high-energy physics – Close Read

The nomenclature of uncertainty

The headline of a Nature article published on December 9 reads ‘LIGO black hole echoes hint at general relativity breakdown’. The article is about the prediction of three scientists that, should LIGO find ‘echoes’ of gravitational waves coming from blackhole-mergers, then it could be a sign of quantum-gravity forces at play.

It’s an exciting development because it presents a simple and currently accessible way of probing the universe for signs of phenomena that show a way to unite quantum physics and general relativity – phenomena that have been traditionally understood to be outside the reach of human experiments until LIGO.

The details of the pre-print paper the three scientists uploaded on arXiv were covered by a number of outlets, including The Wire. And The Wire‘s and Forbes‘s headlines were both questions: ‘Has LIGO already discovered evidence for quantum gravity?’ and ‘Has LIGO actually proved Einstein wrong – and found signs of quantum gravity?’, respectively. Other headlines include:

Gravitational wave echoes might have just caused Einstein’s general theory of relativity to break down – IB Times
A new discovery is challenging Einstein’s theory of relativity – Futurism
Echoes in gravitational waves hint at a breakdown of Einstein’s general relativity – Science Alert
Einstein’s theory of relativity is 100 years old, but may not last – Inverse

The headlines are relevant because: Though the body of a piece has the space to craft what nuance it needs to present the peg, the headline must cut to it as quickly and crisply as possible – while also catching the eye of a potential reader on the social media, an arena where all readers are being inundated with headlines vying for attention.

For example, with the quantum gravity pre-print paper, the headline has two specific responsibilities:

To be cognisant of the fact that scientists have found gravitational-wave echoes in LIGO data at the 2.9-sigma level of statistical significance. Note that 2.9 sigma is evidently short of the threshold at which some data counts as scientific evidence (and well short of that at which it counts as scientific fact – at least in high-energy physics). Nonetheless, it still presents a 1-in-270 chance of, as I’ve become fond of saying, an exciting thesis.
To make reading the article (which follows from the headline) seem like it might be time well spent. This isn’t exactly the same as catching a reader’s attention; instead, it comprises catching one’s attention and subsequently holding and justifying it continuously. In other words, the headline shouldn’t mislead, misguide or misinform, as well as remain constantly faithful to the excitement it harbours.

Now, the thing about covering scientific developments from around the world and then comparing one’s coverage to those from Europe or the USA is that, for publications in those countries, what an Indian writer might see as an international development is in fact a domestic development. So Nature, Scientific American, Forbes, Futurism, etc. are effectively touting local accomplishments that are immediately relevant to their readers. The Wire, on the other hand, has to bank on the ‘universal’ aspect and by extension on themes of global awareness, history and the potential internationality of Big Science.

This is why a reference to Einstein in the headline helps: everyone knows him. More importantly, everyone was recently made aware of how right his theories have been since they were formulated a century ago. So the idea of proving Einstein wrong – as The Wire‘s headline read – is eye-catching. Second, phrasing the headline as a question is a matter of convenience: because the quasi-discovery has a statistical significance of only 2.9 sigma, a question signals doubt.

But if you argued that a question is also a cop-out, I’d agree. A question in a headline can be interpreted in two ways: either as a question that has not been answered yet but ought to be or as a question that is answered in the body. More often than not and especially in the click-bait era, question-headlines are understood to be of the latter kind. This is why I changed The Wire copy’s headline from ‘What if LIGO actually proved Einstein wrong…’ to ‘Has LIGO actually proved Einstein wrong…’.

More importantly, the question is an escapism at least to me because it doesn’t accurately reflect the development itself. If one accounts for the fact that the pre-print paper explicitly states that gravitational-wave echoes have been found in LIGO data only at 2.9 sigma, there is no question: LIGO has not proved Einstein wrong, and this is established at the outset.

Rather, the peg in this case is – for example – that physicists have proposed a way to look for evidence of quantum gravity using an experiment that is already running. This then could make for an article about the different kinds of physics that rule at different energy levels in the universe, and what levels of access humanity has to each.

So this story, and many others like it in the past year that all dealt with observations falling short of the evidence threshold but which have been worth writing about simply because of the desperation behind them, have – or could have – prompted science writers to think about the language they use. For example, the operative words/clause in the respective headlines listed above are:

Nature – hint
IB Times – might have just caused
Futurism – challenging
Science Alert – hint
Inverse – may not

Granted that an informed skepticism is healthy for science and that all science writers must remain as familiar with this notion as with the language of doubt, uncertainty, probability (and wave physics, it seems). But it still is likely the case that writers grappling with high-energy physics have to be more familiar than others, dealing as the latest research does with – yes – hope and desperation.

Ultimately, I may not be the perfect judge of what words work best when it comes to the fidelity of syntax to sentiment; that’s why I used a question for a headline in the first place! But I’m very interested in knowing how writers choose and have been choosing their words, if there’s any friction at all (in the larger scheme) between the choice of words and the prevailing sentiments, and the best ways to deal with such situations.

PS: If you’re interested, here’s a piece in which I struggled for a bit to get the words right (and finally had to resort to using single-quotes).

Featured image credit: bongonian/Flickr, CC BY 2.0

Physicists find exotic particle with five quarks

The Wire
July 14, 2015

An artist's impression of five strongly bonded quarks in a pentaquark. Credit: CERN/LHCb Collaboration — An artist’s impression of five strongly bonded quarks in a pentaquark. Credit: CERN/LHCb Collaboration

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth” – thus spake Sherlock Holmes. Particle physicists at the Large Hadron Collider today announced the discovery of a new particle after an investigation following in the steps of Holmes’ wisdom. The particle is exceedingly rare in the books of fundamental physics, called a pentaquark. It’s named for the fact that it’s composed of five quarks, indivisible particles that in their leagues make up all known matter.

However, this is the first time experimental physicists have observed five quarks coming together to make a bigger particle. They commonly manifest as protons and neutrons, which are clumps of three quarks each.

The collaboration of scientists and engineers of the LHCb detector – which spotted the pentaquarks – uploaded a paper to the arXiv preprint server on July 13 and submitted a copy to the journal Physical Review Letters for publication. The abstract describes two resonances – or unstable particles – at masses 4,380 MeV and 4,449.8 MeV (to compare, a proton weighs 938 MeV), not including uncertainties in the range 40-110 MeV. The have been temporarily designated Pc(4380)+ and Pc(4450)+.

The LHCb detector spotted the pentaquarks during the particle decays of another particle called Λb (read Lambda b). However, instead of discerning their presence by a spike in the data, the scientists spotted them by accounting for all other data points and then figuring out one consistent explanation for what was leftover. And the explanation called for conceding that the scientists had finally spotted the elusive pentaquark. “Benefitting from the large data set provided by the LHC, and the excellent precision of our detector, we have examined all possibilities for these signals, and conclude that they can only be explained by pentaquark states”, said LHCb physicist Tomasz Skwarnicki of Syracuse University in a statement.

According to the pre-print paper, the chances of the observation being a fluke, or due to some other process that could’ve mimicked the production of pentaquarks, are less than 1-in-3.5-million. As a result, the observations are sufficiently reliable and make for a discovery – even if the particle wasn’t observed as much as its unique shadow. At the same time, because the history of the experimental pursuit of pentaquarks is dotted with shepherds crying wolves, the data will be subjected to further scrutiny. In the most recent and famous case in 2003, four research labs from around the world (TJNAF, AITEP, SPring-8, ELSA) claimed to have spotted pentaquarks, only to be disproved by tests at the Istituto Nazionale di Fisica Nucleare in Genova in April 2005.

The LHC, which produces the high-energy collisions that detectors like the LHCb study in detail, shut down in early 2013 for a series of upgrades and reawakened in May 2015. The pentaquark was found in data gathered during the first run, when the LHC produced collisions at an energy of 8 TeV (1 TeV is 1,000 MeV). In the second run, the collision energy has been hiked to 13 TeV, which increases the frequency with which exotic particles like pentaquarks could be produced.

The Large Hadron Collider is back online, ready to shift from the “what” of reality to “why”

The world’s single largest science experiment will restart on March 23 after a two-year break. Scientists and administrators at the European Organization for Nuclear Research – known by its French acronym CERN – have announced the status of the agency’s upgrades on its Large Hadron Collider (LHC) and its readiness for a new phase of experiments running from now until 2018.

Before the experiment was shut down in late 2013, the LHC became famous for helping discover the elusive Higgs boson, a fundamental (that is, indivisible) particle that gives other fundamental particles their mass through a complicated mechanism. The find earned two of the physicists who thought up the mechanism in 1964, Peter Higgs and Francois Englert, a Nobel Prize in that year.

Though the LHC had fulfilled one of its more significant goals by finding the Higgs boson, its purpose is far from complete. In its new avatar, the machine boasts of the energy and technical agility necessary to answer questions that current theories of physics are struggling to make sense of.

As Alice Bean, a particle physicist who has worked with the LHC, said, “A whole new energy region will be waiting for us to discover something.”

The finding of the Higgs boson laid to rest speculations of whether such a particle existed and what its properties could be, and validated the currently reigning set of theories that describe how various fundamental particles interact. This is called the Standard Model, and it has been successful in predicting the dynamics of those interactions.

From the what to the why

But having assimilated all this knowledge, what physicists don’t know, but desperately want to, is why those particles’ properties have the values they do. They have realized the implications are numerous and profound: ranging from the possible existence of more fundamental particles we are yet to encounter to the nature of the substance known as dark matter, which makes up a great proportion of matter in the universe while we know next to nothing about it. These mysteries were first conceived to plug gaps in the Standard Model but they have only been widening since.

With an experiment now able to better test theories, physicists have started investigating these gaps. For the LHC, the implication is that in its second edition it will not be looking for something as much as helping scientists decide where to look to start with.

As Tara Shears, a particle physicist at the University of Liverpool, told Nature, “In the first run we had a very strong theoretical steer to look for the Higgs boson. This time we don’t have any signposts that are quite so clear.”

Higher energy, luminosity

The upgrades to the LHC that would unlock new experimental possibilities were evident in early 2012.

The machine works by using powerful electric currents and magnetic fields to accelerate two trains, or beams, of protons in opposite directions, within a ring 27 km long, to almost the speed of light and then colliding them head-on. The result is a particulate fireworks of such high energy that the most rare, short-lived particles are brought into existence before they promptly devolve into lighter, more common particles. Particle detectors straddling the LHC at four points on the ring record these collisions and their effects for study.

So, to boost its performance, upgrades to the LHC were of two kinds: increasing the collision energy inside the ring and increasing the detectors’ abilities to track more numerous and more powerful collisions.

The collision energy has been nearly doubled in its second life, from 7-8 TeV to 13-14 TeV. The frequency of collisions has also been doubled from one set every 50 nanoseconds (billionth of a second) to one every 25 nanoseconds. Steve Myers, CERN’s director for accelerators and technology, had said in December 2012, “More intense beams mean more collisions and a better chance of observing rare phenomena.”

The detectors have received new sensors, neutron shields to protect from radiation damage, cooling systems and superconducting cables. An improved fail-safe system has also been installed to forestall accidents like the one in 2008, when failing to cool a magnet led to a shut-down for eight months.

In all, the upgrades cost approximately $149 million, and will increase CERN’s electricity bill by 20% to $65 million. A “massive debugging exercise” was conducted last week to ensure all of it clicked together.

Going ahead, these new specifications will be leveraged to tackle some of the more outstanding issues in fundamental physics.

CERN listed a few–presumably primary–focus areas. They include investigating if the Higgs boson could betray the existence of undiscovered particles, the particles dark matter could be made of, why the universe today has much more matter than antimatter, and if gravity is so much weaker than other forces because it is leaking into other dimensions.

Stride forward in three frontiers

Physicists are also hopeful for the prospects of discovering a class of particles called supersymmetric partners. The theory that predicts their existence is called supersymmetry. It builds on some of the conclusions of the Standard Model, and offers predictions that plug its holes as well with such mathematical elegance that it has many of the world’s leading physicists enamored. These predictions involve the existence of new particles called partners.

In a neat infographic by Elizabeth Gibney in Nature, she explains that the partner that will be easiest to detect will be the ‘stop squark’ as it is the lightest and can show itself in lower energy collisions.

In all, the LHC’s new avatar marks a big stride forward not just in the energy frontier but also in the intensity and cosmic frontiers. With its ability to produce and track more collisions per second as well as chart the least explored territories of the ancient cosmos, it’d be foolish to think this gigantic machine’s domain is confined to particle physics and couldn’t extend to fuel cells, medical diagnostics or achieving systems-reliability in IT.

Here’s a fitting video released by CERN to mark this momentous occasion in the history of high-energy physics.

Featured image: A view of the LHC. Credit: CERN

Update: After engineers spotted a short-circuit glitch in a cooled part of the LHC on March 21, its restart was postponed from March 23 by a few weeks. However, CERN has assured that its a fully understood problem and that it won’t detract from the experiment’s goals for the year.

New Higgs results show signs of SUSY

Two years ago, physicists working on the Large Hadron Collider first announced the discovery of a Higgs boson-like particle, setting the high-energy physics community atwitter. And it was only a couple weeks ago that physicists also announced that the particle was definitely the one predicted by the sturdy Standard Model of particle physics, the theory that governs the Higgs boson’s properties and behavior.

But new results from the ongoing International Conference on High Energy Physics in Valencia, Spain, could add a twist to this plot. Physicists announced that they had evidence – albeit not strong enough – that the Higgs boson was showing signs of disobeying the model.

Members of the ATLAS and CMS collaborations, who work with the detectors of that name, said they had results showing the Higgs boson was decaying into a pair of particles called W bosons at a rate some 20% higher than predicted by the Standard Model. This non-compliance will be a breath of fresh air for physicists who have been faithful to a potent but as yet unobserved theory of new physics called supersymmetry, in short and fondly SUSY.

The W boson mediates the decay of radioactive substances in nature. At sufficiently high energies, such as produced inside the Large Hadron Collider (LHC), these bosons are produced by a multitude of particle interactions. Since their discovery in 1983, they have been widely studied. In these circumstances, announcing signs of SUSY through Higgs decays into WW pairs provides little room for uncertainties.

SUSY predicts that for every fermion, or matter particle, of the Standard Model there is a partner particle that is a boson called a sfermion. Conversely, for every boson, or force particle, of the Standard Model there is a partner particle that is a fermion called a bosino. Physicists who believe SUSY is a plausible theory use these extra particles to solve problems that the Standard Model can’t. One of them is that of dark matter; another is to explain why the Higgs boson weighs much lighter than it should.

Jong Soo Kim et al have described how the anomalous decay rates could be explained using a simple version of SUSY in a pre-print paper uploaded to arXiv on June 27. The paper is playfully titled ‘Stop that ambulance! New physics at the LHC?‘. The ‘Stop’ is a reference to the name of the suppersymmetric partner of the top quark. The authors describe how a combination of supersymmetric particles including the stop boson could explain the new results with only a 1-in-370 chance of error. Even though this means physicists have a confidence of 99.7% in the results, it’s still not high to claim evidence. When the LHC comes online in 2015, physicists will be eager to put these results to the test.

The paper’s title might also refer to a comment that physicist Chris Parkes, spokesperson for the UK participation in the LHCB experiment at the LHC, made to the BBC during the Hadron Collider Physics Symposium in Kyoto, Japan, in November 2012. Results had been announced of the B_s meson decaying into lighter particles at a rate predicted exactly by the Standard Model, nudging SUSY further toward impossibility. Parkes had said, “Supersymmetry may not be dead but these latest results have certainly put it into hospital.”