arXiv subjects

The SLD Collaboration

Publications and source records attributed to The SLD Collaboration.

30 records · Page 2Linked to original sources

arXiv1998

Production of pi+, K+, K0, K*0, phi, p and Lambda-0 in Hadronic Z0 Decays

We have measured the differential production cross sections as a function of scaled momentum x_p=2p/E_cm of the identified hadron species pi+, K+, K0, K*0, phi, p, Lambda0, and of the corresponding antihadron species in inclusive hadronic Z0 decays, as well as separately for Z0 decays into light (u, d, s), c and b flavors. Clear flavor dependences are observed, consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results were used to test the QCD predictions of Gribov and Lipatov, the predictions of QCD in the Modified Leading Logarithm Approximation with the ansatz of Local Parton-Hadron Duality, and the predictions of three fragmentation models. Ratios of production of different hadron species were also measured as a function of x_p and were used to study the suppression of strange meson, strange and non-strange baryon, and vector meson production in the jet fragmentation process. The light-flavor results provide improved tests of the above predictions, as they remove the contribution of heavy hadron production and decay from that of the rest of the fragmentation process. In addition we have compared hadron and antihadron production as a function of x_p in light quark (as opposed to antiquark) jets. Differences are observed at high x_p, providing direct evidence that higher-momentum hadrons are more likely to contain a primary quark or antiquark. The differences for pseudoscalar and vector kaons provide new measurements of strangeness suppression for high-x_p fragmentation products.

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arXiv1997

Measurement of the B Hadron Energy Distribution in Z0 Decays

We have measured the B hadron energy distribution in Z0 decays using a sample of semi-leptonic B decays recorded in the SLD experiment at SLAC. The energy of each tagged B hadron was reconstructed using information from the lepton and a partially reconstructed charm-decay vertex. We compared the scaled energy distribution with several models of heavy quark fragmentation. The average scaled energy of primary B hadrons was found to be = 0.716 +- 0.011 (stat.) +0.022 -0.021 (syst.).

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arXiv1997

First Measurement of Leptonic Coupling Asymmetries with Polarized Z bosons

We present direct measurements of the $Z^0$-lepton coupling asymmetry parameters, $A_e$, $A_μ$, and $A_τ$, based on a data sample of 12,063 leptonic $Z^0$ decays collected by the SLD detector. The $Z$ bosons are produced in collisions of beams of polarized $e^-$ with unpolarized $e^+$ at the SLAC Linear Collider. The couplings are extracted from the measurement of the left-right and forward-backward asymmetries for each lepton species. The results are: $A_e=0.152 \pm 0.012 {(stat)} \pm 0.001 {(syst)}$, $A_μ=0.102 \pm 0.034 \pm 0.002$, and $A_τ=0.195 \pm 0.034 \pm 0.003$.

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arXiv1997

Measurement of Leading Particle Effects in Decays of Z0 Bosons into Light Flavors

We present evidence for leading particle production in hadronic decays of the Z0 boson to light-flavor jets. A polarized electron beam was used to tag quark and antiquark jets, and a vertex detector was employed to reject heavy-flavor events. Charged hadrons were identified with a Cherenkov ring imaging detector. In the quark jets, more high-momentum p, Lambda, K-, and anti-K*0 were observed than their antiparticles, and vice versa for antiquark jets, providing direct evidence that the higher-momentum particles in jets are more likely to carry the primary quark or antiquark from the Z0 decay, and that s-s(bar) production is suppressed in fragmentation.

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arXiv1996

Determination of Electroweak Parameters at the SLC

We present an improved measurement of the left-right cross section asymmetry Alr for Z boson production by e+e- collisions. The measurement was performed at a center-of-mass energy of 91.28 GeV with the SLD detector at the SLAC Linear Collider (SLC) during the 1994-95 running period. The luminosity-weighted average polarization of the SLC electron beam during this run was measured to be (77.23 +/- 0.52)%. Using a sample of 93,644 hadronic Z decays, we measure the pole asymmetry Alr0 to be 0.1512 +/- 0.0042(stat.) +/- 0.0011(syst.) which is equivalent to an effective weak mixing angle of 0.23100 +/- 0.00054(stat.) +/- 0.00014(syst.). We also present a preliminary direct measurement of the Z-lepton coupling asymmetries A_e,A_mu, and A_tau extracted from the differential cross section observed in leptonic Z decays. We combine these results with our previous Alr measurement to obtain a combined determination of the weak mixing angle of 0.23061 +/- 0.00047.

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arXiv1996

Measurement of Rb at SLD

We report a new measurement of Rb=Gamma(Z -> bb)/ Gamma(Z -> hadrons) using a double tag technique where the b selection is based on topological reconstruction of the mass of the B-decay vertex. The measurement was performed using a sample of 150k hadronic Z0 events collected with the SLD at the SLAC Linear Collider during the years 1993-1995. The method utilizes the 3-D vertexing abilities of the SLD CCD pixel vertex detector and the small stable SLC beams to obtain a high b tagging efficiency of 37% for a purity of 97.2%. The high purity reduces the systematics introduced by charm contamination and correlations with Rc. We obtain a result of Rb=0.2176+/-0.0033(stat.)+/-0.0017(syst.)+/-0.0008(Rc). (Presented at the XXXIst Rencontres de Moriond Electroweak Interactions and Unified Theories, Les Arcs, Savoie, France, March 16-23, 1996.)

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arXiv1995

Tau Physics with Polarized Beams

We present the first results on tau physics using polarized beams. These include measurements of the $τ$ Michel parameters $ξ$ and $ξδ$ and the $τ$ neutrino helicity $h_ν$. The measurements were performed using the SLD detector at the Stanford Linear Collider (SLC). (Invited talk at the 1995 International Europhysics Conference on High Energy Physics, Brussels, Belgium, July 27 - August 2, 1995.)

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arXiv1995

Measurement of the Average $B$-Hadron Lifetime in $Z^{0}$ Decays

We report a measurement of the average $B$-hadron lifetime using data collected with the SLD detector at the SLC in 1993. An inclusive analysis selected three-dimensional vertices with $B$-hadron lifetime information in a sample of 50k $Z^{0}$ decays. A lifetime of $1.564\pm0.030\,(\rm stat)\pm 0.037\,(\rm syst)$~ps was extracted from the decay length distribution of these vertices using a binned maximum-likelihood method.

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arXiv1995

First Measurement of the T-odd Correlation between the Z0 Spin and the Three-jet Plane Orientation in Polarized Z0 Decays to Three Jets

We present the first measurement of the correlation between the $Z^0$ spin and the three-jet plane orientation in polarized $Z^0$ decays into three jets in the SLD experiment at SLAC utilizing a longitudinally polarized electron beam. The CP-even and T-odd triple product $\vec{S_Z}\cdot(\vec{k_1}\times \vec{k_2})$ formed from the two fastest jet momenta, $\vec{k_1}$ and $\vec{k_2}$, and the $Z^0$ polarization vector $\vec{S_Z}$, is sensitive to physics beyond the Standard Model. We measure the expectation value of this quantity to be consistent with zero and set 95\% C.L. limits of $-0.022 < β< 0.039$ on the correlation between the $Z^0$-spin and the three-jet plane orientation.

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arXiv1995

Measurement of the Tau Lifetime at SLD

A measurement of the lifetime of the tau lepton has been made using a sample of 1671 $Z^0\rightarrowτ^+τ^-$ decays collected by the SLD detector at SLC. The measurement benefits from the small and stable collision region at SLC and the precision vertex detector of SLD. Three analysis techniques have been used: decay length, impact parameter, and impact parameter difference methods. The combined result is $τ_τ= 297\pm 9(stat.)\pm 5(syst.)$ fs.

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arXiv1994

Measurement of the Charged Multiplicity of $Z \rightarrow b \overline{b}$ Events

Using an impact parameter tag to select an enriched sample of $Z \rightarrow b \overline{b}$ events, we have measured the difference between the average charged multiplicity of $Z \rightarrow b \overline{b}$ and $Z^0 \rightarrow hadrons$ to be $\overline{n}_{b} - \overline{n}_{had} = 2.24\pm 0.30(\rm{stat.}) \pm 0.33(\rm{syst.})$ tracks per event. {}From this, we have derived $\overline{n}_{b} - \overline{n}_{uds} = 3.31 \pm 0.41 \pm 0.79.$ Comparing this measurement with those at lower center-of-mass energies, we find no evidence that $\overline{n}_{b} - \overline{n}_{uds}$ depends on energy. This result is in agreement with a precise prediction of perturbative QCD, and supports the notion that QCD remains asymptotically free down to the scale $M_b^2$.

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arXiv1994

Precise Measurement of the Left-Right Cross Section Asymmetry in $Z$ Boson Production by $\ee$ Collisions

We present a precise measurement of the left-right cross section asymmetry ($A_{LR}$) for $Z$ boson production by $\ee$ collisions. The measurement was performed at a center-of-mass energy of 91.26 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (63.0$\pm$1.1)%. Using a sample of 49,392 $\z0$ decays, we measure $A_{LR}$ to be 0.1628$\pm$0.0071(stat.)$\pm$0.0028(syst.) which determines the effective weak mixing angle to be $\swein=0.2292\pm0.0009({\rm stat.})\pm0.0004({\rm syst.})$.}

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