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  • richardmitnick 4:47 pm on January 9, 2020 Permalink | Reply
    Tags: "Department of Energy picks New York over Virginia for site of new particle collider", , , , , Particle Accelerators, , ,   

    From BNL via Science Magazine: “Department of Energy picks New York over Virginia for site of new particle collider” 

    From Brookhaven National Lab

    via

    AAAS
    Science Magazine

    Jan. 9, 2020
    Adrian Cho

    Nuclear physicists’ next dream machine will be built at Brookhaven National Laboratory in Upton, New York, officials with the Department of Energy (DOE) announced today. The Electron-Ion Collider (EIC) will smash a high-energy beam of electrons into one of protons to probe the mysterious innards of the proton. The machine will cost between $1.6 billion and $2.6 billion and should be up and running by 2030, said Paul Dabbar, DOE’s undersecretary for science, in a telephone press briefing.

    6
    This schematic shows how the EIC will fit within the tunnel of the Relativistic Heavy Ion Collider (RHIC, background photo), reusing essential infrastructure and key components of RHIC.

    3
    Electrons will collide with protons or larger atomic nuclei at the Electron-Ion Collider to produce dynamic 3-D snapshots of the building blocks of all visible matter.

    7
    The EIC will allow nuclear physicists to track the arrangement of the quarks and gluons that make up the protons and neutrons of atomic nuclei.

    “It will be the first brand-new greenfield collider built in the country in decades,” Dabbar said. “The U.S. has been at the front end in nuclear physics since the end of the Second World War and this machine will enable the U.S. to stay at the front end for decades to come.”

    The site decision brings to a close the competition to host the machine. Physicists at DOE’s Thomas Jefferson National Accelerator Facility in Newport News, Virginia, had also hoped to build the EIC.

    Protons and neutrons make up the atomic nucleus, so the sort of work the EIC would do falls under the rubric of nuclear physics. Although they’re more common than dust, protons remain somewhat mysterious. Since the early 1970s, physicists have known that each proton consists of a trio of less massive particles called quarks. These bind to one another by exchanging other quantum particles called gluons.

    However, the detailed structure of the proton is far more complex. Thanks to the uncertainties inherent in quantum mechanics, its interior roils with countless gluons and quark-antiquark pairs that flit in and out of existence too quickly to be directly observed. And many of the proton’s properties—including its mass and spin—emerge from that sea of “virtual” particles. To determine how that happens, the EIC will use its electrons to probe the protons, colliding the two types of particles at unprecedented energies and in unparalleled numbers.

    Researchers at Jefferson lab already do similar work by firing their electron beam at targets rich with protons and neutrons. In 2017, researchers completed a $338 million upgrade to double the energy of the lab’s workhorse, the Continuous Electron Beam Accelerator Facility.

    3
    4
    Continuous Electron Beam Accelerator Facility

    With that electron accelerator in hand, Jefferson lab researchers had hoped to build the EIC by adding a new proton accelerator.

    Brookhaven researchers have studied a very different type of nuclear physics. Their Relativistic Heavy Ion Collider (RHIC) [below] collides nuclei such as gold and copper to produce fleeting puffs of an ultrahot plasma of free-flying quarks and gluons like the one that filled the universe in the split second after the big bang. The RHIC is a 3.8-kilometer-long ring consisting of two concentric and counter-circulating accelerators. Brookhaven researchers plan to make the EIC by using one of the RHIC’s rings to accelerate the protons and to add an electron accelerator to the complex.

    To decide which option to take, DOE officials convened an independent EIC site selection committee, Dabbar says. The committee weighed numerous factors, including the relative costs of the rival plans, he says. Proton accelerators are generally larger and more expensive than electron accelerators.

    The Jefferson lab won’t be left out in the cold, Dabbar says. Researchers there have critical expertise in, among other things, making the superconducting accelerating cavities that will be needed for the new collider. So, scientists there will participate in designing, building, and operating the new collider. “We certainly look forward to [the Jefferson lab] taking the lead in these areas,” Dabbar says.

    The site decision does not commit DOE to building the EIC. The project must still pass several milestones before researchers can being construction—including the approval of a detailed design, cost estimate, and construction schedule. That process can take a few years. However, the announcement does signal the end for the RHIC, which has run since 1999. To make way for the new collider, the RHIC will shut down for good in 2024, Dabbar said at the briefing.

    The decision on a machine still 10 years away reflects the relative good times for DOE science funding, Dabbar says. “We’ve been able to start on every major project that’s been on the books for years.” DOE’s science budget is up 31% since 2016—in spite of the fact that under President Donald Trump, the White House has tried to slash it every year.

    See the full article here .


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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 10:57 am on January 9, 2020 Permalink | Reply
    Tags: "New open release allows theorists to explore LHC data in a new way", , , , Particle Accelerators, , , The first open release of full analysis likelihoods from an LHC experiment.   

    From CERN ATLAS: “New open release allows theorists to explore LHC data in a new way” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN

    From CERN ATLAS

    9 January, 2020
    Katarina Anthony

    The ATLAS collaboration releases full analysis likelihoods, a first for an LHC experiment.

    1
    Explore ATLAS open likelihoods on the HEPData platform. (Image: CERN)

    What if you could test a new theory against LHC data? Better yet, what if the expert knowledge needed to do this was captured in a convenient format? This tall order is now on its way from the ATLAS collaboration, with the first open release of full analysis likelihoods from an LHC experiment.

    “Likelihoods allow you to compute the probability that the data observed in a particular experiment match a specific model or theory,” explains Lukas Heinrich, CERN research fellow working for the ATLAS Experiment. “Effectively, they summarise every aspect of a particular analysis, from the detector settings, event selection, expected signal and background processes, to uncertainties and theoretical models.” Extraordinarily complex and critical to every analysis, likelihoods are one of the most valuable tools produced at the LHC experiments. Their public release will now enable theorists around the world to explore ATLAS data in a whole new way.

    The ATLAS open likelihoods are available on HEPData, an open-access repository for experimental particle physics data. The first open likelihoods released were for a search for supersymmetry in proton–proton collision events containing Higgs bosons, numerous jets of b-quarks and missing transverse momentum. “While ATLAS had published likelihood scans focused on the Higgs boson in 2013, those did not expose the full complexity of the measurements,” says Kyle Cranmer, Professor at New York University. “We hope this first release – which provides the full likelihoods in all their glory – will form a new communication bridge between theorists and experimentalists, enriching the discourse between the communities.”

    The search for new physics will benefit significantly from open likelihoods. “If you’re a theorist developing a new idea, your first question is likely: ‘Is my model already excluded by experiments at the LHC?’” says Giordon Stark, postdoctoral scholar at SCIPP, UC Santa Cruz. “Until now, there was no easy way to answer this.”

    2
    Likelihoods are an essential link between theory and ATLAS data. (Image: K. Cranmer/ATLAS)

    “We plan to make the open release of likelihoods a regular part of our publication process, and have already made them available from a search for the direct production of tau slepton pairs,” says Laura Jeanty, ATLAS Supersymmetry working group convenor. “Over the coming months, we aim to collect feedback from theorists outside the collaboration to best understand how they are using this new resource to further refine future releases.”

    Read more on the ATLAS website.

    See the full article here .


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    CERN Courier

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    QuantumDiaries

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    CERN LHC Grand Tunnel
    CERN LHC particles

     
  • richardmitnick 12:18 pm on December 16, 2019 Permalink | Reply
    Tags: "20th Year of Particle Smashups Underway at Relativistic Heavy Ion Collider", , , , Particle Accelerators, ,   

    From Brookhaven National Lab: “20th Year of Particle Smashups Underway at Relativistic Heavy Ion Collider” 

    From Brookhaven National Lab

    December 16, 2019
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350, or

    Peter Genzer
    genzer@bnl.gov
    (631) 344-3174

    Second of three-year program exploring the nuclear phase diagram at different collision energies to search for “critical point”.

    1
    The STAR detector at the Relativistic Heavy Ion Collider (RHIC).

    The 20th year of particle collisions is underway at the Relativistic Heavy Ion Collider (RHIC) [below], a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory. The particle smashups will continue over a range of collision energies through the first half of 2020, with members of RHIC’s STAR collaboration collecting data from millions of collisions that take place at the center of their house-sized particle detector.

    The main goal of this RHIC run is to explore details of how the hot, dense soup of particles that existed just after the Big Bang—known as quark-gluon plasma—transitioned into the protons and neutrons that make up the bulk of visible matter in today’s world.

    “This will be the second in a three-year campaign to scan the phase diagram of hot matter governed by quantum chromodynamics (QCD), the theory that describes the interactions of quarks and gluons,” said Jamie Dunlop, Associate Chair for Nuclear Physics in Brookhaven Lab’s Physics Department. The range of collision energies over the three years will allow nuclear physicists to search for telltale signs of what’s called a critical point—a change in the way the transition from quarks and gluons to ordinary matter takes place.

    “Since RHIC collides only matter (gold on gold nuclei, and not gold on ‘anti-gold’ nuclei), at lower and lower beam energies the ‘little bangs’ we create in the collider are seeded with more and more matter than antimatter,” Dunlop said. “Past a certain point, this seeding is expected to change the nature of the phase transition between the quark-gluon plasma and normal matter from a smooth, continuous crossover (with no pause at a particular ‘temperature’ while the transition takes place), to a first-order phase transition (like steam to water, in which both phases coexist at 100 degrees Celsius until every molecule has condensed). By reducing the energy, we are searching for the point at which this change happens—the critical point.”

    To achieve these goals, Brookhaven’s accelerator physicists will deliver beams at lower energies than in last-year’s run, explained Wolfram Fischer, Associate Chair for Accelerators in Brookhaven’s Collider-Accelerator Department.

    “Last year, we ran the machine at 19.6 billion electron volts (GeV) and 14.6 GeV in two run sequences,” Fischer said. “This year we will run at 11.5 GeV and 9.1 GeV. That’s lower than the energy at which beams are normally injected into RHIC, and the machine was not really built for this regime, which will make operations quite challenging.”

    The most difficult challenge is that the tightly bunched ions tend to heat up and spread out as they circulate around RHIC’s 2.4-mile-circumference accelerator rings.

    “If the particles spread out, the likelihood of collisions diminishes,” Fischer said.

    Fortunately, last year, RHIC physicists successfully implemented a new component of the accelerator designed to cool the low-energy beams to maximize collision rates at these energies. This system brings accelerated “cool” electrons into a section of each RHIC ring to extract heat from the circulating ions.

    “This is somewhat similar to the way the liquid running through your home refrigerator extracts heat to keep your food cool,” Fischer said. “But the technology needed to achieve this beam cooling is quite a bit more complicated. It required a number of ‘world’s first’ advances, which our team achieved in last year’s demonstration.”

    With the Low Energy RHIC electron Cooling (LEReC) system fully implemented this year, the result should be more tightly packed ion bunches that result in more collisions—and more data—when the counter-circulating ion beams cross.

    “The second half of RHIC Run 20, in particular, depends on this cooling process, because that’s when the lowest-energy collisions will take place,” Fischer said. “Using low energy cooling will be another accomplishment that showcases the versatility of RHIC, a machine that has accomplished so much beyond the capabilities for which it was initially designed.”

    Said Dunlop, “We’re really looking forward to compiling the data from the three years of Beam Energy Scan II to greatly enhance our understanding of the phases of nuclear matter.”

    Research at RHIC is funded primarily by the DOE Office of Science.

    3
    Components of the Low Energy RHIC electron Cooling (LEReC) system will keep particle beams tightly packed to maximize collision rates at low energies.

    See the full article here .


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    BNL Campus


    BNL Center for Functional Nanomaterials

    BNL NSLS-II


    BNL NSLS II

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 11:40 am on December 14, 2019 Permalink | Reply
    Tags: , , Femtoscopy, , Hyperons, Particle Accelerators, , ,   

    From Symmetry: “Neutron star particles go under the LHC microscope” 

    Symmetry Mag
    From Symmetry<

    12/12/19
    Mordechai Rorvig

    1
    NASA/CXC/SAO

    Researchers on the ALICE experiment are uncovering the properties of elusive hyperon particles hypothesized to be found inside neutron stars.

    CERN/ALICE Detector

    Scientists know a thing or two about neutron stars, the compacted remains of massive stars that have burned out.

    They know that they’re about 95% made up of neutrons. They know that they’re generally 13 to 16 miles in diameter. Scientists know that, even though neutron stars are a thousandth the size of the Earth, they’re more massive than the sun. And the closest one they know of is about 500 light-years away.

    There’s also a lot they don’t know.

    “Neutron stars are the most dense objects in the universe,” says Laura Fabbietti, a physicist on the ALICE experiment and a professor at Technische Universität München in Germany. “And we don’t know what’s inside because we cannot fly there and look inside.”

    But scientists at CERN have found a way to learn more about the interior of neutron stars from a location that is much safer and easier to access: the Large Hadron Collider, right here on Earth.

    CERN/LHC Map

    Formed under pressure

    For neutron stars, gravity becomes extremely strong, approaching that of black holes. The force of it packs their matter down to high density.

    Neutron stars must be composed of matter that can withstand this pressure. And nature rearranges any matter that can’t into new matter that can.

    Iron, for example, is thought to be a component of the neutron star’s crust, where the pressure is lightest. Slightly deeper in, scientists think that iron atoms get crushed into heavier atoms. Even deeper, the electrons and protons that hold together atoms get crushed into neutrons. In the very interior of the star, those neutrons might get crushed into particles called hyperons.

    Hyperons are akin to heavier versions of neutrons, both of which are composed of quarks.

    Standard Model of Particle Physics

    There are six types of quarks in total. Most of the matter humans interact with, except for electrons, is built with the lightest of these quarks: up and down quarks. Neutrons, for example, are made of one up quark and two down quarks.

    The next heaviest quark is called the strange quark. Replacing an up or down quark in a neutron with a heavier strange quark yields a hyperon.

    Luckily for scientists who want to study this form of matter, all the different kinds of hyperons—different combinations of up, down and strange quarks—are produced in collisions in the Large Hadron Collider.

    Their lives are different there. In experiments at the LHC, hyperons last for less than a billionth of a second before decaying into other, lighter particles. In neutron stars, however, hyperons should be stable. Because they would be pressed in so close together, there would be no room for their decay products to form.

    Their short laboratory lifespans have made hyperons historically difficult to identify and study. But the unique capabilities of the ALICE detector at the LHC allowed Fabbietti and her research team to accurately identify the hyperon decay products and track those products back to their hyperon source. An upgrade of the ALICE detector will soon allow researchers to collect even more hyperon data.

    “We’re hungry for statistics, hungry for data,” says Bernhard Hohlweger, who led analysis to identify the Xi- (pronounced zai-minus) hyperon, a hyperon with a negative electric charge. “We use everything we can get our hands on.”

    Moving in pairs

    Fabbietti’s group didn’t want just to find hyperons, though; they wanted to learn more about what they do. If they could understand hyperon motion in the ALICE detector, then they could hypothesize the way that hyperons might behave while inaccessibly buried in the universe’s densest stars.

    The chief unknown for the ALICE researchers was the way that hyperons interact with the strong force, which binds quarks together and controls particle motion at small scales. Each kind of hyperon has its own unique mathematical function called a “potential” that explains how the hyperon interacts with the strong force to move.

    “For different particle interactions, there are different potentials,” says Anthony Timmins, a member of the ALICE collaboration and a professor at the University of Houston. Timmins recently presented results on proton Xi- hyperon interactions at the annual Division of Particles & Fields meeting in Boston in July.

    To figure out the Xi- hyperon potential, Fabbieti’s group first looked at a different kind of particle that comes from collisions in the LHC: the proton. Protons have never been observed to decay like short-lived LHC hyperons—and may not decay at all—making them easier to understand by comparison. On top of that, researchers already knew the proton potentials, and that those potentials cause protons to attract or repel each other based on how far apart they are.

    The scientists observed that pairs of protons coming out of collisions tend to be pulled into parallel trajectories by their strong-force potentials. They used that observation and a method called femtoscopy to infer the approximate size of the particles’ collision zone.

    Using femtoscopy, which relates particle motions and particle potentials to the size of collision zones, is like watching debris fly out of an explosion to figure out how big an explosive device must have been. (Only in this case, the debris also interact through the strong force.)

    Having analyzed the proton pairs, the researchers then looked at pairs of protons and hyperons coming out of particle collisions. They again observed parallel motions, indicating an attractive strong-force potential at work. Because they knew the size of the collision zone from the proton pairs, the they could solve for the only unknown: the hyperon potential.

    To understand and quantify this measured potential, next they needed a prediction from theory.

    Stiffening stars

    As it turned out, scientists had recently predicted what these potentials would be. They did it theoretically through simulations of quarks.

    These simulation models are general in nature, relying only on knowledge of quarks, with no specific customizations for the LHC experiments. To the researchers’ surprise and excitement, the simulation results and the measurements from Fabbietti’s group matched.

    “If we do some honest calculations and we get the result, then this result should be realized in nature,” says Tetsuo Hatsuda, a program director at the RIKEN institute in Japan, who helped lead the simulation program. And in this case, “the result was realized in nature.”

    Using these precisely calculated potentials, Takashi Inoue from Hatsuda’s HAL QCD collaboration showed how Xi- hyperons should interact with neutrons in neutron star matter. Hyperons and neutrons were found to repel, unlike hyperons and protons measured in the ALICE detector. This repulsion would make neutron stars stiffer and more resistant to gravitational forces if hyperons were present.

    The baton now goes to astrophysicists, who can compare predicted neutron star stiffness with their observations to help answer the question whether hyperons do indeed exist inside stars.

    Fabbietti and her group plan to continue analyzing more data for different kinds of hyperons, with better precision. Fabbietti says that now “this is a factory of results,” results that show how the 17-mile, underground ring of the LHC can act as a microscope into the stars.

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:32 pm on December 9, 2019 Permalink | Reply
    Tags: "Part of a disCERNing crowd", , Australian astrophysicist Martin White discusses life with and around the Large Hadron Collider., , , Particle Accelerators, ,   

    From COSMOS Magazine: “Part of a disCERNing crowd” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    09 December 2019

    Australian astrophysicist Martin White discusses life with and around the Large Hadron Collider.

    1
    An aerial view of the CERN site, enlivened by Martin White’s hand-written annotations. Credit: Atlas experiment / CERN

    It’s lunchtime, and I am standing with a colleague under the main site of the CERN laboratory, trying to work out whether to go right or left.

    With the rainy Geneva winter in full swing, he informs me that he’s found a hidden entrance to a network of tunnels under the foyer of CERN’s main building and has worked out how to get to the fabled Restaurant 2 without getting wet.

    All we have to do is follow his secret route through the tunnels, which it transpires is so secret that he himself has forgotten it. After half an hour squeezing past hanging cables and scary radiation warnings, we emerge starving exactly where we started out.

    This is life at CERN in a nutshell – an endless search for the unknown conducted in a spirit of frivolity by permanently hungry practitioners. Established in 1954, the European Organisation for Nuclear Research (CERN) hosts the largest particle accelerator ever built by humankind, named, rather appropriately, the Large Hadron Collider (LHC).

    It also has an ambitious and wide-ranging program of other experiments, which test various aspects of particle and nuclear physics, and develop practical spin-off applications of the cutting-edge technology required to push our understanding of the universe to deeper and deeper levels.

    Having lived there on and off for many years, the question I get asked more than any other is: “What does a person at CERN actually do all day?”

    2
    Martin White – proudly part of “an endless search for the unknown’. Credit: GLENN HUNT

    I never had a typical day at CERN, since my work brought me into contact with computer scientists, civil and electrical engineers, medical physicists, theoretical physicists, accelerator experts, and detector physicists.

    The only common thread was attendance at a large number of meetings which, when located at opposite ends of the main site, led to frantic daily runs of a few kilometres that contributed to a significant weight loss – until I discovered the CERN cake selection.

    The preferred language is English, but it’s not easy to recognise it as such, due to a heavy reliance on jargon and acronyms.

    Moreover, I met physicists who could answer me in English, before translating for an Italian colleague, and mocking my question in German to a bystander.

    Nevertheless, I am always surprised at how quickly the exotic becomes normalised at CERN, whether that means getting acclimatised to constantly being surrounded by extraordinarily smart people or becoming used to dinner party statements like “I have a terrible day tomorrow – I have to reassemble the positron accumulator!”

    My work at CERN has involved the ATLAS experiment, one of the seven experiments of the LHC whose job is to filter and record the results of proton-proton collisions that occur more than one billion times a second.

    The middle of this detector is effectively a giant digital camera, consisting of 6.3 million strips of silicon, and my first job at CERN was to write the software that monitored each of these strips individually to confirm that the system was operating smoothly.

    I am one of CERN’s 12,000 users, and like most of them I have worked for various universities and research institutes scattered around the world, with frequent travel to the CERN laboratory as an external participant.

    The intense lure of CERN is that it remains the best international facility for discovering the new particles and laws of nature that would explain both how the Universe works on its smallest scales, and how it operated 0.0000000001 seconds after the Big Bang.

    The Standard Model of particle physics that I learnt as an undergraduate, and now pass on to my students, remains incapable of explaining most of the matter in the Universe, and it is widely believed that the LHC will finally shift us to a higher plane of understanding.

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    See the full article here .


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  • richardmitnick 4:25 pm on December 4, 2019 Permalink | Reply
    Tags: "Discovering the Top Quark", , , FNAL Tevatron CDF, , Particle Accelerators, , ,   

    From particlebites: “Discovering the Top Quark” 

    particlebites bloc

    From particlebites

    December 3, 2019
    Adam Green

    This post is about the discovery of the most massive quark in the Standard Model, the Top quark. Below is a “discovery plot” [1] from the Collider Detector at Fermilab collaboration (CDF). Here is the original paper [Physical Review Letters].

    FNAL/Tevatron CDF detector

    FNAL/Tevatron tunnel

    FNAL/Tevatron map

    1
    This plot confirms the existence of the Top quark. Let’s understand how.

    For each proton collision that passes certain selection conditions, the horizontal axis shows the best estimate of the Top quark mass. These selection conditions encode the particle “fingerprint” of the Top quark. Out of all possible proton collisions events, we only want to look at ones that perhaps came from Top quark decays. This subgroup of events can inform us of a best guess at the mass of the Top quark. This is what is being plotted on the x axis.

    On the vertical axis are the number of these events.

    The dashed distribution is the number of these events originating from the Top quark if the Top quark exists and decays this way. This could very well not be the case.

    The dotted distribution is the background for these events, events that did not come from Top quark decays.

    The solid distribution is the measured data.

    To claim a discovery, the background (dotted) plus the signal (dashed) should equal the measured data (solid). We can run simulations for different top quark masses to give us distributions of the signal until we find one that matches the data. The inset at the top right is showing that a Top quark of mass of 175GeV best reproduces the measured data.

    Taking a step back from the technicalities, the Top quark is special because it is the heaviest of all the fundamental particles. In the Standard Model, particles acquire their mass by interacting with the Higgs. Particles with more mass interact more with the Higgs. The Top mass being so heavy is an indicator that any new physics involving the Higgs may be linked to the Top quark.

    References / Further Reading

    [1] – Observation of Top Quark Production in pp Collisions with the Collider Detector at Fermilab – This is the “discovery paper” announcing experimental evidence of the Top.

    [2] – Observation of tt(bar)H Production [Physical Review Letters]– Who is to say that the Top and the Higgs even have significant interactions to lowest order? The CMS collaboration finds evidence that they do in fact interact at “tree-level.”

    [2] – The Perfect Couple: Higgs and top quark spotted together – This article further describes the interconnection between the Higgs and the Top.

    See the full article here .

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    What is ParticleBites?

    ParticleBites is an online particle physics journal club written by graduate students and postdocs. Each post presents an interesting paper in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

    The papers are accessible on the arXiv preprint server. Most of our posts are based on papers from hep-ph (high energy phenomenology) and hep-ex (high energy experiment).

    Why read ParticleBites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. With each brief ParticleBite, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in particle physics.

    Who writes ParticleBites?

    ParticleBites is written and edited by graduate students and postdocs working in high energy physics. Feel free to contact us if you’re interested in applying to write for ParticleBites.

    ParticleBites was founded in 2013 by Flip Tanedo following the Communicating Science (ComSciCon) 2013 workshop.

    2
    Flip Tanedo UCI Chancellor’s ADVANCE postdoctoral scholar in theoretical physics. As of July 2016, I will be an assistant professor of physics at the University of California, Riverside

    It is now organized and directed by Flip and Julia Gonski, with ongoing guidance from Nathan Sanders.

     
  • richardmitnick 12:27 pm on November 27, 2019 Permalink | Reply
    Tags: "The plot thickens for a hypothetical “X17” particle", , Additional evidence of an unknown particle from a Hungarian lab, , , , , Particle Accelerators, ,   

    From CERN: “The plot thickens for a hypothetical “X17” particle” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    27 November, 2019
    Ana Lopes

    Additional evidence of an unknown particle from a Hungarian lab gives a new impetus to NA64 searches.

    CERN NA64


    The NA64 experiment at CERN (Image: CERN)

    Fresh evidence of an unknown particle that could carry a fifth force of nature gives the NA64 collaboration at CERN a new incentive to continue searches.

    In 2015, a team of scientists spotted [Physical Review Letters] an unexpected glitch, or “anomaly”, in a nuclear transition that could be explained by the production of an unknown particle. About a year later, theorists suggested [Physical Review Letters] that the new particle could be evidence of a new fundamental force of nature, in addition to electromagnetism, gravity and the strong and weak forces. The findings caught worldwide attention and prompted, among other studies, a direct search [Physical Review Letters] for the particle by the NA64 collaboration at CERN.

    A new paper from the same team, led by Attila Krasznahorkay at the Atomki institute in Hungary, now reports another anomaly, in a similar nuclear transition, that could also be explained by the same hypothetical particle.

    The first anomaly spotted by Krasznahorkay’s team was seen in a transition of beryllium-8 nuclei. This transition emits a high-energy virtual photon that transforms into an electron and its antimatter counterpart, a positron. Examining the number of electron–positron pairs at different angles of separation, the researchers found an unexpected surplus of pairs at a separation angle of about 140º. In contrast, theory predicts that the number of pairs decreases with increasing separation angle, with no excess at a particular angle. Krasznahorkay and colleagues reasoned that the excess could be interpreted by the production of a new particle with a mass of about 17 million electronvolts (MeV), the “X17” particle, which would transform into an electron–positron pair.

    The latest anomaly reported by Krasznahorkay’s team, in a paper [.pdf above] that has yet to be peer-reviewed, is also in the form of an excess of electron–positron pairs, but this time the excess is from a transition of helium-4 nuclei. “In this case, the excess occurs at an angle 115º but it can also be interpreted by the production of a particle with a mass of about 17 MeV,” explained Krasznahorkay. “The result lends support to our previous result and the possible existence of a new elementary particle,” he adds.

    Sergei Gninenko, spokesperson for the NA64 collaboration at CERN, which has not found signs of X17 in its direct search, says: “The Atomki anomalies could be due to an experimental effect, a nuclear physics effect or something completely new such as a new particle. To test the hypothesis that they are caused by a new particle, both a detailed theoretical analysis of the compatibility between the beryllium-8 and the helium-4 results as well as independent experimental confirmation is crucial.”

    The NA64 collaboration searches for X17 by firing a beam of tens of billions of electrons from the Super Proton Synchrotron accelerator onto a fixed target.

    The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator

    If X17 did exist, the interactions between the electrons and nuclei in the target would sometimes produce this particle, which would then transform into an electron–positron pair. The collaboration has so far found no indication that such events took place, but its datasets allowed them to exclude part of the possible values for the strength of the interaction between X17 and an electron. The team is now upgrading their detector for the next round of searches, which are expected to be more challenging but at the same time more exciting, says Gninenko.

    Among other experiments that could also hunt for X17 in direct searches are the LHCb experiment and the recently approved FASER experiment, both at CERN.

    CERN/LHCb detector

    CERN FASER experiment schematic

    Jesse Thaler, a theoretical physicist from the Massachusetts Institute of Technology, says: “By 2023, the LHCb experiment should be able to make a definitive measurement to confirm or refute the interpretation of the Atomki anomalies as arising from a new fundamental force. In the meantime, experiments such as NA64 can continue to chip away at the possible values for the hypothetical particle’s properties, and every new analysis brings with it the possibility (however remote) of discovery.”

    See the full article here.


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  • richardmitnick 4:10 pm on November 14, 2019 Permalink | Reply
    Tags: , , , , , Particle Accelerators, ,   

    From Fermi National Accelerator Lab: “Discovery of a new type of particle beam instability” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    November 14, 2019
    Alexey Burov

    Accelerated, charged particle beams do what light does for microscopes: illuminate matter. The more intense the beams, the more easily scientists can examine the object they are looking at. But intensity comes with a cost: the more intense the beams, the more they become prone to instabilities.

    One type of instability occurs when the average energy of accelerated particles traveling through a circular machine reaches its transition value. The transition point occurs when the particles revolve around the ring at the same rate, even though they do not all carry the same energy — in fact, they exhibit a range of energies. The specific motion of the particles near the transition energy makes them extremely prone to collective instabilities.

    These particular instabilities were observed for decades, but they were not sufficiently understood. In fact, they were misinterpreted. In a paper published this year, I suggest a new theory about these instabilities. The application of this theory to the Fermilab Booster accelerator predicted the main features of the instability there at the transition crossing, suggesting better ways to suppress the instability. Recent measurements confirmed the predictions, and more detailed experimental beam studies are planned in the near future.

    1
    Recent measurements at the Fermilab Booster accelerator confirmed existence of a certain kind of particle beam instability. More measurements are planned for the near future to examine new methods proposed to mitigate it.

    Accelerating high-intensity beams is a crucial part of the Fermilab scientific program. A solid theoretical understanding of particle beam behavior equips experimentalists to better manipulate the accelerator parameters to suppress instability. This leads to the high-intensity beams needed for Fermilab’s experiments in fundamental physics. It is also useful for any experiment or institution operating circular accelerators.

    Beam protons talk to each other by electromagnetic fields, which are of two kinds. One is called the Coulomb field. These fields are local and, by themselves, cannot drive instabilities. The second kind is the wake field. Wake fields are radiated by the particles and trail behind them, sometimes far behind.

    When a particle strays from the beam path, the wake field translates this departure backward — in the wake left by the particle. Even a small departure from the path may not escape being carried backward by these electromagnetic fields. If the beams are intense enough, their wakes can destabilize them.

    In the new theory, I suggested a compact mathematical model that effectively takes both sorts of fields into account, realizing that both of them are important when they are strong enough, as they typically are near transition energy.

    This kind of huge amplification happens at CERN’s Proton Synchrotron, for example, as I showed in my more recent paper, submitted to Physical Review Accelerators and Beams. If not suppressed one way or another, this amplification may grow until the beam touches the vacuum chamber wall and becomes lost. Recent measurements at the Fermilab Booster confirmed existence of a similar instability there; more measurements are planned for the near future to examine new methods proposed to mitigate it.

    These phenomena are called transverse convective instabilities, and the discoveries of how they arise open new doors to theoretical, numerical and experimental ways to better understanding and better dealing with the intense proton beams.

    This work is supported by the DOE Office of Science.

    Science paper:
    Convective instabilities of bunched beams with space charge
    Physical Review Accelerators and Beams

    See the full here.


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    FNAL Icon

    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 2:25 pm on November 11, 2019 Permalink | Reply
    Tags: "LHCf gears up to probe birth of cosmic-ray showers", , , , Particle Accelerators, ,   

    From CERN: “LHCf gears up to probe birth of cosmic-ray showers” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    11 November, 2019
    Ana Lopes


    CERN LHCf

    1
    One of the LHCf experiment’s two detectors, LHCf Arm2, seen here during installation into a particle absorber that surrounds the LHC’s beam pipe. (Image: Lorenzo Bonechi)

    Cosmic rays are particles from outer space, typically protons, travelling at almost the speed of light. When the most energetic of these particles strike the atmosphere of our planet, they interact with atomic nuclei in the atmosphere and produce cascades of secondary particles that shower down to the Earth’s surface. These extensive air showers, as they are known, are similar to the cascades of particles that are created in collisions inside particle colliders such as CERN’s Large Hadron Collider (LHC). In the next LHC, run starting in 2021, the smallest of the LHC experiments – the LHCf experiment – is set to probe the first interaction that triggers these cosmic showers.

    Observations of extensive air showers are generally interpreted using computer simulations that involve a model of how cosmic rays interact with atomic nuclei in the atmosphere. But different models exist and it’s unclear which one is the most appropriate. The LHCf experiment is in an ideal position to test these models and help shed light on cosmic-ray interactions.

    In contrast to the main LHC experiments, which measure particles emitted at large angles from the collision line, the LHCf experiment measures particles that fly out in the “forward” direction, that is, at small angles from the collision line. These particles, which carry a large portion of the collision energy, can be used to probe the small angles and high energies at which the predictions from the different models don’t match.

    Using data from proton–proton LHC collisions at an energy of 13 TeV, LHCf has recently measured how the number of forward photons and neutrons varies with particle energy at previously unexplored high energies. These measurements agree better with some models than others, and they are being factored in by modellers of extensive air showers.

    In the next LHC run, LHCf should extend the range of particle energies probed, due to the planned higher collision energy. In addition, and thanks to ongoing upgrade work, the experiment should also increase the number and type of particles that are detected and studied.

    What’s more, the experiment plans to measure forward particles emitted from collisions of protons with light ions, most likely oxygen ions. The first interactions that trigger extensive air showers in the atmosphere involve mainly light atomic nuclei such as oxygen and nitrogen. LHCf could therefore probe such an interaction in the next run, casting new light on cosmic-ray interaction models at high energies.

    Find out more in the Experimental Physics newsletter article.

    See the full article here.


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  • richardmitnick 2:23 pm on November 6, 2019 Permalink | Reply
    Tags: , , CERN Council selected Fabiola Gianotti as the Organization’s next Director-General for her second term of office., , Particle Accelerators, ,   

    From CERN: “CERN Council appoints Fabiola Gianotti for second term of office as CERN Director General” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    6 November, 2019

    At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office.

    1
    President of the CERN Council, Ursula Bassler and Director-General of CERN, Fabiola Gianotti (Image: CERN)

    At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office. The appointment will be formalised at the December Session of the Council, and Gianotti’s new five-year term of office will begin on 1 January 2021. This is the first time in CERN’s history that a Director-General has been appointed for a full second term.

    “I congratulate Fabiola Gianotti very warmly for her reappointment as Director-General for another five-year term of office. With her at the helm, CERN will continue to benefit from her strong leadership and experience, especially for important upcoming projects such as the High-Luminosity LHC, implementation of the European Strategy for Particle Physics, and the construction of the Science Gateway,” said President of the CERN Council, Ursula Bassler. “During her first term, she excelled in leading our diverse and international scientific organisation, becoming a role model, especially for women in science”.

    “I am deeply grateful to the CERN Council for their renewed trust. It is a great privilege and a huge responsibility,” said CERN Director-General, Fabiola Gianotti. “The following years will be crucial for laying the foundations of CERN’s future projects and I am honoured to have the opportunity to work with the CERN Member States, Associate Member States, other international partners and the worldwide particle physics community.”

    Gianotti has been CERN’s Director-General since 1 January 2016. She received her Ph.D. in experimental particle physics from the University of Milano in 1989 and has been a research physicist at CERN since 1994. She was the leader of the ATLAS experiment’s collaboration from March 2009 to February 2013, including the period in which the LHC experiments ATLAS and CMS announced the discovery of the Higgs boson. The discovery was recognised in 2013 with the Nobel Prize in Physics being awarded to theorists François Englert and Peter Higgs. Gianotti is a member of many international committees, and has received numerous prestigious awards. She was the first woman to become the Director-General of CERN.

    See the full article here.


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    THE FOUR MAJOR PROJECT COLLABORATIONS

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