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  • richardmitnick 9:31 am on January 27, 2015 Permalink | Reply
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    From Huff Post: “The Future of Physics” 

    Huffington Post
    The Huffington Post


    Dr. Sten Odenwald, Astronomer, National Institute of Aerospace

    In another few months the Large Hadron Collider. will be powered up to explore its maximum energy range. Many physicists fervently hope we will see definite signs of “new physics,” especially a phenomenon called “supersymmetry.” In the simplest view, the Standard Model souped-up with supersymmetry will offer a massive new partner particle for every known particle (electron, quark, neutrino, etc). One of these, called the neutralino, may even explain dark matter itself!

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

    Supersymmetry standard model
    Standard Model of Supersymmetry

    But Wait, There’s More!

    Supersymmetry is the foundational cornerstone on which string theory rests. That’s why physicists call this “stringy” theory of matter “superstring theory.” If the LHC does not turn up any signs of supersymmetry during the next two or three years, not only will simple modifications to the current Standard Model be ruled out, but the most elegant forms of supersymmetry theory will fall too.

    As an astronomer I am not too worried. The verified Standard Model is now fully capable of accounting for everything we see in the universe since a trillion-trillion-trillionth of a second after the Big Bang to the present time, once you include gravity, and don’t worry too much about dark matter and dark energy.

    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 we need some explanation for dark energy and dark matter to complete our understanding of the cosmos, and for that we still need our physicist friends to show the way. Currently their only answers involve supersymmetry theory. If this idea falls, astronomers will be completely stumped to explain what governs our universe on the largest scales.

    Beyond supersymmetry, we also have the huge investment of talent that has pursued superstring theory since the early 1980s. Without supersymmetry, the “super” part of string theory also falls, and you end up with a non-super string theory that is clunky, inelegant and pretty dismal in accounting for the finer details of our physical world, often termed “quantum gravity.” A big part of this is the idea that our universe inhabits more than four dimensions — perhaps as many as 11!

    On April 26, 2006, I had the following exchanges with Stanford theoretical physicist Leonard Susskind, who is widely regarded as one of the fathers of string theory, along with other provocative and foundational ideas such as the “holographic universe.” His comments are still relevant seven years later.


    Odenwald: Why is it so important for physicists to consider the universe having more than four dimensions, as the mathematics of superstring theory seems to require?

    Susskind: Almost all working high-energy theoretical physicists are convinced some sort of extra dimensions are needed to explain the complexity of elementary particles. That particles move in extra dimensions is another way of talking about the fact that they have more complex properties than just position and velocity. It is hard to find a serious paper about particle phenomenology that doesn’t in some way use the tools of superstring theory. Furthermore, we all agree that the origin of elementary particles is most likely at the planck scale and cannot be understood without a good theory of quantum gravity.

    Odenwald: So if superstring theory were found to be an incorrect model for our particular universe, is that like turning the clock back to circa 1978 in physics?

    Susskind: I agree that going back to the ’70s would be turning the clock back in the sense that we would be ignoring the vast amount of mathematical knowledge that has been gained over the subsequent years, mostly from string theory. That is just not going to happen. The changes in our theoretical understanding of quantum field theory, gravity, black holes, are completely irreversible. [String theory mathematics] has even worked its way into nuclear physics and heavy ion collisions as well as into condensed matter physics.

    Odenwald: Kind of a hard place for modern theoreticians to revisit, but for astronomy and cosmology the 1970s seem not such a bad place. Without superstring theory, we would still have cosmological inflation. Without superstring theory, what happened at the instant of the Big Bang would remain unknown, logically indescribable, and still a great puzzle… as it always has.

    Susskind: [Not quite.] Recent cosmology has been completely dominated by studying the cosmic microwave background [CMB] and inflationary theory.

    Cosmic Background Radiation Planck
    CMB per ESA/Planck

    ESA Planck

    Gravitational Wave Background
    Gravitational waves from BICEP2 in support of Inflation theory not yet accepted

    BICEP 2

    The CMB fluctuation spectrum is widely understood as a quantum effect. Inflation is a gravitational effect. Is there any question that quantum gravity (quantum plus gravity) will be the framework for understanding the early universe? No, there is not. Also I might add that the old inflation that you are referring to was a disaster. It didn’t work. Many inflationary cosmologists like Linde, Vilenkin, and Guth are looking to string theory for possible answers to the puzzles of inflation.

    Odenwald: Is it fair to say that superstring theory is “too big to fail”? I am reminded of the alledged quotation by Einstein as he was awaiting news about a major test of relativity in 1919. A reporter is said to have asked, “Well, what would it mean if your theory is wrong?” to which Einstein allegedly replied, “Then I would feel sorry for the good Lord; the theory is correct!” Is the physics community in the same predicament because superstring theory is a “beautiful” theory that seems to explain so much, and its mathematics is so impeccable that it is used in other theoretical settings in physics?

    Susskind: Exactly right. However, it is fair to say that while theorists were developing powerful tools, they mostly had wrong expectations for what the theory was indicating. Most theorists hoped that string theory would lead to an absolutely unique set of particles, coupling constants, with exactly vanishing cosmological constant. What we have learned from the theory itself is that it is a theory of tremendous diversity. Unexpectedly, string theory is most comfortable with a huge multiverse of tremendous variety instead of the small “knowable” and unique universe we once imagined.

    Odenwald: So what would our theoretical explanations for our universe look like without added dimensions, quantum gravity or string theory?

    Susskind: Without these things the world as we know it couldn’t exist. Giving up quantum gravity means giving up either the ideas of quantum [mechanics] or of gravity [and general relativity]. In a cosmological context quantum gravity is responsible for the primordial density fluctuations [we directly observe in the CMB] that ultimately condensed to form stars, galaxies, planets, etc. Without string theory we should not have the diversity of possibilites that allow pocket universes [Alan Guth’s term] with the ultra-fine tuning needed to insure conditions for our kind of life.

    Odenwald: If string theory loses its experimental support at the LHC, wouldn’t it be far worse than merely going back to cosmology circa 1975 or even 1965? We would have to question the very mathematical tools we have been using for the last 50 years!

    Susskind: I agree with your analysis, except that I would add: Expect the unexpected. Unforseen surprises are the rule in science, not the exception. Remember: Stuff happens.

    Odenwald: If superstring theory falls, are there any competing theories out there that could hold out some hope?

    Susskind: Not as far as I know.

    • * * * *

    So there you have it. The Large Hadron Collider absolutely has to find some clue about supersymmetry, or superstring theory is compromised, we will have no good idea about dark matter, and we will definitely be in a bad place until the super-LHC is built in the 2030s.

    Patience, however, is a still a necessary virtue. Physicists were in this same quandary before the Higgs boson was finally discovered after 50 years of increasingly panicked searching.

    See the full article here.

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  • richardmitnick 11:09 am on September 21, 2014 Permalink | Reply
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    From The Daily Galaxy: “”Hidden Supersymmetry?” –Debate Over a New Physics Intensifies (The Weekend Feature)” 

    Daily Galaxy
    The Daily Galaxy

    Theoretical physicists have theorized a possible solution to a longstanding mystery bolstered by the recent discovery of the Higgs boson – a way to preserve the theory of supersymmetry. It was a breakthrough with profound implications for the world as we know it: the Higgs boson, the elementary particle that gives all other particles their mass, discovered at the Large Hadron Collider in 2012. But, for many scientists, it’s only the beginning. When the LHC fires up again in 2015 at its highest-ever collision energy, theorists will be watching with intense interest.
    Earlier this year in Physical Review Letters, Csaba Csaki, Cornell professor of physics, and colleagues theorized a possible solution to a longstanding mystery bolstered by the recent discovery of the Higgs – a way to preserve the theory of supersymmetry, a popular, but experimentally unproven, extension of the Standard Model of particle physics.

    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.

    Depiction of Higgs Boson

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles


    Supersymmetry could help explain the unusual properties of the Higgs boson, why the strong and weak interactions of subatomic particles appear to be so different, as well as the origin of dark matter, which makes up a quarter of the universe.

    The Standard Model deals with three of nature’s fundamental forces: strong, weak and electromagnetic, which govern the relationships between all the known subatomic particles. Supersymmetry extends the Standard Model by introducing new particles, called “superpartners”; every observed particle would have a corresponding superpartner, with similar properties to those of the observed particles, except heavier and with different spin values.

    Some scientists think supersymmetry ought to be abandoned after the LHC failed to detect any of these superpartners; some of them, like the top quark’s superpartner, the “stop,” is predicted to be so light that the LHC should already have seen it.

    In their paper, Csaki and colleagues counter that the particles may be hidden by the noise of other particles formed during the LHC’s unprecedented energy of proton-proton collisions.

    Their idea has to do with a concept called R-parity. All observed particles are assumed to have positive R-parity, while the unobserved superpartners would be negative, implying that the superpartners cannot decay to ordinary particles exclusively.

    Searching for the superpartners at the LHC, Csaki explained, has largely operated under the assumption that this R-parity is always exactly conserved. Csaki and colleagues pose a scenario in which R-parity is violated, and would result in a series of interactions giving rise to particle decays that would be nearly impossible to detect by the LHC’s current parameters.

    “The upshot is that there are ways to hide supersymmetry at the LHC,” Csaki said. “If the signal isn’t very different from the background, it’s very hard to find them. That’s the problem.”

    The LHC, when back online next year, is scheduled to run at a collision energy of 14 TeV (teraelectron volts) – about double the energy of previous runs. It could lead to ultimate proof of the theory of supersymmetry, which Csaki deems the “most beautiful” of the Standard Model extensions offered today – but science must make room for all possibilities.

    “It’s very possible that supersymmetry is not the right theory, and that’s OK,” he said. “The important thing is to understand the way science works, to try and make the best guesses you can, and the experimentalists go and check it. … We have to make sure we are exploring every corner, and we shouldn’t leave some potentially reasonable theory out where things could be hiding.”

    The image at the top of the page is an artist’s simulation of dark matter halo around the Milky Way galaxy.’s own backyard. Credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)

    See the full article here.

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  • richardmitnick 2:21 pm on August 19, 2014 Permalink | Reply
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    From Quanta: “At Multiverse Impasse, a New Theory of Scale” 

    Quanta Magazine
    Quanta Magazine

    August 18, 2014
    Natalie Wolchover

    Mass and length may not be fundamental properties of nature, according to new ideas bubbling out of the multiverse.

    Though galaxies look larger than atoms and elephants appear to outweigh ants, some physicists have begun to suspect that size differences are illusory. Perhaps the fundamental description of the universe does not include the concepts of “mass” and “length,” implying that at its core, nature lacks a sense of scale.

    This little-explored idea, known as scale symmetry, constitutes a radical departure from long-standing assumptions about how elementary particles acquire their properties. But it has recently emerged as a common theme of numerous talks and papers by respected particle physicists. With their field stuck at a nasty impasse, the researchers have returned to the master equations that describe the known particles and their interactions, and are asking: What happens when you erase the terms in the equations having to do with mass and length?

    Nature, at the deepest level, may not differentiate between scales. With scale symmetry, physicists start with a basic equation that sets forth a massless collection of particles, each a unique confluence of characteristics such as whether it is matter or antimatter and has positive or negative electric charge. As these particles attract and repel one another and the effects of their interactions cascade like dominoes through the calculations, scale symmetry “breaks,” and masses and lengths spontaneously arise.

    Similar dynamical effects generate 99 percent of the mass in the visible universe. Protons and neutrons are amalgams — each one a trio of lightweight elementary particles called quarks. The energy used to hold these quarks together gives them a combined mass that is around 100 times more than the sum of the parts. “Most of the mass that we see is generated in this way, so we are interested in seeing if it’s possible to generate all mass in this way,” said Alberto Salvio, a particle physicist at the Autonomous University of Madrid and the co-author of a recent paper on a scale-symmetric theory of nature.

    In the equations of the “Standard Model of particle physics”, only a particle discovered in 2012, called the Higgs boson, comes equipped with mass from the get-go. According to a theory developed 50 years ago by the British physicist Peter Higgs and associates, it doles out mass to other elementary particles through its interactions with them. Electrons, W and Z bosons, individual quarks and so on: All their masses are believed to derive from the Higgs boson — and, in a feedback effect, they simultaneously dial the Higgs mass up or down, too.

    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.

    The new scale symmetry approach rewrites the beginning of that story.

    Alessandro Strumia of the University of Pisa, pictured speaking at a conference in 2013, has co-developed a scale-symmetric theory of particle physics called “agravity.” Thomas Lin/Quanta Magazine

    “The idea is that maybe even the Higgs mass is not really there,” said Alessandro Strumia, a particle physicist at the University of Pisa in Italy. “It can be understood with some dynamics.”

    The concept seems far-fetched, but it is garnering interest at a time of widespread soul-searching in the field. When the Large Hadron Collider at CERN Laboratory in Geneva closed down for upgrades in early 2013, its collisions had failed to yield any of dozens of particles that many theorists had included in their equations for more than 30 years. The grand flop suggests that researchers may have taken a wrong turn decades ago in their understanding of how to calculate the masses of particles.

    “We’re not in a position where we can afford to be particularly arrogant about our understanding of what the laws of nature must look like,” said Michael Dine, a professor of physics at the University of California, Santa Cruz, who has been following the new work on scale symmetry. “Things that I might have been skeptical about before, I’m willing to entertain.”

    The Giant Higgs Problem

    The scale symmetry approach traces back to 1995, when William Bardeen, a theoretical physicist at Fermi National Accelerator Laboratory in Batavia, Ill., showed that the mass of the Higgs boson and the other Standard Model particles could be calculated as consequences of spontaneous scale-symmetry breaking. But at the time, Bardeen’s approach failed to catch on. The delicate balance of his calculations seemed easy to spoil when researchers attempted to incorporate new, undiscovered particles, like those that have been posited to explain the mysteries of dark matter and gravity.

    Instead, researchers gravitated toward another approach called “supersymmetry” that naturally predicted dozens of new particles. One or more of these particles could account for dark matter. And supersymmetry also provided a straightforward solution to a bookkeeping problem that has bedeviled researchers since the early days of the Standard Model.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    In the standard approach to doing calculations, the Higgs boson’s interactions with other particles tend to elevate its mass toward the highest scales present in the equations, dragging the other particle masses up with it. “Quantum mechanics tries to make everybody democratic,” explained theoretical physicist Joe Lykken, deputy director of Fermilab and a collaborator of Bardeen’s. “Particles will even each other out through quantum mechanical effects.”

    This democratic tendency wouldn’t matter if the Standard Model particles were the end of the story. But physicists surmise that far beyond the Standard Model, at a scale about a billion billion times heavier known as the “Planck mass,” there exist unknown giants associated with gravity. These heavyweights would be expected to fatten up the Higgs boson — a process that would pull the mass of every other elementary particle up to the Planck scale. This hasn’t happened; instead, an unnatural hierarchy seems to separate the lightweight Standard Model particles and the Planck mass.

    With his scale symmetry approach, Bardeen calculated the Standard Model masses in a novel way that did not involve them smearing toward the highest scales. From his perspective, the lightweight Higgs seemed perfectly natural. Still, it wasn’t clear how he could incorporate Planck-scale gravitational effects into his calculations.

    Meanwhile, supersymmetry used standard mathematical techniques, and dealt with the hierarchy between the Standard Model and the Planck scale directly. Supersymmetry posits the existence of a missing twin particle for every particle found in nature. If for each particle the Higgs boson encounters (such as an electron) it also meets that particle’s slightly heavier twin (the hypothetical “selectron”), the combined effects would nearly cancel out, preventing the Higgs mass from ballooning toward the highest scales. Like the physical equivalent of x + (–x) ≈ 0, supersymmetry would protect the small but non-zero mass of the Higgs boson. The theory seemed like the perfect missing ingredient to explain the masses of the Standard Model — so perfect that without it, some theorists say the universe simply doesn’t make sense.

    Yet decades after their prediction, none of the supersymmetric particles have been found. “That’s what the Large Hadron Collider has been looking for, but it hasn’t seen anything,” said Savas Dimopoulos, a professor of particle physics at Stanford University who helped develop the supersymmetry hypothesis in the early 1980s. “Somehow, the Higgs is not protected.”

    The LHC will continue probing for convoluted versions of supersymmetry when it switches back on next year, but many physicists have grown increasingly convinced that the theory has failed. Just last month at the International Conference of High-Energy Physics in Valencia, Spain, researchers analyzing the largest data set yet from the LHC found no evidence of supersymmetric particles. (The data also strongly disfavors an alternative proposal called “technicolor.”)

    The multiverse hypothesis has surged in begrudging popularity in recent years. But the argument feels like a cop-out to many, or at least a huge letdown.

    The implications are enormous. Without supersymmetry, the Higgs boson mass seems as if it is reduced not by mirror-image effects but by random and improbable cancellations between unrelated numbers — essentially, the initial mass of the Higgs seems to exactly counterbalance the huge contributions to its mass from gluons, quarks, gravitational states and all the rest. And if the universe is improbable, then many physicists argue that it must be one universe of many: just a rare bubble in an endless, foaming “multiverse.” We observe this particular bubble, the reasoning goes, not because its properties make sense, but because its peculiar Higgs boson is conducive to the formation of atoms and, thus, the rise of life. More typical bubbles, with their Planck-size Higgs bosons, are uninhabitable.

    “It’s not a very satisfying explanation, but there’s not a lot out there,” Dine said.

    As the logical conclusion of prevailing assumptions, the multiverse hypothesis has surged in begrudging popularity in recent years. But the argument feels like a cop-out to many, or at least a huge letdown. A universe shaped by chance cancellations eludes understanding, and the existence of unreachable, alien universes may be impossible to prove. “And it’s pretty unsatisfactory to use the multiverse hypothesis to explain only things we don’t understand,” said Graham Ross, an emeritus professor of theoretical physics at the University of Oxford.

    The multiverse ennui can’t last forever.

    “People are forced to adjust,” said Manfred Lindner, a professor of physics and director of the Max Planck Institute for Nuclear Physics in Heidelberg who has co-authored several new papers on the scale symmetry approach. The basic equations of particle physics need something extra to rein in the Higgs boson, and supersymmetry may not be it. Theorists like Lindner have started asking, “Is there another symmetry that could do the job, without creating this huge amount of particles we didn’t see?”

    Wrestling Ghosts

    Picking up where Bardeen left off, researchers like Salvio, Strumia and Lindner now think scale symmetry may be the best hope for explaining the small mass of the Higgs boson. “For me, doing real computations is more interesting than doing philosophy of multiverse,” said Strumia, “even if it is possible that this multiverse could be right.”

    For a scale-symmetric theory to work, it must account for both the small masses of the Standard Model and the gargantuan masses associated with gravity. In the ordinary approach to doing the calculations, both scales are put in by hand at the beginning, and when they connect in the equations, they try to even each other out. But in the new approach, both scales must arise dynamically — and separately — starting from nothing.

    “The statement that gravity might not affect the Higgs mass is very revolutionary,” Dimopoulos said.

    A theory called “agravity” (for “adimensional gravity”) developed by Salvio and Strumia may be the most concrete realization of the scale symmetry idea thus far. Agravity weaves the laws of physics at all scales into a single, cohesive picture in which the Higgs mass and the Planck mass both arise through separate dynamical effects. As detailed in June in the Journal of High-Energy Physics, agravity also offers an explanation for why the universe inflated into existence in the first place. According to the theory, scale-symmetry breaking would have caused an exponential expansion in the size of space-time during the Big Bang.

    However, the theory has what most experts consider a serious flaw: It requires the existence of strange particle-like entities called “ghosts.” Ghosts either have negative energies or negative probabilities of existing — both of which wreck havoc on the equations of the quantum world.

    “Negative probabilities rule out the probabilistic interpretation of quantum mechanics, so that’s a dreadful option,” said Kelly Stelle, a theoretical particle physicist at Imperial College, London, who first showed in 1977 that certain gravity theories give rise to ghosts. Such theories can only work, Stelle said, if the ghosts somehow decouple from the other particles and keep to themselves. “Many attempts have been made along these lines; it’s not a dead subject, just rather technical and without much joy,” he said.

    Marcela Carena, a senior scientist at Fermi National Accelerator Laboratory in Batavia, Ill.Courtesy of Marcela Carena

    Strumia and Salvio think that, given all the advantages of agravity, ghosts deserve a second chance. “When antimatter particles were first considered in equations, they seemed like negative energy,” Strumia said. “They seemed nonsense. Maybe these ghosts seem nonsense but one can find some sensible interpretation.”

    Meanwhile, other groups are crafting their own scale-symmetric theories. Lindner and colleagues have proposed a model with a new “hidden sector” of particles, while Bardeen, Lykken, Marcela Carena and Martin Bauer of Fermilab and Wolfgang Altmannshofer of the Perimeter Institute for Theoretical Physics in Waterloo, Canada, argue in an Aug. 14 paper that the scales of the Standard Model and gravity are separated as if by a phase transition. The researchers have identified a mass scale where the Higgs boson stops interacting with other particles, causing their masses to drop to zero. It is at this scale-free point that a phase change-like crossover occurs. And just as water behaves differently than ice, different sets of self-contained laws operate above and below this critical point.

    To get around the lack of scales, the new models require a calculation technique that some experts consider mathematically dubious, and in general, few will say what they really think of the whole approach. It is too different, too new. But agravity and the other scale symmetric models each predict the existence of new particles beyond the Standard Model, and so future collisions at the upgraded LHC will help test the ideas.

    In the meantime, there’s a sense of rekindling hope.

    “Maybe our mathematics is wrong,” Dine said. “If the alternative is the multiverse landscape, that is a pretty drastic step, so, sure — let’s see what else might be.

    See the full article here.

    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

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  • richardmitnick 12:33 pm on June 20, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CMS Slicing parameter space with a razor” 

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

    Friday, June 20, 2014
    Jim Pivarski

    Supersymmetry is hard to kill. It is more general than most theories of physics beyond the Standard Model: It is the basic idea that particles and forces are fundamentally the same thing but appear different because something creates an effective distinction between them, similar to the way that the Higgs boson creates an effective distinction between the electric and weak parts of the electroweak force. For supersymmetry, that “something” is unknown — many different models of supersymmetry breaking have been proposed and others could be thought up tomorrow. Each variant, including minor variations in numerical parameters, yields different decay patterns involving different cascades of 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.

    Supersymmetry standard model
    Standard Model for Supersymmetry

    Seekers of supersymmetry are faced with a dilemma: Pick a model of supersymmetry breaking and hope you’re lucky enough to find it, or look at a quantity that is sensitive to a broad class of models, but with less statistical sensitivity. If you pick a specific model and don’t find it, you can set a precise exclusion limit, but only on one model — supersymmetry itself remains elusive. Broad searches, on the other hand, are hard to formulate. You have to think of a signature that is shared by many supersymmetric models yet is different enough from the Standard Model to clearly claim a discovery or set a tight limit.

    One technique, dubbed “the razor,” shares aspects of both. It makes weak assumptions about the mechanism of supersymmetry breaking but also makes a sharp distinction between supersymmetric particles and the Standard Model. Assuming that supersymmetric particles are within reach of the LHC (like squarks and gluinos), and that they are produced in pairs (R-parity is not violated), and that they decay in cascading chains (as many variants of supersymmetry do), they would show up in LHC collisions as two rough bundles of particles, each with an energy that corresponds to the mass of the first supersymmetric particle in the chain. Different models predict different decay patterns within each bundle, but this technique looks only for the bundles.

    A group of CMS scientists selected events using the razor technique and found them to be consistent with the Standard Model. This cuts out a broad range of supersymmetric models, many more than a focused technique would. There are still others that might evade the razor’s weak assumptions, but the remaining space is getting thin.

    See the full article here.

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  • richardmitnick 9:25 am on March 14, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CMS Embracing complexity 

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

    Friday, March 14, 2014

    Fermilab Don Lincoln
    Dr Don Lincoln

    Sometimes you just gotta do things the hard way. Today’s article describes an attempt to do just that.

    While all particle physics is complicated, certain processes are particularly so. Studying the most common kinds of supersymmetric events predicted to be found at the LHC is like putting together an especially complex puzzle.

    Supersymmetry is a principle that one can incorporate into new or existing theories. At its core, it is nothing more than the rule that matter particles (fermions) and force carrying particles (bosons) in the theory’s equations are indistinguishable from each other. While no evidence for supersymmetry has been observed, it is a very popular idea since it can fill in many physics theory holes. It can provide an explanation for why the mass of the Higgs boson is so small, explain the identity of dark matter, and show how the strong, weak and electromagnetic forces are really different faces of the same thing. Supersymmetry really is a versatile idea.

    Supersymmetry itself isn’t a theory. However, many theories include it, and each one makes a very different prediction. The one universal prediction in such theories is that for every known particle, there exists a corresponding, as-yet-undiscovered partner that differs only in its spin. For example, for every known fermion (quark and lepton), there is a cousin supersymmetric boson (squark and slepton). Similarly, for every known boson (photon, W and Z boson, gluon and Higgs), there is a cousin supersymmetric fermion (photino, wino, zino, gluino and higgsino). If supersymmetry is right, we have to find these cousin particles.

    Physicists have been looking for these supersymmetric particles for decades now, with no luck at all. As with most searches for new phenomena, scientists looked for the easier signatures first. Because supersymmetric sleptons decay into (among other things) ordinary leptons, and because ordinary leptons are easy to identify, many early searches focused on sleptons.

    However, the LHC collides not leptons but protons. That means that, if supersymmetry is real, the most likely supersymmetric particles to come out of the LHC are squarks and gluinos. These particles would decay eventually into more common quarks and gluons, which would make jets — little shotgun-like blasts of particles — in the [particle] detector, and often many jets hit the detector simultaneously.

    In one particularly challenging situation, a pair of gluinos would each make a top quark-antiquark pair. Since each top quark can decay into three lighter quarks, such an event would have 12 jets. Visually, you can imagine such a collision as 12 randomly oriented shotguns going off simultaneously, with the pellets hitting the detector. Events like these are horribly, horribly complicated.

    Complicated though these events may be, CMS scientists went looking for them, and find them they did. The problem is that messy events like these can be created by known physics, and new physics requires that researchers find an excess of events with the above-mentioned characteristics. This analysis is similar to a previous Frontier Science Result but uses collisions in the LHC with higher energy than used in the earlier analysis.

    The result of this search was that no evidence was observed for the extra events predicted by supersymmetry. Thus CMS scientists were able to set stringent limits on the mass of the predicted supersymmetric particles. Now it’s back to the drawing board.

    See the full article here.

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  • richardmitnick 5:36 pm on September 20, 2013 Permalink | Reply
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    From Symmetry: “Scientists expand search for light dark matter” 

    Physicists on the CDMS experiment have devised a better way to search for a particle that, if it exists, would revolutionize our ideas about dark matter.

    side view

    September 20, 2013
    Sarah Witman

    After seeing possible hints of surprisingly light dark matter earlier this year, scientists on the Cryogenic Dark Matter Search have found a way to improve their search for such particles.

    The discovery of low-mass dark-matter particles could tell us that dark matter is more complicated than we originally thought.

    Physicists designed CDMS (pictured above) to look for heavy dark-matter particles, the kind predicted by the popular theory of supersymmetry. Supersymmetry posits that every elementary particle we know—the quark, the lepton, and so on—has a massive partner particle. One such partner particle could be what we call dark matter.

    However, a different theory, currently rising in popularity, predicts the existence of a light dark-matter particle that is just one member in a family of “dark sector” particles.

    “We don’t know; there could be both heavy and light-mass dark-matter particles,” says physicist Dan Bauer, project and operations manager for CDMS and leader of the Fermilab CDMS group. “That’s one of the things that has been interesting in the past few years, the realization that dark matter could be every bit as complicated as normal matter.”

    The CDMS experiment searches for dark-matter particles using a detector filled with germanium and silicon crystals cooled to a very low temperature, about -460 degrees Fahrenheit. Atoms in chilled crystals stay very still, making it easier to notice when they are disturbed. If a dark-matter particle knocks against the nucleus of an atom in the CDMS detector, the interaction will release a small amount of heat and charge, which the scientists measure with sensitive electronics.

    The lighter the particle administering this kick, the smaller the amount of heat and charge released. That makes low-mass dark-matter particles are particularly hard to find.

    A modification to the CDMS detector called CDMSlite—“lite” standing for “low-ionization threshold experiment”—combats this problem with the application of a larger voltage across the crystal (a whopping 69 volts instead of the usual 4). This amplifies the signal that low-mass particles release, giving the scientists a much closer look at the energy range where light dark-matter events should appear.

    The experiment has now set the strongest limits in the world for detection of a dark-matter particle with a mass below 6 billion electronvolts.

    “We are excluding new parameter space that hasn’t been probed before,” says Pacific Northwest National Laboratory physicist Jeter Hall, who conceived of and helped realize the idea of using higher voltages.

    While CDMSlite is not well suited for looking for heavy dark-matter particles—their much-larger signals would saturate the experiment’s electronics—CDMS will not give up on its quest for a massive particle. CDMS scientists will operate detectors in different search modes to cover a wide range of dark-matter masses.

    “We should consider a broad range of possibilities, given how little we know about the properties of dark matter,” says physicist Richard Partridge, who heads SLAC National Accelerator Laboratory’s CDMS group.

    Scientists hope to use the technology developed for CDMSlite in the next generation of the experiment, a larger detector to be placed more than a mile underground at SNOLAB in Canada.

    “The search for dark matter has been on for some time now. Recent evidence points to the possibility of particles lighter than we had anticipated. And hunting for such light dark matter requires newer detection technology,” says Fermilab visiting scholar Ritoban Basu Thakur of the University of Illinois, Urbana-Champaign, who is writing his thesis on CDMSlite. “We are pushing the boundaries of detector technology as we try to find dark matter.”

    CDMS Collaboration

    See the full article here.

    [It seems strange to me that this is the first inkling I have had of this experimentation or its mighty collaboration.]

    Symmetry is a joint Fermilab/SLAC publication.

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  • richardmitnick 8:37 am on July 8, 2013 Permalink | Reply
    Tags: , , , , , Supersymmetry   

    From CMS at CERN: “Supersymmetric glue: the search for gluinos” 

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

    Friday, June 28, 2013
    Don Lincoln

    Fermilab Don Lincoln

    “One of the biggest unanswered questions of particle physics is why the mass of the Higgs boson is relatively small when the Standard Model suggests a more natural value would be many thousands of trillions times higher. We don’t know the answer to that question, but a popular proposed explanation invokes the idea of supersymmetry. Theories that include supersymmetry can very easily explain the Higgs boson’s low mass.

    A theory that includes supersymmetry comes with a price. These theories predict that for every known particle, a cousin supersymmetric particle exists. These cousins have the same properties as the familiar ones, except they have a different subatomic spin. There’s only one problem. None of these cousins has been observed. The simplest form of supersymmetry has been definitively ruled out.

    Since the simplest scenario is impossible, physicists turn to theories in which supersymmetry is almost true. Physicists say that in these modified theories, the symmetry of supersymmetry is ‘broken‘, which in layman’s terms simply means that the supersymmetric cousins are heavier than the familiar particles. Under this assumption, supersymmetry is alive and well.

    But ‘alive and well’ doesn’t mean confirmed. For that, you still have to find the cousins. Unfortunately, supersymmetric theories give us very little guidance as to the masses of the cousins. Thus we have to make some sensible assumptions, look at the data and see what it tells us.

    In today’s article, I describe the outcome of a search for particles called gluinos, which are the supersymmetric cousins of the gluon. If gluinos exist and aren’t too massive, they should be made easily at the LHC.

    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 10:24 am on August 17, 2012 Permalink | Reply
    Tags: , , , , Supersymmetry   

    From Fermilab Today: “CMS Result – Taking them all on at once” 

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

    Friday, Aug. 17, 2012
    Jim Pivarski

    Supersymmetry, the notion that matter and forces are two sides of the same coin, is an elegant idea that could explain many of the mysteries of particle physics. Searching for it, however, is not an easy task because there are so many different ways it could manifest itself.

    The Supersymmetry spectrum from Tomasso Dorigo

    How would you search for something that could look like anything? Fortunately, models of broken supersymmetry share a few broad features. For one thing, all of the models predict new particles, the superpartners of the ones we know. These would decay into familiar particles because they maintain part of their identity as they decay— for instance, supersymmetric quarks, called squarks, would decay to quarks. In many models, the lightest supersymmetric particle is invisible, like dark matter, which shows up in a particle collision as an apparent imbalance in the particle debris.

    In a recent paper, CMS scientists used these as criteria in a broad search for new physics. They looked for an excess of collision events with many high-energy particles in a lopsided pattern, as though an invisible particle carried away much of the energy. They found nothing new— all was in agreement with known physics.

    This result has far-reaching consequences. It rules out many of the simplest models of supersymmetry, but as described in last week’s Nutshell, more subtle models lie beyond.”

    See the full article here.

    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.

    ScienceSprings is powered by MAINGEAR computers

  • richardmitnick 7:14 am on May 4, 2011 Permalink | Reply
    Tags: , , , Supersymmetry   

    From the US/LHC Blog – Matthew Tamsett: “Why Frank Wilczek loves SUSY” 

    Matthew Tamsett

    This week I’ve been in Arlington Texas, attending the excellent south western ATLAS analysis jamboree…The key speaker at this event was Frank Wilczek, the 2004 winner of the Nobel prize in physics…Tonight though, he did not talk about this, instead he focused on the LHC and on its ability to discover Supersymmetry (SUSY)…In brief, SUSY solves a number of problems present in the Standard Model by introducing a new symmetry to the theory which allows the transformation of force particle (bosons) into matter particles (fermions). Essentially presenting these as two facets of the same thing.”

    Read the full post here.


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