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  • richardmitnick 9:45 am on October 2, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CDF Looking for rare events” 


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

    Thursday, Oct. 2, 2014
    edited by Andy Beretvas

    In 1977, Fermilab scientists discovered the bottom quark — one of six quarks in the Standard Model — through the production of upsilon mesons. An upsilon meson (Υ) is a bound state of a bottom quark and an antibottom quark.

    graph
    This event display of the observed ΥZ candidate shows the muon candidates identified from the Upsilon (μ3 and μ4) and Z (μ1 and μ2) decays.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    In a new analysis using the full CDF data set, scientists conducted a search for the two mediators of the weak interaction — the W and Z boson — produced in association with an upsilon meson. This is a rare process in the Standard Model, one with a probability that is predicted to be below the sensitivity of the Tevatron.

    FNAL CDF
    CDF

    FNALTevatron
    Tevatron

    For this result, we look for a particular Υ called the Υ(1S), which decays almost immediately. Its lifetime is 1.2 x 10-20 seconds.

    One way the Υ(1S) can decay is into two muons. This decay mode is also rare, occurring in only 
2.5 percent of Υ(1S) decays.

    When we look for the decay of the Υ(1S) in association with a W boson, we look for two muons from the Υ plus an additional muon or electron from the W, as well as so-called missing energy — particles that go undetected but that we know must be present, given the initial energy of the interaction. When we look for the decay of the Υ(1S) in association with a Z boson, we look for two muons from the Υ(1S) plus two additional muons or electrons from the Z.

    The CDF team searched for these two decay patterns. For the full data set, which is about a million detected Υ(1S) decays, we expected an ΥW signal of less than one: only 0.03 ± 0.01 events. The background is expected to be much larger: 1.2 ± 0.5 events. The result of one observed event is in good agreement with the expected background.

    Scientists observed one very nice candidate for Υ and associated Z production (pictured above). The ΥZ signal is expected to be extremely rare, only 0.008 ± 0.002 events from the entire data set. Here the background is expected to be about 0.1 events. This is the first such event of its kind seen.

    The cross section limits resulting from the analysis are currently the world’s best and place restrictions on some new physics scenarios.

    See the full article here.

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  • richardmitnick 11:34 am on August 21, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CDF Testing the Higgs boson’s spin and parity with CDF 


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

    Thursday, Aug. 21, 2014
    Tom Junk and Andy Beretvas

    Since the discovery of the Higgs boson at CERN and the three-standard-deviation excess seen by the CDF and DZero experiments here at Fermilab, the experimental community has been focusing on measuring the properties of this new particle. It’s important to determine whether there is just one new particle or if two or more are contributing to the observed data. The answer at the Tevatron could be different from that at the LHC, as the mixture of production mechanisms and the decays contributing to the most sensitive searches are different.

    Fermilab CDF
    CDF

    Fermilab DZero
    DZero

    Fermilab Tevatron
    Tevatron map

    CERN LHC Map
    LHC map

    The Standard Model’s predictions are that the Higgs boson has all the properties of a heavy piece of the vacuum — there’s no electric charge, or any other kind of charge for that matter. It should have no intrinsic spin, and it should look the same when reflected in a mirror. In short, the only non-zero properties it is expected to have are its mass and its interaction rates with other particles.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    But what if the particle is not the Standard Model Higgs boson but rather an exotic impostor? A Higgs-like particle could have spin, like a graviton. Or, like a pion,

    pion
    The quark structure of the pion.

    it could be a pseudoscalar — that is, its wave function could change sign (from positive to negative or vice versa) when viewed in a mirror. A group of theorists recently suggested that collisions at the Tevatron producing such Higgs impostors in association with the vector bosons W or Z would have very different measurable properties from those predicted for Standard Model Higgs events. The exotic Higgs bosons would have more kinetic energy on average than their Standard Model twins, and the recoiling vector bosons would also be going faster.

    graphs
    Best-fit signal strengths μ for two cases. Left: the Standard Model versus graviton-like boson (spin 2, positive parity) versus the Standard Model Higgs boson (spin 0, positive parity). Right: the pseudoscalar boson (spin 0, negative parity) versus the Standard Model Higgs boson.

    CDF has adapted its sophisticated searches for the Standard Model Higgs boson in the WH→lνbb, the ZH→llbb, and the VH→METbb modes to search for exotic Higgs bosons — the pseudoscalar boson, labeled 0- in the above figure, and a graviton-like spin-2 boson, labeled 2+. The exotic particles were assumed to be produced either in place of the Standard Model Higgs boson or in addition to it. The figure shows the best-fit signal strength parameters μ, which are scaled to the Standard Model Higgs boson signal strength, for both the 0- and 2+ searches.

    In neither combined search is there any hint of the presence of an exotic Higgs boson, and we observe consistency with the presence of the Standard Model Higgs boson.

    See the full article here.

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  • richardmitnick 11:22 am on August 7, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CDF Sifting through the noise to identify single top quarks” 


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

    Thursday, Aug. 7, 2014
    Andy Beretvas

    CDF and DZero discovered the top quark in 1995 from proton-antiproton collisions that produced the top quark together with its antimatter partner, the antitop quark. It took 14 more years for the same collaborations to announce the observation of a top or antitop quark produced without the other. Why the long delay? The main reason has to do with the features of events with only one of the massive quarks. Single-top events are remarkably similar to other more common types of events, and the lack of a clear separation between the single-top signal and other backgrounds made it very difficult to tease it out.

    Fermilab CDF
    Fermilab CDF

    Fermilab DZero
    Fermilab DZero

    Fermilab Tevatron
    Fermilab Tevatron, Home of CDF and DZero

    tq
    A collision event involving top quarks

    In this single-top quark analysis at CDF, we selected events with the following characteristics: a lepton (either an electron or a muon) with high transverse energy; a large imbalance of transverse momentum, which indicates the presence of a neutrino; and two or three jets, at least one of which must originate from a bottom quark. The two main backgrounds are a W boson plus a bottom or charm jet and a W boson plus an up, down or strange jet. Other backgrounds include a Z boson plus jets, top-antitop pairs, two-boson events and events in which a jet has been misidentified as an electron or a muon.

    After applying event selection requirements, we found that the sum of the backgrounds was still about 15 times larger than the signal. Thus, we needed a thorough understanding of the backgrounds to bring the signal to the fore. The solution was to use a set of artificial neural networks. Using a few variables that describe the properties of the events, such as the reconstructed top quark mass and the transverse mass of the reconstructed W boson, we trained the neural networks to separate the signal from the backgrounds. This process is similar to how neurons in our brain work when we engage in pattern recognition. After applying the artificial neural networks in our analysis, we measured a single-top quark cross section of 3.04 +0.57/-0.53 picobarns.

    There are three processes for the production of single top quarks: s-channel, t-channel and associated Wt production. An important feature of this measurement is that we use a next-to-leading-order event generator for the first time to properly include the Wt contribution. In addition to the combined single-top cross section, we also extract separate values for the s-channel process and the sum of the t-channel + Wt processes, as shown in the figure above. The measurements are fully compatible with predictions of the Standard Model.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    See the full article here.

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  • richardmitnick 9:27 am on July 24, 2014 Permalink | Reply
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    From Fermilab: Searching for boosted tops 


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

    Thursday, July 24, 2014
    Pekka Sinervo and Andy Beretvas

    At CDF, protons of energy 1 TeV, or 1 trillion electronvolts, collided with antiprotons of equal energy.

    proton
    The quark structure of the proton. (The color assignment of individual quarks is not important, only that all three colors are present.)

    anti
    The quark structure of the antiproton.

    Fermilab CDF
    CDF

    In many of these events, we observe a phenomenon called a jet. A jet is a spray of particles all moving in the same direction and typically originating from a practically massless subatomic particle, which is why it is also expected to have a low mass. It is fascinating that in some cases these jets have masses that are a substantial fraction of their energy.

    Scientists have studied events in which a very large fraction — at least 40 percent — of the collision energy is transformed into just two such jets. Based on the internal structure of these jets, we have found that they appear mostly to come from very energetic quarks.

    There are six different flavors of quarks, with five of the six having masses that are small compared to the masses of the jets we see in these two-jet (or “dijet”) events.

    quarks
    This plot shows the mjet1 versus mjet2 distribution for the data taken in this experiment.

    If these jets originate from the lighter quarks, then we would expect to see a high occurrence of jets with low masses. The above figure plots the masses of one jet against the other, and indeed we see that most of the events in our sample have two jets where each has a mass between 40 and 60 GeV/c2, or between 50 and 70 proton masses. This amount of mass is consistent with predictions of quantum chromodynamics, the theory describing the strong interaction.

    But what if some of these massive two-jet events were really coming from the production of the super-massive top quark, which has a mass of 173.34 ± 0.76 GeV/c2? We then would expect to see a cluster of events in which both jets had masses between about 140 and 200 GeV/c2. Although there are roughly 30 such events in our data, as seen in the figure, it is only slightly more than we might have expected from the very occasional production of two very massive jets from the lighter quarks.

    top
    A collision event involving top quarks

    We can use these data to set an upper limit on the rate of top quarks being produced at these very high energies at about 40 femtobarns, or no more often than about one collision in every trillion. Our current understanding of the strong interactions is that the expected rate of top quark production corresponding to two-jet events is about 5 femtobarns.

    See the full article here.

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  • richardmitnick 10:24 am on June 26, 2014 Permalink | Reply
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    From Fermilab: “Frontier Science Result: CDF” 


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

    Thursday, June 26, 2014
    Andy Beretvas

    One of the most intriguing elementary particles physicists study is the top quark. Discovered at Fermilab in 1995, it is as heavy as a tungsten atom, and its large mass implies that it decays before joining with lighter quarks to form hadrons. This gives scientists the opportunity to study its properties in detail. Our understanding of the Standard Model predicts that most of the time — 99.83 percent — the top quark decays into a W boson and a b quark.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    tq
    A collision event involving top quarks

    chart
    This plot shows the number of events observed in the data and expected various values of R as a function of identified b jets. No image credit

    That’s the prediction. Researchers need to make a direct measurement to check it, so scientists at Fermilab and the LHC exploit their data to challenge theory and look for the unexpected.

    CERN LHC Map
    CERN LHC

    To answer the question of how often top quarks decay into a W boson and b quark, CDF physicists looked at events in which Tevatron collisions produced a top-antitop quark pair and in which both resulting W bosons decay into an electron (or muon) and a neutrino. The electron and neutrino are accompanied by two additional jets in the final state, producing a peculiar topology.

    Fermilab CDF
    Fermilab/CDF

    Fermilab Tevatron
    Fermilab/Tevatron

    The total sample consists of 286 events with an expected background of 55 events. (From this sample we measure the top-antitop cross section to be 7.64 ± 0.55 picobarns, which is in excellent agreement with previous measurements.)

    As shown in the above figure, scientists at CDF counted how many times one, both or none of the two jets contain an identified b quark. Scientists compare this number with the total number of top decays. The comparison gives them the ratio, R, and if the Standard Model of elementary particles is correct, R should be almost 1. The result is that R is equal to 0.87 ± 0.07. It is tantalizingly close but not equal to the Standard Model expectation. The two largest contributions to the final uncertainty come from the limits in our understanding of the b-tagging efficiency and the statistical size of our sample.

    See the full article here.

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  • richardmitnick 9:31 am on May 8, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CDF Measuring the “direction” of the Standard Model 


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

    May 8, 2014
    edited by Andy Beretvas

    Since the discovery of the top quark in 1995, physicists at the Tevatron have been probing the properties of this mysterious elementary particle to see whether it behaves the way we expect it to. One of these properties is called forward-backward asymmetry.

    Fermilab Tevatron
    Tevatron at Fermilab

    The Tevatron collided protons with antiprotons to produce other particles, including top quark pairs. Forward-backward asymmetry refers to the preference of top quarks to follow the proton direction, forward, and antitops to follow the opposite direction, backward. The asymmetry is the difference between the fraction of top quarks going forward and the fraction of them going backward: the larger its value is, the larger the positive asymmetry.

    Simple theoretical estimates of this asymmetry turned out to be small, but experiment shows otherwise. Larger-than-expected forward-backward asymmetry measurements made at the Tevatron have triggered substantially better theoretical Standard Model predictions and new physics models. These results have pushed scientists for better measurements and a better understanding of top quark physics.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    A powerful independent piece of evidence to help determine whether the observations are in tension with the Standard Model predictions comes from measurements of just the leptons arising from top quark decays. Physicists expect the leptons (electrons or muons) from the top quark decay to follow the directions of their parents. Thus these leptons should inherit the forward-backward asymmetry properties of their respective quarks or antiquarks.

    CDF has just completed a new measurement of the lepton asymmetry using the sample of the full Tevatron Run II data with two charged leptons from top pair decays. The above figure uses a hyperbolic tangent function to recover the total lepton asymmetry both in the detector and in the undetected region. The resultant asymmetry in the two-lepton mode is 7.2 ± 6.0 percent.

    Fermilab CDF
    CDF

    After combining this with the previous measurement, which used data with only one charged lepton from top pair decays, the final CDF measurement of this asymmetry comes to 9.0 +2.8/-2.6 percent (see lower figure). While there are several competing theoretical predictions, most currently predict an asymmetry of about 4 percent, so this result is in moderate disagreement with predictions.

    This new result continues to pique the scientific community’s interest in top quark production. The effort at CDF continues, working on the asymmetry of the top quark pairs in the two-lepton mode. Measurements of the asymmetry of the bottom quark pairs that probe the same physics question are also on the way. It may take a long time before we know if the observed asymmetry is consistent with the Standard Model.

    See the full article here.

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  • richardmitnick 12:29 pm on April 24, 2014 Permalink | Reply
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    From Fermilab: “CDF finalizes its Ωb analysis” 


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

    Thursday, April 24, 2014
    edited by Andy Beretvas

    In addition to the wide program of top quark studies performed at hadron colliders, scientists have obtained many results on the physics of particles containing bottom quarks, also known as b quarks, at these machines over the years.

    LHC Grand Tunnel
    Large Hadron Collider at CERN

    Baryons are particles with three quarks, similar to protons and neutrons. The study of b baryons — baryons with at least one bottom quark — has been particularly fruitful for the hadron colliders. (Although the name might suggest otherwise, colliders known as B factories cannot produce b baryons. B factories, such as those used for the Belle and BaBar experiments, can only produce two-quark b mesons.) The discoveries and first complete reconstructions of several b baryons were made at the Tevatron.

    https://news.slac.stanford.edu/sites/default/files/images/image/fermilab-tevatron.jpg

    The CDF collaboration recently released its measurements of several b baryons based on the entire Tevatron Run II data set. Scientists used several different experimental signatures that rely on the precise tracking chambers and uniform magnetic field that were the heart of the CDF detector.

    Fermilab CDF
    CDF at the Tevatron

    Use of the full available data set increases the precision of our knowledge of several b baryons: the Λb, Ωb and Ξb. It also provides better constraints on the theory that describes particles containing heavy quarks. (As an added side effect of the b baryon program, we also obtained precise mass measurements of two baryons containing charm quarks.)

    graph
    An illustration of the final state used in the reconstruction of the Ξb0 baryon. The data was collected by imposing requirements on the tracks in magenta.

    The upper figure illustrates the final state that is reconstructed for the observation and mass measurement of the particle called Ξb0. The CDF tracking system helped identify seven different tracks, which originate from four different decay points in a cascade comprising five generations of sequentially decaying particles. This rare particle was first discovered at CDF.

    This analysis improved on the existing measurements of mass and lifetime for these rare states of b baryons. In particular, CDF has confirmed its mass measurement of the Ωb – and finds it to be 6,047.5 ± 3.8 (stat) ± 0.6 (syst) MeV/c2. CDF also provides the first evidence for the Ωb – decaying into the final state Ωc0π -.

    Rare phenomena such as these, which appear only after the full data set from Run II is analyzed, are the fruits of the Tevatron’s long run.

    See the full article here.

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  • richardmitnick 12:46 pm on March 19, 2014 Permalink | Reply
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    From Fermilab: “International team of LHC and Tevatron scientists announces first joint result” 


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

    Wednesday, March 19, 2014
    No Writer Credit

    Scientists working on the world’s leading particle collider experiments have joined forces, combined their data and produced the first joint result from Fermilab’s Tevatron and CERN’s Large Hadron Collider (LHC), past and current holders of the record for most powerful particle collider on Earth. Scientists from the four experiments involved—ATLAS, CDF, CMS and DZero—announced their joint findings on the mass of the top quark today at the Rencontres de Moriond international physics conference in Italy.

    Fermilab Tevatron
    Fermilab Tevatron

    CERN LHC
    Inside the LHC

    CERN ATLAS New
    CERN ATLAS

    Fermilab CDF
    Fermilab CDF

    CERN CMS New
    CERN CMS

    Fermilab DZero
    Fermilab DZero

    Together the four experiments pooled their data analysis power to arrive at a new world’s best value for the mass of the top quark of 173.34 plus/minus 0.76 GeV/c2.

    Experiments at the LHC at the CERN laboratory in Geneva, Switzerland and the Tevatron collider at Fermilab near Chicago in Illinois, USA are the only ones that have ever seen top quarks—the heaviest elementary particles ever observed. The top quark’s huge mass (more than 100 times that of the proton) makes it one of the most important tools in the physicists’ quest to understand the nature of the universe.

    The new precise value of the top-quark mass will allow scientists to test further the mathematical framework that describes the quantum connections between the top quark, the Higgs particle and the carrier of the electroweak force, the W boson. Theorists will explore how the new, more precise value will change predictions regarding the stability of the Higgs field and its effects on the evolution of the universe. It will also allow scientists to look for inconsistencies in the Standard Model of particle physics – searching for hints of new physics that will lead to a better understanding of the nature of the universe.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    “The combining together of data from CERN and Fermilab to make a precision top quark mass result is a strong indication of its importance to understanding nature,” said Fermilab director Nigel Lockyer. “It’s a great example of the international collaboration in our field.”

    A total of more than six thousand scientists from more than 50 countries participate in the four experimental collaborations. The CDF and DZero experiments discovered the top quark in 1995, and the Tevatron produced about 300,000 top quark events during its 25-year lifetime, completed in 2011. Since it started collider physics operations in 2009, the LHC has produced close to 18 million events with top quarks, making it the world’s leading top quark factory.

    “Collaborative competition is the name of the game,” said CERN’s Director General Rolf Heuer. “Competition between experimental collaborations and labs spurs us on, but collaboration such as this underpins the global particle physics endeavour and is essential in advancing our knowledge of the universe we live in.”

    Each of the four collaborations previously released their individual top-quark mass measurements. Combining them together required close collaboration between the four experiments, understanding in detail each other’s techniques and uncertainties. Each experiment measured the top-quark mass using several different methods by analysing different top quark decay channels, using sophisticated analysis techniques developed and improved over more than 20 years of top quark research beginning at the Tevatron and continuing at the LHC.

    The joint measurement has been submitted to the electronic arXiv and is available at: http://arxiv.org/abs/1403.4427

    See the full article here.

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  • richardmitnick 1:32 pm on February 24, 2014 Permalink | Reply
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    From Fermilab: “Scientists complete the top quark puzzle” 


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

    Monday, Feb. 24, 2014
    Andre Salles, Fermilab Office of Communication: asalles@fnal.gov, 630-840-6733

    Scientists on the CDF and DZero experiments at the U.S. Department of Energy’s Fermi National Accelerator Laboratory have announced that they have found the final predicted way of creating a top quark, completing a picture of this particle nearly 20 years in the making.

    two
    Matteo Cremonesi, left, of the University of Oxford and the CDF collaboration and Reinhard Schweinhorst of Michigan State University and the DZero collaboration present their joint discovery at a forum at Fermilab on Friday, Feb. 21. The two collaborations have observed the production of single top quarks in the s-channel, as seen in data collected from the Tevatron. Photo: Cindy Arnold

    Fermilab DZero
    DZero

    Fermilab CDF
    CDF

    Tevatron
    Tevatron

    The two collaborations jointly announced on Friday, Feb. 21, that they had observed one of the rarest methods of producing the elementary particle — creating a single top quark through the weak nuclear force, in what is called the s-channel. For this analysis, scientists from the CDF and DZero collaborations sifted through data from more than 500 trillion proton-antiproton collisions produced by the Tevatron from 2001 to 2011. They identified about 40 particle collisions in which the weak nuclear force produced single top quarks in conjunction with single bottom quarks.

    Top quarks are the heaviest and among the most puzzling elementary particles. They weigh even more than the Higgs boson — as much as an atom of gold — and only two machines have ever produced them: Fermilab’s Tevatron and the Large Hadron Collider at CERN. There are several ways to produce them, as predicted by the theoretical framework known as the Standard Model, and the most common one was the first one discovered: a collision in which the strong nuclear force creates a pair consisting of a top quark and its antimatter cousin, the anti-top quark.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Collisions that produce a single top quark through the weak nuclear force are rarer, and the process scientists on the Tevatron experiments have just announced is the most challenging of these to detect. This method of producing single top quarks is among the rarest interactions allowed by the laws of physics. The detection of this process was one of the ultimate goals of the Tevatron, which for 25 years was the most powerful particle collider in the world.

    “This is an important discovery that provides a valuable addition to the picture of the Standard Model universe,” said James Siegrist, DOE associate director of science for high energy physics. “It completes a portrait of one of the fundamental particles of our universe by showing us one of the rarest ways to create them.”

    Searching for single top quarks is like looking for a needle in billions of haystacks. Only one in every 50 billion Tevatron collisions produced a single s-channel top quark, and the CDF and DZero collaborations only selected a small fraction of those to separate them from background, which is why the number of observed occurrences of this particular channel is so small. However, the statistical significance of the CDF and DZero data exceeds that required to claim a discovery.

    “Kudos to the CDF and DZero collaborations for their work in discovering this process,” said Saul Gonzalez, program director for the National Science Foundation. “Researchers from around the world, including dozens of universities in the United States, contributed to this important find.”

    The CDF and DZero experiments first observed particle collisions that created single top quarks through a different process of the weak nuclear force in 2009. This observation was later confirmed by scientists using the Large Hadron Collider.

    Scientists from 27 countries collaborated on the Tevatron CDF and DZero experiments and continue to study the reams of data produced during the collider’s run, using ever more sophisticated techniques and computing methods.

    “I’m pleased that the CDF and DZero collaborations have brought their study of the top quark full circle,” said Fermilab Director Nigel Lockyer. “The legacy of the Tevatron is indelible, and this discovery makes the breadth of that research even more remarkable.”

    See the full article here.

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  • richardmitnick 11:47 am on March 21, 2013 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CDF CDF finalizes its combined Higgs boson results 

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

    Thursday, March 21, 2013
    Andy Beretvas

    “CDF’s physicists have been searching for the Higgs boson since the early days of Run I, publishing their first paper on the search in 1990. If you asked any of them why they did it, they would say it was to learn about what breaks the symmetries of the Standard Model, which is so successful in explaining the data observed at Fermilab and at other particle physics laboratories. Particles cannot have masses if these symmetries hold true, and the Higgs mechanism is the simplest, but not the only, way to resolve this dilemma. On July 4 of last year, two independent experiments at CERN, ATLAS and CMS, announced the observation of a Higgs-like boson. On July 27 Fermilab’s CDF and DZero experiments submitted a combined analysis showing evidence for a Higgs-like particle. The experiments at CERN were primarily finding the decay of the Higgs-like particle into bosons, while the experiments at Fermilab were finding the decay into fermions.

    CDF sought the Higgs boson in many production and decay modes over the years. These searches have now been finalized and documented. The combined results of all of these analyses have been put together and are the last pieces of the chain. Each analysis relied upon the excellent performance of the Tevatron collider and the CDF detector.

    The collaborations will soon submit a new paper that finalizes the combined CDF and DZero result.

    See the full article here.

    graph
    Best-fit cross section for inclusive Higgs boson production, normalized to the Standard Model expectation, for the combination of all CDF search channels as a function of the Higgs boson mass. The solid line indicates the fitted cross section, and the associated shaded regions show the 68 percent and 95 percent credibility intervals, which include both statistical and systematic uncertainties.

    s,
    Standard Model with Higgs

    collab
    The CDF collaboration celebrates the Tevatron on Sept. 30, 2011. Photo: Cindy Arnold

    Fermilab campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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