ASACUSA experiment

Last updated
Antiproton decelerator
(AD)
ELENA Extra low energy antiproton ring – further decelerates antiprotons coming from AD
AD experiments
ATHENA AD-1 Antihydrogen production and precision experiments
ATRAP AD-2 Cold antihydrogen for precise laser spectroscopy
ASACUSA AD-3 Atomic spectroscopy and collisions with antiprotons
ACE AD-4 Antiproton cell experiment
ALPHA AD-5 Antihydrogen laser physics apparatus
AEgIS AD-6 Antihydrogen experiment gravity interferometry spectroscopy
GBAR AD-7 Gravitational behaviour of anti-hydrogen at rest
BASE AD-8 Baryon antibaryon symmetry experiment
PUMA AD-9 Antiproton unstable matter annihilation

Atomic Spectroscopy and Collisions Using Slow Antiprotons (ASACUSA), AD-3, is an experiment at the Antiproton Decelerator (AD) at CERN. The experiment was proposed in 1997, started collecting data in 2002 by using the antiprotons beams from the AD, and will continue in future under the AD and ELENA decelerator facility.

Contents

ASACUSA physics

ASACUSA collaboration is testing for CPT-symmetry by laser spectroscopy of antiprotonic helium and microwave spectroscopy of the hyperfine structure of antihydrogen. It compares matter and antimatter using antihydrogen and antiprotonic helium and looks into matter-antimatter collisions. [1] [2] [3] It also measures atomic and nuclear cross-sections of antiprotons on various targets at extremely low energies. [4]

In 2020 ASACUSA in collaboration with the Paul Scherrer Institut (PSI) reported spectral measurements of long lived pionic helium. [5] [6] [7]

In 2022 ASACUSA reported spectral measurements of antiprotonic helium suspended in gaseous and liquid (He-I and He-II) targets. An abrupt narrowing of spectral lines was discovered at temperatures near the superfluid phase transition temperature. The narrowness and symmetry of the spectral lines for antiprotonic helium contrasts with other types of atoms suspended in He-I and He-II. This is hypothesized to be related to the order of magnitude smaller orbital radius of 40 pm which is comparably unaffected during laser excitation. [8] [9] [10]

Experimental setup

Antiproton Trap

ASACUSA receives antiproton beams from the AD and ELENA decelerator. These beams are decelerated to 0.01 MeV energy using a radiofrequency decelerator and the antiprotons are stored in the MUSASHI traps. The positrons to form antihydrogen atoms are obtained from radioactive source and stored in a positron accumulator. The mixing of antiprotons and positrons forms polarised and cold antihydrogen inside a double-Cusp trap. The polarised antihydrogen atoms from this system then enter the spectrometer where the measurements are done. [11]

ASACUSA team at beam setup preparation in September 2018 Asacusa.jpg
ASACUSA team at beam setup preparation in September 2018

Beam Spectroscopy

Hyperfine spectroscopy measurements on H beams in flight have been made using a Rabi experiment. The collaboration plans to conduct similar measurements on
H
 in flight. [12] [13]

Cryogenic Target Spectroscopy

Electrostatic Beamline

ASACUSA team preparing beam setup for the ELENA beams in September 2018. Asacusa1.jpg
ASACUSA team preparing beam setup for the ELENA beams in September 2018.

Anticipating completion of ELENA, with the aim of making spectral measurements of previously undetected atomic resonances in antiprotonic helium, a new 6 m electrostatic beamline was constructed to transport
p
s to a cryogenic target. [13] (Previous experiments, including the antiprotonic helium spectral measurements of March 2022 used a 3 m Radio-frequency Quadrupole to decelerate
p
s from the Antiproton Decelerator. [14] [8] [15] ) 0.1 MeV ELENA
p
s entering the beamline are focussed to a width of 1 mm and pass through an aperture (30 mm length and 8 mm diameter). The transverse horizontal and vertical dimensions of the beam are determined by beam monitors consisting of a grid of gold-coated tungsten-rhenium wires with grid spacing of 20 μm. [14] (There are 3 such monitors along the beamline, one of which is 300 mm upstream of the cryogenic chamber. [13] ) Further along the beamline, there is a configuration of 3 quadrupole magnets to counteract
p
 beam expansion and 2 more apertures of diameters 30 mm and 16 mm. A beam emerging from the apertures is focussed to 3 mm diameter and impinges on a 6 mm diameter titanium window in an OFHC copper flange mounted on the cryogenic target chamber wall. [13] Acrylic and lead fluoride Čerenkov detectors monitor the beamline for
p
 annihilations. The beamline pressure is 0.8 mb, much higher than the ELENA beamline pressure of mb. The pressure difference is maintained by three 500 L/s titanium ion and 4 turbomolecular pumps. [13]


Cryogenic Chamber

The helium targets are contained in a 35 mm diameter vessel made of titanium (gaseous or supercritical phase with 70% He-I) or OFHC copper (He-I and He-II) mounted on a liquid helium constant-flow cryostat. The vessel is enclosed within copper thermal shielding: an inner shield cooled by coolant helium vapour and an outer shield cooled by liquid nitrogen. A configuration of manometers and temperature sensors provide data used to characterize the state of the helium in the chamber. Pressures 1 MPa can be sustained. [8] The chamber is accessible to antiprotons through an annealed titanium window of diameter 75 μm or 50 μm vacuum brazed into the chamber wall. [8] Opposite this, a 28-mm diameter, 5-mm thick UV-grade sapphire window transmits laser light, antilinear to an incident particle beam. [8] Two 35-mm diameter Brewster windows made of fused silica (SiO
2) mounted on flanges on opposite sides of the chamber walls perpendicular to the beam axis transmit laser light. [13] [8] Near the cryostat, beneath the beampipe, is positioned a 300 200 20 mm Čerenkov detector. Particles emerging from the cryostat, such as pions from
p
-
p
 annihilations emit Čerenkov radiation in the detector which is detected by a photomultiplier. [8]

ASACUSA collaboration

See also

Related Research Articles

<span class="mw-page-title-main">Antimatter</span> Material composed of antiparticles of the corresponding particles of ordinary matter

In modern physics, antimatter is defined as matter composed of the antiparticles of the corresponding particles in "ordinary" matter, and can be thought of as matter with reversed charge, parity, and time, known as CPT reversal. Antimatter occurs in natural processes like cosmic ray collisions and some types of radioactive decay, but only a tiny fraction of these have successfully been bound together in experiments to form antiatoms. Minuscule numbers of antiparticles can be generated at particle accelerators; however, total artificial production has been only a few nanograms. No macroscopic amount of antimatter has ever been assembled due to the extreme cost and difficulty of production and handling. Nonetheless, antimatter is an essential component of widely available applications related to beta decay, such as positron emission tomography, radiation therapy, and industrial imaging.

<span class="mw-page-title-main">Antihydrogen</span> Exotic particle made of an antiproton and positron

Antihydrogen is the antimatter counterpart of hydrogen. Whereas the common hydrogen atom is composed of an electron and proton, the antihydrogen atom is made up of a positron and antiproton. Scientists hope that studying antihydrogen may shed light on the question of why there is more matter than antimatter in the observable universe, known as the baryon asymmetry problem. Antihydrogen is produced artificially in particle accelerators.

An exotic atom is an otherwise normal atom in which one or more sub-atomic particles have been replaced by other particles of the same charge. For example, electrons may be replaced by other negatively charged particles such as muons or pions. Because these substitute particles are usually unstable, exotic atoms typically have very short lifetimes and no exotic atom observed so far can persist under normal conditions.

<span class="mw-page-title-main">Antiproton</span> Subatomic particle

The antiproton,
p
, is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived, since any collision with a proton will cause both particles to be annihilated in a burst of energy.

ATHENA, also known as the AD-1 experiment, was an antimatter research project at the Antiproton Decelerator at CERN, Geneva. In August 2002, it was the first experiment to produce 50,000 low-energy antihydrogen atoms, as reported in Nature. In 2005, ATHENA was disbanded and many of the former members of the research team worked on the subsequent ALPHA experiment and AEgIS experiment.

<span class="mw-page-title-main">Protonium</span> Bound state of a proton and antiprotron

Protonium, also known as antiprotonic hydrogen, is a type of exotic atom in which a proton and an antiproton are bound to each other.

The Antihydrogen Trap (ATRAP) collaboration at the Antiproton Decelerator facility at CERN, Geneva, was responsible for the AD-2 experiment. It was a continuation of the TRAP collaboration, which started taking data for the TRAP experiment in 1985. The TRAP experiment pioneered cold antiprotons, cold positrons, and first made the ingredients of cold antihydrogen to interact. Later ATRAP members pioneered accurate hydrogen spectroscopy and observed the first hot antihydrogen atoms.

<span class="mw-page-title-main">Antiprotonic helium</span> Exotic matter with an antiproton in place of an electron

Antiprotonic helium is a three-body atom composed of an antiproton and an electron orbiting around a helium nucleus. It is thus made partly of matter, and partly of antimatter. The atom is electrically neutral, since an electron and an antiproton each have a charge of −1 e, whereas a helium nucleus has a charge of +2 e. It has the longest lifetime of any experimentally produced matter–antimatter bound state.

<span class="mw-page-title-main">PS210 experiment</span> Scientific experiment

The PS210 experiment was the first experiment that led to the observation of antihydrogen atoms produced at the Low Energy Antiproton Ring (LEAR) at CERN in 1995. The antihydrogen atoms were produced in flight and moved at nearly the speed of light. They made unique electrical signals in detectors that destroyed them almost immediately after they formed by matter–antimatter annihilation.

<span class="mw-page-title-main">Antiproton Decelerator</span> Particle storage ring at CERN, Switzerland

The Antiproton Decelerator (AD) is a storage ring at the CERN laboratory near Geneva. It was built from the Antiproton Collector (AC) to be a successor to the Low Energy Antiproton Ring (LEAR) and started operation in the year 2000. Antiprotons are created by impinging a proton beam from the Proton Synchrotron on a metal target. The AD decelerates the resultant antiprotons to an energy of 5.3 MeV, which are then ejected to one of several connected experiments.

<span class="mw-page-title-main">Low Energy Antiproton Ring</span> Former CERN infrastructure

The Low Energy Anti-Proton Ring (LEAR) was a particle accelerator at CERN which operated from 1982 until 1996. The ring was designed to decelerate and store antiprotons, to study the properties of antimatter and to create atoms of antihydrogen. Antiprotons for the ring were created by the CERN Proton Synchrotron via the Antiproton Collector and the Antiproton Accumulator (AA). The creation of at least nine atoms of antihydrogen were confirmed by the PS210 experiment in 1995.

High-precision experiments could reveal small previously unseen differences between the behavior of matter and antimatter. This prospect is appealing to physicists because it may show that nature is not Lorentz symmetric.

<span class="mw-page-title-main">Antiproton Collector</span> CERN infrastructure

The Antiproton Collector (AC) was part of the antiparticle factory at CERN designed to decelerate and store antimatter, to study the properties of antimatter and to create atoms of antihydrogen. It was built in 1986 around the existing Antiproton Accumulator (AA) to improve the antiproton production by a factor of 10. Together, the Antiproton Collector and the Antiproton Accumulator formed the so-called Antiproton Accumulator Complex (AAC).

Recycling antimatter pertains to recycling antiprotons and antihydrogen atoms.

<span class="mw-page-title-main">ALPHA experiment</span> Antimatter gravitation experiment

The Antihydrogen Laser Physics Apparatus (ALPHA), also known as AD-5, is an experiment at CERN's Antiproton Decelerator, designed to trap antihydrogen in a magnetic trap in order to study its atomic spectra. The ultimate goal of the experiment is to test CPT symmetry through comparing the respective spectra of hydrogen and antihydrogen. Scientists taking part in ALPHA include former members of the ATHENA experiment (AD-1), the first to produce cold antihydrogen in 2002.

AEgIS, AD-6, is an experiment at the Antiproton Decelerator facility at CERN. Its primary goal is to measure directly the effect of Earth's gravitational field on antihydrogen atoms with significant precision. Indirect bounds that assume the validity of, for example, the universality of free fall, the Weak Equivalence Principle or CPT symmetry also in the case of antimatter constrain an anomalous gravitational behavior to a level where only precision measurements can provide answers. Vice versa, antimatter experiments with sufficient precision are essential to validate these fundamental assumptions. AEgIS was originally proposed in 2007. Construction of the main apparatus was completed in 2012. Since 2014, two laser systems with tunable wavelengths and synchronized to the nanosecond for specific atomic excitation have been successfully commissioned.

<span class="mw-page-title-main">GBAR experiment</span> Experiment at the Antiproton Decelerator

GBAR, AD-7 experiment, is a multinational collaboration at the Antiproton Decelerator of CERN.

<span class="mw-page-title-main">Jeffrey Hangst</span> Experimental particle physicist

Jeffrey Scott Hangst is an experimental particle physicist at Aarhus University, Denmark, and founder and spokesperson of the ALPHA collaboration at the Antiproton Decelerator (AD) at CERN, Geneva. He was also one of the founding members and the Physics Coordinator of the ATHENA collaboration at the AD facility.

<span class="mw-page-title-main">Stefan Ulmer (physicist)</span> Particle physicist

Stefan Ulmer is a particle physicist, professor of Physics at Heinrich Heine University Düsseldorf and chief scientist at the Ulmer Fundamental Symmetries Laboratory, RIKEN, Tokyo. He is the founder and the spokesperson of the BASE experiment (AD-8) at the Antiproton Decelerator facility at CERN, Geneva. Stefan Ulmer is well known for his contributions to improving Penning trap techniques and precision measurements on antimatter. He is the first person to observe spin transitions with a single trapped proton as well as single spin transitions with a single trapped antiproton, a significant achievement towards a precision measurement of the antiproton magnetic moment.

Extra Low ENergy Antiproton ring (ELENA) is a 30 m hexagonal storage ring that decelerates antiproton beams and delivers it to different AD experiments. It is situated inside the Antiproton Decelerator (AD) complex at CERN, Geneva. It is designed to further decelerate the antiproton beam coming from the Antiproton decelerator to an energy of 0.1 MeV for more precise measurements. The first beam circulated ELENA on 18 November 2016. The ring is expected to be fully operational by the end of the Long Shutdown 2 (LS2) in 2021.

References

  1. ↑ "ASACUSA – General" . Retrieved 30 July 2022.
  2. ↑ "Archived copy" (PDF). Archived from the original (PDF) on 13 December 2013. Retrieved 9 February 2011.{{cite web}}: CS1 maint: archived copy as title (link)
  3. ↑ "CERN experiment improves precision of antiproton mass measurement with new innovative cooling technique". phys.org.
  4. ↑ "Archived copy". Archived from the original on 15 April 2013. Retrieved 17 February 2010.{{cite web}}: CS1 maint: archived copy as title (link)
  5. ↑ Hori, Masaki; Aghai-Khozani, Hossein; Sótér, Anna; Dax, Andreas; Barna, Daniel (6 May 2020). "Laser spectroscopy of pionic helium atoms". Nature. 581 (7806): 37–41. Bibcode:2020Natur.581...37H. doi:10.1038/s41586-020-2240-x. ISSN   1476-4687. PMID   32376962. S2CID   218527999.
  6. ↑ "ASACUSA sees surprising behaviour of hybrid matter–antimatter atoms in superfluid helium". CERN. Retrieved 2022-03-16.
  7. ↑ "Pionic helium". www.mpq.mpg.de. Retrieved 2022-03-16.
  8. 1 2 3 4 5 6 7 Sótér, Anna; Aghai-Khozani, Hossein; Barna, Dániel; Dax, Andreas; Venturelli, Luca; Hori, Masaki (2022-03-16). "High-resolution laser resonances of antiprotonic helium in superfluid 4He". Nature. 603 (7901): 411–415. Bibcode:2022Natur.603..411S. doi:10.1038/s41586-022-04440-7. ISSN   1476-4687. PMC   8930758 . PMID   35296843.
  9. ↑ "ASACUSA sees surprising behaviour of hybrid matter–antimatter atoms in superfluid helium". CERN. Retrieved 2022-03-17.
  10. ↑ "Icy Antimatter Experiment Surprises Physicists". Quanta Magazine. 2022-03-16. Retrieved 2022-03-17.
  11. ↑ Amsler, C.; Barna, D.; Breuker, H.; Chesnevskaya, S.; Costantini, G.; Ferragut, R.; Giammarchi, M.; Gligorova, A.; Higaki, H. (2021). Status report of the ASACUSA experiment - progress in 2020 and plans for 2021. CERN. Geneva. SPS and PS Experiments Committee, SPSC.
  12. ↑ Malbrunot, C.; Amsler, C.; Arguedas Cuendis, S.; Breuker, H.; Dupre, P.; Fleck, M.; Higaki, H.; Kanai, Y.; Kolbinger, B.; Kuroda, N.; Leali, M.; Mäckel, V.; Mascagna, V.; Massiczek, O.; Matsuda, Y.; Nagata, Y.; Simon, M. C.; Spitzer, H.; Tajima, M.; Ulmer, S.; Venturelli, L.; Widmann, E.; Wiesinger, M.; Yamazaki, Y.; Zmeskal, J.; Zmeskal, J. (2018-02-19). "The ASACUSA antihydrogen and hydrogen program: results and prospects". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. 376 (2116). arXiv: 1710.03288 . Bibcode:2018RSPTA.37670273M. doi:10.1098/rsta.2017.0273. PMC   5829175 . PMID   29459412.
  13. 1 2 3 4 5 6 "PROGRESS REPORT OF THE ASACUSA AD-3 COLLABORATION" (PDF). Archived (PDF) from the original on 7 July 2022. Retrieved 30 July 2022.
  14. 1 2 Hori, Masaka (2018-10-24). "Single-photon laser spectroscopy of cold antiprotonic helium". Hyperfine Interactions. 239 (1): 411–415. Bibcode:2018HyInt.239...44H. doi: 10.1007/s10751-018-1518-y . S2CID   105937408.
  15. ↑ Sótér, Anna; Aghai-Khozani, Hossein; Barna, Dániel; Dax, Andreas; Venturelli, Luca; Hori, Masaki; Hayano, Ryugo; Friedreich, Susanne; Juhász, Bertalan; Pask, Thomas; Horváth, Dezső; Widmann, Eberhard; Venturelli, Luca; Zurlo, Nicola (2011-07-27). "Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio". Nature. 475 (7357): 484–488. arXiv: 1304.4330 . doi:10.1038/nature10260. PMID   21796208. S2CID   4376768.

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