A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV

A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (n_p) and prompt γ rays (γ_p). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including ²³²Th, ^{235, 238}U and ²⁴⁰Pu. It is found that the ²³⁸U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the ²³²Th(γ, f) reaction. In addition, the average multiplicity number of both n_p and γ_p increases with the average excitation energy.     

A study of the nuclear-medium influence on <Emphasis Type="Italic">ρ</Emphasis><Superscript>0</Superscript> neutrinoproduction

The nuclear effects in ρ ⁰-meson neutrino production are investigated using the data obtained with the SKAT bubble chamber. The nuclear-medium influence on the ρ ⁰ total yield and inclusive distributions on z = E _ρ /v and Feynman x _F variable is found to be approximately the same as for pions. It is shown that these distributions with increasing A tend to shift toward smaller values of z and x _F, thus indicating an increasing role of secondary intranuclear interactions. The predictions of a simple model incorporating the latter are found to be in qualitative agreement with experimental data. The text was submitted by the authors in English.     

A simplified model for calculating RAA and RCP of cold nuclear matter effects

An incoherent binary nucleon-nucleon collision model of AA collisions is presented for simulating particle production in cold nuclear matter. With a simple phenomenological parameter, the mean nucleon energy loss fraction, this model yields pseudorapidity density distributions that are comparable to those of experiment, as well as those of HIJING. Particle production data for a given binary collision is extracted from the PYTHIA event generator. The nuclear geometry is described by the Glauber model. The preliminary R _AA and R _CP results are also presented and discussed, with a proposal that R _AA be redefined.     

NeXSPheRIO results on elliptic-flow fluctuations at RHIC

By using the NeXSPheRIO code, we study the elliptic-flow fluctuations in Au + Au collisions at 200 A GeV. It is shown that, by fixing the parameters of the model to correctly reproduce the charged pseudorapidity and the transverse-momentum distributions, reasonable agreement of 〈v ₂〉 with data is obtained, both as function of pseudorapidity as well as of transverse momentum, for charged particles. Our results on elliptic-flow fluctuations are in good agreement with the recently measured data on experiments. The text was submitted by the authors in English.     

Higher-order constraints on the Higgs production rate from fixed-target DIS data

The constraints of fixed-target DIS data in fits of parton distributions including QCD corrections to next-to-next-to leading order are studied. We point out a potential problem in the analysis of the NMC data which can lead to inconsistencies in the extracted value for α _s (M _Z ) and the gluon distribution at higher orders in QCD. The implications for predictions of rates for Standard Model Higgs boson production at hadron colliders are investigated. We conclude that the current range of excluded Higgs boson masses at the Tevatron appears to be much too large.     

Identification of the origin of monojet signatures at the LHC

Several new physics scenarios can lead to monojet signatures at the LHC. If such events are observed above the Standard Model background it will be important to identify their origin. In this Letter we compare and contrast these signatures as produced in two very different pictures: vector or scalar unparticle production in the scale-invariant/conformal regime and graviton emission in the Arkani-Hamed, Dimopoulos and Dvali extra-dimensional model. We demonstrate that these two scenarios can be distinguished at the LHC for a reasonable range of model parameters through the shape of their respective monojet and/or missing E_T distributions.     

Can we get deeper inside the pion at the LHC?

We propose a measurement of leading neutrons spectra at LHC in order to extract inclusive π ⁺ p and π ⁺ π ⁺ cross-sections with high p _T jets production. The cross-sections for these processes are simulated with the use of parton distributions in hadrons. In this work we estimate the possibility to extract parton distributions in the pion from the data on these cross-sections and also search for signatures of fundamental differences in the pion and proton structure.     

Dynamical parton distributions of the nucleon and very small-x physics

Utilizing recent DIS measurements (F_2,L) and data on dilepton and high-E_T jet production we determine the dynamical parton distributions of the nucleon generated radiatively from valence-like positive input distributions at optimally chosen low resolution scales. These are compared with ‘standard’ distributions generated from positive input distributions at some fixed and higher resolution scale. It is shown that up to the next-to-leading order NLO(, DIS) of perturbative QCD considered in this paper, the uncertainties of the dynamical distributions are, as expected, smaller than those of their standard counterparts. This holds true in particular in the presently unexplored extremely small-x region relevant for evaluating ultrahigh energy cross sections in astrophysical applications. It is noted that our new dynamical distributions are compatible, within the presently determined uncertainties, with previously determined dynamical parton distributions.     

The pair distributions and the osmotic coefficient in binary electrolytes up to concentrations c 1 mol/l

Referring to the results of a previous paper dealing with the pair distributions in a fully ionized dilute hydrogen plasma it is concluded that the pair distributions in binary electrolytes up to concentrations c 1 mo1/1 take the form

Full-size image

. Here (r) represents the screened Coulomb potential and V(^hs)(r) a hard sphere potential. The contact distances R of the hard sphere potentials are assumed to be equal for ions with the same sign of their charges, that means R₊₊ = R_-- = R, and to be smaller than R for ions of opposite charges, that means R_+- = qR, 0 < q < 1. With the help of these pair distributions the pressure of the ionic components and the osmotic coefficient are calculated. The numerical evaluation of the osmotic coefficient of hydrous electrolytes at T = 273 K shows that the above pair distributions explain the experimental data of all kinds of 1-1-valent electrolytes, even those of the tetra-alkylammonium halogenids, within a domain of very reasonable values of R and q. No necessity seems to exist for considering additional short range attractive forces. Furthermore, some numerical results for 2-2-valent electrolytes in water are given. It comes out that the osmotic coefficient of all 2-2-valent electrolytes with R 5 Å is larger than the limiting law in a certain domain of concentration.     

Parametrization of nuclear parton distributions

Optimum nuclear parton distributions are obtained by analysing available experimental data on electron and muon deep inelastic scattering (DIS). The distributions are given at Q ²=1 GeV² with a number of parameters, which are determined by a X ² analysis of the data. Valencequark distributions are relatively well determined at medium x, but they are slightly dependent on the assumed parametrization form particularly at small x. Although antiquark distributions are shadowed at small x, their behavior is not obvious at medium x from the F ₂ data. The gluon distributions could not be restricted well by the inclusive DIS data; however, the analysis tends to support the gluon shadowing at small x. We provide analytical expressions and computer subroutines for calculating the nuclear parton distributions, so that other researchers could use them for applications to other high-energy nuclear reactions.     

Measurements of inclusive and exclusive particle production at ZEUS

Charged particle production, scaled momentum distributions of identified particles, K _s ⁰ and Λ, and charged particles for dijet events have been measured in ep scattering with the ZEUS detector. The evolution of these distributions with the photon virtuality, Q ², are studied in the kinematic region 10 < Q ² < 40000 GeV². The calculations reproduce the measured distributions reasonably well.     

Unpolarized structure functions and the parton distributions for nucleon in an independent quark model

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.     

Analyses of the factors for the demagnetization of permanent magnets caused by high‐energy electron irradiation

Demagnetization owing to high‐energy electron irradiation has been analyzed for permanent magnets used in insertion devices of synchrotron radiation sources, using the Monte Carlo code FLUKA. The experimental data of a thermally treated Nd₂Fe₁₄B permanent magnet with a copper or a tantalum block at electron energies ranging from 2 to 8 GeV were compared with the calculation data of the absorbed doses, photoneutron production distributions and star densities. The results indicate that low‐energy photoneutrons and bremsstrahlung photons are not involved in the demagnetization process, and suggest that the star density owing to the photoneutrons is strongly correlated with the demagnetization process.     

Unintegrated parton distributions and inclusive jet productionat HERA

We describe how unintegrated parton distributions can be calculated from conventional integrated distributions. We extend and improve the last-step evolution approach, and explain why doubly unintegrated parton distributions are necessary. We generalise k _t-factorisation to (z,k _t)-factorisation. We apply the formalism to inclusive jet production in deep-inelastic scattering, mainly at leading order, but we also study the extension to next-to-leading order. We compare the predictions with recent HERA data.Received: 19 June 2003, Published online: 19 September 2003     

Higgs boson production at hadron collidersin the kT-factorization approach

We consider the Higgs boson production at high energy hadron colliders in the framework of the k_T-factorization approach. The attention is focused on the dominant gluon-gluon fusion subprocess. We calculate the total cross section and transverse momentum distributions of the inclusive Higgs production using unintegrated gluon distributions in a proton obtained from the full CCFM evolution equation. We show that k_T-factorization gives a possibility to investigate the associated Higgs boson and jets production. We calculate the transverse momentum distributions and study the Higgs-jet and jet-jet azimuthal correlations in the Higgs + one or two jet production processes. We demonstrate the importance of the higher-order corrections within the k_T-factorization approach. These corrections should be developed and taken into account in the future applications. Received: 26 January 2005, Revised: 8 July 2005, Published online: 6 October 2005     

System size, energy, centrality and pseudorapidity dependence of charged-particle density in Au+Au and Cu+Cu collisions at RHIC

Charged particle pseudorapidity distributions are presented from the PHOBOS experiment at RHIC, measured in Au+Au and Cu+Cu collisions at ?{s_NN }\sqrt {s_{NN} } =19.6, 22.4, 62.4, 130 and 200 GeV, as a function of collision centrality. The presentation includes the recently analyzed Cu+Cu data at 22.4 GeV. The measurements were made by the same detector setup over a broad range in pseudorapidity, |η| < 5.4, allowing for a reliable systematic study of particle production as a function of energy, centrality and system size. Comparing Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the overall shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants, N _part. Detailed comparisons reveal that the matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of η is better for the same N _part/2A value than for the same N _part value, where A denotes the mass number. In other words, it is the geometry of the nuclear overlap zone, rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence.     

Dipole properties of PH3, PF3, PF5, PCl3, SiCl4, GeCl4, and SnCl4

Experimental and theoretical photoabsorption cross sections combined with constraints provided by the Kuhn–Reiche–Thomas sum rule, the high-energy behaviour of the dipole oscillator strength density, static dipole polarisabilities, and molar refractivity data when available are used to construct dipole oscillator strength distributions for PH₃, PF₃, PF₅, PCl₃, SiCl₄, GeCl₄, and SnCl₄. The distributions are used to predict dipole sum rules S(k), mean excitation energies I(k), and van der Waals C₆ coefficients.