Search results for "Helicity"
showing 10 items of 208 documents
Measurement of theWboson helicity in top quark decays using5.4 fb−1ofpp¯collision data
2011
We present a measurement of the helicity of the W boson produced in top quark decays using t{bar t} decays in the {ell}+jets and dilepton final states selected from a sample of 5.4 fb{sup -1} of collisions recorded using the D0 detector at the Fermilab Tevatron p{bar p} collider. We measure the fractions of longitudinal and right-handed W bosons to be f{sub 0} = 0.669 {+-} 0.102 [{+-}0.078 (stat.) {+-} 0.065 (syst.)] and f{sub +} = 0.023 {+-} 0.053 [{+-}0.041 (stat.){+-}0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f{sub 0} fixed to the value from the standard model yields f{sub +} = 0.010 {+-} 0.037 [{+-}0.022 (stat.) {…
Covariant trace formalism for heavy mesons-wave top-wave transitions
1993
Heavy meson,s- top-wave, weakb→c transitions are studied in the context of the heavy quark effective theory using covariant meson wave functions. We use the trace formalism to evaluate the weak transitions. As expected from heavy quark symmetry, the eight transitions betweens- andp-wave states are described in terms of only two universal form factors which are given in terms of explicit wave function overlap integrals. We present our results in terms of both invariant and helicity amplitudes. Using our helicity amplitude expressions we discuss rate formulae, helicity structure functions and joint angular decay distributions in the decays $$\bar B \to D^{**} ( \to (D,D^* ) + \pi ) + W^ - ( \…
Measurement ofW-Boson Polarization in Top-Quark Decay inpp¯Collisions ats=1.96 TeV
2010
We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb(-1) of p (p) over bar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c(2), three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f(0)) and right-handed (f(0)) W bosons yields the model- independent results f(0) =0. 88 +/- 0.11(stat) +/- 0.06(syst) and f(+) = 0.15 +/- 0.07(stat) +/- 0.06(syst) with a correlation coefficient of -0.59. A measurement of f(0) [f(+)] constraining f(+) [f(0)] to its standard model value of 0.0 [0.7] yields f(0) 0.70 + 0.07(stat) +/- 0.04(syst) [f(+) - 0.01 +/- 0.02(stat) +/- 0.05(syst)]. All these resu…
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…
QCD Jets at HERA II.O(? s 2 ) four-jet cross-sections
1989
We present exact expressions for theO(α s 2 ) tree graph four-jet cross-sections in neutral current and charged current deep inelasticep scattering initiated by quarks, antiquarks and gluons including lepton polarization effects. Using helicity amplitudes the partonic cross-sections are given in concise form including all colour, flavour and statistical factors. We explicate the electroweak coupling dependence and state how the partonic cross-sections are folded with the respective parton densities to obtain theep jet cross-sections toO(α s 2 ). We present some numerical results for the neutral current one-photon exchange case. We elaborate on the cut dependence of the jet rates and present…
Beam-Recoil Polarization Measurement of π0 Electroproduction on the Proton in the Region of the Roper Resonance
2017
The helicity-dependent recoil proton polarizations P_{x}^{'} and P_{z}^{'} as well as the helicity-independent component P_{y} have been measured in the p(e[over →],e^{'}p[over →])π^{0} reaction at four-momentum transfer Q^{2}≃0.1 GeV^{2}, center-of-mass proton emission angle θ_{p}^{*}≃90°, and invariant mass W≃1440 MeV. This first precise measurement of double-polarization observables in the energy domain of the Roper resonance P_{11}(1440) by exploiting recoil polarimetry has allowed for the extraction of its scalar electroexcitation amplitude at an unprecedentedly low value of Q^{2}, establishing a powerful instrument for probing the interplay of quark and meson degrees of freedom in t…
The dependence of dichroism in VUV-photoemission on the optical properties of adsorbates: Cs-monolayer on W(110)
1998
Abstract We report on the dependence of dichroic photoemission excited by polarised light on the angle of photon incidence. We measured the difference in the angle-resolved photoemission intensities from Cs-5p semi-corelevels excited by photons of opposite helicity, known as CDAD and of orthogonal linear polarisation—LDAD. We found that the dependence of dichroism on the angle of incidence can not be described by the equations used in the photoemission model for free atomic states. A complex consideration of the parallel and perpendicular components of the vector potential of the exciting light is needed, including the phase shift between these components. The phase shift is produced by the…
<‘γ*N→Δtransition form factors: A new analysis of data onp(e,e′p)π0atQ2=2.8and4.0 (GeV/c)2
2001
Recent JLab data of the differential cross section for the reaction ${p(e,e}^{\ensuremath{'}}p){\ensuremath{\pi}}^{0}$ in the invariant mass region of $1.1lWl1.4 \mathrm{GeV}$ at four-momentum transfer squared ${Q}^{2}=2.8$ and $4.0 (\mathrm{GeV}{/c)}^{2}$ are analyzed with two models, both of which give an excellent description of most of the existing pion electroproduction data below $Wl1.5 \mathrm{GeV}.$ We find that at up to ${Q}^{2}=4.0 (\mathrm{GeV}{/c)}^{2},$ the extracted helicity amplitudes ${A}_{3/2}$ and ${A}_{/2}$ remain comparable with each other, implying that hadronic helicity is not conserved at this range of ${Q}^{2}.$ The ratios ${E}_{1+}{/M}_{1+}$ obtained show, starting …
Semileptonic decays ofBcmesons into charmonium states in a relativistic quark model
2005
We use the framework of a relativistic constituent quark model to study the semileptonic transitions of the ${B}_{c}$ meson into $(\overline{c}c)$ charmonium states where $(\overline{c}c)={\ensuremath{\eta}}_{c}(^{1}S_{0})$, $J/\ensuremath{\psi}(^{3}S_{1})$, ${\ensuremath{\chi}}_{c0}(^{3}P_{0})$, ${\ensuremath{\chi}}_{c1}(^{3}P_{1})$, ${h}_{c}(^{1}P_{1})$, ${\ensuremath{\chi}}_{c2}(^{3}P_{2})$, $\ensuremath{\psi}(^{3}D_{2})$. We compute the ${q}^{2}$ dependence of all relevant form factors and give predictions for their semileptonic ${B}_{c}$ decay modes including also their $\ensuremath{\tau}$ modes. We derive a formula for the polar angle distribution of the charged lepton in the $(l{\ens…
Numerical Simulations of a Flux Rope Ejection
2015
Coronal mass ejections (CMEs) are the most violent phenomena observed on the Sun. One of the most successful models to explain CMEs is the flux rope ejection model, where a magnetic flux rope is expelled from the solar corona after a long phase along which the flux rope stays in equilibrium while magnetic energy is being accumulated. However, still many questions are outstanding on the detailed mechanism of the ejection and observations continuously provide new data to interpret and put in the context. Currently, extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evo…