Search results for "Nucleon"
showing 10 items of 1041 documents
Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions ats=7 TeVwith the ATLAS detector
2012
A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy root s = 7 TeV is presented. Photons are ...
Measurement of transverse energy at midrapidity in Pb-Pb collisions atsNN=2.76TeV
2016
We report the transverse energy ($E_{\mathrm T}$) measured with ALICE at midrapidity in Pb-Pb collisions at ${\sqrt{s_{\mathrm {NN}}}}$ = 2.76 TeV as a function of centrality. The transverse energy was measured using identified single particle tracks. The measurement was cross checked using the electromagnetic calorimeters and the transverse momentum distributions of identified particles previously reported by ALICE. The results are compared to theoretical models as well as to results from other experiments. The mean $E_{\mathrm T}$ per unit pseudorapidity ($\eta$), $\langle $d$E_{\mathrm T}/$d$\eta \rangle$, in 0-5% central collisions is 1737 $\pm$ 6(stat.) $\pm$ 97(sys.) GeV. We find a si…
Measurement of hadron form factors at BESIII
2018
The BESIII experiment, operated at the BEPCII e+e- collider in Beijing, has acquired large data sets at center-of-mass energies between 2.0 GeV and 4.6 GeV. One of the key aspects of the physics program of the BESIII collaboration is to test the understanding of QCD at intermediate energies. Applying different experimental techniques, form factors of hadrons are measured. Among these are the pion form factor, as an important input to the (g - 2)μ puzzle, and the electro-magnetic form factors of nucleons and hyperons in the time-like regime. An overview of the recent results and some ongoing studies at BESIII is provided.
Accelerating Ab Initio Nucleon Structure Calculations with All-Mode-Averaging on Gordon
2014
The composition of nucleons has long been known to be sub-atomic particles called quarks and gluons, which interact through the strong force and theoretically can be described by Quantum Chromodynamics (QCD). Lattice QCD (LQCD), in which the continuous space-time is translated into grid points on a four-dimensional lattice and ab initio Monte Carlo simulations are performed, is by far the only model-independent method to study QCD with controllable errors. We report the successful application of a novel algorithm, All-Mode-Averaging, in the LQCD calculations of nucleon internal structure on the Gordon supercomputer our award of roughly 6 million service units through XSEDE. The application …
Isovector charges of the nucleon from 2+1-flavor QCD with clover fermions
2016
Physical review / D 95(7), 074508 (2017). doi:10.1103/PhysRevD.95.074508
The present status of the EPS nuclear PDFs
2010
The recent global analyses of the nuclear parton distribution functions (nPDFs) lend support to the validity of the factorization theorem of QCD in high-energy processes involving bound nucleons. With a special attention on our latest global analysis EPS09, we review the recent developements in the domain of nuclear PDFs.
Hadron structure from lattice QCD
2014
Recent progress in lattice QCD calculations of nucleon structure will be presented. Calculations of nucleon matrix elements and form factors have long been difficult to reconcile with experiment, but with advances in both methodology and computing resources, this situation is improving. Some calculations have produced agreement with experiment for key observables such as the axial charge and electromagnetic form factors, and the improved understanding of systematic errors will help to increase confidence in predictions of unmeasured quantities. The long-omitted disconnected contributions are now seeing considerable attention and some recent calculations of them will be discussed.
KNScattering and the Nucleon Strangeness Radius
1997
The leading non-zero electric moment of the nucleon strange-quark vector current is the mean square strangeness radius, $$. We evaluate the lightest OZI-allowed contribution to $$, arising from the kaon cloud, using dispersion relations. Drawing upon unitarity constraints as well as $K^{+}N$ scattering and $e^+e^-\to K\bar{K}$ cross section data, we find the structure of this contribution differs significantly from that suggested by a variety of QCD-inspired model calculations. In particular, we find evidence for a strong $\phi$-meson resonance which may enhance the scale of kaon cloud contribution to an observable level.
QCD radiative corrections to the soft spectator contribution in the wide angle Compton scattering
2014
We derive the complete factorization formula for the leading power contribution in wide angle Compton scattering. It consists of the soft- and hard-spectator contributions. The hard-spectator contribution is well known and defined in the form of the convolution of a hard kernel with the nucleon distribution amplitudes. The soft-spectator contribution describes the scattering which involves the soft modes. We use the soft collinear effective theory in order to define this term in a field theoretical approach. Using the SCET framework we provide the proof of the factorization formula. We also compute the next-to-leading QCD corrections to the hard coefficient function of the soft spectator co…
Two-photon exchange in elastic electron-proton scattering: a QCD factorization approach.
2009
We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer $Q^2$. It is shown that the leading two-photon exchange amplitude behaves as $1/Q^4$ relative to the one-photon amplitude, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.