From Dr. Don Lincoln at FNAL: “Physics in a Nutshell Epic facepalm”

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Don Lincoln

If you’re a science enthusiast, this week you have likely encountered outlandish headlines invoking Stephen Hawking, the Higgs boson and the end of the universe. I hope you had the presence of mind to react as the famous actor in the picture did. Let’s start with the answer first. The universe is safe and will be for a very long time — for trillions of years. This story as widely reported by the media is a jaw-dropping misrepresentation of science.

To understand how abominably Hawking’s statement was twisted, first we need to understand the statement. To paraphrase just a little, Hawking said that in a world in which the Higgs boson and the top quark have the masses that scientists have measured, the universe is in a metastable state.

So let’s take those pieces one at a time. What does “metastable” mean? Basically, metastable means “kind of stable.” So what does that mean? Let’s consider an example. Take a pool cue and lay it on the pool table. The cue is stable; it’s not going anywhere. Take the same cue and balance it on your finger. That’s unstable; under almost any circumstances, the cue will fall over. So the terms stable and unstable are easy and have familiar, real-world analogues. The analogy for a metastable object is a barstool. Under almost all circumstances, the stool will sit there for all eternity. However, if you bump the stool hard enough, it will fall over. When the stool has fallen over, it is now more stable than it was, just like the pool cue lying on the table.

Now we need to bring in the universe and the laws that govern it. Here is an important guiding principle: The universe is lazy — a giant, cosmic couch potato. If at all possible, the universe will figure out a way to move to the lowest energy state it can. A simple analogy is a ball placed on the side of a mountain. It will roll down the mountainside and come to rest at the bottom of the valley. This ball would then be in a stable configuration. The universe is the same way. After the cosmos was created, the fields that make up the universe should arrange themselves into the lowest possible energy state.

A stable thing is something that won’t change, like this pool cue on the table. An unstable thing is something that will quickly change, like this pool cue balanced on the man’s hand. A metastable thing will eventually change, but will not do so quickly or easily. An example is this stool, which is more stable when it is lying down, but it will stay upright for long periods of time.

There is a proviso. Just as on a slope of a mountain, where there may be a little valley part way up the hill (above the real valley), it is possible that there could be little “valleys” in the energy slope. As the universe cooled, it could be that it might have been caught in one of those little valleys. Ideally, the universe would like to fall into the deeper valley below, but it could be trapped. This is an example of a metastable state. As long as the little valley is deep enough, it’s hard to get out of. Indeed, using classical physics, it is impossible to get out of it.

However, we don’t live in a classical world. In our universe, we must take into account the nature of quantum mechanics. There are many ways to describe the quantum realm, but one of the properties most relevant here is “rare things happen.” In essence, if the universe was trapped in a little valley of metastability, it could eventually tunnel out of the valley and fall down into the deeper valley below.

So what are the consequences of the universe slipping from one valley to another? Well, the rules of the universe are governed by the valley in which it finds itself. In the metastable valley that defines our familiar universe, we have the rules of physics and chemistry that allow matter to assemble into atoms and, eventually, us. If the universe slipped into a different valley, the rules that govern matter and energy would be different. This means, among other things, quarks and leptons might be impossible. The known forces might not apply. In short, there is no reason to think we’d exist at all.

Whether our universe is in a stable configuration, an unstable configuration or a metastable one depends on the mass of the Higgs boson and the mass of the top quark. The dot shows tells us the value of those parameters in our universe. We see that it appears that the universe appears to be metastable but, as noted in the text, there is clearly a lot still to be understood before we can be sure.

This leads us to ask how the transition would occur. Would we have any warning? Actually, we’d have no warning at all. If, somewhere in the cosmos, the universe made a transition from a metastable valley to a deeper one, the laws of physics would change and sweep away at the speed of light. As the shockwave passed over the solar system, we’d simply disappear as the laws that govern the matter that makes us up would just cease to apply. One second we’d be here; the next we’d be gone.

Coming back to the original question, what does the Higgs boson tell us about this? It turns out that we can use the Standard Model to tell us whether we are in a stable, unstable or metastable universe. We know we don’t live in an unstable one, because we’re here, but the other two options are open. So, what is the answer? It depends on two parameters: the mass of the top quark and the mass of the Higgs boson. As we see in the figure [below], our universe appears to be in a metastable state, although it is quite close to the stable region. The size of the box reflects our uncertainty in our measurements.

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

In the context of the cosmos, the universe prefers to be in the lowest energy state. However it is possible that our familiar cosmos is in a little valley higher up the slope. In this little valley, the rules of matter with which we are familiar reign supreme. However, if the universe ever transitions to the lower valley, the rules of physics might change entirely. Those new rules could be anything, including ones in which matter doesn’t exist. It probably doesn’t need saying, but for my Chicago readers, I should caution them that a universe in which the Cubs win the World Series is still exceedingly unlikely.

So if we follow our understanding of the Standard Model, combined with our best measurements, it appears that we live in a metastable universe that could one day disappear without warning. You can be forgiven if you take that pronouncement as a reason to indulge in some sort of rare treat tonight. But before you splurge too much, take heed of a few words of caution. Using the same Standard Model we used to figure out whether the cosmos is metastable, we can predict how long it is likely to take for quantum mechanics to let the universe slip from the metastable valley to the stable one, and it will take trillions of years. Mankind has only existed for about 100,000 years, and the sun will grow to a red giant and incinerate the Earth in about five billion years. Since we’re talking about the universe existing as a metastable state for trillions of years, maybe overindulging tonight might be a bad idea.

It is important to note that finding the Higgs boson has no effect on whether the universe is in a metastable state. If we live in a metastable cosmos, it has been that way since the universe was created. It’s like living in a century-old house that was built with a ticking time bomb hidden in its walls. Finding the Higgs boson is like hearing the ticking of the bomb that was always there. I must repeat: The discovery of the Higgs boson has no effect at all on whether the universe is in a metastable state.

Returning to the original, overly hyped media stories, you can see that there was a kernel of truth and a barrel full of hysteria. There is no danger, and it’s completely OK to resume watching with great interest the news reports of the discovery and careful measurement of the Higgs boson. And, yes, you have to go to work tomorrow.

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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From Fermilab- “Frontier Science Result: CDF Testing the Higgs boson’s spin and parity with CDF

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Thursday, Aug. 21, 2014
Tom Junk and Andy Beretvas

Since the discovery of the Higgs boson at CERN and the three-standard-deviation excess seen by the CDF and DZero experiments here at Fermilab, the experimental community has been focusing on measuring the properties of this new particle. It’s important to determine whether there is just one new particle or if two or more are contributing to the observed data. The answer at the Tevatron could be different from that at the LHC, as the mixture of production mechanisms and the decays contributing to the most sensitive searches are different.

CDF

DZero

Tevatron map

LHC map

The Standard Model’s predictions are that the Higgs boson has all the properties of a heavy piece of the vacuum — there’s no electric charge, or any other kind of charge for that matter. It should have no intrinsic spin, and it should look the same when reflected in a mirror. In short, the only non-zero properties it is expected to have are its mass and its interaction rates with other particles.

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

But what if the particle is not the Standard Model Higgs boson but rather an exotic impostor? A Higgs-like particle could have spin, like a graviton. Or, like a pion,

The quark structure of the pion.

it could be a pseudoscalar — that is, its wave function could change sign (from positive to negative or vice versa) when viewed in a mirror. A group of theorists recently suggested that collisions at the Tevatron producing such Higgs impostors in association with the vector bosons W or Z would have very different measurable properties from those predicted for Standard Model Higgs events. The exotic Higgs bosons would have more kinetic energy on average than their Standard Model twins, and the recoiling vector bosons would also be going faster.

Best-fit signal strengths μ for two cases. Left: the Standard Model versus graviton-like boson (spin 2, positive parity) versus the Standard Model Higgs boson (spin 0, positive parity). Right: the pseudoscalar boson (spin 0, negative parity) versus the Standard Model Higgs boson.

CDF has adapted its sophisticated searches for the Standard Model Higgs boson in the WH→lνbb, the ZH→llbb, and the VH→METbb modes to search for exotic Higgs bosons — the pseudoscalar boson, labeled 0- in the above figure, and a graviton-like spin-2 boson, labeled 2+. The exotic particles were assumed to be produced either in place of the Standard Model Higgs boson or in addition to it. The figure shows the best-fit signal strength parameters μ, which are scaled to the Standard Model Higgs boson signal strength, for both the 0- and 2+ searches.

In neither combined search is there any hint of the presence of an exotic Higgs boson, and we observe consistency with the presence of the Standard Model Higgs boson.

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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From Fermilab: “Got a minute? Which Higgs did we find?

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

August 14, 2014

Really short, but is sums up the swtate of Higgs reseach.

Jun 26, 2014

Dr. John Stupak talks about the discovery of the Higgs boson. Did scientists find the Higgs boson predicted back in 1964 or did they find just one of a group of particles, with the others still to be found?

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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From New Scientist: “Higgs boson glimpsed at work for first time”

New Scientist

17 July 2014
Lisa Grossman

The world’s largest particle collider has given us our first glimpse of the Higgs boson doing its job.

Fresh from the ATLAS detector at the Large Hadron Collider (Image: CERN)

For 50 years, the Higgs boson was the final missing piece in the standard model of particle physics, which elegantly predicts how fundamental particles and forces interact. The ATLAS experiment at the Large Hadron Collider near Geneva, Switzerland, was one of the detectors that helped discover the Higgs in 2012.

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

CERN/ATLAS

CERN/LHC map

Now ATLAS physicists report seeing pairs of particles called W bosons scattering off each other inside the detector. This rare process can be used to test how the Higgs actually operates.

“We know these particles very well, but we have never seen them interact in this way before,” says Marc-André Pleier at Brookhaven National Laboratory in New York. “With this measurement, we can check that the Higgs boson does its job.”

W mystery

The Higgs was dreamed up to explain why some force-carrying particles like the W and Z bosons have mass, while others such as the photon do not. In the process, theorists realised that the Higgs could solve another mystery involving the W boson. When they tried to calculate how often W bosons should interact with each other, the results were physically impossible without the Higgs and the theory started to break down. Allowing W bosons to toss a Higgs between them as they collided solved the problem.

“This is one of the things that people put out there saying there must be a Higgs boson,” says Matthew Herndon at the University of Wisconsin Madison, who works on similar problems with another LHC experiment called CMS. It also makes W scattering one of the best places to look for physics beyond the standard model – which does not take gravity into account and cannot explain mysteries such as dark matter and dark energy.

Since the Higgs’s discovery, physicists have been scrutinising its properties to see if it is the same particle predicted by the standard model or if it is a weird variant that will uncover chinks in the model’s armour.

“We have a pretty good idea of what this boson should look like,” says Pleier. “Like a ‘wanted’ poster in the Wild West, where the eye colour or a scar or whatever correspond to certain quantum properties. This is what we do with direct measurements of the Higgs boson.”
Higgs interrogated

So far the Higgs has been frustratingly picture perfect. With the LHC shut down for an upgrade until 2015, it seemed that physicists would just have to wait to collect more information. But another way to interrogate the Higgs is to test how it operates. If W bosons can exchange more than one Higgs, for example, they should fly off each other much more often than the standard model predicts.

“The rates of these scattering processes and the energies you see them at would be forced to change fairly dramatically,” says Herndon. “So this is a good bet for looking for new physics.”

What has made this a challenge is that W bosons scatter off each other incredibly rarely at the LHC, even less often than a Higgs boson is produced. The LHC works by smashing protons together at close to the speed of light. Every so often, one of those protons will emit a W boson. We can only look for scattering if both protons happen to emit a W at the same time, and if those W bosons happen to be aimed at each other.

ATLAS has seen evidence for 34 of these events among billions of collisions, says Pleier. So far, everything fits with the standard model’s predictions. But seeing the effect at all is a milestone, and Herndon says that the CMS experiment will be releasing its version of these results soon, adding to the data pool.

“We’ve never looked in this corner of the standard model before,” says ATLAS team member Jake Searcy at the University of Michigan, Ann Arbor. “This is the start of something that’s going to be very interesting in the years to come.”

From CMS at CERN: “CMS closes major chapter of Higgs measurements”

2014-07-03
Tiziano Camporesi

The data reveal that the particle discovered at CERN continues to behave just like the Standard Model predicts

The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

Since the discovery of a Higgs boson by the CMS and ATLAS Collaborations in 2012, physicists at the LHC have been making intense efforts to measure this new particle’s properties. The Standard Model Higgs boson is the particle associated with an all-pervading field that is believed to impart mass to fundamental particles via the Brout-Englert-Higgs mechanism [Robert Brout June 14, 1928 – May 3, 2011 deceased, so no Nobel]. Awaited for decades, the 2012 observation was a historical milestone for the LHC and led to the award of the 2013 Nobel Prize in Physics to Peter Higgs and François Englert. An open question arising from the discovery is whether the new particle is the one of the Standard Model – or a different one, perhaps just one of many types of Higgs bosons waiting to be found. Since the particle’s discovery, physicists at the LHC have been making intense efforts to answer this question.

This week, at the 37th International Conference on High Energy Physics, a bi-annual major stage for particle physics, which in 2014 is held in Valencia, Spain, the CMS Collaboration is presenting a broad set of results from new studies of the Higgs boson. The new results are based on the full Run 1 data from pp collisions at centre-of-mass energies of 7 and 8 TeV. The analysis includes the final calibration and alignment constants and contains about 25 fb−1 of data.

Decay to two photons

The Higgs boson is an ephemeral particle. It decays into pairs of lighter particles almost immediately after it is produced in LHC collisions. One such “decay channel” is the one in which the Higgs transforms into two photons. The latest CMS results in this decay channel [1] show a peak in the data with a significance of 5σ; the probability that random fluctuations would give a peak this significant at this mass in the absence of a new boson is less than one in 3,000,000. Figure 1 shows the clear signal of the Higgs over the background in the data. CMS has also measured the mass of the Higgs boson with a precision of a few parts per thousand, with the systematic uncertainty of the measurement four times smaller than the previous preliminary value.

The precision of the new mass measurement testifies to the inspired design and meticulous construction of the CMS detector, its efficient operation and calibration throughout Run 1 of the LHC, and the tireless efforts of the analysis teams in understanding all aspects of the detector performance.

Combining decay channels, production modes

The two-photon analysis completes the set of Run 1 measurements with final calibration and alignment, covering the five primary decay modes of the Higgs boson [2,3,4,5]. This paves the way for a preliminary combination of all the decay channels observed thus far [6], to extract the maximum possible information on the properties of the new boson, including its couplings to the fundamental particles. The combined best-fit ratio of the signal strength observed to that expected in the Standard Model, is found to be 1.00 ± 0.13, in square agreement with state-of-the-art Standard Model calculations. Furthermore, when the data are dissected into the separate production and decay properties of the Higgs boson, no significant deviations from the expectations for the Standard Model are found. In addition to the coupling results, the preliminary combination includes a combined measurement of the Higgs boson mass from the two-photon and ZZ→4ℓ channels: mH = 125.03 ± 0.30 GeV. Taken together, the results represent an impressive tour de force, the culmination of four years of painstaking effort that began with the first CMS searches for the Higgs boson in 2010.

“After half a century of searching, it is exhilarating to piece together the Higgs puzzle, standing on the shoulders of giants, both those who built the experiments and those who carried out the Standard Model calculations,” says Prof Jim Olsen, who is currently convening the Higgs Analysis Group in CMS.

Spin-parity of the particle

Finally, the spin structure of the Higgs boson has been probed with unprecedented detail in a new set of CMS results searching for anomalous couplings to vector bosons. If the new particle is indeed a Higgs boson it should be a scalar, a particle with zero spin and positive parity. The analyses include separate investigations of the WW→2ℓ2ν [7] and ZZ→4ℓ [8] decay channels to test alternative spin-parity assignments against the expected scalar nature of the Standard Model Higgs boson. For the first time, the possibility that the particle is an admixture of different parity states is also investigated. Results are combined for the two channels and all alternative hypotheses studied are found to be significantly disfavoured with respect to the Standard Model hypothesis.

Along with the recent CMS publication in Nature Physics demonstrating strong evidence for the Higgs boson decay to fermions [9], the new results presented in Valencia provide further striking signs of its Standard Model nature. With the wrapping up of Run 1 results, the CMS experiment is now intensely focused on preparations for Run 2, where the centre-of-mass energy of the LHC will be raised to up to 13 TeV and the luminosity will be much increased. With a more powerful accelerator and the upgraded CMS detector, the collaboration looks forward to the promise of new and exciting results on the Higgs boson in Run 2.

Andre Tinoco Mendes, a researcher at CERN who is reporting the Higgs results from CMS at the conference, stressed, “It will take more data and better calculations to sharpen the picture further and exploit the full potential of the LHC.”

Meet CERN in a variety of places:

THE FOUR MAJOR PROJECT COLLABORATIONS

LHC

From Don Lincoln at Fermilab: “Big Mysteries: The Higgs Mass”

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Don Lincoln brings us another interesting video about the Higgs boson.
Learn and enjoy.

Dr. Don Lincoln

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

From CERN: “CERN congratulates Englert and Higgs on Nobel in physics”

8 Oct 2013
Cian O’Luanaigh

CERN congratulates François Englert and Peter W. Higgs on the award of the Nobel prize in physics “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.” The announcement by the ATLAS and CMS experiments took place on 4 July last year.

François Englert (left) and Peter Higgs at CERN on 4 July 2012, on the occasion of the announcement of the discovery of a Higgs boson by the ATLAS and CMS experiments (Image: Maximilien Brice/CERN)

“I’m thrilled that this year’s Nobel prize has gone to particle physics,” says CERN Director-General Rolf Heuer. “The discovery of the Higgs boson at CERN last year, which validates the Brout-Englert-Higgs mechanism, marks the culmination of decades of intellectual effort by many people around the world.”

The Brout-Englert-Higgs (BEH) mechanism was first proposed in 1964 in two papers published independently, the first by Belgian physicists Robert Brout and François Englert, and the second by British physicist Peter Higgs. It explains how the force responsible for beta decay is much weaker than electromagnetism, but is better known as the mechanism that endows fundamental particles with mass. A third paper, published by Americans Gerald Guralnik and Carl Hagen with their British colleague Tom Kibble further contributed to the development of the new idea, which now forms an essential part of the Standard Model of particle physics. As was pointed out by Higgs, a key prediction of the idea is the existence of a massive boson of a new type, which was discovered by the ATLAS and CMS experiments at CERN in 2012.

Standard Model

The Standard Model describes the fundamental particles from which we, and all the visible matter in the universe, are made, along with the interactions that govern their behaviour. It is a remarkably successful theory that has been thoroughly tested by experiment over many years. Until last year, the BEH mechanism was the last remaining piece of the model to be experimentally verified. Now that it has been found, experiments at CERN are eagerly looking for physics beyond the Standard Model.

Meet CERN in a variety of places:

THE FOUR MAJOR PROJECT COLLABORATIONS

LHC

From Fermilab- “Frontier Science Result: CMS The Higgs boson’s big brother

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Friday, May 3, 2013
Jim Pivarski

“Evidence is mounting that the particle discovered last year is the long-sought Higgs boson. When it was announced, no one seemed more cautious of claiming that than its discoverers. But now, as experimental uncertainties shrink, they can confidently say that the particle has no intrinsic spin, it is mirror-symmetric, and it couples to other particles in rough proportion to their masses. These are all properties that the boson predicted by the Higgs mechanism must satisfy.

A heavy variant of the Higgs boson would decay primarily into W bosons or Z bosons. This is a decay mode newly added to the search. No imaged credit.

One property that the theory does not predict well, however, is the mass of that boson. All predictions relied on assumptions about physics beyond the Standard Model, but generally they were in the few-hundred-GeV range. When the LHC experiments began their search, they cast as wide a net as possible and seem to have made a catch at the low end, 125 GeV.

Standard Model

That’s not the end of the story: Even if the 125-GeV boson gives mass to the fundamental particles, it may not be acting alone. Nothing in the theory forbids multiple Higgs bosons. In fact, many of the predictions for a low-mass Higgs were based on supersymmetric extensions of the Standard Model, and these extensions require at least five Higgs bosons. So while some physicists study the properties of the boson in hand, others scour the net for more.”

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

From Fermilab- “Frontier Science Result: CDF CDF finalizes its combined Higgs boson results

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Thursday, March 21, 2013
Andy Beretvas

“CDF’s physicists have been searching for the Higgs boson since the early days of Run I, publishing their first paper on the search in 1990. If you asked any of them why they did it, they would say it was to learn about what breaks the symmetries of the Standard Model, which is so successful in explaining the data observed at Fermilab and at other particle physics laboratories. Particles cannot have masses if these symmetries hold true, and the Higgs mechanism is the simplest, but not the only, way to resolve this dilemma. On July 4 of last year, two independent experiments at CERN, ATLAS and CMS, announced the observation of a Higgs-like boson. On July 27 Fermilab’s CDF and DZero experiments submitted a combined analysis showing evidence for a Higgs-like particle. The experiments at CERN were primarily finding the decay of the Higgs-like particle into bosons, while the experiments at Fermilab were finding the decay into fermions.

CDF sought the Higgs boson in many production and decay modes over the years. These searches have now been finalized and documented. The combined results of all of these analyses have been put together and are the last pieces of the chain. Each analysis relied upon the excellent performance of the Tevatron collider and the CDF detector.

The collaborations will soon submit a new paper that finalizes the combined CDF and DZero result.

Best-fit cross section for inclusive Higgs boson production, normalized to the Standard Model expectation, for the combination of all CDF search channels as a function of the Higgs boson mass. The solid line indicates the fitted cross section, and the associated shaded regions show the 68 percent and 95 percent credibility intervals, which include both statistical and systematic uncertainties.

Standard Model with Higgs

The CDF collaboration celebrates the Tevatron on Sept. 30, 2011. Photo: Cindy Arnold

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

From Fermilab- “Frontier Science Result: CDF Looking for additional Higgs-like particles”

Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

Thursday, Feb. 7, 2013
edited by Andy Beretvas

An exciting part of the much-celebrated particle discovery recently made at the Large Hadron Collider is that it is only the first step on the road to understanding the Higgs boson. Much remains to be discovered about the particle and its properties; knowing its mass is just the beginning. The next step is to study how the particle behaves and how it fits into the big picture of physics as a whole. One of the biggest questions is whether the Higgs boson theorized by the Standard Model (SM) is the only Higgs boson, or rather whether the SM Higgs boson is part of a larger family of particles.

In this analysis CDF physicists investigate a phenomenological model. We assume a heavy neutral Higgs boson decays into a lighter charged intermediate Higgs boson and a charged W [boson], and that the charged intermediate Higgs boson then decays into the SM Higgs and a charged W. The net result of this cascade decay is a final state consisting of two bottom quarks and two W bosons. This model, called a two-Higgs boson doublet, involves four Higgs boson particles: a new neutral heavy Higgs boson, a neutral SM Higgs boson (having a mass of 126 GeV/c2), and two intermediate charged Higgs bosons.”

CDF at Fermilab

Distribution of events, in the signal region. The horizontal axis shows bb invariant mass. The figure shows the data, the signal and four different backgrounds. The signal hypothesis is: a total cross section of 250 femtobarns, a heavy neutral Higgs boson of mass 500 GeV/c2 and lighter charged Higgs boson H± of mass 300 GeV/c2 along with the Standard Model Higgs boson.

By careful comparison to a SM background-only theory (see above figure), we set the world’s first upper limits on a two-Higgs-doublet cascade decay.

See the full article here. For those so inclined, there is a link to the paper regarding this work.

Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

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