Tag Archives: LHC

BigBang

What’s Next For the LHC?

As CERN’s Large Hadron Collider gears up for a restart in March 2015 after a refit that doubled its particle smashing power, researchers are pondering what may come next. During its previous run scientists uncovered signals identifying the long-sought Higgs boson. Now, particle physicists have their eyes and minds on more exotic, but no less significant, particle discoveries. And — of course — these come with suitably exotic names: gluino, photino, selectron, squark, axion — the list goes on. But beyond these creative names lie possible answers to some very big questions: What is the composition of dark matter (and even dark energy)? How does gravity fit in with all the other identified forces? Do other fundamental particles exist?

From the Smithsonian:

The Large Hadron Collider, the world’s biggest and most famous particle accelerator, will reopen in March after a years-long upgrade. So what’s the first order of business for the rebooted collider? Nothing less than looking for a particle that forces physicists to reconsider everything they think they know about how the universe works.

Since the second half of the twentieth century, physicists have used the Standard Model of physics to describe how particles look and act. But though the model explains pretty much everything scientists have observed using particle accelerators, it doesn’t account for everything they can observe in the universe, including the existence of dark matter.

That’s where supersymmetry, or SUSY, comes in. Supersymmetry predicts that each particle has what physicists call a “superpartner”—a more massive sub-atomic partner particle that acts like a twin of the particle we can observe. Each observable particle would have its own kind of superpartner, pairing bosons with “fermions,” electrons with “selectrons,” quarks with “squarks,” photons with “photinos,” and gluons with “gluinos.”

If scientists could identify a single superparticle, they could be on track for a more complete theory of particle physics that accounts for strange inconsistencies between existing knowledge and observable phenomena. Scientists used the Large Hadron Collider to identify Higgs boson particles in 2012, but it didn’t behave quite as they expected. One surprise was that its mass was much lighter than predicted—an inconsistency that would be explained by the existence of a supersymmetric particle.

Scientists hope that the rebooted—and more powerful—LHC will reveal just such a particle. “Higher energies at the new LHC could boost the production of hypothetical supersymmetric particles called gluinos by a factor of 60, increasing the odds of finding it,” reports Emily Conover for Science.

If the LHC were to uncover a single superparticle, it wouldn’t just be a win for supersymmetry as a theory—it could be a step toward understanding the origins of our universe. But it could also create a lot of work for scientists—after all, a supersymmetric universe is one that would hold at least twice as many particles.

Read the entire article here.

 

BigBang

The Large Hadron Collider is So Yesterday

CERN’s Large Hadron Collider (LHC) smashed countless particles into one another to reveal the Higgs Boson. A great achievement for all concerned. Yet what of the still remaining “big questions” of physics, and how will we find the answers?

From Wired:

The current era of particle physics is over. When scientists at CERN  announced last July that they had found the Higgs boson — which is responsible for giving all other particles their mass — they uncovered the final missing piece in the framework that accounts for the interactions of all known particles and forces, a theory known as the Standard Model.

And that’s a good thing, right? Maybe not.

The prized Higgs particle, physicists assumed, would help steer them toward better theories, ones that fix the problems known to plague the Standard Model. Instead, it has thrown the field  into a confusing situation.

“We’re sitting on a puzzle that is difficult to explain,” said particle physicist Maria Spiropulu of Caltech, who works on one of the LHC’s main Higgs-finding experiments, CMS.

It may sound strange, but physicists were hoping, maybe even expecting, that the Higgs would not turn out to be like they predicted it would be. At the very least, scientists hoped the properties of the Higgs would be different enough from those predicted under the Standard Model that they could show researchers how to build new models. But the Higgs’ mass  proved stubbornly normal, almost exactly in the place the Standard Model said it would be.

To make matters worse, scientists had hoped to find evidence for other strange particles. These could have pointed in the direction of theories beyond the Standard Model, such as the current favorite  supersymmetry, which posits the existence of a heavy doppelganger to all the known subatomic bits like electrons, quarks, and photons.

Instead, they were disappointed by being right. So how do we get out of this mess? More data!

Over the next few years, experimentalists will be churning out new results, which may be able to answer questions about dark matter, the properties of neutrinos, the nature of the Higgs, and perhaps what the next era of physics will look like. Here we take a look at the experiments that you should be paying attention to. These are the ones scientists are the most excited about because they might just form the next cracks in modern physics.

ALTAS and CMS
The Large Hadron Collider isn’t smashing protons right now. Instead, engineers are installing upgrades to help it search at even higher energies. The machine may be closed for business until 2015 but the massive amounts of data it has already collected is still wide open. The two main Higgs-searching experiments, ATLAS and CMS, could have plenty of surprises in store.

“We looked for the low-hanging fruit,” said particle physicist David Miller of the University of Chicago, who works on ATLAS. “All that we found was the Higgs, and now we’re going back for the harder stuff.”

What kind of other stuff might be lurking in the data? Nobody knows for sure but the collaborations will spend the next two years combing through the data they collected in 2011 and 2012, when the Higgs was found. Scientists are hoping to see hints of other, more exotic particles, such as those predicted under a theory known as supersymmetry. They will also start to understand the Higgs better.

See, scientists don’t have some sort of red bell that goes “ding” every time their detector finds a Higgs boson. In fact, ATLAS and CMS can’t actually see the Higgs at all. What they look for instead are the different particles that the Higgs decays into. The easiest-to-detect channels include when the Higgs decays to things like a quark and an anti-quark or two photons. What scientists are now trying to find out is exactly what percent of the time it decays to various different particle combinations, which will help them further pin down its properties.

It’s also possible that, with careful analysis, physicists would add up the percentages for each of the different decays and notice that they haven’t quite gotten to 100. There might be just a tiny remainder, indicating that the Higgs is decaying to particles that the detectors can’t see.

“We call that invisible decay,” said particle physicist Maria Spiropulu. The reason that might be exciting is that the Higgs could be turning into something really strange, like a dark matter particle.

We know from cosmological observations that dark matter has mass and, because the Higgs gives rise to mass, it probably has to somehow interact with dark matter. So the LHC data could tell scientists just how strong the connection is between the Higgs and dark matter. If found, these invisible decays could open up a whole new world of exploration.

“It’s fashionable to call it the ‘dark matter portal’ right now,” said Spiropulu.

NOVA and T2K
Neutrinos are oddballs in the Standard Model. They are tiny, nearly massless, and barely like interacting with any other members of the subatomic zoo. Historically, they have been the subject of  many surprising results and the future will probably reveal them to be even stranger. Physicists are currently trying to figure out some of their properties, which remain open questions.

“A very nice feature of these open questions is we know they all have answers that are accessible in the next round of experiments,” said physicist Maury Goodman of Argonne National Laboratory.

The US-based NOvA experiment will hopefully pin down some neutrino characteristics, in particular their masses. There are three types of neutrinos: electron, muon, and tau. We know that they have a very tiny mass — at least 10 billion times smaller than an electron — but we don’t know exactly what it is nor which of the three different types is heaviest or lightest.

NOvA will attempt to figure out this mass hierarchy by shooting a beam of neutrinos from Fermilab near Chicago 810 kilometers away to a detector in Ash River, Minnesota. A similar experiment in Japan called T2K is also sending neutrinos across 295 kilometers. As they pass through the Earth, neutrinos oscillate between their three different types. By comparing how the neutrinos look when they are first shot out versus how they appear at the distant detector, NOvA and T2K will be able to determine their properties with high precision.

T2K has been running for a couple years while NOvA is expected to begin taking data in 2014 and will run six years. Scientists hope that they will help answer some of the last remaining questions about neutrinos.

Read the entire article here.

Image: A simulation of the decay of a Higgs boson in a linear collider detector. Courtesy of Norman Graf / CERN.

BigBang

What’s Next at the LHC: Parallel Universe?

The Large Hadron Collider (LHC) at CERN made headlines in 2012 with the announcement of a probable discovery of the Higgs Boson. Scientists are collecting and analyzing more data before they declare an outright discovery in 2013. In the meantime, they plan to use the giant machine to examine even more interesting science — at very small and very large scales — in the new year.

[div class=attrib]From the Guardian:[end-div]

When it comes to shutting down the most powerful atom smasher ever built, it’s not simply a question of pressing the off switch.

In the French-Swiss countryside on the far side of Geneva, staff at the Cern particle physics laboratory are taking steps to wind down the Large Hadron Collider. After the latest run of experiments ends next month, the huge superconducting magnets that line the LHC’s 27km-long tunnel must be warmed up, slowly and gently, from -271 Celsius to room temperature. Only then can engineers descend into the tunnel to begin their work.

The machine that last year helped scientists snare the elusive Higgs boson – or a convincing subatomic impostor – faces a two-year shutdown while engineers perform repairs that are needed for the collider to ramp up to its maximum energy in 2015 and beyond. The work will beef up electrical connections in the machine that were identified as weak spots after an incident four years ago that knocked the collider out for more than a year.

The accident happened days after the LHC was first switched on in September 2008, when a short circuit blew a hole in the machine and sprayed six tonnes of helium into the tunnel that houses the collider. Soot was scattered over 700 metres. Since then, the machine has been forced to run at near half its design energy to avoid another disaster.

The particle accelerator, which reveals new physics at work by crashing together the innards of atoms at close to the speed of light, fills a circular, subterranean tunnel a staggering eight kilometres in diameter. Physicists will not sit around idle while the collider is down. There is far more to know about the new Higgs-like particle, and clues to its identity are probably hidden in the piles of raw data the scientists have already gathered, but have had too little time to analyse.

But the LHC was always more than a Higgs hunting machine. There are other mysteries of the universe that it may shed light on. What is the dark matter that clumps invisibly around galaxies? Why are we made of matter, and not antimatter? And why is gravity such a weak force in nature? “We’re only a tiny way into the LHC programme,” says Pippa Wells, a physicist who works on the LHC’s 7,000-tonne Atlas detector. “There’s a long way to go yet.”

The hunt for the Higgs boson, which helps explain the masses of other particles, dominated the publicity around the LHC for the simple reason that it was almost certainly there to be found. The lab fast-tracked the search for the particle, but cannot say for sure whether it has found it, or some more exotic entity.

“The headline discovery was just the start,” says Wells. “We need to make more precise measurements, to refine the particle’s mass and understand better how it is produced, and the ways it decays into other particles.” Scientists at Cern expect to have a more complete identikit of the new particle by March, when repair work on the LHC begins in earnest.

By its very nature, dark matter will be tough to find, even when the LHC switches back on at higher energy. The label “dark” refers to the fact that the substance neither emits nor reflects light. The only way dark matter has revealed itself so far is through the pull it exerts on galaxies.

Studies of spinning galaxies show they rotate with such speed that they would tear themselves apart were there not some invisible form of matter holding them together through gravity. There is so much dark matter, it outweighs by five times the normal matter in the observable universe.

The search for dark matter on Earth has failed to reveal what it is made of, but the LHC may be able to make the substance. If the particles that constitute it are light enough, they could be thrown out from the collisions inside the LHC. While they would zip through the collider’s detectors unseen, they would carry energy and momentum with them. Scientists could then infer their creation by totting up the energy and momentum of all the particles produced in a collision, and looking for signs of the missing energy and momentum.

[div class=attrib]Read the entire article following the jump.[end-div]

[div class=attrib]Image: The eight torodial magnets can be seen on the huge ATLAS detector with the calorimeter before it is moved into the middle of the detector. This calorimeter will measure the energies of particles produced when protons collide in the centre of the detector. ATLAS will work along side the CMS experiment to search for new physics at the 14 TeV level. Courtesy of CERN.[end-div]

BigBang

Higgs?

 

A week ago, on July 4, 2012 researchers at CERN told the world that they had found evidence of a new fundamental particle — the so-called Higgs boson, or something closely similar. If further particle collisions at CERN’s Large Hadron Collider uphold this finding over the coming years, this will rank as significant a discovery as that of the proton or the electro-magnetic force. While practical application of this discovery, in our lifetimes at least, is likely to be scant, it undeniably furthers our quest to understand the underlying mechanism of our existence.

So where might this discovery lead next?

[div class=attrib]From the New Scientist:[end-div]

“As a layman, I would say, I think we have it,” said Rolf-Dieter Heuer, director general of CERN at Wednesday’s seminar announcing the results of the search for the Higgs boson. But when pressed by journalists afterwards on what exactly “it” was, things got more complicated. “We have discovered a boson – now we have to find out what boson it is,” he said cryptically. Eh? What kind of particle could it be if it isn’t the Higgs boson? And why would it show up right where scientists were looking for the Higgs? We asked scientists at CERN to explain.

If we don’t know the new particle is a Higgs, what do we know about it?
We know it is some kind of boson, says Vivek Sharma of CMS, one of the two Large Hadron Collider experiments that presented results on Wednesday. There are only two types of elementary particle in the standard model: fermions, which include electrons, quarks and neutrinos, and bosons, which include photons and the W and Z bosons. The Higgs is a boson – and we know the new particle is too because one of the things it decays into is a pair of high-energy photons, or gamma rays. According to the rules of mathematical symmetry, only a boson could decay into exactly two other photons.

Anything else?
Another thing we can say about the new particle is that nothing yet suggests it isn’t a Higgs. The standard model, our leading explanation for the known particles and the forces that act on them, predicts the rate at which a Higgs of a given mass should decay into various particles. The rates of decay reported for the new particle yesterday are not exactly what would be predicted for its mass of about 125 gigaelectronvolts (GeV) – leaving the door open to more exotic stuff. “If there is such a thing as a 125 GeV Higgs, we know what its rate of decay should be,” says Sharma. But the decay rates are close enough for the differences to be statistical anomalies that will disappear once more data is taken. “There are no serious inconsistencies,” says Joe Incandela, head of CMS, who reported the results on Wednesday.

In that case, are the CERN scientists just being too cautious? What would be enough evidence to call it a Higgs boson?
As there could be many different kinds of Higgs bosons, there’s no straight answer. An easier question to answer is: what would make the new particle neatly fulfil the Higgs boson’s duty in the standard model? Number one is to give other particles mass via the Higgs field – an omnipresent entity that “slows” some particles down more than others, resulting in mass. Any particle that makes up this field must be “scalar”. The opposite of a vector, this means that, unlike a magnetic field, or gravity, it doesn’t have any directionality. “Only a scalar boson fixes the problem,” says Oliver Buchmueller, also of CMS.

When will we know whether it’s a scalar boson?
By the end of the year, reckons Buchmueller, when at least one outstanding property of the new particle – its spin – should be determined. Scalars’ lack of directionality means they have spin 0. As the particle is a boson, we already know its spin is a whole number and as it decays into two photons, mathematical symmetry again dictates that the spin can’t be 1. Buchmueller says LHC researchers will able to determine whether it has a spin of 0 or 2 by examining whether the Higgs’ decay particles shoot into the detector in all directions or with a preferred direction – the former would suggest spin 0. “Most people think it is a scalar, but it still needs to be proven,” says Buchmueller. Sharma is pretty sure it’s a scalar boson – that’s because it is more difficult to make a boson with spin 2. He adds that, although it is expected, confirmation that this is a scalar boson is still very exciting: “The beautiful thing is, if this turns out to be a scalar particle, we are seeing a new kind of particle. We have never seen a fundamental particle that is a scalar.”

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image: A typical candidate event including two high-energy photons whose energy (depicted by dashed yellow lines and red towers) is measured in the CMS electromagnetic calorimeter. The yellow lines are the measured tracks of other particles produced in the collision.[end-div]

BigBang

CDM: Cosmic Discovery Machine

We think CDM sounds much more fun than LHC, a rather dry acronym for Large Hadron Collider.

Researchers at the LHC are set to announce the latest findings in early July from the record-breaking particle smasher buried below the French and Swiss borders. Rumors point towards the discovery of the so-called Higgs boson, the particle theorized to give mass to all the other fundamental building blocks of matter. So, while this would be another exciting discovery from CERN and yet another confirmation of the fundamental and elegant Standard Model of particle physics, perhaps there is yet more to uncover, such as the exotically named “inflaton”.

[div class=attrib]From Scientific American:[end-div]

Within a sliver of a second after it was born, our universe expanded staggeringly in size, by a factor of at least 10^26. That’s what most cosmologists maintain, although it remains a mystery as to what might have begun and ended this wild expansion. Now scientists are increasingly wondering if the most powerful particle collider in history, the Large Hadron Collider (LHC) in Europe, could shed light on this mysterious growth, called inflation, by catching a glimpse of the particle behind it. It could be that the main target of the collider’s current experiments, the Higgs boson, which is thought to endow all matter with mass, could also be this inflationary agent.

During inflation, spacetime is thought to have swelled in volume at an accelerating rate, from about a quadrillionth the size of an atom to the size of a dime. This rapid expansion would help explain why the cosmos today is as extraordinarily uniform as it is, with only very tiny variations in the distribution of matter and energy. The expansion would also help explain why the universe on a large scale appears geometrically flat, meaning that the fabric of space is not curved in a way that bends the paths of light beams and objects traveling within it.

The particle or field behind inflation, referred to as the “inflaton,” is thought to possess a very unusual property: it generates a repulsive gravitational field. To cause space to inflate as profoundly and temporarily as it did, the field’s energy throughout space must have varied in strength over time, from very high to very low, with inflation ending once the energy sunk low enough, according to theoretical physicists.

Much remains unknown about inflation, and some prominent critics of the idea wonder if it happened at all. Scientists have looked at the cosmic microwave background radiation—the afterglow of the big bang—to rule out some inflationary scenarios. “But it cannot tell us much about the nature of the inflaton itself,” says particle cosmologist Anupam Mazumdar at Lancaster University in England, such as its mass or the specific ways it might interact with other particles.

A number of research teams have suggested competing ideas about how the LHC might discover the inflaton. Skeptics think it highly unlikely that any earthly particle collider could shed light on inflation, because the uppermost energy densities one could imagine with inflation would be about 10^50 times above the LHC’s capabilities. However, because inflation varied with strength over time, scientists have argued the LHC may have at least enough energy to re-create inflation’s final stages.

It could be that the principal particle ongoing collider runs aim to detect, the Higgs boson, could also underlie inflation.

“The idea of the Higgs driving inflation can only take place if the Higgs’s mass lies within a particular interval, the kind which the LHC can see,” says theoretical physicist Mikhail Shaposhnikov at the École Polytechnique Fédérale de Lausanne in Switzerland. Indeed, evidence of the Higgs boson was reported at the LHC in December at a mass of about 125 billion electron volts, roughly the mass of 125 hydrogen atoms.

Also intriguing: the Higgs as well as the inflaton are thought to have varied with strength over time. In fact, the inventor of inflation theory, cosmologist Alan Guth at the Massachusetts Institute of Technology, originally assumed inflation was driven by the Higgs field of a conjectured grand unified theory.

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image courtesy of Physics World.[end-div]

BigBang

Tour de France and the Higgs Particle

Two exciting races tracked through Grenoble, France this passed week. First, the Tour de France held one of the definitive stages of the 2011 race in Grenoble, the individual time trial. Second, Grenoble hosted the European Physical Society conference on High-Energy Physics. Fans of professional cycling and high energy physics would not be disappointed.

In cycling, Cadel Evans set a blistering pace in his solo effort on stage 20 to ensure the Yellow Jersey and an overall win in this year’s Tour.

In the world of high energy physics, physicists from Fermilab and CERN presented updates on their competing searches to discover (or not) the Higgs boson. The two main experiments at Fermilab, CDF and DZero, are looking for traces of the Higgs particle in the debris of Tevatron collider’s proton-antiproton collisions. At CERN’s Large Hadron Collider scientists working at the two massive detectors, Atlas and CMS, are sifting through vast mountains of data accumulated from proton-proton collisions.

Both colliders have been smashing particles together in their ongoing quest to refine our understanding of the building blocks of matter, and to determine the existence of the Higgs particle. The Higgs is believed to convey mass to other particles, and remains one of the remaining undiscovered components of the Standard Model of physics.

The latest results presented in Grenoble show excess particle events, above a chance distribution, across the search range where the Higgs particle is predicted to be found. There is a surplus of unusual events at a mass of 140-145 GeV (gigaelectronvolts), which is at the low end of the range allowed for the particle. Tantalizingly, physicists’ theories predict that this is the most likely region where the Higgs is to be found.

[div class=attrib]Further details from Symmetry Breaking:[end-div]

Physicists could be on their way to discovering the Higgs boson, if it exists, by next year. Scientists in two experiments at the Large Hadron Collider pleasantly surprised attendees at the European Physical Society conference this afternoon by both showing small hints of what could be the prized particle in the same area.

“This is what we expect to find on the road to the Higgs,” said Gigi Rolandi, physics coordinator for the CMS experiment.

Both experiments found excesses in the 130-150 GeV mass region. But the excesses did not have enough statistical significance to count as evidence of the Higgs.

If the Higgs really is lurking in this region, it is still in reach of experiments at Fermilab’s Tevatron. Although the accelerator will shut down for good at the end of September, Fermilab’s CDF and DZero experiments will continue to collect data up until that point and to improve their analyses.

“This should give us the sensitivity to make a new statement about the 114-180 mass range,” said Rob Roser, CDF spokesperson. Read more about the differences between Higgs searches at the Tevatron and at the LHC here.

The CDF and DZero experiments announced expanded exclusions in the search for their specialty, the low-mass Higgs, this morning. On Wednesday, the two experiments will announce their combined Higgs results.

Scientists measure statistical significance in units called sigma, written as the Greek letter ?. These high-energy experiments usually require 3?  level of confidence, about 99.7 percent certainty, to claim they’ve seen evidence of something. They need 5? to claim a discovery. The ATLAS experiment reported excesses at confidence levels between 2 and 2.8?, and the CMS experiment found similar excesses at close to 3?.

After the two experiments combine their results — a mathematical process much more arduous than simple addition — they could find themselves on new ground. They hope to do this in the next few months, at the latest by the winter conferences, said Kyle Cranmer, an assistant professor at New York University who presented the results for the ATLAS collaboration.

“The fact that these two experiments with different issues, different approaches and different modeling found similar results leads you to believe it might not be just a fluke,” Cranmer said. “This is what it would look like if it were real.”

[div class=attrib]More from theSource here.[end-div]

[div class=attrib]CERN photograph courtesy Fabrice Coffrini/AFP/Getty Images. Tour de France image courtesy of NBCSports.[end-div]

BigBang

The LHC Begins Its Search for the “God Particle

[div class=attrib]From Discover:[end-div]

The most astonishing thing about the Large Hadron Collider (LHC), the ring-shaped particle accelerator that revved up for the first time on September 10 in a tunnel near Geneva, is that it ever got built. Twenty-six nations pitched in more than $8 billion to fund the project. Then CERN—the European Organization for Nuclear Research—enlisted the help of 5,000 scientists and engineers to construct a machine of unprecedented size, complexity, and ambition.

Measuring almost 17 miles in circumference, the LHC uses 9,300 superconducting magnets, cooled by liquid helium to 1.9 degrees Kelvin above absolute zero (–271.3º C.), to accelerate two streams of protons in opposite directions. It has detectors as big as apartment buildings to find out what happens when these protons cross paths and collide at 99.999999 percent of the speed of light. Yet roughly the same percentage of the human race has no idea what the LHC’s purpose is. Might it destroy the earth by spawning tiny, ravenous black holes? (Not a chance, physicists say. Collisions more energetic than the ones at the LHC happen naturally all the time, and we are still here.)

In fact, the goal of the LHC is at once simple and grandiose: It was created to discover new particles. One of the most sought of these is the Higgs boson, also known as the God particle because, according to current theory, it endowed all other particles with mass. Or perhaps the LHC will find “supersymmetric” particles, exotic partners to known particles like electrons and quarks. Such a discovery would be a big step toward developing a unified description of the four fundamental forces—the “theory of everything” that would explain all the basic interactions in the universe. As a bonus, some of those supersymmetric particles might turn out to be dark matter, the unseen stuff that seems to hold galaxies together.

[div class=attrib]More from theSource here.[end-div]

[div class=attrib] Image courtesy of Maximillien Brice/CERN.[end-div]