B0 ? ffB^0 \to \phi\phi decay in perturbative QCD approach

The rare decay can occur only via the penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small: around 10^-8. We also give the polarization fractions, which show that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM makes it sensitive to any new physics contributions.Received: 29 January 2005, Published online: 28 April 2005     

Measurement of ω/? → e+e? in proton + proton collisions at ?s \sqrt s = 200 GeV at RHIC-PHENIX

The PHENIX experiment at RHIC has measured ω and ϕ meson production using di-electron decay mode over a psude-rapidity range of |η| ≤ 0.35 and a transverse momentum range of 0 < p _T < 5 GeV/c in proton + proton collisions at $ \sqrt s $ \sqrt s = 200 GeV. The spectra of production cross section as a function of p _T for ω and ϕ → e ⁺ e ⁻ show good agreement with other hadornic decay channels ω → π ⁰ γ, ω ⁰ π ⁺ π ⁻ and ϕ → K ⁺ K ⁻, respectively.     

J/ψ production in pp collisions at ?s \sqrt s = 200GeV in the STAR experiment

In this work we present the J/ψ measurement in p+p collisions within the STAR collaboration Quarkonium program. This measurements aim to be the baseline measurement of a more comprehensive systematic study of quarkonium states production in order to understand their in medium modification. Here we report the total cross section and p _T distribution, and find them to be consistent with pQCD CEM predictions as well as to previous measurements at the same center-of-mass energy.     

Inclusive measurement of [`(p)]\bar p annihilation at rest in gaseous hydrogen to final states containingρ andf2

Antiproton annihilation at rest in gaseous hydrogen (16 bar pressure) to the final states (770)X andf ₂(1270)X, whereX stands for one or more neutral mesons, has been studied at LEAR using the CPLEAR detector. Relative branching ratios are given forX = ⁰,2 ⁰, 3 ⁰ in the case, and forX = ⁰, in thef ₂ case. The annihilation channel has not been measured before. The fraction of P-wave annihilation is deduced from the ratiof ₂ ⁰/ ⁰ to be 0.38±0.07, in good agreement with the result previously obtained by CPLEAR from the ratioK ⁺ K ^-/ ^{+ -}.     

Spin correlations of \varLambda[`\varLambda]\varLambda{\bar{\varLambda}} pairs as a probe of quark–antiquark pair production

The polarizations of Λ and [`\varLambda]{\bar{\varLambda}} are thought to retain memories of the spins of their parent s quarks and [`(s)]{\bar{s}} antiquarks, and are readily measurable via the angular distributions of their daughter protons and antiprotons. Correlations between the spins of Λ and [`\varLambda]{\bar{\varLambda}} produced at low relative momenta may therefore be used to probe the spin states of s [`(s)]s {\bar{s}} pairs produced during hadronization. We consider the possibilities that they are produced in a ³P₀ state, as might result from fluctuations in the magnitude of á[`(s)] s ?\langle {\bar{s}} s \rangle, a <sup>1</sup>S<sub>0</sub> state, as might result from chiral fluctuations, or a <sup>3</sup>S<sub>1</sub> or other spin state, as might result from production by a quark–antiquark or gluon pair. We provide templates for the p [`(p)]p {\bar{p}} angular correlations that would be expected in each of these cases, and discuss how they might be used to distinguish s [`(s)]s {\bar{s}} production mechanisms in pp and heavy-ion collisions.     

Correlations between D and [`(D)]{\overline D} mesons produced in 500 GeV/cπ?-nucleon interactions

We present a study of correlations between D and mesons produced in 500 GeV/cπ⁻-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed 791 ± 44 charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the , and significant correlations between the azimuthal angle of the D and the . The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the PYTHIA/JETSET Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production.The relative production rates for the four sets of charm pairs, as calculated in the PYTHIA/JETSET event generator with the default parameters, agree with data as far as the relative ordering, but predict too many pairs and too few pairs.     

Measurement of D* mesons in jets from p + p collisions at ?s \sqrt s = 200 GeV

We report the measurement of charged D* mesons in jets produced in proton-proton collisions at a center of mass energy $ \sqrt s $ \sqrt s = 200 GeV with the STAR experiment at RHIC. The production rate is found to be N(D*⁺ + D*⁻)/N (jet) = 0.015 ± 0.008 (stat) ± 0.007 (sys) for D* mesons with fractional momenta 0.2 < z < 0.5 in jets with 11.5 GeV mean transverse energy. This rate is consistent with perturbative QCD evalulation of gluon splitting into a pair of charm quarks and subsequent hadronization.     

Logics from ?{￠}\sqrt{^{\prime}} Quasi-MV Algebras

The purpose of the present article is to extend the scope of some investigations about abstract logics arising quite naturally out of Quasi-MV algebras (for short, qMV algebras) also to ?{^￠}\sqrt{^{\prime}} qMV algebras. We will therefore introduce, mutually compare and (in some cases) axiomatise several logics arising out of the variety of ?{^￠}\sqrt{^{\prime}} qMV algebras and out of some important subclasses of such. Subsequently, we will investigate the same logics by resorting to the methods and techniques of abstract algebraic logic.     

Baryon-charge transfer and production asymmetry of Λ0/ [`(L)] 0\bar \Lambda ^0 in hadron interactions

Predictions were made for asymmetry between production spectra of Λ⁰ and at the energy of LHC experiments. The value of A(s) should be situated in the corridor between two curves calculated in the quark-gluon string model with two possible values of intercept α _SJ(0) = 0.5 and 0.9. Both curves describe the asymmetries measured at lower energies up to RHIC experiments. The data of the H1 experiment can be fitted only with α _SJ(0) = 0.9. The text was submitted by the author in English.     

Measurement of π0 and η mesons with PHENIX in ?[`(sNN )]\surd \overline {s_{NN} } 200 GeV Au+Au collisions at RHIC

The π ^o meson has been a crucial probe for observing jet quenching in ultrarelativistic heavy-ion collisions at RHIC. Measurements of the η meson in the same collisions have also shed light on a possible dependence of the observed suppression on the particle species. The preliminary π ⁰ nuclear modification factor R _AA from the 2004 RHIC run allowed a first systematic comparison between a precise measurement with high statistics and theoretical calculations, constraining model parameters such as the initial gluon density dN^g/dy, and the transport coefficient [^(q)]\hat q. The final π ⁰ spectra and R _AA are shown as well as the first η results obtained with both PHENIX electromagnetic calorimeters.     

Pion correlations and resonance effects in [`(p)]p\bar pp annihilation at rest to 2π+2π-π0

We study ππ correlations in the exclusive reaction at rest with complete reconstruction of the kinematics for each event. Inclusive and differential distributions properly normalized show an enhancement for small invariant masses M ₊₊,M _-- of like-pion pairs. An even stronger enhancement is seen for the double differential distributions for low pion-pair masses. The signal is strongest when the π₀ energy is large and much weaker when this energy is small. Dynamical models with resonances in the final state are confronted with the data. For the kinematic situation where the ρ3π channel is important the simulation predicts a large pion correlation for the double differential density, qualitatively explaining the observed bahaviour. The stochastic HBT mechanism is not supported by these findings for the exclusive annihilation reaction studied.     

Search for a fourth generation b’-quark at LEP-II at ?s= \sqrt{s}=\,196–209?GeV

A search for the pair production of fourth generation b’-quarks was performed using data taken by the DELPHI detector at LEP-II. The analysed data were collected at centre-of-mass energies ranging from 196 to 209 GeV, corresponding to an integrated luminosity of 420 pb^-1. No evidence for a signal was found. Upper limits on BR(b’→bZ) and BR(b’→cW) were obtained for b’ masses ranging from 96 to 103 GeV/c ². These limits, together with the theoretical branching ratios predicted by a sequential four generations model, were used to constrain the value of , where V_cb′, V_tb′ and V_tb are elements of the extended CKM matrix.     

Measurement of ω mesons via radiative decay mode in ?s\surd s = 200 GeV Au+Au collisions at RHIC-PHENIX

We report on ω mesons’ production via radiative decay mode (ω → π ⁰ γ, π ⁰ → 2γ) in ?s\sqrt s = 200 GeV Au+Au collisions at RHIC-PHENIX. The main difficulty of this analysis is the huge combinatorial background inevitable for reconstructing particles from the three- body decay mode. The emphasis is on the feasibility study using both simulation and real data to search the best parameters that improve S/?BS/\sqrt B . For this purpose, we examine several sets of energy and momentum cuts for selecting π ⁰ and γ. To evaluate the remaining background, we consider three background sources; correlated/uncorrelated background and K _s ⁰ contribution, then we subtract them. The amount of these contributions is determined by a fit on a mass spectrum. The result suggests that ω meson production is suppressed in central Au+Au collisions at high pT region.     

η, h￠ \eta{^\prime} → πl+l- in a chiral unitary approach

The decays η, → π⁺π^- l ⁺ l ^- (with l = e,μ are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels Bethe-Salpeter equation. Predictions for the decay widths and spectra are given.     

Stopping in ?{sNN } \sqrt {s_{NN} } = 62.4 GeV Au+Au collisions

Stopping in heavy ion collisions has been measured at several energies from AGS to RHIC (spanning $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 5 GeV to $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 200 GeV).The systematics of stopping hint the onset of a collision regime that might include LHC energies. Stopping in $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 62.4 GeV Au+Au collisions contribute to the understanding of different collision systems.     

Charged kaon spectra from Au+Au collisions at ?{sNN }\sqrt {s_{NN} } = 200 GeV

The Time-of-Flight detector, based on MRPC technology, has greatly enhanced particle identification capability in STAR. By combining dE/dx measured by the TPC and velocity information from the TOF, we have extended the charged kaon transverse momentum spectra measurements up to ρ _T − 5 GeV/c at mid-rapidity for Au+Au collisions at ?{s_NN }\sqrt {s_{NN} } = 200 GeV. Estimation of charged kaon’s contribution factors from K* and ϕ is also made.     

B-meson measurement via secondary J/ψ production in Pb-Pb collisions at ?{sNN } \sqrt {s_{NN} } = 5.5 TeV in the CMS

The production of heavy quarks in heavy-ion collisions is important because it is expected to give information about high-density QCD matter. One interesting channel of heavy quark measurements at LHC is the decay of B to J/ψ. The J/ψ mesons from this channel can be separated from the primary J/ψ (produced at collision vertex) by using the secondary vertex which is efficiently reconstructed with the CMS tracker. In this work, the generator level results for the primary and secondary J/ψ obtained through dimuon pairs are presented for pp and PbPb collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 5.5 TeV.     

Search for pair-produced neutralinos in events with photons and missing energy from e+e- collisions at ?s = 130 - 183\sqrt s = 130 - 183 GeV

The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e⁺e^- → YY with the subsequent decay Y → X7, where X is an undetectable neutral particle. Reactions of this kind are expected in supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles, a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path.     

PHENIX study of dihadron correlation in Au+Au collision at ?{sNN } \sqrt {s_{NN} } = 200 GeV: jet quenching and medium response

We provide a detailed survey study of dihadron azimuthal angle (Δϕ) correlations in a broad range of transverse momentum (0.4 < p _T < 10 GeV/c) and centrality (0–92%) in Au+Au collisions at 149-2 = 200 GeV. The evolution of the jet shape and yield with p _T seems to suggest two distinct components at the away-side pairs: a suppressed jet fragmentation component around Δϕ ∼ π, and a medium-induced components around |Δϕ − π| ∼ 1.1. The former dominates p _T > 5 GeV/c and the later dominates at p _T < 4 GeV/c.