The Large Hadron Collider, on the Franco-Swiss border near Geneva. Photo: Getty Images
Show Hide image

The Large Hadron Collider has made another exciting quantum discovery

Scientists working on one of the four experiments at the LHC have gathered enough evidence to confirm the existence of a four-quark particle.

Since the spectacular discovery of the Higgs boson in 2012, physicists at the Large Hadron Collider (LHC), the gigantic particle accelerator outside Geneva, have suffered a bit of a drought when it comes to finding new particles. In a welcome relief, the LHCb collaboration, who run one of four large experiments at the LHC, have announced one of the most genuinely exciting observations to come out of the 27km super-collider so far – an exotic particle that cannot be explained by current theories.

In the early 1930s physicists had a clean picture of the subatomic particles that make up our world. Every known atom has a tiny nucleus at its heart surrounded by a cloud of electrons, and each nucleus was made out of varying numbers of protons and neutrons. However, as the decades wore on a number of new, and somewhat unwelcome, particles were discovered, at first in detectors studying particles from outer space and later in particle-collider experiments.

By the 1950s, dozens of apparently elementary particles had been discovered, causing frustration among physicists who often brandish an inability to memorise a list of facts as a badge of honour. The famous physicist Enrico Fermi perhaps best expressed the mood of his colleagues in an infamous remark:

Young man, if I could remember the names of these particles, I would have been a botanist.”

Help came in the 1950s when physicists came up with a new model that explained most of these particles as being made up of a small number of truly elementary particles. Borrowing a line from James Joyce’s Finnegans Wake (a book that is even harder to understand than quantum field theory), Murray Gell-Mann dubbed these new particles “quarks”.

By the late 1960s the existence of quarks had been verified experimentally. We now know that there are six in total – the up, down, strange, charm, bottom and top quarks, along with six antiquarks (their anti-matter copies).

The quark model neatly explained all these peculiar particles. Protons, neutrons and many others besides are made of three quarks, belonging to a family known as baryons. Alternatively, a quark and an antiquark can pair up to form a meson.

Since then the quark model has been extremely successful, and is now a cornerstone of our understanding of particle physics. It was only at the turn of the millennium that some strange results started to suggest that the model might be incomplete. Until 2003 quarks had only been seen in twos or threes, but then a number of particles that looked like combinations of four quarks started to reveal themselves.

In 2008 the Belle Collaboration in Japan reported the observation of a new exotic particle – the unfortunately drably named Z(4430) (where for its negative charge). This has a mass that places it in a dense forest of charmonium states – particles that are made up of a charm quark and a charm antiquark. Crucially though, the Z is electrically charged whereas all charmonium states must be neutral, clearly marking it out as something unusual.

After a careful analysis of data from 25,000 decays of mesons resulting from more than 180 trillion collisions at the LHC in 2011 and 2012, the new announcement confirms the existence of Z(4430) with extremely high confidence. The particle was observed with an overwhelming significance of 13.9 sigma, well above the usual 5 sigma threshold required to declare a discovery. LHCb also went further than Belle by measuring the spin and parity of Z(4430), two quantum-mechanical properties that give a firm handle on the internal makeup of the particle.

The observation by LHCb is important because few physicists will take a result seriously until it has been seen by two independent experiments. This is why hundreds of millions of Euros were spent building two large detectors at the LHC. The observation of the Higgs boson by two independent teams, ATLAS and CMS, was what really convinced the scientific community that the particle was real.

This result is the clearest evidence yet of the existence of a tetraquark – a four-quark state, with the LHCb analysis suggesting that Z(4430) is most likely to be made of a charm, anti-charm, down and anti-up quark. Theorists are now able to add a whole new type of particle to the quark model and begin the hard work of trying to understand exactly how these four quarks are bound together.

Meanwhile, physicists working at the LHC experiments will continue to explore unmapped regions of the subatomic world, with the hope of turning up more members of this exotic new family. Now that we know that at least one is out there, it is very unlikely that Z(4430) is alone.The Conversation

Harry Cliff is affiliated with the University of Cambridge, CERN, the LHCb experiment.

This article was originally published on The Conversation. Read the original article.

Show Hide image

“Socialism with an iPad” isn't as ludicrous as it sounds

Technology is changing the labour market faster than ever before. John McDonnell argues that it's the state's responsibility to make sure the outcome is fair for everyone. 

The speech shadow chancellor John McDonnell gave at Imperial College earlier today started fine. As my colleague George Eaton points out, McDonnell was valiantly attempting to reframe the economic debate – to show how investment, especially in technology research and infrastructure, could reinvigorate the economy in ways austerity can’t. 

But then he got to the last line. “It’s socialism,” he summed up, “but socialism with an iPad.”

The clunky slogan sailed a thousand The Thick of it references (Bat People and App Britain featured prominently), and its use as a soundbite across the media made McDonnell’s argument look out-of-touch and embarrassing. But in the context of his argument, the line isn’t as nonsensical as it sounds.

Buried in the speech were a number of important arguments about how we let technological advancement come about. It’s lazy to assume that technology is inherently democratic, and will necessarily bring about a fairer society – as things stand, it’s deepy embedded in capitalism. But it's also changing the labour market faster than ever before: automation and robotics will soon mean that most tasks can be carried out  by machine, making those who control those machines vastly more powerful than those who don’t. 

In his speech, McDonnell pointed out that automation will replace low-paid workers first:

Technological advance is forcing the pace of change. Bank of England research suggests that 15 million jobs could be at risk of automation over the next decade or so. And those most at risk from automation are the lowest-paid.

He added that technological advances, and the changes they’ll make to the labour market, must be managed by the state so that workers don't lose out. Technology contributes to the wealth gap, and could well make it worse, unless, as McDonnell says, the government “understands and accepts the strategic role it has to play in our new economy”. This sounds woolly, but it's an important point - Tory policy on issues like tax or the the Transatlantic Trade Partnership (TTIP) has been remarkably hands-off in ceding power to large corporations. 

McDonnell implied that a large and involved state is crucial in a globalised, technological world, to ensure that workers' rights don't fall through the cracks and inequalities don't widen. A large welfare state would help cushion workers in a changing economy -  tax credits, as McDonnell explained earlier, can help make up for low wages in small, start-up businesses. 

Corporations have a poor record of improving working life and helping out those unable to work, or whose skills become redundant. These safeguards will become ever-more important as technology changes the labour market forever. And it’s here, McDonnell argued, that a bit of socialism will be needed. Even if it's carrying an iPad. 

Barbara Speed is a technology and digital culture writer at the New Statesman and a staff writer at CityMetric.