Particle Physicists Put the Squeeze on the Higgs Boson; Look for Conclusive Results in 2012

by Nancy Atkinson on December 13, 2011

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Scientists gather as the ATLAS and CMS experiments present the status of their searches for the Standard Model Higgs boson. Credit: CERN

With “freshly squeezed” plots from the latest data garnered by two particle physics experiments, teams of scientists from the Large Hadron Collider at CERN, the European Center for Nuclear Research, said Tuesday they had recorded “tantalizing hints” of the elusive subatomic particle known as the Higgs Boson, but cannot conclusively say it exists … yet. However, they predict that 2012 collider runs should bring enough data to make the determination.

“The very fact that we are able to show the results of very sophisticated analysis just one month after the last bit of data we used has been recorded is very reassuring,” Dr. Greg Landsberg, physics coordinator for the Compact Muon Solenoid (CMS) detector at the LHC told Universe Today. “It tells you how quick the turnaround time is. This is truly unprecedented in the history of particle physics, with such large and complex experiments producing so much data, and it’s very exciting.”

For now, the main conclusion of over 6,000 scientists on the combined teams from CMS and the ATLAS particle detectors is that they were able to constrain the mass range of the Standard Model Higgs boson — if it exists — to be in the range of 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS.

The Standard Model is the theory that explains the interactions of subatomic particles – which describes ordinary matter that the Universe is made of — and on the whole works very well. But it doesn’t explain why some particles have mass and others don’t, and it also doesn’t describe the 96% of the Universe that is invisible.

In 1964, physicist Peter Higgs and colleagues proposed the existence of a mysterious energy field that interacts with some subatomic particles more than others, resulting in varying values for particle mass. That field is known as the Higgs field, and the Higgs Boson is the smallest particle of the Higgs field. But the Higgs Boson hasn’t been discovered yet, and one of the main reasons the LHC was built was to try to find it.

To look for these tiny particles, the LHC smashes high-energy protons together, converting some energy to mass. This produces a spray of particles which are picked up by the detectors. However, the discovery of the Higgs relies on observing the particles these protons decay into rather than the Higgs itself. If they do exist, they are very short lived and can decay in many different ways. The problem is that many other processes can also produce the same results.

How can scientists tell the difference? A short answer is that if they can figure out all the other things that can produce a Higgs-like signal and the typical frequency at which they will occur, then if they see more of these signals than current theories suggest, that gives them a place to look for the Higgs.

The experiments have seen excesses in similar ranges. And as the CERN press release noted, “Taken individually, none of these excesses is any more statistically significant than rolling a die and coming up with two sixes in a row. What is interesting is that there are multiple independent measurements pointing to the region of 124 to 126 GeV.”

“This is very promising,” said Landsberg, who is also a professor at Brown University. “This shows that both experiments understand what is going on with their detectors very, very well. Both calibrations saw excesses at low masses. But unfortunately the nature of our process is statistical and statistics is known to play funny tricks once in a while. So we don’t really know — we don’t have enough evidence to know — if what we saw is a glimpse of the Higgs Boson or these are just statistical fluctuations of the Standand Model process which mimic the same type of signatures as would come if the Higgs Boson is produced.”

Landsberg said the only way to cope with statistics is to get more data, and the scientists need to increase the size of the data samples considerably in order to definitely answer the question on whether the Higgs Boson exists at the mass of 125 GeV or any mass range which hasn’t been excluded yet.

The good news is that loads of data are coming in 2012.

“We hope to quadruple the data sample collected this year,” Landsberg said. “And that should give us enough statistical confidence to essentially solve this puzzle and tell the world whether we saw the first glimpses of the Higgs Boson. As the team showed today, we will keep increasing until we reach a level of statistical significance which is considered to be sufficient for discovery in our field.”

Landsberg said that within this small range, there is not much room for the Higgs to hide. “This is very exciting, and it tells you that we are almost there. We have enough sensitivity and beautiful detectors; we need just a little bit more time and a little more data. I am very hopeful we should be able to say something definitive by sometime next year.”

So the suspense is building and 2012 could be the year of the Higgs.

More info: CERN press release, ArsTechnica

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Lord Haw-Haw. December 13, 2011 at 8:18 PM

Another outstanding up-to-the-minute article Nancy well done! An additional complication with the SM it does not encompass gravity, bar string theory this is a conundrum for the physicist to construct a workable consistent quantum theory of gravity confirmed by experiment, there may exist different varieties of Higgs so roll out the International Linear Collider.

Just loved the comment from a wag in the media recently:
“If the Higgs boson is not found will it be known as the Lord Lucan?”…. You would have to be British to comprehend the irony! (Haw-Haw).

-Kudos to the ATLAS & CMS teams on their detective work.

Anonymous December 14, 2011 at 2:44 AM

The lack of a clear signal for the Higgs particle is probably telling us something. Even if next year the signal for the Higgs particle reaches 3 sigma there may still be something funny going on. Based on the standard model the Higgs particle should be screaming at us at sqrt{s} = 7 TeV. We should be getting clear signal at 5-sigma or better, the corks should be popping off the champagne bottles and the Nobel nominations submitted for next year. The ATLAS/CMS Higgs search update meeting only resulted in data at around ? = 2.5, which is suggestive but not conclusive. Fabiola Gianotti and Guido Tonelli gave their reports for ATLAS and CMS respectively, but the data over all is weak. There is a small rise above the exclusion zone at 120-130 GeV, but nothing yet to pin much on. Honestly I think it shouldn’t be this way if the standard model is taken as the benchmark. Even with SUSY MSSM the story should be much the same.

It is important not to confuse the Higgs field and the Higgs particle. The Higgs particle everyone is searching for is the unpaired doublet element which remains after the other 3 are absorbed by the electroweak bosons. The Higgs field is the entire gemish, which was proposed to exist because physics kept coming up with evidence for a massive boson field for the weak interactions. There is a problem with this. If the spin is s = 1?, then in a massless theory the spin is projected along the momentum as m = 1 or -1. However, if this particle has a mass the spin can be projected normal to the momentum, or equivalently there is a frame of zero momentum for the particle. So we have m = 1, 0, -1. Such a quantum field has longitudinal modes, and in a highly relativistic field interaction this means one can have longitudinal field information outracing the field faster than light. The field theory goes sick. So the logic behind the Higgs theory is that the high energy theory has a Lagrangian with a full symmetry, here SU(2)xU(1), but that at low energy the symmetries of the vacuum are restricted and particles have masses.

The Higgs theory works this way. The weak interactions are mediated by massive bosons, which means something goes horribly wrong with QFT. So enter the Higgs field. This is a scalar field in the vacuum composed of two doublets

(H^+,H_0) and (H^-,H’_0).

At very high energy the gauge particles of the electroweak theory (W^+, W^-, Z^0, ?) are not coupled to the Higgs field (or very weakly coupled) and are massless, or nearly so. The covariant differential of the Higgs field H is given by ?H — > (? + igA)H which results in coupling between the gauge potential and the Higgs field that increases near the Higgs potential minimum. The field then contains a term A*HA, which is similar to a mass term in a Proca equation. The fields then absorb the Higgs degrees of freedom W^+ + H^+ — > W^+, W^- + H^- — > W^- and Z^0 + H_0 — > Z^0, which are massive, plus a remaining H’ left over. The left over H’ is what the Higgs-hunt is looking for.

This left over H’, sometimes called little h, is then thought to decay by various modes. The h might decay as h — > T + T-bar, which might mean the Higgs is heavier since the top quark comes in at 176 GeV. The data so far is running against this idea by excluding “heavy Higgs” at around 400 GeV. Hence the T-T-bar decay mode for h might only occur if it interacts with some other particle. There are some technicolor models which have the Higgs as a fermionic component, which has various Regge poles for different angular momentum for the pair as they are spun up. The top of the trajectory curve (line of spin and energy) is a T-T-bar pair. Thus the Higgs field could be a form of quark condensate, or top quark condensate, similar to Cooper pairing of electrons in a superconductor. It then could be that the decay channels observed for qq-bar states could in fact be involved with the Higgs field.

LC

Meteodan December 14, 2011 at 5:13 AM

5 sigma by now, really?

It was my understanding that the excesses seen were actually a bit higher than what would be expected for a standard-model Higgs at ~125 GeV for the amount of data analyzed. In other words, the experiments may have “gotten lucky” with a statistical upward fluctuation in events. But, I could be missing something, seeing as I’m just an interested scientist-who-is-not-a-particle-physicist.

It still could be, however, that the whole thing is a statistical fluke that will go away with more data next year. Either way, we’re closer than we think, and we’re standing on the brink, to borrow a line from Kansas.

Anonymous December 14, 2011 at 1:10 PM

Back in the late 1970s it was thought that the tevatron would clinch the Higgs particle. At 1 TeV and with the Higgs field vacuum at 174GeV and particle mass at 125 GeV that seemed likely. The tevatron energy would be close to the threshold energy of production, but enough. There were some weak signals reported but nothing at all conclusive. Then through the LHC construction it was thought that at multi-TeV energy the Higgs would be almost a slam dunk. The LHC is running at half power, and the luminosity is yet not up to spec limits. Yet just a year ago people were saying the Higgs should be found by now.

Now lots of things are being said about how this is hard to detect. The main data is di-photon measurement. If the Higgs decays into photons these events should be quite measurable. Photons are about the easiest particle in physics to detect. Yet we are having what I think is a far more difficult time than we should be seeing if the h particle exists according to most standard model work.

LC

Lord Haw-Haw. December 14, 2011 at 11:36 AM

Precisely the point of physicist Jeff Forsham at Manchester University, quote:
“There is definitely a hint of something around 125GeV but it’s not a discovery yet, we need more data! I’m keeping my champagne on ice.”

While the initial data is not a clear signal as you note a 2.3 sigma peak (possible Higgs boson of 126GeV) and 1.9 sigma peak (giving a mass of some 124GeV) they jointly exhibit the strongest evidence to date though inconclusive results narrowing the region parameters. It is feasible that with the pooling of CMS & ATLAS data in 2012 a calibrated resultant 3 sigma would thus be upgraded to an observation the precursor to a discovery announcement.

Many thanks Lawrence for your meritorious comments during 2011 wishing you & yours Seasons Greetings & celebratory champagne popping for 2012.

Anonymous December 14, 2011 at 1:25 PM

The two detectors have 2.3 and 1.8 sigma respectively. The combined sigma turns out to be 2.5 or with another analysis 2.7. This means we have a confidence that these data are correct above 90%, with 5-10% probability they are statistical fluctuations. This is not up to QA standards, so the data is not definitive.

Happy Holidays, and may 2012 bring better things than this year. ON balance this year has been rather crappy.

LC

Baksa Péter December 14, 2011 at 7:18 AM

LHC is thriving for 5 sigma, I wonder if the exclusions were also 5 sigma? Maybe “everything happening as usual” was just a trick of statistics?

Wezley Jackson December 14, 2011 at 8:57 AM

Hello All,

I have to admit its been a humbling experience trying to follow recent scientific developments at CERN, Grand Sasso, and other facilities.

I await the results keenly and wonder if the Higgs Boson will be statistically identified by these brilliant scientists.

Wezley Jackson digs:
http://universe-review.ca/R15-12-QFT.htm
http://arxiv.org/abs/hep-th/0005231
http://www.preston.u-net.com/AGMatter/Index.htm

Cannot vouch for the truth of any theories but find it interesting trying to follow along.

Thanks and Happy Holidays.

Anonymous December 14, 2011 at 9:35 AM

An excellent article, and fascinating video: both helped me to comprehend the mass-imparting Energy Field of the Higgs Boson, as never before. And also helped me to understand a bit better, the significance of the LHC research. A more grounded look at whats actually going on there, behind the sensational, somewhat misleading headlines.

Torbjörn Larsson December 15, 2011 at 12:19 PM

I assume these uncertainties are without the look-elsewhere effect (searching a large region for a signal) since the search is narrowing down. Then it is perhaps stronger than the usual 3 sigma signal that goes away more often than not.

Interestingly, a standard 125 GeV Higgs may or may not give a marginally stable vacuum. If it is a standard Higgs it is finely tuned, in much the same manner as our vacuum energy seems to be.

AFAIU the Standard Model for particles is severely finetuned before putting such a Higgs in there. It will be interesting if it competes with the finetuning of cosmological constant (putatively our vacuum energy). And interesting to see if, besides supersymmetry, other TOE mechanisms fail and it perchance all derives from environmental selection. That would be fun!

Torbjörn Larsson December 15, 2011 at 2:43 PM

[deleted]

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