Multiple solutions in supersymmetry and the Higgs

susyB.C. Allanach
Weak-scale supersymmetry is a well motivated, if speculative, theory beyond the Standard Model of particle physics.
It solves the thorny issue of the Higgs mass, namely: how can it be stable to quantum corrections, when they are expected to be 1015 times bigger than its mass? The experimental signal of the theory is the production and measurement of supersymmetric particles in the Large Hadron Collider experiments.
No such particles have been seen to date, but hopes are high for the impending run in 2015. Searches for supersymmetric particles can be difficult to interpret.
Here, we shall discuss the fact that, even given a well defined model of supersymmetry breaking with few parameters, there can be multiple solutions.
These multiple solutions are physically different, and could potentially mean that points in parameter space have been ruled out by interpretations of LHC data when they shouldn’t have been.
We shall review the multiple solutions and illustrate their existence in a universal model of supersymmetry breaking.
Read more at http://arxiv.org/pdf/1401.8185v1.pdf

Peter Higgs: I wouldn’t be productive enough for today’s academic system

Physicist doubts work like Higgs boson identification achievable now as academics are expected to ‘keep churning out papers’

Peter Higgs: 'Today I wouldn't get an academic job. It's as simple as that'. Photograph: David Levene for the Guardian

Peter Higgs: ‘Today I wouldn’t get an academic job. It’s as simple as that’. Photograph: David Levene for the Guardian

Peter Higgs, the British physicist who gave his name to the Higgs boson, believes no university would employ him in today’s academic system because he would not be considered “productive” enough.

The emeritus professor at Edinburgh University, who says he has never sent an email, browsed the internet or even made a mobile phone call, published fewer than 10 papers after his groundbreaking work, which identified the mechanism by which subatomic material acquires mass, was published in 1964.

He doubts a similar breakthrough could be achieved in today’s academic culture, because of the expectations on academics to collaborate and keep churning out papers. He said: “It’s difficult to imagine how I would ever have enough peace and quiet in the present sort of climate to do what I did in 1964.”

Speaking to the Guardian en route to Stockholm to receive the 2013 Nobel prize for science, Higgs, 84, said he would almost certainly have been sacked had he not been nominated for the Nobel in 1980.

Edinburgh University’s authorities then took the view, he later learned, that he “might get a Nobel prize – and if he doesn’t we can always get rid of him”.

Higgs said he became “an embarrassment to the department when they did research assessment exercises”. A message would go around the department saying: “Please give a list of your recent publications.” Higgs said: “I would send back a statement: ‘None.’ ”

By the time he retired in 1996, he was uncomfortable with the new academic culture. “After I retired it was quite a long time before I went back to my department. I thought I was well out of it. It wasn’t my way of doing things any more. Today I wouldn’t get an academic job. It’s as simple as that. I don’t think I would be regarded as productive enough.”

Higgs revealed that his career had also been jeopardised by his disagreements in the 1960s and 70s with the then principal, Michael Swann, who went on to chair the BBC. Higgs objected to Swann’s handling of student protests and to the university’s shareholdings in South African companies during the apartheid regime. “[Swann] didn’t understand the issues, and denounced the student leaders.”

He regrets that the particle he identified in 1964 became known as the “God particle”.

He said: “Some people get confused between the science and the theology. They claim that what happened at Cern proves the existence of God.”

An atheist since the age of 10, he fears the nickname “reinforces confused thinking in the heads of people who are already thinking in a confused way. If they believe that story about creation in seven days, are they being intelligent?”

He also revealed that he turned down a knighthood in 1999. “I’m rather cynical about the way the honours system is used, frankly. A whole lot of the honours system is used for political purposes by the government in power.”

He has not yet decided which way he will vote in the referendum on Scottish independence. “My attitude would depend a little bit on how much progress the lunatic right of the Conservative party makes in trying to get us out of Europe. If the UK were threatening to withdraw from Europe, I would certainly want Scotland to be out of that.”

He has never been tempted to buy a television, but was persuaded to watch The Big Bang Theory last year, and said he wasn’t impressed.
Read more at http://www.theguardian.com/science/2013/dec/06/peter-higgs-boson-academic-system

The tao of modern physics

Shivaji Sondhi
In the bulk of the commentary on the discovery of the Higgs particle at CERN and the recent award of the Nobel prize to Peter Higgs and François Englert, one astonishing aspect has been largely overlooked. This discovery points to one of the most central aspects of postwar physics — its unity across domains at distances (or energies) separated by vast gulfs that have allowed ideas to jump between very different physical problems. In the case of the Higgs particle, its discovery at an energy of one hundred billion electron volts in a complicated special purpose machine is, in a mathematical sense, a precise analogue of a well-understood phenomenon in ordinary metals at an energy of a thousandth of an electron volt — one hundred trillion times lower!

Indeed, this analogy is how the puzzle underlying the Higgs particle was first solved by Philip Anderson in 1963, a year before the papers by Higgs and Englert and Robert Brout that were honoured with the Nobel. Anderson, now 89, is widely regarded as the greatest living condensed matter physicist, a maestro of the part of physics that tries to understand how the small set of subatomic forces and particles can lead to the infinite variety of the matter we see around us. He has led a spectacular career during which he picked up a Nobel in 1977 for completely different work, and could have collected at least two more.

Back in 1963, Anderson had already played a key role in understanding the general phenomenon of “spontaneous symmetry breaking” in condensed matter physics in parallel with important developments in particle physics. An everyday example of this phenomenon is the formation of ice from water. While the molecules in water resemble the crowd in Times Square on a busy day with no clear preference for where they want to be, the molecules in ice are arranged in an array like an honour guard at attention. Their choice of particular positions breaks the symmetry embodied in a lack of positional preference.

More immediately, Anderson had been one of the central players in elucidating the physics of superconductivity, or why metals permit electric current to flow without loss when sufficiently cold. Superconductivity involves an unusual broken symmetry, but with the complication of electromagnetic forces that act over large distances. It was understood by Anderson that a “massless gauge field” (describing ordinary electromagnetic forces) could combine with a “massless Goldstone mode” (a signature of symmetry breaking) to yield purely massive excitations. Roughly, this reflects the dislike that superconductors exhibit for magnetic fields, termed the Meissner effect and often dramatised by levitating magnets above pieces of superconductors.

At this point, Anderson came across particle physicists trying to rescue an appealing potential description of short-ranged forces among the zoo of particles being discovered in accelerators. This description had one key thing wrong — the gauge fields were massless and thus described long-ranged forces. Anderson realised that by introducing a second wrong — a massless Goldstone boson due to symmetry breaking — he could make a right. Today, this magic trick is commonly referred to as the Anderson-Higgs mechanism, to credit Higgs with the subsequent realisation that the mechanism implied a specific additional massive particle Anderson had overlooked. In any event, by staring into a piece of metal, Anderson had divined the solution to a puzzle about fundamental particles.

Now, the energy involved in superconductivity is a thousandth of an electron volt while the energy of the Higgs particle is a hundred trillion times larger, or alternately the size of the Higgs particle is a hundred trillion times smaller than the size of the smallest superconducting unit, the so-called “Cooper pair” of electrons. Why is it that the same mathematics can be used to describe both?

The explanation for this astonishing fact is a central meta-idea in postwar physics, that of the effective field theory. It states that if you don’t look too closely at the spatial details, the mathematics simplifies greatly into a set of “field theories”, which then provide a unifying mathematical framework for a vast range of phenomena. This meta-idea itself has a precise mathematical formulation known as “universality under renormalisation group flows”.

Metals are made of electrons and nuclei, but when we smooth over such detail, we end up with the field theory Anderson considered. In particle physics, the details being smoothed over are unknown — perhaps described by string theory — and we end up with a close cousin of Anderson’s field theory. What Anderson called a mode, Higgs called a particle, but both were describing a disturbance in an underlying medium, one known and the other unknown.

The ubiquity of effective field theories means that the Anderson-Higgs mechanism is by no means the only example of tight analogies between far separated phenomena in modern physics. To take one recent example, the work of particle physicist Edward Witten on topological field theories in the 1980s, for which he won a Fields medal in mathematics, has turned out to be central to our understanding of the quantum Hall effect in semiconductor systems, even though it was designed to do no such thing. Even this writer, also a condensed matter physicist, has had the (far more modest) pleasure of discovering in the same semiconductor systems “skyrmions” 15 orders of magnitude larger than those considered by particle physicist Tony Skyrme as descriptions of protons and neutrons.

So, the discovery of the Higgs particle is a triumph for this syncretic view built into modern physics. It turns out that space devoid of visible particles has something deeply in common with a superconducting metal. Further, it tells us that it was not always so: when the universe was younger and hotter, it resembled more a piece of superconductor heated to the point where the superconductivity vanishes, and thus there was no Higgs particle to speak of.

This brings me to the Nobel prize. I believe the committee missed an opportunity in not including Anderson along with Higgs and Englert. It would have been a more accurate accounting of the credit on this particular discovery and a deserved honour for a man whose contributions are legion. Above all, it would have paid tribute to the remarkable intellectual unity of modern physics.

The writer is a professor of physics at Princeton University, US

http://www.indianexpress.com/news/the-tao-of-modern-physics/1195124/0

Stephen Hawking: physics would be ‘more interesting’ if Higgs boson hadn’t been found

Professor Stephen Hawking: 'Throughout my life, I have had a gambling problem.' Photograph: Murdo MacLeod for the Guardian

Professor Stephen Hawking: ‘Throughout my life, I have had a gambling problem.’ Photograph: Murdo MacLeod for the Guardian

Physics would have been “far more interesting” if scientists had been unable to find the Higgs boson at the Large Hadron Collider (LHC) in Cern, according to Stephen Hawking, who has admitted to losing a bet as a result of the discovery in July last year.
The world-famous cosmologist was speaking at an event to mark the launch of a new exhibit on the LHC at London’s Science Museum and, in a speech, discussing the unanswered questions at the edges of modern physics as part of a history of his own work in the field.

Though the Higgs boson was predicted by theory in the early 1960s, not everyone believed it would be found. If it had not been found, physicists would have had to go back to the drawing board and rethink many of their fundamental ideas about the nature of particles and forces – an exciting prospect for some scientists.

“Physics would be far more interesting if it had not been found,” said Hawking. “A few weeks ago, Peter Higgs and François Englert shared the Nobel Prize for their work on the boson and they richly deserved it. Congratulations to them both. But the discovery of the new particle came at a personal cost. I had a bet with Gordon Kane of Michigan University that the Higgs particle wouldn’t be found. The Nobel Prize cost me $100.”

Hawking hoped the LHC would now move on from the Higgs boson to looking for evidence of more fundamental theories that explain the nature universe and, in particular, he hoped it would find the first evidence for the M theory, which is the best candidate that physicists have to unify all the four fundamental forces of nature. It unites gravity (which rules at the largest scales of the universe) with quantum mechanics (which controls the behaviour atoms and below). As yet there has been no incontrovertible experimental evidence to show that M theory is correct.

“There is still hope that we see the first evidence for M theory at the LHC particle accelerator in Geneva,” said Hawking. “From an M theory perspective, the collider only probes low energies, but we might be lucky and see a weaker signal of fundamental theory, such as supersymmetry. I think the discovery of supersymmetric partners for the known particles would revolutionise our understanding of the universe.”

Supersymmetry is the concept that each known particle – such as electrons, quarks and photons – has a heavier and as-yet-undetected “superpartner”. The superpartners of quarks and electrons, for example, are called squarks and selectrons; the superpartners of the Higgs, and of force carriers such as the photon, are the higgsino and photino. Experimental evidence for the idea has, however, been elusive.

In recalling the bet he made with physicist Gordon Kane about the Higgs boson, Hawking admitted to enjoying gambling. “Throughout my life, I have had a gambling problem. When I was 12, one of my friends bet another friend a bag of sweets that I would never come to anything. I don’t know if this bet was ever settled, and if so, which way it was decided. I had six or seven close friends, and we used to have long discussions and arguments about everything, from radio-controlled models to religion. One of the things we talked about was the origin of the universe, and whether it required a God to create it and set it going.”

Hawking is no stranger to losing bets about the nature of cosmos. Along with Kip Thorne, he bet John Preskill that information should be destroyed when something fell into a black hole. The so-called “information paradox” was troubling because Hawking’s calculations suggested that anything that fell into a black hole would be obliterated, including the information about what that stuff was. But destroying information is not allowed under the rules of quantum mechanics.

After 30 years of arguing, Hawking said he eventually found a resolution. “Information is not lost in black holes, but it is not returned in a useful way,” he said. “It is like burning an encyclopaedia. Information is not lost, but it is very hard to read.”

He gave Preskill a baseball encyclopaedia to concede his side of the bet. “Maybe I should have just given him the ashes. The fact that I used to think that information was destroyed in black holes was my biggest blunder. Well, at least it was my biggest blunder in science.”

Many of Hawking’s insights have come from studying the cosmos, and the scientist said people needed to get more interested in the space around us for more prosaic reasons. “We must also continue to go into space for the future of humanity. I don’t think we will survive another thousand years without escaping beyond our fragile planet. I therefore want to encourage public interest in space, and I’ve been getting my training in early,” he said. Hawking recently took part in a zero-gravity flight, which is part of the training for astronauts to experience the weightlessness of space.

Hawking said that the recent Nobel prize for Engelert and Higgs had been a reminder to him that it was “a glorious time to be alive, and doing research in theoretical physics. Our picture of the universe has changed a great deal in the last 50 years, and I’m happy if I have made a small contribution.”

He added: “So remember to look up at the stars and not down at your feet. Try to make sense of what you see and hold on to that childlike wonder about what makes the universe exist.”
Read more at http://www.theguardian.com/science/2013/nov/12/stephen-hawking-physics-higgs-boson-particle

2013 Nobel Prize in Physics: François Englert and Peter Higgs

François Englert and Peter W. Higgs are jointly awarded the Nobel Prize in Physics 2013 “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider”

François Englert and Peter Higgs meet for the first time, at CERN when the discovery of a Higgs particle was announced to the world on 4 July 2012. Photo: CERN, http://cds.cern.ch/record/1459503

François Englert and Peter Higgs meet for the first time, at CERN when the discovery of a Higgs particle was announced to the world on 4 July 2012. Photo: CERN, http://cds.cern.ch/record/1459503

François Englert and Peter W. Higgs are jointly awarded the Nobel Prize in Physics 2013 for the theory of how particles acquire mass. In 1964, they proposed the theory independently of each other (Englert together with his now deceased colleague Robert Brout). In 2012, their ideas were confirmed by the discovery of a so called Higgs particle at the CERN laboratory outside Geneva in Switzerland.

The awarded mechanism is a central part of the Standard Model of particle physics that describes how the world is constructed. According to the Standard Model, everything, from flowers and people to stars and planets, consists of just a few building blocks: matter particles. These particles are governed by forces mediated by force particles that make sure everything works as it should.

The entire Standard Model also rests on the existence of a special kind of particle: the Higgs particle. It is connected to an invisible field that fills up all space. Even when our universe seems empty, this field is there. Had it not been there, electrons and quarks would be massless just like photons, the light particles. And like photons they would, just as Einstein’s theory predicts, rush through space at the speed of light, without any possibility to get caught in atoms or molecules.
Nothing of what we know, not even we, would exist.

The Higgs particle, H, completes the Standard Model of particle physics that describes building blocks of the universe.

The Higgs particle, H, completes the Standard Model of particle physics that describes building blocks of the universe.

Both François Englert and Peter Higgs were young scientists when they, in 1964, independently of each other put forward a theory that rescued the Standard Model from collapse. Almost half a century later, on Wednesday 4 July 2012, they were both in the audience at the European Laboratory for Particle Physics, CERN, outside Geneva, when the discovery of a Higgs particle that finally confirmed the theory was announced to the world.

The model that created order

The idea that the world can be explained in terms of just a few building blocks is old. Already in 400 BC, the philosopher Democritus postulated that everything consists of atoms —átomos is Greek for indivisible.

Today we know that atoms are not indivisible. They consist of electrons that orbit an atomic
nucleus made up of neutrons and protons. And neutrons and protons, in turn, consist of smaller particles called quarks. Actually, only electrons and quarks are indivisible according to the Standard Model.
The atomic nucleus consists of two kinds of quarks, up quarks and down quarks. So in fact, three elementary particles are needed for all matter to exist: electrons, up quarks and down quarks. But during the 1950s and 1960s, new particles were unexpectedly observed in both cosmic radiation and at newly constructed accelerators, so the Standard Model had to include these new siblings of electrons and quarks.

Besides matter particles, there are also force particles for each of nature’s four forces — gravitation, electro magnetism, the weak force and the strong force. Gravitation and electromagnetism are the most well-known, they attract or repel, and we can see their effects with our own eyes. The strong force acts upon quarks and holds protons and neutrons together in the nucleus, whereas the weak force is responsible for radioactive decay, which is necessary, for instance, for nuclear processes inside the Sun.

The Standard Model of particle physics unites the fundamental building blocks of nature and three of the four forces known to us (the fourth, gravitation, remains outside the model). For long, it was an enigma how these forces actually work. For instance, how does the piece of metal that is attracted to the magnet know that the magnet is lying there, a bit further away? And how does the Moon feel the gravity of Earth?

Invisible fields fill space

The explanation offered by physics is that space is filled with many invisible fields. The gravitational field, the electromagnetic field, the quark field and all the other fields fill space, or rather, the four dimensional space-time, an abstract space where the theory plays out. The Standard Model is a quantum field theory in which fields and particles are the essential building blocks of the universe.

In quantum physics, everything is seen as a collection of vibrations in quantum fields. These vibrations are carried through the field in small packages, quanta, which appear to us as particles. Two kinds of fields exist: matter fields with matter particles, and force fields with force particles — the mediators of forces. The Higgs particle, too, is a vibration of its field — often referred to as the Higgs field.

Without this field the Standard Model would collapse like a house of cards, because quantum field theory brings infinities that have to be reined in and symmetries that cannot be seen. It was not until François Englert with Robert Brout, and Peter Higgs, and later on several others, showed that the Higgs field can break the symmetry of the Standard Model without destroying the theory that the model got accepted.

This is because the Standard Model would only work if particles did not have mass. As for the electromagnetic force, with its massless photons as mediators, there was no problem. The weak force, however, is mediated by three massive particles; two electrically charged W particles and one Z particle. They did not sit well with the light-footed photon. How could the electroweak force, which unifies electromagnetic and weak forces, come about? The Standard Model was threatened. This is where Englert, Brout and Higgs entered the stage with the ingenious mechanism for particles to acquire mass that managed to rescue the Standard Model.

The ghost-like Higgs field

The Higgs field is not like other fields in physics. All other fields vary in strength and become zero at their lowest energy level. Not the Higgs field. Even if space were to be emptied completely, it would still be filled by a ghost-like field that refuses to shut down: the Higgs field. We do not notice it; the Higgs field is like air to us, like water to fish. But without it we would not exist, because particles acquire mass only in contact with the Higgs field. Particles that do not pay attention to the Higgs field do not acquire mass, those that interact weakly become light, and those that interact intensely become heavy. For example, electrons, which acquire mass from the field, play a crucial role in the creation and holding together of atoms and molecules. If the Higgs field suddenly disappeared, all matter would collapse as the suddenly massless electrons dispersed at the speed of light.

So what makes the Higgs field so special? It breaks the intrinsic symmetry of the world. In nature, symmetry abounds; faces are regularly shaped, flowers and snowflakes exhibit various kinds of geometric symmetries. Physics unveils other kinds of symmetries that describe our world, albeit on a deeper level. One such, relatively simple, symmetry stipulates that it does not matter for the results if a laboratory experiment is carried out in Stockholm or in Paris. Neither does it matter at what time the experiment is carried out. Einstein’s special theory of relativity deals with symmetries in space and time, and has become a model for many other theories, such as the Standard Model of particle physics. The equations of the Standard Model are symmetric; in the same way that a ball looks the same from whatever angle you look at it, the equations of the Standard Model remain unchanged even if the perspective that defines them is changed.

The principles of symmetry also yield other, somewhat unexpected, results. Already in 1918, the
German mathematician Emmy Noether could show that the conservation laws of physics, such as the laws of conservation of energy and conservation of electrical charge, also originate in symmetry.
Symmetry, however, dictates certain requirements to be fulfilled. A ball has to be perfectly round; the tiniest hump will break the symmetry. For equations other criteria apply. And one of the symmetries of the Standard Model prohibits particles from having mass. Now, this is apparently not the case in our world, so the particles must have acquired their mass from somewhere. This is where the now-awarded mechanism provided a way for symmetry to both exist and simultaneously be hidden from view.

The symmetry is hidden but is still there

Our universe was probably born symmetrical. At the time of the Big Bang, all particles were massless and all forces were united in a single primordial force. This original order does not exist anymore — its symmetry has been hidden from us. Something happened just 10–11 seconds after the Big Bang. The Higgs field lost its original equilibrium. How did that happen?

It all began symmetrically. This state can be described as the position of a ball in the middle of a round bowl, in its lowest energy state. With a push the ball starts rolling, but after a while it returns down to the lowest point.

However, if a hump arises at the centre of the bowl, which now looks more like a Mexican hat, the position at the middle will still be symmetrical but has also become unstable. The ball rolls downhill in any direction. The hat is still symmetrical, but once the ball has rolled down, its position away from the centre hides the symmetry. In a similar manner the Higgs field broke its symmetry and found a stable energy level in vacuum away from the symmetrical zero posi tion. This spontaneous symmetry breaking is also referred to as the Higgs field’s phase transition; it is like when water freezes to ice.

The universe was probably created symmetric, and the invisible Higgs field had a symmetry that corresponds to the stable position of a ball in the middle of a round bowl. But already 10–11 seconds after the Big Bang, the Higgs field broke the symmetry when it moved its lowest level of energy away from the symmetrical centre-point.

The universe was probably created symmetric, and the invisible Higgs field had a symmetry that corresponds to the stable position of a ball in the middle of a round bowl. But already 10–11 seconds after the Big Bang, the Higgs field broke the symmetry when it moved its lowest level of energy away from the symmetrical centre-point.

In order for the phase transition to occur, four particles were required but only one, the Higgs particle, survived. The other three were consumed by the weak force mediators, two electrically charged W particles and one Z particle, which thereby got their mass. In that way the symmetry of the electroweak force in the Standard Model was saved — the symmetry between the three heavy particles of the weak force and the massless photon of the electromagnetic force remains, only hidden from view.

Extreme machines for extreme physics

The Nobel Laureates probably did not imagine that they would get to see the theory confirmed in their lifetime. It took an enormous effort by physicists from all over the world. For a long time two laboratories, Fermilab outside Chicago, USA, and CERN on the Franco-Swiss border, competed in trying to discover the Higgs particle. But when Fermilab’s Tevatron accelerator was closed down a couple of years ago, CERN became the only place in the world where the hunt for the Higgs particle would continue.

CERN was established in 1954, in an attempt to reconstruct European research, as well as relations between European countries, after the Second World War. Its membership currently comprises twenty states, and about a hundred nations from all over the world collaborate on the projects.

CERN’s grandest achievement, the particle collider LHC (Large Hadron Collider) is probably the largest and the most complex machine ever constructed by humans. Two research groups of some 3,000 scientists chase particles with huge detectors — ATLAS and CMS. The detectors are located 100 metres below ground and can observe 40 million particle collisions per second. This is how often the particles can collide when injected in opposite directions into the circular LHC tunnel, 27 kilometres long.

Protons are injected into the LHC every ten hours, one ray in each direction. A hundred thousand billion protons are lumped together and compressed into an ultra-thin ray — not entirely an easy endeavour since protons with their positive electrical charge rather aim to repel one another. They move at 99.99999 per cent of the speed of light and collide with an energy of approximately 4 TeV each and 8 TeV combined (one teraelectronvolt = a thousand billion electronvolts). One TeV may not be that much energy, it more or less equals that of a flying mosquito, but when the energy is packed into a single proton, and you get 500 trillion such protons rushing around the accelerator, the energy of the ray equals that of a train at full speed. In 2015 the energy will be almost the double in the LHC.

A possible discovery in the ATLAS detector shows tracks of four muons (red) that have been created by the decay of the short-lived Higgs particle. Image: CERN, http://cds.cern.ch/record/1459496

A possible discovery in the ATLAS detector shows tracks of four muons (red) that have been created by the decay of the short-lived Higgs particle.
Image: CERN, http://cds.cern.ch/record/1459496

A Higgs particle can have been created and almost instantly decayed into two photons. Their tracks (green) are visible here in the CMS detector. Image: CERN, http://cds.cern.ch/record/1459459

A Higgs particle can have been created and almost instantly decayed into two photons. Their tracks (green) are visible here in the CMS detector. Image: CERN, http://cds.cern.ch/record/1459459

A puzzle inside the puzzle

Particle experiments are sometimes compared to the act of smashing two Swiss watches together in order to examine how they are constructed. But it is actually much more difficult than so, because the particles scientists look for are entirely new — they are created from the energy released in the collision.

According to Einstein’s well-known formula E = mc2, mass is a kind of energy. And it is the magic of this equation that makes it possible, even for massless particles, to create something new when they collide; like when two photons collide and create an electron and its antiparticle, the positron, or when a Higgs particle is created in the collision of two gluons, if the energy is high enough.
The protons are like small bags filled with particles — quarks, antiquarks and gluons. The majority of them pass one another without much ado; on average, each time two particle swarms collide only twenty full frontal collisions occur. Less than one collision in a billion might be worth following through. This may not sound much, but each such collision results in a sparkling explosion of about a thousand particles. At 125 GeV, the Higgs particle turned out to be over a hundred times heavier than a proton and this is one of the reasons why it was so difficult to produce.
However, the experiment is far from finished. The scientists at CERN hope to bring further ground breaking discoveries in the years to come. Even though it is a great achievement to have found the Higgs particle — the missing piece in the Standard Model puzzle — the Standard Model is not the final piece in the cosmic puzzle.

One of the reasons for this is that the Standard Model treats certain particles, neutrinos, as being vir tually massless, whereas recent studies show that they actually do have mass. Another reason is that the model only describes visible matter, which only accounts for one fifth of all matter in the universe.
The rest is dark matter of an unknown kind. It is not immediately apparent to us, but can be observed by its gravitational pull that keeps galaxies together and prevents them from being torn apart.

In all other respects, dark matter avoids getting involved with visible matter. Mind you, the Higgs
particle is special; maybe it could manage to establish contact with the enigmatic darkness. Scientists hope to be able to catch, if only a glimpse, of dark matter, as they continue the chase of unknown particles in the LHC in the coming decades.

http://www.nobelprize.org/index.html

Higgs Boson: The Inside Scoop

IhiggsIn July of 2012, physicists found a particle that might be the long-sought Higgs boson. In the intervening months, scientists have worked hard to pin down the identity of this newly-found discovery. In this video, Fermilab’s Dr. Don Lincoln describes researcher’s current understanding of the particle that might be the Higgs. The evidence is quite strong but the final chapter of this story might well require the return of the Large Hadron Collider to full operations in 2015.

On the Trail of Dark Energy: Physicists Propose Higgs Boson ‘Portal’

One of the biggest mysteries in contemporary particle physics and cosmology is why dark energy, which is observed to dominate energy density of the universe, has a remarkably small (but not zero) value. This value is so small, it is perhaps 120 orders of magnitude less than would be expected based on fundamental physics.

Illustration of Standard Model particles. (Credit: Image courtesy of DOE/Fermi National Accelerator Laboratory)

Illustration of Standard Model particles. (Credit: Image courtesy of DOE/Fermi National Accelerator Laboratory)

Resolving this problem, often called the cosmological constant problem, has so far eluded theorists.
Now, two physicists — Lawrence Krauss of Arizona State University and James Dent of the University of Louisiana-Lafayette — suggest that the recently discovered Higgs boson could provide a possible “portal” to physics that could help explain some of the attributes of the enigmatic dark energy, and help resolve the cosmological constant problem.
In their paper, “Higgs Seesaw Mechanism as a Source for Dark Energy,” Krauss and Dent explore how a possible small coupling between the Higgs particle, and possible new particles likely to be associated with what is conventionally called the Grand Unified Scale — a scale perhaps 16 orders of magnitude smaller than the size of a proton, at which the three known non-gravitational forces in nature might converge into a single theory — could result in the existence of another background field in nature in addition to the Higgs field, which would contribute an energy density to empty space of precisely the correct scale to correspond to the observed energy density.
The paper was published online, Aug. 9, in Physical Review Letters.
Current observations of the universe show it is expanding at an accelerated rate. But this acceleration cannot be accounted for on the basis of matter alone. Putting energy in empty space produces a repulsive gravitational force opposing the attractive force produced by matter, including the dark matter that is inferred to dominate the mass of essentially all galaxies, but which doesn’t interact directly with light and, therefore, can only be estimated by its gravitational influence.
Because of this phenomenon and because of what is observed in the universe, it is thought that such ‘dark energy’ contributes up to 70 percent of the total energy density in the universe, while observable matter contributes only 2 to 5 percent, with the remaining 25 percent or so coming from dark matter.
The source of this dark energy and the reason its magnitude matches the inferred magnitude of the energy in empty space is not currently understood, making it one of the leading outstanding problems in particle physics today.
“Our paper makes progress in one aspect of this problem,” said Krauss, a Foundation Professor in ASU’s School of Earth and Space Exploration and Physics, and the director of the Origins Project at ASU. “Now that the Higgs boson has been discovered, it provides a possible ‘portal’ to physics at much higher energy scales through very small possible mixings and couplings to new scalar fields which may operate at these scales.”….

Read more at http://www.sciencedaily.com/releases/2013/08/130810063645.htm