Jet fragmentation function moments in heavy ion collisions

The nature of a jet’s fragmentation in heavy-ion collisions has the potential to cast light on the mechanism of jet quenching. However, the presence of the huge underlying event complicates the reconstruction of the jet fragmentation function as a function of the momentum fraction z of hadrons in the jet. Here we propose the use of moments of the fragmentation function. These quantities appear to be as sensitive to quenching modifications as the fragmentation function directly in z. We show that they are amenable to background subtraction using the same jet-area-based techniques proposed in the past for jet p _t ’s. Furthermore, complications due to correlations between background-fluctuation contributions to the jet’s p _t and to its particle content are easily corrected for.     

Correlation between the pionization region and the fragmentation region in high energy proton-proton collisions

Measurements are reported of two-particle correlations in high energy proton-proton collisions with one particle in the pionization region and the other a proton in the fragmentation region. The correlation function is independent of x of the fragmentation proton for 0.55 ? x ? 0.9 and rises at small x. There is an indication that the correlation is an energy-independent function of x. The measurements for two values of the rapidity of the pionization particle give similar results.     

Polarization effects in proton-proton collisions

The single-spin and double-spin asymmetries in pp→(γ*, Z)+X processes induced by collisions of polarized protons are investigated on the basis of QCD and electroweak interaction by using the method of helicity amplitudes. Analytic expressions for the single-spin (A _L) and double-spin (A _LL) asymmetries are obtained, and their dependence on the dilepton transverse momentum is investigated at three values of the dilepton invariant mass. The results obtained in this study make it possible to explore the spin structure of the proton.     

Non-leptonic B decays into two light mesons in soft-collinear effective theory

We consider non-leptonic B decays into two light mesons at leading order in soft-collinear effective theory, and show that the decay amplitudes are factorized at next-to-leading order in _s. The operators for non-leptonic B decays in the full theory are first matched to the operators in SCET_I, which is the effective theory appropriate for with Λ0.5 GeV. We evolve the operators and the relevant time-ordered products in SCET_I to SCET_II, which is appropriate for . Using the gauge-invariant operators in SCET_II, we compute non-leptonic B decays in SCET, including the non-factorizable spectator contributions and spectator contributions to the heavy-to-light form factor. As an application, we present the decay amplitudes for in soft-collinear effective theory.     

Muon-electron events in high-energy proton-proton collisions

The tube models of nuclear production are questioned by pointing out that they cannot explain the dependence of the inclusive rapidity distribution width and the two-particle correlation function on the atomic number of the target nucleus.     

Super-transfer within the fragmentation theory of heavy-ion collisions

With the mass-asymmetry described by the dynamical collective fragmentation coordinateη, relevant collective potentials and mass parameters in heavy-ion fusion and collision processes calculated for the U-U system are considered and the structure of the collective Hamiltonian is examined. Conclusions on supertransfer leading to the eventual formation of superheavy elements are indicated.     

Antideuteron production in proton-proton and proton-nucleus collisions

The experimental data of the antideuteron production in proton-proton and proton-nucleus collisions are analyzed within a simple model based on the diagrammatic approach to the coalescence model. This model is shown to be able to reproduce most of the existing data without any additional parameter. Received: 18 April 2002 / Accepted: 30 August 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: duperray@isn.in2p3.fr RID="b" ID="b"e-mail: protasov@isn.in2p3.fr RID="c" ID="c"e-mail: avoronin@aha.ru Communicated by A. Molinari     

Large transverse momentum jets in high-energy proton-proton collisions

We present a study of pp collisions producing large transverse momentum π⁰'s. The data collected at c.m. energies √s=52.4 and 62.7 GeV, give evidence for a two-jet structure. The fragmentation of the jets is studied and correlations between the two jets are investigated. Results are compared with e⁺e^? and νp data.     

Aspects of φ-meson production in proton-proton collisions

We analyze near-threshold cross-section data for the reaction pp → ppφ published by the DISTO Collaboration and recent, still preliminary results presented by the ANKE Collaboration. We formulate a procedure to evaluate the OZI ratio at low energies by taking into account corrections from the kinematics and the final-state interaction. Combining the new data with the few measurements available at higher energies we give a limit for the OZI rule violation. We also demonstrate and discuss the effect of a possible contribution from a five-quark baryonic resonance coupled to the φp system on the pp → ppφ cross-section and the φp and pp invariant mass spectra.     

Gluon saturation and entropy production in proton-proton collisions

We study properties of high energy factorisable gluon densities focusing on saturation effects. In particular we show that the property of saturation of unintegrated gluon density allows for introduction of thermodynamical entropy associated with production of gluons. This is due to the observation that saturation scale acts like a mass of a gluon which related with temperature via thermodynamical relations allows for calculations of entropy. We also show that obtained entropy behaves like multiplicity of produced gluons.     

Photoproduction of quarkonium in proton-proton and nucleus-nucleus collisions

We discuss the photoproduction of Upsilon and J/psi at high energy pp, pp, and heavy ion colliders. We predict large rates in pp interactions at the Fermilab Tevatron and in pp and heavy ion interactions at the CERN Large Hadron Collider. The J/psi is also produced copiously at the Relativistic Heavy Ion Collider. These reactions can be used to study the gluon distribution in protons and heavy nuclei. We also show that the different CP symmetries of the initial states lead to large differences in the transverse momentum spectra of mesons produced in pp vs pp collisions.