Left-right Forward-backward Asymmetry Research Articles

Fermion pair production at e−e+ linear collider experiments in GUT inspired gauge-Higgs unification

Fermion pair production at $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z'$s, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^-e^+$ linear collider experiments with energies 250$\,$GeV to 1$\,$TeV.

Light quark fragmentation in polarized Z0 decays at SLD

We report results on two physics topics from the SLD experiment at the SLAC Linear Collider, using our full sample of 550,000 events of the type e + e − → Z 0 → q q . The electron beam was polarized, enabling the quark and antiquark hemispheres to be tagged in each event. One physics topic is 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 are analyzed, providing the first direct observation of baryon number ordering along the q q axis. The other topic is the first direct measurement of A s , the parity-violating coupling of the Z 0 to strange quarks, by measuring the left-right forward-backward production asymmetry in polar angle of the tagged s quark. We obtain A s = 0.895 ± 0.066( stat.) ± 0.062( syst.), which is consistent with the Standard Model and is currently the most precise measurement of this quantity.

Direct Measurement ofAbinZ0Decays Using Charged Kaon Tagging

We present a direct measurement of the parity-violating asymmetry A{sub b} in the Z{sup 0} to b anti-b coupling using a new technique to distinguish the b and anti-b quarks using charged kaons from B decays. The Z{sup 0} bosons are produced in e{sup +}e{sup -} collisions at the SLC with longitudinally polarized electrons. b anti-b events are selected using a secondary vertex mass tag and A{sub b} is determined from the left-right forward-backward asymmetry. From the 1994-1995 data sample, selected from 100,000 hadronic Z{sup 0} decays, we obtain A{sub b} = 0.855 {+-} 0. 088{sub stat} {+-} 0.102{sub sys}.

Three-jet event orientation in e +e − annihilation: new tests of the Standard Model

We discuss the orientation of e +e − → qq̄g events in terms of the polar and azimuthal angles of the event plane w.r.t. the electron beam direction. We define an asymmetry of the azimuthal-angle distribution which, along with the left-right forward-backward polar-angle asymmetry, is sensitive to parity-violating effects in three-jet events; these have yet to be explored experimentally. We have evaluated these observables at O( α s ) in perturbative QCD and present their dependence on longitudinal beam polarisation and c.m. energy. We also define a moments analysis in terms of the orientation angles that allows a new and more detailed test of QCD by isolating the six independent helicity cross-sections.

Review of recent neutral current results

The status of neutral current measurements are reviewed with emphasis placed on those measurements related to the tau lepton. These include preliminary results from LEP on the Z0 lineshape using data from the most recent centre-of-mass energy scan in the vicinity of the Z0 resonance; results of the forward-backward asymmetries of the electron, muon and tau lepton and the most recent measurements of the the tau polarisation at LEP. The status of the left-right asymmetry and forward-backward left-right asymmetries for the muon and tau lepton as measured at SLC are summarised. Interpretation of these results in terms of standard model parameters are discussed.

γ-Z interferometry at a Φ-factory

We analyze the possibilities that the proposed Φ-factories offer to measure γ-Z interference. In the unpolarized beam case, we study different signatures in the ϱπ channel, taking advantage of the presence of the nearby α 1 resonance. We build a C-odd forward-backward asymmetry, estimated to be around 10 −5, and ( P-even, T-even) and ( P-odd, T-odd) alignments of the ϱ, to be seen from the angular distribution of its ππ decay products. With polarized electrons a left-right asymmetry around 2 x 10 −4 is present in all channels. At leading order this asymmetry is independent of hadronic matrix elements and is sensitive to the Z 0-s s vector coupling. In the ϱπ channel, a combined left-right forward-backward asymmetry is considered.

Production of charm and beauty in e+e− with polarized electron beams

The test of the Standard Model through the measurements of Z ° to fermion couplings can benefit from much enhanced sensitivity by using longitudinally polarized electron beams. This paper reviews preliminary electroweak measurements from SLD on heavy-quark production at the Z °, using 150000 hadronic Z ° decays accumulated during the 1993-1995 runs with high electron beam polarization. The parity-violating parameters Ab and A~ of the Zbb and Zcc couplings are measured directly from the left-right forward-backward asymmetries. A measurement of Rb with a lifetime double tag and a summary of the preliminary measurement of ALR from the 1993-1995 SLD data are also included in this report.

Measurement of the left-right forward-backward asymmetry for charm quarks with D*+ and D+ mesons.

We present a direct measurement of {ital A}{sub {ital c}}=2{ital v}{sub {ital c}}{ital a}{sub {ital c}}/({ital v}{sup 2}{sub {ital c}}+{ital a}{sup 2}{sub {ital c}}) from the left-right forward-backward asymmetry of {ital D}{sup *}+ and {ital D}{sup +} mesons in {ital Z}{sup 0} events produced with the longitudinally polarized SLAC Linear Collider beam. These {ital Z}{sup 0}{r_arrow}{ital c} over bar events are tagged on the basis of event kinematics and decay topology from a sample of hadronic {ital Z}{sup 0} decays recorded by the SLAC Large Detector. We measure {ital A}{sup 0}{sub {ital c}} = 0.73 {plus_minus} 0.22(stat) {plus_minus} 0.10(syst). {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Measurement of the parity-violation parameters Ab and Ac from the left-right forward-backward asymmetry of leptons in hadronic events at the Z0 resonance.

The parity-violating parameters ${A}_{b}$ and ${A}_{c}$ are directly measured by the SLD experiment at the SLAC Linear Collider in ${e}^{+}{e}^{\ensuremath{-}}$ collisions with polarized electrons at the ${Z}^{0}$ resonance. Leptons with distinctive total and transverse momenta are used to select and analyze ${Z}^{0}\ensuremath{\rightarrow}b\overline{b}$ and ${Z}^{0}\ensuremath{\rightarrow}c\overline{c}$ events. ${A}_{b}$ and ${A}_{c}$ are extracted by forming the left-right forward-backward asymmetry in electron beam polarization and quark polar angle. From our 1993 sample of 1.8 p${\mathrm{b}}^{--1}$ of ${Z}^{0}$ decay data with an average electron beam polarization of 63% we find ${A}_{b}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.91\ifmmode\pm\else\textpm\fi{}0.14$ (stat) $\ifmmode\pm\else\textpm\fi{}0.07$ (syst) and ${A}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.37\ifmmode\pm\else\textpm\fi{}0.23$ (stat) $\ifmmode\pm\else\textpm\fi{}0.21$ (syst).

Measurement of the parity-violation parameter Ab from the left-right forward-backward asymmetry of b quark production in Z0 decays using a momentum-weighted track-charge technique.

Using an impact parameter tag to select an enriched sample of {ital Z}{sup 0}{r_arrow}{ital bb}{ovr bar} events, and the net momentum-weighted track charge to identify the sign of the charge of the underlying {ital b} quark, we have measured the left-right forward-backward asymmetry for {ital b} quark production as a function of polar angle. Based on 1.8pb{sup {minus}1} of {ital Z}{sup 0} decay data produced with a mean electron beam polarization of {ital P}{sub {ital e}}=63%, this yields a direct measurement of the extent of parity violation in the {ital Zbb} coupling of {ital A}{sub {ital b}}=0.87{plus_minus}0.11(stat){plus_minus}0.09(syst).