Search results for "Nucleon"
showing 10 items of 1041 documents
Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions atsNN=2.76 TeV
2011
The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.
A test of charge-parity-time invariance at the atto-electronvolt scale
2017
We developed a novel fast measurement procedure for cyclotron frequency comparisons of two individual particles in a Penning trap, which enabled us to compare the charge-to-mass ratio of the proton and the antiproton with a fractional precision of 69 parts per trillion. To date this is the most precise test of charge-parity-time invariance using baryons. Our measurements were performed at cyclotron frequencies of about 30 MHz, which means that charge-parity-time symmetry holds at the atto-electronvolt scale.
Baryon resonances in nuclei
2005
The field of baryon resonances in nuclei is reviewed. Theoretical developments and experimental evidence as well are discussed. Special emphasis is laid on electromagnetic processes for the two nucleon system. Some aspects of real isobars in nuclei are touched upon.
Many Body Modes of Excitation in Heavy Ion Collisions
1989
The one step excitation of two particle holes in heavy ion collisions is shown to be an important channel in the reaction. Pion production has to compete against this new channel, not present in the NN free reaction, and is reduced sensibly. The effective NN cross section is increased leading to a more effective stopping of the nucleons.
Nuclear pion photoproduction in theΔresonance region
1999
A measurement of the /sup 12/C( gamma , pi /sup +/n)/sup 11/B reaction in quasifree pi -production kinematic regimes has been performed using tagged photons in conjunction with large solid angle pi and n detectors. The aim of the experiment was to investigate predicted modifications to the Delta excitation of nucleons and their subsequent propagation and decay, brought about by the nuclear medium. Differential cross sections are presented for photon energies spanning the Delta (1232) excitation region. The measurements are consistent with distorted wave impulse approximation calculations in which the amplitude for proton Delta excitation, followed by Delta propagation and decay to pi /sup +…
Contributions of internal nucleon structure to the nuclear charge and current operators
1983
The relativistic pair current and contributions of nucleon isobars are evaluated in the constituent-quark model. Isovector charge and isoscalar current contributions change substantially compared to previous calculations. The magnetic form factor of the deuteron and the charge form factors of3He and3H are modifed significantly and the previously predicted large differences in the form factors of3He and3H are considerably reduced.
Zemach moments and radii of H2,3 and He3,4
2019
We present benchmark calculations of Zemach moments and radii of $^{2,3}\mathrm{H}$ and $^{3,4}\mathrm{He}$ using various few-body methods. Zemach moments are required to interpret muonic atom data measured by the CREMA collaboration at the Paul Scherrer Institute. Conversely, radii extracted from spectroscopic measurements can be compared with ab initio computations, posing stringent constraints on the nuclear model. For a given few-body method, different numerical procedures can be applied to compute these quantities. A detailed analysis of the numerical uncertainties entering the total theoretical error is presented. Uncertainties from the few-body method and the calculational procedure …
The influence of a bag deformation on N-N-scattering
1984
We present a model calculation to study the influence of an intrinsic nucleon deformation on the elastic scattering of nucleons. The nucleons are visualized as deformed sources for the exchange of bosons. Both static changes in the derived OBEP and the admixtures of rotational states give rise to only small effects even for large bag deformation, in addition, the two contributions tend to cancel each other.
Nucleon Form Factor Measurements in Mainz: Past and Future
2007
The form factors of proton and neutron provide a natural and direct insight into their internal structure. They were a main research goal in the nuclear physics program of the Universitat Mainz, which led to some of the most precise measurements to date. This article gives an overview, starting from the very first experiments at the now obsolete linear accelerator and ending at the exhaustive experiments currently underway at the Mainz Microtron (MAMI) facilities.