THERE IS A LOT MORE TO CERN THAN THE LHC.
15 Jan 2013
“At CERN today, representatives of the experiments that use beams from the Antiproton Decelerator presented their progress in 2012, and their plans for the New Year.
The Antiproton Decelerator provides beams of low-energy antiprotons to experiments, mainly for studies of antimatter (Image: CERN)
The Antiproton Decelerator (AD) provides low-energy antiprotons mainly for studies of antimatter. Previously, “antiparticle factories” at CERN and elsewhere consisted of chains of accelerators, each performing one of the steps needed to provide antiparticles for experiments. Now the AD performs all the tasks alone, from making antiprotons to delivering them to the experiments.
Michael Doser started proceedings with an update from the AEGIS experiment. AEGIS uses a beam of antiprotons from the Antiproton Decelerator to measure the value of Earth’s gravitational acceleration.
‘The primary scientific goal of the Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy (AEGIS) is the direct measurement of the Earth’s gravitational acceleration, g, on antihydrogen.
A system of gratings in the deflectometer splits the antihydrogen beam into parallel rays, forming a periodic pattern. From this pattern, the physicists can measure how much the antihydrogen beam drops during its horizontal flight. Combining this shift with the time each atom takes to fly and fall, the AEGIS team can then determine the strength of the gravitational force between the Earth and the antihydrogen atoms.
The AEGIS experiment will represent the first direct measurement of a gravitational effect on an antimatter system.’
Michael Holzscheiter of the University of New Mexico presented the status of the Antiproton Cell Experiment (ACE), which compares the effectiveness of protons and antiprotons in the treatment of cancer.
‘The Antiproton Cell Experiment (ACE) started in 2003…To date, particle-beam therapy has used mainly protons to destroy cancer cells. The particles are sent into a patient’s body with a pre-determined amount of energy, just enough that they stop when they reach the specific depth of a tumour. When such a beam of heavy, charged particles enters a human body, it initially inflicts very little damage. Only in the last few millimetres of the journey, as the beam ends its gradual slow-down and comes to an abrupt stop does significant damage occur. Unfortunately, although the beam destroys the cancer it does affect healthy cells along its path, so the damage to healthy tissues increases with repeat treatments.
The ACE experiment is testing the idea of using antiprotons as an alternative treatment, by directly comparing the effectiveness of cell irradiation using protons and antiprotons. When matter (in this case, the tumour cells) and antimatter (the antiprotons) meet, they annihilate (destroy each other), transforming their mass into energy. The aim is to make use of this effect, allowing an antiproton to annihilate with part of the nucleus of an atom in a cancer cell. The energy released by the annihilation should blow the nucleus apart and project the fragments into adjacent cancer cells, which should in turn be destroyed…Initial results showed that four times fewer antiprotons than protons were needed to inflict the same level of cell damage. In treatment, this would mean significantly reduced damage to the healthy tissues. An antiproton beam could be highly valuable in treating cases of recurring cancer, where it is vital to avoid repeated damage to healthy cells.’
David Lunney of the Université de Paris Sud in Orsay, France, spoke on behalf of the GBAR project, which was approved by CERN in May 2012.
‘One of the fundamental questions of todays physics concerns the action of gravity upon antimatter. No experimental direct measurement has ever been successfully performed with antimatter particles. CERN has thus launched a research program with the Antiproton Decelerator (AD) allowing to prepare a measurement of the effect of gravity on antihydrogen atoms. The primary aim of this experiment is to determine how antimatter reacts to gravity. A first test will be to verify the sign of the gravitational acceleration for antimatter, as a theory opens the possibility for it to be negative, which would translate as an elevation rather than a fall of an antimatter atom only submitted to the gravity force of the Earth. Other theories predicting less spectacular deviations with respect to standard gravitation will also be tested.’
ATRAP spokesperson Gerald Gabrielse of Harvard University in the US had mixed news from ATRAP in 2012. The experiment measured the antiproton magnetic moment to 4.4 parts per million – decreasing the uncertainty in the measurement by a factor of 680 compared to previous attempts. But technical glitches delayed a parallel programme of antihydrogen studies. ATRAP will use the long shutdown to produce and test replacement apparatus, ready for antiproton beams in 2014.
‘The Antihydrogen trap (ATRAP) is an experiment to compare hydrogen atoms with their antimatter equivalents – antihydrogen atoms. In 2002, ATRAP provided the first glimpse inside antihydrogen atoms after researchers successfully created and measured a large number of them.
An atom of antihydrogen consists of an antiproton and a positron (an antielectron). One of the difficulties in making antimatter is the energy the antiprotons possess when they are first made, shooting out of the apparatus at close to the speed of light. The researchers use a process called “cooling” to slow the antiprotons down so that they can be studied.’
ALPHA spokesperson Jeffrey Hangst of Aarhus University, Denmark, described how ALPHA traps antihydrogen, and how the team uses microwaves to determine its properties. A completely new experiment, ALPHA-2, was installed in 2012 with the aim of adding laser access for the spectroscopy of antihydrogen.
‘ALPHA makes, captures and studies atoms of antihydrogen and compares these with hydrogen atoms…Creating antihydrogen depends on bringing together the two component antiparticles, antiprotons and positrons, in a trapping device for charged particles. Since antihydrogen atoms have no electric charge, once they form they can’t be confined in such a device.
In June 2011, ALPHA reported that it had succeeded in trapping antimatter atoms for over 16 minutes: long enough to begin to study their properties in detail. This should give the physicists time to take measurements and to find more answers to the antimatter mystery.’
Ryugo S. Hayano of the University of Tokyo presented changes and improvements to the detectors, lasers and beam that make up ASACUSA.
The ASACUSA experiment compares matter and antimatter using atoms of antiprotonic helium.
‘The Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) experiment focuses on the fundamental differences in the behaviour of matter and antimatter. Instead of directly comparing atoms with their corresponding antiatoms (as do the ATRAP and ALPHA experiments), ASACUSA’s physicists are creating hybrid atoms such as “antiprotonic helium’.
Helium has the second simplest atomic structure after hydrogen. It contains two electrons orbiting a central nucleus. The ASACUSA team make antiprotonic helium by replacing one of these electrons with an antiproton (the antimatter equivalent of a proton). This is possible because, like the electron, the antiproton has negative charge. The process of creating these hybrid atoms is easier than making antihydrogen atoms (the antimatter version of hydrogen), and they can also be kept for longer.’ ”
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