We measured the spin asymmetry in the scattering of 100 GeV longitudinally-polarized muons on transversely polarized protons. The asymmetry was found to be compatible with zero in the kinematic range $0.006<x<0.6$, $1<Q~2<30\,\mbox{GeV}~2$. {}From this result we derive the upper limits for the virtual photon--proton asymmetry $A_2$, and for the spin structure function $g_2$. For $x<0.15$, $A_2$ is significantly smaller than its positivity limit $\sqrt{R}$.
No description provided.
Nucleon spin structure function g2.
We present a measurement of the left-right cross-section asymmetry (ALR) for Z boson production by e+e- collisions. The measurement includes the final data taken with the SLD detector at the SLAC Linear Collider (SLC) during the period 1996-1998. Using a sample of 383,487 Z decays collected during the 1996-1998 runs we measure the pole-value of the asymmetry, ALR0, to be 0.15056+-0.00239 which is equivalent to an effective weak mixing angle of sin2th(eff) = 0.23107+-0.00030. Our result for the complete 1992-1998 dataset comprising 537 thousand Z decays is sin2th(eff) = 0.23097+-0.00027.
The observed, corrected asymmetry measurement using the 1997-98 data sets.
The observed, corrected asymmetry measurement using the 1996 data sets.
The pole asymmetry for the 1997-98 data sets.
The charge asymmetry has been measured using $19,039W$ decays recorded by the CDF detector during the 1992-93 run of the Tevatron Collider. The asymmetry is sensitive to the ratio of $d$ and $u$ quark distributions to $x<0.01$ at $Q~2 \approx M_W~2$, where nonperturbative effects are minimal. It is found that of the two current sets of parton distributions, those of Martin, Roberts and Stirling (MRS) are favored over the sets most recently produced by the CTEQ collaboration. The $W$ asymmetry data provide a stronger constraints on $d/u$ ratio than the recent measurements of $F_2~{\mu n}/F_2~{\mu p}$ which are limited by uncertainties originating from deutron corrections.
Charge asymmetry defined as (DSIG(Q=L+)/DYRAP - DSIG(Q=L-)/DYRAP)/ (DSIG(Q=L+)/DYRAP + DSIG(Q=L-)/DYRAP). Here LEPTON are E and MU.
We report on a measurement of the mass dependence of the forward-backward charge asymmetry, A_FB, and production cross section dsigma/dM for e+e- pairs with mass M_ee>40 GeV/c2. The data sample consists of 108 pb-1 of p-pbar collisions at sqrt(s)=1.8 TeV taken by the Collider Detector at Fermilab during 1992-1995. The measured asymmetry and dsigma/dM are compared with the predictions of the Standard Model and a model with an extra Z' gauge boson.
The E+ E- production cross section and the forward-backward asymmetry. The errors contain the statistical and systematic uncertainties combined in quadrature, but not the additional uncertainty of the luminosity.
Experiment WA82 studied charm production by a π − beam of 340 GeV/ c at the CERN Ω′ spectrometer, using a silicon microstrip vertex detector and an impact parameter trigger. Results on the x F distributions of D + and D − mesons are presented and discussed. A clear excess of D − over D + , increasing at high x F , is observed.
No description provided.
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 measurements of Rb = sigma(e+e- -> bb~)/sigma(e+e- -> qq~) and of the b quark forward-backward charge asymmetry, A^b_fb, at centre-of-mass energies above the Z pole are described. The measurement of Rb is performed at \root{s} between 130 and 189 GeV using a b-tagging method that exploits the relatively large decay length of b-hadrons. The measurement of A^b_fb is performed using the large statistics event sample collected at \root{s}=189 GeV with a lepton-tag analysis based on the selection of prompt muons and electrons. The results at \root{s}=189 GeV are: Rb = 0.163 +/- 0.013 (stat.) +/- 0.005 (syst.), A^b_fb = 0.61 +/- 0.18 (stat.) +/- 0.09 (syst.).
No description provided.
We present a LO evaluation of helicity densities of valence, \Delta u_v+\Delta d_v, non-strange sea, \Delta\bar{u}+\Delta\bar{d}, and strange quarks, \Delta s (assumed to be equal to \Delta\bar{s}). They have been obtained from the inclusive asymmetry A_{3,d} and the semi-inclusive asymmetries A^{\pi+}_{1,d}, A^{\pi-}_{1,d}, A^{K+}_{1,d}, A^{K-}_{1,d} measured in polarised deep inelastic muon-deuteron scattering. The full deuteron statistics of COMPASS (years 2002-2004 and 2006) has been used. The data cover the range Q^2 > 1 (GeV/c)^2 and 0.004<x<0.3. Both non-strange densities are found to be in a good agreement with previous measurements. The distribution of \Delta s(x) is compatible with zero in the whole measured range, in contrast to the shape of the strange quark helicity distribution obtained in most LO and NLO QCD fits. The sensitivity of the values of \Delta s(x) upon the choice of fragmentation functions used in the derivation is discussed.
Inclusive asymmetry as a function of X.
Charged pion and kaon semi-inclusive asymmetries as functions of X.
We report the double helicity asymmetry, $A_{LL}^{J/\psi}$, in inclusive $J/\psi$ production at forward rapidity as a function of transverse momentum $p_T$ and rapidity $|y|$. The data analyzed were taken during $\sqrt{s}=510$ GeV longitudinally polarized $p
$A_{LL}^{J/\psi}$ as a function of $p_T$ or $|y|$. $N_{J/\psi}^{2\sigma}$ is the $J/\psi$ counting within its $2\sigma$ mass window. The column of Type A systematic uncertainties are a statistically weighted quadratic combination of the background fraction and run grouping uncertainties. $\Delta A_{LL}$ (Rel. Lumi.) is the global systematic uncertainty from relative luminosity measurements. $\Delta A_{LL}$ (Polarization) is the systematic uncertainty from the beam polarization measurement: a zero indicates an uncertainty $< 0.001$.
We measure forward cross sections for production of D+, D0, Ds, D*+, and Λc in collisions of π±, K±, and p on a nuclear target. Production induced by different beam particles is found to be the same within statistics. Strange and baryonic final states are seen to contribute appreciably to the total charm cross section, which our measurements indicate is larger than but consistent with QCD predictions. The energy dependence mapped out by these and previous measurements is consistent with theory. Leading-particle asymmetry measurements for K and p-induced charm production are also presented.
Leading particle asymmetries defined as (SIG(LEADING)- SIG(NONLEADING))/(SIG(LEADING)+SIG(NONLEADING)).
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