178 research outputs found
Annihilation of low energy antiprotons in silicon
The goal of the AEIS experiment at the Antiproton
Decelerator (AD) at CERN, is to measure directly the Earth's gravitational
acceleration on antimatter. To achieve this goal, the AEIS
collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a
velocity of a few 100 m/s and measure the magnitude of the vertical deflection
of the beam from a straight path. The final position of the falling
antihydrogen will be detected by a position sensitive detector. This detector
will consist of an active silicon part, where the annihilations take place,
followed by an emulsion part. Together, they allow to achieve 1 precision on
the measurement of with about 600 reconstructed and time tagged
annihilations.
We present here, to the best of our knowledge, the first direct measurement
of antiproton annihilation in a segmented silicon sensor, the first step
towards designing a position sensitive silicon detector for the
AEIS experiment. We also present a first comparison with
Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table
Prospects for measuring the gravitational free-fall of antihydrogen with emulsion detectors
The main goal of the AEgIS experiment at CERN is to test the weak equivalence
principle for antimatter. AEgIS will measure the free-fall of an antihydrogen
beam traversing a moir\'e deflectometer. The goal is to determine the
gravitational acceleration g for antihydrogen with an initial relative accuracy
of 1% by using an emulsion detector combined with a silicon micro-strip
detector to measure the time of flight. Nuclear emulsions can measure the
annihilation vertex of antihydrogen atoms with a precision of about 1 - 2
microns r.m.s. We present here results for emulsion detectors operated in
vacuum using low energy antiprotons from the CERN antiproton decelerator. We
compare with Monte Carlo simulations, and discuss the impact on the AEgIS
project.Comment: 20 pages, 16 figures, 3 table
SDR, EVC, and SDREVC: Limitations and Extensions
Methods for reducing the radius, temperature, and space charge of nonneutral
plasma are usually reported for conditions which approximate an ideal Penning
Malmberg trap. Here we show that (1) similar methods are still effective under
surprisingly adverse circumstances: we perform SDR and SDREVC in a strong
magnetic mirror field using only 3 out of 4 rotating wall petals. In addition,
we demonstrate (2) an alternative to SDREVC, using e-kick instead of EVC and
(3) an upper limit for how much plasma can be cooled to T < 20 K using EVC.
This limit depends on the space charge, not on the number of particles or the
plasma density.Comment: Version 2: a small discrepancy between the N values for Table 1 and
Fig. 3 led to an investigation of the charge counting diagnostic. There is a
small energy dependence which only became apparent following improvements to
pre-SDREVC. The pulsed dump was modified to reduce this dependence. The data
for Table 1 and Fig. 3 was taken again with the improved method
SDR, EVC, and SDREVC: Limitations and Extensions
Methods for reducing the radius, temperature and space charge of a non-neutral plasma are usually reported for conditions which approximate an ideal Penning Malmberg trap. Here, we show that (i) similar methods are still effective under surprisingly adverse circumstances: we perform strong drive regime (SDR) compression and SDREVC in a strong magnetic mirror field using only 3 out of 4 rotating wall petals. In addition, we demonstrate (ii) an alternative to SDREVC, using e-kick instead of evaporative cooling (EVC) and (iii) an upper limit for how much plasma can be cooled to T < 20 K using EVC. This limit depends on the space charge, not on the number of particles or the plasma density
Slow positron production and storage for the ASACUSA-Cusp experiment
The ASACUSA Cusp experiment requires the production of dense positron plasmas
with a high repetition rate to produce a beam of antihydrogen. In this work,
details of the positron production apparatus used for the first observation of
the antihydrogen beam, and subsequent measurements are described in detail.
This apparatus replaced the previous compact trap design resulting in an
improvement in positron accumulation by a factor of (Comment: 9 pages, 7 figure
Upgrade of the positron system of the ASACUSA-Cusp experiment
The ASACUSA-Cusp collaboration has recently upgraded the positron system to
improve the production of antihydrogen. Previously, the experiment suffered
from contamination of the vacuum in the antihydrogen production trap due to the
transfer of positrons from the high pressure region of a buffer gas trap. This
contamination reduced the lifetime of antiprotons. By adding a new positron
accumulator and therefore decreasing the number of transfer cycles, the
contamination of the vacuum has been reduced. Further to this, a new rare gas
moderator and buffer gas trap, previously used at the Aarhus University, were
installed. Measurements from Aarhus suggested that the number of positrons
could be increased by a factor of four in comparison to the old system used at
CERN. This would mean a reduction of the time needed for accumulating a
sufficient number of positrons (of the order of a few million) for an
antihydrogen production cycle. Initial tests have shown that the new system
yields a comparable number of positrons to the old system.Comment: 10 pages, 5 figures, under consideration for the Special Collection
"Non-Neutral Plasmas: Achievements and Perspectives" in JP
Slow positron production and storage for the ASACUSA-Cusp experiment
The ASACUSA (atomic spectroscopy and collisions using slow antiprotons) Cusp experiment requires the production of dense positron plasmas with a high repetition rate to produce a beam of antihydrogen. In this work, details of the positron production apparatus used for the first observation of the antihydrogen beam, and subsequent measurements, are described in detail. This apparatus replaced the previous compact trap design resulting in an improvement in the positron accumulation rate by a factor of 52 +/- 3
Hyperfine spectroscopy of hydrogen and antihydrogen in ASACUSA
The ASACUSA collaboration at the Antiproton Decelerator of CERN aims at a
precise measurement of the antihydrogen ground-state hyperfine structure as a
test of the fundamental CPT symmetry. A beam of antihydrogen atoms is formed in
a CUSP trap, undergoes Rabi-type spectroscopy and is detected downstream in a
dedicated antihydrogen detector. In parallel measurements using a polarized
hydrogen beam are being performed to commission the spectroscopy apparatus and
to perform measurements of parameters of the Standard Model Extension (SME).
The current status of antihydrogen spectroscopy is reviewed and progress of
ASACUSA is presented.Comment: Proceedings of the 7th International Syposium on Symmetries in
Subatomic Physics SSP2018, Aachen (Germany), 10 - 15 Jun 2018. Corrected
error in Fig. 1, updated caption, add titles to reference
Minimizing plasma temperature for antimatter mixing experiments
The ASACUSA collaboration produces a beam of antihydrogen atoms by mixing pure positron and antiproton plasmas in a strong magnetic field with a double
cusp geometry. The positrons cool via cyclotron radiation inside the cryogenic trap. Low positron temperature is essential for increasing the fraction of antihydrogen atoms which reach the ground state prior to exiting the trap. Many experimental groups observe that such plasmas reach equilibrium at a temperature well above the temperature of the surrounding electrodes. This problem is typically attributed to electronic noise and plasma expansion, which heat the plasma. The present work reports anomalous heating far beyond what can be attributed to those two sources. The heating seems to be a result of the axially open trap geometry, which couples the plasma to the external (300 K) environment via microwave radiation
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