Production of polarized baryons in polarized and unpolarizede + e − collisions

Polarized and unpolarizede ⁺ e ^? annihilation is considered in lowest order at energies 30–150 GeV taking γ andZ ⁰ exchange in the standardSU(2)×U(1) model into account. The fragmentation of polarized quarks into polarized baryons is described by two kinds of fragmentation functions; the first is based onSU(6) weights and empirical expressions for favoured and disfavoured fragmentation; the second is based upon a Monte Carlo model of the chain decay including helicities of quarks and hadrons. From the cross sections for \(e^ + e^ - \to q\bar q\) and the fragmentation functions we obtain predictions for the baryon polarization as function of the collision energy and of kinematical variables.     

Measurement of the η production in proton-proton collisions with the COSY time-of-flight spectrometer

The reaction pp → ppη was measured at excess energies of 15 and 41 MeV at an external target of the Jülich Cooler Synchrotron COSY with the time-of-flight spectrometer. About 25000 events were measured for the excess energy of 15 MeV and about 8000 for 41 MeV. Both protons of the process ppη were detected with an acceptance of nearly 100% and the η was reconstructed by the missing-mass technique. For both excess energies the angular distributions are found to be nearly isotropic. In the invariant-mass distributions strong deviations from the pure phase space distributions are seen. Received: 24 May 2002 / Accepted: 20 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: e.roderburg@fz-juelich.de Communicated by M. Gar?on     

Measurement of the parity-violating longitudinal single-spin asymmetry for W± boson production in polarized proton-proton collisions at sqrt[s] = 500 GeV

We report the first measurement of the parity-violating single-spin asymmetries for midrapidity decay positrons and electrons from W+ and W- boson production in longitudinally polarized proton-proton collisions at sqrt[s] = 500 GeV by the STAR experiment at RHIC. The measured asymmetries, A(L)(W+) = -0.27 ± 0.10(stat.) ± 0.02(syst.) ± 0.03(norm.) and A(L)(W-) = 0.14 ± 0.19(stat.) ± 0.02(syst.) ± 0.01(norm.), are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized deep-inelastic scattering measurements.     

Radiation effects in the production and decay of ψ mesons by leptons

A new expression _e is obtained for resonance in the reaction e⁺e^– ar ^+– with allowance for the radiative corrections, which also contain the emission of hard photons by the final leptons and the final value of the energy resolution E. An expression is obtained for the total probability of radiative lepton decay. A numerical analysis of the experimental data is made for the reaction ^+–, and the parameters e⁺e^– (3, 1) e⁺e^–, and _e ² /, _e, and are determined for (3, 1) resonance-with allowance for the radiative corrections.This paper was read (November 17–21, 1975) at a session on high-energy physics of the Department of Nuclear Physics of the Academy of Sciences of the USSR.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 29–34, March, 1977.     

Measurements of forward jet production in polarized pp collisions at √s = 500 GeV

The A _N DY project at RHIC was proposed to measure the analyzing power for Drell-Yan production. Test runs took place during polarized proton operations of RHIC in 2011 and 2012 with a model of the A _N DY apparatus in place. In total, an integrated luminosity of 9 pb^?1 with beam polarization of 50% was sampled. The primary detector components were a hadron calorimeter (HCal) that spanned the pseudorapidity interval 2.4 < η < 4.0 and a small electromagnetic calorimeter (ECal). Basic goals for A _N DY test running were to establish the impact of a third interaction region on RHIC performance and to demonstrate HCal calibration. Energy scale of HCal was established using neutral pion reconstruction and checked with hadronic response. In addition, data with a trigger based on HCal energy sum were taken to study jet events. First measurements of analyzing power in the forward jet production are reported.     

Vector boson pair production in e−e− collisions with polarized beams

The W-boson pair production in e⁻e⁻ collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.     

Proton and Λ hyperon production in nucleus-nucleus collisions

Experimental data obtained by the NA35 Collaboration for the difference of the p and \(\bar p\) spectra and the difference of the Λ and \(\bar \Lambda\) spectra (net proton and Λ-hyperon spectra), as well as the inclusive Λ and \(\bar \Lambda\) spectra measured by the NA49, NA57, and STAR Collaborations, are compared with the predictions of the quark-gluon string model. The contribution of string-junction diffusion is calculated, and interaction with nuclear clusters is taken into account along with the corrections for inelastic screening. The level of numerical agreement with experimental data is between 20 and 30%. The predictions for the LHC energy are given.     

Di-electrons from η -meson Dalitz decay in proton-proton collisions

The reaction is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction . Our focus is on di-electrons from Dalitz decays of η -mesons, , and the role of the corresponding transition form factor . Numerical results are presented for the intermediate-energy kinematics of HADES experiments.     

ω- πγtransition form factor in proton-proton collisions

Dalitz decays of ω and ρ mesons, and , produced in pp collisions are calculated within a covariant effective meson-nucleon theory. We argue that the ω transition form factor is experimentally accessible in a fairly model-independent way in the reaction pp → ppπ⁰ e ⁺ e ^- for invariant masses of the π⁰ e ⁺ e ^- subsystem near the ω pole. Numerical results are presented for the intermediate-energy kinematics of envisaged HADES experiments.     

Longitudinal spin transfer to Λ and \bar \Lambda in polarized proton-proton collisions at √s = 200 GeV at STAR

The longitudinal spin transfer D _LL of Λ and $\bar \Lambda$ hyperons is expected to be sensitive to the helicity distribution function of strange (anti-)quarks, and to the polarized fragmentation functions. We report new results on D _LL , extracted from √s = 200 GeV polarized pp collisions recorded at the STAR detector during the 2009 RHIC run. These new results cover mid-rapidity |η| < 1.2, with extended p _T up to 6 GeV/c.     

Study of ππ production in two-photon collisions at Belle

We have measured the cross section for π+π- production in two-photon collisions using a data sample with an integrated luminosity of 85.9 fb-1 collected with the Belle detector. The f0(980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ→π0π0 with two-photon center-of-mass energies ranging from 0.6 to 4.0 GeV, based on a 95 fb-1 data sample. We find at least four resonant structures including a peak from f0(980). In addition, there is evidence for Xc0 production. We also make a preliminary discussion of the angular dependence and cross section ratio of γγ→π+π- and γγ→π0π0.     

Study of ππ production in two-photon collisions at Belle

We have measured the cross section for π⁺π^－ production in two-photon collisions using a data sample with an integrated luminosity of 85.9fb^－1 collected with the Belle detector. The f₀(980) resonance is observed as a peak in the energy spectrum of the cross section. We also report preliminary results for γγ→π⁰π⁰ with two-photon center-of-mass energies ranging from 0.6 to 4.0GeV, based on a 95fb^－1 data sample. We find at least four resonant structures including a peak from f₀(980). In addition, there is evidence for χ_c0 production. We also make a preliminary discussion of the angular dependence and cross section ratio of γγ→π⁺π^－ and γγ→π⁰π⁰.     

Probing Higgs boson — and supersymmetry-induced CP violation in top quark production by (un-) polarized electron-positron collisions

We consider, both for unpolarized and longitudinally polarized electron beams, the reaction $e^ + e^ - \to t\bar t$ with subsequent semileptonict and nonleptonic $\bar t$ decay and vice versa and investigate optimized angular correlations which are sensitive to CP non-conservation in the $t\bar t$ production vertex. We calculate these correlations for two-Higgs-doublet extensions and the minimal super-symmetric extension of the Standard Model (SM) with CP violation beyond the Kobayashi-Maskawa phase. While the sensitivity of the optimal correlation for tracing dispersive CP effects is enhanced with longitudinally polarized electron beams, we find that the sensitivity of the best correlation for probing absorptive CP effects is almost independent of the polarization degree.     

Near-threshold η production in pp collisions

We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances,and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced,and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements.Besides, the invariant mass spectra of pp and pη explain the data well at excess energy of 15 Me V, and are basically consistent with the data at excess energy of 40 Me V. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 Me V, which suggests that a more complicated mechanism is needed at higher energy region.     

d′ production in heavy-ion collisions

The production of d′ dibaryons in heavy-ion collisions due to the elementary process NN → d′π is considered. The NN → d′π cross section is estimated using the vacuum d′ width Γ_d′ ≈ 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d′ production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NNπ system in order to search for an abundance of events with the invariant mass of the d′ dibaryon. The d′ peak is found to exceed the statistical fluctuations of the background at a 6σ level for 2 × 10⁵ · A central collisions of heavy ions with the atomic number A.     

Hadroproduction of ψ and Υ

We show that inclusive ψ hadroproduction cross sections andx _F -distributions are quantitatively consistent with calculations based on the lowest order \(q\bar q \to c\bar c\) andgg→ \(c\bar c\) QCD subprocesses using a duality ansatz. Data in the πN, KN, NN and \(\bar NN\) channels are considered. They provide determinations of the gluon distributions within the nucleon, the pion, and the kaon at the ψ mass scale. AvailableNN→ΥX data aty=0 are consistent with the same model, using gluon distributions appropriate to the Υ mass: predictions ofx _F -distributions are made.