Tag: AEgIS

Which way does antimatter swing?

In our universe, matter is king: it makes up everything. Its constituents are incredibly tiny particles – smaller than even the protons and neutrons they constitute – and they work together with nature’s forces to make up… everything.

There was also another form of particle once, called antimatter. It is extinct today, but when the universe was born 13.82 billion years ago, there were equal amounts of both kinds.

Nobody really knows where all the antimatter disappeared to or how, but they are looking. Some others, however, are asking another question: did antimatter, while it lasted, fall downward or upward in response to gravity?

Joel Fajans, a professor at the University of California, Berkeley, is one of the physicists doing the asking. “It is the general consensus that the interaction of matter with antimatter is the same as gravitational interaction of matter,” he told this correspondent.

But he wants to be sure, because what he finds could revolutionize the world of physics. Over the years, studying particles and their antimatter counterparts has revealed most of what we know today about the universe. In the future, physicists will explore their minuscule world, called the quantum world, further to see if answers to some unsolved problems are found. If, somewhere, an anomaly is spotted, it could pave the way for new explanations to take over.

“Much of our basic understanding of the evolution of the early universe might change. Concepts like dark energy and dark matter might have be to revised,” Fajans said.

Along with his colleague Jonathan Wurtele, Fajans will work with the ALPHA experiment at CERN to run an elegant experiment that could directly reveal gravity’s effect on antimatter. ALPHA stands for Anti-hydrogen Laser Physics Apparatus.

We know gravity acts on a ball by watching it fall when dropped. On Earth, the ball will fall toward the source of the gravitational pull, a direction called ‘down’. Fajans and Wurtele will study if down is in the same place for antimatter as for matter.

An instrument at CERN called the anti-proton decelerator (AD) synthesizes the antimatter counterpart of protons for study in the lab at a low energy. Fajans and co. will then use the ALPHA experiment’s setup to guide them into the presence of anti-electrons derived from another source using carefully directed magnetic fields.

When an anti-proton and an anti-electron come close enough, their charges will trap each other to form an anti-hydrogen atom.

Because antimatter and matter annihilate each other in a flash of energy, they couldn’t be let near each other during the experiment. Instead, the team used strong magnetic fields to form a force-field around the antimatter, “bottling” it in space.

Once this was done, the experiment was ready to go. Like fingers holding a ball unclench, the magnetic fields were turned off – but not instantaneously. They were allowed to go from ‘on’ to ‘off’ over 30 milliseconds. In this period, the magnetic force wears off and lets gravitational force take its place.

And in this state, Fajans and his team studied which way the little things moved: up or down.

The results

The first set of results from the experiment have allowed no firm conclusions to be drawn. Why? Fajans answered, “Relatively speaking, gravity has little effect on the energetic anti-atoms. They are already moving so fast that they are barely affected by the gravitational forces.” According to Wurtele, about 411 out 434 anti-atoms in the trap were so energetic that the way they escaped from the trap couldn’t be attributed to gravity’s pull or push on them.

Among them, they observed roughly equal numbers of anti-atoms to falling out at the bottom of the trap as at the top (and sides, for that matter.)

They shared this data with their ALPHA colleagues and two people from the University of California, lecturer Andrew Charman and postdoc Andre Zhmoginov. They ran statistical tests to separate results due to gravity from results due to the magnetic field. Again, much statistical uncertainty remained.

The team has no reason to give up, though. For now, they know that gravity would have to be 100 times stronger than it is for them to see any of its effects on anti-hydrogen atoms. They have a lower limit.

Moreover, the ALPHA experiment is also undergoing upgrades to become ALPHA-2. With this avatar, Fajans’s team also hopes to incorporate laser-cooling, a method of further slowing the anti-atoms, so that the effects of gravity are enhanced. Michael Doser, however, is cautious.

The future

As a physicist working with antimatter at CERN, Doser says, “I would be surprised if laser cooling of antihydrogen atoms, something that hasn’t been attempted to date, would turn out to be straightforward.” The challenge lies in bringing the systematics down to the point at which one can trust that any observation would be due to gravity, rather than due to the magnetic trap or the detectors being used.

Fajans and co. also plan to turn off the magnets more slowly in the future to enhance the effects of gravity on the anti-atom trajectories. “We hope to be able to definitively answer the question of whether or not antimatter falls down or up with these improvements,” Fajans concluded.

Like its larger sibling, the Large Hadron Collider, the AD is also undergoing maintenance and repair in 2013, so until the next batch of anti-protons are available in mid-2014, Fajans and Wurtele will be running tests at their university, checking if their experiment can be improved in any way.

They will also be taking heart from there being two other experiments at CERN that can verify their results if they come up with something anomalous, two experiments working with antimatter and gravity. They are the Anti-matter Experiment: Gravity, Interferometry, Spectrocopy (AEGIS), for which Doser is the spokesperson, and the Gravitational Behaviour of Anti-hydrogen at Rest (GBAR).

Together, they carry the potential benefit of an independent cross-check between techniques and results. “This is less important in case no difference to the behaviour of normal matter is found,” Doser said, “but would be crucial in the contrary case. With three experiments chasing this up, the coming years look to be interesting!”

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This post, as written by me, originally appeared in The Copernican science blog at The Hindu on May 1, 2013.

A different kind of experiment at CERN

This article, as written by me, appeared in The Hindu on January 24, 2012.

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At the Large Hadron Collider (LHC) at CERN, near Geneva, Switzerland, experiments are conducted by many scientists who don’t quite know what they will see, but know how to conduct the experiments that will yield answers to their questions. They accelerate beams of particles called protons to smash into each other, and study the fallout.

There are some other scientists at CERN who know approximately what they will see in experiments, but don’t know how to do the experiment itself. These scientists work with beams of antiparticles. According to the Standard Model, the dominant theoretical framework in particle physics, every particle has a corresponding particle with the same mass and opposite charge, called an anti-particle.

In fact, at the little-known AEgIS experiment, physicists will attempt to produce an entire beam composed of not just anti-particles but anti-atoms by mid-2014.

AEgIS is one of six antimatter experiments at CERN that create antiparticles and anti-atoms in the lab and then study their properties using special techniques. The hope, as Dr. Jeffrey Hangst, the spokesperson for the ALPHA experiment, stated in an email, is “to find out the truth: Do matter and antimatter obey the same laws of physics?”

Spectroscopic and gravitational techniques will be used to make these measurements. They will improve upon, “precision measurements of antiprotons and anti-electrons” that “have been carried out in the past without seeing any difference between the particles and their antiparticles at very high sensitivity,” as Dr. Michael Doser, AEgIS spokesperson, told this Correspondent via email.

The ALPHA and ATRAP experiments will achieve this by trapping anti-atoms and studying them, while the ASACUSA and AEgIS will form an atomic beam of anti-atoms. All of them, anyway, will continue testing and upgrading through 2013.

Working principle

Precisely, AEgIS will attempt to measure the interaction between gravity and antimatter by shooting an anti-hydrogen beam horizontally through a vacuum tube and then measuring how it much sags due to the gravitational pull of the Earth to a precision of 1 per cent.

The experiment is not so simple because preparing anti-hydrogen atoms is difficult. As Dr. Doser explained, “The experiments concentrate on anti-hydrogen because that should be the most sensitive system, as it is not much affected by magnetic or electric fields, contrary to charged anti-particles.”

First, antiprotons are derived from the Antiproton Decelerator (AD), a particle storage ring which “manufactures” the antiparticles at a low energy. At another location, a nanoporous plate is bombarded with anti-electrons, resulting in a highly unstable mixture of both electrons and anti-electrons called positronium (Ps).

The Ps is then excited to a specific energy state by exposure to a 205-nanometre laser and then an even higher energy state called a Rydberg level using a 1,670-nanometre laser. Last, the excited Ps traverses a special chamber called a recombination trap, when it mixes with antiprotons that are controlled by precisely tuned magnetic fields. With some probability, an antiproton will “trap” an anti-electron to form an anti-hydrogen atom.

Applications

Before a beam of such anti-hydrogen atoms is generated, however, there are problems to be solved. They involve large electric and magnetic fields to control the speed of and collimate the beams, respectively, and powerful cryogenic systems and ultra-cold vacuums. Thus, Dr. Doser and his colleagues will spend many months making careful changes to the apparatus to ensure these requirements work in tandem by 2014.

While antiparticles were first discovered in 1959, “until recently, it was impossible to measure anything about anti-hydrogen,” Dr. Hangst wrote. Thus, the ALPHA and AEgIS experiments at CERN provide a seminal setting for exploring the world of antimatter.

Anti-particles have been used effectively in many diagnostic devices such as PET scanners. Consequently, improvements in our understanding of them feed immediately into medicine. To name an application: Antiprotons hold out the potential of treating tumors more effectively.

In fact, the feasibility of this application is being investigated by the ACE experiment at CERN.

In the words of Dr. Doser: “Without the motivation of attempting this experiment, the experts in the corresponding fields would most likely never have collaborated and might well never have been pushed to solve the related interdisciplinary problems.”