Search results for "quantum chromodynamics"
showing 10 items of 1027 documents
ηandη′transition form factors from rational approximants
2014
The $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ transition form factors in the spacelike region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. The slope and curvature parameters of the form factors as well as their values at zero and infinity are extracted from experimental data. The impact of these results on the mixing parameters of the $\ensuremath{\eta}$-${\ensuremath{\eta}}^{\ensuremath{'}}$ system and the pseudoscalar-exchange contributions to the hadronic light-by-light scattering part of the anomalous magnetic moment ${a}_{\ensuremath{\mu}}$ are also discussed.
Atiyah-Manton Approach to Skyrmion Matter
2002
We propose how to approach, and report on the first results in our effort for, describing nuclear matter starting from the solitonic picture of baryons which is supposed to represent QCD for large number of colors. For this purpose, the instanton-skyrmion connection of Atiyah and Manton is exploited to describe skyrmion matter. We first modify 't Hooft's multi-instanton solution so as to suitably incorporate proper dynamical variables into the skyrmion matter and then by taking these variables as variational parameters, we show that they cover a configuration space sufficient to adequately describe the ground state properties of nuclear matter starting from the skyrmion picture. Our results…
Branching fraction and form-factor shape measurements of exclusive charmless semileptonicBdecays, and determination of|Vub|
2012
We report the results of a study of the exclusive charmless semileptonic decays, B0→π-l+ν, B+→π0l+ν, B+→ωl+ν, B+→ηl+ν, and B+→η′l+ν (l=e or μ) undertaken with approximately 462×106 BB pairs collected at the Υ(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q2, the square of the momentum transferred to the lepton-neutrino pair, for B0→π-l+ν, B+→π0l+ν, B+→ωl+ν, and B+→ηl+ν. From these distributions, we extract the form-factor shapes f+(q2) and the total branching fractions B(B0→π-l+ν)=(1.45±0.04stat±0.06syst)×10-4 (combined π- …
Improved measurement of time-dependentCPasymmetries and theCP-odd fraction in the decayB0→D*+D*−
2007
We present an updated measurement of time-dependent CP asymmetries and the CP-odd fraction in the decay B0-->D*+D*- using 232x10(6)BB pairs collected by the BABAR detector at the SLAC PEP-II B factory. We determine the CP-odd fraction to be 0.125+/-0.044(stat)+/-0.007(syst). The time-dependent CP asymmetry parameters C+ and S+ are determined to be 0.06+/-0.17(stat)+/-0.03(syst) and -0.75+/-0.25(stat)+/-0.03(syst), respectively. The standard model predicts these parameters to be 0 and -sin2beta, respectively, in the absence of penguin amplitude contributions.
τ hadronic spectral function moments in a nonpower QCD perturbation theory
2016
Abstract The moments of the hadronic spectral functions are of interest for the extraction of the strong coupling and other QCD parameters from the hadronic decays of the τ lepton. We consider the perturbative behavior of these moments in the framework of a QCD nonpower perturbation theory, defined by the technique of series acceleration by conformal mappings, which simultaneously implements renormalization-group summation and has a tame large-order behavior. Two recently proposed models of the Adler function are employed to generate the higher order coefficients of the perturbation series and to predict the exact values of the moments, required for testing the properties of the perturbativ…
BK-parameter fromNf=2twisted mass lattice QCD
2011
We present an unquenched Nf=2 lattice computation of the B K parameter which controls K0-K0 oscillations. A partially quenched setup is employed with two maximally twisted dynamical (sea) light Wi ...
Predictions for low-pTand high-pThadron spectra in nearly central Pb+Pb collisions atsNN=5.5TeV tested atsNN=130and 200 GeV
2005
We study the hadron spectra in nearly central $A+A$ collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) in a broad transverse momentum range. We cover the low-${p}_{T}$ spectra using longitudinally boost-invariant hydrodynamics with initial energy and net-baryon number densities from the perturbative QCD (pQCD)+saturation model. Buildup of the transverse flow and sensitivity of the spectra to a single decoupling temperature ${T}_{\mathrm{dec}}$ are studied. Comparison with RHIC data at $\sqrt{{s}_{\mathit{NN}}}=130$ and 200 GeV suggests a rather high value ${T}_{\mathrm{dec}}=150$ MeV. The high-${p}_{T}$ spectra are computed using factorized pQCD cro…
Measurement of the pp¯→W+b+X production cross section at s=1.96 TeV
2013
We present a measurement of the cross section for $W$ boson production in association with at least one {$b$-quark} jet in proton-antiproton collisions. The measurement is made using data corresponding to an integrated luminosity of 6.1\ifb recorded with the D0 detector at the Fermilab Tevatron \ppbar Collider at $\sqrt{s}=1.96$ TeV. We measure an inclusive cross section of {$\sigma(W \sim(\to\mu\nu) + b + X) = 1.04 \pm 0.05\thinspace$(stat.) $\pm 0.12 \thinspace$(syst.) pb} and $\sigma(W (\to e\nu) + b + X) = 1.00$ \pm 0.04 \thinspace$(stat.) $\pm 0.12 \thinspace$(syst.) pb in the phase space defined by $p_T^\nu > 25$ GeV, $p_T^{\text{$b$-jet}}>20$ GeV, $|\eta^{\text{$b$-jet}}| 20$ GeV and…
Measurements of inclusive W+jets production rates as a function of jet transverse momentum in pp¯ collisions at s=1.96 TeV
2011
This Letter describes measurements of inclusive W (--> e nu) + n jet cross sections (n = 1-4), presented as total inclusive cross sections and differentially in the nth jet transverse momentum. The measurements are made using data corresponding to an integrated luminosity of 4.2 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider, and achieve considerably smaller uncertainties on W +jets production cross sections than previous measurements. The measurements are compared to next-to-leading order perturbative QCD (pQCD) calculations in the n =1-3 jet multiplicity bins and to leading order pQCD calculations in the 4-jet bin. The measurements are generally in agreement with pQCD…
Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers
2012
We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance Delta-R in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of Delta-R and for different tran…