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  • richardmitnick 10:42 am on July 31, 2015 Permalink | Reply
    Tags: , , , , , , Particle Accelerators,   

    From FNAL- “Frontier Science Result: CMS Shedding light on the invisible Higgs” 

    FNAL II photo

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

    July 31, 2015
    Jim Pivarski

    1
    Event recorded with the CMS detector in 2012 at a proton-proton center of mass energy of 8 TeV. The event shows characteristics expected from the decay of the Standard Model Higgs boson to a pair of photons (dashed yellow lines and green towers). The event could also be due to known standard model background processes..

    There are basically two types of detectors used in collider experiments: trackers, which are sensitive to any particles that interact electromagnetically, and calorimeters, which are sensitive to any particles that interact electromagnetically or through the strong force. That’s only two of the four forces — there’s also the weak force and gravity. Anything that interacts exclusively through the latter two forces would be invisible.

    This is not a speculative point. Neutrinos are effectively invisible in collider experiments. Even specialized neutrino detectors can detect only a small fraction of the neutrinos that pass through them. Dark matter is known purely through its gravitational effect on galaxies; no one even knows if it interacts via the weak force as well. Invisible particles could be slipping through detectors at the LHC right now.

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

    But if you can’t see them, how can you find them? Fortunately, physicists have developed a few tricks, mostly involving conservation laws. For instance, conservation of charge forces some particles and antiparticles to be produced in pairs, and one may be detected while the other decays invisibly. Conservation of momentum requires particles to be produced symmetrically around the beamline; if the observed distribution is highly asymmetric, that’s an indication of an unseen particle.

    In a recent study, CMS physicists used the latter technique to determine how often Higgs bosons decay into invisible particles and also a photon.

    CERN CMS Detector
    CMS in the LHC at CERN

    This is interesting because Higgs bosons have been observed only in a few of their predicted decay modes — the rest could be wildly different from expectations. In particular, Higgs bosons could interact with new phenomena like dark matter or supersymmetry, and most of these particles would be invisible.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    One of the ways supersymmetry might be hiding is by decaying into gravitinos (gravity only), neutralinos (gravity and weak only) and a visible photon.

    Through this analysis, the mostly invisible signature has been partially ruled out: At most 7 to 13 percent of Higgs bosons might decay this way, if any at all. Before the measurement, it could have been as much as 57 percent. That’s a lot for one bite!

    See the full article here.

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    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. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 8:38 am on July 31, 2015 Permalink | Reply
    Tags: , , , , Particle Accelerators,   

    From LC Newsline: “Learn from the experience of others – Tohoku University campus planning group visits DESY” 

    Linear Collider Collaboration header
    Linear Collider Collaboration

    23 July 2015
    Ricarda Laasch

    Temp 1
    Tohoku University campus planning group at DESY (from left: Tokiko Onuki, Nick Walker, Eisaku Nashiyama, and Akihiko Nagasaka)

    German national laboratory Deutsches Elektronen Synchrotron (DESY) welcomed three Japanese visitors on 30 June, 2015, who asked to be introduced to DESY – its campus and organizational structure as an example of a research institute. The group is studying the size and needs of a possible International Linear Collider (ILC) campus in Tohoku.

    ILC schematic
    Possible ILC

    Tokiko Onuki, Campus Designer of Tohoku University, together with Eisaku Nashiyama, General Manager of the Industry and Economy Group from Tohoku Economic Federation and also the Executive Director of the Tohoku ILC Promotion Council, and Akihiko Nagasaka, ILC Promotion Division of the Mayor’s Office at Ichinoseki City, were welcomed at DESY by Manfred Fleischer, Deputy Director of the High Energy Physics Department of DESY, and Nick Walker, Global Coordinator for ILC Accelerator Design & Integration.

    A program alternating between tours around the campus and presentations by different departments of DESY was the day filling schedule which Fleischer and his colleagues presented to the Japanese visitors. The program started with a historical overview of DESY and the present status of the institute as a national laboratory with many international projects. The broad variety of topics encompassed: civil architecture and planning of the campus, needed infrastructure for a laboratory, transportation along the DESY sites (mainly during HERA times), introduction of foreign researcher’s families to life in Germany and the DESY’s social support systems, possible schools and education for researcher’s children, and regional impact of DESY in many facets of life.

    Onuki was interested in different models for office space and their functionality within the research community. The ILC will need offices for resident staff, long-term guest-scientists and also short-term visitors. At DESY different models for the different groups are used which were presented to the visitors. Further needs concerning seminar rooms and other equipment was addressed and also well received by the visitors.
    Of course an institute for the ILC needs more than office buildings. A tour through workshops and a look inside the cavity testing facility AMTF was part of the visit at DESY. “Such a facility like AMTF or even bigger will be needed for the building phase of the ILC.” was a statement from Nick Walker during the tour through AMTF. The ILC will use the same accelerating technology but it has 20 times as many accelerating structures than the European XFEL (which already needed a mass production). Here additional space and planning for the necessary mass production of accelerating structures is needed for the ILC campus. Walker could give many important insights about the ongoing European XFEL production as stepping stones for the ILC.

    Campus transportation of equipment and personnel will also be an issue for the possible site of the 30km long ILC with all buildings and needed infrastructure. “A good number of bicycles are in use at DESY but they also need maintenance and parking space.” was one of the first answers which were given by Fleischer. DESY solved some of the issues of transportation on campus site by using bicycles, installing a car pool (including transport vans) and during the time of the use of the HERA accelerator a bus shuttle was provided towards the experimental halls. Onuki and their colleagues were interested in all those solutions and of course how these things are used and received within DESY staff.

    Steffi Killough, Leader of the International Office at DESY, was giving helpful insights about social support which would be needed for foreign researchers and their families. DESY supports the guest-scientists starting with the visa application until the end of their stay in the country. Especially the tax system, insurances and other legal matters need explanations and advising. Also the education system for children is an important topic to visiting scientists and support for the integration into those systems needs to be provided. This issue is also very important for the ILC and its possible host nation Japan. “What would you like to provide if you had more resources?” was one of the questions from Onuki and her colleagues. Here the answer was very clear to Killough: more time which can be dedicated to provide support for each individual, also to provide more language support to address a greater variety of visitors in their native language, and to organize more social events.

    At the end of the day many other topics had been addressed like: scientific outreach, visitor numbers to DESY on open house days and the cooperation with the University of Hamburg and other Universities. “A key factor in the 50 year history of DESY was a close collaboration between Hamburg University and DESY, which has grown over the years.” is one of the statements of Frank Lehner towards the visitors from Tohoku University.
    Also the regional impact of DESY towards Hamburg was detailed and discussed in all areas like economy and education. The possibility for spin-off companies, regional investment for the needed infrastructure, training of skilled personnel in a variety of professions which are needed to provide the support system of a laboratory and growth for the regional economy were also further topics of the discussions.

    The Campus Planning Group from Tohoku University was given as many answers as possible from DESY in all possible areas to assist with the future ILC campus plans.

    See the full article here.

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    The Linear Collider Collaboration is an organisation that brings the two most likely candidates, the Compact Linear Collider Study (CLIC) and the International Liner Collider (ILC), together under one roof. Headed by former LHC Project Manager Lyn Evans, it strives to coordinate the research and development work that is being done for accelerators and detectors around the world and to take the project linear collider to the next step: a decision that it will be built, and where.

    Some 2000 scientists – particle physicists, accelerator physicists, engineers – are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.

    Linear Collider Colaboration Banner

     
  • richardmitnick 3:00 pm on July 30, 2015 Permalink | Reply
    Tags: , , , , Particle Accelerators, , ,   

    From Symmetry: “One Higgs is the loneliest number” 

    Symmetry

    July 30, 2015.
    Katie Elyce Jones

    Physicists discovered one type of Higgs boson in 2012. Now they’re looking for more.

    1

    When physicists discovered the Higgs boson in 2012, they declared the Standard Model of particle physics complete; they had finally found the missing piece of the particle puzzle.

    2
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    And yet, many questions remain about the basic components of the universe, including: Did we find the one and only type of Higgs boson? Or are there more?

    A problem of mass

    The Higgs mechanism gives mass to some fundamental particles, but not others. It interacts strongly with W and Z bosons, making them massive. But it does not interact with particles of light, leaving them massless.

    These interactions don’t just affect the mass of other particles, they also affect the mass of the Higgs. The Higgs can briefly fluctuate into virtual pairs of the particles with which it interacts.

    Scientists calculate the mass of the Higgs by multiplying a huge number—related to the maximum energy for which the Standard Model applies—with a number related to those fluctuations. The second number is determined by starting with the effects of fluctuations to force-carrying particles like the W and Z bosons, and subtracting the effects of fluctuations to matter particles like quarks.

    While the second number cannot be zero because the Higgs must have some mass, almost anything it adds up to, even at very small numbers, makes the mass of the Higgs gigantic.

    But it isn’t. It weighs about 125 billion electronvolts; it’s not even the heaviest fundamental particle.

    “Having the Higgs boson at 125 GeV is like putting an ice cube into a hot oven and it not melting,” says Flip Tanedo, a theoretical physicist and postdoctoral researcher at the University of California, Irvine.

    A lightweight Higgs, though it makes the Standard Model work, doesn’t necessarily make sense for the big picture. If there are multiple Higgses—much heavier ones—the math determining their masses becomes more flexible.

    “There’s no reason to rule out multiple Higgs particles,” says Tim Tait, a theoretical physicist and professor at UCI. “There’s nothing in the theory that says there shouldn’t be more than one.”

    The two primary theories that predict multiple Higgs particles are Supersymmetry and compositeness.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Supersymmetry

    Popular in particle physics circles for tying together all the messy bits of the Standard Model, Supersymmetry predicts a heavier (and whimsically named) partner particle, or “sparticle,” for each of the known fundamental particles. Quarks have squarks and Higgs have Higgsinos.

    “When the math is re-done, the effects of the particles and their partner particles on the mass of the Higgs cancel each other out and the improbability we see in the Standard Model shrinks and maybe even vanishes,” says Don Lincoln, a physicist at Fermi National Accelerator Laboratory.

    The Minimal Supersymmetric Standard Model—the supersymmetric model that most closely aligns with the current Standard Model—predicts four new Higgs particles in addition to the Higgs sparticle, the Higgsino.

    While Supersymmetry is maybe the most popular theory for exploring physics beyond the Standard Model, physicists at the LHC haven’t seen any evidence of it yet. If Supersymmetry exists, scientists will need to produce more massive particles to observe it.

    “Scientists started looking for Supersymmetry five years ago in the LHC,” says Tanedo. “But we don’t really know where they will find it: 10 TeV? 100 TeV?”

    Compositeness

    The other popular theory that predicts multiple Higgs bosons is compositeness. The composite Higgs theory proposes that the Higgs boson is not a fundamental particle but is instead made of smaller particles that have not yet been discovered.

    “You can think of this like the study of the atom,” says Bogdan Dobrescu, a theoretical physicist at Fermi National Accelerator Laboratory. “As people looked closer and closer, they found the proton and neutron. They looked closer again and found the ‘up’ and ‘down’ quarks that make up the proton and neutron.”

    Composite Higgs theories predict that if there are more fundamental parts to the Higgs, it may assume a combination of masses based on the properties of these smaller particles.

    The search for composite Higgs bosons has been limited by the scale at which scientists can study given the current energy levels at the LHC.

    On the lookout

    Physicists will continue their Higgs search with the current run of the LHC.

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

    At 60 percent higher energy, the LHC will produce Higgs bosons more frequently this time around. It will also produce more top quarks, the heaviest particles of the Standard Model. Top quarks interact energetically with the Higgs, making them a favored place to start picking at new physics.

    Whether scientists find evidence for Supersymmetry or a composite Higgs (if they find either), that discovery would mean much more than just an additional Higgs.

    “For example, finding new Higgs bosons could affect our understanding of how the fundamental forces unify at higher energy,” Tait says.

    “Supersymmetry would open up a whole ‘super’ world out there to discover. And a composite Higgs might point to new rules on the fundamental level beyond what we understand today. We would have new pieces of the puzzle to look at it.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:25 am on July 30, 2015 Permalink | Reply
    Tags: , , Particle Accelerators,   

    From FNAL: “Fishing for the weak and the charmed” 

    FNAL Home

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

    July 30, 2015
    Keith Matera and Andy Beretvas

    Temp 1
    The top plot shows the observed and predicted rates of vector boson plus charmed meson production at different energies for a type of vector boson called a W boson. The bottom plot shows the ratio of the observed to predicted rates. Observation and prediction are in agreement even at low energies, providing confirmation that we understand how these events behave. A well-tested model makes it easier to pick out anomalies, such as dark matter candidates.

    You collect coins, and you’re on the trail of a legend: According to rumor, a manufacturing defect led to one in every thousand 1939 nickels replacing Thomas Jefferson with a Sasquatch (also known as Bigfoot). But all of these weathered nickels now look about the same. How can you tell that you have found your elusive quarry?

    Finding something new in particle physics is much the same. We frequently know roughly what a new particle might look like, but this “signature” is often similar to that of other particles. One of the best ways to aid our search is to paint extremely accurate pictures of known particles and then look for exceptions to that rule.

    Heavy particles like dark matter candidates, the Higgs boson or particles predicted by supersymmetry share a common signature: They may decay into particles including a “vector boson V,” (a type of particle that transmits the weak force), and a “charmed meson,” D* (a particle made of two quarks, one of which is a charm quark).

    CDF physicists performed a search for these V+D* events — the normal nickels — to make certain that our picture of them is accurate.

    FNAL CDF
    CDF

    Models of events such as these are known to be accurate at high energies; however, at lower energies, subtleties in the strong force that binds together fundamental particles become more important, and the models may break down.

    This study was the first to test V+D* production at lower energies in hadron collisions. The V particle is either the W boson or the Z boson. The full Tevatron Run II data sample was used (9.7 inverse femtobarns).

    FNALTevatron
    Tevetron

    The figure shows the data when the V particle is the W particle. The experiment measured 634 ± 39 such events. The W particle is found by looking for an energetic lepton (a muon or an electron) and missing transverse energy (neutrino). The D* particle is observed from its decay into the D0 particle and a low-energy pion. The D0 decays into a negative kaon and a positive pion.

    Several sources of systematic uncertainty cancel in calculating the ratio of the decay probabilities for these two processes. We found that V+D* production behaves just as predicted. Providing such a stringent test of these models widens the net that we can cast in future studies. This, in turn, betters our chances of fishing out something new and exciting, perhaps previously undiscovered particles or particle decays.

    See the full article here.

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    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. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 8:21 am on July 29, 2015 Permalink | Reply
    Tags: , , , , Particle Accelerators, , Pentaquarks   

    From NOVA: “What the Heck is a Pentaquark?” 

    PBS NOVA

    NOVA

    28 Jul 2015
    FNAL Don Lincoln
    Don Lincoln

    What do you get when you combine four quarks and an antiquark?

    If you think this sounds like the opening of a particle physicists’ riddle, you aren’t too far off. Hypothetically, this particular quark combo makes a “pentaquark.” Despite decades of searching, physicists haven’t been able to actually find a pentaquark. Now, though, there’s a hint that two pentaquarks have unexpectedly come out of hiding.

    2
    Illustration of a possible layout of the quarks in a pentaquark particle such as those discovered at LHCb. © CERN

    If the new result holds up—a big if—the unexpected discovery would add a new species of particle to the standard model’s menagerie. But the measurements, recently announced by the team collaborating on the LHCb experiment, are truly perplexing.

    2
    LHCb on the LHC at CERN

    While the results were submitted for publication a couple of days ago, the first discussion in a large public conference occurred on July 23 at the 2015 meeting of the high energy physics division of the European Physical Society, where I had the opportunity to hear Sheldon Stone, who led the analysis, talk about the result. It’s certainly a topic of both excited and skeptical discussion here at the conference.

    Pentaquarks were first predicted in 1964 by Murray Gell-man and George Zweig in the separate and competing papers in which they first hypothesized the existence of quarks. (Gell-man’s name “quark” has stood the test of time, while Zweig independently proposed the now-defunct “aces.”) Physicists have looked for pentaquarks for a long time, unsuccessfully. We don’t know why there has been no evidence for their existence for so long. Maybe they don’t exist. Or maybe they do and the LHCb experiment has finally found them.

    Quarks are the building blocks of protons and neutrons and, as far as we know, they are the smallest basic units of matter. Quarks combine with other quarks according to the rules of quantum chromodynamics (QCD), which is the theory describing the behavior of the strong nuclear force, which is the strongest of the known subatomic forces. Pair a quark with an antiquark, and you’ve got a particle called a meson; three quarks make a baryon, like a proton or neutron. The new pentaquark—if it really is a pentaquark—seems to be made up of two up quarks, a down quark, and a charm quark/antiquark pair.

    The announcement is the latest chapter in a somewhat dubious story of now-you-see-now-you-don’t discovery. In 2002, scientists in Japan announced the discovery of a particle with a mass about 1.5 times that of a proton. They called it the Θ+, and argued that it was a kind of pentaquark. This announcement triggered a flurry of searches by other groups of experimenters, with some groups confirming the Θ+ and finding other particles that were claimed to be different pentaquark candidates, while other researchers found no evidence for any new particles at all. The excitement continued for three years until 2005, when the community decided that the original announcement was wrong. The death knell of the Θ+ sounded when a group of scientists at the Thomas Jefferson National Accelerator Facility (TJNAF) in Newport News, Virginia, repeated the initial Japanese measurement with far more data. The TJNAF scientists saw no evidence for the existence of the Θ+, and the community consigned it to the dustbin of history as one of many particle “discoveries” that ultimately didn’t pan out.

    The particles recently announced by the LHCb experiment aren’t the Θ+. Instead, the new particles have a mass of about 4.5 times that of the proton. The LHCb team wasn’t actually searching for pentaquarks when they made their measurements. Instead, they were studying how a particle called the Λb baryon decays. To their surprise, they found that a fraction of the time, some of the “daughter” particles left behind by the decay seemed to be coming from an unknown parent particle. So what the heck was it?

    3
    The LCHb team found the potential pentaquarks while investigating how a Λb baryon decays into a J/ψ meson and a Λ* baryon, which in turn decays into a K- meson and a proton (p+). In such a complicated decay mode, it is customary to look at the three daughter particles two at a time and calculate what the mass of the parent particle could have made them. In the case of the K- meson and a proton, you’d expect to see that they preferentially came from a particle with a mass of a Λ* baryon. Since the J/ψ and the proton weren’t thought to come from the decay of a single particle, you’d expect to see no particular mass looking special—but, as seen here, the researchers saw that a fraction of the time, these two particles seemed to come from a parent with a specific mass. Could pentaquarks be the culprit? Image adapted by Don Lincoln.

    The LHCb team was unable to reconcile their measurements with any of the known or predicted particles of the Standard Model.

    3
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    They seemed to need something new. After testing out lots of hypotheses, they considered the discredited pentaquarks. (Remember that pentaquarks are a prediction of the theory of QCD, they’ve just never been seen before.) One pentaquark wasn’t enough to fit their data, but two did the trick. When they included two new pentaquark particles in their calculations, the data and theory agreed.

    The two new particles have an unusual amount of quantum mechanical spin, specifically 3/2 and 5/2. (Protons, neutrons and electrons are all spin ½.) Like all particles that are bound by the strong nuclear force and decay under its rules, they live for a very short time, specifically about 10-23 seconds.

    Given the checkered history of previous pentaquark searches, physicists are naturally skeptical. So it is worth dissecting the claim. The first question is whether scientists are confident that they’ve discovered some kind of new particle. Here, the claim is on firmer ground: the two detections have significance of nine and 12 standard deviations respectively. (The usual standard in particle physics to claim the discovery of a phenomenon is five standard deviations, and larger numbers mean more certainty. Nine and 12 are very strong numbers.)

    It’s less certain whether the new particles are really pentaquarks. There are good reasons for skepticism: For one thing, the makeup of the new pentaquarks—two ups, a down, and a charm quark/antiquark pair—seems improbable. It should be easier to make a pentaquark consisting of only up and down quarks, which are lighter than charm quarks, and such a particle has never been discovered. Discovering a charm pentaquark first feels like going fishing and pulling up two sharks and no trout. A second possibility is that the new discovery is actually a sort of “molecule”: a particle called a J/ψ attached to a proton, roughly similar to how a deuteron is a proton and neutron bound together. Both have the same quark content, but only “five things in a bag” qualifies as a “real” pentaquark.

    When I caught up with Sheldon Stone during the coffee break after his talk at the conference, he speculated that the higher mass of the charm quarks could make the resulting pentaquark more stable or perhaps somehow makes this sort of pentaquark more likely to form. He cautioned, however, that this was speculation on his part and more work would be required to substantiate these ideas.

    Theoretical physicists are likewise skeptical. Frank Wilczek, professor of physics at MIT and winner of the Nobel Prize in physics for his contributions to the development of the theory of QCD was excited about the possibility of the existence of the pentaquark, but cautious about the measurement.

    So what will it take for the community to embrace this exciting development? Well, as Carl Sagan is famous for noting, extraordinary claims require extraordinary evidence. It is also true that independent confirmation is key. Accordingly, other LHC experiments will try to repeat the analysis approach reported by the LHCb collaboration in order to see if their measurement can be replicated. In addition, theorists will try to see if they can find a mechanism within QCD that will explain why pentaquarks containing charm quarks are more likely to form than ones with lighter quarks.

    Now, taking a more personal perspective, what do I think? First, Sheldon Stone made a persuasive and thorough case at his talk. I think the LHCb experiment is a world class collaboration, with some of the finest minds on the planet and ample experience in the subject matter. Further, they are well aware of the history of the pentaquark and would not lightly propose this hypothesis without adequate care. However, I am very cautious of claims of this nature, especially without confirmation from other experiments. I think the only sensible approach is to view the claim charitably, but critically. Taking a phrase from President Ronald Reagan, I “trust, but verify.” I think the next few months will be very interesting.

    See the full article here.

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
  • richardmitnick 10:13 am on July 28, 2015 Permalink | Reply
    Tags: , , , , Particle Accelerators, ,   

    From Discovery: “LHC Keeps Bruising ‘Difficult to Kill’ Supersymmetry” 

    Discovery News
    Discovery News

    Jul 27, 2015
    AFP

    1

    In a new blow for the futuristic “supersymmetry” theory of the universe’s basic anatomy, experts reported fresh evidence Monday of subatomic activity consistent with the mainstream Standard Model of particle physics.

    New data from ultra high-speed proton collisions at Europe’s Large Hadron Collider (LHC) showed an exotic particle dubbed the “beauty quark” behaves as predicted by the Standard Model, said a paper in the journal Nature Physics.

    2
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

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

    Previous attempts at measuring the beauty quark’s rare transformation into a so-called “up quark” had yielded conflicting results. That prompted scientists to propose an explanation beyond the Standard Model — possibly supersymmetry.

    2

    But the latest observations were “entirely consistent with the Standard Model and removes the need for this hypothesis” of an alternative theory, Guy Wilkinson, leader of LHC’s “beauty experiment” told AFP.

    “It would of course have been very exciting if we could show that there was something wrong with the Standard Model — I cannot deny that would have been sensational,” he said.

    The Standard Model is the mainstream theory of all the fundamental particles that make up matter, and the forces that govern them.

    But the model has weaknesses: it doesn’t explain dark matter or dark energy, which jointly make up 95 percent of the universe. Nor is it compatible with Einstein’s theory of general relativity — the force of gravity as we know it does not seem to work at the subatomic quantum scale.

    Supersymmetry, SUSY for short, is one of the alternatives proposed for explaining these inconsistencies, postulating the existence of a heavier “sibling” for every particle in the universe.

    This may also explain dark matter and dark energy.

    ‘Many-Headed Monster’

    But no proof of supersymmetric twins has been found at the LHC, which has observed all the particles postulated by the Standard Model — including the long-sought Higgs boson, which confers mass to matter.

    Supersymmetry predicts the existence of at least five types of Higgs boson, but only one, believed to be the Standard Model Higgs, has so far been found.

    Wilkinson said it was “too soon” to write off supersymmetry.

    “It is very difficult to kill supersymmetry: it is a many-headed monster,” he said.

    But “if nothing is seen in the next couple of years, supersymmetry would be in a much harder situation. The number of true believers would drop.”

    Quarks are the most basic particles, building blocks of protons and neutrons, which in turn are found in atoms.

    There are six types of quarks — the most common are the “up” and “down” quarks, while the others are called “charm”, “strange”, “beauty” and “top.”

    The beauty quark, heavier than up and down quarks, can shift shape, and usually takes the form of a charm quark when it does.

    Much more rarely, it morphs into an up quark. Wilkinson’s team have now measured — for the first time — how often that happens.

    “We are delighted because it is the sort of measurement nobody thought was possible at the LHC,” he said. It had been thought that an even more powerful machine would be needed.

    The revamped LHC, a facility of the European Organisation for Nuclear Research (CERN), was restarted in April after a two-year revamp to boost its power from eight to 13, potentially 14, teraelectronvolts (TeV).

    “If you expect Earth-shattering news from the new run, it’s a bit early,” CERN director-general Rolf Heuer told journalists in Vienna Monday at a conference of the European Physical Society.

    “The main harvest will come in the years to come, so you have to stay tuned.”

    So far, the new run at 13 TeV has re-detected all the Standard Model particles except for the Higgs boson, but Heuer insisted: “We are sure that it is there.

    See the full article here.

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  • richardmitnick 9:31 am on July 28, 2015 Permalink | Reply
    Tags: , , , Particle Accelerators   

    From CERN: “A miniature accelerator to treat cancer” 

    CERN New Masthead

    28 Jul 2015
    Matilda Heron

    1
    Serge Mathot with the first of the four modules that will make up the miniature accelerator (Image: Maximilien Brice/CERN)

    CERN, home of the 27-kilometre Large Hadron Collider (LHC), is developing a new particle accelerator. just two metres long.

    The miniature linear accelerator (mini-Linac) is designed for use in hospitals for imaging and the treatment of cancer. It will consist of four modules, each 50cm long, the first of which has already been constructed. “With this first module we have validated all of the stages of construction and the concept in general”, says Serge Mathot of the CERN engineering department.

    Designing an accelerator for medical purposes presented a new technological challenge for the CERN team. “We knew the technology was within our reach after all those years we had spent developing Linac4,” says Maurizio Vretenar, coordinator of the mini-Linac project. Linac4, a larger accelerator designed to boost negative hydrogen ions to high energies, is scheduled to be connected to the CERN accelerator complex in 2020.

    The miniature accelerator is a radiofrequency quadrupole (RFQ), a component found at the start of all proton accelerator chains. RFQs are designed to produce high-intensity beams. The challenge for the mini-Linac was to double the operating frequency of the RFQ in order to shorten its length. This desired high frequency had never before been achieved. “Thanks to new beam dynamics and innovative ideas for the radiofrequency and mechanical aspects, we came up with an accelerator design that was much better adapted to the practical requirements of medical applications,” says Alessandra Lombardi, in charge of the design of the RFQ.

    The “mini-RFQ” can produce low-intensity beams, with no significant losses, of just a few microamps that are grouped at a frequency of 750 MHz. These specifications make the “mini-RFQ” a perfect injector for the new generation of high-frequency, compact linear accelerators used for the treatment of cancer with protons.

    And the potential applications go beyond hadron therapy. The accelerator’s small size and light weight mean that is can be set up in hospitals to produce radioactive isotopes for medical imaging. Producing isotopes on site solves the complicated issue of transporting radioactive materials and means that a wider range of isotopes can be produced.

    The “mini-RFQ” will also be capable of accelerating alpha particles for advanced radiotherapy. As the accelerator can be fairly easily transported, it could also be used for other purposes, such as the analysis of archaeological materials.

    See the full article here.

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  • richardmitnick 7:53 am on July 28, 2015 Permalink | Reply
    Tags: , , , Particle Accelerators,   

    From CERN: “The latest results from the LHC experiments are presented in Vienna” 

    CERN New Masthead

    27 Jul 2015
    NO Writer Credit

    The world particle-physics community has convened in Vienna for the 2015 European Physical Society Conference on High Energy Physics (EPS-HEP2015), where the latest results in the field are being presented and discussed. These include the first results from Run 2 of the Large Hadron Collider (LHC) at CERN1, which are being presented for the very first time, less than two months after the experiments started to take data at the unprecedented energy of 13 TeV, following a two-year long shutdown.

    “It is much too early to expect any discovery, we will have to be patient,” said CERN Director General Rolf Heuer. “Nevertheless, the LHC experiments have already recorded 100 times more data for the summer conferences this year than they had around the same time after the LHC started up at 7 TeV in 2010. We can sense a fantastic pioneering spirit as the physicists are looking at completely new data at an unexplored energy.”

    As for any machine exploring a new energy frontier, operators at the LHC face many challenges on a daily basis. Since the start of Run 2, they have been gradually increasing the intensity of the LHC’s two beams, which travel in opposite directions around the 27-kilometre ring at almost the speed of light. The LHC has run at the record high energy with each beam containing up to 476 bunches of 100 billion protons, delivering collisions every 50 nanoseconds. In the coming days, the intensity should increase further with a new rhythm of 25 nanoseconds. After a planned technical stop in early September, the teams will also be able to increase the number of bunches with the goal of reaching more than 2000 bunches per beam by the end of 2015.

    “During the hardware-commissioning phase, we have learnt to manage carefully the huge energy stored in the magnets. Now with beam commissioning we have to learn progressively how to store and handle the beam energy,” said CERN Director of Accelerators and Technology Frédérick Bordry. “Our goal for 2015 is to reach the nominal performance of the LHC at 13 TeV so as to exploit its potential from 2016 to 2018.”

    The LHC has already delivered over 10 thousand billion collisions to the large experiments since the start of Run 2. This has allowed the LHC collaborations to measure a full suite of detector performance parameters that demonstrate the readiness of the experiments for discovery physics and precision measurements. The next step was to confirm the Standard Model at the new energy of 13 TeV. After only a few weeks of data taking, the experiments have now “rediscovered” all of the known fundamental particles, apart from the so-called Higgs boson, for which more data are still required. The collaborations are thus ready to test the Standard Model at 13 TeV and the hope is to find evidence of new physics beyond this well-established theory.

    At the EPS-HEP2015 conference, the ATLAS and CMS collaborations presented the first measurements at 13 TeV on the production of charged strongly-interacting particles (hadrons). CMS has already submitted this result for publication (link is external) – the first for the new energy region. Such measurements are important in understanding the basic production mechanism for hadrons.

    The LHC experiments have also made the first measurements of cross-sections at 13 TeV. Cross-sections are quantities related to the probability for particles to interact, and their measurement is essential for identifying any new phenomena. For example, ATLAS has measured the cross-section for the production of pairs of top quarks and antiquarks, which is some three times higher at 13 TeV than at the energy of Run 1.

    In addition, the conference is providing the opportunity for all of the LHC experiments to present many new or final results from the first run at the LHC. These include searches for dark matter, supersymmetric and other exotic particles, as well as new precision measurements of Standard Model processes.

    1
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    In this respect, one highlight in Vienna is the presentation for the first time at an international conference of the recent discovery by the LHCb experiment of a new class of particles known as pentaquarks (see press release). LHCb also published today in Nature Physics a result confirming that a certain decay involving the weak force happens with beauty quarks having a “left-handed” spin. This result is consistent with the Standard Model, in contrast with previous measurements that allowed for a right-handed contribution.

    In other highlights from Run 1, the ALICE and LHCb experiments have new results on long-range correlations in proton–lead collisions. The latest measurements show that the so-called “ridges” seen in the most violent collisions span across even larger longitudinal distances. In Run 2 data, ATLAS reported that the near-side ridge is seen in 13 TeV proton–proton collisions, with characteristics very similar to those observed by CMS in Run 1.

    See the full article here.

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  • richardmitnick 5:43 pm on July 27, 2015 Permalink | Reply
    Tags: , , Particle Accelerators, ,   

    From Symmetry: “W bosons remain left-handed” 

    Symmetry

    July 27, 2015
    Sarah Charley

    1
    LHCb. Courtesy of CERN

    A new result from the LHCb collaboration weakens previous hints at the existence of a new type of W boson.

    A measurement released today by the LHCb collaboration dumped some cold water on previous results that suggested an expanded cast of characters mediating the weak force.

    The weak force is one of the four fundamental forces, along with the electromagnetic, gravitational and strong forces. The weak force acts on quarks, fundamental building blocks of nature, through particles called W and Z bosons.

    2
    The Feynman diagram for beta decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy W boson

    3
    A Feynman diagram showing the exchange of a pair of W bosons. This is one of the leading terms contributing to neutral Kaon oscillation

    Just like a pair of gloves, particles can in principle be left-handed or right-handed. The new result from LHCb presents evidence that the W bosons that mediate the weak force are all left-handed; they interact only with left-handed quarks.

    This weakens earlier hints from the Belle and BaBar experiments of the existence of right-handed W bosons.

    The LHCb experiment at the Large Hadron Collider examined the decays of a heavy and unstable particle called Lambda-b—a baryon consisting of an up quark, down quark and bottom quark.

    CERN LHC Map
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    CERN LHC particles
    LHC

    Weak decays can change a bottom quark into either a charm quark, about 1 percent of the time, or into a lighter up quark. The LHCb experiment measured how often the bottom quark in this particle transformed into an up quark, resulting in a proton, muon and neutrino in the final state.

    “We found no evidence for a new right-handed W boson,” says Marina Artuso, a Professor of Physics at Syracuse University and a scientist working on the LHCb experiment.

    If the scientists on LHCb had seen bottom quarks turning into up quarks more often than predicted, it could have meant that a new interaction with right-handed W bosons had been uncovered, Artuso says. “But our measured value agreed with our model’s value, indicating that the right-handed universe may not be there.”

    Earlier experiments by the Belle and BaBar collaborations studied transformations of bottom quarks into up quarks in two different ways: in studies of a single, specific type of transformation, and in studies that ideally included all the different ways the transformation occurs.

    If nothing were interfering with the process (like, say, a right-handed W boson), then these two types of studies would give the same value of the bottom-to-up transformation parameter. However, that wasn’t the case.

    The difference, however, was small enough that it could have come from calculations used in interpreting the result. Today’s LHCb result makes it seem like right-handed W bosons might not exist after all, at least not in a way that is revealed in these measurements.

    Michael Roney, spokesperson for the BaBar experiment, says, “This result not only provides a new, precise measurement of this important Standard Model parameter, but it also rules out one of the interesting theoretical explanations for the discrepancy… which still leaves us with this puzzle to solve.”

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:32 am on July 24, 2015 Permalink | Reply
    Tags: , , , Particle Accelerators,   

    From ATLAS at CERN: “Early Run 2 results test event generator energy extrapolation” 

    CERN New Masthead

    23 July 2015

    ATLAS presented its first measurements of soft strong interaction processes using charged particles produced in proton–proton collisions at 13 TeV centre-of-mass energy delivered by the Large Hadron Collider at CERN. These measurements were performed with a dataset collected beginning of June under special low-luminosity conditions during which the frequency of multiple proton–proton scattering occurring in the same recorded collision event was strongly reduced.

    Measurements like this are important for understanding the collision energy dependence of such processes, as well as ensuring a successful description of the data by the Monte Carlo (MC) event generators. The accuracy of these simulations is critical for their subsequent use in ATLAS searches and measurements.

    Performing these measurements at an unprecedented collision energy with upgraded detector components in such a short scale was a challenge. During the Long Shutdown, many improvements were made to the detector, most relevant among them for these results was the addition of the innermost pixel layer, the insertable B-layer (IBL). Adding the IBL dramatically improved the accuracy of the track reconstruction and the identification of jets originating from bottom quarks, which is important for many searches. The commissioning of the IBL, alignment of different detector components and assessment of passive detector material is still ongoing. Figure 1 shows the number of hits in pixel layer per track. Generally, good agreement is observed, indicating a very good understanding of the ATLAS four-layer pixel system. The minor disagreements stem from the mismatch in simulation and data of the number of modules not working properly during that period of data-taking.

    The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity (which essentially represents the angular position from beam axis) and the dependence of the mean transverse momentum on the charged-particle multiplicity were presented, based on about 9 million events. The events contained at least one charged particle with transverse momentum greater than 500 MeV in the central part of the detector. The data were corrected with minimal model dependence to obtain inclusive distributions. Overall the Monte Carlo models, which were tuned to such similar measurements performed at lower centre-of-mass energies, seem to describe the data reasonably well. Figure 2 shows the mean number of charged particles in the central region compared to previous measurements at different collision energies, together with the MC predictions. The mean number of charged particles increases by a factor of 2.2 when collision energy increases from 0.9 TeV to 13 TeV.

    In the events where the leading track had a transverse momentum of at least 1 GeV, the accompanying activity was studied at the detector level. The azimuthal region perpendicular to the direction of the leading track is most sensitive to this accompanying activity, termed the underlying event (UE). The average number of tracks in each event and their transverse momentum sum are seen to show a gradual rise towards a “plateau” with rising leading track transverse momentum, a trend seen in previous measurements. Figure 3 shows the latter in the transverse region. Compared to 7 TeV results a 20% increase to the UE activity is observed and is predicted well by most of the models.

    These early measurements show a good understanding of the performance the upgraded ATLAS detector as well as the ability of the Monte Carlo event generators to describe the data at new collision energy.

    1
    Figure 1: Comparison of number of pixel hits distributions in data and simulation.

    2
    Figure 2: The average charged-particle multiplicity per unit of rapidity for eta= 0 as a function of the centre-of-mass energy.

    3
    Figure 3: Comparison of detector level data and MC predictions for average scalar pT sum density of tracks as a function of leading track pT.

    See the full article here.

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