Search results for "Proton"
showing 10 items of 5886 documents
Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions atsNN=2.76TeV
2016
We report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at √sNN=2.76 TeV. By selecting events in the same centrality interval, but with very different average flow, different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic flow coefficient v2 to be almost independent of transverse momentum pT, which is as expected if this effect is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow, indicating an interplay between radial and ell…
Where Do Diffractive Nucleons Go?
1974
Nucleon and pion-nucleon distributions from the diffractive component in pp collisions are analysed. Diffractive events are assumed to come from a mechanism pp → N*p, in which a proton is diffractively excited to a nova N*. The decay properties of N* are determined by assuming that a Pomeron-proton collision behaves as a proton-proton collision. Correlations within the diffractive component are computed and seen to be numerically small. Even interference with the pionization component does not reproduce the observed pattern of pion (in the plateau)-proton (in the fragmentation region) correlations. This may imply the existence of long-range correlations within the pionization component.
ϒ photoproduction on the proton at the Electron-Ion Collider
2020
We present a dispersive analysis with the aim to extract the $\mathrm{\ensuremath{\Upsilon}}\text{\ensuremath{-}}p$ scattering length from $\ensuremath{\gamma}p\ensuremath{\rightarrow}\mathrm{\ensuremath{\Upsilon}}p$ experiments. In this framework, the imaginary part of the $\mathrm{\ensuremath{\Upsilon}}\text{\ensuremath{-}}p$ forward scattering amplitude is obtained from $\ensuremath{\gamma}p\ensuremath{\rightarrow}\mathrm{\ensuremath{\Upsilon}}p$ cross section measurements and is constrained at high energies from existing HERA and LHC data. Its real part is calculated through a once-subtracted dispersion relation, and the subtraction constant is proportional to the $\mathrm{\ensuremath{\…
One-Particle Measurement of the Antiproton Magnetic Moment
2013
\DeclareRobustCommand{\pbar}{\HepAntiParticle{p}{}{}\xspace} \DeclareRobustCommand{\p}{\HepParticle{p}{}{}\xspace} \DeclareRobustCommand{\mup}{$\mu_{p}${}{}\xspace} \DeclareRobustCommand{\mupbar}{$\mu_{\pbar}${}{}\xspace} \DeclareRobustCommand{\muN}{$\mu_N${}{}\xspace For the first time a single trapped \pbar is used to measure the \pbar magnetic moment ${\bm\mu}_{\pbar}$. The moment ${\bm\mu}_{\pbar} = \mu_{\pbar} {\bm S}/(\hbar/2)$ is given in terms of its spin ${\bm S}$ and the nuclear magneton (\muN) by $\mu_{\pbar}/\mu_N = -2.792\,845 \pm 0.000\,012$. The 4.4 parts per million (ppm) uncertainty is 680 times smaller than previously realized. Comparing to the proton moment measured using…
Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton
2009
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…
ϕ meson transparency in nuclei from ϕN resonant interactions
2017
We investigate the $\ensuremath{\phi}$ meson nuclear transparency using some recent theoretical developments on the $\ensuremath{\phi}$ in medium self-energy. The inclusion of direct resonant $\ensuremath{\phi}N$ scattering and the kaon decay mechanisms leads to a $\ensuremath{\phi}$ width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced $\ensuremath{\phi}$ production from COSY finding an overall good agreement. The results support the need of a quite large direct $\ensuremath{\phi}N$-scattering contribution to the self-energy.
Low-energy doubly virtual Compton scattering from dilepton electroproduction on a nucleon
2020
We propose a new way to experimentally determine the subleading low-energy structure constant of doubly virtual Compton scattering on a proton. Such empirical determination will reduce the theoretical model error in estimates of the hadronic correction to the muonic hydrogen Lamb shift. We demonstrate that the dilepton forward-backward asymmetry in the e−p→e−pe−e+ process, which can be accessed at electron scattering facilities, yields a large sensitivity to this so far unknown low-energy constant.
Production ofWbosons in proton-nucleus collisions
1979
It is shown that nuclear effects can cause an enhancement in the cross section for production of $W$ bosons in a proton-nucleus collision. The cross section near threshold is a few orders of magnitude higher than expected from a linear dependence on the atomic number. Encouraging implications for experiments with fixed targets at laboratory energies of ${10}^{3}$ GeV and higher are discussed. We also discuss lepton-pair production off nuclei.
Helicity Dependence ofγp→Nπbelow 450 MeV and Contribution to the Gerasimov-Drell-Hearn Sum Rule
2000
The helicity dependence of the single pion photoproduction on the proton has been measured in the energy range from 200 to 450 MeV for the first time. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a frozen-spin target. The data obtained provide new information for multipole analyses of pion photoproduction and determine the main contributions to the Gerasimov-Drell-Hearn sum rule and the forward spin polarizability gamma(0).
Weak production of strange Ξ baryons off the nucleon
2019
The authors would like to thank Luis Alvarez-Ruso and Manuel Jose Vicente Vacas for useful discussions. One of the authors (MRA) would like to thank the pleasant hospitality at University of Granada where part of the work has been done.