4,126 research outputs found

    Top quark tensor couplings

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    We compute the real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the tbWtbW vertex in the Standard Model (SM). For both tensorial couplings we find that the real part of the electroweak SM correction is close to 10% of the leading contribution given by the QCD gluon exchange. We also find that the electroweak real and imaginary parts for the anomalous right coupling are almost of the same order of magnitude. The one loop SM prediction for the real part of the left coupling is close to the 3ŌÉ\sigma discovery limit derived from b‚Üíső≥b\rightarrow s \gamma. Besides, taking into account that the predictions of new physics interactions are also at the level of a few percents when compared with the one loop QCD gluon exchange, these electroweak corrections should be taken into account in order to disentangle new physics effects from the standard ones. These anomalous tensorial couplings of the top quark will be investigated at the LHC in the near future where sensitivity to these contributions may be achieved.Comment: 16 pages, 2 figure

    Measurement of the Branching Fraction for B- --> D0 K*-

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    We present a measurement of the branching fraction for the decay B- --> D0 K*- using a sample of approximately 86 million BBbar pairs collected by the BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the K*- through its decay to K0S pi-. We measure the branching fraction to be B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid Communications

    A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)

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    We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb‚ąí1{\rm fb}^{-1} recorded at the ő•(4S)\Upsilon(4S) resonance and 3.9 fb‚ąí1{\rm fb}^{-1} off-resonance. One of the neutral B mesons, which are produced in pairs at the ő•(4S)\Upsilon(4S), is fully reconstructed in the CP decay modes J/ŌąKS0J/\psi K^0_S, Ōą(2S)KS0\psi(2S) K^0_S, Ōác1KS0\chi_{c1} K^0_S, J/ŌąK‚ąó0J/\psi K^{*0} (K‚ąó0‚ÜíKS0ŌÄ0K^{*0}\to K^0_S\pi^0) and J/ŌąKL0J/\psi K^0_L, or in flavor-eigenstate modes involving D(‚ąó)ŌÄ/ŌĀ/a1D^{(*)}\pi/\rho/a_1 and J/ŌąK‚ąó0J/\psi K^{*0} (K‚ąó0‚ÜíK+ŌÄ‚ąíK^{*0}\to K^+\pi^-). The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample finds őĒmd=0.516¬Ī0.016(stat)¬Ī0.010(syst)ps‚ąí1\Delta m_d = 0.516\pm 0.016 {\rm (stat)} \pm 0.010 {\rm (syst)} {\rm ps}^{-1}. The value of the asymmetry amplitude sin‚Ā°2ő≤\sin2\beta is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B0B^0 decays in the CP-eigenstate modes. We find sin‚Ā°2ő≤=0.59¬Ī0.14(stat)¬Ī0.05(syst)\sin2\beta=0.59\pm 0.14 {\rm (stat)} \pm 0.05 {\rm (syst)}, demonstrating that CP violation exists in the neutral B meson system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review

    Direct Measurement of the Top Quark Mass at D0

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    We determine the top quark mass m_t using t-tbar pairs produced in the D0 detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar W^- final states with one W boson decaying to q-qbar and the other to e-nu or mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +- 5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +- 4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst) GeV/C^2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.Comment: 43 pages, 53 figures, 33 tables. RevTeX. Submitted to Phys. Rev.

    The Azimuthal Decorrelation of Jets Widely Separated in Rapidity

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    This study reports the first measurement of the azimuthal decorrelation between jets with pseudorapidity separation up to five units. The data were accumulated using the D{\O}detector during the 1992--1993 collider run of the Fermilab Tevatron at s=\sqrt{s}= 1.8 TeV. These results are compared to next--to--leading order (NLO) QCD predictions and to two leading--log approximations (LLA) where the leading--log terms are resummed to all orders in őĪS\alpha_{\scriptscriptstyle S}. The final state jets as predicted by NLO QCD show less azimuthal decorrelation than the data. The parton showering LLA Monte Carlo {\small HERWIG} describes the data well; an analytical LLA prediction based on BFKL resummation shows more decorrelation than the data.Comment: 6 pages with 4 figures, all uuencoded and gzippe

    Evidence for the Rare Decay B -> K*ll and Measurement of the B -> Kll Branching Fraction

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    We present evidence for the flavor-changing neutral current decay B‚ÜíK‚ąó‚Ąď+‚Ąď‚ąíB\to K^*\ell^+\ell^- and a measurement of the branching fraction for the related process B‚ÜíK‚Ąď+‚Ąď‚ąíB\to K\ell^+\ell^-, where ‚Ąď+‚Ąď‚ąí\ell^+\ell^- is either an e+e‚ąíe^+e^- or őľ+őľ‚ąí\mu^+\mu^- pair. These decays are highly suppressed in the Standard Model, and they are sensitive to contributions from new particles in the intermediate state. The data sample comprises 123√ó106123\times 10^6 ő•(4S)‚ÜíBBňČ\Upsilon(4S)\to B\bar{B} decays collected with the Babar detector at the PEP-II e+e‚ąíe^+e^- storage ring. Averaging over K(‚ąó)K^{(*)} isospin and lepton flavor, we obtain the branching fractions B(B‚ÜíK‚Ąď+‚Ąď‚ąí)=(0.65‚ąí0.13+0.14¬Ī0.04)√ó10‚ąí6{\mathcal B}(B\to K\ell^+\ell^-)=(0.65^{+0.14}_{-0.13}\pm 0.04)\times 10^{-6} and B(B‚ÜíK‚ąó‚Ąď+‚Ąď‚ąí)=(0.88‚ąí0.29+0.33¬Ī0.10)√ó10‚ąí6{\mathcal B}(B\to K^*\ell^+\ell^-)=(0.88^{+0.33}_{-0.29}\pm 0.10)\times 10^{-6}, where the uncertainties are statistical and systematic, respectively. The significance of the B‚ÜíK‚Ąď+‚Ąď‚ąíB\to K\ell^+\ell^- signal is over 8ŌÉ8\sigma, while for B‚ÜíK‚ąó‚Ąď+‚Ąď‚ąíB\to K^*\ell^+\ell^- it is 3.3ŌÉ3.3\sigma.Comment: 7 pages, 2 postscript figues, submitted to Phys. Rev. Let
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