Measurement Of Charge Asymmetry Research Articles

Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders

Several models predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range that might be discovered at the CERN LHC. In some of those models, moreover, a sizable charge asymmetry of top versus antitop quarks might be generated. The detection of these exotic resonances, however, requires selecting data samples where the top and the antitop quarks are highly boosted, which is experimentally very challenging. We asses that the measurement of the top quark charge asymmetry at the LHC is very sensitive to the existence of excited states of the gluon with axial-vector couplings to quarks. We use a toy model with general flavor independent couplings, and show that a signal can be detected with relatively not too energetic top and antitop quarks. We also compare the results with the asymmetry predicted by QCD, and show that its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses.

Measurement of the Electron Charge Asymmetry inpp¯→W+X→eν+XEvents ats=1.96 TeV

We present a measurement of the electron charge asymmetry in pp[over ]-->W+X-->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.

Measurement of the Forward-Backward Charge Asymmetry and Extraction ofsin2θWeffinpp¯→Z/γ*+X→e+e−+XEvents Produced ats=1.96 TeV

We present a measurement of the forward-backward charge asymmetry (A FB) in pp-->Z/gamma* + X-->e+e(-) + X events at a center-of-mass energy of 1.96 TeV using 1.1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider. A FB is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the A FB measurement to extract the effective weak mixing angle sin2thetaWeff = 0.2326+/-0.0018(stat)+/-0.0006(syst).

Measurement of the muon charge asymmetry fromWboson decays

We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb−1 of data collected at s=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron pp¯ Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.Received 27 September 2007DOI:https://doi.org/10.1103/PhysRevD.77.011106©2008 American Physical Society

CP Violation Studies at Tevatron

We present an overview of a few recent results related to CP-violation from the Tevatron. First, we discuss a measurement of the dimuon charge asymmetry from D{\O}that extracts the CP-violation parameter of $\Bo$ mixing and decay. This is followed by the CDF measurement of the CP-violating asymmetry in $\bdkpi$ decays. Finally we give the CDF result on the ratio $R = \frac{BR(B \to D^0 K)}{BR(B \to D^0 \pi)}$

Measurement of the Charge Asymmetry in SemileptonicBs0Decays

We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unt by comparing the decay rate of Bs0-->micro+Ds-nuX, where Ds- -->phipi- and phi-->K+K-, with the charge-conjugate Bs0 decay rate. This sample was selected from 1.3 fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unt=[1.23+/-0.97(stat)+/-0.17(syst)]x10(-2). Assuming that Deltam(s)/Gamma(s)>>1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: DeltaGamma(s)/Deltam(s)tanphi(s)=[2.45+/-1.93(stat)+/-0.35(syst)]x10(-2).

Measurement of Branching Fractions and Charge Asymmetries inB+Decays toηπ+,ηK+,ηρ+, andη′π+, and Search forB0Decays toηK0andηω

We present measurements of branching fractions and charge asymmetries for six B-meson decay modes with an eta or eta(') meson in the final state. The data sample corresponds to 232 x 10(6) BB pairs collected with the BABAR detector at the PEP-II asymmetric-energy e(+)e(-) B Factory at SLAC. We measure the branching fractions (in units of 10(-6)): B(B+ -->eta pi(+))=5.1+/-0.6+/-0.3, B(B+ etaK+)=3.3+/-0.6+/-0.3, B(B0-->etaK0)=1.5+/-0.7+/-0.1 (<2.5 at 90% C.L.), B(B+-->eta rho(+))=8.4+/-1.9+/-1.1, B(B0-->eta omiga)=1.0+/-0.5+/-0.2 (<1.9 at 90% C.L.), and B(B+-->eta(')pi(+))=4.0+/-0.8+/-0.4, where the first uncertainty is statistical and second systematic. For the charged modes we also determine the charge asymmetries, all found to be compatible with zero.

Measurement of Branching Fractions and Charge Asymmetries for ExclusiveBDecays to Charmonium

We report measurements of branching fractions and charge asymmetries of exclusive decays of neutral and charged B mesons into two-body final states containing a charmonium state and a light strange meson. The charmonium mesons considered are J/psi, psi(2S) and chi(c1), and the light meson is either K or K(*). We use a sample of about 124x10(6) BB pairs collected with the BABAR detector at the PEP-II storage ring at the Stanford Linear Accelerator Center.

Measurement of the forward-backward charge asymmetry fromW→eνproduction inpp¯collisions ats=1.96 TeV

We report a measurement of the forward-backward charge asymmetry of electrons from W boson decays in p anti-p collisions at s**(1/2) = 1.96 TeV using a data sample of 170 pb-1 collected by the Collider Detector at Fermilab. The asymmetry is measured as a function of electron rapidity and transverse energy and provides new input on the momentum fraction dependence of the u and d quark parton distribution within the proton.

Branching Fractions andCPAsymmetries inB0→K+K−KS0andB+→K+KS0KS0

We measure the branching fractions and CP asymmetries in the decays B0-->K(+)K(-)K(0)(S) and B+-->K(+)K(0)(S)K(0)(S) using a sample of approximately 122x10(6) BB pairs collected by the BABAR detector. From a time-dependent analysis of the K(+)K(-)K(0)(S) sample that excludes phiK(0)(S), the values of the CP-violation parameters are S=-0.56+/-0.25+/-0.04 and C=-0.10+/-0.19+/-0.10, where the first uncertainty is statistical and the second is systematic. We confirm that the final state is nearly purely CP even and extract the standard model parameter sin(2beta=0.57+/-0.26+/-0.04(+0.17)(-0) where the last error is due to uncertainty on the CP content. We present the first measurement of the CP-violating charge asymmetry A(CP)(B+-->K(+)K(0)(S)K(0)(S))=-0.04+/-0.11+/-0.02. The branching fractions are B(B0-->K+K-K0)=(23.8+/-2.0+/-1.6)x10(-6) and B(B+-->K(+)K(0)(S)K(0)(S))=(10.7+/-1.2+/-1.0)x10(-6).

Measurement of branching fractions and charge asymmetries in B+/--->rho+/-pi0 and B+/--->rho0pi+/- decays, and search for B0-->rho0pi0.

We present measurements of branching fractions and charge asymmetries in B-meson decays to rho(+)pi(0), rho(0)pi(+), and rho(0)pi(0). The data sample comprises 89x10(6) Upsilon(4S)-->BBmacr; decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We find the charge-averaged branching fractions B(B+-->rho(+)pi(0))=[10.9+/-1.9(stat)+/-1.9(syst)]x10(-6) and B(B+-->rho(0)pi(+))=(9.5+/-1.1+/-0.9)x10(-6), and we set a 90% confidence-level upper limit B(B0-->rho(0)pi(0))<2.9x10(-6). We measure the charge asymmetries ACP(pi(0))(rho(+))=0.24+/-0.16+/-0.06 and ACP(pi(+))(rho(0))=-0.19+/-0.11+/-0.02.

Observation of B0-->omega K0, B+-->eta pi+, and B+-->eta K+ and study of related decays.

We present measurements of branching fractions and charge asymmetries for seven B-meson decays with an eta, eta', or omega meson in the final state. The data sample corresponds to 89x10(6) BB pairs produced from e(+)e(-) annihilation at the Upsilon(4S) resonance. We measure the following branching fractions in units of 10(-6): B(B+-->eta pi(+))=5.3+/-1.0+/-0.3, B(B+-->eta K+)=3.4+/-0.8+/-0.2, B(B0-->eta K0)=2.9+/-1.0+/-0.2 (<5.2, 90% C.L.), B(B+-->eta(')pi(+))=2.7+/-1.2+/-0.3 (<4.5, 90% C.L.), B(B+-->omega pi(+))=5.5+/-0.9+/-0.5, B(B+-->omega K+)=4.8+/-0.8+/-0.4, and B(B0-->omega K0)=5.9(+1.6)(-1.3)+/-0.5. The charge asymmetries are A(ch)(B+-->eta pi(+))=-0.44+/-0.18+/-0.01, A(ch)(B+-->eta K+)=-0.52+/-0.24+/-0.01, A(ch)(B+-->omega pi(+))=0.03+/-0.16+/-0.01, and A(ch)(B+-->omega K+)=-0.09+/-0.17+/-0.01.

Measurements of the branching fractions and bounds on the charge asymmetries of charmless three-body charged B decays.

We present measurements of branching fractions and charge asymmetries for charmless B-meson decays to three-body final states of charged pions and kaons. The analysis uses 81.8 fb(-1) of data collected at the Upsilon(4S) resonance with the BABAR detector at the SLAC PEP-II asymmetric B Factory. We measure the branching fractions B(B+-->pi(+)pi(-)pi(+))=(10.9+/-3.3+/-1.6)x10(-6), B(B+-->K+pi(-)pi(+))=(59.1+/-3.8+/-3.2)x10(-6), and B(B+-->K+K-K+)=(29.6+/-2.1+/-1.6)x10(-6) and provide 90% C.L. upper limits for other decays. We observe no charge asymmetries for these modes.

Implication ofW-Boson Charge Asymmetry Measurements inpp¯Collisions for Models of Charge Symmetry Violations in Parton Distributions

A surprisingly large charge symmetry violation of the sea quarks in the nucleon has been proposed in a recent article by Boros et al. as an explanation of the discrepancy between neutrino and muon nucleon structure function data at low $x$. We show that these models are ruled out by the published CDF $W$ charge asymmetry measurements, which strongly constrain the ratio of $d$ and $u$ quark momentum distributions in the proton over the $x$ range of $0.006$ to $0.34$. This constraint also limits the systematic error from possible charge symmetry violation in the determinations of ${sin}^{2}{\ensuremath{\theta}}_{W}$ from $\ensuremath{\nu}N$ scattering experiments.

Direct measurement of valence charge asymmetry in GaAs using X-ray standing waves.

Direct measurement of valence charge asymmetry in GaAs using X-ray standing waves.

First Measurement of the Left-Right Charge Asymmetry in HadronicZBoson Decays and a New Determination ofsin2θWeff

We present the first measurement of the left-right charge asymmetry ${A}_{Q}^{\mathrm{obs}}$ in hadronic $Z$ boson decays. This was performed at ${E}_{\mathrm{c}.\mathrm{m}.}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}91.27\mathrm{GeV}$ with the SLD at the SLAC Linear Collider with a polarized electron beam. Using 89 838 events we obtain ${A}_{Q}^{\mathrm{obs}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.225\ifmmode\pm\else\textpm\fi{}0.056\ifmmode\pm\else\textpm\fi{}0.019$, which leads to a measurement of the electron left-right asymmetry parameter, ${A}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.162\ifmmode\pm\else\textpm\fi{}0.041\ifmmode\pm\else\textpm\fi{}0.014$, and ${sin}^{2}{\ensuremath{\theta}}_{W}^{\mathrm{eff}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2297\ifmmode\pm\else\textpm\fi{}0.0052\ifmmode\pm\else\textpm\fi{}0.0018$. Also, the ${A}_{Q}^{\mathrm{obs}}$ measurement combined with the left-right cross section asymmetry determines ${A}_{e}$ independent of the value of the electron-beam polarization.

Forward-Backward Charge Asymmetry of Electron Pairs above the Z0 Pole.

We present a measurement of the forward-backward charge asymmetry of the process pp¯→Z0/γ+X,Z0/γ→e+e− at Mee>MZ, using 110pb−1 of data at s=1.8TeV collected at the Collider Detector at Fermilab. The measured charge asymmetries are 0.43±0.10 in the invariant mass region Mee>105GeV/c2, and 0.070±0.016 in the region 75<Mee<105GeV/c2. These results are consistent with the standard model values of 0.528±0.009 and 0.052±0.002, respectively.Received 22 March 1996DOI:https://doi.org/10.1103/PhysRevLett.77.2616©1996 American Physical Society

Fragmentation function method for charge asymmetry measurements in e+e− collisions

We propose a method for measuring the hadron charge asymmetry in e + e − collisions which is based upon the fragmentation function formalism, and is largely independent of modelling of fragmentation effects. Furthermore, in this method, QCD radiative corrections can be accounted for in a systematic way.

Forward-backward charge asymmetry of quark pairs produced at the KEK TRISTAN e+e- collider.

We report on a measurement of the forward-backward charge asymmetry in e+e- --> qqBAR at KEK TRISTAN, where. the asymmetry is near maximum. We sum over all flavors and measure the asymmetry by determining the charge of the quark jets. In addition we exploit flavor dependencies in the jet charge determination to enhance the contributions of certain flavors. This provides a check on the asymmetries of individual flavors. The measurement agrees with the standard model expectations.

Results from the L3 experiments at LEP

In this report we summarize the major results from the first three years of running of the L3 detector at the Large Electron Positron collider (LEP). The L3 detector was designed to measure electrons, photons and muons with high precision; it has achieved ( ΔE/ E0 ≃ 1.4% for electrons and photons at E = 45 GeV and ( Δp/ p) ≃ 2.5% for muons at p = 45 GeV. Most of the experimental results presented are based on approximately 500 000 Z events. The data provide foue independent checks of the Standard Model weak neutral currents to an accuracy of ≃ 1%. These are: the measurement of Z parameters; the measurement of the forward-backward charge asymmetry of ;epton pairs; the measurement of asymmetry parameters from Z→bb̄ decays; and the measurement of the gp lepton polarization asymmetry. The data also information on weak charged currents from measurements of b hadrons such as decay width, lifetime, and B 0−B 0 mixing, and from measurements of τ leptons such as their lifetime and branching ratios.The large number of Z events and the resoltuion of the L3 detector allow presicion tests of QED and QCD, including the production of π 0, η and hard photons.Leptonic final states with hard isolated photons are analyzed and high mass photon pairs are observed. Higgs boson production has not been observed and limits are given in the context of the standard Model and its supersymmetric extensions. We also present upper limits on rare Z decays such as Z → γγγ and on flavor violating decays such as Z → τ, μτ. Finally, upper limits obtained in the search for various new particles and new interactions are reported.