arXiv subjects
Publications and source records attributed to Bo-Wen Xiao.
We discuss the behaviour of R(pA), the ratio of the unintegrated gluon distribution of a nucleus over the unintegrated gluon distribution of a proton scaled up by A^{1/3}, at high energy and fixed coupling. We show that R(pA) exhibits a rising gluon shadowing with growing rapidity, approaching 1/A^{1/3} at asymptotic rapidity, which means total gluon shadowing due to gluon number fluctuations or Pomeron loops.
We discuss a new physical phenomenon for R_pA in the fixed coupling case, the total gluon shadowing, which arises due to the effect of gluon number fluctuations.
Having calculated the light-cone wave function of the pseudoscalar meson by using two equivalent and fully covariant methods, we generalize such methods to the valence Fock states of the vector meson in the light-cone formalism. We investigate the decay constant of the $ρ$ meson $f_ρ$, the $γ^{\ast} π\to ρ$ and $γ^* ρ\to π$ transition form factors and especially the transition magnetic moments. By using two groups of constraint parameters, we predict the space-like and time-like form factors $F_{πρ}(Q^2)$ and $F_{ρπ}(Q^2)$ at low and moderate energy scale and the electromagnetic radius of these transition processes. In addition, we extend our calculation to $γ^* π\to ω$ space-like and time-like form factors by using the same sets of parameters.
We show a new physical phenomenon expected for the ratio R_{pA} of the unintegrated gluon distribution of a nucleus over the unintegrated gluon distribution of a proton scaled up by the atomic factor A^{1/3} in the fluctuation-dominated (diffusive scaling) region at high energy. We calculate the dependence of R_{pA} on the atomic number A, the rapidity Y and the transverse gluon momentum k_{\perp}. We find that R_{pA} exhibits an increasing gluon shadowing with growing rapidity, approaching 1/A^{1/3} at asymptotic rapidities which means total gluon shadowing, due to the effect of gluon number fluctuations or Pomeron loops. The increase of R_{pA} with rising gluon momentum decreases as the rapidity grows. In contrast, in the geometric scaling region where the effect of fluctuations is negligible, the ratio R_{pA} shows only partial gluon shadowing in the fixed-coupling case, basically independent on the rapidity and the gluon momentum.
We have recently studied the QCD pomeron loop evolution equations in zero transverse dimensions [Shoshi:2005pf]. Using the techniques developed in [Shoshi:2005pf] together with the AGK cutting rules, we present a calculation of single, double and central diffractive cross sections (for large diffractive masses and large rapidity gaps) in zero transverse dimensions in which all dominant pomeron loop graphs are consistently summed. We find that the diffractive cross sections unitarise at asymptotic energies and that they are suppressed by powers of alpha_s. Our calculation is expected to expose some of the diffractive physics in hadron-hadron collisions at high energy.
It was recently noticed that high-energy scattering processes in QCD have a stochastic nature. An event-by-event scattering amplitude is characterised by a saturation scale which is a random variable. The statistical ensemble of saturation scales formed with all the events is distributed according to a probability law whose cumulants have been recently computed. In this work, we obtain the probability distribution from the cumulants. We prove that it can be considered as Gaussian over a large domain that we specify and our results are confirmed by numerical simulations.
We analyze a toy model which has a structure similar to that of the recently found QCD evolution equations, but without transverse dimensions. We develop two different but equivalent methods in order to compute the leading-order and next-to-leading order Pomeron loop diagrams. In addition to the leading-order result which has been derived from Mueller's toy model~\cite% {Mueller:1994gb}, we can also calculate the next-to-leading order contribution which provides the $(α_{s}^{2}αY)$ correction. We interpret this result and discuss its possible implications for the four-dimensional QCD evolution.
We present a simple gluon production picture which is based on the McLerran-Venugopalan model and gluon BFKL evolution in relativistic heavy ion collision. Results for the multiplicity and transverse energy distribution in both the central and forward rapidity regions for gluon production in early stages of heavy ion collisions at the LHC are given. Finally, we provide a general qualitative discussion of the consequences of the forward rapidity behavior of produced gluons.
The photon-meson transition form factors of light pseudoscalar mesons $π^{0}$, $η$, and $η^{\prime}$ are systematically calculated in a light-cone framework, which is applicable as a light-cone quark model at low $Q^{2}$ and is also physically in accordance with the light-cone pQCD approach at large $Q^{2}$. The calculated results agree with the available experimental data at high energy scale. We also predict the low $Q^{2}$ behaviors of the photon-meson transition form factors of $π^{0}$, $η$ and $η^{\prime }$, which are measurable in $e+A({Nucleus})\to e+A+M$ process via Primakoff effect at JLab and DESY.
We derive the minimal Fock-state expansions of the pion and the photon wave functions in light-cone formalism, then we calculate the pion-photon and the photon-pion transition form factors of $γ^{\ast}π^{0}\to γ$ and $γ^{\ast}γ\to π^{0}$ processes by employing these quark-antiquark wave functions of the pion and the photon. We find that our calculation for the $γ^{\ast}γ\to π^{0}$ transition form factor agrees with the experimental data at low and moderately high energy scale. Moreover, the physical differences and inherent connections between the transition form factors of $γ^{\ast}π^{0}\to γ$ and $ γ^{\ast}γ\to π^{0}$ have been illustrated, which indicate that these two physical processes are intrinsically related. In addition, we also discuss the $π^{0}\to γγ$ form factor and the decay width $ \mathitΓ(π\to γγ)$ at $Q^{2}=0$.
The electromagnetic form factor of the kaon meson is calculated in the light-cone formalism of the relativistic constituent quark model. The calculated $K^+$ form factor is consistent with almost all of the available experimental data at low energy scale, while other properties of kaon could also be interrelated in this representation with reasonable parameters. Predictions of the form factors for the charged and neutral kaons at higher energy scale are also given, and we find non-zero $K^0$ form factor at $Q^2 \ne 0$ due to the mass difference between the strange and down quarks inside $K^0$.