Search results for "Chromodynamics"
showing 10 items of 1030 documents
Pion–nucleus Drell–Yan data as a novel constraint for nuclear PDFs
2017
We have studied the prospects of using the Drell-Yan dilepton process in pion-nucleus collisions as a novel input in the global analysis of nuclear parton distribution functions (nPDFs). In a NLO QCD framework, we find the measured nuclear cross-section ratios from the NA3, NA10 and E615 experiments to be largely insensitive to the pion parton distributions and also compatible with the EPS09 and nCTEQ15 nPDFs. These data sets can thus be, and in EPPS16 have been, included in global nPDF analyses without introducing significant new theoretical uncertainties or tension with the other data. In particular, we explore the constraining power of these data sets on the possible flavour asymmetry in…
B0−B¯0Mixing beyond Factorization in QCD Sum Rules
2003
We present a calculation of the B°-B° mixing matrix element in the framework of QCD sum rules for three-point functions. We compute α s corrections to a three-point function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element with next-to-leading order (NLO) accuracy. This calculation is imperative for a consistent evaluation of experimentally measured mixing parameters since the coefficient functions of the effective Hamiltonian for B 0 -B 0 mixing are known at NLO. We find that radiative corrections violate factorization at NLO; this violation is under full control and amounts to 10%. The resulting value of the B parameter is found to be B B …
QCD at non-zero temperature from the lattice
2015
I review the status of lattice QCD calculations at non-zero temperature. After summarizing what is known about the equilibrium properties of strongly interacting matter, I discuss in more detail recent results concerning the quark-mass dependence of the thermal phase transition and the status of calculations of non-equilibrium properties.
The Pinch Technique and its Applications to Non-Abelian Gauge Theories
2010
Non-Abelian gauge theories, such as quantum chromodynamics (QCD) or electroweak theory, are best studied with the aid of Green's functions that are gauge-invariant off-shell, but unlike for the photon in quantum electrodynamics, conventional graphical constructions fail. The Pinch Technique provides a systematic framework for constructing such Green's functions, and has many useful applications. Beginning with elementary one-loop examples, this book goes on to extend the method to all orders, showing that the Pinch Technique is equivalent to calculations in the background field Feynman gauge. The Pinch Technique Schwinger-Dyson equations are derived, and used to show how a dynamical gluon m…
Search for Axionlike Dark Matter Using Solid-State Nuclear Magnetic Resonance.
2021
Physical review letters 126(14), 141802 (2021). doi:10.1103/PhysRevLett.126.141802
Complete amplitude and cross section structure of one-loop contributions toe + e ??q $$\bar q$$ g
1985
We calculate theO(α 2 ) one-loop contributions to the seven (inn≠4) independent invariant amplitudes describinge + e −→q $$\bar q$$ g in massless QCD. After folding with theO(α 1/2 ) Born term contribution we obtain the nine independentO(α 2 ) structure functions that describe the parity-conserving and parity-violating contributions toe + e −→q $$\bar q$$ g. We use dimensional regularization to control infrared and ultraviolet divergencies.
TheA 1-and the ϕ-meson in QCD
1993
Recently we used a method of stable analytic extrapolation to test whether strictly local duality between the asymptotic and the resonance region, which is believed to be valid in QCD, appears already at the present stage of QCD calculations. Probing the QCD ϱ-amplitude, we found a prominent bump structure in the resonance region, i.e. a rather direct evidence for the validity of local duality. In the present paper we confirm and extend this result by giving two further applications, theA1-meson and the ϕ-meson. While we do not meet theA1, as was to be expected since other sum rules can not separate it from the continuum, too, the extrapolation of the ϕ-amplitude leads to an enormous bump. …
Determination of the Pseudoscalar Decay Constant fDs+ via Ds+→μ+νμ
2019
Using a 3.19 fb^{-1} data sample collected at an e^{+}e^{-} center-of-mass energy of E_{cm}=4.178 GeV with the BESIII detector, we measure the branching fraction of the leptonic decay D_{s}^{+}→μ^{+}ν_{μ} to be B_{D_{s}^{+}→μ^{+}ν_{μ}}=(5.49±0.16_{stat}±0.15_{syst})×10^{-3}. Combining our branching fraction with the masses of the D_{s}^{+} and μ^{+} and the lifetime of the D_{s}^{+}, we determine f_{D_{s}^{+}}|V_{cs}|=246.2±3.6_{stat}±3.5_{syst} MeV. Using the c→s quark mixing matrix element |V_{cs}| determined from a global standard model fit, we evaluate the D_{s}^{+} decay constant f_{D_{s}^{+}}=252.9±3.7_{stat}±3.6_{syst} MeV. Alternatively, using the value of f_{D_{s}^{+}} calculat…
Spectrum of SU(2) gauge theory with two fermions in the adjoint representation
2008
We present preliminary results of lattice simulations of SU(2) gauge theory with two Wilson fermions in the adjoint representation. This theory has recently attracted considerable attention because it might possess an infrared fixed point (or an almost-fixed-point), and hence be a candidate for a walking technicolor theory. In this work we study the particle spectrum of the theory, and compare it with more familiar spectrum of the theory with SU(2) gauge fields and two flavors of fundamental representation fermions.
Four-quark operators and non-leptonic weak transitions
1991
72 páginas, 12 figuras, 6 tablas.-- CERN-TH-5906-90 ; CPT-2393.