SwePub
Sök i SwePub databas

  Utökad sökning

Träfflista för sökning "WFRF:(Povilus A.) "

Sökning: WFRF:(Povilus A.)

  • Resultat 1-10 av 16
  • [1]2Nästa
Sortera/gruppera träfflistan
   
NumreringReferensOmslagsbildHitta
1.
  • Ahmadi, M., et al. (författare)
  • An improved limit on the charge of antihydrogen from stochastic acceleration
  • 2016
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 529:7586, s. 373-
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Antimatter continues to intrigue physicists because of its apparent absence in the observable Universe. Current theory requires that matter and antimatter appeared in equal quantities after the Big Bang, but the Standard Model of particle physics offers no quantitative explanation for the apparent disappearance of half the Universe. It has recently become possible to study trapped atoms(1-4) of antihydrogen to search for possible, as yet unobserved, differences in the physical behaviour of matter and antimatter. Here we consider the charge neutrality of the antihydrogen atom. By applying stochastic acceleration to trapped antihydrogen atoms, we determine an experimental bound on the antihydrogen charge, Qe, of vertical bar Q vertical bar &lt; 0.71 parts per billion (one standard deviation), in which e is the elementary charge. This bound is a factor of 20 less than that determined from the best previous measurement(5) of the antihydrogen charge. The electrical charge of atoms and molecules of normal matter is known(6) to be no greater than about 10(-21)e for a diverse range of species including H-2, He and SF6. Charge-parity-time symmetry and quantum anomaly cancellation(7) demand that the charge of antihydrogen be similarly small. Thus, our measurement constitutes an improved limit and a test of fundamental aspects of the Standard Model. If we assume charge superposition and use the best measured value of the antiproton charge(8), then we can place a new limit on the positron charge anomaly (the relative difference between the positron and elementary charge) of about one part per billion (one standard deviation), a 25-fold reduction compared to the current best measurement(8),(9).</p>
  •  
2.
  • Amole, C., et al. (författare)
  • Silicon vertex detector upgrade in the ALPHA experiment
  • 2013
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002 .- 1872-9576. ; 732, s. 134-136
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The Silicon Vertex Detector (SVD) is the main diagnostic tool in the ALPHA-experiment. It provides precise spatial and timing information of antiproton (antihydrogen) annihilation events (vertices), and most importantly, the SVD is capable of directly identifying and analysing single annihilation events, thereby forming the basis of ALPHA's analysis. This paper describes the ALPHA SVD and its upgrade, installed in the ALPHA's new neutral atom trap.</p>
  •  
3.
  • Amole, C., et al. (författare)
  • An experimental limit on the charge of antihydrogen
  • 2014
  • Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 5, s. 3955
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The properties of antihydrogen are expected to be identical to those of hydrogen, and any differences would constitute a profound challenge to the fundamental theories of physics. The most commonly discussed antiatom- based tests of these theories are searches for antihydrogen- hydrogen spectral differences (tests of CPT (charge- parity- time) invariance) or gravitational differences (tests of the weak equivalence principle). Here we, the ALPHA Collaboration, report a different and somewhat unusual test of CPT and of quantum anomaly cancellation. A retrospective analysis of the influence of electric fields on antihydrogen atoms released from the ALPHA trap finds a mean axial deflection of 4.1 +/- 3.4mm for an average axial electric field of 0.51Vmm1. Combined with extensive numerical modelling, this measurement leads to a bound on the charge Qe of antihydrogen of Q (+/- 1.3 +/- 1.1 +/- 0.4)10 8. Here, e is the unit charge, and the errors are from statistics and systematic effects.</p>
  •  
4.
  • Amole, C., et al. (författare)
  • The ALPHA antihydrogen trapping apparatus
  • 2014
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002 .- 1872-9576. ; 735, s. 319-340
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The ALPHA collaboration, based at CERN, has recently succeeded in confining cold antihydrogen atoms in a magnetic minimum neutral atom trap and has performed the first study of a resonant transition of the anti-atoms. The ALPHA apparatus will be described herein, with emphasis on the structural aspects, diagnostic methods and techniques that have enabled antihydrogen trapping and experimentation to be achieved.</p>
  •  
5.
  • Amole, C., et al. (författare)
  • Autoresonant-spectrometric determination of the residual gas composition in the ALPHA experiment apparatus
  • 2013
  • Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 84:6, s. 065110
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Knowledge of the residual gas composition in the ALPHA experiment apparatus is important in our studies of antihydrogen and nonneutral plasmas. A technique based on autoresonant ion extraction from an electrostatic potential well has been developed that enables the study of the vacuum in our trap. Computer simulations allow an interpretation of our measurements and provide the residual gas composition under operating conditions typical of those used in experiments to produce, trap, and study antihydrogen. The methods developed may also be applicable in a range of atomic and molecular trap experiments where Penning-Malmberg traps are used and where access is limited.</p>
  •  
6.
  • Amole, C., et al. (författare)
  • Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap
  • 2012
  • Ingår i: New Journal of Physics. - 1367-2630 .- 1367-2630. ; 14, s. 015010
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilate. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antiproton and antihydrogen trajectories in this magnetic geometry, and reconstruct the antihydrogen energy distribution from the measured annihilation time history.</p>
  •  
7.
  • Andresen, G. B., et al. (författare)
  • Antihydrogen annihilation reconstruction with the ALPHA silicon detector
  • 2012
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - 0168-9002 .- 1872-9576. ; 684, s. 73-81
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The ALPHA experiment has succeeded in trapping antihydrogen, a major milestone on the road to spectroscopic comparisons of antihydrogen with hydrogen. An annihilation vertex detector, which determines the time and position of antiproton annihilations, has been central to this achievement. This detector, an array of double-sided silicon microstrip detector modules arranged in three concentric cylindrical tiers, is sensitive to the passage of charged particles resulting from antiproton annihilation. This article describes the method used to reconstruct the annihilation location and to distinguish the annihilation signal from the cosmic ray background. Recent experimental results using this detector are outlined.</p>
  •  
8.
  • Andresen, G. B., et al. (författare)
  • The ALPHA-detector : Module Production and Assembly
  • 2012
  • Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 7, s. C01051
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>ALPHA is one of the experiments situated at CERN's Antiproton Decelerator (AD). A Silicon Vertex Detector (SVD) is placed to surround the ALPHA atom trap. The main purpose of the SVD is to detect and locate antiproton annihilation events by means of the emitted charged pions. The SVD system is presented with special focus given to the design, fabrication and performance of the modules.</p>
  •  
9.
  • Andresen, G. B., et al. (författare)
  • Trapped antihydrogen
  • 2010
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 468:7324, s. 673-676
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Antimatter was first predicted<sup>1</sup> in 1931, by Dirac. Work with high-energy antiparticles is now commonplace, and anti-electrons are used regularly in the medical technique of positron emission tomography scanning. Antihydrogen, the bound state of an antiproton and a positron, has been produced<sup>2, 3</sup> at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. The charge conjugation/parity/time reversal (CPT) theorem, a crucial part of the foundation of the standard model of elementary particles and interactions, demands that hydrogen and antihydrogen have the same spectrum. Given the current experimental precision of measurements on the hydrogen atom (about two parts in 10<sup>14</sup> for the frequency of the 1<em>s</em>-to-2s transition<sup>4</sup>), subjecting antihydrogen to rigorous spectroscopic examination would constitute a compelling, model-independent test of CPT. Antihydrogen could also be used to study the gravitational behaviour of antimatter<sup>5</sup>. However, so far experiments have produced antihydrogen that is not confined, precluding detailed study of its structure. Here we demonstrate trapping of antihydrogen atoms. From the interaction of about 10<sup>7</sup> antiprotons and 7 × 10<sup>8</sup> positrons, we observed 38 annihilation events consistent with the controlled release of trapped antihydrogen from our magnetic trap; the measured background is 1.4 ± 1.4 events. This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.</p>
  •  
10.
  • Andresen, G. B., et al. (författare)
  • Autoresonant Excitation of Antiproton Plasmas
  • 2011
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106:2, s. 025002
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We demonstrate controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense, and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination</p>
  •  
Skapa referenser, mejla, bekava och länka
  • Resultat 1-10 av 16
  • [1]2Nästa
 
pil uppåt Stäng

Kopiera och spara länken för att återkomma till aktuell vy