Editing Antihydrogen (section)

===Low-energy antihydrogen===
Experiments by the [[ATRAP]] and ATHENA collaborations at CERN, brought together positrons and antiprotons in [[Penning trap]]s, resulting in synthesis at a typical rate of 100 antihydrogen atoms per second. Antihydrogen was first produced by ATHENA in 2002,<ref>{{cite journal |author=Amoretti |first=M. |display-authors=etal |year=2002 |title=Production and detection of cold antihydrogen atoms |url=https://cds.cern.ch/record/581488/files/cer-2340034.pdf |journal=[[Nature (journal)|Nature]] |volume=419 |issue=6906 |pages=456–459 |bibcode=2002Natur.419..456A |doi=10.1038/nature01096 |pmid=12368849 |s2cid=4315273}}</ref> and then by ATRAP<ref>{{cite journal |author=Gabrielse |first=G. |display-authors=etal |year=2002 |title=Driven Production of Cold Antihydrogen and the First Measured Distribution of Antihydrogen States |url=http://juser.fz-juelich.de/record/25767/files/17128.pdf |journal=Physical Review Letters |volume=89 |issue=23 |page=233401 |bibcode=2002PhRvL..89w3401G |doi=10.1103/PhysRevLett.89.233401 |pmid=12485006}}</ref> and by 2004, millions of antihydrogen atoms were made. The atoms synthesized had a relatively high temperature (a few thousand [[kelvins]]), and would hit the walls of the experimental apparatus as a consequence and annihilate. Most precision tests require long observation times.

ALPHA, a successor of the ATHENA collaboration, was formed to stably trap antihydrogen.<ref name=madsen/> While electrically neutral, its spin [[magnetic moment]]s interact with an inhomogeneous magnetic field; some atoms will be attracted to a magnetic minimum, created by a combination of mirror and multipole fields.<ref>{{cite journal
 |author=Pritchard, D. E. 
 |year=1983
 |title=Cooling neutral atoms in a magnetic trap for precision spectroscopy
 |journal=Physical Review Letters
 |volume=51  |page=1983
 |doi= 10.1103/PhysRevLett.51.1983
|bibcode = 1983PhRvL..51.1983T
 |last2=Heinz
 |first2=T.
 |last3=Shen
 |first3=Y.
 |issue=21 }}</ref>

In November 2010, the ALPHA collaboration announced that they had trapped 38 antihydrogen atoms for a sixth of a second,<ref>
{{cite journal
 |author=Andresen, G. B. ([[ALPHA Collaboration]])
 |year=2010
 |title=Trapped antihydrogen
 |journal=[[Nature (journal)|Nature]]
 |doi=10.1038/nature09610
|bibcode = 2010Natur.468..673A
 |volume=468
 |issue=7324
 |pages=673–676
 |pmid=21085118|s2cid=2209534
 |display-authors=etal}}</ref> the first confinement of neutral antimatter. In June 2011, they trapped 309 antihydrogen atoms, up to 3 simultaneously, for up to 1,000 seconds.<ref>{{cite journal
 |author=Andresen, G. B. ([[ALPHA Collaboration]])
 |title=Confinement of antihydrogen for 1,000 seconds
 |journal=[[Nature Physics]]
 |doi=10.1038/nphys2025
 |volume=7
 |issue=7
 |bibcode = 2011NatPh...7..558A
 |year=2011
 |pages=558–564 |arxiv = 1104.4982 |s2cid=17151882
 |display-authors=etal}}</ref> They then studied its hyperfine structure, gravity effects, and charge. ALPHA will continue measurements along with experiments ATRAP,  [https://aegis.web.cern.ch/ AEgIS] and GBAR.

In 2018, [https://aegis.web.cern.ch/ AEgIS] has produced a novel pulsed source of antihydrogen atoms with a production time spread of merely 250 nanoseconds. <ref>{{cite journal
 |author=Amsler, C. et al. ([[AEgIS experiment]])
 |title=Pulsed production of antihydrogen
 |journal=[[Communications Physics]]
 |doi=10.1038/s42005-020-00494-z
 |volume=4
 |year=2021
 |issue=1
 |pages=19
 |bibcode=2021CmPhy...4...19A
 |display-authors=etal|hdl=2434/813338
 |hdl-access=free
 }}</ref>
The pulsed source is generated by the [[charge exchange]] reaction between Rydberg [[positronium]] atoms -- produced via the injection of a pulsed positron beam into a nanochanneled Si target, and excited by laser pulses -- and antiprotons, trapped, cooled and manipulated in electromagnetic traps. The pulsed production enables the control of the antihydrogen temperature, the formation of an antihydrogen beam, and in the next phase a precision measurement on the gravitational behaviour using an atomic interferometer, the so-called [[Moiré deflectometry|Moiré deflectormeter]].