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  • richardmitnick 10:22 am on October 24, 2017 Permalink | Reply
    Tags: A new chapter in Fermilab’s electron lens legacy, , , , , FNAL Tevatron, Scientists at Fermilab invented and developed one novel collider component 20 years ago: the electron lens   

    From FNAL: “A new chapter in Fermilab’s electron lens legacy” 

    FNAL II photo

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    FNAL Art Image by Angela Gonzales

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

    October 18, 2017
    Leah Poffenberger

    Sending bunches of protons speeding around a circular particle collider to meet at one specific point is no easy feat. Many different collider components work keep proton beams on course — and to keep them from becoming unruly.

    Scientists at Fermilab invented and developed one novel collider component 20 years ago: the electron lens. Electron lenses are beams of electrons formed into specific shapes that modify the motion of other particles — usually protons — that pass through them.

    The now retired Tevatron, a circular collider at Fermilab, and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory have both benefited from electron lenses, a concept originally developed at Fermilab.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    “Electron lenses are like a Swiss Army knife for accelerators: They’re relatively simple and inexpensive, but they can be applied in a wide variety of ways,” said Alexander Valishev, a Fermilab scientist who co-authored a recent study for a new electron lens application, which could be crucial to forthcoming colliders.

    The innovation is detailed in an article published on Sept. 27 in Physical Review Letters. (The article was also recently selected for presentation in the Physics Central’s Physics Buzz Blog.)

    “This little breakthrough in the physics of beams and accelerators is kind of a beginning of a bigger invention — it’s a new thing,” said Fermilab’s Vladimir Shiltsev, an author of the published paper. Shiltsev also played a major role in the origination of electron lenses in 1997. “Fermilab is known for inventions and developments that are, first, exciting, and then, functional. That’s what national labs are built for, and that’s what we’ve achieved.”

    1
    An electron lens introduces differences in the movement of particles that constitute a particle bunch. In the illustration, the perspective is looking down the beam pipe — down the path of the particle bunch. The bunch is seen as approaching the viewer (as the circle increases in size). Left: the particle bunch, represented as a uniformly blue circle, contains particles that all behave in the same way. Because the constituent particles follow the exact same trajectory, the bunch is more susceptible to wild deviations from its path, resulting from electromagnetic wake-fields. Right: Treated by an electron lens, the particle bunch, represented by red and blue, contains particles that move slightly differently from one another. For example, particles closer to the interior of the bunch move differently from those closer to the outside. This variegation helps confine the particle bunch to the more desirable straightforward path. Illustration: Diana Brandonisio

    A lens into the future

    This new type of electron lens, called the Landau damping lens, will be a critical part of a huge, prospective project in particle physics research: the Future Circular Collider at CERN.

    CERN Future Circular Collider

    The FCC would push the boundaries of traditional collider design to further study the particle physics beyond the Higgs boson, a fundamental particle discovered only five years ago.

    The proposed FCC has to be a high-luminosity machine: Its particle beams will need to be compact and densely packed. Compared with CERN’s Large Hadron Collider, the beams will also have a dramatic increase in energy — 50 trillion electronvolts, compared with the LHC’s beam energy of 7 trillion electronvolts. That involves an equally dramatic increase in the size of the accelerator. With a planned circumference of 100 kilometers, the FCC would dwarf the 27-kilometer LHC.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    These high-energy, high-luminosity supercolliders all experience a problem, regardless of size: An intense beam of protons packed into the width of human hair traveling over a long distance can become unstable, especially if all the protons travel in exactly the same way.

    In a collider, particles arrive in packets called bunches — roughly foot-long streams packed with hundreds of billions of particles. A particle beam is formed of dozens, hundreds or thousands of these bunches.

    Imagine a circular collider as a narrow racetrack, with protons in a bunch as a tight pack of racecars. A piece of debris suddenly appears in the middle of the track, disrupting the flow of traffic. If every car reacts in the same way, say, by veering sharply to the left, it could lead to a major pileup.

    Inside the collider, it’s not a matter of avoiding just one bump on the track, but adjusting to numerous dynamic obstacles, causing the protons to change their course many times over. If an anomaly, such as a kink in the collider’s magnetic field, occurs unexpectedly, and if the protons in the beam all react to it in the same way at the same time, even a slight change of course could quickly go berserk.

    One could avoid the problem by thinning the particle beam from the get-go. By using lower-density proton beams, you provide less opportunity for protons to go off course. But that would mean removing protons and so missing out on potential for scientific discovery.

    Another, better way to address the problem is to introduce differences into the beam so that not all the protons in the bunches behave the same way.

    To return to the racetrack: If the drivers all react to the piece of debris different ways —some moving slightly to the right, others slightly to the left, one brave driver just skips over the top — the cars can all merge back together and continue the race, no accidents.

    Creating differentiations within a proton bunch would do essentially the same thing. Each proton follows its own, ever-so-slightly different course around the collider. This way, any departure from the course is isolated, rather than compounded by protons all misbehaving in concert, minimizing harmful beam oscillations.

    “Particles at the center of the bunch will move differently than particles around the outside,” Shiltsev said. “The protons will all be kind of messed up, but that’s what we want. If they all move together, they become unstable.”

    These differences are usually created with a special type of magnet called octupoles. The Tevatron, before its decommissioning in 2011, had 35 octupole magnets, and the LHC now has 336.

    But as colliders get larger and achieve greater energies, they need exponentially higher numbers of magnets: The FCC will require more than 10,000 octupole magnets, each a meter long, to achieve the same beam-stabilizing results as previous colliders.

    That many magnets take up a lot of space: as much as 10 of the FCC’s 100 kilometers.

    “That seems ridiculous,” Shiltsev said. “We’re looking for a way to avoid that.”

    The scientific community recognizes the Landau damping nonlinear lens as a likely solution to this problem: A single one-meter-long electron lens could replace all 10,000 octupole magnets and possibly do a better job keeping beams stable as they speed toward collision, without introducing any new problems.

    “At CERN they’ve embraced the idea of this new electron lens type, and people there will be studying them in further detail for the FCC,” Valishev said. “Given what we know so far about the issues that the future colliders will face, this would be a device of extremely high criticality. This is why we’re excited.”

    Electron Legos

    The Landau damping lens will join two other electron lens types in the repertoire of tools physicists have to modify or control beams inside a collider.

    “After many years of use, people are very happy with electron lenses: It’s one of the instruments used for modern accelerators, like magnets or superconducting cavities,” Shiltsev said. “Electron lenses are just one of the building blocks or Lego pieces.”

    Electron lenses are a lot like Legos: Lego pieces are made of the same material and can be the same color, but a different shape determines how they can be used. Electron lenses are all made of clouds of electrons, shaped by magnetic fields. The shape of the lens dictates how the lens influences a beam of protons.

    Scientists developed the first electron lens at Fermilab in 1997 for use to compensate for so-called beam-beam effects in the Tevatron, and a similar type of electron lens is still in use at the Brookhaven’s RHIC.

    In circular colliders, particle beams pass by each other, going in opposing directions inside the collider until they are steered into a collision at specific points. As the beams buzz by one another, they exert a small force on each other, which causes the proton bunches to expand slightly, decreasing their luminosity.

    That first electron lens, called the beam-beam compensation lens, was created to combat the interaction between the beams by squeezing them back to their original, compact state.

    After the success of this electron lens type in the Tevatron, scientists realized that electron beams could be shaped a second way to create another type of electron lens.

    Scientists designed the second lens to be shaped like a straw, allowing the proton beam to pass through the inside unaffected. The occasional proton might try to leave its group and stray from the center of the beam. In the LHC, losing even one-thousandth of the total number of protons in an uncontrolled way could be dangerous. The electron lens acts as a scraper, removing these rogue particles before they could damage the collider.

    “It’s extremely important to have the ability to scrape these particles because their energy is enormous,” Shiltsev said. “Uncontrolled, they can drill holes, break magnets or produce radiation.”

    Both types of electron lens have made their mark in collider design as part of the success of the Tevatron, RHIC and the LHC. The new Landau damping lens may help usher in the next generation of colliders.

    “The electron lens is an example of something that was invented here at Fermilab 20 years ago,” Shiltsev said. “This is a one of the rare technologies that wasn’t just brought to perfection at Fermilab: It was invented, developed and perfected and still continues to shine.”

    See the full article here .

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    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.

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  • richardmitnick 3:26 pm on October 23, 2017 Permalink | Reply
    Tags: , ATLAS and CMS join forces to tackle top-quark asymmetry, , FNAL Tevatron, , ,   

    From CERN: “ATLAS and CMS join forces to tackle top-quark asymmetry” 

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    CERN

    20 Oct 2017
    Matthew Chalmers
    Henry Bennie

    1
    Event display of a tt̄ event candidate in the 2015 data (Image: ATLAS/CERN)

    2
    All matter around us is made of elementary particles called quarks and leptons. Each group consists of six particles, which are related in pairs, or “generations” – the up quark and the down quark form the first, lightest and most stable generation, followed by the charm quark and strange quark, then the top quark and bottom (or beauty) quark, the heaviest and least stable generation. (Image: Daniel Dombinguez/CERN)

    In their hunt for new particles and phenomena lurking in LHC collisions, the ATLAS and CMS experiments have joined forces to investigate the top quark. As the heaviest of all elementary particles, weighing almost as much as an atom of gold, the top quark is less well understood than its lighter siblings. With the promise of finding new physics hidden amongst the top quark’s antics, ATLAS and CMS have combined their top-quark data for the first time.

    There were already hints that the top quark didn’t play by the rules in data collected at the Tevatron collider at Fermilab in the US (the same laboratory that discovered the particle in 1995).

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Around a decade ago, researchers found that, when produced in pairs from the Tevatron’s proton-antiproton collisions, top quarks tended to be emitted in the direction of the proton beam, while anti-tops aligned in the direction of the antiproton beam. A small forward-backward asymmetry is predicted by the Standard Model, but the data showed the measured asymmetry to be tantalisingly bigger than expected, potentially showing that new particles or forces are influencing top-quark pair production.

    “As physicists, when we see something like this, we get excited,” says ATLAS researcher Frederic Deliot. If the asymmetry is much larger than predicted, it means “there could be lots of new physics to discover.”

    The forward-backward asymmetry measured at the Tevatron cannot be seen at the LHC because the LHC collides protons with protons, not antiprotons. But a related charge asymmetry, which causes top quarks to be produced preferentially in the centre of the LHC’s collisions, can be measured. The Standard Model predicts the effect to be small (around 1%) but, as with the forward-backward asymmetry, it could be made larger by new physics. The ATLAS and CMS experiments both measured the asymmetry by studying differences in the angular distributions of top quarks and antiquarks produced at the LHC at energies of 7 and 8 TeV.

    Alas, individually and combined, their results show no deviation from the latest Standard Model calculations.

    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.

    These calculations have in fact recently been improved, and show that the predicted asymmetry is slightly higher than previously thought. This, along with improvements in data analysis, even brings the earlier Tevatron result into line with the Standard Model.

    ATLAS and CMS will continue to subject the heavyweight top quark to tests at energies of 13 TeV to see if it deviates from its expected behaviour, including precision measurements of its mass and interactions with other Standard Model particles. But measuring the asymmetry will get even tougher, because the effect is predicted be half as big at a higher energy. “It’s going to be difficult,” says Deliot. “It will be possible to explore using the improved statistics at higher energy, but it is clear that the space for new physics has been severely restricted.”

    The successful combination of the charge-asymmetry measurements was achieved within the LHC top-quark physics working group, where scientists from ATLAS and CMS and theory experts work together intensively towards improving the interplay between theory and the two experiments, explains CMS collaborator Thorsten Chwalek. “Although the combination of ATLAS and CMS charge asymmetry results didn’t reveal any hints of new physics, the exercise of understanding all the correlations between the measurements was very important and paved the way for future ATLAS+CMS combinations in the top-quark sector.”

    See the full article here.

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  • richardmitnick 10:10 am on July 9, 2017 Permalink | Reply
    Tags: , , CERN LHC LHCb, CERN Physicists Find a Particle With a Double Dose of Charm, FNAL Tevatron, , , ,   

    From NYT: “CERN Physicists Find a Particle With a Double Dose of Charm” 

    New York Times

    The New York Times

    JULY 6, 2017
    KENNETH CHANG

    3
    The new particle, awkwardly known as Xi-cc++ (pronounced ka-sigh-see-see-plus-plus)

    1
    The Vertex Locator detector is part of an experiment at CERN’s Large Hadron Collider that discovered a particle that contains two charm quarks. Credit CERN

    Physicists have discovered a particle that is doubly charming.

    Researchers reported on Thursday that in debris flying out from the collisions of protons at the CERN particle physics laboratory outside Geneva, they had spotted a particle that has long been predicted but not detected until now.

    The new particle, awkwardly known as Xi-cc++ (pronounced ka-sigh-see-see-plus-plus), could provide new insight into how tiny, whimsically named particles known as quarks, the building blocks of protons and neutrons, interact with each other.

    Protons and neutrons, which account for the bulk of ordinary matter, are made of two types of quarks: up and down. A proton consists of two up quarks and one down quark, while a neutron contains one up quark and two down quarks. These triplets of quarks are known as baryons.

    There are also heavier quarks with even quirkier names — strange, charm, top, bottom — and baryons containing permutations of heavier quarks also exist.

    An experiment at CERN, within the behemoth Large Hadron Collider, counted more 300 Xi-cc++ baryons, each consisting of two heavy charm quarks and one up quark.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    The discovery fits with the Standard Model, the prevailing understanding of how the smallest bits of the universe behave, and does not seem to point to new physics.

    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.

    “The existence of these particles has been predicted by the Standard Model,” said Patrick Spradlin, a physicist at the University of Glasgow who led the research. “Their properties have also been predicted.”

    Dr. Spradlin presented the findings on Thursday at a European Physical Society conference in Venice, and a paper describing them has been submitted to the journal Physical Review Letters.

    Up and down quarks have almost the same mass, so in protons and neutrons, the three quarks swirl around each other in an almost uniform pattern. In the new particle, the up quark circulates around the two heavy charm quarks at the center. “You get something far more like an atom,” Dr. Spradlin said.

    Quark interactions are complex and difficult to calculate, and the structure of the new particles will enable physicists to check the assumptions and approximations they use in their calculations. “It’s a new regime in quark-quark dynamics,” said Jonathan L. Rosner, a retired theoretical physicist at the University of Chicago.

    The mass of the Xi-cc++ is about 3.8 times that of a proton. The particle is not stable. Dr. Spradlin said the scientists had not yet figured out its lifetime precisely, but it falls apart after somewhere between 50 millionths of a billionth of a second and 1,000 millionths of a billionth of a second.

    For Dr. Rosner, the CERN results appear to match predictions that he and Marek Karliner of Tel Aviv University made.

    What is less clear is how the new particle fits in with findings from 2002, when physicists working at Fermilab outside Chicago made the first claim of a doubly charmed baryon, one consisting of two charm quarks plus a down quark (instead of the up quark seen in the CERN experiment).

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    The two baryons should be very close in mass, but the Fermilab one was markedly lighter than what the CERN researchers found for Xi-cc++, and it appeared to decay instantaneously, in less than 30 millionths of a billionth of a second.

    Theorists like Dr. Rosner had difficulty explaining the behavior of the Fermilab particle within the Standard Model. “I didn’t have an honest alternative to allow me to believe that result,” he said.

    Peter S. Cooper, a deputy spokesman for the Fermilab experiment, congratulated the CERN researchers on their discovery. “That paper smells sweet,” he said. “From an experimental point of view, there’s nothing wrong. They definitely have something.”

    But he said the Fermilab findings still stood, too. He acknowledged that the two results do not readily make sense together.

    “I consider this a problem for my theoretical brethren to work out,” Dr. Cooper said. He added that it was a textbook example of the scientific method: “Our theoretical colleagues make a prediction. We go out and make a measurement and see if it’s right. If it isn’t, they go back and think harder.”

    It is possible one of the experiments is wrong. Researchers at other laboratories, including at CERN, have sought to detect the Fermilab baryon without success. Dr. Spradlin said he and his colleagues are searching the same data that revealed the Xi-cc++ for the baryon with two charm quarks and one down quark. That could confirm the Fermilab findings or reveal a mass closer to theorists’ expectations.

    “We should be able to see it with the data we have,” Dr. Spradlin said. “I think we are very close to resolving this controversy.”

    I presented an earlier post from LHCb, but it contained no reference to the paper in Physical Review Letters.

    See the full article here .

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  • richardmitnick 12:11 pm on June 10, 2017 Permalink | Reply
    Tags: , , FNAL Tevatron, , , , Tevatron first accelerator to use electron lens   

    From FNAL: “Tevatron first accelerator to use electron lens” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    accelerator to use electron lens

    June 10, 2017
    Troy Rummler
    1

    Tevatron is the first accelerator to use an electron lens

    Fermilab’s Tevatron was the first particle accelerator to make use of an electron lens, a technique that allowed the machine to compensate for destabilizing forces unavoidably generated by the colliding beams. Proposed in 1997, the lenses were installed in 2001 and 2004 in the Tevatron, where they demonstrated beam-beam compensation. They were also used in the removal of unwanted particles. The innovation earned Fermilab scientist Vladimir Shiltsev a European Physical Society Accelerator Prize.

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    FNAL/Tevatron CDF detector

    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 3:46 pm on May 24, 2017 Permalink | Reply
    Tags: , , Early days, FNAL Tevatron, , ,   

    From FNAL: “Early Tevatron design days” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    May 24, 2017
    Tom Nicol

    1
    Fermilab technicians assemble a magnet spool piece for the Tevatron. Photo: Fermilab

    When I started at the lab in December 1977, work on the dipole magnets for the Tevatron was well under way in what was then called the Energy Doubler Department in the Technical Services Section.

    My first project was to work on the quadrupole magnets and spools, which hadn’t really been started yet. The spool is a special unit that attaches to each quadrupole and the adjacent dipole. It contains what we used to call “the stuff that wouldn’t fit anywhere else” – correction magnets and their power leads, quench stoppers to dump the energy from all the magnets, beam position monitors, relief valves, things like that.

    At the time, we were located in the Village in the old director’s complex, which now houses the daycare center. We had a large open area where the engineers, designers and drafters worked and a small conference room where we kept up-to-date models of some of the things we were working on.

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    A team tests a magnet spool piece. Photo: Fermilab

    For several weeks we worked feverishly on the design of the quadrupole and spool combination — we in the design room and the model makers in the model shop on their full-scale models. We would work all week, then have a meeting with the lab director, Bob Wilson. Dr. Wilson would come out to see how we were doing, but more importantly to see what our designs looked like.

    It turns out he was very interested in that and very fussy that things — even those buried in the tunnel — looked just so.

    After every one of those meetings we’d walk back into the design room and tell everyone to tear up what we’d been working on and start over. The same would hold for the model makers. This went on for several weeks until Dr. Wilson was happy. We began to really dread going into those meetings, but in the end they served us very well.

    FNAL Tevatron

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    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 1:55 pm on May 24, 2017 Permalink | Reply
    Tags: , , Charm mesons and baryons, FNAL Tevatron, , , ,   

    From FNAL: ” Fermilab measures lifetimes and properties of charm mesons and baryons” 

    FNAL II photo

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

    properties of charm mesons and baryons

    May 24, 2017
    Troy Rummler

    1

    Heavy quarks produced in high-energy collisions decay within a tiny fraction of a second, traveling less than a few centimeters from the collision point. To study properties of these particles, Fermilab began using microstrip detectors in the late 1970s. These detectors are made of thin slices of silicon and placed close to the interaction point in order to take advantage of the microstrip’s tremendous position resolution. Over time, Fermilab developed this technology, improving our understanding of silicon’s capabilities and adapting the technology to other detectors, including those at CDF and DZero.

    FNAL Tevatron

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    FNAL/Tevatron CDF detector

    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 11:11 am on May 24, 2017 Permalink | Reply
    Tags: , , , , FNAL Tevatron, , Our failure in resolve,   

    From FNAL: “Fermilab scientists set upper limit for Higgs boson mass” 

    FNAL II photo

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

    In 1977, theoretical physicists at Fermilab — Ben Lee and Chris Quigg, along with Hank Thacker — published a paper setting an upper limit for the mass of the Higgs boson. This calculation helped guide the design of the Large Hadron Collider by setting the energy scale necessary for it to discover the particle. The Large Hadron Collider turned on in 2008, and in 2012, the LHC’s ATLAS and CMS discovered the long-sought Higgs boson — 35 years after the seminal paper.

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    CERN CMS Higgs Event


    CERN/CMS Detector


    CERN ATLAS Higgs Event


    CERN/ATLAS detector

    Where it all started:

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Where we failed and handed it to Europe:

    3
    Sight of the planned Superconducting Super Collider, in the vicinity of Waxahachie, Texas. Cancelled by our idiot Congress under Bill Clinton in 1993. We could have had it all.

    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 3:14 pm on December 13, 2016 Permalink | Reply
    Tags: , ATLAS releases first measurement of W mass using LHC data, , , FNAL Tevatron, , , ,   

    From CERN ATLAS: “ATLAS releases first measurement of W mass using LHC data” 

    Cern New Bloc

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    CERN

    13 Dec 2016
    Harriet Kim Jarlett

    1
    ATLAS is one of the four major experiments at the LHC. It is a general-purpose particle physics experiment run by an international collaboration (Image: Claudia Marcelloni/ CERN)

    The ATLAS collaboration today reports the first measurement of the W boson mass using Large Hadron Collider (LHC) proton–proton collision data at a centre-of-mass energy of 7 TeV.

    2
    The ATLAS measurement of the W boson mass (in red) is compared to the Standard Model prediction (in purple), and to the combined values measured at the LEP and Tevatron collider (in blue) (Image: ATLAS Collaboration/CERN)

    The W boson was discovered in 1983 at the CERN SPS collider and led to a Nobel prize in physics in 1984.

    3
    Super Proton Synchrotron (SPS)

    Although the properties of the W boson have been studied for more than 30 years, measuring its mass remains a major challenge. A precise measurement of the W boson mass is vital, as a deviation from the Standard Model’s predictions could hint at new physics.

    The latest results from ATLAS show a measured value of 80370±19 MeV, which is consistent with the Standard Model prediction. It is also consistent with the combined values measured at the LEP and Tevatron colliders, and with the world average (see graph above).

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    Large Electron Positron collider

    FNAL/Tevatron machine
    FNAL/Tevatron

    Measuring the W mass is particularly challenging at the LHC, compared to previous colliders, due to the large number of interactions per beam crossing. Despite this, the ATLAS result matches the best single-experiment measurement of the W mass (performed by the CDF collaboration).

    FNAL/Tevatron CDF detector
    FNAL/Tevatron CDF detector

    Read more on the ATLAS experiment’s website: http://cern.ch/go/p6sN

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 4:13 pm on September 13, 2016 Permalink | Reply
    Tags: , , D+ mesons, , FNAL Tevatron, Strong interaction   

    From FNAL: “CDF can’t stop being charming” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    September 8, 2016
    Jeffrey Appel

    FNAL/Tevatron map
    FNAL/Tevatron map

    FNAL/Tevatron CDF detector
    FNAL/Tevatron CDF detector

    Good news: there is a theory to describe the strong interaction, the interactions that bind the constituents of protons and neutrons together and create the strong force. Bad news: Calculations using the theory can be made in only a limited selection of natural phenomena.

    Quantitative predictions for interactions beyond that subset depend on measurements. This can be either for direct use or to help guide the theory about the inputs used in calculations, such as the distributions of the quark and gluon constituents inside protons and neutrons. Using the production of particles containing heavy charm and bottom quarks helps especially with gluon distributions.

    CDF is now reporting new measurements of the rate of production at the Tevatron of D+ mesons, which contain charm quarks. Furthermore, the new measurements are made in the region where the D+ mesons have the smallest momentum transverse to the incident beams. This is the region that is the hardest to calculate using the theory of strong interactions and has never been explored in proton-antiproton collisions.

    1
    This plot shows the measures, in bins of momentum transverse to incident protons, of the average probability of producing a D+ meson at the Tevatron. Shown as bands are the averages predicted in the same bins by the latest theoretical calculations.

    To probe such small transverse momenta, CDF physicists examined all types of interactions of the incoming protons and antiprotons, not just those selected to study rare occurrences.

    The results of this new analysis appear in the figure. The measurements lie within the band of uncertainty of the theoretical predictions. Using the results here, theorists can reduce the size of the band of uncertainty. They might also be able to improve the general trend of the predictions to agree better with the trends in the measurements.

    This measurement is an example of CDF’s continuing effort to produce unique and useful results that complement and supplement those of the LHC. These help improve our understanding of the fundamental forces of nature.

    Learn more.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    FNAL Icon
    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 5:26 pm on September 29, 2015 Permalink | Reply
    Tags: , , , FNAL Tevatron, , ,   

    From SMU: “Top Quark: New precise particle measurement improves subatomic tool for probing mysteries of universe” 

    SMU

    SMU Research

    September 28, 2015
    Margaret Allen

    In post-Big Bang world, nature’s top quark — a key component of matter — is a highly sensitive probe that physicists use to evaluate competing theories about quantum interactions

    Physicists at Southern Methodist University, Dallas, have achieved a new precise measurement of a key subatomic particle, opening the door to better understanding some of the deepest mysteries of our universe.

    The researchers calculated the new measurement for a critical characteristic — mass — of the top quark.

    1
    A collision event involving top quarks

    Quarks make up the protons and neutrons that comprise almost all visible matter. Physicists have known the top quark’s mass was large, but encountered great difficulty trying to clearly determine it.

    The newly calculated measurement of the top quark will help guide physicists in formulating new theories, said Robert Kehoe, a professor in SMU’s Department of Physics. Kehoe leads the SMU group that performed the measurement.

    Top quark’s mass matters ultimately because the particle is a highly sensitive probe and key tool to evaluate competing theories about the nature of matter and the fate of the universe.

    Physicists for two decades have worked to improve measurement of the top quark’s mass and narrow its value.

    “Top” bears on newest fundamental particle, the Higgs boson

    The new value from SMU confirms the validity of recent measurements by other physicists, said Kehoe.

    But it also adds growing uncertainty about aspects of physics’ Standard Model.

    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.

    The Standard Model is the collection of theories physicists have derived — and continually revise — to explain the universe and how the tiniest building blocks of our universe interact with one another. Problems with the Standard Model remain to be solved. For example, gravity has not yet been successfully integrated into the framework.

    The Standard Model holds that the top quark — known familiarly as “top” — is central in two of the four fundamental forces in our universe — the electroweak force, by which particles gain mass, and the strong force, which governs how quarks interact. The electroweak force governs common phenomena like light, electricity and magnetism. The strong force governs atomic nuclei and their structure, in addition to the particles that quarks comprise, like protons and neutrons in the nucleus.

    The top plays a role with the newest fundamental particle in physics, the Higgs boson, in seeing if the electroweak theory holds water.

    Some scientists think the top quark may be special because its mass can verify or jeopardize the electroweak theory. If jeopardized, that opens the door to what physicists refer to as “new physics” — theories about particles and our universe that go beyond the Standard Model.

    Other scientists theorize the top quark might also be key to the unification of the electromagnetic and weak interactions of protons, neutrons and quarks.

    In addition, as the only quark that can be observed directly, the top quark tests the Standard Model’s strong force theory.

    “So the top quark is really pushing both theories,” Kehoe said. “The top mass is particularly interesting because its measurement is getting to the point now where we are pushing even beyond the level that the theorists understand.”

    He added, “Our experimental errors, or uncertainties, are so small, that it really forces theorists to try hard to understand the impact of the quark’s mass. We need to observe the Higgs interacting with the top directly and we need to measure both particles more precisely.”

    The new measurement results were presented in August and September at the Third Annual Conference on Large Hadron Collider Physics, St. Petersburg, Russia, and at the 8th International Workshop on Top Quark Physics, Ischia, Italy.

    “The public perception, with discovery of the Higgs, is ‘Ok, it’s done,’” Kehoe said. “But it’s not done. This is really just the beginning and the top quark is a key tool for figuring out the missing pieces of the puzzle.”

    The results were made public by DZero, a collaborative experiment of more than 500 physicists from around the world. The measurement is described in Precise measurement of the top quark mass in dilepton decays with optimized neutrino weighting and is available online at arxiv.org/abs/1508.03322.

    SMU measurement achieves surprising level of precision

    To narrow the top quark measurement, SMU doctoral researcher Huanzhao Liu took a standard methodology for measuring the top quark and improved the accuracy of some parameters. He also improved calibration of an analysis of top quark data.

    “Liu achieved a surprising level of precision,” Kehoe said. “And his new method for optimizing analysis is also applicable to analyses of other particle data besides the top quark, making the methodology useful within the field of particle physics as a whole.”

    The SMU optimization could be used to more precisely understand the Higgs boson, which explains why matter has mass, said Liu.

    The Higgs was observed for the first time in 2012, and physicists keenly want to understand its nature.

    “This methodology has its advantages — including understanding Higgs interactions with other particles — and we hope that others use it,” said Liu. “With it we achieved 20-percent improvement in the measurement. Here’s how I think of it myself — everybody likes a $199 iPhone with contract. If someday Apple tells us they will reduce the price by 20 percent, how would we all feel to get the lower price?”

    Another optimization employed by Liu improved the calibration precision by four times, Kehoe said.

    Shower of Top quarks post Big Bang

    Top quarks, which rarely occur now, were much more common right after the Big Bang 13.8 billion years ago. However, top is the only quark, of six different kinds, that can be observed directly. For that reason, experimental physicists focus on the characteristics of top quarks to better understand the quarks in everyday matter.

    To study the top, physicists generate them in particle accelerators, such as the Tevatron, a powerful U.S. Department of Energy particle accelerator operated by Fermi National Laboratory in Illinois, or the Large Hadron Collider in Switzerland, a project of the European Organization for Nuclear Research, CERN.

    FNAL Tevatron
    FNAL DZero
    FNAL CDF
    Tevatron, DZero, CDF

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    CERN ATLAS New
    CERN CMS Detector
    LHC, ATLAS, CMS

    SMU’s measurement draws on top quark data gathered by DZero that was produced from proton-antiproton collisions at the Tevatron, which Fermilab shut down in 2011.

    The new measurement is the most precise of its kind from the Tevatron, and is competitive with comparable measurements from the Large Hadron Collider. The top quark mass has been precisely measured more recently, but there is some divergence of the measurements. The SMU result favors the current world average value more than the current world record holder measurement, also from Fermilab. The apparent discrepancy must be addressed, Kehoe said.

    Critical question: Universe isn’t necessarily stable at all energies

    “The ability to measure the top quark mass precisely is fortuitous because it, together with the Higgs boson mass, tells us whether the universe is stable or not,” Kehoe said. “That has emerged as one of today’s most important questions.”

    A stable universe is one in a low energy state where particles and forces interact and behave according to theoretical predictions forever. That’s in contrast to metastable, or unstable, meaning a higher energy state in which things eventually change, or change suddenly and unpredictably, and that could result in the universe collapsing. The Higgs and top quark are the two most important parameters for determining an answer to that question, Kehoe said.

    Recent measurements of the Higgs and top quark indicate they describe a universe that is not necessarily stable at all energies.

    “We want a theory — Standard Model or otherwise — that can predict physical processes at all energies,” Kehoe said. “But the measurements now are such that it looks like we may be over the border of a stable universe. We’re metastable, meaning there’s a gray area, that it’s stable in some energies, but not in others.”

    Are we facing imminent doom? Will the universe collapse?

    That disparity between theory and observation indicates the Standard Model theory has been outpaced by new measurements of the Higgs and top quark.

    “It’s going to take some work for theorists to explain this,” Kehoe said, adding it’s a challenge physicists relish, as evidenced by their preoccupation with “new physics” and the possibilities the Higgs and Top quark create.

    “I attended two conferences recently,” Kehoe said, “and there’s argument about exactly what it means, so that could be interesting.”

    So are we in trouble?

    “Not immediately,” Kehoe said. “The energies at which metastability would kick in are so high that particle interactions in our universe almost never reach that level. In any case, a metastable universe would likely not change for many billions of years.”

    Top quark — a window into other quarks

    As the only quark that can be observed, the top quark pops in and out of existence fleetingly in protons, making it possible for physicists to test and define its properties directly.

    “To me it’s like fireworks,” Liu said. “They shoot into the sky and explode into smaller pieces, and those smaller pieces continue exploding. That sort of describes how the top quark decays into other particles.”

    By measuring the particles to which the top quark decays, scientists capture a measure of the top quark, Liu explained

    But study of the top is still an exotic field, Kehoe said. “For years top quarks were treated as a construct and not a real thing. Now they are real and still fairly new — and it’s really important we understand their properties fully.” — Margaret Allen

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    SMU Campus

    A nationally ranked private university with seven degree-granting schools, SMU is a distinguished center for teaching and research located near the heart of Dallas. SMU’s 11,000 students benefit from small classes, leadership opportunities, international study and innovative programs.

    SMU is celebrating the centennial of its founding in 1911 and its opening in 1915. As SMU enters a second century of achievement, it is recognized as a university of increasing national prominence.

    SMU prepares students for leadership in their professions and in their communities. The University’s location near the heart of Dallas – a thriving center of commerce and culture – offers students enriching experiences on campus and beyond. Relationships in the Dallas area provide a platform for launching careers throughout the world.

    The University offers a strong foundation in the humanities and sciences and undergraduate, graduate and professional degree programs through seven schools. The learning environment includes opportunities for research, community service, internships, mentoring and study abroad.

     
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