Search results for "quantum chromodynamics"
showing 10 items of 1027 documents
Dynamically generated resonances
2010
We study the radiative decay properties of the charmonium-like X, Y and Z mesons generated dynamically from vector meson-vector meson interaction in the framework of a unitarized hiddengauge formalism. In the present work we calculate the one- and two-photon decay widths of the hidden-charm Y (3940), Z(3930) (or X(3915)) and X(4160) mesons in the framework of the vector meson dominance formalism. We obtain good agreement with experiment in case of the two photon width of the X(3915) which we associate with the 2 + resonance that we find at 3922 MeV.
TheN-? transition form factor and anomalous?-decays into octet-decuplet baryon-antibaryon Pairs
1987
We develop a Generalized-Vector-Meson Dominance Model (GVDM) for the invariantN-Δ transition form factors which incorporates the correct largeq2 power behaviour of QCD and describes the available lowq2 space-like data. We then use this GVDM transition form factor in the time-like region to calculate theSU (3) singlet and octet contributions to Ψ-decays into octet-decuplet baryon-antibaryon pairs. The results are compared to recent data on Ψ-decays into octet-decuplet baryon-antibaryon pairs.
Lattice calculations of the leading hadronic contribution to g-2
2012
We report on our ongoing project to calculate the leading hadronic contribution to the anomalous magnetic moment of the muon aHLO μ using two dynamical flavours of non-perturbatively O(a) improved Wilson fermions. In this study, we changed the vacuum polarisation tensor to a combination of local and point-split currents which significantly reduces the numerical effort. Partially twisted boundary conditions allow us to improve the momentum resolution of the vacuum polarisation tensor and therefore the determination of the leading hadronic contribution to (g− 2)μ . We also extended the range of ensembles to include a pion mass below 200MeV which allows us to check the non-trivial chiral behav…
Comparison between two strictly local QCD sum rules
1989
Two strictly local QCD sum rules, analytic extrapolation by conformal mapping and analytic continuation by duality, are developed and presented in full detail. They allow the extrapolation of the QCD amplitude to a single point near zero in the complex {ital q}{sup 2} plane. Being orthogonal to the usual QCD sum rules, they present a drastic enlargement of phenomenological applications. In addition, the stability of both methods is shown explicitly, a fact which makes them particularly reliable. The difference between the two methods is illustrated in connection with the determination of the hadronic ({ital g}{minus}2) factor of the muon. Their effectiveness is demonstrated in the calculati…
B and B(S) decay constants from moments of finite energy sum rules in QCD
2004
We use an appropriate combination of moments of finite energy sum rules in QCD in order to compute the B_q-meson decays constants f_B and f_{B_s}.We perform the calculation using a two-loop computation of the imaginary part of the pseudoscalar two point function in terms of the running bottom quark mass. The results are stable with the so called QCD duality threshold and they are in agreement with the estimates obtained from Borel transform QCD sum rules and lattice computations.
Relativistic corrections to the static potential at O(1/m) and O(1/m^2)
2007
We investigate the relativistic corrections to the static potential, i.e. the O(1/m) potential and the O(1/m^2) velocity-dependent potentials, in SU(3) lattice gauge theory. They are important ingredients of potential nonrelativistic QCD for heavy quarkonium. Utilizing the multi-level algorithm, we obtain remarkably clean signals of these potentials up to r=0.9 fm. We observe long range nonperturbative contributions to these corrections.
Nucleon Structure Functions and Light-Front Dynamics
1999
We present a quark-parton model to describe polarized and unpolarized nucleon structure functions. The twist-two matrix elements for the QCD evolution analysis of lepton-hadron scattering are calculated within a light-front covariant quark model. The relativistic effects in the three-body wave function are discussed for both the polarized and unpolarized cases. Predictions are given for the polarized gluon distributions as will be seen in future experiments.
QCD Perturbative Calculation of the Scattering Processes at Hadron Colliders
2015
When two high energetic particles A and B collide, a large number of final-state particles can be produced.
Inclusive π±, K± and(p,p¯) differential cross-sections at the Z resonance
1995
Inclusive π±, K± and $$(p,\bar p)$$ differential cross-sections in hadronic decays of the Z have been measured as a function ofz=P hadron/P beam, the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified by their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, ξ*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD.
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…