284 research outputs found
Theoretical study of the two-proton halo candidate Ne including contributions from resonant continuum and pairing correlations
With the relativistic Coulomb wave function boundary condition, the energies,
widths and wave functions of the single proton resonant orbitals for Ne
are studied by the analytical continuation of the coupling constant (ACCC)
approach within the framework of the relativistic mean field (RMF) theory.
Pairing correlations and contributions from the single-particle resonant
orbitals in the continuum are taken into consideration by the resonant
Bardeen-Cooper-Schrieffer (BCS) approach, in which constant pairing strength is
used. It can be seen that the fully self-consistent calculations with NL3 and
NLSH effective interactions mostly agree with the latest experimental
measurements, such as binding energies, matter radii, charge radii and
densities. The energy of 2s orbital is slightly higher than that
of orbital, and the occupation probability of the
2s orbital is about 20%, which are in accordance with the
shell model calculation and three-body model estimation
The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array
We have already reported the first result on the all-particle spectrum around
the knee region based on data from 2000 November to 2001 October observed by
the Tibet-III air-shower array. In this paper, we present an updated result
using data set collected in the period from 2000 November through 2004 October
in a wide range over 3 decades between eV and eV, in which
the position of the knee is clearly seen at around 4 PeV. The spectral index is
-2.68 0.02(stat.) below 1PeV, while it is -3.12 0.01(stat.) above 4
PeV in the case of QGSJET+HD model, and various systematic errors are under
study now.Comment: 12 pages, 7 figures, accepted by Advances in space researc
Moon Shadow by Cosmic Rays under the Influence of Geomagnetic Field and Search for Antiprotons at Multi-TeV Energies
We have observed the shadowing of galactic cosmic ray flux in the direction
of the moon, the so-called moon shadow, using the Tibet-III air shower array
operating at Yangbajing (4300 m a.s.l.) in Tibet since 1999. Almost all cosmic
rays are positively charged; for that reason, they are bent by the geomagnetic
field, thereby shifting the moon shadow westward. The cosmic rays will also
produce an additional shadow in the eastward direction of the moon if cosmic
rays contain negatively charged particles, such as antiprotons, with some
fraction. We selected 1.5 x10^{10} air shower events with energy beyond about 3
TeV from the dataset observed by the Tibet-III air shower array and detected
the moon shadow at level. The center of the moon was detected
in the direction away from the apparent center of the moon by 0.23 to
the west. Based on these data and a full Monte Carlo simulation, we searched
for the existence of the shadow produced by antiprotons at the multi-TeV energy
region. No evidence of the existence of antiprotons was found in this energy
region. We obtained the 90% confidence level upper limit of the flux ratio of
antiprotons to protons as 7% at multi-TeV energies.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic
Approximate relativistic bound state solutions of the Tietz-Hua rotating oscillator for any -state
Approximate analytic solutions of the Dirac equation with Tietz-Hua (TH)
potential are obtained for arbitrary spin-orbit quantum number using the
Pekeris approximation scheme to deal with the spin-orbit coupling terms In the
presence of exact spin and pseudo-spin (pspin) symmetric limitation, the bound
state energy eigenvalues and associated two-component wave functions of the
Dirac particle moving in the field of attractive and repulsive TH potential are
obtained using the parametric generalization of the Nikiforov-Uvarov (NU)
method. The cases of the Morse potential, the generalized Morse potential and
non-relativistic limits are studied.Comment: 19 pages; 7 figures; Few-Body Systems (2012) (at press
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Are protons still dominant at the knee of the cosmic-ray energy spectrum?
A hybrid experiment consisting of emulsion chambers, burst detectors and the
Tibet II air-shower array was carried out at Yangbajing (4,300 m a.s.l., 606
g/cm) in Tibet to obtain the energy spectra of primary protons and heliums.
From three-year operation, these energy spectra are deduced between
and eV by triggering the air showers associated with a high energy
core and using a neural network method in the primary mass separation. The
proton spectrum can be expressed by a single power-law function with a
differential index of and based on the
QGSJET+HD and SIBYLL+HD models, respectively, which are steeper than that
extrapolated from the direct observations of in the energy
range below eV. The absolute fluxes of protons and heliums are
derived within 30% systematic errors depending on the hadronic interaction
models used in Monte Carlo simulation. The result of our experiment suggests
that the main component responsible for the change of the power index of the
all-particle spectrum around eV, so-called ``knee'', is
composed of nuclei heavier than helium. This is the first measurement of the
differential energy spectra of primary protons and heliums by selecting them
event by event at the knee energy region.Comment: This paper has been accepted for publication Physics Letters B on
October 19th, 2005. This paper has been accepted for publication Physics
Letters B on October 19th, 200
Search for electroweak production of single top quarks in collisions.
We present a search for electroweak production of single top quarks in the electron+jets and muon+jets decay channels. The measurements use ~90 pb^-1 of data from Run 1 of the Fermilab Tevatron collider, collected at 1.8 TeV with the DZero detector between 1992 and 1995. We use events that include a tagging muon, implying the presence of a b jet, to set an upper limit at the 95% confidence level on the cross section for the s-channel process ppbar->tb+X of 39 pb. The upper limit for the t-channel process ppbar->tqb+X is 58 pb. (arXiv
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