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  • richardmitnick 8:14 pm on November 24, 2014 Permalink | Reply
    Tags: , , , Cosmic Inflation, , Don Lincoln,   

    From FNAL- Video: Dr Don Lincoln on Cosmic Inflation 


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

    In 1964, scientists discovered a faint radio hiss coming from the heavens and realized that the hiss wasn’t just noise. It was a message from eons ago; specifically the remnants of the primordial fireball, cooled to about 3 degrees above absolute zero. Subsequent research revealed that the radio hiss was the same in every direction. The temperature of the early universe was uniform to at better than a part in a hundred thousand.

    And this was weird. According to the prevailing theory, the two sides of the universe have never been in contact. So how could two places that had never been in contact be so similar? One possible explanation was proposed in 1979. Called inflation, the theory required that early in the history of the universe, the universe expanded faster than the speed of light. Confused? Watch this video as Fermilab’s Dr. Don Lincoln makes sense of this mind-bending idea.

    Watch, enjoy, learn.

    See the full article here.

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  • richardmitnick 10:31 am on October 31, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS Boosted W’s” 


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

    Friday, Oct. 31, 2014

    FNAL Don Lincoln
    Don Lincoln

    Today’s article covers an interesting topic. It’s interesting not because it explores new physics, but because of how it reveals some of the mundane aspects of research at the LHC. It also shows how the high energy of the LHC makes certain topics harder to study than they were during the good old days at lower-energy accelerators.

    At the LHC, quarks or gluons are scattered out of the collision. It’s the most common thing that happens at the LHC. Regular readers of this column know that it is impossible to see isolated quarks and gluons and that these particles convert into jets as they exit the collision. Jets are collimated streams of particles that have more or less the same energy as the parent quark or gluon. Interactions that produce jets are governed by the strong force.

    map
    In the green region, we show what a W boson looks like before it decays. Moving left to right, the boson is created with more and more momentum. In the yellow region, we repeat the exercise, this time looking at the same W boson after it decays into quarks, which have then turned into jets. Finally in the pink region, we look at a jet originating from a quark or gluon. This looks much like a high-momentum W boson decaying into quarks. Because ordinary jets are so much more common, this highlights the difficulty inherent in finding high-momentum W bosons that decay into jets.
    No image credit

    Things get more interesting when a W boson is produced. One reason for this is that making a W boson requires the involvement of the electroweak force, which is needed for the decay of heavy quarks. Thus studies of W bosons are important for subjects such as the production of the top quark, which is the heaviest quark. W bosons are also found in some decays of the Higgs boson.

    A W boson most often decays into two light quarks, and when it decays, it flings the light quarks into two different directions, which can be seen as two jets.

    But there’s a complication in this scenario at the LHC, where the W bosons are produced with so much momentum that it affects the spatial distribution of particles in those two jets. As the momentum of the W boson increases, the two jets get closer together and eventually merge into a single jet.

    As mentioned earlier, individual jets are much more commonly made using the strong force. So when one sees a jet, it is very hard to identify it as coming from a W boson, which involves the electroweak force. Since identifying the existence of W bosons is very important for certain discoveries, CMS scientists needed to figure out how to tell quark- or gluon-initiated jets from the W-boson-initiated jets. So they devised algorithms that could identify when a jet contained two lumps of energy rather than one. If there were two lumps, the jet was more likely to come from the decay of a W boson.

    CERN CMS New
    CMS

    In today’s paper, CMS scientists explored algorithms and studied variables one can extract from the data to identify single jets that originated from the decay of W bosons. The data agreed reasonably well with calculations, and the techniques they devised will be very helpful for future analyses involving W bosons. In addition, the same basic technique can be extended to other interesting signatures, such as the decay of Z and Higgs bosons.

    See the full article here.

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  • richardmitnick 12:56 pm on October 3, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS Subatomic hydrodynamics” 


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

    Friday, Oct. 3, 2014
    This column was written by Don Lincoln
    FNAL Don Lincoln
    Dr. Don Lincoln

    It’s hard for most people to imagine what it’s like at the heart of a particle collision. Two particles speed toward one another from opposite directions and their force fields intertwine, causing some of the particles’ constituents to be ejected. Or possibly the energy embodied in the interaction might be high enough to actually create matter and antimatter. It’s no wonder the whole process seems confusing.

    crash
    The same basic equations that govern the flow of water are important for describing the collisions of lead nuclei. In today’s article, we’ll get a glimpse of how this works.

    Things get a little easier to imagine when the particles are the nuclei of atoms (note that I said easier, not easy). For collisions between two nuclei of lead, one can imagine two small spheres, each containing 208 protons and neutrons, coming together to collide. Depending on the violence of the collision, some or many of the protons and neutrons might figuratively melt, releasing their constituent quarks so they can scurry around willy-nilly. Physicists call this form of matter a quark-gluon plasma, and it acts much like a liquid.

    pro
    The quark structure of the proton. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons

    neut
    The quark structure of the neutron. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons

    Part of this liquid-like behavior is due to the fact that so many particles are involved. An LHC collision between two lead nuclei might involve thousands or tens of thousands of particles. Because these particles are quarks and gluons, they experience the strong nuclear force. So as long as they are close enough to each other, the particles interact strongly enough that they clump a bit together. The net outcome is that the flow of particles from collision between lead nuclei looks vaguely like splashes of water. In these cases, the equations of hydrodynamics apply. Mathematical descriptions like these have been used to make sense of other features we see in LHC collisions between lead nuclei.

    glu
    In Feynman diagrams, emitted gluons are represented as helices. This diagram depicts the annihilation of an electron and positron.

    However, there is more to understand. We can imagine collisions between the collective 416 protons and neutrons of lead nuclei as splashes of water, but when a pair of protons collide, the collision doesn’t yield enough particles to exhibit hydrodynamic behavior. So as the number of particles involved goes down, the “splash” behavior must slowly go away. In addition, in the first studies of lead nuclei collisions, only the grossest features of the collision were studied. This is because it is impossible to identify individual quarks and gluons.

    There are ways to dig into these sorts of questions. One way is to look at collisions in which one beam is a proton and the other is a lead nucleus. This is a halfway point between the usual LHC proton-proton collisions and the lead-lead ones. In addition, we can turn our attention to quarks that we can unambiguously identify, such as bottom, charm and strange quarks, to better understand the hydrodynamic behavior.

    In this study, physicists looked at particles containing strange quarks. Since strange quarks don’t exist in the beam protons, studying them gives a unique window into the dynamics of lead-lead collisions. By combining studies of particles with strange quarks in lead-lead and lead-proton collisions, scientists hope to better understand the complicated and liquid-like behavior that is just beginning to reveal its secrets.

    See the full article here.

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  • richardmitnick 2:04 pm on October 2, 2014 Permalink | Reply
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    From Don Lincoln in Scientific American: “Particle Physics Informs the Ultimate Questions” 

    Scientific American

    Scientific American

    October 1, 2014
    Don Lincoln
    FNAL Don Lincoln
    Dr. Don Lincoln

    Editor’s Note: Author and Fermilab Senior Scientist Don Lincoln is set to teach “Mysteries of the Universe” from October 13 – 24 for Scientific American’s Professional Learning Program. We recently talked with Dr. Lincoln about why he became a physicist and his motivations to share what he discovers.

    When I was a young boy, I was insatiably curious. I must have driven my parents crazy with my incessant questions about why kittens had fur and why the moon was so much dimmer than the sun. I wanted to know the answer to everything. I still do.

    As I grew older, I began to see a pattern. While the answer to the kitten question might have started with biology and the answer to the moon question involved a combination of gravity, fusion and surface reflectivity, these weren’t the final answers. These interim answers led to new questions, which predictably led to atoms, then electrons and nuclei, to protons and neutrons. It became increasingly clear that what I really wanted to know was what [Albert] Einstein poetically called “God’s thoughts.” No matter your opinion on religion, the meaning of the phrase is clear: I wanted to know nothing less than the ultimate building blocks of the universe and the rules that bind them together. I wanted to know why the world was the way it was.

    As I matured intellectually, I came to realize that I wasn’t the first to ask these questions; indeed, they are among the oldest and grandest questions of all. For millennia, they were debated within the confines of philosophy and religion, but this began to change in the mid-1500s as the modern scientific method was being developed. Empirical testing replaced pure logic as the ultimate arbiter of ideas, leading to the approach still followed today.

    The Large Hadron Collider at the CERN laboratory is the world’s highest energy particle accelerator, a title that it is expected to hold for at least the next two decades. In this facility, scientists collide protons together at nearly the speed of light, generating temperatures at which the very idea of matter becomes hazy. Matter and energy convert back and forth, allowing physicists to gain new insights into the birth of the universe.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    For those of us interested in the ultimate questions of the universe, there are really only two fields of interest: cosmology and particle physics. Cosmology deals with the universe as a whole: its birth, evolution and even its death. There is nothing small about cosmology. Particle physics, on the other hand, is concerned with the tiniest objects, the ultimate building blocks of the cosmos, usually studied by smashing two subatomic particles together at prodigious energies.

    These two realms—the grandness of the heavens for as far as we can see with our biggest telescopes and objects so unimaginably tiny that we needed to invent an entirely new form of physics to describe them—are intricately intertwined and the fact that we know this is one of the crowning triumphs of modern physics. Through centuries of effort, we now believe that the universe began about 14 billion years ago, in an awe-inspiring explosion that we call the Big Bang. At the moment of creation, the cosmos was much denser and hotter, with matter bathed in energies comparable to those achievable by modern particle accelerators.

    Using detectors weighing thousands of tons, particle physicists can record the behavior of matter at unprecedented energies and explore the environment last common at the very moment of creation. It was by studying collisions like the one shown here that scientists came to believe that they had discovered the Higgs boson.

    In essence, using a device like the Large Hadron Collider, we can create the conditions of the universe just fractions of a second after the Big Bang.

    While I’d love to know the answers to the ultimate questions of creation, these answers still elude us. So I elected to do the next best thing. I became a scientist and joined a multi-generational journey of discovery. It was through centuries of effort by curious men and women that we have come to our current understanding of the cosmos. In turn, my contemporaries and I are working to add to that long tradition, to write our own page in the book of knowledge, a book whose first pages were penned thousands of years ago. While it is unlikely any of us currently alive will see the final answer, for our brief time on Earth, we will follow the path laid out for us by the scientific greats of the past and point the way for those who come after. We must be satisfied by the wisdom that fulfillment is not about the destination, but in the way that we travel.

    Like many of my colleagues, I have joined the effort to use the Large Hadron Collider, located at the CERN laboratory in Europe, to better understand the behavior of matter under extreme conditions. The temperatures and pressures generated at the LHC haven’t been common since about a tenth of a trillionth of a second after the universe began. We’ve come a long way since our forebears stared at the stars under a clear and moonless sky and wondered. Being part of this community is how I’ve always wanted to live my life. As kids say nowadays, I am living the dream.

    However, for all of the successes of science, you should not think that we’ve understood everything. Far from it. There are many questions for which we don’t know the answer. For instance, we know that ordinary matter makes up only about 4 percent of the matter and energy in the universe. We don’t understand why our universe is made of matter, when we make matter and antimatter in equal quantities. While our current understanding would awe the best scientific minds of a century ago, there are certainly plenty of mysteries left for future generations. If you’re the sort who pestered your parents with questions about kittens and the moon, come join my colleagues and me. You’ll be among friends.

    Don Lincoln About the Author: Don Lincoln is a senior scientist at Fermi National Accelerator Laboratory.

    FNALTevatron
    Tevatron at Fermilab

    FNAL Wilson Hall
    Wilson Hall

    When he isn’t exploring the energy frontier, he is busy bringing that information to the public as the author of four books – including the newly released “The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Things That Will Blow Your Mind,” blogs for Nova and Johns Hopkins and numerous magazine articles, including two for Scientific American. He has created a series of You Tube videos and is teaching Mysteries of the Universe for the Professional Learning Program

    See the full article here.

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  • richardmitnick 4:26 pm on October 1, 2014 Permalink | Reply
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    From Don Lincoln at Fermilab: “The Big Bang Theory” video 


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

    From Don Lincoln at Fermilab

    FNAL Don Lincoln

    The Big Bang is the name of the most respected theory of the creation of the universe. Basically, the theory says that the universe was once smaller and denser and has been expending for eons. One common misconception is that the Big Bang theory says something about the instant that set the expansion into motion, however this isn’t true. In this video, Fermilab’s Dr. Don Lincoln tells about the Big Bang theory and sketches some speculative ideas about what caused the universe to come into existence.

    Watch, enjoy, learn.

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  • richardmitnick 9:49 am on September 11, 2014 Permalink | Reply
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    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.

    FNAL Don Lincoln
    Don Lincoln

    face

    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.

    pool
    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.

    graph
    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.

    sm
    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.

    measure
    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.

    See the full article here.

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  • richardmitnick 4:04 pm on September 7, 2014 Permalink | Reply
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    From Don Lincoln for JHU Press: “Damage to the Large Hadron Collider” 

    jhu

    FNAL Don Lincoln
    FNAL’s Dr. Don Lincoln

    September 5, 2014

    A spark. That’s all it was . . . just a little spark . . . in a vacuum, no less. It sounds so harmless. What could it hurt? Let’s see how the story unfolds.

    Well, time, which is measured in microseconds at this point, moved on. The spark jumped from copper conductor to copper conductor, causing copper atoms to be knocked off into the vacuum. As the amount of copper vapor grew, the vacuum became less of an insulator and more conductive, letting more electricity flow. That’s when things began to get interesting. Like opening a faucet completely, the trickle of the initial spark grew until it became a torrent of electricity: ten thousand amperes, enough to simultaneously start thirty or so cars in the dead of winter. The onslaught of electricity was enough to melt a chunk of copper the size an adult fist. This would be bad, but, if you will excuse the pun, things were just beginning to heat up.

    The tipping point from annoying incident to serious disaster occurred when the heat from the electrical arc punctured the volume filled with the liquid helium used to cool the Large Hadron Collider magnets to more than 450° Farenheit below zero. Luckily, helium is an inert gas, so an explosion in the usual sense of the word was impossible. However, the helium was in liquid form, and when it encountered more ordinary temperatures, it boiled and turned into gas. When any liquid turns to gas at atmospheric temperature, it expands in volume to 700 times its ordinary size. And the LHC magnets contain an awful lot of helium . . . as in 96 tons of helium. (Although, in the end, only six tons were released.)

    As the helium vented from the storage volume, it jetted out with tremendous force. And by “tremendous force,” I mean enough force to move a 50-foot-long magnet weighing 35 tons and anchored to the concrete floor about two feet. As the helium gas expanded in the LHC tunnel, it pushed air out of the way. The boundary between an environment containing ordinary air and one containing only helium moved up the tunnel at incredible speed. It was possible for a human to outrun the helium monster, but only if the person could run a four-minute mile. Run any slower, and you would be overtaken by helium. Soon, you would fall down and die, suffocated by lack of oxygen.

    Luckily, there was nobody near the punctured helium volume to be in danger. Actually, luck had nothing to do with it. The CERN (European Organization for Nuclear Research) safety professionals were aware of the danger of a catastrophic failure. Although such an incident was extremely unlikely, people are allowed in the Large Hadron Collider tunnel only rarely. If they are allowed inside, they must have special training and carry oxygen tanks and protective clothing. In this case, however, the nearest CERN personnel were miles away from the incident, and even the civilians who lived above the LHC were separated by at least 300 feet of solid rock. No people were ever in danger.

    I was in the United States on the day in September 2008 when the LHC broke. My colleagues and I were getting reports second-hand, and I remember well the group sitting around a table, looking shell-shocked, and asking each other, “How bad can it be?”

    So now, in the fullness of time, we can answer that question. How bad was it? Pretty bad. Repairing the LHC cost tens of millions of dollars and took about a year. In the end, fifty-three magnets, each fifty feet long and weighing thirty-five tons, needed to be removed, repaired, cleaned, and replaced. While the true damage was relatively localized, among the collateral damage was a breeching of the LHC’s beam pipe, into which soot and debris spread for a mile or so. The technicians were busy.

    It is now six years later, and perhaps it is time for a broader viewpoint. Yes, the damage was grave, and yes, it took a year to repair. However, the repair costs were about two percent the cost of the entire LHC, and the delay was only about five percent of the schedule. Granted, if you were a graduate student who was hoping to graduate on the first year’s data, the incident was an awful delay. However, now, in 2014, what was the real consequence? Well, we now have an accelerator that is better instrumented against similar incidents. The damage of 2008 won’t occur again. We have studied billions of particle collisions and begun to explore the behavior of matter under conditions never before possible. We have discovered the Higgs boson and facilitated a Nobel Prize in physics. There have been some considerable successes, and the debacle of 2008 is now fading into distant memory.

    It’s all a matter of perspective. And, let us not forget, the data of 2015 beckons alluringly. Soon the universe will give up some more of her mysteries and scientists will do what they have for millennia: they will take up their pens and begin writing a new page in the book of knowledge, a book whose first pages were penned over two thousand years ago.

    Perspective.

    Don Lincoln is a senior scientist at Fermi National Accelerator Laboratory and an adjunct professor of physics at the University of Notre Dame. He is the author of

    The Large Hadron Collider: The Extraordinary Story of the Higgs Boson and Other Stuff That Will Blow Your Mind
    book

    , Alien Universe: Extraterrestrials in Our Minds and in the Cosmos
    book3

    and The Quantum Frontier: The Large Hadron Collider,
    book2

    all published by Johns Hopkins.

    See the full article here.

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  • richardmitnick 12:18 pm on August 30, 2014 Permalink | Reply
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    From Don Lincoln at Fermilab: “Particle Detectors Subatomic Bomb Squad ” a Great Video 


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

    The manner in which particle physicists investigate collisions in particle accelerators is a puzzling process. Using vaguely-defined “detectors,” scientists are able to somehow reconstruct the collisions and convert that information into physics measurements. In this video, Fermilab’s Dr. Don Lincoln sheds light on this mysterious technique. In a surprising analogy, he draws a parallel between experimental particle physics and bomb squad investigators and uses an explosive example to illustrate his points. Be sure to watch this video… it’s totally the bomb.

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  • richardmitnick 1:57 pm on August 15, 2014 Permalink | Reply
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    From Fermilab: “Physics in a Nutshell What is a WIMP?” 


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

    Friday, Aug. 15, 2014
    Fermilab Don Lincoln
    Don Lincoln

    If you want to understand dark matter, you need to understand terms such as MACHO and WIMP. It’s enough to recall one of those 1970s comic book advertisements for Charles Atlas’ body building program (well, for those of us of a certain age anyway).

    To understand the term WIMP, we need to go back to the idea of dark matter and why we think it exists. The easiest-to-understand evidence for the existence of dark matter involves spinning galaxies. As early as the 1930s, scientists combined measurements of the rotational speed of galaxies with [Isaac] Newton’s theory of gravity and determined that something was awry. The galaxies were spinning so fast that they could not be held together by the gravitational force of the observed matter and should have torn themselves apart. After decades of studies, scientists have determined that the most probable explanation is that there exists another form of matter that we now call dark matter. It is generally imagined that dark matter is essentially a diffuse gas of massive subatomic particles.

    wimp
    Possibility

    Astronomical evidence has allowed us to determine a fairly specific list of properties for dark matter, if it exists. Because this matter neither emits nor absorbs light, it neither is charged nor contains charge within it. This is why we call it dark. It is also stable. We know this because galaxies persist for billions of years. It does not interact via the strong force, as we see no evidence of cosmic rays (made of protons) interacting with it. And because this matter causes galaxies to rotate quickly, we know it both contains mass and participates in the gravitational force.

    That last point is crucial. There are four known forces: the strong and weak nuclear forces, electromagnetism and gravity. We know that dark matter does not experience the strong or electromagnetic forces. We know it does experience gravity. We don’t know about the weak force.

    So let’s think about that for a bit. While the weak force is … well, weak … gravity is incredibly weak, about a trillion trillion trillion times weaker than the weak force. We have never measured the force due to gravity between two subatomic particles (and we probably never will). So if gravity is the only force that dark matter feels, we will likely never detect it, nor will we ever make it any conceivable particle accelerator.

    So how is it that Fermilab (and others) have a vibrant research program looking for dark matter? Is it all wishful thinking?

    The answer is, “Of course not.” However, it does bring forward an assumption buried inside most dark matter searches. This assumption is that dark matter also experiences the weak nuclear force. Like weakly interacting neutrinos, maybe dark matter will occasionally experience an interaction with ordinary matter and be detected.

    So why would scientists postulate that dark matter experiences the weak force? One answer is that if it doesn’t, we’ll never detect it. But that’s not a very good answer. A better answer involves the Higgs boson. Because the Higgs field gives mass to ordinary matter, maybe it also gives mass to dark matter. Further, since the Higgs field was invented to solve a problem with early attempts to unify the weak and electromagnetic forces, maybe the interaction of the Higgs boson with dark matter also ties dark matter to the weak force. And this would be great, as we know from experience that we can detect weak force interactions.

    So this leads us to the meaning of the term “WIMP.” It is a weakly interacting massive particle — the name is quite literal. It is not necessary that dark matter interact via the weak force, and dark matter may not be a WIMP. If dark matter does not interact via the weak force, we’ll probably never detect it directly. In short, the success of all direct dark matter searches depends crucially on dark matter being WIMP-y.

    —Don Lincoln

    See the full article here.

    Fermilab Campus

    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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  • richardmitnick 2:53 pm on July 31, 2014 Permalink | Reply
    Tags: Don Lincoln, , , ,   

    From Don Lincoln of Fermilab: The Origin of Mass, a Really Cool Video 


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

    Don Lincoln at his best.

    Learn and enjoy

    Fermilab Campus

    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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