CERN Axion Solar Telescope (CAST) solar tracking
(© 2015 CERN)
Twice a day, and without blinking, the CAST experiment (CERN Axion Solar Telescope) stares at the Sun in the hope of spotting two proposed particles that are suspects in the mystery of dark matter and dark energy.
Using a prototype dipole magnet from the LHC mounted on a frame that can pivot and track the Sun, CAST was set up to look into the solar core for axions, a hypothetical light neutral particle that is supposed to interact with other particles extraordinarily weakly, and are candidates for the dark matter in the Universe. For the last two years, it has also been looking for solar chameleons (particles with variable mass depending on the density of their surroundings, following recent theoretical ideas related to the dark energy puzzle).
Every year, the collaboration checks alignment of the magnet with the Sun. Whilst the method has become more sophisticated, the timing hasn’t - it depends on the visibility of the Sun through a small window in the corner of the building that houses the experiment.
Martyn Davenport (CERN) is the Technical Coordinator for the experiment, “We track the Sun from 8° below the horizon to 8° above the horizon at dawn and dusk every day. Everything about our experiment depends on detector sensitivity and magnet pointing precision, so we need to check the tracking regularly.”
Whilst the experiment doesn’t need to be in visual contact with the Sun to detect an axion or a solar chameleon, the optics that carry out the alignment checks do. And the Sun only comes into view through the tiny window in the corner for 10 days in March and September each year.
At these times of year, clouds or low-lying mist can often obscure the view of the Sun so the members of the collaboration might only have minutes with a clear view to check the alignment. “A bigger window wouldn’t help us too much,” explains Martyn, “there are lots of buildings and a 100 year old oak forest outside our zone, so we couldn’t get a better view.”
Initially, the collaboration used a webcam mounted on the top of the experiment, but the collaboration now uses more sophisticated optics.
Since it started collecting data in 2003, CAST hasn’t detected either an axion or a solar chameleon. But this doesn’t mean that they’re not out there or that the experiment has not been a success. Other experiments had sought but not found the Higgs boson before it was discovered by ATLAS and CMS. These experiments were looking in different energy ranges and were able to gradually reduce the possible hiding places for the elusive particle. CAST is contributing to the search for the proposed particles in a similar way.
CAST alignment with the Sun has just been re-checked. It was the last check for solar axion physics but future alignment checks will still be needed for solar chameleon physics although the target is now much larger (70% of the solar disc rather than just the solar core).
From the start of 2016, CAST will turn its attention away from solar axions and prepare to look for relic axions – cold dark matter axions that could be responsible for the large scale structures we observe in the Universe and through which the Earth continuously sweeps in its orbit around the Sun.
CAST’s new program will be split into dawn tracking for solar chameleons whilst the rest of the day the magnet will be at rest whilst searching for relic axions.
“When I joined CAST, I thought it was a rather esoteric experiment,” says Martyn, “but I’ve been won over: none of the other dark matter candidates have so far been discovered, so that means that the axion is still very much in the frame. Relic axions will extend our search region for axions over the coming years. Nowadays chameleons are the more esoteric topic; our first paper on the search for solar chameleons has just been published and very soon CAST will start a program of high sensitivity searches for solar chameleons”.
Dan Tovey (Sheffield): Deputy Physics Coordinator for ATLAS Collaboration, and Lego fan.
(Credit: D Tovey)
On 1 October, Dan Tovey (Sheffield) took up a new role as Deputy Physics Coordinator for the ATLAS Collaboration. We asked Dan to tell us a bit more about what he’ll be doing for the next 12 months:
UKNFC: In practical terms, what does the Deputy Physics Coordinator do?
DT: The Physics Coordinator is responsible for overseeing and guiding the physics analysis programme of the ATLAS collaboration. This involves ensuring that data is analysed quickly and efficiently to produce robust scientific results exploiting the full power of the LHC to search for new physics and measure the properties of Standard Model particles. As Deputy Physics Coordinator I will be supporting the new Physics Coordinator Marumi Kado and at the same time learning the ropes in preparation for taking over from him in a year’s time. I am expecting a very steep learning curve!
UKNFC:What do you think will be the main challenges?
DT: For a collaboration of the size and complexity of ATLAS a key challenge is ensuring that all the many different analysis teams have the software, data samples and analysis tools they require to produce the best possible results in a coherent and timely fashion. This is a particularly exciting time for ATLAS as the new 13 TeV data from Run-2 of the LHC will dramatically increase the potential for making major discoveries of new physics – for instance supersymmetric particles, dark matter or
additional Higgs bosons.
The LHC machine is performing so well at this world-record collision energy that evidence for new phenomena could appear very quickly. It is therefore crucial that we analyse our data as rapidly as possible while also ensuring that our results are robust and rigorously checked. One of my main tasks will be to ensure that we can do this effectively.
UKNFC: Is this your first long-term ‘posting’ to CERN?
It is indeed. Of course I’ve spent a lot of time at CERN in the past, but always on relatively short trips from the UK. Many years ago my PhD was carried out on direct dark matter searches, so unlike many ATLAS students and post-docs I’ve never actually lived in the area.
UKNFC: What additional opportunities does spending time at CERN bring?
DT: CERN is a fantastic place to work and I feel really privileged to be able to spend time based here. Working closely with some of the world’s most talented and dedicated scientists, all of whom are committed to understanding more about how the universe works, is a wonderful opportunity. I’d like to say that I’m also looking forward to exploring the wonderful local scenery and mountains at the weekends, however it remains to be seen whether I actually have any time for that!
LHC National Welsh Assembly
STFC’s travelling exhibition about the Large Hadron Collider will be at the Welsh Assembly’s Senedd building in Cardiff 17 – 22 October; don’t miss the chance to see a full-size section of the LHC tunnel, complete with a dipole magnet! Entry is completely free.
Presenter, Simeon Courtie discovers the corridor where the World Wide Web was born.
(Credit: BBC Wiltshire/A Martin)
CERN is the UK’s national laboratory for particle physics; it may be in an international location, but every region of the UK is benefiting from membership. The people of Wiltshire found out about their connection to CERN when morning show presenter Simeon Courtie and his producer Annie Martin broadcast their show live from the lab.
Sim and Annie had discovered that a school from Chippenham would be visiting CERN and decided to tag along. In addition, Swindon is home to STFC, the research council that manages UK membership of CERN, so there’s a strong local link.
What started out as a plan to record a few interviews with the students from Abbeyfield School quickly became a more ambitious project, and a first for UK radio.
Sim and Annie pre-recorded the students’ reactions as they saw
behind the scenes at CERN and interspersed these with live chats with members of the UK research community.
Broadcasting from five different locations including the very seat where Peter Higgs was sitting when the discovery of his eponymous particle was announced, the topics covered everything from extra dimensions, dark matter and the birth of the web to the Oxford Cambridge Women’s Boat Race, career paths that aren’t exactly direct and how you find skiable snow for 18 consecutive months of the year. The team back in the studio in Swindon mixed in a great selection of songs with a science theme.
The Jobs behind the Science
(© 2015 CERN)
Looking for a fresh challenge? Would you like to work in an international environment at the forefront of scientific discovery? CERN needs people with all sorts of professional skills and qualifications, from engineers and technicians to accountants and lawyers. Take a look at some of the current vacancies!
Last updated: 29 October 2015