Search

The deconfined state of strongly interacting quarks and gluons, quark–gluon plasma, may be formed in relativistic ion collisions at sufficient temperature and energy density. The signatures of quark–gluon plasma formation were observed in heavy-ion collisions by studying meson production. In small-collision systems, such as , , , and , the volume and lifetime of the produced medium might be insufficient for observation of quark–gluon plasma effects. However various physics mechanisms reflecting initial state of the collision, cold nuclear matter effects, may lead to a collective-like behavior in small-collision systems without quark–gluon plasma formation. The nuclear modified parton distribution functions are considered to be an underlying physics mechanism of cold nuclear matter effects. This paper presents the comparison of meson production in , , , and collisions at GeV at midrapidity ( , measured by PHENIX, to PYTHIA calculations with nuclear modified parton distribution functions EPPS16 and CTEQ15. The meson production in collisions at GeV might be driven by mechanisms additional to nuclear modification of parton distribution functions. [ABSTRACT FROM AUTHOR]

The photoproduction of J/ψ mesons off nuclei at the energies of 8 and 11 GeV, which are close to the threshold for their production on a free nucleon, is considered on the basis of the first-collisionmodel relying on the nuclear spectral function and including incoherent processes of charmonium production in photon-nucleon collisions. The model takes into account the absorption of final J/ψ mesons, the binding of target nucleons, and their Fermi motion, as well as the effect of the scalar J/ψ-nucleus potential (or the inmedium shift of the J/ψ-meson mass) on these processes. Under various assumptions on the magnitude of this shift, the momentum dependences of various observables, such as the relative transparency of carbon and gold nuclei and the J/ψ-meson yields, are calculated for meson production on these nuclei. The observables in question include the relative transparencies of these nuclei to J/ψ mesons and the absolute and relativemeson yields from them. It is shown that, at the energy of 11 GeV, which is above the threshold, the first observable is virtually independent of the in-medium change in the J/ψ-meson mass. At the same time, it is moderately sensitive to this change at the subthreshold energy of 8 GeV. On the other hand, it is shown that, at these photon energies, the absolute and relative values of the differential cross sections, especially for the the heavy nucleus of 197 Au, in the momentum range of 4-6 GeV/с are highly sensitive to the in-medium change in the J/ψ-meson mass. Therefore, the present calculations can be used to determine the unknown shift of the J/ψ-meson mass in nuclei by means of comparing their results with data expected from experiments in Hall C at the Continuous Electron Beam Accelerator Facility (CEBAF, USA) upgraded to the energy of 12 GeV. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Interpretations of the most recent experimental data on double J/ ψ production are discussed. It is shown that a significant signal in the region of high invariant masses of a J/ ψ pair may be a piece of evidence not only in favor of the dominance of double parton scattering in this region. The diagrams involving two-gluon exchange in the t channel, which are considered in the present study, make a commensurate contribution to the above production process in the region in question and also to the double production of J/ ψ mesons characterized by a large rapidity difference. [ABSTRACT FROM AUTHOR]

The results obtained by studying the production of six-nucleon systems and nuclei that is accompanied by the yield of charged pions in O p collisions at a momentum of 3.25 GeV/ c per nucleon are presented. It is shown that the correlation of the yield of mirror H (He) nuclei with the production of π ( π) mesons is due to the charge-exchange process involving an oxygen-nucleus proton (neutron) knocked out predominantly from an alpha-particle cluster. [ABSTRACT FROM AUTHOR]

Cross sections for Jψ-meson pair production in proton-proton interaction at the c.m. collision energy of $$\sqrt s = 7$$ TeV were theoretically predicted under conditions of various kinematical cuts. The possible contribution to this process from the decays of 4 c tetraquarks, new hypothetic particles consisting of two valence c quarks and two valence $$\bar c$$ antiquarks, was studied. It is shown that at least one such state (tensor 4 c tetraquark) can in principle be observed experimentally under conditions of the LNCb experiment. [ABSTRACT FROM AUTHOR]

Multiparticle azimuthal correlations of π mesons have been studied in dC, HeC, CC, CNe, MgMg, ( d, He)Ta, CCu, CTa, and OPb collisions at momentum of 4.2, 4.5 GeV/ c per nucleon within the standard transverse momentum analysis method of P. Danielewicz and G. Odyniec. The data were obtained by SKM-200-GIBS and Propane Bubble Chamber Collaborations of JINR. The axis has been selected in the phase space and with respect to this axis π meson correlations were observed. The values of the coefficient of the correlations linearly depend on the mass numbers of projectile ( A) and target ( A) nuclei. The Quark-Gluon String Model satisfactorily describes the experimental results. [ABSTRACT FROM AUTHOR]

Light hadrons provide a convenient tool for studying the properties of hot and dense media formed in central collisions of relativistic heavy nuclei. The results obtained in the PHENIX experiment at the relativistic heavy-ion collider (RHIC, Brookhaven National Laboratory, USA) by measuring nuclearmodification factors for light hadrons in various colliding systems ( pp, dAu, CuCu, and AuAu) at the c.m. energies of √ s = 62.4 and 200 GeV are presented. [ABSTRACT FROM AUTHOR]

The results of data handling for the E-184 experiment involving the irradiation of the active target, consisting of carbon, silicon, and lead plates by a 70-GeV proton beam are presented. When the two-prong neutral charmed meson decay signal was selected and the cross section for charm production at a near-threshold energy was estimated ( σ( c $$ \bar c $$) = 7.1 ± 2.4(stat.) ± 1.4(syst.) µb/nucleon), some properties of D and $$ \bar D^0 $$ were investigated. These include the atomic-weight dependence of the cross section on the target mass number (its A dependence); the differential cross sections dσ/dp and dσ/dx; and the dependence of the parameter α on x, p, and p. The experimental results are compared with the predictions of the FRITIOF7.02 program. [ABSTRACT FROM AUTHOR]

New experimental data on π-meson production in interactions between carbon and tantalum nuclei at amomentumof 4.2 GeV/ c per nucleon are presented. These results are compared with predictions based of themodel of quark-gluon strings (QGS) that is adapted to intermediate energies ( $$ \sqrt 4 $$ ≤ 4 GeV). It is shown that the QGS model only qualitatively reproduces the behavior of experimental kinematical features of π mesons. [ABSTRACT FROM AUTHOR]

In the framework of k f-factorization approach, inclusive production of J/ψ mesons at HERA is considered. The differential cross sections and spin-density matrix elements are calculated. Theoretical predictions are compared with recent H1 experimental data. [ABSTRACT FROM AUTHOR]

The dependence of the nucleon magnetic moments on the pion mass is studied in the framework of the extended linear sigma model. The field equations have been solved in the mean-field approximation. A remarkable agreement is observed in comparison with other models. [ABSTRACT FROM AUTHOR]

Using the extrapolation of existing data, estimations of prompt-photon production at FAIR energies have been made. At y = yc.m. the rapidity density of prompt photons with p t > 1.5 GeV/ c per central Au + Au event at 25 A GeV is estimated as ∼10−4. With the planned beam intensity 109 per second and 1% interaction probability, for 10% of most central events one can expect the prompt-photon rate ∼102 photons per second. Direct photons from the hadron scenario of ion collisions generated by the Hadron-String-Dynamics (HSD) transport approach with implemented meson scatterings πρ → πγ, ππ → ργ have been analyzed. Photons from short-living resonances (e.g., ω → π0 γ) decaying during the dense phase of the collision should be considered as direct photons. They contribute significantly in the directphoton spectrum at p t = 0.5–1 GeV/ c. At the FAIR energy 25 A GeV in Au + Au central collisions the HSD generator predicts, as a lower estimate, γdirect/ $$ \gamma _{\pi ^0 } $$ ≃ 0.5% in the region p t = 0.5–1 GeV/ c. At p t = 1.5–2 GeV/ c γprompt/ $$ \gamma _{\pi ^0 } $$ ≃ 2%. Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics (BHD) model. The BHD spectra differ strongly from the HSD predictions. The direct-photon spectrumis very sensitive to the initial temperature parameter T0 of the model. The 10-MeV increase in the T0 value leads to ∼2 times higher photon yield. [ABSTRACT FROM AUTHOR]

The results of theoretical calculations within the semihard ( k T-factorization) approach are compared with the latest data obtained in the ZEUS experiment at the HERA collider for the inelastic electroproduction of J/ψ mesons in the kinematical region specified by the inequalities 2 GeV2 < Q 2 < 80 GeV2, 50 GeV < W < 250 GeV, 0.2 < z < 0.9, and −1.6 < y ψlab < 1.3. The dependence of these theoretical results on the choice of parametrization among three widely used parametrizations of unintegrated gluon distributions is studied. [ABSTRACT FROM AUTHOR]

The process of Λ-baryon production in πp collisions is considered. The contribution of the string-junction mechanism to the strange-baryon production in meson-baryon scattering is analyzed. The results of numerical calculations in the framework of the quark-gluon string model are in reasonable agreement with the data. [ABSTRACT FROM AUTHOR]

The inelastic photo- and electroproduction of J/ψ mesons at the HERA collider are considered within the semihard (kT-factorization) QCD approach and the color-singlet model. The total, differential, and double-differential cross sections for the inelastic production of J/ψ mesons are investigated versus the Pomeron intercept Δ, which is the basic parameter of low-x physics; also studied here is the spin alignment parameter α versus the square of the transverse momentum, pψT², and the variable z. The theoretical results obtained in the present study are compared with the latest experimental data of the H1 and ZEUS Collaborations. It is shown that experimental investigations of the polarization properties of J/ψ mesons at the HERA collider for Q² < 1 GeV² may provide an additional test of the Balitsky-Fadin-Kuraev-Lipatov dynamics of gluon distributions. [ABSTRACT FROM AUTHOR]

The normalized single-particle semi-inclusive double-differential spectrum of π[sup –] mesons from pp interactions at 6.6–400 GeV/c and the relative concentration of π[sup 0] and K[sup 0][sub S] mesons in such events of fixed multiplicity of π[sup –] mesons are completely determined by specifying any feature of this spectrum—for example, 〈y[sup 2]〉[sub n] or [sub n]. Therefore, a two-parameter sample of semi-inclusive events that depends on the energy and the multiplicity reduces to a one-parameter sample.© 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We consider near-threshold a[sub 0](980)-meson production in πN and NN collisions. An effective Lagrangian approach with one-pion exchange is applied to analyze different contributions to the cross section for different isospin channels. The Reggeon exchange mechanism is also evaluated for comparison. The results from πN reactions are used to calculate the contribution of the a[sub 0] meson to the cross sections and invariant KK mass distributions of the reactions pp → pnK[sup +]K[sup 0] and pp → ppK[sup +]K[sup –]. It is found that the experimental observation of a[sub 0][sup +] mesons in the reaction pp → pnK[sup +]K[sup 0] is much more promising than the observation of a[sub 0][sup 0] mesons in the reaction pp → ppK[sup +]K[sup –]. Effects of isospin violation in the reactions pN → da[sub 0], pd → [sup 3]He([sup 3]H)a[sub 0], and dd → [sup 4]Hea[sub 0], which are induced by a[sub 0](980)–f[sub 0](980) mixing, are also analyzed.© 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

We present a comparative analysis of three different theoretical approaches to the production of B[sub s] and B[sub c] mesons in high-energy hadron collisions. Our attention focuses on the azimuthal and pseudorapidity correlations between B[sub s] or B[sub c] mesons and accompanying strange or charmed particles. The corresponding kinematical distributions are found to exhibit a high sensitivity to details of the production mechanism and can therefore serve as indicators of interaction dynamics. [ABSTRACT FROM AUTHOR]

The spectra of π[sup -] mesons originating from pC, HeC, CC, and CTa collisions are analyzed in terms of the light-front variables ξ and ζ. The angular and momentum distributions of π[sup -] mesons are studied in various regions of the variables ξ[sup ±] and ζ[sup ±]. These distributions in the regions ξ[sup +] < &ζtilde;[sup +] and ξ[sup +] > &ξtilde;[sup +] do not admit a unified description. In the region ξ[sup +] < &ξtilde;[sup +], the distributions in question are consistent with predictions of the statistical model. The temperature parameter T decreases almost linearly with increasing product of the mass numbers of colliding nuclei (that is, with increasing number of interacting nucleons). The distributions in the region ξ[sup +] > &ξtilde;[sup +] are fitted to semiempirical forms. [ABSTRACT FROM AUTHOR]