A study of the angular distributions of leptons from decays of J/psi's produced in p-C and p-W collisions at sqrt{s}=41.6 GeV has been performed in the Feynman-x region -0.34 < x_F < 0.14 and for transverse momentum up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3 x 10^5 J/psi's reconstructed in both the e^+ e^- and mu^+ mu^- decay channels, indicate that J/psi's are produced with longitudinal polarization. The magnitude of the effect is maximal at low p_T. For p_T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.
Output parameters obtained by fitting the distributions.
Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed p_T for combined carbon and tungsten data.
Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed x_F for combined carbon and tungsten data.
We report results from a study of Λ0 polarization in the exclusive reaction pp→pf(Λ0K+) at 800−GeV/c. We observe a dependence of the polarization on the Λ0K+ invariant mass with large (+71%) positive polarization at small mass (1.63−GeV/c2) and large (−43%) negative polarization at large mass (2.75−GeV/c2). This observation confirms the result of the CERN ISR R608 experiment and extends the range over which the effect is observed. The strong dependence of the polarization on the Λ0K+ invariant mass suggests that the origin of the polarization is closely related to the production dynamics of the diffractively produced Λ0K+ system.
The measured LAMBDA polarisation as a function of the (LAMBDA K+) invariantmass.
The measured LAMBDA polarisation as functions of the LAMBDA transverse momentum and Feynman X.
Measurements of the tau lepton polarization and forward-backward polarization asymmetry near the Z resonance using the OPAL detector are described. The measurements are based on analyses of tau -> e nu_e nu_tau, tau -> mu nu_mu nu_tau, tau -> pi nu_tau, tau -> rho nu_tau and tau -> a1 nu_tau decays from a sample of 144810 e+e- -> tau+ tau- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the tau lepton decays according to V-A theory, we measure the average tau polarization near Ecm = MZ to be <Ptau> = (-14.10 +/- 0.73 +/- 0.55)% and the tau polarization forward-backward asymmetry to be Afb = (-10.55 +/- 0.76 +/- 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: Atau = 0.1456 +/- 0.0076 +/- 0.0057, Ae = 0.1454 +/- 0.0108 +/- 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give Al = 0.1455 +/- 0.0073. Within the context of the Standard Model this combined result corresponds to sin^2(theta)(lept,effective) = 0.23172 +/- 0.00092. Combing these results with those from the other OPAL neutral current measurements yields a value of sin^2(theta)(lept,effective) = 0.23211 +/- 0.00068.
No description provided.
The$\tau$polarisation has been studied with the${\rm e^+e^-}\to \tau^+\tau^-$data collected by the DELPHI detector at LEP in
The errors are statistical and systematic combined in quadrature.
No description provided.
In order to improve existing I=0 phase shift solutions, the spin correlation parameter ANN and the analyzing powers A0N and AN0 have been measured in n-p elastic scattering over an angular range of 50°–150° (c.m.) at three neutron energies (220, 325, and 425 MeV) to an absolute accuracy of ±0.03. The data have a profound effect on various phase parameters, particularly the P11, D23, and ε1 phase parameters which in some cases change by almost a degree. With the exception of the highest energy, the data support the predictions of the latest version of the Bonn potential. Also, the analyzing power data (A0N and AN0) measured at 477 MeV in a different experiment over a limited angular range [60°–80° (c.m.)] are reported here.
The beam analysing power at incident kinetic energy 220 MeV. Additional systematic uncertainty of +- 0.015 and a scalar error of 3.5 PCT.
The beam analysing power at incident kinetic energy 325 MeV. Additional systematic uncertainty of +- 0.018 and a scalar error of 3.1 PCT.
The beam analysing power at incident kinetic energy 425 MeV. Additional systematic uncertainty of +- 0.022 and a scalar error of 3.3 PCT.
We report results of the first measurements of Lambda and Antilambda polarization produced in deep inelastic polarized muon scattering on the nucleon. The results are consistent with an expected trend towards positive polarization with increasing x_F. The polarizations of Lambda and Antilambda appear to have opposite signs. A large negative polarization for Lambda at low positive x_F is observed and is not explained by existing models.A possible interpretation is presented.
The measured and corrected (undiluted) polarizations.
The measured and corrected (undiluted) polarizations.
In the Standard Model, b quarks produced in e^+e^- annihilation at the Z^0 peak have a large average longitudinal polarization of -0.94. Some fraction of this polarization is expected to be transferred to b-flavored baryons during hadronization. The average longitudinal polarization of weakly decaying b baryons, <P_L^{\Lambda_b}>, is measured in approximately 4.3 million hadronic Z^0 decays collected with the OPAL detector between 1990 and 1995 at LEP. Those b baryons that decay semileptonically and produce a \Lambda baryon are identified through the correlation of the baryon number of the \Lambda and the electric charge of the lepton. In this semileptonic decay, the ratio of the neutrino energy to the lepton energy is a sensitive polarization observable. The neutrino energy is estimated using missing energy measurements. From a fit to the distribution of this ratio, the value <P_L^{\Lambda_b}> = -0.56^{+0.20}_{-0.13} +/- 0.09 is obtained, where the first error is statistical and the second systematic.
Charge conjugate states are included.
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58 GeV. From the kinematical distributions of daughter particles in tau --> e nu nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of tau- and its forward-backward asymmetry have been evaluated to be 0.012 +- 0.058 and 0.029 +- 0.057, respectively.
Charged-conjugated states are included. The polarization is measured from final charged-particle energy spectrum. The last value is the combination of the results for all decay modes. The systematic error is not given.
Charged-conjugated states are included. The forward-backward asymmetry of the polarization is defined as (SIG(F)*POL-SIG(B)*POL)/(SIG(F)*POL+SIG(B)*POL). The last value is the combination of the results for all decay modes. The systematic error is not given.
In an experiment at the CERN intersecting storage rings with √ s = 31 GeV, we have measured αP , the product of asymmetry parameter and polarization, for Λ 0 's and Λ 0 's produced in p p and pp interactions, respectively. The ratio, (αP) Λ /(αP Λ = −1.04±0.29 , is consistent with the value −1, and constitutes the first test of CP invariance in Λ decay.
The ratio CONST/CONST is obtained under assumption of POL(LAMBDA) = POL(LAMBDABAR).
The considerable polarization of hyperons produced at high xF has been known for a long time and has been interpreted with various theoretical models in terms of the constituents' spin. Recently, the analyzing power in inclusive Λ0 hyperon production has also been measured using the 200GeV/c Fermilab polarized proton beam. The covered kinematic range is 0.2≤xF≤1.0 and 0.1≤pT≤1.5GeV/c. The data indicate a negative asymmetry at large xF and moderate pT. These results can further test the current ideas on the underlying mechanisms for hyperon polarization.
No description provided.
No description provided.
No description provided.