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  • richardmitnick 12:06 pm on August 10, 2022 Permalink | Reply
    Tags: "Charming particle has a record-breaking lifetime", , , , , , , , , Tetraquarks   

    From “Physics Today” : “Charming particle has a record-breaking lifetime” 

    Physics Today bloc

    From “Physics Today”

    Heather M. Hill

    Four quarks form a particle that outlives other exotic matter.

    [For display only as the tetraquark pictured in the article would not copy and paste.]

    When quarks come together to form composite particles known as hadrons, they’re typically trios or quark–antiquark pairs. Although the possibility of more complex structures was hypothesized in the 1970s, it took about 30 years to find the first confirmed particle with four quarks. In the intervening years, researchers have observed nearly two dozen so-called tetraquarks and even several pentaquarks (see the Quick Study by Steve Olsen, Physics Today, September 2014, page 56). Those exotic particles offer a window to a particular regime of quantum chromodynamics, which describes the strong force (see the article by Frank Wilczek, Physics Today, August 2000, page 22).

    Quantum chromodynamics readily predicts the behaviors of high-energy particles, but at the lower energies found for quarks in hadrons, it struggles. At those energies, experiments, in particular on exotic particles, are a better guide. Now the Large Hadron Collider beauty (LHCb) collaboration has identified a new tetraquark with an impressively long lifetime.

    The tetraquark—composed of two charm quarks, an up antiquark, and a down antiquark—is promising for future research and hints at the existence of a similar particle of even greater interest.

    For the data set of proton–proton collisions at the LHC between 2011 and 2018, the LHCb collaboration found a sharp peak in the mass spectrum of events with two DØ mesons and a π+ meson, the decay products of the proposed tetraquark. The peak corresponds to a particle mass of about 3875 MeV and falls just below the value for the summed masses of a DØ meson, which comprises a charm quark and an up antiquark, and a D*+ meson, which comprises a charm quark and a down antiquark.

    The signal isn’t noise or chance—the statistical significance is more than 22σ. And the lifetime, as determined from the inverse of the peak’s width, is the longest of the tetraquarks found thus far. Most decay in just 10^−23 seconds, a lifetime the new tetraquark outlasts by two orders of magnitude. A longer lifetime and corresponding narrower signal peak make detecting the particle’s properties easier and more accurate.

    The four quarks could take two different structures: together in a single compact cluster or in two separated lobes, akin to a diatomic molecule but made of a DØ and a D*+ meson. So far, the LHCb results aren’t conclusive but suggest a molecule-type structure.

    Values for the tetraquark’s quantum numbers are among the next tasks for the collaboration. The researchers also hope, inspired by their result, that they might find a tetraquark in which the charm quarks are replaced with two beauty quarks. The beauty version of the tetraquark is predicted to be stable with respect to the strong interaction, so its decay would happen even more slowly through the weak interaction. (R. Aaij et al., LHCb collaboration, Nat. Phys. 18, 751, 2022 [below]; R. Aaij et al., LHCb collaboration, Nat. Commun. 13, 3351, 2022 [below].)

    Nature Physics
    Nature Communications

    See the full article here .


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  • richardmitnick 8:53 am on November 22, 2017 Permalink | Reply
    Tags: , , , , , , , , Tetraquarks   

    From Futurism: “Quantum Physicists Conclude Necessary Makeup of Elusive Tetraquarks” 



    Mesons Baryons Tetraquarks

    , https://blog.cerebrodigital.org/tetraquark-particula-exotica-descubierta-en-fermilab/

    November 20, 2017
    Abby Norman

    Everything in the universe is made up of atoms — except, of course, atoms themselves. They’re made up of subatomic particles, namely, protons, neutrons, and electrons. While electrons are classified as leptons, protons and neutrons are in a class of particles known as quarks. Though, “known” may be a bit misleading: there is a lot more theoretical physicists don’t know about the particles than they do with any degree of certainty.

    As far as we know, quarks are the fundamental particle of the universe. You can’t break a quark down into any smaller particles. Imagining them as being uniformly minuscule is not quite accurate, however: while they are tiny, they are not all the same size. Some quarks are larger than others, and they can also join together and create mesons (1 quark + 1 antiquark) or baryons (3 quarks of various flavors).

    In terms of possible quark flavors, which are respective to their position, we’ve identified six: up, down, top, bottom, charm, and strange. As mentioned, they usually pair up either in quark-antiquark pairs or a quark threesome — so long as the charges ( ⅔, ⅔, and ⅓ ) all add up to positive 1.

    The so-called tetraquark pairing has long-eluded scientists; a hadron which would require 2 quark-antiquark pairs, held together by the strong force. Now, it’s not enough for them to simply pair off and only interact with their partner. To be a true tetraquark, all four quarks would need to interact with one another; behaving as quantum swingers, if you will.

    “Quarky” Swingers

    It might seem like a pretty straightforward concept: throw four quarks together and they’re bound to interact, right? Well, not necessarily. And that would be assuming they’d pair off stably in the first place, which isn’t a given. As Marek Karliner of Tel Aviv University explained to LiveScience, two quarks aren’t any more likely to pair off in a stable union than two random people you throw into an apartment together. When it comes to both people and quarks, close proximity doesn’t ensure chemistry.

    “The big open question had been whether such combinations would be stable,
    or would they instantly disintegrate into two quark-antiquark mesons,” Karliner told Futurism. “Many years of experimental searches came up empty-handed, and no one knew for sure whether stable tetraquarks exist.”

    Most discussions of tetraquarks up until recently involved those “ad-hoc” tetraquarks; the ones where four quarks were paired off, but not interacting. Finding the bona-fide quark clique has been the “holy grail” of theoretical physics for years – and we’re agonizingly close.

    Recalling that quarks are not something we can actually see, it probably goes without saying that predicting the existence of such an arrangement would be incredibly hard to do. The very laws of physics dictate that it would be impossible for four quarks to come together and form a stable hadron. But two physicists found a way to simplify (as much as you can “simplify” quantum mechanics) the approach to the search for tetraquarks.

    Several years ago, Karliner and his research partner, Jonathan Rosner of the University of Chicago, set out to establish the theory that if you want to know the mass and binding energy of rare hadrons, you can start by comparing them to the common hadrons you already know the measurements for. In their research [Nature] they looked at charm quarks; the measurements for which are known and understood (to quantum physicists, at least).

    Based on these comparisons, they proposed that a doubly-charged baryon should have a mass of 3,627 MeV, +/- 12 MeV [Physical Review Letters]. The next step was to convince CERN to go tetraquark-hunting, using their math as a map.

    For all the complex work it undertakes, the vast majority of which is nothing detectable by the human eye, The Large Hadron Collider is exactly what the name implies: it’s a massive particle accelerator that smashes atoms together, revealing their inner quarks.


    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    If you’re out to prove the existence of a very tiny theoretical particle, the LHC is where you want to start — though there’s no way to know how long it will be before, if ever, the particles you seek appear.

    It took several years, but in the summer of 2017, the LHC detected a new baryon: one with a single up quark and two heavy charm quarks — the kind of doubly-charged baryon Karliner and Rosner were hoping for. The mass of the baryon was 3,621 MeV, give or take 1 MeV, which was extremely close to the measurement Karliner and Rosner had predicted. Prior to this observation physicists had speculated about — but never detected — more than one heavy quark in a baryon. In terms of the hunt for the tetraquark, this was an important piece of evidence: that more robust bottom quark could be just what a baryon needs to form a stable tetraquark.

    The perpetual frustration of studying particles is that they don’t stay around long. These baryons, in particular, disappear faster than “blink-and-you’ll-miss-it” speed; one 10/trillionth of a second, to be exact. Of course, in the world of quantum physics, that’s actually plenty of time to establish existence, thanks to the LHC.

    The great quantum qualm within the LHC, however, is one that presents a significant challenge in the search for tetraquarks: heavier particles are less likely to show up, and while this is all happening on an infinitesimal level, as far as the quantum scale is concerned, bottom quarks are behemoths.

    The next question for Rosner and Karliner, then, was did it make more sense to try to build a tetraquark, rather than wait around for one to show up? You’d need to generate two bottom quarks close enough together that they’d hook up, then throw in a pair of lighter antiquarks — then do it again and again, successfully, enough times to satisfy the scientific method.

    “Our paper uses the data from recently discovered double-charmed baryon to point, for the first time, that a stable tetraquark *must* exist,” Karliner told Futurism, adding that there’s “a very good chance” the LHCb at CERN would succeed in observing the phenomenon experimentally.

    That, of course, is still a theoretical proposition, but should anyone undertake it, the LHC would keep on smashing in the meantime — and perhaps the combination would arise on its own. As Karliner reminded LiveScience, for years the assumption has been that tetraquarks are impossible. At the very least, they’re profoundly at odds with the Standard Model of Physics. But that assumption is certainly being challenged. “The tetraquark is a truly new form of strongly-interacting matter,” Karliner told Futurism,” in addition to ordinary baryons and mesons.”

    If tetraquarks are not impossible, or even particularly improbable, thanks to the Karliner and Rosner’s calculations, at least now we have a better sense of what we’re looking for — and where it might pop up.

    Where there’s smoke there’s fire, as they say, and while the mind-boggling realm of quantum mechanics may feel more like smoke and mirrors to us, theoretical physicists aren’t giving up just yet. Where there’s a 2-bottom quark, there could be tetraquarks.

    See the full article here .

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  • richardmitnick 10:22 am on February 25, 2016 Permalink | Reply
    Tags: , , , , , , Tetraquarks   

    From Symmetry: “Fermilab scientists discover new four-flavor particle” 


    Leah Hesla

    FNAL Four flavour particle

    Scientists on the DZero collaboration at the U.S. Department of Energy’s Fermilab have discovered a new particle—the latest member to be added to the exotic species of particle known as tetraquarks.

    FNAL DZero

    Quarks are point-like particles that typically come in packages of two or three, the most familiar of which are the proton and neutron (each is made of three quarks). There are six types, or [flavours], of quark to choose from: up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart.

    Over the last 60 years, scientists have observed hundreds of combinations of quark duos and trios.

    In 2008 scientists on the [KEK]Belle experiment in Japan reported the first evidence of quarks hanging out as a foursome, forming a tetraquark.

    KEK Belle detector
    KEK Belle detector

    Since then physicists have glimpsed a handful of different tetraquark candidates, including now the recent discovery by DZero—the first observed to contain four different quark [flavours].

    DZero is one of two experiments at Fermilab’s Tevatron collider.

    FNAL Tevatron machine

    Although the Tevatron was retired in 2011, the experiments continue to analyze billions of previously recorded events from its collisions.

    As is the case with many discoveries, the tetraquark observation came as a surprise when DZero scientists first saw hints in July 2015 of the new particle, called X(5568), named for its mass—5568 megaelectronvolts.

    “At first, we didn’t believe it was a new particle,” says DZero co-spokesperson Dmitri Denisov. “Only after we performed multiple cross-checks did we start to believe that the signal we saw could not be explained by backgrounds or known processes, but was evidence of a new particle.”

    Mesons Baryons Tetraquarks

    And the X(5568) is not just any new tetraquark. While all other observed tetraquarks contain at least two of the same flavor, X(5568) has four different flavors: up, down, strange and bottom.

    “The next question will be to understand how the four quarks are put together,” says DZero co-spokesperson Paul Grannis. “They could all be scrunched together in one tight ball, or they might be one pair of tightly bound quarks that revolves at some distance from the other pair.”

    Four-quark states are rare, and although there’s nothing in nature that forbids the formation of a tetraquark, scientists don’t understand them nearly as well as they do two- and three-quark states.

    This latest discovery comes on the heels of the first observation of a pentaquark—a five-quark particle—announced last year by the LHCb experiment at the Large Hadron Collider.

    CERN LHCb pentaquark
    Pentaquark. CERN LHCb

    Scientists will sharpen their picture of the quark quartet by making measurements of properties such as the ways X(5568) decays or how much it spins on its axis. Like investigations of the tetraquarks that came before it, the studies of the X(5568) will provide another window into the workings of the strong [interaction] that holds these particles together.

    And perhaps the emerging tetraquark species will become an established class in the future, showing themselves to be as numerous as their two- and three-quark siblings.

    “The discovery of a unique member of the tetraquark family with four different quark [flavours] will help theorists develop models that will allow for a deeper understanding of these particles,” says Fermilab Director Nigel Lockyer.

    Seventy-five institutions from 18 countries collaborated on this result from DZero.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.

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