Se celebra estos días en Kioto (Japón) la conferencia Neutrino 2012, el principal evento científico dedicado a la física que se realiza sobre esta elusiva partícula elemental. En los primeros días, dos experimentos internacionales con participación española, Double Chooz y T2K, presentaron actualizaciones de importantes resultados recientes en la medición de un parámetro conocido como theta 13 (Ɵ13), fundamental para comprobar un fenómeno que se conoce como ‘oscilación de neutrinos’.
Described as a “machine physicist's concert platform”, the Low Energy Antiproton Ring (LEAR) was everything at once: an accelerator, a storage ring, a decelerator, a cooler ring and a beam stretcher. 2012 marks the 30th anniversary of its start-up and an opportunity for the Bulletin to take a look back at the history of this remarkable machine.
This article is a tribute to Dieter Möhl, one of LEAR's founding fathers, who passed away at the end May.
Like most great CERN projects, LEAR began with a dream and a coffee between colleagues. The year was 1976, the coffee was shared by Kurt Kilian and Dieter Möhl, and the dream was of a machine that could deliver a million low-energy antiprotons in a single cycle. Such a machine could further hadron spectroscopy and open the way to the study of anti-atoms.
The idea seemed to be ahead of its time; the technology and physics of the era were just not up to the challenge. Pioneering experiments exploiting low-energy antiprotons were receiving fewer than 100 per PS cycle, and there seemed to be no way to increase that number. What was a dream to some seemed a pipedream to others.
But, as Dieter Möhl describes in his history of the accelerator, 1976 was just the right time to consider the large-scale production of cold antiprotons. Electron and stochastic cooling techniques had been proven only a few years before, and led Carlo Rubbia and his working group to look into the possibility of cooling antiprotons for injection into SPS. The seeds of an idea had been sown.
Reviewing the literature on antiproton production, including work by Rubbia’s group, it took Kurt Kilian only a few days to realise the potential of antiproton cooling. He gathered his predictions into a graph (see first illustration) that would define the future of LEAR. It showed how using cooling techniques, LEAR could gather five orders of magnitude more antiprotons than traditional techniques.
With CERN’s physics programme firmly set on high-energy antiproton-proton collision physics, the idea of such precision physics had not initially held much appeal. But Kilian’s graph caught the attention of many experts and by 1979 LEAR’s Conceptual Design Report was on the table along with a Letter of Intent that involved around 240 physicists from 44 research centres. LEAR was finally approved in 1980, and was constructed in just 16 months with a budget of 12.6 million CHF, under the leadership of Pierre Lefèvre.
LEAR debuted to little fanfare in 1982, overshadowed, no doubt, by the first signs of the W and Z particles at the SPS. The following year it started delivering unprecedented rates of low-energy antiprotons to 16 different experiments. In the 1990s, LEAR delivered a record one million low-energy antiprotons per second over one hour spills. In its early days, LEAR received only 6% of the available antiprotons, as the majority were sent on to the ISR and the SPS. By 1988, however, LEAR was receiving six times more antiprotons - a level that continued up to its shutdown in 1996.
LEAR’s impact on cooling techniques was undoubtedly one of its greatest successes. In order to shape its beams, engineers developed a technique that could provide stochastic cooling for a range of energies in the same cycle. LEAR's Werner Hardt, following work by Simon Van der Meer, also pioneered an ultraslow extraction technique that allowed particles to be delicately removed from a circulating beam. This allowed for record-length spills out of LEAR.
Although LEAR has been offline for well over a decade now – and has long since been transformed into the Low Energy Ion Ring (LEIR) that serves the heavy ion needs of the LHC – its influence can still be seen in the accelerators of today. It was the first accelerator to truly consider and implement cooling techniques for accelerator physics, and much of its technology continues to be in use today. Numerous accelerators worldwide – including LEAR’s successor at CERN, the Antiproton Decelerator (AD) – can trace their history back to LEAR and the graph that started it all.
For more about the machine's accomplishments, make sure to read Philippe Bloch's article on LEAR's physics legacy.
An obituary celebrating the life and accomplishments of Dieter Möhl will appear in the next issue of the Bulletin.
An English Oral Expression course will take place this summer at some time between 25 June and 28 September. The exact dates will be decided according to the preferences of the students.
Schedule: to be determined (2 sessions of 2 hours per week).
Please note that this course is for learners who have a good knowledge of English (CERN level 7 upwards).
If you are interested in following this course, please enroll through this link.
Please be sure to indicate your planned absences in the comments field so we can schedule the course.
If you need more information please send a message to English.email@example.com
The NA62 straw tracker is using pioneering CERN technology to measure charged particles from very rare kaon decays. For the first time, a large straw tracker will be placed directly into an experiment’s vacuum tank, allowing physicists to measure the direction and momentum of charged particles with extreme precision. NA62 measurements using this technique will help physicists take a clear look at the kaon decay rate, which might be influenced by particles and processes that are not included in the Standard Model.
“Although straw detectors have been around since the 1980s, what makes the NA62 straw trackers different is that, for the first time, they can work under vacuum,” explains Hans Danielsson from the PH-DT group leading the NA62 straw project. Straw detectors are basically small drift chambers, where particles ionize a gas inside a thin tube containing a wire that records a signal and measures the drift time.
After 3 years of research and development, NA62 straws are able to withstand the high pressure exerted by the gas once the straws are placed inside the experiment’s vacuum tank, which is over 100 m long and 2.5 m in diameter. Traditional strategies would have either installed a support structure or increased the thickness of the straws to withstand the pressure. Sound practices, but they would have created an unwanted interaction source for particles in the vacuum. Yet the NA62 straws are mechanically stable for over 2 m while remaining leak-proof in order to preserve the integrity of the vacuum.
The secret of their success was finding a new way to build the straws. “Straw trackers are usually made by winding two conductive tapes in a spiral – rather like the centre of a paper towel roll,” says Hans. “This technique worked well for the ATLAS TRT straw detectors, but it does not make mechanically stable and leak-proof straws.”
Instead, in collaboration with the Joint Institute for Nuclear Research (JINR) in Russia, the team developed a technique whereby a 31 mm wide band is rolled into a straw shape and then welded shut, leaving a single, 0.6 mm thick seam along its length. “We used ultrasonic welding to close the straw,” explains Hans. “We discovered that this welding technique not only made the straws completely leak-proof but also gave them the strength to keep them straight and withstand the vacuum pressure without breaking.”
With R&D complete, the NA62 straw tracker is making its way down the assembly line at CERN. Around 2000 straws are now being assembled into eight modules. Every module has eight rows of straws, and each row is rotated 90 degrees to ensure that at least two coordinates are measured for each particle. The eight modules will be installed in the vacuum tank at four different locations.
“We’re testing every straw individually, fitting them into the modules and connecting the electronics,” says Hans. “Of course, we also have to check the modules at every step of assembly to make sure they meet the strict specifications of the detector. A team from the JINR is working with us for a few weeks. They are learning the different steps of module assembly, and should assemble some of the modules back at their home institute.”
CERN physicists, take out your smartphones! Two new particle physics applications for Android phones have been developed by a physicist from the University of Bern: “Particle Properties” and “Particle Physics Booklet 2010”.
“When I'm on shift, I enjoy looking at the online event displays,” says Igor Kreslo from the Laboratory for High Energy Physics at the University of Bern, the physicist who has developed the two particle physics applications for Android. “Sometimes very beautiful events appear, with many different particles. I like to discuss these displays with my students, just to develop their ability to identify particles. We try to find out which particle is which and how it might decay… I think that's the best way to teach students the phenomenology of particle physics.”
When scientists study particle physics, they require some vital information, such as the decay branching ratios: “details” which are not so easy to remember by heart… “I thought it would be nice to have a handy thing to tell you these numbers,” says Igor. Thus, the idea of the first application was born: an online database for the properties of elementary particles.
“Actually, when you're on shift you have some spare time if everything is going well,” explains Igor. “So while I was on shift at T2K in Japan, I had the opportunity to develop the 'Particle Properties' application. I also decided to create an application for the 'Particle Physics Booklet'*, which I use almost every day.”
Designed at first for physicists in Igor’s laboratory, the two applications met with great success, encouraging Igor to put them on Google Play. “I received some very nice feedback from my colleagues, so I thought that they might be interesting to other physicists too, especially at CERN,” adds Igor. “If people want to send me comments or suggestions for new applications, I would be happy to hear from them, although I should emphasize that I'm not a professional Android programmer - developing applications is just a hobby.” A very useful one, we might add…
*This application is based on the collected work of the Particle Data Group (PDG) with its permission, but is nevertheless not supported by the group.
e-EPS News is a monthly addition to the CERN Bulletin line-up, showcasing articles from e-EPS – the European Physical Society newsletter – as part of a collaboration between the two publications.
Asian experiments unlock neutrino oscillation mystery
Two reactor experiments, China’s Daya Bay and Korea’s RENO, have made the best measurement of the neutrino mixing angle, θ13, an essential property for neutrino research. The discovery of a non-zero θ13 at approximately 9˚ – which was published in March and April this year – completes our picture of neutrino mixing. This quite large value for the mixing angle will make it easier to conduct future long baseline neutrino experiments. This, in turn, may lead to a better understanding of the matter-antimatter asymmetry seen in the Universe.
Neutrino oscillations – the change in flavour seen as neutrinos move – were discovered in Japan in 1998. The three mixing angles – θ12, θ23, and θ13 – describe the relationship between certain flavour and mass states of neutrinos. They can be seen as the Euler angles between flavour (ve, vμ, vτ) and mass (v1, v2, v3) states, considered as two sets of orthogonal axes. θ12and θ23 were known – and large – but before now, we had only hints at the smallest value, θ13.
Johanna Stachel new DPG president
Johanna Stachel took office as president of the Deutsche Physikalische Gesellschaft (DPG) on 16 March this year. Stachel, a professor of experimental physics at the University of Heidelberg, is the first female physicist to head the DPG since its founding in 1845.
Stachel presented her presidential agenda during her inaugural speech, which took place in the Magnus-Haus Berlin. Besides the promotion of fundamental research, the main concerns of the new president are education, the training of physics teachers and the encouragement of women in physics – with focus on equal opportunity.
Particle physics outreach database launched by IPPOG
A database of resources and tools for particle physics education and outreach has been published by the International Particle Physics Outreach Group. The collection aims to help and inspire physicists, communicators and teachers with useful and imaginative ways of teaching students and the public about particle physics.
“The idea behind the database was to create a basket of tools where people can go and dip in and use them for their own needs,” says Lisa Mc Carthy, the IPPOG staff member who helped to set up the database. Submissions to the resource library can be made by anyone – after registering – extending the IPPOG tradition of sharing outreach tools, practices and successes.
The database can be searched by a number of parameters, including the learning topic, nature, intended audience and language. The site also features a rating system – similar to those seen on sites such as amazon and youtube – through which submissions may be reviewed by the community, with popular items earning featured status.
The database is still in its early stages, and the creators are inviting users to provide feedback, and make suggestions as to how it could be improved. Comments should be sent to IPPOG by email.
For more information on IPPOG, please see the e-EPS article “International Particle Physics Outreach Group meeting”.