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  • richardmitnick 11:40 am on July 6, 2021 Permalink | Reply
    Tags: "The odd(eron) couple", , , , CERN totem, , FNAL Tevatron DØ detector, , , , ,   

    From Symmetry: “The odd(eron) couple” 

    Symmetry Mag

    From Symmetry

    07/06/21
    Sarah Charley

    Scientists discovered a new particle by comparing data recorded at the LHC and the Tevatron.


    In 2018, physicist Carlos Avila received a thrilling request from an old colleague.

    “It was the type of call that every scientist wants to have,” says Avila, who is a professor at the University of The Andes [Universidad de los Andes] (COL).

    The TOTEM experiment at CERN near Geneva, Switzerland, had recently announced evidence for an elusive quasi-particle that had been a missing link in physicists’ understanding of protons.

    But according to physicist Christophe Royon, the “TOTEM data alone was not enough.” To get the complete picture, Royon, who is a physicist at the University of Kansas (US), wanted to revisit data from the DØ experiment at the Tevatron, a particle accelerator that operated between 1987 and 2011 at the DOE’s Fermi National Accelerator Laboratory (US).

    “It was very exciting that these old measurements we had published in 2012 were still very important and could still play a role in this ongoing research,” Avila says.

    Conducting a joint analysis with two experiments from different generations wasn’t easy. It required rewriting decades-old software and inventing a new way to compare different types of data. In the end, the collaboration led to the discovery of a new particle: the odderon.

    Past-generation accelerator

    The Tevatron and its two experiments—DØ and CDF—rose to fame in 1995 with the discovery of the top quark, the heaviest known fundamental particle.

    “It was really a high point,” says DØ co-spokesperson Paul Grannis. “Everybody was walking on air.”

    At the time of the top quark discovery, CERN was constructing a new particle accelerator, the Large Hadron Collider [above], designed to reach energies an order of magnitude greater than the Tevatron. As the name suggests, the LHC collides a type of subatomic particle called hadrons, usually protons. The Tevatron also used protons, but collided them with their antimatter equivalents, antiprotons.

    The LHC started colliding protons in March 2010. A year and a half later, operators at Fermilab threw a big red switch and reverentially ended operations at the Tevatron. Over the next few years, Grannis watched the DØ collaboration shrink from several hundred scientists to just a handful of active researchers.

    “The people move on,” Grannis says. “There is less and less memory of the details of the experiment.”

    Avila and Royon were among the physicists that transitioned from DØ at the Tevatron to experiments at the LHC. Before bidding adieu, Avila worked on one last paper that compared DØ’s results with the first data from the LHC’s TOTEM experiment. Even though the energies of the two accelerators were different, many theorists expected DØ and TOTEM’s results to look similar. But they didn’t.

    “The DØ paper said that—despite all possible interpretation—they did not have the same pattern as seen at the LHC,” says TOTEM spokesperson Simone Giani. “That paper was the spark that triggered us to see the possibility of working together.”

    When protons don’t collide

    DØ and TOTEM were both looking at patterns from a type of interaction called elastic scattering, in which fast-moving hadrons meet and exchange particles without breaking apart. Grannis likens it to two hockey players passing a heavy puck.

    “If Sam slides a big hockey puck to Flo, Sam is going to recoil when he throws it, and Flo will recoil when she catches it,” he says.

    Like the hockey players, the hadrons drift off course after passing the “puck.” Both DØ and TOTEM have specialized detectors a few hundred meters from the interaction points to capture the deflected “Sams” and “Flos.” By measuring their momenta and how much their trajectories changed, physicists can deduce the properties of the puck that passed between them.

    Gluons à la carte

    In the elastic scattering that DØ and TOTEM study, these subatomic pucks are almost exclusively gluons: force-carrying subatomic particles that live inside hadrons. Because of quantum mechanical conservation laws, the exchanged gluons must always clump with other gluons. Scientists study these gluon-clump exchanges to learn about the structure of matter.

    “Every time we turn on a new accelerator, we hope to reach a high enough energy to see the internal workings of protons,” Giani says. “There is this ambition to purely distill the effect of the gluons and not that of the quarks.”

    Scattering data had already revealed that gluons can clump in even numbers and move between passing hadrons. But scientists were unsure if this same principle would apply to clumps consisting of an odd number of gluons. Theorists predicted the existence of these odd-numbered clumps, which they called odderons, 50 years ago. But odderons had never been observed experimentally.

    An emerging puzzle

    When physicists build a new flagship accelerator, they almost always make a major leap in energy. But they also make other changes, such as what kinds of particles to use in the collider. Because of this, comparing scattering data from different generations of accelerators—such as the Tevatron and LHC—has been difficult.

    “It has been impossible to disentangle if the scattering discrepancies are because of the intrinsic differences between protons and antiprotons, or because the energy of the accelerator is different every time,” Giani says.

    But physicists realized that these discrepancies between the Tevatron and LHC might be a blessing and not a curse. In fact, they thought they could be essential for uncovering the odderon.

    The matter or antimatter nature of the colliding hadrons would be unimportant if odderons didn’t exist and all the gluon “pucks” contained an even number of gluons. But the identities of these hadronic “Sams” and “Flos” (and specifically, whether Sam and Flo are both made from matter, or whether one of them is made from antimatter) should influence how easily they can exchange odderons.

    “The cleanest way to observe the odderon would be to look for differences between proton-proton and proton-antiproton interactions,” says Royon. “And what is the only recently available data for proton-antiproton interactions? This is the Tevatron.”

    Blast from the past

    The plan for TOTEM to work with DØ solidified in 2018 over drinks at CERN’s Restaurant 1.

    “When we did a rough comparison [between the Tevatron and LHC results] on a piece of paper, we already saw some differences,” Royon says. “This was the starting point.”

    A few months later, Avila was remotely logging into his old Fermilab account and trying to access the approximately 20 gigabytes of Tevatron data that he and his colleagues had analyzed years earlier.

    “The first time we tried to look at the data, none of the codes that we were using 10 years ago were working,” Avila says. “The software was already obsolete. We had to restore all the software and put it together with newer versions.”

    Another big challenge was comparing the Tevatron data with the LHC data and compensating for the different energies of the two accelerators. “That was the tricky part,” Grannis says.

    The DØ and TOTEM researchers regularly met over Zoom to check in on their progress and discuss ideas for how they could compare their data in the same energy regime.

    “The DØ people were concentrating on extracting the best possible information from DØ data, and the TOTEM people were doing the same for TOTEM,” Royon says. “My job was to unify the two communities.”

    If the odderon didn’t exist, then DØ and TOTEM should have seen the same scattering patterns in their data after adjusting for the energy differences between the Tevatron and LHC. But no matter how they processed the data, the scattering patterns remained distinct.

    “We did many cross checks,” Royon says. “It took one year to make sure we were correct.”

    The discrepancy between the proton-proton and proton-antiproton data showed that these hadrons were passing a new kind of subatomic puck. When combined with the 2018 TOTEM analysis, they had a high enough statistical significance to claim a discovery: They had finally found the odderon.

    An international team of scientists worked on the research. The US contribution was funded by the Department of Energy (US) and the National Science Foundation (US). “This is definitely the result of hard work from hundreds of people originating from everywhere in the world,” Royon says.

    For Avila, the discovery was just one of the many bonuses associated with teaming up with his old DØ colleagues on this new project. “You build strong friendships while doing research,” he says. “Even if you don’t stay in touch closely, you know these people and you know that working with them is really exciting.”

    Avila also says this discovery shows the value of keeping the legacy of older experiments alive.

    “We shouldn’t forget about this old data,” Avila says. “It can still bring new details about how nature behaves. It has a good scientific value no matter how many years have passed.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:38 am on March 10, 2021 Permalink | Reply
    Tags: "Odderon discovered", , , CERN totem, , FNAL Tevatron DØ collaboration, , , ,   

    From CERN(CH) Courier and DOE’s Fermi National Accelerator Laboratory(US): “Odderon discovered” 


    From CERN(CH) Courier

    and

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From DOE’s Fermi National Accelerator Laboratory(US) , an enduring source of strength for the US contribution to scientific research world wide.

    9 March 2021
    Matthew Chalmers

    1
    Excavating odderons Part of the TOTEM installation in the LHC tunnel 220m downstream from the CMS experiment. Credit: M. Brice/CERN.

    CERN TOTEM.

    The TOTEM collaboration at the LHC, in collaboration with the DØ collaboration at the former Tevatron collider at Fermilab, have announced the discovery of the odderon — an elusive three-gluon state predicted almost 50 years ago. The result was presented in a “discovery talk” on Friday 5 March during the LHC Forward Physics meeting at CERN, and follows the joint publication of a CERN/Fermilab science paper by TOTEM and DØ reporting the observation in December 2020.

    FNAL/Tevatron DØ detector

    “This result probes the deepest features of Quantum Chromodynamics, notably that gluons interact between themselves and that an odd number of gluons are able to be ‘colourless’, thus shielding the strong interaction,” says TOTEM spokesperson Simone Giani of CERN. “A notable feature of this work is that the results are produced by joining the LHC and Tevatron data at different energies.”

    States comprising two, three or more gluons are usually called “glueballs”, and are peculiar objects made only of the carriers of the strong force. The advent of quantum chromodynamics (QCD) led theorists to predict the existence of the odderon in 1973. Proving its existence has been a major experimental challenge, however, requiring detailed measurements of protons as they glance off one another in high-energy collisions.

    While most high-energy collisions cause protons to break into their constituent quarks and gluons, roughly 25% are elastic collisions where the protons remain intact but emerge on slightly different paths (deviating by around a millimetre over a distance of 200 m at the LHC). TOTEM measures these small deviations in proton-proton (pp) scattering using two detectors located 220 m on either side of the CMS experiment, while DØ employed a similar setup at the Tevatron proton-antiproton (pp̄) collider.

    Pomerons and odderons

    At low energies, differences in pp vs pp̄ scattering are due to the exchange of different virtual mesons. At multi-TeV energies, on the other hand, proton interactions are expected to be mediated purely by gluons. In particular, elastic scattering at low-momentum transfer and high energies has long been explained by the exchange of a pomeron — a colour-neutral virtual glueball made up of an even number of gluons.

    However, in 2018 TOTEM reported measurements at high energies that could not easily be explained by this traditional picture. Instead, a further QCD object seemed to be at play, supporting models in which a three-gluon compound, or one containing higher odd numbers of gluons, was being exchanged. The discrepancy came to light via measurements of a parameter called ρ, which represents the ratio of the real and imaginary parts of the forward elastic-scattering amplitude when there is minimal gluon exchange between the colliding protons and thus almost no deviation in their trajectories. The results were sufficient to claim evidence for the odderon, although not yet its definitive observation.

    The new work is based on a model-independent analysis of data at medium-range momenta transfer. The TOTEM and DØ teams compared LHC pp data (recorded at collision energies of 2.76, 7, 8 and 13 TeV and extrapolated to 1.96 TeV), with Tevatron pp̄ data measured at 1.96 TeV. The odderon would be expected to contribute with different signs to pp and pp̄ scattering. Supporting this picture, the two data sets disagree at the 3.4σ level, providing evidence for the t-channel exchange of a colourless, C-odd gluonic compound.

    “When combined with the ρ and total cross-section result at 13 TeV, the significance is in the range 5.2-5.7σ and thus constitutes the first experimental observation of the odderon,” said Christophe Royon of University of Kansas, who presented the results on behalf of DØ and TOTEM last week. “This is a major discovery by CERN/Fermilab.”

    In addition to the new TOTEM-DØ model-independent study, several theoretical papers based on data from the ISR, SPS, Tevatron and LHC, and model-dependent inputs, provide additional evidence supporting the conclusion that the odderon exists.

    The new work is based on a model-independent analysis of data at medium-range momenta transfer. The TOTEM and DØ teams compared LHC pp data (recorded at collision energies of 2.76, 7, 8 and 13 TeV and extrapolated to 1.96 TeV), with Tevatron pp̄ data measured at 1.96 TeV. The odderon would be expected to contribute with different signs to pp and pp̄ scattering. Supporting this picture, the two data sets disagree at the 3.4σ level, providing evidence for the t-channel exchange of a colourless, C-odd gluonic compound.

    “When combined with the ρ and total cross-section result at 13 TeV, the significance is in the range 5.2-5.7σ and thus constitutes the first experimental observation of the odderon,” said Christophe Royon of University of Kansas, who presented the results on behalf of DØ and TOTEM last week. “This is a major discovery by CERN/Fermilab.”

    In addition to the new TOTEM-DØ model-independent study, several theoretical papers based on data from the ISR, SPS, Tevatron and LHC, and model-dependent inputs, provide additional evidence supporting the conclusion that the odderon exists.

    See the full article here .


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  • richardmitnick 3:19 pm on February 9, 2018 Permalink | Reply
    Tags: , , CERN totem, Elastic scattering, , , ,   

    From CERN: “Odd gluon compounds may be lurking in the protons” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    9 Feb 2018.
    Iva Raynova


    CERN TOTEM

    Protons are known to contain quarks and gluons. But are gluons behaving as expected?

    Scientists from the TOTEM (Total, elastic and diffractive cross-section measurement) collaboration may have found indirect evidence of a subatomic gluon-compound in proton-proton collisions. First theorised in the 1970s, such a state, then dubbed “Odderon”, consists of an odd number of gluons.

    Usually, the protons that collide in the LHC shatter and create new particles. Sometimes though, in about 25 percent of the time, they survive the encounter intact. Instead of breaking in pieces, they only change their direction and emerge from the detector at very small angles to the beampipe – their deviation at a 200-metre distance is in the order of one millimetre. This kind of interaction is called “elastic scattering” and it is the specialty of TOTEM, CERN’s longest experiment. To be able to detect the survived protons, its detectors are spread across almost half a kilometre around the CMS interaction point.

    The quarks in the proton are bound by gluons, the carriers of the strong force. Physicists have successfully explained elastic scattering at low-momentum transfer and high energies with the exchange of a “Pomeron”, which in modern language is a state of two teamed-up gluons.

    TOTEM precisely measured the elastic-scattering process at 13 TeV to extract the total probability for proton-proton collisions as well as the so-called rho parameter that helps to explain the difference in proton-proton and antiproton-proton scattering.

    Combining these two measurements, TOTEM finds better agreement with theoretical models that indicate the exchange of three aggregated gluons. Although this exchange has been predicted by the Quantum Chromodynamics (QCD) theory back in the 1980s, no experimental evidence had been presented to date.

    The measurements also hint towards a slow-down of the total probability of scattering with energy. While somewhat expected at the very highest energy, there has been no indication of such an effect in previous data.

    “These measurements explore for the first time the behaviour of protons in elastic interactions at the highest energy of 13 TeV. These results obtained with a record precision were made possible by the excellent performance of the TOTEM detectors and the exceptional capabilities of the Large Hadron Collider,” observed Simone Giani, the TOTEM spokesperson.

    If three gluons really were to form a compound, it should appear in other scattering experiments. Physicists are hence looking forward to dedicated experiments to establish whether such a compound is actually being formed. In order to further explore and confirm the theoretical interpretations, a special LHC proton run at an energy of 900 GeV is planned to take place in 2018 to collect more data and it will involve also other LHC experiments.

    See the full article here.

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  • richardmitnick 2:49 pm on February 5, 2018 Permalink | Reply
    Tags: , CERN Physicists Find Evidence of Long-Sought Quasiparticle: Odderon, CERN totem,   

    From SciNews: “CERN Physicists Find Evidence of Long-Sought Quasiparticle: Odderon” 


    SciNews

    Feb 5, 2018

    Physicists from the TOTEM experiment at CERN’s Large Hadron Collider have uncovered evidence of a subatomic quasiparticle dubbed an ‘odderon’ that — until now — had only been theorized to exist. The results will be published in two papers in the journal Physical Review D, https://arxiv.org/abs/1712.06153; https://cds.cern.ch/record/2298154

    1
    View of the tunnel where the TOTEM experiment’s proton detectors are located. Image credit: TOTEM Collaboration.

    “We’ve been looking for this since the 1970s,” said University of Kansas’ Professor Christophe Royon, a member of the TOTEM (TOTal cross section, Elastic scattering and diffraction dissociation Measurement) Collaboration.

    The findings concern hadrons, the family of particle that includes protons and neutrons, which are composed of quarks ‘glued’ together with gluons.

    This particular experiment involves ‘collisions’ where the protons remain intact after the interaction. In all previous experiments, physicists detected collisions involving only even numbers of gluons exchanged between different protons.

    Professor Royon and colleagues now report evidence of an odd number of gluons, without any quarks, exchanged in the collisions.

    “Until now, most models were thinking there was a pair of gluons — always an even number,” Professor Royon said.

    “Now we measure for the first time the higher number of events and properties and at a new energy. We found measurements that are incompatible with this traditional model of assuming an even number of gluons.”

    “It’s a kind of discovery that we might have seen for the first time, this odd exchange of the number of gluons. There may be three, five, seven or more gluons.”

    The odderon can be seen as the total contribution coming from all types of odd gluon exchange. It represents the involvement of all of three, five, seven or other odd number numbers of gluons.

    By contrast, the older model assumes a contribution from all even numbers of gluons, so it includes contributions from two, four, six or more even-numbered gluons together.

    “Our findings give fresh detail to the Standard Model of particle physics, a widely accepted physics theory that explains how the basic building blocks of matter interact,” the researchers said.

    “This doesn’t break the Standard Model, but there are very opaque regions of the Standard Model, and this work shines a light on one of those opaque regions,” said Dr. Timothy Raben, a particle theorist at the University of Kansas.

    Physicists have imagined the existence of the odderon for many decades, but until the Large Hadron Collider began operating at its highest energies in 2015, the odderon remained mere conjecture.

    The data presented in the new papers were collected at 13 teraelectronvolts (TeV), the fastest scientists have ever been able to collide protons.

    “These ideas date back to the ‘70s, but even at that time it quickly became evident we weren’t close technologically to being able to see the odderon, so while there are several decades of predictions, the odderon has not been seen,” Dr. Raben said.

    See the full article here .

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