Dark matter remains dark - for now

CDMS detector. Courtesy of Fermilab.

For the past month and a bit, the biggest story in physics has undoubtedly been dark matter.

When Sam Ting, the charismatic Nobel Prize winning director of the AMS project, announced in February that the team who monitor his orbiting Alpha Magnetic Spectrometer, latched to the ISS, would be announcing 'significant results' in the search for dark matter, the whole physics community held its breath.  Somewhat skeptically.

The results, when they were announced on 30 March at CERN, seemed to add weight to the measurements made by PAMELA, in 2008, and were certainly of significant interest.

AMS-02 on ISS. Courtesy of CERN

But they perhaps fell short of what many were hoping for. As theoretical physicist, Katie Mack put it on 5 April in Physics Focus - somewhat bluntly, it should be said, "the AMS-02 detector on the International Space Station has not detected dark matter. It hasn't found 'indications' of dark matter, or even 'hints'. It certainly is not providing the 'best evidence yet' of dark matter's existence."

She did, however, acknowledge the important measurements the AMS-02 detector has made:

"What AMS has done is measure, to very high accuracy, the amount of antimatter the galaxy is bombarding us with. [....]. The AMS experiment detects cosmic rays - protons, electrons, and the antimatter counterparts of each, antiprotons and positrons. Before the experiment ran, we had predictions of how the matter/antimatter fraction should vary with the energy of the particles. AMS tells us our predictions were wrong. The antiprotons look about right, but there's a huge excess of high-energy positrons over what astrophysical models predict, and a bump in the electron flux at high energies. All of these results were actually seen by earlier experiments PAMELA and Fermi, but AMS confirms them to higher precision and higher energies. There's more antimatter than we thought; now we have to figure out why."

This is a concise explanation of the so-called 'positron-excess', which is one of the key indicators that dark matter - whatever it is - exists.  Mack goes on to explain, that the radio astronomers' favourite phenomenon, pulsars, are thought by many astrophysicists to be the cause of the positron excess.

"Pulsars [...] can use their extreme magnetic fields to accelerate particles and create electron-positron pairs. The fact that pulsars do this is solidly in the realm of known physics, and theoretical models can easily fit the signals seen in the cosmic ray experiments."

This is far from an accepted theory of the origin of dark matter, but it is a fascinating one nonetheless.  But where else might we look to find out about the origins of dark matter? The answer is: the mines.

Far beneath the surface of the earth, some of the most significant searches for dark matter have been underway for years. This week, one of the most notable of these, the CDMS experiment (the Cryogenic Dark Matter Search) in the Soudan mine in Minnesota, posted some extremely interesting results. Graduate student, Kevin McCarthy, reported at the American Physical Society meeting in Denver on 13 April that CDMS has found "three promising clues" of dark matter. The their silicon detectors had picked up possible signs of three weakly interacting massive particles (or 'WIMPs', as physicists call them).  Their evidence is verifiable to a level of three-sigma.

As Jason Palmer explains, particle physics has an accepted definition for a "discovery": a five-sigma level of certainty. "The number of standard deviations, or sigmas, is a measure of how unlikely it is that an experimental result is simply down to chance, in the absence of a real effect Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin The "three sigma" level represents about the same likelihood of tossing nine heads in a row. Five sigma, on the other hand, would correspond to tossing more than 21 in a row. With independent confirmation by other experiments, five-sigma findings become accepted discoveries."

So CDMS' three-sigma result falls short of this, but it most certainly counts as a 'tantalising hint'.

As science writer Valerie Jamieson notes, the CDMS dark matter signal fits with recent theories that suggest dark matter is, "not a single entity, but a 'dark sector of particles' that could include dark antimatter".

"This may be the start of a very big deal" observes dark matter theorist Dan Hooper, of Fermilab, who manage CDMS.

So whilst dark matter remains enigmatic, and most certainly dark, for now, there's some hope we may be closing in on its secrets.

Sources:

http://www.aps.org/meetings/april/

http://is.gd/coldwater

http://cdms.berkeley.edu/

Storifying Critical Citizen Science

MadLab Scientists investigating food products. Image (cc) MadLabUK, 2013.

Alice Bell recently drew my attention to a fascinating piece of writing by the Goldsmiths academic, Dan McQuillan. The piece entitled, What is Critical Citizen Science? (A Dialogue), is a meditation on the emerging field of citizen science. It takes the form of a fictional dialogue between 'nomad', the apotheosis of a free-thinking scientist-cum-hacker, and 'royalist', a caricature of an antediluvian traditionalist academic. Through the voices of these archetypes, McQuillan sets out what he refers to as 'critical citizen science', a bottom-up, participative scientific movement.

The piece is published on Storify, the social media service that lets users create stories using elements from other platforms such as Twitter, YouTube or Instagram.  Users build a story from video, images, and quotations from various places, using their own words to formulate a narrative.

Through a combination of well-chosen references, polemics and poetry, a sense of what 'critical citizen science' might be, gradually emerges from McQuillan's text. The dialogic format inevitably calls to mind the conversations between Achilles and the tortoise in Zeno, Carroll, and perhaps most fittingly, Hofstadter's Gödel, Escher, Bach. In McQuillan's work too, the medium of dialogue lends itself well to an inquiry into the complex ethics, aesthetics and politics that 'critical citizen science' might be engaged with.

Intriguingly, over the course of the dialogue, McQuillan correlates emerging community science and technology practices, exemplified by crowdmapping initiatives like Harassmap, hackerspaces such as MadLab, and open hardware projects such as Safecast and Water Hack, with an analysis of radical media art practice of the late 20th century, particularly the Electronic Disturbance Theater.

Ricardo Dominguez, Electronic Disturbance Theater

As someone very much engaged with the wider context of tactical media as a cultural strategy in the 1990s, and now equally fascinated by emerging forms of participatory science, I found McQuillan's juxtaposition of these two discrete areas, deeply compelling.

Here's a short extract, where we listen in on nomad and royalist, discussing new sites of scientific learning:

nomad: there is already an emerging set of learning spaces for critical citizen science; hackerspaces, makerspaces and fablabs...

royalist: what nonsense. these aren't labs, they're garages; and it's not science, merely an obsessive meddling with hardware.

nomad: popularly known as hacking. i refer you to early hacktivists the Electronic Disturbance Theater and their 'science of the oppressed" - "...alternative social forms of life and art that fall between the known and unknown, between fiction and the real, between clean science and dirty science - each a part of a long history of an epistemology of social production which privileges the standpoint of the proletariat, the multitude, the open hacks of the DIY moments, and of autonomous investigators who stage test zones of cognitive styles... concrete practices as speculation and speculation as concrete practices - at the speed of dreams."

This is not a manifesto for 'critical citizen science' (or perhaps just as accurately, 'tactical citizen science'?). It's more of a persuasive suggestion.  But one can't help but recall another grass-roots movement which argues for a similarly critically engaged approach to science and technology. In October 2011, Julian Oliver, Gordan Savicic and Danja Vasiliev published the Critical Engineering Manifesto.  It begins by stating:

"The Critical Engineer considers Engineering to be the most transformative language of our time, shaping the way we move, communicate and think. It is the work of the Critical Engineer to study and exploit this language, exposing its influence."

As co-author, Oliver noted in an interview in 2012, "as thinkers with technical abilities in several areas, we want to take on our built and increasingly automated environment by the terms in which it's given, opening it up for post-utilitarian conversation, for play and interrogation. If there's ever a time to be doing that, it's now, especially with opaque and hidden infrastructure in the telecommunications space deeply impacting diplomatic relations and civil liberties world wide."

The manifesto provides an analytical framework for artistic practice which exposes the technological and scientific systems which unpin much of society. By making these infrastructures and systems visible, the 'critical engineer' reveals the political and power structures at play, instigates critical discussion, and questions who has agency within these systems.

Transparency Grenade (2011) by Julian Oliver

Projects such as Oliver's Transparency Grenade (2011) and Oliver and Vasiliev's Newstweek (2011) are designed as both functional tools, which both reveal and disrupt the invisible information and communication networks that surround us, and conversation-starters about our unquestioning reliance on technological systems we often don't understand.  Their intention is to expose the deep reach that science and technology have in our lives, and to try and encourage more active forms of intervention and agency.  As Oliver (2012) has noted, we all "think through tools both before and while we use them and the more we depend upon a tool the more we are changed by it."

McQuillan's speculations on critical citizen science seem to originate from a similar desire to question the power structures and politics of scientific practice. He insinuates an anxiety about popular citizen-science efforts such as Galaxy Zoo and LHC@Home, which harness the labour of users, without deeply engaging them in the scientific process.  To frame that concern, he cites Tiziana Terranova's critique of user-generated content outlined in her text, Free Labor: Producing Culture for the Digital Economy (2000).

His text also conveys an unease with the exponential hype surrounding 'big data' and 'open data':

royalist: [...]  The networks you rely on for your delocalised tinkering have already given birth to a new science; and it's name is Data Science; and its Data shall be Big.

nomad: [...] As our data is always ambiguous, we shall Glitch; becoming the discontinuities and unexpected artefacts in the big data you crave.

Later, McQuillan points to the value of critical citizen scientists in bearing witness to events which governments and bureaucracies would prefer citizens not to see, let alone intervene into:

nomad: [....] Why not look to the example of white coated citizens weapons inspectors for responsible empiricism. In a horsemeat crisis, the critical citizen scientist packs their DIY bio and flashmobs the nearest Lidl. This isn't an idle fantasy; only recently, Madlab testers set up shop as the Deptford Market DNA FoodLab.

Elsewhere the piece, McQuillan muses whether 'critical citizen science' could be the site at which the Internet of Things becomes the "Parliament of Things" as described by Bruno Latour in his 1991 book, We Have Never Been Modern. By this, Latour was referring to a kind of symmetry between people and what he calls "non-human entities" (or "things"). He argues that our society is comprised of people assembled around "things". Latour dismantles the barrier between culture and nature, between subject and object, proposing more subtle relations between humans and "things", in which the latter are granted the same amount of agency as we are. McQuillan spiritedly picks this up, in the voice of nomad, contending:

"Through citizen science, the Parliament of Things will become the Occupy of Objects."

Whilst I was originally drawn to the subject of the piece - its evocation of radical tactical art media practices, entwined with new community science efforts, and echoing (perhaps inadvertently) the philosophy of the critical engineering movement - the methodology of the story construction is also worthy of note.  When I first read the piece and started thinking about it, I opined to the science policy researcher, Justin Pickard, that such evocative material deserved to be written up in a more formal manner.  He responded by saying:

"This *is* it written up properly. Storify-native STS. Look how reliant it is on the video clips, images, and hyperlinks."

So, tools like Storify enable writers and makers to build layered, interwoven narratives around science and technology research and ideas. These tools provide us with a different vector to be able to express heterogeneous, emerging and often conflicting ideas.  As such, they have the potential to develop into an intriguing and valuable alternative platforms for science communication, and the analysis of scientific research.

Source:

http://storify.com/danmcquillan/what-is-critical-citizen-science-a-dialogue/

Neutrinos back in the spotlight

It's been a big couple of weeks for neutrinos. First, the OPERA experiment in Italy revealed that they had detected the transformation of a muon neutrino to a tau neutrino for only the third time in their history. Soon after, Fermilab's NOvA neutrino detector in the States published their first three-dimensional images of the elusive particles (pictured above).  All this followed hard on the heels of one of the most discussed and celebrated science results of the year so far - the new Planck measurement of the cosmic microwave background - which has interesting implications for neutrino physics.

Neutrinos are among the more mysterious and slippery inhabitants of the fundamental particle zoo. They can be created by certain types of radioactive decay, or nuclear reactions like those that take place in stars, or when cosmic rays hit atoms. They have barely any mass and therefore rarely interact with other types of matter.  This makes them fiendishly difficult to observe.  But they are a fascinating area of study for physicists.  Many of the neutrinos around today are thought to have originated in the Big Bang, so understanding their properties will give us important new insights into what the universe was like 13.7 billion years ago, and how it operates on a fundamental level now.

Neutrinos come in three different types, called "flavours": electron, muon and tau.  Forty years ago physicists posited that these particles may occasionally be able to change from flavour to flavour - for instance starting out as a muon neutrino and ending up as a tau neutrino. This transformation could explain one of the great puzzles of neutrino physics.  Theoretical models imply there should be far more neutrinos raining down on the Earth from nuclear reactions in the Sun, than there actually are.  So the mystery of the 'missing neutrinos' has been bothering physicists for over a generation. If it could be proven that the missing particles are actually neutrinos which have changed flavour as they move through space, then this mystery could be solved.

The OPERA experiment in Gran Sasso, Italy was set up specifically for this purpose. It is designed to detect and analyse exactly these kinds of transformations.  But spotting them is no easy matter. On 26 March 2013, OPERA announced that it had observed this exceptionally rare act of 'shape-shifting' for just the third time.  A muon-type neutrino produced at CERN in Geneva arrived at the Gran Sasso laboratory as a tau neutrino. This has only been observed only twice before, once in 2010 and again last year.

OPERA works by studying beams of neutrinos produced at CERN in Switzerland, which travel 732km to the underground laboratory at the Gran Sasso facility, where they can be studied by physicists working on the OPERA detector.   As Kathryn Jepsen, writing in Symmetry, puts it, "the OPERA experiment is a fast-moving, long-distance game of catch, with CERN laboratory at the border of France and Switzerland pitching a concentrated beam of neutrinos toward the 1250-ton OPERA detector. The neutrino is a difficult ball to snag; it interacts so rarely with matter that it can zip unflinchingly through an entire planet."

The neutrinos which leave CERN are muon neutrinos. OPERA is configured to detect tau neutrinos. If it spots one, it can deduce that a 'change of flavour' has occurred en-route.  Detecting such a flavour oscillation, as the team did this March, is significant.  Not only is it, "an important confirmation of the two previous observations", as the the head of OPERA's international research team, Giovanni De Lellis, has said; it also provides more evidence that flavour oscillation may indeed be the reason why the flux of neutrinos from the Sun and Earth's atmosphere is so much smaller than what theorists predict it should be.

Over on the other side of the Atlantic, Fermilab are in the process of establishing the NOvA experiment as the most powerful neutrino detector in the States. They recently took a significant step towards this goal, by releasing their first three-dimensional images of particles analysed in the under-construction detector.

NOvA detector in construction - near Ash River, USA, photographed in 2012. Image courtesy NOvA collaboration.

NOvA is a collaboration of 180 scientists, technicians and students from 20 universities and laboratories in the U.S and another 14 institutions around the world.  Later this year, the NOvA detector at Ash River, near the Canadian border will start receiving beams of neutrinos sent from Fermilab, the US equivalent of CERN, which is based near Chicago. The beams of neutrinos will travel 500km from Fermilab to NOvA.  As they say, "when a neutrino interacts with the detector, the particles it produces leave trails of light in their wake. The detector records these streams of light, enabling physicists to identify the original neutrino and measure the amount of energy it had."

Using the first completed section of the NOvA detector, physicists have begun collecting data from cosmic rays - the particles produced by a constant stream of atomic nuclei falling on the Earth's atmosphere from space. The 3D particle images they have produced as a result of this work are helping the physicists fine-tune the instrument. When cosmic rays pass through the NOvA detector, they leave straight tracks and well-understood energy signatures. As Mat Muether, a Fermilab researcher, notes, "they are great for calibration. Everybody loves cosmic rays for this reason. They are simple and abundant and a perfect tool for tuning up a new detector."

Fermilab state, "the detector at its current size catches more than 1000 cosmic rays per second. Naturally occurring neutrinos from cosmic rays, supernovae and the sun stream through the detector at the same time. But the flood of more visible cosmic-ray data makes it difficult to pick them out. Once the upgraded Fermilab neutrino beam starts, the NOvA detector will take data every 1.3 seconds to synchronize with the Fermilab accelerator. Inside this short time window, the burst of neutrinos from Fermilab will be much easier to spot."

And this is important. As Gary Feldman of Harvard University says, "the more we know about neutrinos, the more we know about the early universe and about how our world works at its most basic level".

The most headline-stealing physics result of the year so far has given us breathtaking new insights into the early universe and our world at it's most basic level. On the 21 March 2013, scientists working with the Planck Space Telescope unveiled the most detailed map ever created of the cosmic microwave background (CMB) - the leftover radiation from the Big Bang.  Whilst the Planck measurement of the CMB hasn't given us that many clues as to what the fundamental properties of neutrinos are, it may have helped us learn what they are not. In recent times, physicists have begun to speculate that there may be a fourth type of neutrino flavour - the sterile neutrino, so called because it is not effected by the weak nuclear force, and therefore interacts even less with other particles than it's shy and retiring, tau, muon and electron neutrino cousins.  But as John Matson writing in Scientific American has noted, Planck's findings suggest that physicists hoping for experimental proof of the sterile neutrino are going to have to look harder or rethink altogether.

All and all, these are fascinating times for neutrino physics, and we shouldn't be surprised if these ghostly little particles take their share of the limelight in the coming year.

Sources:

http://www.fnal.gov/

http://www.infn.it/news/newsen.php?id=663

http://www.symmetrymagazine.org/