Start of LHC's 2016 Run Suffused With Hopes of a New Particle

This year is when we might discover another foundational piece of our origins or when we realise the breadth of the epistemic emptiness that stretches between ourselves and the physics that made us.

A computer's reconstruction of the diphoton event, indicating a particle weighing around 750 GeV/c2, observed by the ATLAS detector. Credit: ATLAS/CERN

A computer’s reconstruction of the diphoton event, indicating a particle weighing around 750 GeV/c2, observed by the ATLAS detector. Credit: ATLAS/CERN

What else remains to be understood that can be understood? What, perchance, is not dreamt of in our philosophies? … Surely, there have to be some clues somewhere. Or maybe we’re just not being clever enough? Are we misunderstanding what nature is telling us?

– Leon Lederman & Christopher Hill, Beyond the God Particle, p. 251

In April 2015, the Large Hadron Collider (LHC) was switched on after 18 months of maintenance and repairs. Two months later, it smashed protons together at record energies, yielding a flood of new data. In November, it wound down for the winter. In March 2016, the machine reopened for business. In the first week of June this year, it will smash protons together at the same high energies to probe their innards. The data recorded from these collisions will be accumulated until July; cleaned up for presentation in August; and the final results made available by December 2016. Then come either celebrations or low spirits.

Every week or so, Europe’s premier nuclear research facility (CERN), which maintains the LHC, holds a seminar presenting new results gleaned from data and corresponding research. These are droll affairs – at least to the mediapersons listening in – because they often present incremental and anodyne results. On December 15, 2015, however, the seminar hall was packed while hundreds of people from around the world tuned in to the live webcast. The reason? Physicists were presenting the latest data from collisions conducted in June that year. A few charts in particular showed something odd.

The oddity was apparent because of its well-defined background, the Standard Model of particle physics, a clutch of equations dictating how elementary particles should behave. Since the 1970s, the Standard Model has been the final word on all things particle physics. It started off with a few particles, putting them together to predict patterns in their behaviour, and based on that predicted newer particles. They were all found (the last prediction to be found was the Higgs boson in 2013), and the Standard Model became preeminent. But then came the darkness.

At the December 2015 seminar, physicists James Olsen and Marumi Kado were presenting some numbers that seemed to suggest there was a new particle weighing about 750 GeV/c2 (a proton at rest weighs about 0.9 GeV/c2; the Higgs boson, about 126 GeV/c2). That’s one heavy particle – and more importantly, the Standard Model doesn’t predict such a particle. Because the LHC smashes together many billions of protons together in a single experiment, physicists have to deal with a preponderance of noise in the resulting data. And the numbers Olsen and Kado were presenting weren’t as free of noise as the watching attending hundreds would’ve liked it to be. The process was like trying to glimpse the shape of a pebble from a few metres away in a dust-storm. More work was needed to clean the picture up, separating the relevant collisions from a graffiti of irrelevant ones. In the meantime, however, the possibility of a new particle at 750 GeV was in itself exciting.

Why? Because the Standard Model must be wrong, one or some of its equations faulty in some way – though physicists know not how. For all its excellent predictions, the model hasn’t been able to answer some fundamental questions in physics. For example, it cannot say how the Higgs boson gets its own mass or why the force of gravity is a 100-million-trillion-trillion-times weaker than the fundamental nuclear forces. Answering these questions would indeed patch some big holes in the Standard Model – but so far, physicists haven’t found a way to patch them without causing a tear in another part of the model’s fabric. In other words, the Standard Model is in some way incomplete, and the only way to verify would be to find something it doesn’t predict.

In March this year, at an annual conference held in an Italian town named La Thuile, physicists presented marginally enhanced versions of the December 2015 data. Earlier, Olsen’s team had presented more pessimistic prospects for the particle than Kado’s had. But at La Thuile, Olsen & co. came through as well, slightly bolstering the odds of its existence. The hope and muted excitement carried over from December had already produced over 200 research papers by then, and the numbers have only risen since.

A few ideas have taken greater hold of physicists’ imaginations of what the new particle could be (should it be found) from among all the speculations. A fascinating one among them posits that the 750 GeV/c2 particle could be a kind of a graviton, a fundamental particle mediating the force of gravity (the leader of one of the experimental groups at the LHC had said that they stumbled upon the possible-particle when looking for the graviton). Lawrence M. Krauss and the Nobel Laureate Frank Wilczek argued in a March 2014 paper that, should the theory of cosmic inflation also become validated, gravity could be dealt with through the principles of quantum mechanics. Currently, our best understanding of this force is via Albert Einstein’s theories of relativity, which have resisted reconciliation with quantum mechanics.

Some also believe the particle could be a heavier version of the Higgs boson. Others believe it could be a constituent of dark matter, or a supersymmetric particle – a particle whose existence is implied by the theory of supersymmetry, a frontrunner to subsume the Standard Model but which hasn’t been observed in action yet. Some others don’t want to get their hopes up, suggesting that it is a heavy composite of 12 particles – to be precise, six matter-making particles called top quarks and six of their antimatter counterparts. (Why don’t they immediately annihilate? Because when six quarks and six antiquarks are bound together as a bigger particle, their interactions and exchange of energies make for a more complex system than is conducive to simple annihilation.) Even others take a “nonstandard” view of the data, arguing that the shadow glimpsed at 750 GeV/c2 could’ve been cast by a much heavier particle.

For each of these speculations, the June collisions can’t happen soon enough (already thwarted once by an unfortunate weasel that chewed through a power line leading to one of the LHC’s pre-accelerators, postponing experiments by two weeks and killing itself). In fact, more than the detectors just being tuned to observe collisions even more intently this time, physicist Tommaso Dorigo reports that two of them (TOTEM and CMS) are going to be teamed up so their combined readings have drastically reduced noise.

There is a small chance that the fate of the Standard Model hangs in the balance and many of the physicists who contributed to its growth wish they are proved wrong, that the model breaks. On the other hand, if the 750 GeV/csignal turns out to be something the Standard Model is able to account for, it will be more of the old and nagging discomfiture. The LHC is the most powerful microscope (technically a femtoscope) we have, and its not finding anything will signal that we still remain – despite millions of human-hours and billions of dollars spent – out of reach of the forces that created the universe we inhabit.

And why should you care? Don’t – at the risk of missing out on having a window seat at either the moment we might discover another foundational piece of our origins… or the moment we realise the true breadth of the epistemic emptiness that stretches between ourselves and the ultimate physics that made us. Wouldn’t that be maddening?

Out of the mid-wood’s twilight
Into the meadow’s dawn,
Ivory limbed and brown-eyed,
Flashes my Faun!

He skips through the copses singing,
And his shadow dances along,
And I know not which I should follow,
Shadow or song!

O Hunter, snare me his shadow!
O Nightingale, catch me his strain!
Else moonstruck with music and madness
I track him in vain!

– Oscar Wilde, In the Forest