Study of the nuclear interaction of isoscalar <Emphasis Type="Italic">η</Emphasis>-, <Emphasis Type="Italic">ω</Emphasis>-, <Emphasis Type="Italic">ή</Emphasis>-, and <Emphasis Type="Italic">ϕ</Emphasis>-mesons

The possibility of experimental study of the nuclear interaction of mesons with nucleons and nuclei is considered.     

Global analysis of <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> suppression in cold nuclear matter

Interpreting the J/ψ suppression reported in nucleus–nucleus collisions at SPS and RHIC requires a quantitative understanding of cold nuclear-matter effects, such as the inelastic rescattering of J/ψ states in nuclei or the nuclear modification of parton densities. With respect to our former Glauber analysis, we include in the present work the new PHENIX d–Au measurements, and we analyze as well all existing data using the EPS08 nuclear parton densities recently released. The largest suppression reported in the new PHENIX analysis leads in turn to an increase of σ _J/ψN from 3.5±0.3 to 5.4±2.5 mb using the PDF of the proton. The stronger x-dependence of the G ^A /G ^p ratio in EPS08 as compared to e.g. EKS98 shifts the cross section towards larger values at fixed-target energies (x ₂∼0.1), while decreasing somehow the value extracted at RHIC (x ₂∼10⁻²).     

<Emphasis Type="Italic">α</Emphasis>-cluster and <Emphasis Type="Italic">α</Emphasis>-binucleon states of 1<Emphasis Type="Italic">p</Emphasis>-shell nuclei

States that exhibit the properties of an α-cluster or an α-binucleon condensate are studied in 1p-shell nuclei. The generalized Hamiltonian of the Elliott SU(3) model is used to classify these states and to calculate their spectra. The results of the calculations are found to be in good agreement with experimental data. States not observed so far in the cluster spectra of the ¹²C, ¹⁶O, ¹⁰Be, and ¹²Be nuclei are predicted.     

Near-threshold <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis>-meson photoproduction on nuclei

On the basis of the first-collision model that relies on the nuclear spectral function and which includes incoherent processes involving charmonium production in proton–nucleon collisions, the photoproduction of J/ψ mesons on nuclei is considered at energies close to the threshold for their production on a nucleon. The absorption of final J/ψ mesons, their formation length, and the binding and Fermi motion of target nucleons are taken into account in this model along with the effect of the nuclear potential on these processes. The A dependences of the absolute and relative charmonium yields are calculated together with absolute and relative excitation functions under various assumptions on the magnitude of the cross section for J/ψN absorption, the J/ψ-meson formation length, and their inmedium modification. It is shown that, at energies above the threshold, these features are virtually independent of the formation length and the change in the J/ψ-meson mass in nuclear matter but are rather highly sensitive to the cross section for J/ψN interaction. The calculations performed in the present study can be used to determine the unknown cross section for J/ψ-meson absorption in nuclei from a comparison of their results with data expected from experiments in the Hall C of the CEBAF (USA) facility upgraded to the energy of 12 GeV. It is also shown that the absolute and relative excitation functions for J/ψ mesons in photon–nucleus reactions at subthreshold energies are sensitive to the change in the meson mass and, hence, carry information about the properties of charmonium in nuclear matter.     

The cusp effect in <Emphasis Type="Italic">η</Emphasis>′→<Emphasis Type="Italic">η</Emphasis><Emphasis Type="Italic">π</Emphasis><Emphasis Type="Italic">π</Emphasis> decays

Strong final-state interactions create a pronounced cusp in η′→η π ⁰ π ⁰ decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π ⁺ π ⁻ threshold.     

Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.     

Contribution of final-state interaction to the branching ratio of <Emphasis Type="Italic">B</Emphasis>→<Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis><Emphasis Type="Italic">D</Emphasis>

To test the validity of perturbative QCD (pQCD) and investigate its range of application, one should look for a suitable process. B→J/ψ D is a promising candidate. The linear momentum of the products is relatively small, so that there may exist a region where exchanged gluons are soft and the perturbative treatment may fail, so that the non-perturbative effect would be significant. We attribute such non-perturbative QCD effects to the long-distance final-state interaction (FSI) which is estimated in this work. We find that the contribution from the FSI to the branching ratio is indeed sizable and may span the rather wide range of 10⁻⁶∼10⁻⁵ and cover a region where the pQCD prediction is of the same order. A more accurate measurement of its branching ratio may provide important information about the application region of pQCD and help to clarify the picture of inelastic rescattering (i.e. FSI), which is generally believed to play an important role in B decays.     

On a Ströbel-Inspired <Emphasis Type="Italic">k</Emphasis>(<Emphasis Type="Italic">t</Emphasis>) FLRW Ansatz in a Class of Metric <Emphasis Type="Italic">F</Emphasis>(<Emphasis Type="Italic">R</Emphasis>) Models

Assuming a D≥4 dimensional FLRW (Friedmann–Lemaître–Robertson–Walker) inspired ansatz with spatial curvature being a non-trivial function of time k(t) in a class of metric and Jordan frame F(R) gravity models, non-existence theorems for several types of sources are derived in a simple manner (using specific form of the modified gravity Einstein tensor components).     

Near-threshold radiative 3<Emphasis Type="Italic">π</Emphasis> production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

We consider the π⁺π^?π₀γ final state in electron-positron annihilation at c.m.s. energies not far from the threshold. Both initial-and final-state radiations of the hard photon are considered, but without interference between them. The amplitude for the final-state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments, energies are never so small that ρ and ω mesons would have a negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final-state radiation amplitude to account for the vector mesons' influence. Using radiative 3π production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies.     

Final state interactions in the decays <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis>→<Emphasis Type="Italic">VPP</Emphasis>

We investigate the interplay between crossed channel final state interactions and the constraints from two-particle unitarity for the reactions J/ψ→V π π and VK[`(K)]VK\bar{K} , where V is either ω or φ. Using a model where the parameters are largely constrained by other sources, we find that, although small, crossed channel final state interaction can influence the amplitudes considerably, in special areas of phase space. These results cast doubt on the inapplicability of unitarity constraints on production amplitudes as recently claimed in the literature.     

Study of Inelastic <Emphasis Type="Italic">A</Emphasis>(<Emphasis Type="Italic">p,p′</Emphasis>)<Emphasis Type="Italic">X</Emphasis> Reaction with Nuclei at 1 GeV

The secondary-proton polarization and differential cross sections for the (p, p') inelastic reaction on ²⁸Si and ⁵⁶Fe nuclei at the initial proton energy of 1 GeV were measured over a wide range of the scattered-proton momenta at a laboratory angle of Θ = 21?. Scattered protons were detected by means of a magnetic spectrometer equipped with a polarimeter based on multiwire proportional chambers and a carbon analyzer. A structure in the polarization and cross section data, which is probably related to quasielastic scattering off nucleon correlations in the ²⁸Si and ⁵⁶Fe nuclei, was observed as earlier in the analogous data for ¹²C and ⁴⁰Ca nuclei. Momentum intervals within which cross-section ratios for nuclei did not depend on the scattered-proton momentum were found.     

Revised Spherically Symmetric Solutions of <Emphasis Type="Italic">R</Emphasis>+<Emphasis Type="Italic">ε</Emphasis>/<Emphasis Type="Italic">R</Emphasis> Gravity

We study spherically symmetric static empty space solutions in R+ε/R model of f(R) gravity. We show that the Schwarzschild metric is an exact solution of the resulted field equations and consequently there are general solutions which are perturbed Schwarzschild metric and viable for solar system. Our results for large scale contains a logarithmic term with a coefficient producing a repulsive gravity force which is in agreement with the positive acceleration of the universe.     

Measurement of <Emphasis Type="Italic">Z</Emphasis> → <Emphasis Type="Italic">ττ</Emphasis> → <Emphasis Type="Italic">e</Emphasis>µ inclusive process at Large Hadron Collider

In several scenarios of beyond Standard Model physics a new heavy resonance is invoked which may decay preferentially, to a pair of taus. Identification of the decay of Standard Model Z resonance to tau pairs at LHC via subsequent decays of the taus to leptons as well as hadrons is the first step towards the discovery. A method has been suggested to discriminate Z to tau pair to electron+muon final state against various backgrounds, for early phase of 14 TeV LHC.     

Inclusive <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> photoproduction and polarization at HERA in the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k _T -factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics.     

On the <Emphasis Type="Italic">Λ</Emphasis>CDM Universe in <Emphasis Type="Italic">f</Emphasis>(<Emphasis Type="Italic">G</Emphasis>) gravity

In the context of the so-called Gauss–Bonnet gravity, where the gravitational action includes function of the Gauss–Bonnet invariant, we study cosmological solutions, especially the well-known ΛCDM model. It is shown that the dark energy contribution and even the inflationary epoch can be explained in the frame of this kind of theories with no need of any other kind of component. Other cosmological solutions are constructed and the rich properties that this kind of theories provide are explored.     

Transverse-momentum dependence of <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> shadowing effects

We present a new approach to estimate the effect of gluon shadowing in nucleus + nucleus collisions and its consequences on the J/ψ production yield. Using kinematical information available from the measured J/ψ production in proton + proton collisions at  GeV, we build a Glauber Monte Carlo code which takes into account shadowing in two alternative ways: multiple-scattering corrections or Q ² evolution of parton densities. We exploit the dependence of these different parameterizations to the J/ψ transverse momentum and we give the first predictions on the resulting p _T dependence of the nuclear modification factor in deuteron + gold collisions at the same energy.     

Study of in-medium <Emphasis Type="Italic">ω</Emphasis>-meson properties in <Emphasis Type="Italic">Ap</Emphasis> and <Emphasis Type="Italic">pA</Emphasis> collisions

The possibility to investigate the in-medium properties of the vector ω mesons at normal nuclear density is considered. The folding model and simulations with the RQMD generator have been used for studying of the ω-resonance production in Ap and pA reactions and its ω → π ⁰ γ → 3γ decay. We show that measurements in the inverse Ap kinematics is an effective way to get information about the ω-meson mass modification especially in not yet explored range of small meson momenta relative to the projectile nuclei where the strength of the effect is expected to be most strong. The traditional pA kinematics appears to be more preferable for the investigation of the in-medium ω-meson width. Using of compact electromagnetic calorimeter provides the possibility to collect large statistics and study the momentum dependencies of both the ω-meson mass and width at the density of normal nuclei.     

<Emphasis Type="Italic">η</Emphasis><Superscript>7</Superscript>Li Scattering in the <Emphasis Type="Italic">αt</Emphasis>-Cluster Model

The cross sections for elastic and inelastic η-meson scattering on ⁷Li nuclei are obtained on the basis of the αt-cluster representation of the target nucleus. The experimentally known values of the parameters of elastic ηα and αt scattering are used in exactly solving three-body Faddeev equations with separable two-body potentials. The η⁷Li elastic-scattering scattering length found from respective calculations is a_η7Li = ?0.310 ? i0.198 fm.