ATLAS

Hope for a New Particle Fizzles at the LHC

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A curious signal of a potentially revolutionary new particle detected last year turned out to be a fluke.

A portion of the ATLAS detector, one of the two massive experiments at the Large Hadron Collider that reported—and have now refuted—what could have been a revolutionary new subatomic particle. 

For months, the world of physics has been abuzz with rumors about a potential new subatomic particle that could revolutionize our entire view of physics. But new results presented today by physicists from the Large Hadron Collider (LHC) today have, for now, quashed the revolution.

The first hints of a new particle appeared in December 2015, when two independent experiments at the LHC, ATLAS and CMS, each announced the same tantalizing quirk in their data. Both experiments smash together protons at nearly the speed of light, searching for new fundamental particles produced by the enormously energetic collisions. When they ramped up to their highest energies yet, the two experiments detected a mysterious signal: more pairs of photons with a combined energy of 750 giga-electron volts (GeV) than expected.

This “diphoton bump” was not a prediction of the Standard Model of physics—a rigorously tested and profoundly successful theory forged in the 1970s that incorporates all known fundamental particles and forces. Despite its success, however, the Standard Model does not explain what lies at the hearts of black holes, the nature of dark matter and dark energy, the quantum behavior of gravity, and other deep mysteries of the universe. With their shared diphoton bumps, ATLAS and CMS appeared on the verge of peering into physics beyond the Standard Model’s musty confines. Within weeks, the little bump had inspired hundreds of speculative papers by theorists. “At the LHC, physicists are looking very intensively for new particles and new laws of physics so it’s easy to get excited about something that seems very convincing,” says Michael Peskin, a theoretical physicist at Stanford’s SLAC National Accelerator Laboratory.

Whatever produced the diminutive diphoton bump didn’t neatly fit into any theory. Many scientists suggested that the bump was produced by a heavier cousin of the Higgs boson, another particle that similarly showed up as an eyebrow-raising blip in the data about four years ago. Others suggested that it could be a kind of dark matter particle, or even the vaunted graviton, the predicted carrier particle for gravity itself.

But as scientists at the LHC started collecting more data this year, the 750 GeV diphoton bump started disappearing. Now, after analyzing nearly five times the amount of data that they had last year, ATLAS and CMS physicists have watched the bump diminish to statistical insignificance. Presenting at the International Conference on High Energy Physics in Chicago, particle physicist and ATLAS spokesperson Dave Charlton said that when looking at all the data, the 750GeV signal now only has a significance of 2 sigma, which is much less than the 5 sigma (or 1 in 3.5 million chance) that is needed to confirm a new discovery in physics. Simply put, the diphoton bump was a false alarm. “It is a bit surprising that we saw the fluctuation on both instruments but it was just that—a fluctuation or statistical fluke,” said Charlton.

Seeing anomalies in the data is not uncommon at the LHC. The collider crashes so many protons together and churns out so much raw data that occasionally finding extra pairs of photons in the wreckage was bound to happen. “If you conduct many, many searches you come across these kinds of coincidences,” says Guy Wilkinson, a member of the LHCb collaboration.

Although the diphoton bump has now evaporated under closer scrutiny, researchers remain optimistic that the LHC will still lead them to new physics beyond the Standard Model. The multibillion-dollar project has years of operations left during which it will produce far more data for physicists to parse for elusive new particles. “We would have been very lucky if we found something, some new phenomenon or some new state of matter at this early stage,” says CMS physicist Tiziano Camporesi. “But we have to be patient.”

 

The Pentagon produces an impressive, humanlike robot. Where all this headed?

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In what could be the last time that a human taunts a robot with a hockey stick and lives to brag about it, the latest demonstration of the Atlas Robot has prompted renewed fears about the future of intelligent machines.

Born in 2013, Atlas is a DARPA-funded robot developed by Boston Dynamics. Its latest iteration stands at a very human-proportioned 5’9, weighing 180lbs. Like Lee Majors circa 1974, each successive version of Atlas has gotten better, stronger, faster than it was before.

What can Atlas do? Aside from scaring the bejesus out of genius technophobic Oxbridge physicists, it’s intended to perform tasks in emergency situations too dangerous for humans. Climbing ladders, driving vehicles, carrying heavy objects, and negotiating rough terrain are all in its disaster response repertoire.

One task Atlas won’t attempt anytime soon is cleaning up Japan’s Fukushima Daiichi nuclear plant. Custom built robots were designed to swim underwater and negotiate its damaged tunnels, in order to find and remove hundreds of tons of melted radioactive fuel rods. So far, every robot sent into the reactor has failed, their wiring nuked by the intense radiation.

The Department of Defense has stated that it has no interest in using Atlas in warfare. That may well be so. But the next generation of intelligent robots may be capable of reacting to dubious Pentagon claims with human-like incredulity.

Does this new species of Robo sapiens gives you hope for the future? Or does it cause more anxiety than Sarah Connor in a mental institution? The wildly popular Atlas video struck a nerve with YouTubers, prompting ample portions of both wonder and worry.

One futurist who’s brimming with techno-optimism is Jason Silva, the host of Brain Games on the National Geographic Channel. In a recent interview with Reason TV, the loquacious Silva told us why Stephen Hawking is wrong about the future: we should look forward to our benevolent robot overlords, because we will become them.

Watch the video. URL: https://youtu.be/rVlhMGQgDkY

Pentagon-funded Atlas robot refuses to be knocked over.

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Boston Dynamics road-tests its Atlas robot on rough terrain

Meet Atlas, a humanoid robot capable of crossing rough terrain and maintaining its balance on one leg even when hit from the side.

And WildCat, the four-legged robot that can gallop untethered at up to 16mph (26km/h).

These are the latest creations of Boston Dynamics, a US robotics company part-funded by the Defense Advanced Research Projects Agency (Darpa).

The robots are part of Darpa’s Maximum Mobility and Manipulation programme.

Darpa says such robots “hold great promise for amplifying human effectiveness in defence operations”.

Referring to Atlas’s ability to remain balanced despite being hit by a lateral weight, Noel Sharkey, professor of Artificial Intelligence and Robotics at the University of Sheffield, told the BBC: “This is an astonishing achievement… quite a remarkable feat.”

This version of Atlas is one of seven humanoid robots Boston Dynamics is developing in response to the Darpa Robotics Challenge.

In December, competing robots will be set eight tasks to test their potential for use in emergency-response situations, including crossing uneven ground, using power tools and driving a rescue vehicle.

Darpa wants to improve the manoeuvrability and controllability of such robots while reducing manufacturing costs.

WildCat strike?

Boston Dynamics puts its WildCat robot through its paces

WildCat can bound, gallop and turn, mimicking the movements of quadruped animals. It is powered by an internal combustion engine.

“It is a shame that such technology is not being developed with other research funding,” said Prof Sharkey, who is also chair of the International Committee for Robot Arms Control.

“We do not know what military purpose it will serve but certainly it is a step towards a high-speed ground robot that could be weaponised to hunt and kill.”

The video shows WildCat performing on a flat surface, but Prof Sharkey said: “It would be good to see how well it could perform in a muddy field.”

Last year, Boston Dynamics’ Cheetah robot reached a sprint speed of 28.3mph tethered to a treadmill.

Geoff Pegman, managing director of RURobots, told the BBC: “Robotics has been making important strides in recent years, and these are a couple of demonstrations of the technology moving forward.

“However, their application may be limited to areas such as defence and, maybe specialised construction or demolition tasks.

“In other applications there are more efficient ways of achieving the mobility more cost effectively.”

Particle physics is at a turning point.

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The discovery of the Higgs boson will complete the standard model — but it could also point the way to a deeper understanding.

Let’s tentatively agree that the Large Hadron Collider (LHC) detectors ATLAS and the Compact Muon Solenoid have discovered a Higgs boson, with a mass of about 125 gigaelectronvolts (GeV). Although standard statistical measures might not consider the situation settled, it seems very likely that there has indeed been a discovery at CERN, Europe’s high-energy physics lab near Geneva, Switzerland, given that two quite different detectors both see a signal of some significance at about the same mass, and that both see the expected signals in two or more channels.

This is a profound turning point in the quest for a fundamental unified theory of the physical world. The properties and mass of the LHC’s Higgs boson suggest that physicists will soon find superpartners for particles, and that we have begun to connect string theory to the real world.

The Higgs boson, an as-yet-unknown kind of matter thought to generate mass in other particles, is the final ingredient needed to complete and confirm the standard model of particle physics. This amazing theory describes the particles (quarks and leptons) and the strong, weak and electromagnetic forces that interact to make our world (with the addition of the theory of gravity). Quarks combine to make protons and neutrons; protons and neutrons to make nuclei; nuclei and electrons (a type of lepton) to make atoms, then molecules and chocolate and people and planets and stars and so on. The standard model has no puzzles or problems, and incorporates at a fundamental level everything from condensed-matter physics to astrophysics. It achieves the goals of four centuries of physics. The Higgs itself has been sought for decades: the main route through which its signal was reported at the LHC was the particle’s decay into two photons. Collaborators and I first studied this signal in the mid 1980s, as a possible method for detecting the Higgs boson at the Superconducting Super Collider, which was to be built at Waxahachie in Texas but was cancelled in 1993.

Besides completing the standard model, the discovery of the Higgs tells us that a future, deeper underlying theory of the law(s) of nature must include and account for fundamental Higgs bosons. (Physicists have suggested alternative theories that include oddities such as composite Higgs bosons, but the CERN discovery essentially excludes them.) That will extend the standard model, and go beyond it to illumi­nate issues such as supersymmetry and the origin of dark matter.

“The properties and mass of the Higgs boson  strongly suggest that we have begun to connect string theory to the real world.”

A major and unexpected clue to the future offered by the CERN discovery is that the reported Higgs boson signal seems to behave as if it were a ‘standard-model Higgs boson’. Under the standard model, this should not be possible, because relativistic quantum field theory shows that the Higgs’ mass must experience quantum corrections that are much, much larger than the mass itself. Because the masses of quarks, leptons and the W and Z bosons that mediate the weak force are themselves dependent on the Higgs mass, the standard model predicts masses for them many orders of magnitude larger than what we observe.

This can be fixed. When the standard model is extended to a supersymmetric theory, the nature of the predicted Higgs boson changes. Its mathematical behaviour improves and the resulting theory is realistic.

Physicists thought that a Higgs boson, when discovered, would take this supersymmetric form, so how have we discovered one so apparently identical to the impossible standard-model version? Working out how to interpret this could be a large step towards the underlying broader theory that will extend the standard model.

One explanation could come from an unexpected source: string theory or its extension, M-theory. Contrary to what you may have heard, predictions about the real world can be made from string theory, although the 10- or 11-dimensional theory must first be ‘compactified’ to 4 dimensions (with 6 or 7 small dimensions left curled up). There has been considerable progress on that, as well as on how to stabilize the fields that describe the curled-up dimensions.

My collaborators and I have shown that in generic string and M-theories — consistent with constraints from cosmology and incorporating the Higgs mechanism for generating mass — the lightest Higgs boson behaves very much like the standard-model Higgs boson. And it has a mass of about 125 GeV, just as observed.

We first reported these results at the inter­national String Phenomenology Conference in Madison, Wisconsin, in August; and just days before the CERN data were reported, we posted a paper containing a significantly more precise prediction .

The same string theory (actually M-theory) that predicts the Higgs mass correctly also predicts that a spectrum of superpartners and some of their associated signals should now be discovered at the LHC. Particles such as gluinos — superpartners to gluons, which mediate the strong force — have not yet been searched for explicitly in the decay modes predicted by the string theories, mainly decay to top and bottom quarks. They could be found in these modes by the middle of next year. If so, the discovery may have a lower profile than the news of the Higgs boson, but the implications could be even greater. String theory could have come of age at last.

Source:Nature Physics