A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete ...operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem-experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.
High rate production of antihydrogen Amoretti, M; Amsler, C; Bazzano, G ...
Physics letters. B,
01/2004, Letnik:
578, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
We show that antihydrogen production is the dominant process when mixing antiprotons and positrons in the ATHENA apparatus, and that the initial production rate exceeds 300 Hz, decaying to 30 Hz ...within 10 s. A fraction of 65% of all observed annihilations is due to antihydrogen.
Cold antihydrogen atoms were produced by mixing cold samples of antiprotons and positrons. The temperature of the positron plasma was increased by controlled radio-frequency (RF) heating, and the ...antihydrogen production was measured. Formation is observed to decrease with increased temperature but a simple power law scaling is not observed. Significant production is still present at room temperature.
The temperature dependence of the light emission for pure CsI crystals has been measured with photomultipliers, and photodiodes with wavelength shifters from 80–
300
K
. The light yield at
80
K
is
N
...γ=50,000±5000 photons/MeV. This number was deduced from the number of electron–hole pairs produced in the photodiode,
N
eh=39,600±1200. The light yield at room temperature is lower by a factor of 15.8±1.0, giving 3200±400 photons/MeV. Decay times were measured with a photomultiplier. At room temperature two fast decay components were observed with decay times of 6±1 and
28±2
ns
. Below
180
K
only one component is observed and at
80
K
the decay time is
1015±17
ns
.
We demonstrate three-dimensional imaging of antiprotons in a Penning trap, by reconstructing annihilation vertices from the trajectories of the charged annihilation products. The unique capability of ...antiparticle imaging has allowed, for the first time, the observation of the spatial distribution of the particle loss in a Penning trap. The radial loss of antiprotons on the trap wall is localized to small spots, strongly breaking the azimuthal symmetry expected for an ideal trap. Our observations have important implications for detection of antihydrogen annihilations.
The light generated by an ionizing particle crossing a scintillator is collected by means of light guides coupled to two proximity focused Hybrid Photo Diodes (HPDs) and used to measure the position ...along the slab. Two scintillators with dimensions
(20×3.1×0.23)
cm
3
and
(60×5×0.5)
cm
3
have been tested with a collimated
90
Sr
source. The relation between reconstructed position and nominal position of the source is linear through all the scintillator length. The accuracy in the position depends on the attenuation length, the number of photoelectrons and the signal-to-noise ratio of the HPD. The resolutions obtained with a MIP for the two slabs are
σ
z=3.8
cm
and
σ
z=15.9
cm
, respectively. This method will be used in the inner scintillator array of the FINUDA experiment.
A novel system to monitor the intensity and the stability of a bunched beam of ≃1.2×10
7 antiprotons
(
p
̄
s)
with a length of
≃250
ns
(FWHM) and to measure its trapping efficiency in a Penning trap ...is described. This system operates parasitically detecting the pions from the annihilation of part of the beam in a degrader.
Six plastic scintillators have been coupled from one side to six proximity focused HPDs without preamplifiers and operating in current mode. This device works in the stray field of the ATHENA magnet with no loss of efficiency; the gain can be varied from zero to a few thousands with a precision better than 0.1% and the dynamic range is larger than 8 orders of magnitude. Linearity and stability have been measured up to charge responses of
100
nC
, corresponding to the beam completely dumped. The beam counter has been calibrated in two different and independent ways giving consistent results.
HPD readout based TOF scintillator detector for the FINUDA trigger Filippini, V.; Marchesotti, M.; Marciano, C.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/1999, Letnik:
424, Številka:
2
Journal Article
Recenzirano
A barrel scintillator detector based on Hybrid Photo Diode (HPD) readout to be employed in the inner region of the FINUDA experiment is described. An array of 12 scintillator slabs of
(200×31×2.3)
mm
...3
is read by 24 HPDs. This device, designed to work in a 1.1 T uniform magnetic field, will provide a fast first level trigger to discriminate signal from background events and the start signal for TOF measurements and for the drift chambers. The overall performances of a module have been tested using minimum ionizing electrons from a
90Sr source.
A dedicated X-ray tomograph has been developed at CERN to control the required wire placement accuracy of better than 20
μm of the 1200 Monitored Drift Tube Chambers which make up most of the ...precision chamber part of the ATLAS Muon Spectrometer. The tomograph allows the chamber wire positions to be measured with a 2
μm statistical and 2
μm systematic uncertainty over the full chamber cross-section of 2.2×0.6
m
2. Consistent chamber production quality over the 4-year construction phase is ensured with a ∼15% sampling rate. Measurements of about 70 of the 650 MDT chambers so far produced have been essential in assessing the validity and consistency of the various construction procedures.
The first cold antihydrogen Fujiwara, M.C.; Amoretti, M.; Amsler, C. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2004, Letnik:
532, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
Antihydrogen, the atomic bound state of an antiproton and a positron, was produced at low energy for the first time by the ATHENA experiment, marking an important first step for precision studies of ...atomic antimatter. This paper describes the first production and some subsequent developments.
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