A Second Higgs Boson? Physicists Debate New Particle

Stephanie Pappas, LiveScience Senior Writer, 04/14/13

DENVER — The discovery of the Higgs boson is real. But physicists are cagey about whether the new particle they've found will fit their predictions or not.

So far, the data suggest that the Higgs, the particle thought to explain how other particles get their mass, is not presenting any surprises, physicists said here today (April 13) at the April meeting of the American Physical Society. But that doesn't mean that it won't in the future — or that there might not be other Higgs bosons lurking out there.

"There's a large number of theoretical models that predict, actually, that this Higgs field is more complicated," said Markus Klute, a physicist at the Massachusetts Institute of Technology. Some of these theories predict five or more Higgs bosons of different masses, Klute told reporters. [The Top 5 Implications of Finding the Higgs]

The mystery of the Higgs

Physicists confirmed in March that a new particle discovered at the world's largest atom smasher, the Large Hadron Collider (LHC), is, in fact, the Higgs boson. This particle, which weighs about 126 times the mass of a proton, appears to fit the Standard Model of physics, the dominant theory of particle physics. In this model, the Higgs boson is related to the Higgs field, an energy field that pervades space and is thought to imbue many particles with mass. The thinking goes that just as swimmers would get wet moving through a pool, as particles move through the Higgs field they would gain mass.

This "vanilla" Higgs has been something of a disappointment to physicists hoping to find something that would upend their theories.

"Sometime in November, I was depressed a little bit by the fact that everything lines up so well," Klute said. "They call this 'post-discovery depression.'"

But researchers say there's more to learn about the Higgs, including whether it's the only one. It's possible that when the Large Hadron Collider revs up again in 2015 with more power, scientists may be able to detect heavier variations of the Higgs boson. Or variations may be hiding in the data collected already.

"As far as 'Is the Higgs standard or not standard,' we're not in the game yet," said Michael Peskin, a physicists at SLAC National Accelerator Laboratory at Stanford University. "We will be in the game later this decade, but right now it's just an open question."

A secondary spike in Higgs data presented in December 2012 led to speculation that physicists had perhaps found a second Higgs boson of a different mass. However, that spike showed up in only one LHC experiment. Other lines of evidence produced at the collider have failed to show similar anomalies.

Questions ahead

The 17-mile-long (27 kilometers) underground loop that is the Large Hadron Collider is currently shut down until 2015 as engineers tinker to bring the atom smasher to its fullest potential. Upping the energy levels of the LHC will allow for more collisions, and up to five times the precision in measurements as seen today, Klute said.

One popular theory physicists hope to put to an experimental test is "supersymmetry," which holds that every subatomic particle has a secret twin that has yet to be observed. "Superpartners" could help explain dark matter, a mysterious substance that may makes up a quarter of the entire universe.

So far, physicists can only account for 4 percent of what the universe is made of, said Thomas Koffas, a physicist at Carleton University in Canada.

"The remaining 96 percent," Koffas said, "we have no idea."

 Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.

• 5 Reasons We May Live in a Multiverse

• Beyond Higgs: 5 Elusive Particles That May Lurk in the Universe

• Photos: The World's Largest Atom Smasher (LHC)

Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

http://news.yahoo.com/second-higgs-boson-physicists-debate-particle-164951108.html

Top 5 Implications of Finding the Higgs Boson

Clara Moskowitz, LiveScience Senior Writer, 13/12/11

Particles Collide

Scientists announced today (Dec. 13) that they're closing in on the elusive Higgs boson, a subatomic particle that's been predicted but never detected. Now researchers at the world's largest particle accelerator, the Large Hadron Collider in Geneva, Switzerland, say they've narrowed down the mass range of the Higgs, and even see preliminary hints that it might exist.

If physicists can definitively detect the Higgs boson and determine its mass, the discovery would have wide-reaching implications. Here are five of the biggest.

The Origin of Mass

The Higgs boson has long been thought the key to resolving the mystery of the origin of mass. The Higgs boson is associated with a field, called the Higgs field, theorized to pervade the universe. As other particles travel though this field, they acquire mass much as swimmers moving through a pool get wet, the thinking goes.

"The Higgs mechanism is the thing that allows us to understand how the particles acquire mass," said Joao Guimaraes da Costa, a physicist at Harvard University who is the Standard Model Convener at the LHC's ATLASexperiment. "If there was no such mechanism, then everything would be massless."

If physicists confirm that the Higgs boson exists, the discovery would also confirm that the Higgs mechanism for particles to acquire mass is correct. And, it may offer clues to the next mystery down the line, which is why individual particles have the masses that they do.

"That could be part of a much larger theory," said Harvard University particle physicist Lisa Randall."Knowing what the Higgs boson is, is the first step of knowing a little more about what that theory could be. It's connected."

The Standard Model

The Standard Model is the reigning theory of particle physics that describes the universe's very small constituents.

Every particle predicted by the Standard Model has been discovered — except one: the Higgs boson.

"It's the missing piece in the Standard Model," said Jonas Strandberg, a researcher at CERN working on the ATLAS experiment. "So it would definitely be a confirmation that the theories we have now are right. If we don't [find the Higgs] it means we made some assumptions that are wrong, and we have to go back to the drawing board."

While the discovery of the Higgs boson would complete the Standard Model, and fulfill all its current predictions, the Standard Model itself isn't thought to be complete. It doesn't encompass gravity (so don't count on catching that fly ball), for example, and leaves out the dark matter thought to make up 98 percent of all matter in the universe.

"The Standard Model describes what we have measured, but we know it doesn’t have gravity in it, it doesn't have dark matter," said CERN physicist William Murray, the senior Higgs convener at ATLASand a physicist at the U.K.'s Science and Technology Facilities Council."So we're hoping to extend it to include more."

The Electroweak Force

Discovering the Higgs boson would also help explain how two of the fundamental forces of the universe — the electromagnetic force that governs interactions between charged particles, and the weak force that's responsible for radioactive decay — can be unified.

Every force in nature is associated with a particle. The particle tied to electromagnetism is the photon, a tiny, massless particle. The weak force is associated with particles called the W and Z bosons, which are very massive.

The Higgs mechanism is thought to be responsible for this.

"If you introduce the Higgs field, the W and Z bosons mix with the field, and through this mixing they acquire mass," Strandberg said."This explains why the W and Z bosons have mass, and also unifies the electromagnetic and weak forces into the electroweak force."

Supersymmetry

Another theory that would be affected by the discovery of the Higgs is called supersymmetry. This idea posits that every known particle has a "superpartner" particle with slightly different characteristics.

Supersymmetry is attractive because it could help unify some of the other forces of nature, and even offers a candidate for the particle that makes up dark matter. Depending on the actual mass of the Higgs boson, it could lend credence to supersymmetry, or cast doubt on the theory.

"If the Higgs boson is found at a low mass, which is the only window still open, this would make supersymmetry a viable theory," Strandberg said."We'd still have to prove supersymmetry exists."

Validation of LHC

The Large Hadron Collider is the world's largest particle accelerator. It was built for around $10 billion by the European Organization for Nuclear Research (CERN) to probe higher energies than had ever been reached on Earth. Finding the Higgs boson was touted as one of the machine's biggest goals.

The discovery of the Higgs would offer major validation for the LHC and for the scientists who've worked on the search for many years.

"If the Higgs eventually gets discovered it would be a very big step," said Guimaraes da Costa. "You have to invest lots of years, and getting to see it is quite exciting. It's quite good for the field because to build these machines [it] costs a lot of money, and you need to justify why we build these machines. If we make such an important discovery about the universe, it's a justification for why we should be investing in these things."

The discovery of the Higgs would also have major implications for scientist Peter Higgs and his colleagues who first proposed the Higgs mechanism in 1964.

"If it is found there are several people who are going to get a Nobel prize," said Vivek Sharma, a physicist at the University of California, San Diego, and the leader of the Higgs search at LHC's CMS experiment.

http://www.livescience.com/17433-implications-higgs-boson-discovery-lhc.html

How the Higgs Boson Might Spell Doom for the Universe

Saswato R. Das, Scientific American, 03/28/13

Physicists recently confirmed that the Large Hadron Collider (LHC) at CERN, the particle physics laboratory in Geneva, had indeed found a Higgs boson last July, marking a culmination of one of the longest and most expensive searches in science. The finding also means that our universe could be doomed to fall apart. "If you use all the physics that we know now and you do what you think is a straightforward calculation, it is bad news," says Joseph Lykken, a theorist who works at the Fermilab National Accelerator Laboratory in Illinois. "It may be that the universe we live in is inherently unstable."

The Higgs boson helps explain why particles have the mass they do. The Higgs particle that the LHC has found possesses a mass of approximately 126 giga-electron volts (GeV)—roughly the combined mass of 126 protons (hydrogen nuclei). (One GeV equals a billion electron volts.)

Based on the data analysis so far, the discovered particle is consistent with the Standard Model of particle physics, the highly successful theory that describes the subatomic world, although other models cannot be ruled out. "It is looking very much like the Standard Model Higgs boson—although there may be a very massive Higgs particle that also exists, and which our experiment is not sensitive enough to detect," says Joseph Incandela, the spokesman for the CMS (Compact Muon Solenoid) experiment at the LHC, one of the two experiments that detected the current Higgs particle,

And that very nature of being a Standard Model Higgs may be the reason our universe is ultimately unstable. It has to do with the so-called vacuum stability in the Standard Model.

According to the description currently favored by physicists, a vacuum is not completely devoid of matter but instead teems with particles and antiparticles that pop into existence and then run into one another and annihilate themselves, all in very short times. The inherent uncertainty embodied in quantum mechanics permits these spontaneous fluctuations—as long as the particles don't live for more than a fleeting instant, the process violates no laws of physics.

The Standard Model also says, as Lykken puts it, that "for the vacuum of empty space to be stable, we should be living at a minimum of potential energy." In other words, most things end up resting in a place of lowest energy. A ball rolls downhill and settles in a low point; getting it to move away from this point requires a kick of energy. In the case of the universe it would be like living at the bottom of a valley bordered by hills: the value of the Higgs potential would be lowest point of the valley.

Our universe might end if our valley really isn't the lowest one around. Physicist Benjamin Allanach of the University of Cambridge explains:

"The shape of the Higgs potential is determined precisely by the Higgs mass."

The observed 126 GeV mass seems to imply the universe does not exist in the lowest possible energy state but is in fact positioned in a slightly unusual place.

"It turns out that for a Higgs boson of 126 GeV, we might be in the gray area where the universe is at a local minimum that is not the global minimum," says physicist Matthew Strassler of Rutgers University.

It is sort of like being in a valley whose floor is higher than that of an adjoining valley. If you didn't know that a deep valley was on the other side of the hill, you would think you were at the lowest level you could be. If you somehow managed to get to the other side, however, you could fall much lower.

This situation would normally not pose a problem, as you couldn't travel between valleys—except in quantum mechanics, which allows particles to tunnel through hills unpredictably. As a result, "in the future our universe could spontaneously and randomly tunnel through to the deeper one, with potentially catastrophic consequences," Allanach says.

Such a metastable universe is not a new idea. As far back as 1979, physicists were trying to calculate the implications of the mass of the Higgs boson on cosmology. In 2001 theoretical physicists Paul Steinhardt of Princeton University and Neil Turok of the Perimeter Institute for Theoretical Physics in Canada described a cyclic universe, which alternates between expansion and contraction, and is consistent with the sort of metastability implied by the observed mass of the Higgs boson. More recently, Giuseppe Degrassi of the University of Rome and Jose Espinosa of the Autonomous University of Barcelona and their collaborators have calculated the broad implications of the Higgs mass.

"We now know with a large degree of confidence that our vacuum is on the unstable side and we were able to calculate its decay lifetime," Espinosa says. "This lifetime turns out to be way larger than the [present] age of the universe."

Most theorists don't seem to be too worried about the destruction of our universe, because metastability would not manifest itself anytime soon—if ever. Also, they expect that the LHC will find other particles in due course. Then, new calculations could indicate that the universe has more stability. Specifically, the fate of the universe depends quite sensitively not only on the Higgs but also on the mass of the top quark, another fundamental particle whose mass hovers at about 180 GeV. "The top quark strongly affects the vacuum by its quantum fluctuations because it is so heavy," Allanach says. "If the Higgs mass were really 127 GeV and the top mass were a little lower than its most likely value, then actually the universe would be completely stable and the vacuum would be in the true minimum."

Steinhardt says, "There is a tiny sliver of metastability. Why is the universe just at this point? Is this actually a profound thing we have to understand?"

But assuming that everything is known about the Standard Model and no new particles and forces will be found in the future, then the universe might be in the gray region where it is long-lived but somewhat unstable and therefore might disappear a few billions of eons from now.  "And maybe not even billions of years, but billions of eons or billions of billions" of eons, Strassler stresses. "This is not something that keeps me awake."

Follow Scientific American on Twitter @SciAm and @SciamBlogs.

Visit ScientificAmerican.com for the latest in science, health and technology news.

© 2013 ScientificAmerican.com. All rights reserved.

http://news.yahoo.com/higgs-boson-might-spell-doom-universe-110000933.html

New Particle at World's Largest Atom Smasher is Likely Higgs Boson

Clara Moskowitz, LiveScience, 07/04/12

Physicists are more than 99 percent sure that they've found a new elementary particle that is likely the long-sought Higgs boson.

Evidence for the new particle was reported today (July 4) by scientists from the world's largest atom smasher, the Large Hadron Collider in Switzerland. Researchers reported they'd seen a particle weighing roughly 125 times the mass of the proton, with a level of certainty that all but seals the deal it's the Higgs boson.

"This is indeed a new particle. We know it must be a boson and it’s the heaviest boson ever found," Joe Incandela, spokesperson for LHC's CMS experiment, said in a statement. "The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks."

The Higgs, nicknamed the "God particle" (to the chagrin of many scientists, who prefer its official name), is thought to hold the key to one of the mysteries of the universe: Why do things have mass?

Its discovery represents a major step forward in our understanding of why the universe exists as it does, with matter clumping together to form galaxies, stars, planets and us, scientists say. [Top 5 Implications of Finding the Higgs Boson]

To be absolutely sure they've made a true new discovery, rather than simply seen a fluke, physicists wait for enough data so that their statistics reach a level called 5 sigma, meaning that there is only a one in 3.5 million chance the signal isn't real.

"We observe in our data clear signs of a new particle, at the level of 5 sigma, in the mass region around 126 GeV," said Fabiola Gianotti, spokesperson of LHC's ATLAS experiment. (GeV stands for gigaelecton volts, a unit of mass roughly equivalent to the weight of a proton.) Gianotti presented the findings to loud applause from physicists gathered at CERN (LHC's home facility) to hear the LHC's results.

The LHC's CMS experiment saw signs of a new particle with a mass of 125.3 GeV at a certainty level of 4.9 sigma.

"As a layman I would now say, I think we have it," CERN director general Rolf Heuer said during a presentation at the Geneva, Switzerland lab reporting the results today. "Do you agree?" he asked the gathered physicists, who responded with loud applause.

The Higgs boson is the last undiscovered piece of the puzzle predicted by the reigning theory of particle physics, called the Standard Model. Yet the model does not predict what its mass is, so physicists have to search through a wide territory to find it. The researchers can't yet be absolutely sure that the new particle they've found actually is the Higgs.

"The work now is to actually measure its quantum identity (all its quantum properties)," Caltech physicist Maria Spiropulu, who was in the audience at the LHC announcement, told LiveScience in an email. "Then we can say if it THE minimal standard model Higgs or a Higgs look-alike. We have been propelled to the future of particle physics towards the understanding of the fundamental properties of our universe in its entirety."

The LHC is the most powerful machine on Earth, capable of smashing protons together to produce huge explosions of energy that transform into new and exotic particles inside its17-mile (27 kilometer) underground loop. Yet the Higgs boson is so rare only one out of a trillion of the collisions inside the accelerator are likely to produce it, and even then, it decays almost immediately into other particles.

"This is not a needle in a haystack — it's much worse than a needle in a haystack," said Joe Lykken, a theoretical physicist at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Ill.

Over the past few years, researchers have been able to exclude certain possible masses for the Higgs, narrowing the possible window for Higgs further and further. Just this week, Fermi scientists announced that data from the largest U.S. particle accelerator, the Tevatron (which shut down last year), show the Higgs, if it exists at all, must have a mass between 115 and 135 GeV.

In December 2011, the LHC teams announced their latest findings, which restricted the Higgs to a mass between115 and 130 GeV, though with less certainty than the new Tevatron results.

"This is a really special time," said Fermilab physicist Dan Green, a member of LHC's CMS experiment, said Monday (July 2). "I remember when the top [quark] was discovered 20 years ago. This is one of the most exciting weeks I've had for a very long time." [9 Unsolved Physics Mysteries]

Today's findings come from the two general-purpose experiments at LHC, ATLAS and CMS. Both observed particle collisions independently and analyzed their observations separately. In fact, scientists from each team were not allowed to tell each other what they found until today, for fear their results would bias the other experiment's researchers toward looking for the same results.

Follow Clara Moskowitz on Twitter @ClaraMoskowitz or LiveScience @livescience. We're also on Facebook & Google+.

• Gallery: Search for the Higgs Boson
• Photos: The World's Largest Atom Smasher (LHC)
• Wacky Physics: The Coolest Little Particles in Nature

Copyright 2012 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.