Al2O3 samples grown with natural well-ordered channels (having sizes of 30-90 nm in diameter) perpendicular to the surface, one side closed, were measured by means of Doppler broadening (DB) by ...variable energy positron (VEP) beam and positron annihilation lifetime (PAL) spectroscopy. The samples annealed at 300 and 560 deg C showed amorphous structure and no positronium (Ps) formation. The sample annealed at 850 deg C showed gamma-phase polycrystalline structure and Ps formation. We were not able to prove from the PAL spectroscopy results themselves whether Ps is confined to the channels. We discuss the results of decomposition of the DB annihilation peak into four Gaussians. We conclude that the greater Ps fraction is confined to the channels. From the Compton-to-peak ratio analysis, the fraction of all the injected positrons which form o-Ps and in this form escape from the sample (for a VEP experiment, we have e+ injected from the open side of the channels) has been estimated as being ~20%.
Proposed antimatter gravity measurement with an antihydrogen beam Kellerbauer, A.; Amoretti, M.; Belov, A.S. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
02/2008, Letnik:
266, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The principle of the equivalence of gravitational and inertial mass is one of the cornerstones of general relativity. Considerable efforts have been made and are still being made to verify its ...validity. A quantum-mechanical formulation of gravity allows for non-Newtonian contributions to the force which might lead to a difference in the gravitational force on matter and antimatter. While it is widely expected that the gravitational interaction of matter and of antimatter should be identical, this assertion has never been tested experimentally. With the production of large amounts of cold antihydrogen at the CERN Antiproton Decelerator, such a test with neutral antimatter atoms has now become feasible. For this purpose, we have proposed to set up the AEGIS experiment at CERN/AD, whose primary goal will be the direct measurement of the Earth’s gravitational acceleration on antihydrogen with a classical Moiré deflectometer.
Doppler broadening of annihilation gamma-line combined with a slow positron beam was used to measure the momentum density distribution of annihilating pair in a set of sintered UO2 samples. The ...influence of surface polishing, of implantation with 800-keV 136Xe2+ at fluences of 1×1015 and 1×1016 Xecm−2, and of annealing were studied by following the changes of the momentum distribution shape by means of S and W parameters. The program used for this purpose was VEPFIT. At the two fluences in the stoichiometric as-implanted UO2, formation of Xe bubbles was not detected. The post-implantation annealing and over-stoichiometry in the as-implanted sample caused Xe precipitation and formation of Xe bubbles.
We report on a direct search for a three-body decay of the orthopositronium into a photon and two penetrating particles, o-Ps→
γ+X
1+X
2. The existence of this decay could explain the discrepancy ...between the measured and the predicted values of the orthopositronium decay rate. From the analysis of the collected data a single candidate event is found, consistent with the expected background. This allows to set an upper limit on the branching ratio
B(o-Ps→
γ+X
1+X
2)<4.4×10
−5 (at the 90% confidence level), for the photon energy in the range from 40 keV <
E
γ
< 400 keV and for mass values in the kinematical range 0⩽
m
X
1
+
m
X
2
⩽900 keV. This result unambiguously excludes the o-Ps→
γ+X
1+X
2 decay mode as the origin of the discrepancy.
We present a measurement of the muon neutrino–nucleon inclusive charged current cross section, off an isoscalar target, in the neutrino energy range 2.5⩽Eν⩽40 GeV. The significance of this ...measurement is its precision, ±4% in 2.5⩽Eν⩽10 GeV, and ±2.6% in 10⩽Eν⩽40 GeV regions, where significant uncertainties in previous experiments still exist, and its importance to the current and proposed long baseline neutrino oscillation experiments.
AEgIS (Expérience sur l'Antimatière: Gravité, Interférométrie, Spectrométrie) est une expérience approuvée par le CERN qui vise une étude globale de la physique de l'anti-hydrogène. Dans AEgIS, ...l'anti-hydrogène sera produit par des réactions d'échange de charges d'anti-protons froids avec des atomes de positronium excités dans un état de Rydberg (n > 20). Dans la première phase de l'expérience, l'accélération est contrôlée par un gradient de champ électrique (effet Stark); une mesure subséquente en chute libre dans un déflectomètre de Moiré nous fournira un test du principe d'équivalence faible. Dans une deuxième phase, l'anti-hydrogène sera ralenti, confiné et refroidi par laser pour des études de CPT et de spectroscopie de précision. Après une description générale de l'expérience, nous passons ici en revue l'état d'avancement des travaux en accordant une attention particulière à la production et l'excitation des atomes de positronium.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
An electronic system, designed to provide a relative calibration for the readout of the CMS electromagnetic calorimeter (CMS-ECAL), is described. On request, this system injects a pulse at the input ...of a predetermined group of preamplifiers with preselected amplitude and a shape identical to the one produced by the photodetectors. Several chips, in DMILL 0.8
μm technology, have been developed for integration on the front-end electronics. We describe the principle, the testing, the measurement of their precision, and radiation hardness.
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