicities identical to the helicity of the incoming gluon. The recurrence relations for the gluon wave functions are derived. In the case when the virtuality of the incoming gluon is neglected the exact form of the multi-gluon wave function is obtained. Furthermore, we propose an approximate scheme to treat the kinematic effects in the color dipole evolution kernel. The new kernel entangles longitudinal and transverse degrees of freedom and leads to a reduced diffusion in the impact parameter. When evaluated in the next-to-leading logarithmic (NLL) accuracy, the kernel reproduces the correct form of the double logarithmic terms of the dipole size ratios present in the exact NLL dipole kernel. Finally, we analyze the scattering of the incoming gluon light cone components off a gluon target and the fragmentation of the scattered state into the final state. The equivalence of the resulting amplitudes and the maximally-helicity-violating amplitudes is demonstrated in the special case when the target gluon is far in rapidity from the evolved gluon wave function.
We present nonlinear (NL) and higher twist (HT) corrections to the color dipole model (CDM) bounds at low values of $x$ and $Q^{2}$ using the parameterization method. Consistency between the bounds at this region describe that a transition from the linear to the nonlinear behavior is dependence on the behavior of the gluon distribution function. The parameters in the color dipole model are comparable with the color dipole bounds at low values of $Q^{2}$. Consequently, the obtained reduced cross sections at low and moderate $Q^{2}$ values due to the NL+HT effects show a good agreement with the …
We evaluate the unintegrated gluon distribution of the proton starting from a parametrization of the color dipole cross section including DGLAP evolution and saturation effects. To this end, we perform the Fourier-Bessel transform of $σ(x,r)/α(r)$. At large transverse momentum of gluons we match the so-obtained distribution to the logarithmic derivative of the collinear gluon distribution. We check our approach by calculating the proton structure function $F_L(x,Q^2)$ finding good agreement with HERA data.
We present a study of the impact of the expansion of deconfined medium on single-gluon emission spectra and the jet suppression factor ($Q_{AA}$) within the BDMPS-Z formalism. These quantities are calculated for three types of media (static medium, exponentially decaying medium and Bjorken expanding medium). The distribution of medium-induced gluons and the jet $Q_{AA}$ are calculated using the evaluation of in-medium evolution with splitting kernels derived from the gluon emission spectra. Scaling behavior of splitting kernels is derived for low-x and high-x regimes in the asymptote of large …
Going beyond the simplified gluonic cascades, we introduce both gluon and quark degrees of freedom for partonic cascades inside the medium. We then solve the set of coupled evolution equations numerically with splitting kernels calculated for static, exponential, and Bjorken expanding media to arrive at medium-modified parton spectra for quark and gluon initiated jets. Using these, we calculate the inclusive jet $R_{AA}$ where the phenomenologically driven combinations of quark and gluon jet fractions are included. Then, the rapidity dependence of the jet $R_{AA}$ is examined. We also study th…
We investigate the radiative break-up of a highly energetic quark or gluon in a high-temperature QCD plasma. Within an inertial range of momenta $T \ll ω\ll E$, where $E$ denotes the energy of the original hard parton (jet) and $T$ the temperature of of the medium, we find that, as a result of the turbulent nature of the underlying parton cascade, the quark to gluon ratio of the soft fragments tends to a universal constant value that is independent of the initial conditions. We discuss implications of this result to jet quenching physics and the problem of thermalization of the quark-gluon pla…
In this paper we present solutions of evolution equations for inclusive distribution of gluons as produced by jet traversing quark-gluon plasma. We reformulate the original equations in such a form that the virtual and unresolved-real emissions as well as unresolved collisions with medium are resummed in a Sudakov-type form factor. The resulting integral equations are then solved most efficiently with use of newly developed Markov Chain Monte Carlo algorithms implemented in a dedicated program called MINCAS. Their results for a gluon energy density are compared with an analytical solution and …
Two-loop matching of the dipole operators for $b \to s γ$ and $b \to s gluon$
对于$b \to s γ$的分支比的完整的次领先对数计算，在匹配尺度$μ=m_W$下对偶极算子的威尔逊系数（$O_7,O_8$）的阶$α_s$校正是至关重要的成分。考虑到现象学的相关性以及到目前为止只有一个小组[1]完成了这种双循环计算的事实，我们使用不同的方法进行了详细的重新计算。我们的结果与文献[1]中的结果完全一致。
The ratio of the cross sections for the transversely and longitudinally virtual photon polarizations, $σ^{γ^{*}p}_{L/T}$, at high photon-hadron energy scattering is studied. I investigate the relationship between the gluon distribution obtained using the color dipole model and standard gluons obtained from the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution and the Altarelli-Martinelli equations. It is shown that the color dipole bounds are dependent on the gluon distribution behavior. This behavior is considered by the expansion and Laplace transform methods. Numerical calculatio…
We present an analysis of the most precise set of HERA data within the color dipole formalism, by using an analytical gluon density, based on the double-logarithm approximation of the DGLAP equations in the asymptotic limit of the scaling variable, $σ=\log{(1/x)}\log{(\log{(Q^2/Q_ 0^2)})}\rightarrow \infty$. Fits to data, including charm and bottom quarks are performed and demonstrate the efficiency of the model in describing the reduced cross section, $σ_{r}$, in the wide range $Q^2:(1.5,500)$ GeV$^2$ for two dipole models including parton saturation effects. We also give predictions to $F_{2…
Gluon saturation and Feynman scaling in leading neutron production
在本文中，我们扩展的颜色偶极子形式主义的领导中子生产的研究在$e + p \rightarrow e + n + X$碰撞在高能量和估计相关的可观测量，这是在HERA测量，并可能在未来的电子-质子（$ep$）对撞机进行分析。特别地，我们计算了领先中子的Feynman $x_F$分布，它用π介子通量和光子-π介子总截面表示。在色偶极理论中，光子-π散射截面用偶极-π散射振幅来描述，它包含了高能QCD动力学和胶子饱和效应的信息。我们考虑不同的模型的散射振幅，这已被用来描述包容性和衍射$ep$ HERA数据。此外，我们的预测与描述的π通量的模型依赖性进行了详细的分析。我们发现最近公布的H1领先中子谱可以用色偶极形式再现，这些谱可以帮助我们更清楚地观察胶子饱和效应在未来的$ep$对撞机。
Constraining the Dipole Amplitude at NLO with HERA Data and Probing Gluon Saturation in SIDIS
Department of Physics, University of Jyv\"askyl\"a, P.O. Box 35, 40014 University of Jyv\"askyl\"a, Finland；Helsinki Institute of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
Detailed insight into the interplay between parton energy loss and the way deconfined medium created in heavy-ion collisions expands is of great importance for improving the understanding of the jet quenching phenomenon. In this paper we study the impact of the expansion of deconfined medium on the single-gluon emission spectrum, its resummation and the jet suppression factor ($Q_{AA}$) within the BDMPS-Z formalism. We calculate these quantities for three types of expansion scenarios, namely static, exponentially decaying and Bjorken expanding media. The distribution of medium-induced gluons i…
