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  • richardmitnick 1:34 pm on February 4, 2020 Permalink | Reply
    Tags: "Misbehaving kaons could hint at the existence of new particles", , J-PARC-Japan Proton Accelerator Research Complex, KOTO experiment, ,   

    From Science News and J-PARC: “Misbehaving kaons could hint at the existence of new particles” 

    From Science News



    J-PARC Facility Japan Proton Accelerator Research Complex , located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    Emily Conover

    A little-known type of particle called a kaon may be stepping into the spotlight.

    The exotic subatomic particles are attracting attention for their unexpected behavior in an experiment at a Japanese particle accelerator. Rare kaon decays seem to be happening more frequently than expected, according to the KOTO experiment. If the result holds up to further scrutiny, it could hint at never-before-seen particles that would dethrone particle physicists’ reigning theory, the standard model.

    There’s still a good chance KOTO’s result will be overturned, says Yuval Grossman of Cornell University. But “there’s the extremely exciting possibility that they see something totally new.”

    The standard model describes the particles and forces that underpin the universe. But there are still puzzles to solve, such as why there’s more matter than antimatter in the universe (SN: 11/25/19). So physicists are leaving no stone — or kaon — unturned in efforts to test the theory. One realm subject to scrutiny is very rare decays of kaons. The standard model predicts precisely how rare those decays are, and KOTO, based at the Japan Proton Accelerator Research Complex in Tokai, was built to test that prediction.

    Certain extremely rare decays seem to be happening more often than expected.

    New subatomic particles could explain a surprisingly large number of decays of particles called kaons seen in the KOTO experiment (detector shown). Japan Proton Accelerator Research Complex (J-PARC) Center

    According to the standard model, KOTO should have seen only a fraction of a decay, on average, over a few years’ worth of data. But last September, at the International Conference on Kaon Physics in Perugia, Italy, researchers from KOTO preliminarily reported a bounty of four potential decays.

    “It’s hair-raising for sure,” says physicist Yau Wah of the University of Chicago, co-spokesperson of KOTO. But particle physics experiments are notorious for spurious signals that can mimic real particles (SN: 8/5/16). Additional studies must be done before claiming the decays are real, Wah says.

    That hasn’t stopped physicists from considering implications. Already, a flurry of scientific papers have proposed explanations for the anomaly.

    KOTO is searching for a particular decay of a kaon into three other particles. One of those particles, a pion, produces light that KOTO detects. The other two, a neutrino and an antineutrino, sail through the detector without a blip. That means KOTO is looking for a specific signature: one pion and nothing else. One possible explanation for the four decays is that the kaon might be decaying into a pion plus a new type of particle that, like neutrinos, leaves no trace. That scenario would reproduce the one-pion signature KOTO is searching for, and might happen more often, explaining the extra decays.

    But there’s a catch. KOTO studies kaons that have no electric charge, but other experiments studying charged kaons see no anomaly. That discrepancy is difficult to explain: If the new particle really existed, it should show up for both types of kaons.

    Still, there are ways around this problem, physicist Teppei Kitahara and colleagues report in a paper accepted in Physical Review Letters. For example, the differing sizes of kaon experiments could be part of the answer. At just a few meters long, “KOTO is very small” compared with other kaon experiments, says Kitahara, of Nagoya University in Japan. “This means unstable new particles can easily escape the detector.”

    In a larger detector, it’s harder for particles to escape unobserved. The new particle could decay into other particles that could be spotted, so that the one-pion signature of decaying kaons wouldn’t be reproduced. That could explain why KOTO sees excess decays but other experiments don’t.

    Problems arise not only in the particles’ potential escape from laboratory apparatuses, but also from exploding stars, or supernovas, which could produce the new particles. If those particles escape a supernova, they would carry energy with them. But that energy loss would muck up the known energy budget of supernovas, making some explanations for the kaon decays untenable, physicist Bhupal Dev of Washington University in St. Louis and colleagues report November 27 at arXiv.org. So Dev and colleagues propose a particle that would be trapped inside supernovas by its interactions with other particles.

    Scientists are also considering potential connections to other physics puzzles. For example, experimental measurements disagree with predictions for the magnetic properties of electron-like particles called muons (SN: 9/19/18). “If you want to explain this … you need a model beyond the standard model,” says physicist Xiaoping Wang of Argonne National Laboratory in Lemont, Ill. She and colleagues have come up with a hypothetical particle that could simultaneously explain the muon conundrum and the unexpected kaon decays, the team reports January 17 at arXiv.org.

    While Grossman is skeptical that KOTO’s result will stand, he admits that, deep down, he hopes it is real. “When you go to totally unexplored territory, you always have to be ready for surprises.”

    See the full article here .


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  • richardmitnick 10:55 am on July 11, 2018 Permalink | Reply
    Tags: , E821 storage-ring experiment at Brookhaven National Laboratory, , J-PARC-Japan Proton Accelerator Research Complex, , ,   

    From CERN Courier: “Muons accelerated in Japan” 

    From CERN Courier

    9 July 2018

    Installation. No image credit.

    Muons have been accelerated by a radio-frequency accelerator for the first time, in an experiment performed at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, Japan. The work paves the way for a compact muon linac that would enable precision measurements of the muon anomalous magnetic moment and the electric dipole moment.

    Japan Proton Accelerator Research Complex J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    Japan Proton Accelerator Research Complex J-PARC, located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    Around 15 years ago, the E821 storage-ring experiment at Brookhaven National Laboratory (BNL) reported the most precise measurement of the muon anomalous magnetic moment (g-2).

    E821 storage-ring experiment at Brookhaven National Laboratory (BNL)

    Achieving an impressive precision of 0.54 parts per million (ppm), the measured value differs from the Standard Model prediction by more than three standard deviations. Following a major effort over the past few years, the BNL storage ring has been transported to and upgraded at Fermilab and recently started taking data to improve on the precision of E821.

    FNAL Muon g-2 studio

    In the BNL/Fermilab setup, a beam of protons enters a fixed target to create pions, which decay into muons with aligned spins. The muons are then transferred to the 14 m-diameter storage ring, which uses electrostatic focusing to provide vertical confinement, and their magnetic moments are measured as they precess in a magnetic field.

    The new J-PARC experiment, E34, proposes to measure muon g-2 with an eventual precision of 0.1 ppm by storing ultra-cold muons in a mere 0.66 m-diameter magnet, aiming to reach the BNL precision in a first phase. The muons are produced by laser-ionising muonium atoms (bound states of a positive muon and an electron), which, since they are created at rest, results in a muon beam with very little spread in the transverse direction – thus eliminating the need for electrostatic focusing.

    The ultracold muon beam is stored in a high-precision magnet where the spin-precession of muons is measured by detecting muon decays. This low-emittance technique, which allows a smaller magnet and lower muon energies, enables researchers to circumvent some of the dominant systematic uncertainties in the previous g-2 measurement. To avoid decay losses, the J-PARC approach requires muons to be accelerated via a conventional radio-frequency accelerator.

    In October 2017, a team comprising physicists from Japan, Korea and Russia successfully demonstrated the first acceleration of negative muonium ions, reaching an energy of 90 keV. The experiment was conducted using a radio-frequency quadrupole linac (RFQ) installed at a muon beamline at J-PARC, which is driven by a high-intensity pulsed proton beam. Negative muonium atoms were first accelerated electrostatically and then injected into the RFQ, after which they were guided to a detector through a transport beamline. The accelerated negative muonium atoms were identified from their time of flight: because a particle’s velocity at a given energy is uniquely determined from its mass, its type is identified by measuring the velocity (see figure).

    The researchers are now planning to further accelerate the beam from the RFQ. In addition to precise measurements in particle physics, the J-PARC result offers new muon-accelerator applications including the construction of a transmission muon microscope for use in materials and life-sciences research, says team member Masashi Otani of KEK laboratory. “Part of the construction of the experiment has started with partial funding, which includes the frontend muon beamline and detector. The experiment can start properly three years after full funding is provided.”

    Muon acceleration is also key to a potential muon collider and neutrino factory, for which it is proposed that the large, transverse emittance of the muon beam can be reduced using ionisation cooling (see Muons cooled for action).

    See the full article here .

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  • richardmitnick 3:06 pm on January 6, 2018 Permalink | Reply
    Tags: , J-PARC-Japan Proton Accelerator Research Complex, , , Neutrinos Suggest Solution to Mystery of Universe’s Existence, , , ,   

    From Quanta: “Neutrinos Suggest Solution to Mystery of Universe’s Existence” 

    Quanta Magazine
    Quanta Magazine

    December 12, 2017
    Katia Moskvitch

    A neutrino passing through the Super-Kamiokande experiment creates a telltale light pattern on the detector walls. T2K Experiment/Super-Kamiokande Collaboration, Institute for Cosmic Ray Research, University of Tokyo

    T2K Experiment, Tokai to Kamioka, Japan

    T2K Experiment, Tokai to Kamioka, Japan

    From above, you might mistake the hole in the ground for a gigantic elevator shaft. Instead, it leads to an experiment that might reveal why matter didn’t disappear in a puff of radiation shortly after the Big Bang.

    I’m at the Japan Proton Accelerator Research Complex, or J-PARC — a remote and well-guarded government facility in Tokai, about an hour’s train ride north of Tokyo.

    J-PARC Facility Japan Proton Accelerator Research Complex , located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    The experiment here, called T2K (for Tokai-to-Kamioka) produces a beam of the subatomic particles called neutrinos. The beam travels through 295 kilometers of rock to the Super-Kamiokande (Super-K) detector, a gigantic pit buried 1 kilometer underground and filled with 50,000 tons (about 13 million gallons) of ultrapure water. During the journey, some of the neutrinos will morph from one “flavor” into another.

    In this ongoing experiment, the first results of which were reported last year, scientists at T2K are studying the way these neutrinos flip in an effort to explain the predominance of matter over antimatter in the universe. During my visit, physicists explained to me that an additional year’s worth of data was in, and that the results are encouraging.

    According to the Standard Model of particle physics, every particle has a mirror-image particle that carries the opposite electrical charge — an antimatter particle.

    Standard Model of Particle Physics from Symmetry Magazine

    When matter and antimatter particles collide, they annihilate in a flash of radiation. Yet scientists believe that the Big Bang should have produced equal amounts of matter and antimatter, which would imply that everything should have vanished fairly quickly. But it didn’t. A very small fraction of the original matter survived and went on to form the known universe.

    Researchers don’t know why. “There must be some particle reactions that happen differently for matter and antimatter,” said Morgan Wascko, a physicist at Imperial College London. Antimatter might decay in a way that differs from how matter decays, for example. If so, it would violate an idea called charge-parity (CP) symmetry, which states that the laws of physics shouldn’t change if matter particles swap places with their antiparticles (charge) while viewed in a mirror (parity). The symmetry holds for most particles, though not all. (The subatomic particles known as quarks violate CP symmetry, but the deviations are so small that they can’t explain why matter so dramatically outnumbers antimatter in the universe.)

    Last year, the T2K collaboration announced the first evidence that neutrinos might break CP symmetry, thus potentially explaining why the universe is filled with matter. “If there is CP violation in the neutrino sector, then this could easily account for the matter-antimatter difference,” said Adrian Bevan, a particle physicist at Queen Mary University of London.

    Researchers check for CP violations by studying differences between the behavior of matter and antimatter. In the case of neutrinos, the T2K scientists explore how neutrinos and antineutrinos oscillate, or change, as the particles make their way to the Super-K detector. In 2016, 32 muon neutrinos changed to electron neutrinos on their way to Super-K. When the researchers sent muon antineutrinos, only four became electron antineutrinos.

    That result got the community excited — although most physicists were quick to point out that with such a small sample size, there was still a 10 percent chance that the difference was merely a random fluctuation. (By comparison, the 2012 Higgs boson discovery had less than a 1-in-1 million probability that the signal was due to chance.)

    This year, researchers collected nearly twice the amount of neutrino data as last year. Super-K captured 89 electron neutrinos, significantly more than the 67 it should have found if there was no CP violation. And the experiment spotted only seven electron antineutrinos, two fewer than expected.

    Lucy Reading-Ikkanda for Quanta Magazine

    Researchers aren’t claiming a discovery just yet. Because there are still so few data points, “there’s still a 1-in-20 chance it’s just a statistical fluke and there isn’t even any violation of CP symmetry,” said Phillip Litchfield, a physicist at Imperial College London. For the results to become truly significant, he added, the experiment needs to get down to about a 3-in-1000 chance, which researchers hope to reach by the mid-2020s.

    But the improvement on last year’s data, while modest, is “in a very interesting direction,” said Tom Browder, a physicist at the University of Hawaii. The hints of new physics haven’t yet gone away, as we might expect them to do if the initial results were due to chance. Results are also trickling in from another experiment, the 810-kilometer-long NOvA at the Fermi National Accelerator Laboratory outside Chicago.

    FNAL/NOvA experiment map

    FNAL NOvA Near Detector

    Last year it released its first set of neutrino data, with antineutrino results expected next summer. And although these first CP-violation results will also not be statistically significant, if the NOvA and T2K experiments agree, “the consistency of all these early hints” will be intriguing, said Mark Messier, a physicist at Indiana University.

    A planned upgrade of the Super-K detector might give the researchers a boost. Next summer, the detector will be drained for the first time in over a decade, then filled again with ultrapure water. This water will be mixed with gadolinium sulfate, a type of salt that should make the instrument much more sensitive to electron antineutrinos. “The gadolinium doping will make the electron antineutrino interaction easily detectable,” said Browder. That is, the salt will help the researchers to separate antineutrino interactions from neutrino interactions, improving their ability to search for CP violations.

    “Right now, we are probably willing to bet that CP is violated in the neutrino sector, but we won’t be shocked if it is not,” said André de Gouvêa, a physicist at Northwestern University. Wascko is a bit more optimistic. “The 2017 T2K result has not yet clarified our understanding of CP violation, but it shows great promise for our ability to measure it precisely in the future,” he said. “And perhaps the future is not as far away as we might have thought last year.”

    See the full article here .

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

  • richardmitnick 11:38 am on January 5, 2018 Permalink | Reply
    Tags: HANARO research reactor at the Korean Atomic Energy Research Institute South Korea, J-PARC-Japan Proton Accelerator Research Complex, , , ,   

    From physicsworld.com: “Neutrons probe gravity’s inverse square law” 


    Jan 4, 2018
    Edwin Cartlidge

    Gravitating toward Newton’s law: the J-PARC neutron facility

    A spallation neutron source used by physicists in Japan to search for possible violations of the inverse square law of gravity. By scattering neutrons off noble-gas nuclei, the researchers found no evidence of any deviation from the tried and tested formula. However, they could slightly reduce the wiggle room for any non-conventional interactions at distances of less than 0.1 nm, and are confident they can boost the sensitivity of their experiment over the next few months.

    According to Newton’s law of universal gravitation, the gravitational force between two objects is proportional to each of their masses and inversely proportional to the square of the distance between them. This relationship can also be derived using general relativity, when the field involved is fairly weak and objects are travelling significantly slower than the speed of light. However, there are many speculative theories – some designed to provide a quantum description of gravity – that predict that the relationship breaks down at small distances.

    Physicists have done a wide range of different experiments to look for such a deviation. These include torsion balances, which measure the tiny gravitational attraction between two masses suspended on a fibre and two fixed masses. However, this approach is limited by environmental noise such as seismic vibrations and even the effects of dust particles. As a result such experiments cannot probe gravity at very short distances, with the current limit being about 0.01 mm.

    Scattered in all directions

    Neutrons, on the other hand, can get down to the nanoscale and beyond. The idea is to fire a beam of neutrons at a gas and record how the neutrons are scattered by the constituent nuclei. In the absence of any new forces modifying gravity at short scales, the neutrons and nuclei essentially only interact via the strong force (neutrons being electrically neutral). But the strong force acts over extremely short distances – roughly the size of the nucleus, about 10–14 m – while the neutrons have a de Broglie wavelength of around 1 nm. The neutrons therefore perceive the nuclei as point sources and as such are scattered equally in all directions.

    Any new force, however, would likely extend beyond the nucleus. If its range were comparable to the neutrons’ wavelength then those neutrons would be scattered more frequently in a forward direction than at other angles. Evidence of such a force, should it exist, can therefore be sought by firing in large numbers of neutrons and measuring the distribution of their scattering angles.

    In 2008, Valery Nesvizhevsky of the Institut Laue-Langevin in France and colleagues looked for evidence of such forward scattering in data from previous neutron experiments. They ended up empty handed but could place new upper limits on the strength of any new forces, improving on the existing constraints for scales between 1 pm and 5 nm by several orders of magnitude. Those limits were then pushed back by about another order of magnitude two years ago, when Sachio Komamiya at the University of Tokyo and team scattered neutrons off atomic xenon at the HANARO research reactor at the Korean Atomic Energy Research Institute in South Korea.

    HANARO research reactor at the Korean Atomic Energy Research Institute in South Korea

    Time of flight

    In the new research, Tamaki Yoshioka of Kyushu University in Japan and colleagues use neutrons from a spallation source at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, which they fire at samples of xenon and helium. Because the J-PARC neutrons come in pulses, the researchers can easily measure their time of flight, and, from that, work out their velocity and hence their wavelength.

    J-PARC Facility Japan Proton Accelerator Research Complex J-PARC, located in Tokai village, Ibaraki prefecture, Japan

    Armed with this information, the team can establish whether any forward scattering is due to a new force or simply caused by neutrons bouncing off larger objects in the gas, such as trace amounts of atmospheric gases. At any given wavelength, both types of scattering would be skewed in the forward direction and so would be indistinguishable from one another. But across a range of wavelengths different patterns would emerge. For atmospheric gases, the scattering angle would simply be proportional to the neutrons’ wavelength. In the case of a new force, on the other hand, the relationship would be more complex because the effective size of the nucleus would itself vary with neutron wavelength.

    Reactors can also be used to generate pulses, by “chopping” a neutron beam. But that process severely limits the beam’s intensity. Taking advantage of the superior statistics at J-PARC, Yoshioka and colleagues were able to reduce the upper limit on any new forces below 0.1 nm by about an order of magnitude over the HANARO results – showing that their inherent strength can at most be 10^24 times that of gravity’s (gravity being an exceptionally weak force).

    Cost-effective search

    That is still nowhere near the sensitivity of torsion balance searches at bigger scales – which can get down to the strength of gravity itself. As Nesvizhevsky points out, torsion balances use macroscopic masses with “Avogadro numbers” (1023) of atoms, whereas neutron scattering experiments involve at most a few tens of millions of neutrons. Nevertheless, he believes that the new line of research is well worth pursuing, pointing out that many theories positing additional gravity-like forces “predict forces in this range of observations”. Such experiments, he argues, represent “an extremely cost-effective way of looking for a new fundamental force” when compared to searches carried out in high-energy physics.

    Spurred on by the prospect of discovery, Yoshioka and colleagues are currently taking more data. The lead author of a preprint on arXiv describing the latest research, Christopher Haddock of Nagoya University, says that they hope to have new results by the summer. A series of improvements to the experiment, including less scattering from the beam stop, he says, could boost sensitivity to new forces in the sub-nanometre range by up to a further order of magnitude and should also improve existing limits at distances of up to 10 nm.

    See the full article here .

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    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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