Antishadowing Effects Research Articles

Exploring the impact of anti-shadowing effect on unintegrated gluon distributions in the MD-BFKL equation* *Supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030301), the Major Project of Basic and Applied Basic Research of Guangdong Province, China (2020B0301030008), the Education Department of Guizhou Province, China (QJJ[2022]016), and the Basic Research Program (Natural Science) of Guizhou Province, China

This paper presents a comprehensive analysis of the MD-BFKL equation, considering both shadowing and anti-shadowing effects in gluon recombination processes. By deriving analytical expressions for unintegrated gluon distributions through the solution of the MD-BFKL equation, with and without the incorporation of the anti-shadowing effect, we offer new insights into the influence of these effects on the behavior of unintegrated gluon distributions. Our results, when compared to those from the CT18NLO gluon distribution function, demonstrate that the anti-shadowing effect has a notably stronger impact on the characteristics of unintegrated gluon distributions, particularly in regions of high rapidity and momentum. This work significantly contributes to the understanding of gluon recombination mechanisms and their implications in high energy physics.

Small-x analysis on the effect of gluon recombinations inside hadrons in light of the GLR-MQ-ZRS equation

We present a study of the contribution of antishadowing effects on the gluon distribution functions G(x,Q2) in light of the Gribov-Levin-Ryskin-Mueller-Qiu, Zhu-Ruan-Shen (GLR-MQ-ZRS) nonlinear equation at small-x, where x is the momentum fraction or Bjorken variable and Q2 is the four momentum transfer squared or photon virtuality. In this work, we have solved the GLR-MQ-ZRS nonlinear equation using Regge like behaviour of gluons in the kinematic range of 10−2≤x≤10−6 and 5GeV2≤Q2≤100GeV2 respectively. We have obtained the solution of G(x,Q2) by considering two particular cases: (a) αs fixed; and (b) the leading order QCD dependency of αs on Q2. A comparative analysis is also performed where we compare the gluon distribution function due to inclusion of the antishadowing effect with that of the gluon distribution without including the antishadowing effect. Our obtained results of G(x,Q2) are compared with NNPDF3.0, CT14 and PDF4LHC. We also compare our results with the result obtained from the IMParton C++ package. Using the solutions of G(x,Q2), we have also predicted x and Q2 evolution of the logarithmic derivative of proton's F2 structure function i.e. dF2(x,Q2)/dln⁡Q2. We incorporated both the leading order(LO) and next-to-leading order (NLO) QCD contributions of the gluon-quark splitting kernels, in dF2(x,Q2)/dln⁡Q2. Our result of dF2(x,Q2)/dln⁡Q2 agrees reasonably well with the experimental data recorded by HERA's H1 detector.

The gluon condensation at high energy hadron collisions

We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing–antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton–proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron–hadron colliders.

ForwardDpredictions forpPbcollisions, and sensitivity to cold nuclear matter effects

Predictions are provided for double differential cross sections and forward-backward ratios of $D^{0}$ production in $p\rm Pb$ (forward) and $\rm{Pb}$$p$ (backward) collisions at 5.02~TeV. The effect of nuclear corrections on the ratio of differential cross sections ratios is estimated to be $\simeq$ (10-30)\% in the kinematically accessible region of LHCb, and interestingly this ratio is approximately flat with respect to $p_T(D^0)$ due to a compensation of shadowing and anti-shadowing effects arising from the input nuclear PDFs. In comparison to $J/\psi(\rightarrow\mu^-\mu^+)$ measurements which have already been performed with the available data, the cross section for $D^{0}(\rightarrow K^-\pi^+)$ production is expected to be two-orders of magnitude higher.

Antishadowing Effect on Charmonium Production at a Fixed-Target Experiment Using LHC Beams

We investigate charmonium production in Pb + Pb collisions at LHC beam energyElab=2.76A TeV at fixed-target experiment (sNN= 72 GeV). In the frame of a transport approach including cold and hot nuclear matter effects on charmonium evolution, we focus on the antishadowing effect on the nuclear modification factorsRAAandrAAfor theJ/ψyield and transverse momentum. The yield is more suppressed at less forward rapidity (ylab≃2) than that at very forward rapidity (ylab≃4) due to the shadowing and antishadowing in different rapidity bins.

FROM EMC AND CRONIN EFFECTS TO SIGNALS OF QUARK–GLUON PLASMA

The EMC and Cronin effects are explained by a unitarized evolution equation, in which the shadowing and antishadowing corrections are dynamically produced due to gluon fusions. For this sake, an alternative form of the GLR–MQ–ZRS equation is derived. The resulting gluon distributions, integrated and unintegrated, in protons and nuclei are used for analysis of the contributions of the initial parton distributions to the nuclear suppression factor in heavy-ion collisions. A simulation of the fractional energy loss is extracted from the data of RHIC and LHC, where the contributions of both nuclear shadowing and nuclear antishadowing effects are considered. We find a rapid crossover from weak energy loss to strong energy loss with the gluon jet at a universal critical energy, Ec ~ 10 GeV .

Nuclear effects on J/ψ production in proton–nucleus collisions

The study of nuclear effects for J/{\psi} production in proton-nucleus collisions is crucial for a correct interpretation of the J/{\psi} suppression patterns experimentally observed in heavy-ion collisions. By means of three representative sets of nuclear parton distribution, the energy loss effect in the initial state and the nuclear absorption effect in the final state are taken into account in the uniform framework of the Glauber model. A leading order phenomenological analysis is performed on J/{\psi} production cross-section ratios RW/Be(xF) for the E866 experimental data. The J/{\psi} suppression is investigated quantitatively due to the different nuclear effects. It is shown that the energy loss effect with resulting in the suppression on RW/Be(xF) is more important than the nuclear effects on parton distributions in high xF region. The E866 data in the small xF keep out the nuclear gluon distribution with a large anti-shadowing effect. However, the new HERA-B measurement is not in support of the anti-shadowing effect in the nuclear gluon distribution. It is found that the J/{\psi}-nucleon inelastic cross section {\sigma} J/{\psi} abs depends on the kinematical variable xF, and increases as xF in the region xF > 0.2. 1 Introduction

ϒ production in d+Au collisions at STAR

We present the analysis of ϒ → e + e − production in d+Au collisions at s N N = 200 GeV from the STAR experiment. Using higher level dedicated ϒ triggers, STAR has sampled 32 nb − 1 of integrated luminosity in year 2008 d+Au run. The cross section is found as B R × ( d σ d y ) y = 0 ϒ ( 1 S + 2 S + 3 S ) = 35 ± 4 ( s t a t . ) ± 5 ( s y s . ) nb and it is consistent with NLO CEM prediction with anti-shadowing effects. In addition we calculated the nuclear modification factor R d A u = 0.98 ± 0.32 ( s t a t . ) ± 0.28 ( s y s . ) , which suggests the ϒ ( 1 S + 2 S + 3 S ) production follows N b i n scaling.

Development and characterization of the control assembly system for the large 2400 MWth Generation IV gas-cooled fast reactor

The present paper is related to the design and neutronic characterization of the principal control assembly system for the reference large (2400 MWth) Generation IV gas-cooled fast reactor (GFR), which makes use of ceramic–ceramic (CERCER) plate-type fuel-elements with (U–Pu) carbide fuel contained within a SiC inert matrix. For the neutronic calculations, the deterministic code system ERANOS-2.0 has been used, in association with a full core model including a European fast reactor (EFR)-type pattern for the control assemblies as a starting point. More specifically, the core contains a total of 33 control (control system device: CSD) and safety (diverse safety device: DSD) assemblies implemented in three banks. In the design of the new control assembly system, particular attention was given to the heat generation within the assemblies, so that both neutronic and thermal–hydraulic constraints could be appropriately accounted for. The thermal–hydraulic calculations have been performed with the code COPERNIC, significant coolant mass flow rates being found necessary to maintain acceptable cladding temperatures of the absorber pins. Complementary to the design study, neutronic investigations have been performed to assess the impact of the control assemblies in the GFR core in greater detail (rod interactions, shift of the flux, peaking factors, etc.). Thus, considerable shadowing effects have been observed between the first bank and the safety bank, as also between individual assemblies within the first bank. Large anti-shadowing effects also occur, the most prominent being that between the two CSD banks, where the total assembly worth is almost doubled in comparison to the sum of the individual values. Additional investigations have been performed and, in this context, it has been found that computation of the first-order eigenvalue and the eigenvalue separation is a robust tool to anticipate control assembly interactions in a large fast-spectrum core. One interesting finding is that the interactions are lower when one of the control assembly banks is located at a radial position corresponding to the minimum in the first-order eigenvalue (at approximately half the core radius). An important aspect of the design optimization process has been to obtain a low heterogeneity effect for the control assembly worth. This was achieved by applying a methodology based on reactivity equivalence, with the optimization goal set at minimizing the shadowing effects between the absorber pins as well as the self-shielding within the absorber pins. A relatively low reduction of ∼13% was obtained as the heterogeneity effect for the control assembly worth, the corresponding value in the case of Super-phénix being significantly higher, viz. about 20%.

Nuclear shadowing and antishadowing in a unitarized BFKL equation**Supported by National Natural Science Foundation of China (10135060, 10475028, 10205004)

The nuclear shadowing and antishadowing effects are explained by a unitarized BFKL equation. The Q2- and x-variations of the nuclear parton distributions are detailed based on the level of the unintegrated gluon distribution. In particular, the asymptotical behavior of the unintegrated gluon distribution near the saturation limit in nuclear targets is studied. Our results in the nuclear targets are insensitive to the input distributions if the parameters are fixed by the data of a free proton.

Antishadowing effects in the unitarized BFKL equation

A unitarized BFKL equation incorporating shadowing and antishadowing corrections of the gluon recombination is proposed. This equation reduces to the Balitsky–Kovchegov evolution equation near the saturation limit. We find that the antishadowing effects have a sizable influence on the gluon distribution function in the preasymptotic regime.

Nuclear effects in deep inelastic scattering of charged-current neutrino off nuclear target

The nuclear effects in the neutrino–nucleus charged-current inelastic scattering process is studied by analyzing the CCFR and NuTeV data. The structure functions F2(x,Q2) and xF3(x,Q2) as well as differential cross sections are calculated by using CTEQ parton distribution functions and the EKRS and HKN nuclear parton distribution functions, and these are compared with the CCFR and NuTeV data. It is found that the corrections of the nuclear effect to the differential cross section for the charged-current antineutrino scattering on the nucleus are negligible, the EMC effect exists in the neutrino structure function F2(x,Q2) in the large x region, the shadowing and anti-shadowing effect occur in the distribution functions of valence quarks in the small and medium x region, respectively. It is also found that shadowing effects on F2(x,Q2) in the small x region in the neutrino–nucleus and the charged-lepton–nucleus deep inelastic scattering processes are different. It is clear that the neutrino–nucleus deep inelastic scattering data should further be employed in restricting the nuclear parton distributions.

Predictions for the low- x structure function in the modified GLR equation

The predictions for the proton structure function F 2 at small x are presented by using the modified Gribov-Levin-Ryskin evolution equation which restores the momentum sum rule in the evolution processes. It turns out that the shadowing effect is weakened by the antishadowing effect in the region x > 10 −3 and that the net shadowing effect will appear in the region x < 10 −3 and low Q 2.

K+-nucleus interactions at low momenta

The ratios of the K+ total cross-section on nuclei to that on deuteron,RT, are calculated in the Glauber approach, to demonstrate the antishadowing in double scattering. The K+N amplitudes derived from the Bonn meson exchange potential are used as input parameters. TheRT is sensitive to K+ɛ total cross-section and the ratioɛ of the real to imaginary part of the elementary K+RT amplitude. TheRT depends on the mass numberA of the target nucleus. |ɛ|>1 is essential to give rise to the antishadowing effects for light nuclei.

Antishadowing Corrections in the Evolution Equation of Quark Distributions

We introduce the antishadowing effect to restore the momentum sum rule in the quantum chromodynamics evolution equation for quarks in small x region.

Unified Description of the EMC Effect and Nuclear Shadowing Effect

The parton evolution model is improved by using the modified Alteralli-Parisi equation which can describe the nuclear shadowing and antishadowing effects in the small x region. Within the theoretical framework of the improved parton evolution model, the unified description of the European Muon Collaboration (EMC) effect, and nuclear shadowing and antishadowing effects is given without introducing the nuclear shadowing factor.

High energy hadron-nucleus diffraction scattering and nuclear structure

Two possible effects are suggested at high energy hadron-nucleus diffraction scattering if the nucleus behaves as a composite system of continuous (big-drop) or discrete non-nucleonic constituents. One is the appearance of the secondary dip in hadron-deuteron elastic differential cross sections and another is a small shadowing (eclipse) effect in the total cross section or even an antishadowing effect in light nuclei.