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  • richardmitnick 11:23 am on June 17, 2014 Permalink | Reply
    Tags: , CERN ALPHA, ,   

    From Berkeley Lab: “Precision Physics of Antiatoms: Berkeley Lab Physicists Bound the Charge of Antihydrogen” 

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    Berkeley Lab

    June 13, 2014
    Kate Greene

    Hydrogen is a neutral atom. Its single electron orbits a single proton, and the net effect is no electrical charge. But what about hydrogen’s antimatter counterpart, antihydrogen? Made of a positron that orbits an antiproton, the antihydrogen atom should be neutral too. Various results have indicated as much, but because the charge of antiatoms is difficult to measure, it has remained an open question.

    A recent experiment to measure the charge of antihydrogen has now placed a bound on the atom’s charge. Physicists from Berkeley Lab, the University of California, and other institutions part of the ALPHA collaboration at CERN, have published in Nature Communications a new measurement of the charge of antihydrogen, determined with unprecedented precision.

    The result: effectively zero. Specifically, antihydrogen’s charge is less than 20 billionths of the magnitude of the electron charge, a measurement that’s a million-fold improvement over the best previous experiment. This is good news for fundamental theories of physics.

    “We would expect the charge of hydrogen and antihydrogen to be the same,” says Jonathan Wurtele, physicist at Berkeley Lab and UC and author on the paper. “If we had seen a charge, we would have new physics. ”

    Antihydrogen resists easy measurement for a number of reasons, starting with its production. While positrons are relatively straightforward to obtain, low energy antiprotons are only available at the Antiproton Decelerator at CERN. (Antiprotons were first created in 1955 at Berkeley Lab’s now decommissioned Bevatron accelerator.)

    Once produced through high-energy collisions, the particles then need to be slowed down and cooled. Next, electrodes manipulate the electric field to mix antiprotons with positrons, making a few atoms of antihydrogen. These atoms are then trapped in a magnetic “bottle.” It takes thousands of positron-antiproton mixings to produce just 500 atoms of trapped antihydrogen.

    The experimental measurements only happens when the magnetic field trap is turned off, effectively pouring atoms out of the bottle and into a vacuum chamber. Once free, an atom of antihydrogen will contact an atom of normal matter on the trap wall, and the two annihilate each other. This annihilation leaves a signal, evidence of the antihydrogen’s position.

    For the charge-measurement experiment, the scientists took advantage of the fact that there were strong electric fields within the trap. “If the antiatom were charged”, says Joel Fajans, physicist at UC and Berkeley Lab “these fields would push the antiatom to the left side or to the right side of the trap, depending on the putative sign of antihydrogen charge.” Analysis of data showed that there was no tendency for the anti-atoms to go to the left or right, implying that the atom was electrically neutral.

    When an anti-atom is put into an electric field, does it feel a force? It will only feel a force if it has a net charge. Normal matter atoms are known to be charge neutral to an extraordinary precision, and modern physics theories assert that anti-atoms would be similarly charge neutral. New Berkeley Lab research confirms that antihydrogen atoms are indeed charge neutral to at least nearly 10ppb of the unit charge. Credit: Joel Fajans, Berkeley

    Fajans, Wurtele, and Marcello Baquero-Ruiz and Alex Povilus, both graduate students in the physics department at the University of California, as well as Berkeley post-doc Andre Zhmoginov, Berkeley instructor Andrew Charman, and Berkeley undergraduate Arielle Little, did much of the simulation work and modeling of the system as well as developing statistical techniques for data analysis. The data itself was collected by the entire ALPHA collaboration.

    Other recent work by the Berkeley group and Francis Robicheaux at Purdue indicates that future experimental bounds could reach approximately 100 times higher precision using a technique based on an approach called stochastic acceleration.

    Previously, Fajans and Wurtele were involved in ALPHA experiments to measure the microwave spectrum of antihydrogen as well as the effects of gravity on antihydrogen, which, as far as experiments can currently determine, interacts with it the same as it does hydrogen. Next up are measurements of the anti-atoms’ energy levels.

    A better understanding of the properties of antimatter in general and anti atoms in particular is important to solving the so-called baryogenesis problem, which essentially questions why the universe has more matter than antimatter.

    “People have been trying to explain the baryogenesis problem for years without success. It seems that our current understanding is incomplete,” says Fajans. “There are some possible straightforward explanations out there, but physicists wonder if the baryogenesis problem can only be explained by something more interesting or exotic. Anomalies with antihydrogen could be the answer.”

    This research was funded in part by the U.S. Department of Energy and the Laboratory Directed Research and Development program at Berkeley Lab.

    See the full article here.

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  • richardmitnick 5:24 pm on June 3, 2014 Permalink | Reply
    Tags: , Antihydrogen, , CERN ALPHA,   

    From CERN: “CERN’s ALPHA experiment measures charge of antihydrogen” 

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    3 Jun 2014
    Cian O’Luanaigh

    In a paper published in the journal Nature Communications today, the ALPHA experiment at CERN’s Antiproton Decelerator (AD) reports a measurement of the electric charge of antihydrogen atoms, finding it to be compatible with zero to eight decimal places. Although this result comes as no surprise, since hydrogen atoms are electrically neutral, it is the first time that the charge of an antiatom has been measured to high precision.

    Antiproton Decelerator

    “This is the first time we have been able to study antihydrogen with some precision,” said ALPHA spokesperson Jeffrey Hangst. “We are optimistic that ALPHA’s trapping technique will yield many such insights in the future. We look forward to the restart of the AD program in August, so that we can continue to study antihydrogen with ever increasing accuracy.”

    Antiparticles should be identical to matter particles except for the sign of their electric charge. So while the hydrogen atom is made up of a proton with charge +1 and an electron with charge -1, the antihydrogen atom consists of a charge -1 antiproton and a charge +1 positron. We know, however, that matter and antimatter are not exact opposites – nature seems to have a one-part in 10 billion preference for matter over antimatter, so it is important to measure the properties of antimatter to great precision: the principal goal of CERN’s AD experiments. ALPHA achieves this by using a complex system of particle traps that allow antihydrogen atoms to be produced and stored for long enough periods to study in detail. Understanding matter antimatter asymmetry is one of the greatest challenges in physics today. Any detectable difference between matter and antimatter could help solve the mystery and open a window to new physics.

    Detail of the ALPHA experiment: Insertion of the ALPHA Penning trap into the cryostat that holds the antihydrogen trapping magnets (Image: Niels Madsen)

    To measure the charge of antihydrogen, the ALPHA experiment studied the trajectories of antihydrogen atoms released from the trap in the presence of an electric field. If the antihydrogen atoms had an electric charge, the field would deflect them, whereas neutral atoms would be undeflected. The result, based on 386 recorded events, gives a value of the antihydrogen electric charge as (-1.3±1.1±0.4) × 10-8, the plus or minus numbers representing statistical and systematic uncertainties on the measurement.

    With the restart of CERN’s accelerator chain getting underway, the laboratory’s antimatter research programme is set to resume. Experiments including ALPHA-2, an upgraded version of the ALPHA experiment, will be taking data along with the ATRAP and ASACUSA experiments and newcomer AEGIS, which will be studying the influence of gravity on antihydrogen.




    Read more: An experimental limit on the charge of antihydrogen

    See the full article here.

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  • richardmitnick 2:25 pm on April 14, 2014 Permalink | Reply
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    From PhysicsWorld.com: “Interferometry tips the scales on antimatter” 


    Apr 7, 2014

    Tushna Commissariat

    A new technique for measuring how antimatter falls under gravity has been proposed by researchers in the US. The team says that its device – based on cooling atoms of antimatter and making them interfere – could also help to test Einstein’s equivalence principle with antihydrogen – something that could have far-reaching consequences for cosmology. Finding even the smallest of differences between the behaviour of matter and antimatter could shine a light on why there is more matter than antimatter in the universe today, as well as help us to better understand the nature of the dark universe.

    Trapping potential: The ALPHA experiment at CERN

    Up or down?

    First detected at CERN in 1995, physicists have long wondered how antimatter is affected by gravity – does it fall up or down? Most theoretical and experimental work suggests that gravity probably acts in exactly the same way on antimatter as it does on matter. The problem is that antimatter is difficult to produce and study, meaning that no direct experimental measurements of its behaviour under gravity have been made to date.

    One big step forward took place last year, when researchers at the ALPHA experiment at CERN measured how long it takes atoms of antihydrogen – made up of a positron surrounding an antiproton – to reach the edges of a magnetic trap after it is switched off. Although ALPHA did not find any evidence of the antihydrogen responding differently to gravity, the team was able to rule out the possibility that antimatter responds much more strongly to gravity than matter.

    Alpha Collaboration’s Official image

    Waving matter

    Such experiments are hard to carry out, however – antimatter is difficult to produce on a large scale and it annihilates when it comes into contact with regular matter, making it difficult to trap and hold. The new interferometry technique – proposed by Holger Müller and colleagues at the University of California, Berkeley, and Auburn University in Alabama – exploits the fact that a beam of antimatter atoms can, like light, be split, sent along two paths and made to interfere, with the amount of interference depending on the phase shift between the two beams. The researchers say the light-pulse atom interferometer, which they plan to install at the ALPHA experiment, could work not only with almost any type of atom or anti-atom, but also with electrons and protons.

    In the proposed interferometer, the matter waves would be split and recombined using pulses of laser light. If an atom interacts with the laser beam, it will receive a “kick” from the momentum of a pair of photons, creating the split, explains Müller. By tuning the laser to the correct pulse energy, this process can be made to happen with a probability of 50%, sending the matter waves along either of the two arms of the interferometer. When the paths join again, the probability of detecting the anti-atom depends on the amplitude of the matter wave, which becomes a function of the phase shift.

    Annihilation danger?

    Müller adds that the phase shift depends on the acceleration due to gravity (g), the momentum of the photons (and so the magnitude of the kick) and the time interval between each laser pulse. Measuring the phase shift is therefore a way of measuring g, because the momentum and the time interval are both known. The biggest advantage of the technique is that the anti-atoms will not be in danger of annihilating because they will never come close to any mechanical objects, being moved with light and magnetic fields only.

    Müller’s idea is to combine two proven technologies: light-pulse atom interferometry and ALPHA’s method of producing antihydrogen using its Penning trap. He points out that the team’s proposed method does not assume availability of a laser resonant with the Lyman-alpha transition in hydrogen, which can be very difficult to build. To make the whole experiment even more efficient, the team has also developed what Müller describes as an “atom recycling method”, which allows the researchers to work with “realistic” atom numbers. “The atom is enclosed inside magnetic fields that prevent it from going away. Thus, an atom that hasn’t been hit by the laser on our first attempt has a chance to get hit later. This way, we can use almost every single atom – a crucial feat at a production rate of one every 15 minutes,” he explains. This would let ALPHA measure the gravitational acceleration of antihydrogen to a precision of 1%.

    Precise and accurate

    The team plans to build a demo set-up at Berkeley, which will work with regular hydrogen, and hopes to secure funding for this soon. Müller and colleagues are now also part of the APLHA collaboration. “The work at CERN will proceed in several steps,” he says. “The first is an up/down measurement telling [us] whether the antimatter will go up or down,” he says. This will be followed by a measurement of per-cent-level accuracy. Müller’s long-term aim is get to a precision of 10–6, which would be vastly superior to ALPHA’s measurement last year, which has an error bar of 102. ALPHA can currently trap and hold atoms at the rate of four each hour, but thanks to recent upgrades at its source of antiprotons – the ELENA ring – CERN could theoretically produce nearly 3000 atoms per month. In addition to ALPHA, the GBAR and AEgIS collaborations are also planning to measure gravity’s effects on antimatter.

    While Müller agrees that the gravitational behaviour of antimatter can be studied from experiments with normal matter, a direct observation is essential, and that is what Müller, the ALPHA collaboration and the other teams at CERN are keen to accomplish in the near future. “No matter how sound one’s theory, there is no substitute in science for a direct observation,” he says.

    See the full article here.

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    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.

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