Measurement of Sivers Asymmetries for Di-jets in \sqrt{s}=200 GeV pp Collisions at STAR

Measurement of the transverse spin dependence of the di-jet opening angle in pp collisions at sqrt{s}=200 GeV has been performed by the STAR collaboration. An analyzing power consistent with zero has been observed over a broad range in pseudorapidity sum of the two jets with respect to the polarized beam direction. A non-zero (Sivers) correlation between transverse momentum direction of partons in the initial state and transverse spin orientation of the parent proton has been previously observed in semi-inclusive deep inelastic scattering (SIDIS). The present measurements are much smaller than deduced from predictions made for STAR di-jets based on non-zero quark Sivers functions deduced from SIDIS, and furthermore indicate that gluon Sivers asymmetries are comparably small.Comment: 4 pages, 3 figures, talk presented at SPIN 2006, Kyoto, October 200

Helicity Parton Distributions from Spin Asymmetries in W-Boson Production at RHIC

We present a next-to-leading order QCD calculation of the cross section and longitudinal spin asymmetry in single-inclusive charged-lepton production, pp -> l X, at RHIC, where the lepton is produced in the decay of an electroweak gauge boson. Our calculation is presented in terms of a multi-purpose Monte-Carlo integration program that may be readily used to include experimental spin asymmetry data in a global analysis of helicity parton densities. We perform a toy global analysis, studying the impact of anticipated RHIC data on our knowledge about the polarized anti-quark distributions.Comment: 22 pages, 13 figures included. Typos in Figs 2, 6, 8 and scales correcte

Lambda-N scattering length from the reaction gamma d -> K^+ Lambda n

The perspects of utilizing the strangeness-production reaction gamma d -> K^+ Lambda n for the determination of the Lambda n low-energy scattering parameters are investigated. The spin observables that need to be measured in order to isolate the Lambda n singlet (1S0) and triplet (3S1) states are identified. Possible kinematical regions where the extraction of the Lambda n scattering lengths might be feasible are discussed.Comment: 8 pages, 4 figure

Rydberg trimers and excited dimers bound by internal quantum reflection

Quantum reflection is a pure wave phenomena that predicts reflection of a particle at a changing potential for cases where complete transmission occurs classically. For a chemical bond, we find that this effect can lead to non-classical vibrational turning points and bound states at extremely large interatomic distances. Only recently has the existence of such ultralong-range Rydberg molecules been demonstrated experimentally. Here, we identify a broad range of molecular lines, most of which are shown to originate from two different novel sources: a single-photon associated triatomic molecule formed by a Rydberg atom and two ground state atoms and a series of excited dimer states that are bound by a so far unexplored mechanism based on internal quantum reflection at a steep potential drop. The properties of the Rydberg molecules identified in this work qualify them as prototypes for a new type of chemistry at ultracold temperatures.Comment: 6 pages, 3 figures, 1 tabl

Parametrization of cross sections for neutron interaction with 1^{1}H, 2^{2}H and 12^{12}C nuclei at energies between 20 and 90 MeV

The experimental data for neutron interaction with $^{1}$H, $^{2}$H and $^{12}$C nuclei are parametrized in energy range 20 to 90 MeV. The energy dependence of the total and reaction cross section is represented in the form of a series of orthogonal polynomials. The logarithm of differential cross section for the angular distribution is expressed as a linear combination of Legendre polynomials with the energy dependence of their coefficients described by a series of orthogonal polynomials

Near Threshold K+K- Meson-Pair Production in Proton-Proton Collisions

The near threshold total cross section and angular distributions of K+K- pair production via the reaction pp --> ppK+K- have been studied at an excess energy of Q = 17 MeV using the COSY-11 facility at the cooler synchrotron COSY. The obtained cross section as well as an upper limit at an excess energy of Q = 3 MeV represent the first measurements on the K+K- production in the region of small excess energies where production via the channel pp --> pp Phi --> ppK+K- is energetically forbidden. The possible influence of a resonant production via intermediate scalar states f0(980) and a0(980) is discussed.Comment: 8 pages, 6 figures, replaced with revised version, accepted for publication in Phys. Lett.

Near-Threshold eta Meson Production in Proton-Proton Collisions

The production of eta mesons has been measured in the proton-proton interaction close to the reaction threshold using the COSY-11 internal facility at the cooler synchrotron COSY. Total cross sections were determined for eight different excess energies in the range from 0.5 MeV to 5.4 MeV. The energy dependence of the total cross section is well described by the available phase-space volume weighted by FSI factors for the proton-proton and proton-eta pairs.Comment: 9 pages, 1 table, 5 figure

Recent results from the STAR spin program at RHIC

The STAR experiment uses polarized p+p collisions at RHIC to determine the contributions to the spin of the proton from gluon spin and from orbital angular momentum of the quarks and gluons. Selective STAR measurements of the longitudinal double spin asymmetry for inclusive jet and inclusive hadron production are presented here. In addition, we report measurements of the transverse spin asymmetry for di-jet production at mid-rapidity and the transverse single-spin asymmetry for forward pi0 productionComment: 4 pages, 5 figures, presented at GHP06 conferenc