Search results for "annihilation"
showing 10 items of 1016 documents
Resummed jet rates for heavy quark production in e+e– annihilation
2004
Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.
Improved Measurement ofB+→ρ+ρ0and Determination of the Quark-Mixing Phase Angleα
2009
We present improved measurements of the branching fraction ${\cal B}$, the longitudinal polarization fraction $f_L$, and the direct {\ensuremath{CP}\xspace} asymmetry {\ensuremath{{\cal A}_{CP}}\xspace} in the $B$ meson decay channel $B^+\to\rho^+\rho^0$. The data sample was collected with the {{\slshape B\kern-0.1em{\smaller A}\kern-0.1em B\kern-0.1em{\smaller A\kern-0.2em R}}} detector at SLAC. The results are ${\cal B} (\Bp\ra\rprz)=(23.7\pm1.4\pm1.4)\times10^{-6}$, $f_L=0.950\pm0.015\pm0.006$, and $\Acp=-0.054\pm0.055\pm0.010$, where the uncertainties are statistical and systematic, respectively. Based on these results, we perform an isospin analysis and determine the CKM weak phase ang…
Improved measurements of electroweak parameters from Z decays into fermion pairs
1992
The properties of the Z resonance are measured on the basis of 190000 Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality, M(Z) = (91.182 +/- 0.009exp +/- 0.020L;P) GeV, GAMMA(Z) = (2484 +/- 17) MeV, sigma(had)0 = (41.44 +/- 0.36) nb, and GAMMA(had)/GAMMA(ll) = 21.00 +/- 0.20. The corresponding number of light neutrino species is 2.97 +/- 0.07. The forward-backward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons: g(V)2(M(Z)2)/g(A)2(M(Z)2) = 0.0072 +/- 0.0027. Combining these results with ALEPH results on quark charge and bbBAR asymmetries, and tau-polarization, sin2 theta(W)(M(…
Inclusive production of neutral vector mesons in hadronic Z decays
1996
Data on the inclusive production of the neutral vector mesons rho(0)(770), omega(782), K*(0)(892), and phi (1020) in hadronic Z decays recorded with the ALEPH detector at LEP are presented and compared to Monte Carlo model predictions. Bose-Einstein effects are found to be important in extracting a reliable value for the p(0) production rate. An average p(0) multiplicity of 1.45 +/- 0.21 per event is obtained. The omega is detected via its three pion decay mode omega --> pi(+)pi(-)pi(0) and has a total rate of 1.07 +/- 0.14 per event. The multiplicity of the K*(0) is 0.83 +/- 0.09, whilst that of the phi is 0.122 +/- 0.009, both measured using their charged decay modes. The measurements pro…
First Evidence for cos2β>0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity
2018
We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}→D^{(*)}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] p…
Evidence forB0→ρ0ρ0Decays and Implications for the Cabibbo-Kobayashi-Maskawa Angleα
2007
We search for the decays B(0) --> rho(0)rho(0), B(0) --> rho(0)f(0)(980), and B(0) --> f(0)(980)f(0)(980) in a sample of about 384 x 10(6) Upsilon(4S) --> BB[over] decays collected with the BABAR detector at the PEP-II asymmetric-energy e(+)e(-) collider at Stanford Linear Accelerator Center. We find evidence for B(0) --> rho(0)rho(0) with 3.5 sigma significance and measure the branching fraction B = (1.07 +/- 0.33 +/- 0.19) x 10(-6) and longitudinal polarization fraction f(L) = 0.87 +/- 0.13 +/- 0.04, where the first uncertainty is statistical, and the second is systematic. The uncertainty on the Cabibbo-Kobayashi-Maskawa quark-mixing matrix unitarity angle alpha due to penguin contributio…
O(αs) longitudinal spin polarization in heavy-quark production
1995
We present the massive one-loop QCD corrections to the production cross sections of polarized quarks in the annihilation process ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}(g) for bottom, top, and charm quarks. From the full analytical expressions for the production cross sections, Schwinger-type interpolation formulas for all parity-parity combinations (VV, VA, AA) are derived. The parity-odd interpolation formula contains the correct limit for vanishing quark masses taking into account a residual coupling of left- and right-chiral states in the massless theory. Numerical results for the total cross section and …
Do the Quark Masses Run? Extractingm¯b(mZ)from CERN LEP Data
1997
We present the first results of next-to-leading order QCD corrections to three-jet heavy quark production at the CERN ${e}^{+}{e}^{\ensuremath{-}}$ collider LEP including mass effects. Among other applications, this calculation can be used to extract the bottom-quark mass from LEP data and, therefore, to test the running of masses as predicted by QCD.
Dimensional reduction methods in QCD
1994
We apply the technique of dimensional reduction to massless quantum chromodynamics. It is shown that compared to conventional dimensional regularization methods calculations of radiative corrections at the one-loop level are less involved. We discuss the use of helicity methods within this framework and as an application we evaluate the one-loop corrections to the parity-violating cross sections and to the quark forwardbackward asymmetric polarization in\(e^ + e^ - \to V \to q\bar q(g)\). Finally, we demonstrate that further simplifications occur in the computation of structure functions including the parity-violating structure function in quark- and gluoninitiated electroproduction process…
Longitudinal contribution to the alignment polarization of quarks produced in e + e - -annihilation: an O (α s ) effect
1996
We calculate the longitudinal contribution to the alignment polarization Pl of quarks produced in e+e− annihilation. In the Standard Model, the longitudinal alignment polarization vanishes at the Born term level and thus receives its first non-zero contribution from the O(αs) tree graph process. We provide analytical and numerical results for the longitudinal alignment polarization of massless and massive quarks, in particular for the recently discovered top quark.