arXiv subjects

The SLD Collaboration

Publications and source records attributed to The SLD Collaboration.

At least 19 recordsLinked to original sources

arXiv2003

Production of pi+, pi-, K+, K-, p and p-bar in Light (uds), c and b Jets from Z0 Decays

We present improved measurements of the differential production rates of stable charged particles in hadronic Z0 decays, and of charged pions, kaons and protons identified over a wide momentum range using the SLD Cherenkov Ring Imaging Detector. In addition to flavor-inclusive Z0 decays, measurements are made for Z0 decays into light (u, d, s), c and b primary flavors, selected using the upgraded Vertex Detector. Large differences between the flavors are observed that are qualitatively consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results are used to test the predictions of QCD in the Modified Leading Logarithm Approximation, with the ansatz of Local Parton-Hadron Duality, and the predictions of three models of the hadronization process. The light-flavor results provide improved tests of these predictions, as they do not include the contribution of heavy-hadron production and decay; the heavy-flavor results provide complementary model tests. In addition we have compared hadron and antihadron production in light quark (as opposed to antiquark) jets. Differences are observed at high momentum for all three charged hadron species, providing direct probes of leading particle effects, and stringent constraints on models.

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arXiv2000

An improved direct measurement of leptonic coupling asymmetries with polarized Z bosons

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.

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arXiv2000

Direct measurement of Ab at the Z0 pole using a lepton tag

We present a direct measurement of the parity violation parameter Ab, derived from the left-right forward-backward asymmetry of b quarks tagged via leptons from semileptonic decays. The lepton identification algorithm combines information from tracking, calorimetry and from the SLD Cherenkov Ring Imaging Detector. The value of Ab is extracted using a maximum likelihood fit to the differential cross section for fermion production. Vertexing information and decay kinematics have been used to discriminate among the different sources of tagged leptons. A new treatment of mixing effects and of background contamination has been introduced and a new vertexing algorithm has been used in the muon analysis. Based on the 1993-1998 SLD sample of 550K hadronic Z0 decays with highly polarized electron beams, we have measured Ab with a ~3% statistical error.

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arXiv2000

Measurement of $A_c$ with Charmed Mesons at SLD

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 ($π_s$) produced in the decay of $D^{\ast+}\to D^0 π_s^+$. 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 $A_c = 0.688 \pm 0.041.$

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arXiv2000

First Direct Measurement of the Parity-Violating Coupling of the Z^0 to the s-Quark

We have made the first direct measurement of the parity-violating coupling of the Z^0 boson to the strange quark, A_s, using ~550,000 e^+e^- ->Z^0->hadrons events produced with a polarized electron beam and recorded by the SLD experiment. Z^0 -> s-sbar events were tagged by the absence of B or D hadrons and the presence in each hemisphere of a high-momentum K^+- or K^0_s. From the polar angle distributions of the strangeness-signed thrust axis, we obtained A_s=0.895+-0.066(stat.)+-0.062(syst.). The analyzing power and u-ubar plus d-dbar background were constrained using the data.

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arXiv2000

Measurements of Z0 Electroweak Couplings at SLD

We present a summary of the results of several electroweak measurements performed by the SLD experiment at the Stanford Linear Collider (SLC). Most of these results are preliminary and are based, unless otherwise indicated, on the full 1993-8 data set of approximately 550,000 hadronic decays of Z0 bosons produced with an average electron beam polarization of 73%.

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arXiv1999

Precise measurement of the b-quark fragmentation function in Z0 boson decays

We have developed a new technique for inclusive reconstruction of the energy of B hadrons. The excellent efficiency and resolution of this technique allow us to make the most precise determination of the b-quark fragmentation function, using e+e- -> Z0 decays recorded in the SLD experiment at SLAC. We compared our measurement with the predictions of a number of fragmentation models. We excluded several of these models and measured the average scaled energy of weakly-decaying B hadrons to be =0.714+-0.005(stat)+-0.007(syst) +-0.002(model dependence).

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arXiv1999

A Preliminary Direct Measurement of the s-Quark Coupling

We present an updated direct measurement of the parity-violating coupling of the Z boson to strange quarks, A_s, derived from the full SLD data sample of approximately 550,000 hadronic decays of Z bosons produced with a polarized electron beam and recorded by the SLD experiment at SLAC between 1993 and 1998. Events with primary strange quarks are tagged by the presence in each event hemisphere of a high-momentum charged K meson, neutral K meson or Lambda hyperon identified using the Cherenkov Ring Imaging Detector and/or a mass tag. The CCD vertex detector is used to suppress the background from heavy flavor events. The strangeness of the tagged particle is used to sign the event thrust axis in the direction of the initial strange quark. The coupling A_s is obtained directly from a measurement of the left-right-forward-backward production asymmetry in polar angle of the tagged strange quark. The background from primary up and down events is measured from the data, as is the analyzing power of the method for primary strange events. We measure: A_s = 0.85 +- 0.06(stat.) +- 0.07(syst.) (preliminary).

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arXiv1999

Production of Charged pi, K and p in Hadronic Z0 Decays

We have updated our results on identified charged hadron production using the full SLD data sample of 550,000 hadronic Z^0 decays taken between 1993 and 1998. The SLD Cherenkov Ring Imaging Detector allows the identification of clean samples of charged pions, kaons and protons over a wide momentum range, providing precise tests of perturbative QCD calculations and of fragmentation models. We have studied flavor-inclusive Z^0 decays, as well as decays into light, c and b flavors, selected using the SLD vertex detector. In addition we have updated our comparison of hadron and antihadron production in light quark (rather than antiquark) jets, selected using the high SLC electron beam polarization. Differences between hadron and antihadron production at high momentum fraction provide precise measurements of leading particle production and new, stringent tests of fragmentation models.

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arXiv1999

A Study of Correlations between Identified Charged Hadrons in Hadronic Z^0 Decays

We present a preliminary study of correlations in rapidity between pairs of identified charged pions, kaons and protons using the entire SLD data sample of 550,000 hadronic Z^0 decays. Short range charge correlations are observed between all combinations of these hadron species, indicating local conservation of quantum numbers and charge ordering in the jet fragmentation process. The rapidity range of this effect is found to be independent of particle momentum. A strong long-range K^+K^- correlation is observed at high-momentum and weaker long-range pi^+pi^-, pi^+K^-, pK^- and pp-bar correlations are observed in light flavor events, providing new information on leading particle production in u, d and s jets. The long-range correlations observed in c-cbar and bb-bar events are markedly different and consistent with expectations based on known decay properties of the leading heavy hadrons. In addition, the SLC electron beam polarization is used to tag the quark hemisphere in each event, allowing the first study of rapidities signed such that positive rapidity is along the quark rather than antiquark direction. Distributions of ordered differences in signed rapidity between pairs of particles provide a direct probe of quantum number ordering along the quark-antiquark axis and other new insights into the fragmentation process.

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arXiv1999

An Improved Direct Measurement of Leptonic Coupling Asymmetries with Polarized $Z^0$'s

We report new direct measurements of the $Z^0$-lepton coupling asymmetry parameters $A_e$, $A_μ$ and $A_τ$, with polarized $Z^0$'s collected by the SLD detector at the SLAC Linear Collider. The parameters are extracted from the measurement of the left-right-forward-backward asymmetries for each lepton species. The 1996, 1997 and 1998 SLD runs are included in this analysis and combined with published data from the 1993-95 runs. Preliminary results are $A_e = 0.1558 \pm 0.0064$, $A_μ=0.137 \pm 0.016 $ and $A_τ=0.142 \pm 0.016$. If lepton universality is assumed, a combined asymmetry parameter $A_{l} = 0.1523 \pm 0.0057$ results. This translates into an effective weak mixing angle $\sin^2θ^{eff}_W = 0.23085 \pm 0.00073$ at the $Z^0$ resonance.

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arXiv1999

Direct Measurement of A_c using Inclusive Charm Tagging at the SLD Detector

We report a new measurement of A_c using data obtained by SLD in 1993-98. This measurement uses a vertex tag technique, where the selection of a c hemisphere is based on the reconstructed mass of the charm hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high c-event tagging efficiency and purity of 28% and 82%, respectively. Charged kaons identified by the CRID detector and the charge of the reconstructed vertex provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of A_c = 0.603 \pm 0.028 \pm 0.023

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arXiv1999

Direct Measurement of A_b using Charged Kaons at the SLD Detector

We report a new measurement of A_b using data obtained by SLD in 1997-98. This measurement uses a vertex tag technique, where the selection of a b hemisphere is based on the reconstructed mass of the bottom hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high b-event tagging efficiency and purity of 78% and 97%, respectively. Charged kaons identified by the CRID detector provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of A_b = 0.997 \pm 0.044 \pm 0.067

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arXiv1999

Combined SLD Measurement of Ab at the Z Resonance using Various Techniques

We present a new preliminary combination of measurements of the parity-violation parameter Ab made by the SLD collaboration using various experimental techniques. The techniques differ in detail, but in general a sample of bb events is selected or enhanced by using the topologically reconstructed mass of the separated vertices formed by decaying B hadrons. The direction of the b(bbar) quark is signed by one of four final state tags: jet charge, vertex charge, leptons, or identified K+- from the b vertex. We account for statistical and systematic correlations between the four analyses to arrive at our combined result: Ab=0.905 +/- 0.017 {stat} +/- 0.020 (syst).

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arXiv1999

New Measurement of Ab at the Z Resonance using a Vertex-Charge Technique

We present a new preliminary measurement of the parity-violation parameter Ab using a self-calibrating vertex-charge technique. In the SLD experiment we observe hadronic decays of polarized Z bosons produced in collisions between longitudinally polarized electrons and unpolarized positrons at the SLAC Linear Collider. A sample of bb events is selected using the topologically reconstructed mass of B hadrons. From out 1996-8 data sample of approximately 400,000 hadronic Z decays, we obtain Ab = 0.897 +/- 0.027 (stat) +0.036/-0.034 (syst).

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arXiv1999

Measurement of the B+ and B0 Lifetimes using Topological Vertexing at SLD

The lifetimes of B+ and B0 mesons have been measured using the entire sample of 550,000 hadronic Z0 decays collected by the SLD experiment at the SLC between 1993 and 1998. In this paper, we describe the inclusive analysis of the 350,000 hadronic Z0 decays collected in 1997-98 with the upgraded SLD vertex detector. In this data period, a high statistics sample of 30903 (20731) charged (neutral) vertices with good charge purity is obtained. The charge purity is enhanced by using the vertex mass, the SLC electron beam polarization (73% for 1997-8) and an opposite hemisphere jet charge technique. Combining the results of this data sample with the results from the earlier data yield the following preliminary values: $τ_{B^+}=1.623\pm0.020($stat$)\pm0.034$(syst) ps, $τ_{B^0}=1.589\pm0.021($stat$)\pm0.043$(syst) ps, $τ_{B^+}/τ_{B^0} = 1.037\pm^{0.025}_{0.024}($stat$) \pm0.024$(syst).

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arXiv1999

Measurement of $A_c$ with charmed mesons at SLD

We present a direct measurement of the parity-violation parameter A_c. The measurement is based on 550k Z^0 decays collected by the SLD detector. The mean electron-beam polarization is |P_e| = 73 %. The tagging of c-quark events was performed using two methods: The exclusive reconstruction of D^*+, D^+, and D^0 mesons, and the inclusive P_T spectrum of soft-pions (pi_s) in the decay of D^*+ -> D^0 pi_s^+. The results of these two methods are combined to give A_c = 0.688 +- 0.035(stat.) +- 0.025(sys.) (preliminary).

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arXiv1999

Tests of QCD using Heavy Flavors at SLD

We present preliminary results on three SLD analyses: the gluon energy spectrum in 3-jet bbg events, the rate of g->bb, and the b fragmentation function in Z0 decays. The gluon energy spectrum, measured over the full kinematic range, is compared with perturbative QCD predictions. We set new 95% C.L. limits on the anomalous chromomagnetic coupling of the b quark: -0.09 bb is measured to be (3.07 +/- 0.71(stat) +/- 0.66(syst)) X 10^-3. The inclusive B hadron energy distribution in Z0 decays is measured for the first time over the full kinematic range, using a novel B hadron energy reconstruction technique. Several models of b fragmentation including JETSET + Peterson are excluded by the data. The average scaled B hadron energy of the weakly decaying B hadron is measured to be XB = 0.713 +/- 0.005(stat) +/- 0.007(syst) +/- 0.002 (model). All three measurements take advantage of the small and stable SLC interaction point as well as the excellent vertexing and tracking capabilities of the upgraded CCD-pixel vertex detector.

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