A high-statistics measurement has been made of the process e+e−→μ+μ− at s=29 GeV with the MAC detector at the SLAC storage ring PEP. The electroweak forward-backward charge asymmetry for a sample of approximately 16 000 events was measured to be Aμμ=−0.063±0.008±0.002. The ratio of the cross section to the lowest-order QED cross section was measured to be Rμμ=1.01±0.01±0.03. From these results the weak neutral axial-vector and vector couplings are determined to be gAegAμ=0.25±0.03±0.01 and gVegVμ=−0.02±0.03±0.09.
Data are fully corrected, including radiative effects.
Asymmetry determined from a two parameter fit to the angular distribution proportional to R*(1 + cos(theta)**2 + (8/3)*A*cos(theta)). R is then the total ratio relative to the lowest order QED cross section and A is the forward-backward asymmetry.
No description provided.
A high-statistics measurement is presented of the cross section for the process e+e−→τ+τ− at s=29 GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with |cosθ|<0.9 gives an asymmetry Aττ=−0.055±0.012±0.005 from which we find the product of electron and tau axial-vector weak neutral couplings gAegAτ=0.22±0.05.
Data fully corrected up to O(ALPHA**3) radiative effects. Data requested from authors.
Data extrapolated to full acceptance.
No description provided.
A measurement of the cross section for production of collinear muon pairs based upon a sample of about 3000 events observed in the MAC detector at the storage ring PEP is presented. From the angular asymmetry Aμμ=0.076±0.018 the axial-vector weak neutral coupling is found to be given by gAegAμ=0.31±0.08.
Data on non-collinearity and angular distribution.
Asymmetry measurement based on extrapolation of number of events to 4 PI acceptance.
None
No description provided.
Data extrapolated to full solid angle.
High p ⊥ inclusive muon events produced in e + e − annihilations at √ s =29 GeV have been analyzed to obtain a measurement of the b b forward-backward charge asymmetry. The result A b =0.034±0.070±0.035 differs from the theoretical expectation (−0.16) unless substantial B 0 B 0 mixing is assumed.
No description provided.
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Updated values of coupling constants and electroweak mixing angle.
Cross sections for hadron production from the 1993 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.105 PCT.
Cross sections for hadron production from the 1994 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.088 PCT.
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.
We present measurements of Collins asymmetries in the inclusive process $e^+e^- \rightarrow h_1 h_2 X$, $h_1h_2=KK,\, K\pi,\, \pi\pi$, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb$^{-1}$ collected by the BaBar experiment at the PEP-II $B$ factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike- to like-sign, and unlike- to all charged $h_1 h_2$ pairs, which increase with hadron energies. The $K\pi$ asymmetries are similar to those measured for the $\pi\pi$ pairs, whereas those measured for high-energy $KK$ pairs are, in general, larger.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for kaon pairs. In the first column, the $z$ bins and their respective mean values for the kaon in one hemisphere are reported; in the following column, the same variables for the second kaon are shown; in the third column the mean value of $\sin^2\theta_{th}/(1+\cos^2\theta_{th})$ is summarized, calculated in the RF12 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $KK$ pair and dividing by the number of $KK$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for kaon pairs. In the first column, the $z$ bins and their respective mean values for the kaon in one hemisphere are reported; in the following column, the same variables for the second kaon are shown; in the third column the mean value of $\sin^2\theta_{2}/(1+\cos^2\theta_{2})$ is summarized, calculated in the RF0 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $KK$ pair and dividing by the number of $KK$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
Light quark ($uds$) Collins asymmetries obtained by fitting the U/L and U/C double ratios as a function of ($z_1$,$z_2$) for $K\pi$ hadron pairs. In the first column, the $z$ bins and their respective mean values for the hadron ($K$ or $\pi$) in one hemisphere are reported; in the following column, the same variables for the second hadron ($K$ or $\pi$) are shown; in the third column the mean value of $\sin^2\theta_{th}/(1+\cos^2\theta_{th})$ is summarized, calculated in the RF12 frame; in the last two columns the asymmetry results are summarized. The mean values of the quantities reported in the table are calculated by summing the corresponding values for each $K\pi$ pair and dividing by the number of $K\pi$ pairs that fall into each ($z_1$,$z_2$) interval. Note that the $A^{UL}$ and $A^{UC}$ results are strongly correlated since they are obtained by using the same data set.
We present final measurements of the Z boson-lepton coupling asymmetry parameters Ae, Amu, and Atau with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure Ae = 0.1544 +- 0.0060, Amu = 0.142 +- 0.015, and Atau = 0.136 +- 0.015. Combined with our left-right asymmetry measured from hadronic decays, we find Ae = 0.1516 +- 0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin**2 theta^{eff}_W = 0.23098 +- 0.00026.
No description provided.
We present a direct measurement of the parity-violation parameter $A_c$ in the coupling of the $Z^0$ to $c$-quarks with the SLD detector. The measurement is based on a sample of 530k hadronic $Z^0$ decays, produced with a mean electron-beam polarization of $|P_e| = 73 %$. The tagging of $c$-quark events is performed using two methods: the exclusive reconstruction of $D^{\ast+}$, $D^+$, and $D^0$ mesons, and the soft-pions ($\pi_s$) produced in the decay of $D^{\ast+}\to D^0 \pi_s^+$. The large background from $D$ mesons produced in $B$ hadron decays is separated efficiently from the signal using precision vertex information. The combination of these two methods yields $A_c = 0.688 \pm 0.041.$
CONST(NAME=A_C) is connected with the forward-backward asymmetry by following way: ASYM(NAME=FB) = ABS(P_e)*CONST(NAME=A_C)*2z/(1 + z**2), where z = cos(theta), theta is the polar angle of the outgoing fermion relative to the incident electron, P_e is the longitudinal polarization of the electron beam. Two values for constant A_c were obtained using two different c-quark tagging methods: exclusive charmed-meson reconstruction (C=EXCLUSIVE) and inclusive soft-pion analysis (C=SOFT_PIONS).
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