Initial state effects on J/ψ production at RHIC energy: from d+Au to Au+Au

We present a calculation of the cold nuclear matter effect on inclusive production of J/ψ in d+A and A+A collisions in the framework of the gluon saturation/CGC approach. Our model is based on the observation that the leading production mechanism involves odd number of inelastic interactions with the nuclei. Our numerical calculations are in good agreement with the experimental data in the case of d+Au collisions. However, in Au+Au collisions the cold nuclear matter effect is not suffcient to describe the data.     

An interpretation of saturation phenomena as Glauber-Gribov multiple parton scatterings

We compare two formalism that describe minijet production in pA and AA: pQCD supplemented by Glauber-Gribov multiple semi-hard parton scatterings (pQCD + Glauber), and the Color Glass Condensate (CGC). We argue that in a suitable limit they are equivalent to each other, the PQCD + Glauber model being more accurate from a numerical point of view. Finally, we analyze RHIC data on Au?Au integrated charged multiplicities in the pQCD + Glauber framework, and conclude that at least at central rapidity there is no sign of gluon saturation.     

Asymmetry in charmed-particle production in a Σ− beam

We present a calculation of the inclusive x _F distributions of charmed hadrons produced in a high-energy Σ^? beam. The calculation is based on the modified mechanism of charmed-quark fragmentation, as well as on the mechanism of c-quark recombination with the valence quarks from initial hadrons. We predict additional asymmetry in the production of charmed hadrons due to different distributions of the valence s and d quarks in a Σ^? beam.     

Flavor non-universal gauge interactions and anomalies in B-meson decays

Motivated by flavor non-universaity and anomalies in semi-leptonic B-meson decays, we present a general and systematic discussion about how to construct anomaly-free U(1)' gauge theories based on an extended standard model with only three right-handed neutrinos. If all standard model fermions are vector-like under this new gauge symmetry, the most general family non-universal charge assignments,(a,b,c) for three-generation quarks and(d,e,f)for leptons, need satisfy just one condition to be anomaly-free, 3(a+b+c) =-(d+e+f). Any assignment can be linear combinations of five independent anomaly-free solutions. We also illustrate how such models can generally lead to flavor-changing interactions and easily resolve the anomalies in B-meson decays. Probes with B_s-B_s mixing, decay into τ~±, dilepton and dijet searches at colliders are also discussed.     

Geometric scaling behavior of the scattering amplitude for DIS with nuclei

The main question, that we answer in this paper, is whether the initial condition can influence on the geometric scaling behavior of the amplitude for DIS at high energy. We re-write the non-linear Balitsky-Kovchegov equation in the form which is useful for treating the interaction with nuclei. Using the simplified BFKL kernel, we find the analytical solution to this equation with the initial condition given by the McLerran-Venugopalan formula. This solution does not show the geometric scaling behavior of the amplitude deeply in the saturation region. On the other hand, the BFKL Pomeron calculus with the initial condition at xA=1/mRA given by the solution to Balitsky-Kovchegov equation, leads to the geometric scaling behavior. The McLerran-Venugopalan formula is the natural initial condition for the Color Glass Condensate (CGC) approach. Therefore, our result gives a possibility to check experimentally which approach: CGC or BFKL Pomeron calculus, is more satisfactory.     

Pion and K meson production in the multiperipheral model

A simple multiperipheral model, that utilizes only three parameters, two coupling constants and exponential damping for each momentum transfer is developed and applied to the calculation of inclusive distributions. The pion rapidity and p_⊥² distributions are successfully predicted; as are the energy dependences of strange particle production cross sections. The development of inclusive distributions with increasing energy and possible improvements to the model are discussed.     

Disordered two-dimensional electron systems with chiral symmetry

We review the results of our recent numerical investigations on the electronic properties of disordered two dimensional systems with chiral unitary, chiral orthogonal, and chiral symplectic symmetry. Of particular interest is the behavior of the density of states and the logarithmic scaling of the smallest Lyapunov exponents in the vicinity of the chiral quantum critical point in the band center at E=0. The observed peaks or depressions in the density of states, the distribution of the critical conductances, and the possible non-universality of the critical exponents for certain chiral unitary models are discussed.     

On the transverse energy distributions in the central rapidity region of 16O+Pb collisions at 200 GeV per nucleon

We point out that the recent data obtained by the NA35 collaboration at the CERN SPS on E_T distributions in ¹⁶O + Pb collisions can be understood within the wounded nucleon model with a simple geometrical calculation of the number of interacting nucleons in ¹⁶O. Although the large E_T trigger increases the average E_T per final state hadron, we are unable to explain in this way the observed rather large value of this quantity.     

Is the peak value of σ xx at the quantum Hall transition universal?

The question of the universality of the longitudinal peak conductivity at the integer quantum Hall transition is considered. For this purpose, a system of 2D Dirac fermions with random mass characterised by variance g is proposed as a model which undergoes a quantum Hall transition. Whilst for some specific models the longitudinal peak conductivity σ _xx was found to be universal (in agreement with the conjecture of Lee et al. as well as with some numerical work), we find that σ _xx is reduced by a factor (1 + g/2π)^?1, at least for small g. This provides some theoretical evidence for the non-universality of σ _xx , as observed in a number of experiments.     

Generalized parton distributions of the photon for nonzero skewness

We present a calculation of the generalized parton distributions of the photon when there is nonzero momentum transfer both in the transverse and longitudinal directions. We consider only the contributions when the photon helicity is not flipped and calculate those at leading order in electromagnetic coupling α and zeroth order in the strong coupling αs. We keep the leading logarithmic terms as well as the quark mass terms in the vertex. By taking Fourier transforms of the GPDs with respect to the transverse and longitudinal momentum transfer, we obtain the parton distributions of the photon in position space.     

Radiative corrections to high-energy neutrino scattering

Motivated by precise neutrino experiments, we reconsider the electromagnetic radiative corrections to the data. We investigate the usefulness and demonstrate the simplicity of the “leading log” approximation: the calculation to order α ln (Q/μ), α ln (Q/m_q). Here Q is an energy scale of the overall process, μ is the lepton mass and m_q is a hadronic mass, the effective quark mass in a parton model. We identify those questions the answers to which do not depend on unknown hadron parameters like quark masses. The leading log radiative corrections to dδ/dy distributions and to suitably interpreted dδ/dx distributions are quark-mass independent. We improve upon the conventional leading log approximation and compute explicitly the largest terms that lie beyond the leading log level. In practice this means that our model-independent formulae, though approximate, are likely to be excellent estimates everywhere except at low energy or very large y. We point out that radiative corrections to measurements of deviations from the Callan-Gross relation and to measurements of the “sea” constituency of nucleons are gigantic. The QCD inspired study of deviations from scaling is of particular interest. We compute, beyond the leading log level, the radiative corrections to the QCD predictions.     

Characterization of Porous Materials by Magnetic Relaxometry in the Earth’s Field

In this paper, it is shown how free induction decay signals recorded in the Earth’s magnetic field from water protons confined in porous media can be used to derive transversal relaxation times (T ₂) and their distributions. After T ₂ determination of six sintered glass samples with various pore sizes, the common theoretical model can be fitted to the data set. The T ₂ distribution of water protons in a bimodal porous system is analyzed and compared to mercury porosimetry results. The implications for the calculation of pore sizes and pore size distributions of porous media by this method are discussed.     

Three-body final state breakup in the27Al(14N,X) reaction at 116 MeV bombarding energy

The energy spectra and angular distributions of products in the reaction²⁷Al(¹⁴N,X) have been measured at 116 MeV bombarding energy. It is shown that the energy spectra of the products lighter than the projectile, are well described by a three-body breakup calculation. The experimental total breakup cross-section estimated in the present work, together with Glas-Mosel calculation of the fusion cross-section, are in a reasonable agreement with the optical model total reaction cross-section.     

Generalized parton distributions of the photon

We present a first calculation of the generalized parton distributions of the photon (both polarized and unpolarized) using overlaps of light-front wave functions at leading order in α and zeroth order in αs; for non-zero transverse momentum transfer and zero skewness. We present the novel parton content of the photon in transverse position space.     

Relativistic calculation for the reactions\bar p d → 5πp and\bar p d → 3πp at rest

We present a fully relativistic calculation for ¯pd → 5πp and ¯pd → 3πp that includes angular momentum and spin dynamics. We calculate the inclusive proton distributions from two diagrams: the leading “tree” diagram, and the diagram for pion rescattering. Pion-nucleon rescattering proceeds through the Δ, in the RaritaSchwinger formalism, thus preserving the correct angular dependence. We use realistic parameterizations of the deuteron, keeping both theS andD states. The loop integrations for the rescattering amplitude and the phase space integrations have been done numerically. We find that the combined effects of a correct treatment of the rescattered pion and relativity are small in comparison with a simple non-relativistic calculation.     

Pair production of squarks inep-collisions

The production of squarks atep colliders is studied by comparing the Weizsäcker-Williams approximation and an exact tree level calculation. We consider the processep→eqqX→eqqγγX. For this calculation, on the amplitude level, the Feynman diagrams can be split into sub-diagrams. This splitting has great advantages for numerical calculations. Using these techniques the dependence of the cross section on the mass of the squark is computed. We also present various kinematical distributions. An elegant method for calculating tree amplitudes with external fermions of arbitrary mass and spin is given for completeness.     

Energy scaling of minimum-bias tunes

We propose that the flexibility offered by modern event-generator tuning tools allows for more than just obtaining “best fits” to a collection of data. In particular, we argue that the universality of the underlying physics model can be tested by performing several, mutually independent, optimizations of the generator parameters in different physical regions. For regions in which these optimizations return similar and self-consistent parameter values, the model can be considered universal. Deviations from this behavior can be associated with a breakdown of the modeling, with the nature of the deviations giving clues as to the nature of the breakdown. We apply this procedure to study the energy scaling of a class of minimum-bias models based on multiple parton interactions (MPI) and p _⊥-ordered showers, implemented in the Pythia 6.4 generator. We find that a parameter controlling the strength of color reconnections in the final state is the most important source of non-universality in this model.     

Cluster growth poised on the edge of break-up: Size distributions with small exponent power-laws

In many naturally occurring growth processes, cluster size distributions of power-law form n(s)∝s^−τ with small exponents 0<τ<1 are observed. We suggest here that such distributions emerge naturally from cluster growth, where size dependent aggregation is counterbalanced by size dependent break-up. The model used in the study is a simple reaction kinetic model including only monomer-cluster processes. It is shown that under such conditions power-law size distributions with small exponents are obtained. Therefore, the results suggest that the ubiquity of small exponent power-law distributions is related to the growth process, where aggregation driven cluster growth is poised on the edge of cluster break-up.     

Target mass dependence and intranuclear cascade in high energy nucleus-nucleus collisions

Intranuclear cascade, one of the most important non-linear effects in high energy nucleus-nucleus collisions, is investigated, its influence on the target mass dependence of the distributions of final state particles is discussed. Using hydrodynamical model to treat non-linear effects, the main features of the rapidity distributions and their dependence on the target mass are naturally explained. The results of numerical calculation for¹⁶O-A central collisions at 60 and 200A GeV agree with the existing data.     

Hadron production ine +e− annihilation and μ-p collisions under the assumption of longitudinal phase space dominance

Rapidity and multiplicity distributions are calculated for the hadrons produced ine ⁺e^? annihilation and deep inelastic muon-proton collisions for c.m. energies of 10 to 40 GeV. The hypothesis of longitudinal phase space dominance leads to a probability distribution which is identical to that of a grand canonical ensemble of non-interacting particles. We successfully describe experimental rapidity distributions, domains of Feynman-x scaling and scaling violations and the rapidity dependence of the mean transverse momentum. Multiplicity distributions are derived to be close to negative binomial distributions even for finite rapidity intervals. The plateau in the rapidity distribution is the origin for the negative binomial distribution in multiplicity. The mean number of hadrons of each species and the mean overall transverse momentum are the main input parameters in our calculation and are taken from experiment.