DOCSLIB.ORG

Top Quark Discovered

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Top Quark Discovered Top quark discovered Schematic of a decay pattern for the top quark-antiquark pair formed when a high energy proton and antiproton collide. Analys­ ing the emerging particles, physicists can track back to the top quark dynamics. ine months after a careful N announcement of tentative evidence for the long-awaited sixth 'top' quark, physicists from the CDF and DO experiments at Fermilab's Tevatron proton-antiproton collider declared on 2 March that they had finally discovered the top quark. Last year (June 1994, page 1), the CDF experiment at the Tevatron reported a dozen candidate top events. These, said CDF, had all the characteristics expected of top, but the difficulties of extracting the tiny signal from a trillion proton-antiproton collisions made them shy of claiming a discovery. For its part, the compan­ ion DO Tevatron experiment reported a few similar events but were even more guarded about their interpreta­ tion as top quarks. Just after these hesitant announce­ ments, performance at the Tevatron improved dramatically last summer. After the commissioning of a new linear accelerator and a magnet realignment, the machine reached a new world record proton-antiproton collision luminosity of 1.28 x 1031 per sq cm per s, ten times that originally planned. Data began to pour in at an unprecedented rate and the data frustrated by its heaviness - the top is but nevertheless was consistent with sample grew to six trillion collisions. some 40 times the mass of its 'beau­ no top production. When other Luminosity has subsequently climbed tiful' partner. Not only is the top quark scientific discoveries are claimed on to 1.7 x 1031. the heaviest by far, but it is the only the basis of much more flimsy evi­ The top quark is the final letter in quark which has been actively dence, the objectivity of these the alphabet of Standard Model hunted. After the quarry was Tevatron experiment analyses was particles. According to this picture, all glimpsed last year, the net has now widely admired. matter is composed of six strongly- been closed. Meanwhile a lot more Tevatron interacting subnuclear particles, the The painstaking analysis of the top proton-antiproton collision data have quarks, and six weakly interacting quark data was the highlight at major been scrutinized. As well as the particles, the leptons. Both sextets meetings last summer. At the Glas­ 1992-1993 run (Run la) which pro­ are neatly arranged as three pairs in gow conference (October, page 2), vided the initial samples, data from order of increasing mass. Hans Jensen of CDF cautiously said the subsequent 1994-1995 run (Run The fifth quark, the 'beauty' or 'b' 'This gives evidence for the top quark lb) have become available. quark, was also discovered at but does not firmly establish its After carefully trimming the raw 6 Fermilab, back in 1977. Since then existence.' For DO, Paul Grannis trillion collision sample to 40 million physicists have been eagerly waiting stated their sample had a small promising events, this information for the top to turn up, but have been excess over expected background, was painstakingly sifted, looking for CERN Courier, April/ May 1995 1 Top quark discovered Below, the CDF experiment (seen here in the Right, at Fermilab's Tevatron proton-antiproton 'exploded' maintenance position) at Fermilab's collider, the DO detector (seen here in its Tevatron has seen 43 examples of top quark assembly position) has, with its partner production in six trillion proton-antiproton Tevatron experiment CDF, finally produced collisions. hard evidence for the long awaited sixth 'top' (Photos Fermilab) quark. proton-antiproton collision point. DO found 17 top events, including 3 dilepton pairs, against an estimated background of about 4. Careful analysis of the decay kinematics of a suitable subset of top events reveals the mass of the decaying top quark. Finding the expected patterns of top decay is one thing, but the mass analysis is another. The decay patterns would be meaningless if they did not point to a narrow mass band. CDF reports a mass of 176 GeV, with an overall uncertainty of ± 13 GeV. This overlaps with the 174 GeV ±10% claimed last year, and is totally compatible with the accumulated Standard Model data (November signs of the daughter particles into teristic confined 'jets' of particles. 1994, page 5). DO gives a slightly which the top quark decays. The two However this top decay channel is higher top quark mass of 199 ± 30 experiments see these events easily polluted by background, and to GeV, but still bracketing the Standard distributed among the different types clean up the sample the experiments Model prediction. of decay expected after a top quark- look for signs of the b-quark or for In physics-speak, the statistical antiquark pair is formed in a proton- special event patterns expected from significance of the new top quark antiproton annihilation. top production. The b-quark can be measurement is expressed in likeli­ There are several such decay recognized either by its characteristi­ hood units of about 4.7 standard signatures. One occurs when both cally short decay time (picked up as deviations for each detector. This the top quark and antiquark decay a short track stub between the means that the overall possibility of (each via a W boson) to produce an original proton-antiproton collision some fluctuation in the background electron and an electron-neutrino or and the secondary decay) or by its count is less than about one part in a a muon and a muon-neutrino. The (semileptonic) decay products. million for either experiment. resultant electron and/or muon CDF found 43 top events, 6 with The experiments expect to amass (dilepton) pairs provide a clean dilepton pairs, compared to an twice the current data by December, source of top signals. expected background of 8 events when the Tevatron will be temporarily More probable but less clean is the from other processes which could shut down for routine maintenance process in which one top quark (or 'fake' a top quark signal. Recent CDF and to prepare for upgrades to the antiquark) decays as above while its analysis has benefited from an experiments to work with the still partner gives, via a W, another quark improved microvertex detector which higher collision luminosities expected pair. These quarks produce charac- picks up particle tracks close to the in the era of Fermilab's Main Injector. 2 CERN Courier, April//May 1995 .
Load more

Recommended publications
  • Interactions of Antiprotons with Atoms and Molecules
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln US Department of Energy Publications U.S. Department of Energy 1988 INTERACTIONS OF ANTIPROTONS WITH ATOMS AND MOLECULES Mitio Inokuti Argonne National Laboratory Follow this and additional works at: https://digitalcommons.unl.edu/usdoepub Part of the Bioresource and Agricultural Engineering Commons Inokuti, Mitio, "INTERACTIONS OF ANTIPROTONS WITH ATOMS AND MOLECULES" (1988). US Department of Energy Publications. 89. https://digitalcommons.unl.edu/usdoepub/89 This Article is brought to you for free and open access by the U.S. Department of Energy at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in US Department of Energy Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. /'Iud Tracks Radial. Meas., Vol. 16, No. 2/3, pp. 115-123, 1989 0735-245X/89 $3.00 + 0.00 Inl. J. Radial. Appl .. Ins/rum., Part D Pergamon Press pic printed in Great Bntam INTERACTIONS OF ANTIPROTONS WITH ATOMS AND MOLECULES* Mmo INOKUTI Argonne National Laboratory, Argonne, Illinois 60439, U.S.A. (Received 14 November 1988) Abstract-Antiproton beams of relatively low energies (below hundreds of MeV) have recently become available. The present article discusses the significance of those beams in the contexts of radiation physics and of atomic and molecular physics. Studies on individual collisions of antiprotons with atoms and molecules are valuable for a better understanding of collisions of protons or electrons, a subject with many applications. An antiproton is unique as' a stable, negative heavy particle without electronic structure, and it provides an excellent opportunity to study atomic collision theory.
    [Show full text]
  • The Particle World
    The Particle World ² What is our Universe made of? This talk: ² Where does it come from? ² particles as we understand them now ² Why does it behave the way it does? (the Standard Model) Particle physics tries to answer these ² prepare you for the exercise questions. Later: future of particle physics. JMF Southampton Masterclass 22–23 Mar 2004 1/26 Beginning of the 20th century: atoms have a nucleus and a surrounding cloud of electrons. The electrons are responsible for almost all behaviour of matter: ² emission of light ² electricity and magnetism ² electronics ² chemistry ² mechanical properties . technology. JMF Southampton Masterclass 22–23 Mar 2004 2/26 Nucleus at the centre of the atom: tiny Subsequently, particle physicists have yet contains almost all the mass of the discovered four more types of quark, two atom. Yet, it’s composite, made up of more pairs of heavier copies of the up protons and neutrons (or nucleons). and down: Open up a nucleon . it contains ² c or charm quark, charge +2=3 quarks. ² s or strange quark, charge ¡1=3 Normal matter can be understood with ² t or top quark, charge +2=3 just two types of quark. ² b or bottom quark, charge ¡1=3 ² + u or up quark, charge 2=3 Existed only in the early stages of the ² ¡ d or down quark, charge 1=3 universe and nowadays created in high energy physics experiments. JMF Southampton Masterclass 22–23 Mar 2004 3/26 But this is not all. The electron has a friend the electron-neutrino, ºe. Needed to ensure energy and momentum are conserved in ¯-decay: ¡ n ! p + e + º¯e Neutrino: no electric charge, (almost) no mass, hardly interacts at all.
    [Show full text]
  • First Determination of the Electric Charge of the Top Quark
    First Determination of the Electric Charge of the Top Quark PER HANSSON arXiv:hep-ex/0702004v1 1 Feb 2007 Licentiate Thesis Stockholm, Sweden 2006 Licentiate Thesis First Determination of the Electric Charge of the Top Quark Per Hansson Particle and Astroparticle Physics, Department of Physics Royal Institute of Technology, SE-106 91 Stockholm, Sweden Stockholm, Sweden 2006 Cover illustration: View of a top quark pair event with an electron and four jets in the final state. Image by DØ Collaboration. Akademisk avhandling som med tillst˚and av Kungliga Tekniska H¨ogskolan i Stock- holm framl¨agges till offentlig granskning f¨or avl¨aggande av filosofie licentiatexamen fredagen den 24 november 2006 14.00 i sal FB54, AlbaNova Universitets Center, KTH Partikel- och Astropartikelfysik, Roslagstullsbacken 21, Stockholm. Avhandlingen f¨orsvaras p˚aengelska. ISBN 91-7178-493-4 TRITA-FYS 2006:69 ISSN 0280-316X ISRN KTH/FYS/--06:69--SE c Per Hansson, Oct 2006 Printed by Universitetsservice US AB 2006 Abstract In this thesis, the first determination of the electric charge of the top quark is presented using 370 pb−1 of data recorded by the DØ detector at the Fermilab Tevatron accelerator. tt¯ events are selected with one isolated electron or muon and at least four jets out of which two are b-tagged by reconstruction of a secondary decay vertex (SVT). The method is based on the discrimination between b- and ¯b-quark jets using a jet charge algorithm applied to SVT-tagged jets. A method to calibrate the jet charge algorithm with data is developed. A constrained kinematic fit is performed to associate the W bosons to the correct b-quark jets in the event and extract the top quark electric charge.
    [Show full text]
  • Searching for a Heavy Partner to the Top Quark
    SEARCHING FOR A HEAVY PARTNER TO THE TOP QUARK JOSEPH VAN DER LIST 5e Abstract. We present a search for a heavy partner to the top quark with charge 3 , where e is the electron charge. We analyze data from Run 2 of the Large Hadron Collider at a center of mass energy of 13 TeV. This data has been previously investigated without tagging boosted top quark (top tagging) jets, with a data set corresponding to 2.2 fb−1. Here, we present the analysis at 2.3 fb−1 with top tagging. We observe no excesses above the standard model indicating detection of X5=3 , so we set lower limits on the mass of X5=3 . 1. Introduction 1.1. The Standard Model One of the greatest successes of 20th century physics was the classification of subatomic particles and forces into a framework now called the Standard Model of Particle Physics (or SM). Before the development of the SM, many particles had been discovered, but had not yet been codified into a complete framework. The Standard Model provided a unified theoretical framework which explained observed phenomena very well. Furthermore, it made many experimental predictions, such as the existence of the Higgs boson, and the confirmation of many of these has made the SM one of the most well-supported theories developed in the last century. Figure 1. A table showing the particles in the standard model of particle physics. [7] Broadly, the SM organizes subatomic particles into 3 major categories: quarks, leptons, and gauge bosons. Quarks are spin-½ particles which make up most of the mass of visible matter in the universe; nucleons (protons and neutrons) are composed of quarks.
    [Show full text]
  • ANTIPROTON and NEUTRINO PRODUCTION ACCELERATOR TIMELINE ISSUES Dave Mcginnis August 28, 2005
    ANTIPROTON AND NEUTRINO PRODUCTION ACCELERATOR TIMELINE ISSUES Dave McGinnis August 28, 2005 INTRODUCTION Most of the accelerator operating period is devoted to making antiprotons for the Collider program and accelerating protons for the NUMI program. While stacking antiprotons, the same Main Injector 120 GeV acceleration cycle is used to accelerate protons bound for the antiproton production target and protons bound for the NUMI neutrino production target. This is designated as Mixed-Mode operations. The minimum cycle time is limited by the time it takes to fill the Main Injector with two Booster batches for antiproton production and five Booster batches for neutrino production (7 x 0.067 seconds) and the Main Injector ramp rate (~ 1.5 seconds). As the antiproton stack size grows, the Accumulator stochastic cooling systems slow down which requires the cycle time to be lengthened. The lengthening of the cycle time unfortunately reduces the NUMI neutrino flux. This paper will use a simple antiproton stacking model to explore some of the tradeoffs between antiproton stacking and neutrino production. ACCUMULATOR STACKTAIL SYSTEM After the target, antiprotons are injected into the Debuncher ring where they undergo a bunch rotation and are stochastically pre-cooled for injection into the Accumulator. A fresh beam pulse injected into the Accumulator from the Debuncher is merged with previous beam pulses with the Accumulator StackTail system. This system cools and decelerates the antiprotons until the antiprotons are captured by the core cooling systems as shown in Figure 1. The antiproton flux through the Stacktail system is described by the Fokker –Plank equation ∂ψ ∂φ = − (1) ∂t ∂E where φ the flux of particles passing through the energy E and ψ is the particle density of the beam at energy E.
    [Show full text]
  • Muon Neutrino Mass Without Oscillations
    The Distant Possibility of Using a High-Luminosity Muon Source to Measure the Mass of the Neutrino Independent of Flavor Oscillations By John Michael Williams [email protected] Markanix Co. P. O. Box 2697 Redwood City, CA 94064 2001 February 19 (v. 1.02) Abstract: Short-baseline calculations reveal that if the neutrino were massive, it would show a beautifully structured spectrum in the energy difference between storage ring and detector; however, this spectrum seems beyond current experimental reach. An interval-timing paradigm would not seem feasible in a short-baseline experiment; however, interval timing on an Earth-Moon long baseline experiment might be able to improve current upper limits on the neutrino mass. Introduction After the Kamiokande and IMB proton-decay detectors unexpectedly recorded neutrinos (probably electron antineutrinos) arriving from the 1987A supernova, a plethora of papers issued on how to use this happy event to estimate the mass of the neutrino. Many of the estimates based on these data put an upper limit on the mass of the electron neutrino of perhaps 10 eV c2 [1]. When Super-Kamiokande and other instruments confirmed the apparent deficit in electron neutrinos from the Sun, and when a deficit in atmospheric muon- neutrinos likewise was observed, this prompted the extension of the kaon-oscillation theory to neutrinos, culminating in a flavor-oscillation theory based by analogy on the CKM quark mixing matrix. The oscillation theory was sensitive enough to provide evidence of a neutrino mass, even given the low statistics available at the largest instruments. J. M. Williams Neutrino Mass Without Oscillations (2001-02-19) 2 However, there is reason to doubt that the CKM analysis validly can be applied physically over the long, nonvirtual propagation distances of neutrinos [2].
    [Show full text]
  • Three Lectures on Meson Mixing and CKM Phenomenology
    Three Lectures on Meson Mixing and CKM phenomenology Ulrich Nierste Institut f¨ur Theoretische Teilchenphysik Universit¨at Karlsruhe Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany I give an introduction to the theory of meson-antimeson mixing, aiming at students who plan to work at a flavour physics experiment or intend to do associated theoretical studies. I derive the formulae for the time evolution of a neutral meson system and show how the mass and width differences among the neutral meson eigenstates and the CP phase in mixing are calculated in the Standard Model. Special emphasis is laid on CP violation, which is covered in detail for K−K mixing, Bd−Bd mixing and Bs−Bs mixing. I explain the constraints on the apex (ρ, η) of the unitarity triangle implied by ǫK ,∆MBd ,∆MBd /∆MBs and various mixing-induced CP asymmetries such as aCP(Bd → J/ψKshort)(t). The impact of a future measurement of CP violation in flavour-specific Bd decays is also shown. 1 First lecture: A big-brush picture 1.1 Mesons, quarks and box diagrams The neutral K, D, Bd and Bs mesons are the only hadrons which mix with their antiparticles. These meson states are flavour eigenstates and the corresponding antimesons K, D, Bd and Bs have opposite flavour quantum numbers: K sd, D cu, B bd, B bs, ∼ ∼ d ∼ s ∼ K sd, D cu, B bd, B bs, (1) ∼ ∼ d ∼ s ∼ Here for example “Bs bs” means that the Bs meson has the same flavour quantum numbers as the quark pair (b,s), i.e.∼ the beauty and strangeness quantum numbers are B = 1 and S = 1, respectively.
    [Show full text]
  • PSI Muon-Neutrino and Pion Masses
    Around the Laboratories More penguins. The CLEO detector at Cornell's CESR electron-positron collider reveals a clear excess signal of photons from rare B particle decays, once the parent upsilon 4S resonance has been taken into account. The convincing curve is the theoretically predicted spectrum. could be at the root of the symmetry breaking mechanism which drives the Standard Model. PSI Muon-neutrino and pion masses wo experiments at the Swiss T Paul Scherrer Institute (PSI) in Villigen have recently led to more precise values for two important physics quantities - the masses of the muon-type neutrino and of the charged pion. The first of these experiments - B. Jeckelmann et al. (Fribourg Univer­ sity, ETH and Eidgenoessisches Amt fuer Messwesen) was originally done about a decade ago. To fix the negative-pion mass, a high-precision crystal spectrometer measured the energy of the X-rays emitted in the 4f-3d transition of pionic magnesium atoms. The result (JECKELMANN 86 in the graph, page 16), with smaller seen in neutral kaon decay. can emerge. Drawing physics conclu­ errors than previous charged-pion CP violation - the disregard at the sions from the K* example was mass measurements, dominated the few per mil level of a invariance of therefore difficult. world average. physics with respect to a simultane­ Now the CLEO group has collected In view of more recent measure­ ous left-right reversal and particle- all such events producing a photon ments on pionic magnesium, a re- antiparticle switch - has been known with energy between 2.2 and 2.7 analysis shows that the measured X- for thirty years.
    [Show full text]
  • Antiproton–Proton Scattering Experiments with Polarization ( Collaboration) PAX Abstract
    Technical Proposal for Antiproton–Proton Scattering Experiments with Polarization ( Collaboration) PAX arXiv:hep-ex/0505054v1 17 May 2005 J¨ulich, May 2005 2 Technical Proposal for PAX Frontmatter 3 Technical Proposal for Antiproton–Proton Scattering Experiments with Polarization ( Collaboration) PAX Abstract Polarized antiprotons, produced by spin filtering with an internal polarized gas target, provide access to a wealth of single– and double–spin observables, thereby opening a new window to physics uniquely accessible at the HESR. This includes a first measurement of the transversity distribution of the valence quarks in the proton, a test of the predicted opposite sign of the Sivers–function, related to the quark dis- tribution inside a transversely polarized nucleon, in Drell–Yan (DY) as compared to semi–inclusive DIS, and a first measurement of the moduli and the relative phase of the time–like electric and magnetic form factors GE,M of the proton. In polarized and unpolarized pp¯ elastic scattering, open questions like the contribution from the odd charge–symmetry Landshoff–mechanism at large t and spin–effects in the extraction | | of the forward scattering amplitude at low t can be addressed. The proposed de- | | tector consists of a large–angle apparatus optimized for the detection of DY electron pairs and a forward dipole spectrometer with excellent particle identification. The design and performance of the new components, required for the polarized antiproton program, are outlined. A low–energy Antiproton Polarizer Ring (APR) yields an antiproton beam polarization of Pp¯ = 0.3 to 0.4 after about two beam life times, which is of the order of 5–10 h.
    [Show full text]
  • Neutrino Vs Antineutrino Lepton Number Splitting
    Introduction to Elementary Particle Physics. Note 18 Page 1 of 5 Neutrino vs antineutrino Neutrino is a neutral particle—a legitimate question: are neutrino and anti-neutrino the same particle? Compare: photon is its own antiparticle, π0 is its own antiparticle, neutron and antineutron are different particles. Dirac neutrino : If the answer is different , neutrino is to be called Dirac neutrino Majorana neutrino : If the answer is the same , neutrino is to be called Majorana neutrino 1959 Davis and Harmer conducted an experiment to see whether there is a reaction ν + n → p + e - could occur. The reaction and technique they used, ν + 37 Cl e- + 37 Ar, was proposed by B. Pontecorvo in 1946. The result was negative 1… Lepton number However, this was not unexpected: 1953 Konopinski and Mahmoud introduced a notion of lepton number L that must be conserved in reactions : • electron, muon, neutrino have L = +1 • anti-electron, anti-muon, anti-neutrino have L = –1 This new ad hoc law would explain many facts: • decay of neutron with anti-neutrino is OK: n → p e -ν L=0 → L = 1 + (–1) = 0 • pion decays with single neutrino or anti-neutrino is OK π → µ-ν L=0 → L = 1 + (–1) = 0 • but no pion decays into a muon and photon π- → µ- γ, which would require: L= 0 → L = 1 + 0 = 1 • no decays of muon with one neutrino µ- → e - ν, which would require: L= 1 → L = 1 ± 1 = 0 or 2 • no processes searched for by Davis and Harmer, which would require: L= (–1)+0 → L = 0 + 1 = 1 But why there are no decays µµµ →→→ e γγγ ? 2 Splitting lepton numbers 1959 Bruno Pontecorvo
    [Show full text]
  • Neutrino-Electron Scattering: General Constraints on Z 0 and Dark Photon Models
    Neutrino-Electron Scattering: General Constraints on Z 0 and Dark Photon Models Manfred Lindner,a Farinaldo S. Queiroz,b Werner Rodejohann,a Xun-Jie Xua aMax-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany bInternational Institute of Physics, Federal University of Rio Grande do Norte, Campus Univer- sitário, Lagoa Nova, Natal-RN 59078-970, Brazil E-mail: [email protected], [email protected], [email protected], [email protected] Abstract. We study the framework of U(1)X models with kinetic mixing and/or mass mixing terms. We give general and exact analytic formulas and derive limits on a variety of U(1)X models that induce new physics contributions to neutrino-electron scattering, taking into account interference between the new physics and Standard Model contributions. Data from TEXONO, CHARM-II and GEMMA are analyzed and shown to be complementary to each other to provide the most restrictive bounds on masses of the new vector bosons. In particular, we demonstrate the validity of our results to dark photon-like as well as light Z0 models. arXiv:1803.00060v1 [hep-ph] 28 Feb 2018 Contents 1 Introduction 1 2 General U(1)X Models2 3 Neutrino-Electron Scattering in U(1)X Models7 4 Data Fitting 10 5 Bounds 13 6 Conclusion 16 A Gauge Boson Mass Generation 16 B Cross Sections of Neutrino-Electron Scattering 18 C Partial Cross Section 23 1 Introduction The Standard Model provides an elegant and successful explanation to the electroweak and strong interactions in nature [1].
    [Show full text]
  • Θc Βct Ct N Particle Nβ 1 Nv C
    SectionSection XX TheThe StandardStandard ModelModel andand BeyondBeyond The Top Quark The Standard Model predicts the existence of the TOP quark ⎛ u ⎞ ⎛c⎞ ⎛ t ⎞ + 2 3e ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝d ⎠ ⎝ s⎠ ⎝b⎠ −1 3 e which is required to explain a number of observations. Example: Absence of the decay K 0 → µ+ µ− W − d µ − 0 0 + − −9 K u,c,t + ν B(K → µ µ )<10 W µ s µ + The top quark cancels the contributions from the u, c quarks. Example: Electromagnetic anomalies This diagram leads to infinities in the f γ theory unless Q = 0 γ f ∑ f f f γ where the sum is over all fermions (and colours) 2 1 ∑Q f = []3×()−1 + []3×3× 3 + [3×3×(− 3 )]= 0 244 f 0 At LEP, mt too heavy for Z → t t or W → tb However, measurements of MZ, MW, ΓZ and ΓW are sensitive to the existence of virtual top quarks b t t t W + W + Z 0 Z 0 Z 0 W t b t b Example: Standard Model prediction Also depends on the Higgs mass 245 The top quark was discovered in 1994 by the CDF experiment at the worlds highest energy p p collider ( s = 1 . 8 TeV ), the Tevatron at Fermilab, US. q b Final state W +W −bb g t W + Mass reconstructed in a − t W similar manner to MW at q LEP, i.e. measure jet/lepton b energies/momenta. mtop = (178 ± 4.3) GeV Most recent result 2005 246 The Standard Model c. 2006 MATTER: Point-like spin ½ Dirac fermions.
    [Show full text]