It was only back in August that most Scientists at CERN thought that most probably the elusive Higgs Boson Particle does not exist. Last week the ultra-shy Higgs boson is thought to have finally shown itself at the LHC. Both of the main detectors, ATLAS and CMS, have uncovered hints of a lightweight Higgs. If this is true then, the only remaining hole in the standard model would be filled.
What CERN reported on Tuesday was the midpoint results from two separate experiments that independently arrived at the same conclusion. The Web-cast presentation was made before several hundred scientists in an atmosphere charged with excitement and punctuated with applause.
Taken together, the results provide “tantalising hints” that the sought-after particle is hiding inside a narrow range of mass, CERN said in a statement. “If it exists, it is most likely to have a mass constrained to the range of 116 to 130 gigaelectronvolts (GeV),” CERN said, using the standard measure for the mass of sub-atomic particles.
"One GeV is roughly equivalent to the mass of a proton"
The Huge particle detector at CERN employs 3,600 scientists, Guido Tonelli, is the spokesman for the Compact Muon Solenoid Detector that said: 'If we exclude the existence of the Higgs this will be a major discovery - it would completely review our vision of nature.'
Tonelli said, 'We should be patient in this search,' he said, 'This machine is so powerful we will be able to explore completely new territory.' 'The standard model of particle physics has lasted for forty years,' CERN spokesman James Gillies told Mail Online today, 'But it's a flawed theory. Something within it has got to give. At the kind of energies the LHC is probing, we are investigating what generates the mass of particles. Higgs is just one theory.
Chimera or reality? Rolf Heuer, director general of CERN, says the team will know by the end of 2011 if the mythical 'God particle' exists or not. The main reason that Higgs is so popular is because it's mathematically appealing,' and 'If we don't find the Higgs, we will go on to find whatever else it is that is generating mass.'
Initial signals seemed to indicate that the Higgs could be within a range of 120 and 140GeV, 'detectable' by looking for 'events' created by the short-lived particle's decay into pairs of other subatomic particles – At ATLAS and CMS physicists will be crunching more data to find out if the hints of a lightweight Higgs hold up. Rigorously combining the two current data sets would effectively double the statistics; This will firm up the statistical significance to between 3.7 and 3.9 sigma, or a 1 in 10,000 chance of the result being a fluke.
Assuming the collider keeps working well, both experiments should have enough data to confirm or deny the simplest version of the Higgs by the end of 2012. By then, physicists might look back on this moment as their first glimpse of a major discovery. "This is why there is some excitement," says Tonneli.
It would also be thrilling if the Higgs never showed up at all. If the current hints disappear, physicists will wait until the LHC revs up to its full energy in 2015 to look for other particles or phenomena that could give particles mass without any need for the Higgs. "There must be something else that plays that role," Gianotti says. "We will be after that something else."
Short Story on Higgs Boson (newscientist.com)
If our ideas about the Higgs boson turn out to be correct, then everything we see is a kind of window dressing based on an underlying fabric of reality in which we shouldn't exist. The particles that make us up – which bind together to form protons, neutrons, nuclei and ultimately atoms – have mass. Without the Higgs, these particles would be massless, like photons.
We all know from our own experience that how heavy something feels depends on where it is located. For example, objects that are heavy on land appear lighter in water. Similarly, if you try to push a spoon through treacle it appears heavier than if you push it through air.
The standard model of particle physics implies that there is a "Higgs field" that permeates all space. This field interacts with particles, and does so with varying strengths. Particles that interact more strongly experience more resistance to their motion and appear heavier. Some particles, such as photons, do not interact with the field at all and remain massless.
In this way, the mass of everything is determined by the existence of the field, and mass is an accident of our circumstances because we exist in a universe in which such a background field happens to have arisen.
Getting something from nothing (Guardian NewsPaper)
To produce matter from Nothing has been one of the great developments in physics in the past century, from understanding how to create a universe from nothing, to our current understanding of how one might endow another form of nothing – namely empty space – with energy. But perhaps there is no better example relevant to our direct experience of how to get something from nothing than the phenomenon called "spontaneous symmetry breaking" that the Higgs boson represents.
If our ideas about the Higgs turn out to be true, then everything we see is a kind of window dressing based on an underlying fabric of reality in which we shouldn't exist. The particles from which we're made are massive and bind together to form protons, neutrons, nuclei, and ultimately atoms. But without the Higgs, these particles would actually be massless, like photons, which are required to move restlessly at the speed of light and cannot be confined, except perhaps in a black hole.
We have all experienced how the heaviness of an object depends on where it is located. In water, for example, with buoyant forces present, objects that are heavy on the land seem lighter. Similarly, if you try and push something through a very thick fluid it may appear heavier (giving you more resistance to the force of your pushing) than it would if you were pushing it through the air.
The Standard Model of particle physics implies that there is an otherwise invisible background "Higgs field" that permeates all of space. This field interacts with other particles with varying degrees of strength. As particles move through space, they interact with the background Higgs field, and those that interact more strongly will experience more resistance to their motion, and will act heavier. Some particles, like the photon, do not interact with the field at all, and remain massless.
In this way, the mass of everything we see is determined by the existence of this field, and if it didn't exist, essentially all particles would be massless. According to this picture, mass is an "accident" of our circumstances because we exist in a universe in which such a background field happens to have arisen.
But why a Higgs "particle"? Well, relativity tells us that no signal can travel faster than light. Incorporating this into quantum mechanics tells us that forces we think of as being due to fields like the electric field are actually transmitted between objects by the exchange of particles, and that these particles travel on average at the speed of light or slower.
Why particles transmit forces is like thinking of playing catch. If I throw a ball to you and you catch it, then you will be pushed backwards by the force of my ball, and I will be pushed backward by the act of throwing the ball. Thus we act as though we are repelling each other.
So, if there is a Higgs field, it turns out that there has to be a new particle associated with this field, and this is the Higgs particle.
Playing subatomic catch (NewScientist.com)
But why a Higgs particle? Relativity tells us that no signal can travel faster than light. Incorporating this into quantum mechanics tells us that forces which we think of as being due to fields are actually transmitted between objects by the exchange of particles. The way particles transmit forces is a bit like a game of catch: if I throw a ball and you catch it, I will be pushed backwards by the act of throwing and you will be pushed backwards by the act of catching. Thus we act as if we repel each other.
So if there is a Higgs field, it turns out that there has to be a particle associated with this field, and this is the Higgs particle.
This seems a fanciful framework, rather like imagining angels on the head of a pin. What would drive scientists to imagine such a scenario? One of the greatest successes of the past 50 years was the unification of two of the forces of nature: electromagnetism and the weak interaction. In this "electroweak" theory, electromagnetic forces arise by the long-range exchange of massless photons, and the short-range weak force is due to the exchange of massive particles called W and Z particles, predicted in the 1960s and discovered in the 1980s at CERN, the European particle physics laboratory near Geneva, Switzerland, which is now the home of the LHC.
In order for this theoretical unification to make mathematical sense, all three particles have to be massless in the underlying theory, and therefore the forces they mediate would be almost identical. Only if the W and Z particles obtain a mass by interacting with a background field – the Higgs field – will the underlying unified theory explain why the two forces appear different at the scales we measure them today, while remaining mathematically consistent.
High mass
Theory suggests that the mass of a Higgs particle should be about 100 times the mass of the proton; however, the exact mass is not predicted.
For over 25 years since the discovery of the W and Z particles, experimental physicists have been trying to build particle accelerators with the energy necessary to produce a Higgs particle, if it exists. The Tevatron accelerator at Fermilab in Batavia, Illinois, was able to reach up to about 120 times the mass of the proton (about 120 gigaelectronvolts) but did not find the Higgs.
The LHC was designed to probe for Higgs masses heavier than this. If the Higgs
03001301305particle is announced with a mass of 125 GeV, as the rumours suggest, it will be the crown jewel of our theoretical understanding of the electroweak unified theory, our own origins and the origin of almost all mass we measure in the universe.
Fermilab scientist Don Lincoln describes the concept of how the search for the Higgs boson is accomplished. Several large experimental groups are hot on the trail of this elusive subatomic particle which is thought to explain the origins of particle mass.
BIG QUESTIONS FOR 2012
This plot basically shows the energy of detected particles along the bottom (x-axis) and "confidence level" (CL) up the side (y-axis). The dotted, curved line (inside the green band), is the energy of the particles that would theoretically be detected if the Higgs boson doesn't exist.
However, the dark wavy line represents the particles that the ATLAS detector has actually detected so far. As you can see, this line differs greatly from the theoretical line -- the bump skyrockets at around the 125 GeV (Giga-electronvolts), approximately 125-times the mass-energy of a single proton -- breaking the green barrier (representing "1-sigma") and the yellow barrier (representing "2-sigma"). In fact, this peak represents a "2.4 sigma" result.
"Ah ha!" say physicists when they see this, "something 'exotic' is going on."
The 2.4-sigma result represents a 98 percent certainty that this bump is real and not experimental error. What's more, the bump lies right around the predicted energy of a "light" Higgs boson as predicted by the Standard Model -- the theory that governs all known particles and forces (except gravity).
A 98 percent certainty is promising, but it's not a discovery. LHC physicists will be getting excited about this, but until these excesses (or "bumps") in the data reach the "5-sigma" threshold -- when the certainty becomes 99.99994 percent, or one-in-a-million chance that it's wrong -- the Champagne corks will remain plugged inside their bottles.
What is now needed is basically, more data. It's a bit like exposing an old photographic plate to a very dim light. Cover the plate up quickly, and only a small number of photons from the light source has hit it. A very dim, fuzzy and low-definition image is the result.
However, leave the photographic plate uncovered for longer, and more photons from the light source will hit the plate, making the resulting photograph brighter, clearer and more defined.
This is exactly what the LHC detectors need: more time to collect more particle detections, making any "bumps" in the data more prominent and more certain. However, there is a small chance that with more collisions, this particular bump in the ATLAS and CMS data is an artifact, error or just noise, and will start to fade from view.
But the fact that two detectors have independently spotted a faint signal, around about the predicted range (115-130 GeV) that theorists expected to find a Higgs boson... to a certainty of 1.9 sigma (for the CMS result) and 2.4 sigma (for the ATLAS result), it's hard not to get excited.
The next few months will be crucial for the Higgs boson hunt, and it's looking like 2012 will be the year for the LHC. |
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