Search results for "Polar"
showing 10 items of 3817 documents
Inclusive double-helicity asymmetries in neutral-pion and eta-meson production inp→+p→collisions ats=200 GeV
2014
Results are presented from data recorded in 2009 by the PHENIX experiment at the Relativistic Heavy Ion Collider for the double-longitudinal spin asymmetry, A(LL), for pi(0) and eta production in root s = 200 GeV polarized p + p collisions. Comparison of the pi(0) results with different theory expectations based on fits of other published data showed a preference for small positive values of gluon polarization, Delta G, in the proton in the probed Bjorken x range. The effect of adding the new 2009 pi(0) data to a recent global analysis of polarized scattering data is also shown, resulting in a best fit Delta G(DSSV)([0.05,0.2]) = 0.06(-0.15)(+0.11) in the range 0.05 < x < 0.2, with the unce…
Polarization in fragmentation,gfactor of35K
1998
Spin polarization $Pg1%$ has been observed for ${}^{37}\mathrm{K}$ fragments produced in the reaction ${}^{40}\mathrm{Ca}{+}^{9}\mathrm{Be}$ at 500 MeV/nucleon. The polarization was measured as a function of fragment longitudinal momentum (Goldhaber distribution). The experimental results are well described by a new Monte Carlo\char21{}based model. The $\ensuremath{\beta}$-decay half-life of ${}^{35}\mathrm{K}$ was remeasured as ${t}_{1/2}=178(8)$ ms. Using polarized ${}^{35}\mathrm{K}$ fragments, the $g$ factor ${g}_{\mathrm{exp}}{(}^{35}\mathrm{K})=0.24(2)$ was measured. The magnetic moments of isospin $|{T}_{z}|=3/2$ mirror pairs are discussed.
Calculation of the two-loop heavy-flavor contribution to Bhabha scattering
2008
We describe in detail the calculation of the two-loop corrections to the QED Bhabha scattering cross section due to the vacuum polarization by heavy fermions. Our approach eliminates one mass scale from the most challenging part of the calculation and allows us to obtain the corrections in a closed analytical form. The result is valid for arbitrary values of the heavy fermion mass and the Mandelstam invariants, as long as s,t,u >> m_e^2.
A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment
2004
Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (K0s, Lambda, Lambda-bar) have been measured. Decays of resonances and heavy hyperons with an identified K0s or Lambda in the final state have been analyzed. Clear signals corresponding to K* and Sigma(1385) have been observed. First results on the measurements of the Lambda polarization in neutral current interactions have been obtained.
Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production
2013
We present measurements of lepton (l) angular distributions in ttbar -> W+ b W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using data corresponding to an integrated luminosity of 5.4fb^-1, collected with the D0 detector at the Fermilab Collider, we find that the angular distributions of l- relative to anti-protons and l+ relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat) +- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted…
Inclusive decays of B mesons into Ds and at O(αs) including polarization effects
2000
The dominant contribution to the inclusive decays of B mesons into the charm-strangeness mesons Ds and Ds∗ is expected to be given by the partonic process b→c+(Ds−,Ds∗−). We determine the nonperturbative O(1/mb2) and the O(αs) radiative corrections to b→c+(Ds−,Ds∗−) and thereby to the inclusive decays B→Xc+(Ds−,Ds∗−). The new feature of our calculation is that we separately determine the nonperturbative and the O(αs) corrections to the longitudinal (L) and transverse (T) pieces of the spin 1 Ds∗− meson. The longitudinal/transverse composition of the Ds∗− can be probed through its two principal decay modes Ds∗−→Ds−+γand Ds∗−→Ds−+π0 for which we write down the angular decay distributions.
Leptonicμandτdecays: Mass effects, polarization effects, andO(α)radiative corrections
2003
We calculate the radiative corrections to the unpolarized and the four polarized spectrum and rate functions in the leptonic decay of a polarizedinto a polarized electron. The new feature of our calculation is that we keep the mass of the final state electron finite which is mandatory if one wants to investigate the threshold region of the decay. Analytical results are given for the energy spectrum and the polar angle distribution of the final state electron whose longitudinal and transverse polarization is calculated. We also provide analytical results on the integrated spec- trum functions. We analyze the me → 0 limit of our general results and investigate the quality of the me → 0 approx…
Electromagnetic investigations of nucleon resonances and sum rules
2000
Abstract Pion photoproduction is analyzed by dispersion relations at fixed t . The results for s-wave production at threshold and p-wave production in the Δ(1232) resonance region are compared to the experimental data. These investigations are extended to the case of pion electroproduction in the framework of the Unitary Isobar Model. Recent developments to explore the spin structure of the nucleon by double-polarization observables are summarized, and new results for the spin polarizability, the Gerasimov-Drell-Hearn and related sum rules are presented.
Polarization effects in exclusive semi-leptonic Λc and Λb charm and bottom baryon decays
1992
Abstract We discuss polarization effects in semi-leptonic decays of polarized and unpolarized heavy Λ-type baryons into heavy and into light Λ-type baryons. We use the non-leptonic decay of the daughter baryon and the leptonic decay of the Woff-shell into a lepton pair as polarization analyzers to analyze the polarization of the daughter baryon and the Woff-shell. Technically this is done by writing down joint angular decay distributions. We calculate the values of the various asymmetry parameters that characterize the angular dependence of the angular decay distributions where we use the predictions of the heavy quark effective theory (HQET) supplemented by simple ansatze for the q2-depend…
Die zirkulare Polarisation der inneren Bremsstrahlung beim K-Einfang von A37
1958
The circular polarization of the internal bremsstrahlung was measured for various photon energies by scattering on magnetized iron. In the spectral range investigated, complete polarization was found within the measuring error. An average value of P/sub c/ = +1.03 plus or minus 0.04 was obtained. This shows that the maximum parity violation occurs also in K-capture. (tr-auth)