ψ′ to J/ψ ratio measurements in PHENIX at RHIC

The ratio of the ψ′ over the J ψ production cross section in the dielectron channel has been measured in $ \sqrt s $ \sqrt s = 200 GeV p + p collisions with the PHENIX detector at RHIC. The analysis is based on fitting of the dielectron invariant mass spectra in the area around the J ψ and ψ′ signals in order to extract a ratio ψ′ over J ψ of 0.019 ± 0.005 (stat) ± 0.002 (sys) and a fractional feed-down contribution to J ψ from ψ′ of 8.6 ± 2.5%.     

Angular distributions of leptons from J/ψ’s produced in 920?GeV fixed-target proton-nucleus collisions

A study of the angular distributions of leptons from decays of J/ψ’s produced in p-C and p-W collisions at has been performed in the J/ψ Feynman-x region −0.34<x _F <0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×10⁵ J/ψ’s reconstructed in both the e ⁺ e ⁻ and μ ⁺ μ ⁻ decay channels, indicate that J/ψ’s are produced polarized. The magnitude of the effect is maximal at low p _T . For p _T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises. Many thanks to Antonio Vitale (1943–2008). Deceased. Supported by the Foundation for Fundamental Research on Matter (FOM), 3502 GA Utrecht, The Netherlands. Visitor from Dipartimento di Energetica dell’ Università di Firenze and INFN Sezione di Bologna, Italy. Visitor from P.N. Lebedev Physical Institute, 117924 Moscow B-333, Russia. Visitor from Moscow Physical Engineering Institute, 115409 Moscow, Russia. Visitor from Moscow State University, 119992 Moscow, Russia. Visitor from Institute for High Energy Physics, Protvino, Russia. Visitor from High Energy Physics Institute, 380086 Tbilisi, Georgia. Also from Fondazione Giuseppe Occhialini, 61034 Fossombrone (Pesaro Urbino), Italy. Supported by the CICYT contract AEN99-0483. Supported by the German Research Foundation, Graduate College GRK 271/3.     

Di-jet production in γ γ collisions at LEP2

The production of two high-p _T jets in the interactions of quasi-real photons in e ⁺ e ⁻ collisions at from 189 GeV to 209 GeV is studied with data corresponding to an integrated e ⁺ e ⁻ luminosity of 550 pb⁻¹. The jets reconstructed by the k _⊥ -cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p _T , above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum of the jets and is compared to perturbative QCD calculations. Deceased     

Simulation study of χc→J/Ψ+γ detection with J/Ψ→e+e? in pp collisions in the ALICE experiment at LHC

We present Monte Carlo preliminary results about the feasibility to detect the χ _c family in p-p collisions at 14 TeV in the ALICE Central Barrel at CERN LHC. The χ _c1 and χ _c2 were forced to decay in the radiative channel J/Ψ+γ→e ⁺ e ⁻+γ and were merged with a proton-proton non-biased collision. After Monte Carlo transport and simulation of the detector response, the e ⁺, e ⁻ and converted γ were reconstructed and identified in the ALICE ITS, TPC and TRD detectors. Separate signals corresponding to γ from χ _c1 and from χ _c2 were observed. The position and relative weight of the fit to gaussians agreed with the input values within the statistical limits. An erratum to this article can be found at     

Measurements of dihadron correlations relative to the event plane in Au+Au collisions at √sNN=200 GeV

Dihadron azimuthal correlations containing a high transverse momentum (PT) trigger particle are sensitive to the properties of the nuclear medium created at RHI...     

Study of B c → J / ψ π , η c π decays with?perturbative?QCD?approach

The B _c →J/ψ π, η _c π decays are studied with the perturbative QCD approach. It is found that the form factors and for the B _c →J/ψ, η _c transitions and the branching ratios are sensitive to the parameters ω, v, f _J/ψ and , where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively, and f _J/ψ and are the decay constants of the J/ψ and η _c mesons, respectively. The large branching ratios and the clear signals of the final states make the B _c →J/ψ π, η _c π decays the prospective channels for measurements at the hadron colliders.     

Breakup of an oxygen nucleus to light fragments of mass number in the range A ? 4 in 16Op interactions at a momentum of 3.25 GeV/c per nucleon

New experimental data on the correlations of the yields of ⁴He and ²H nuclei in semi-inclusive reactions involving by the production of ³He and ³H mirror nuclei in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. The mean multiplicities of protons and neutrons appearing as fragments are found to be independent of the number of associated deuterons, this indicating that a considerable part of these fragments originate from the breakup of the alpha-particle clusters forming the oxygen nucleus.     

Delicate interplay between the D0D?0, ρ0J/ψ, and ωJ/ψ channels in the X(3872) resonance

The nature of the X(3872) enhancement is analyzed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular J ^PC =1⁺⁺ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo–Zweig–Iizuka-forbidden ρ ⁰ J/ψ and ωJ/ψ channels are coupled as well, but effectively smeared out by using complex ρ ⁰ and ω masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the D ⁰ D ^∗0, ρ ⁰ J/ψ, and ωJ/ψ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector c[`(c)]c\bar{c} resonance, with a pole at or slightly below the D ⁰ D ^∗0 threshold.     

Characteristics of Λ andK 0 particles produced in central nucleus nucleus collisions at a 4.5 GeV/c momentum per incident nucleon

Data on Λ's andK ⁰'s, produced in central nucleus-nucleus collisions (C?C, C?Ne, O?Ne, C?Cu, C?Zr, C?Pb, O?Pb) at a 4.5 GeV/c momentum per incident nucleon obtained in the streamer chamber spectrometer SKM-200, are presented. Multiplicities, transverse momenta, rapidities and other characteristics are considered and compared with those for inelastic He?Li interactions. The polarization of Λ's was found to be consistent with zero. The upper limit of \(\bar \Lambda /\Lambda \) production ratio was estimated to be ≤10^?2 with a 90% confidence level. The results are compared with data of other experiments and some model calculations.     

First measurement of J/ψ anisotropy by PHENIX experiment at RHIC

Understanding the J/ψ suppression and possible recombination mechanisms at RHIC is one of the outstanding challenges for theorists and experimentalists. Recent results provided by PHENIX showed a stronger suppression at forward rapidity, while at mid-rapidity the suppression is similar to lower energy collision experiments. A large sample of Au + Au collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV was collected in 2007 with the PHENIX experiment at RHIC. Using this sample, J/ψs were identified in the di-electron decay channel. In order to probe the charm coalescence as an additional J/ψ production mechanism at RHIC, we studied the first determination of its v ₂ elliptic flow parameter at mid-rapidity.     

J/ψ suppression vs centrality at forward and mid-rapidity in Au+Au collisions at RHIC in colour screening mechanism

We extend our previous formalism [Phys. Lett. B 656 45 (2007)] on J/ψ suppression at midrapidity using the colour screening framework. Our formalism is more general as the complete rapidity, transverse momentum and centrality dependence including J/ψ suppression at forward as well as mid-rapidity can be computed directly from it. We have assumed that QGP fluid is expanding obeying Bjorken’s boost invariant scaling law and bag model EOS is used. Sequential melting of χ _c (1P) as well as ψ′ (2S) higher resonances is incorporated. We find that our model shows a reasonable agreement with the mid and forward rapidity data. Furthermore, we observe a larger suppression at forward rapidity in our model which is again well supported by the PHENIX data.     

Reaction e + e ? → π + π ? π + π ? at energies of √ s ≤ 1 GeV

The e ⁺ e ⁻ → π ⁺ π ⁻ π ⁺ π ⁻ cross section is calculated for energies of 0.65 ≤ √s ≤ 1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2 and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations with the data. It is found that, at √s ≈ 1 GeV, the contributions of the above resonances are much larger, by a factor of 30, than the ρ(770) one, and amount to a considerable fraction ∼0.3–0.6 of the latter at √s ∼ m _ρ. The text was submitted by the authors in English.     

Inclusive J/ψ and χc meson production in pp collisions at RHIC

Inclusive cross sections for J/ψ and χ _c production in pp collisions were calculated in the k _t -factorization approach for the RHIC energy. Several mechanisms were considered. Radiative χ _c decays and direct color-singlet contributions constitute the dominant mechanisms of J/ψ production. The results are compared with recent RHIC data.     

α-particle spectrum in the reaction p + 11B → α + 8Be* → 3α

Using a simple phenomenological parametrization of the reaction amplitude we calculated α-particle spectrumin the reaction p + ¹¹B → α + ⁸Be* → 3α at the resonance proton energy of 675 keV. The parametrization includes Breit-Wigner factor with an energy-dependent width for intermediate ⁸Be* state and the Coulomb and the centrifugal factors in α-particle-emission vertices. The shape of the spectrum consists of a well-defined peak corresponding to emission of the primary α and a flat shoulder going down to very low energy. We found that below 1.5MeV there are 17.5% of α’s and below 1MeV there are 11% of them. The text was submitted by the author in English.     

Λp femtoscopy in collisions of Ar + KCl at 1.76 A GeV with HADES

Results on Λp femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76.A GeV, the reaction Ar + KCl was studied with HADES at SIS18/GSI. A high-statistics and high-purity Λ sample was collected, allowing for the investigation of Λp correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations allowing the determination of the space-time extent of the Λp emission source. The Λp radius is found significantly smaller than that for Au + Au/Pb + Pb collisions in the AGS, SPS and RHIC energy domains, but larger than that for electroproduction from He. Taking into account all available data, we find the Λp source radius to increase almost linearly with the number of participants to the power of one-third.     

Properties of the ? meson at high temperatures and densities

We calculate the spectral density of the ϕ meson in a hot bath of nucleons and pions using a general formalism relating self-energy to the forward scattering amplitude (FSA) [1,2]. In order to describe the low energy FSA, we use experimental data along with a background term. For the high energy FSA, a Regge parameterization is employed. We verify the resulting FSA using dispersion techniques. We find that the position of the peak of the spectral density is slightly shifted from its vacuum position and that its width is considerably increased. The width of the spectral density at a temperature of 150 MeV and at normal nuclear density is more than 90 MeV.     

Rare decays of Λ b → Λ γ and Λ b → Λ l + l ? in universal extra-dimension model

The exclusive weak decay of Λ _b →Λ γ and Λ _b →Λ l ⁺ l ⁻ are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the branching ratio of Λ _b →Λ γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ _b →Λ l ⁺ l ⁻. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ _b →Λ μ ⁺ μ ⁻ is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ _b decays are not a useful tool to provide any valuable information for the universal extra-dimension model.     

Signals of α clusters in 16O+16O collisions at the LHC from relativistic hydrodynamic simulations

In relativistic heavy ion collisions, the fluctuations of initial entropy density convert to the correlations of final state hadrons in momentum space through the collective expansion of strongly interacting QCD matter. Using a (3+1)D viscous hydrodynamic program, CLVisc, we consider whether the nuclear structure, which provides initial state fluctuations as well as correlations, can affect the final state of heavy ion collisions, and whether one can find signals of α cluster structures in oxygen using final state observables in \begin{document}$ ^{16}\text{O}+{}^{16}\text{O} $\end{document} collisions at the CERN Large Hadron Collider. For the initial nucleon distributions in oxygen nuclei, we compare three different configurations, a tetrahedral structure with four-α clusters, the deformed Woods-Saxon distribution, and a spherical symmetric Woods-Saxon distribution. Our results show that the charged multiplicity as a function of centrality and the elliptic flow at the most central collisions using the four-α structure differs from those with the Woods-Saxon and deformed Woods-Saxon distributions, which may help to identify α clustering structures in oxygen nuclei.     

Spectral temperatures of Δ0(1232) resonances produced in p 12C and d 12C collisions at 4.2 GeV/c per nucleon

The reconstructed experimental transverse momentum (p _t ) distributions of Δ⁰(1232) resonances produced in p ¹²C and d ¹²C collisions at 4.2 A GeV/c and the corresponding spectra calculated using Modified FRITIOF model were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of Δ⁰(1232) resonances were extracted from fitting their p _t spectra with one-temperature Hagedorn function. The extracted spectral temperatures of Δ⁰(1232) were compared with the corresponding temperatures of π ^? mesons in p ¹²C and d ¹²C collisions at 4.2 A GeV/c obtained similarly from fitting the p _t spectra of π ^? by one-temperature Hagedorn function. The spectral temperatures of Δ⁰(1232) resonances agreed within uncertainties with the corresponding temperatures of π ^? mesons produced in p ¹²C and d ¹²C collisions at 4.2 A GeV/c.