Search Results (11 total)

We present a measurement of the longitudinal spin cross section asymmetry for deep-inelastic muon-nucleon interactions with two high transverse momentum hadrons in the final state. Two methods of event classification are used to increase the contribution of the photon-gluon fusion process to above 30%. The most effective one, based on a neural network approach, provides the asymmetries A_p^lN→lhhX=0.030±0.057(stat)±0.010(syst) and A_d^lN→lhhX=0.070±0.076(stat)±0.010(syst). From these values we derive an averaged gluon polarization ΔG/G=-0.20±0.28(stat)±0.10(syst) at an average fraction of nucleon momentum carried by gluons 〈η〉=0.07.

Possible single productions of fourth family u₄ and d₄ quarks via anomalous q₄qV interactions at the Fermilab Tevatron are studied. The signatures of such processes are discussed and compared with the recent results from Tevatron.

The pseudoscalar quarkonium state η₄ (¹S₀), formed by the standard model fourth generation quarks, is the best candidate among the fourth generation quarkonia to be produced at the CERN Large Hadron Collider and Very Large Hadron Collider. The production of this J^PC=0^-+ resonance is discussed and the background processes are studied to obtain the integrated luminosity limits for the discovery, depending on its mass.

The latest electroweak precision data allow the existence of additional chiral generations in the standard model. We study the influence of extra generations on the production of the standard model Higgs boson at hadron colliders. Because of the enhancement of the gluon fusion channel, the “golden mode” becomes more promising even at the upgraded Fermilab Tevatron. Furthermore, the formation of the fourth family quarkonia with the subsequent η→Zh decay introduces an additional tool for investigation of Higgs boson properties.

We present the results of the spin asymmetries A₁ of the proton and the deuteron in the kinematic region extending down to x=6×10^-5 and Q²=0.01 GeV². The data were taken with a dedicated low x trigger, which required hadron detection in addition to the scattered muon, so as to reduce the background at low x. The results complement our previous measurements and the two sets are consistent in the overlap region. No significant spin effects are found in the newly explored region.

Pair production of the fourth standard model (SM) family up quarks at the CERN Large Hadron Collider (LHC) has been investigated. It is shown that the LHC will provide clarifying information on the existence of the fourth SM family.

We present a next-to-leading order QCD analysis of the presently available data on the spin structure function g₁ including the final data from the Spin Muon Collaboration. We present results for the first moments of the proton, deuteron, and neutron structure functions, and determine singlet and nonsinglet parton distributions in two factorization schemes. We also test the Bjorken sum rule and find agreement with the theoretical prediction at the level of 10%.

We present the final results of the spin asymmetries A₁ and the spin structure functions g₁ of the proton and the deuteron in the kinematic range 0.0008<x<0.7 and 0.2<Q²<100 GeV². For the determination of A₁, in addition to the usual method which employs inclusive scattering events and includes a large radiative background at low x, we use a new method which minimizes the radiative background by selecting events with at least one hadron as well as a muon in the final state. We find that this hadron method gives smaller errors for x<0.02, so it is combined with the usual method to provide the optimal set of results.

We have measured the spin-dependent structure function g₁^p in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range 0.003<x<0.7 and 1 GeV²<Q²<60 GeV². A next-to-leading order QCD analysis is used to evolve the measured g₁^p(x,Q²) to a fixed Q₀². The first moment of g₁^p at Q₀²=10 GeV² is Γ₁^p=0.136±0.013 (stat) ±0.009 (syst) ±0.005 (evol). This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge a₀ is found to be 0.28±0.16. In the Adler-Bardeen factorization scheme, Δg≃2 is required to bring ΔΣ in agreement with the quark-parton model. A combined analysis of all available proton, deuteron, and ³He data confirms the Bjorken sum rule.

A counter-spark-chamber experiment has been done in the alternating-gradient synchrotron's 23-GeV/c charged hyperon beam to study Y^* production in reactions of Σ^- on H₂, Al, Cu, W, and Pb in which the Y^* decays into the Λ⁰-π^- final state. We observe the Σ^*(1385) and place upper limits on possible diffractively produced Y^* resonances and on the Coulomb production of the Σ^*-(1385).