DOCSLIB.ORG

Exotic Hadronic States

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exotic Hadronic States Exotic Hadronic States Jeff Wheeler May 1, 2018 Abstract Background: The current model of particle physics predicts all hadronic ​ matter in nature to exist in one of two families: baryons or mesons. However, the laws do not forbid larger collections of quarks from existing. Tetraquark and ​ pentaquark particles have long been postulated. Purpose: Advance the particle ​ ​ landscape into a regime including more complex systems of quarks. Studying these systems could help physicists gain greater insight into the nature of the strong force. Methods: Many different particle colliders and detectors of varying ​ ​ energies and sensitivities were used to search for evidence of four- or five-quark states. Results: After a few false alarms, evidence for the existence of both ​ ​ tetraquark and pentaquark was obtained from multiple experiments. Conclusion: ​ Positive results from around the world have shown exotic hadronic states of matter to exist, and extended research will continue to test the leading theories of today and help further our understanding of the laws of physics. I. Introduction Since the discovery of atomic particles, scientists have attempted to determine their individual properties and produce a systematic method of grouping based on those properties. In the early days of particle physics, little was known besides the mere existence of protons and neutrons. With the advent of particle colliders and detectors, however, the collection of known particles grew rapidly. It wasn’t until 1961 that a successful classification system was produced independently by American physicist Murray Gell-Mann and Israeli physicist Yuval Ne’eman. This method was built upon the symmetric representation group SU(3). In this configuration, the spin-1/2 baryons were arranged in an octet (see fig. 1), which is what model. Gell-Mann and Russian-American inspired Gell-Mann to dub the system the physicist George Zweig postulated three new “eightfold way”. With this system, other particles, called quarks, that would constitute categories of particles could be grouped the triplet. With the triplet in place, along with similarly; for example, spin-3/2 baryons and its conjugate, all of the other representations vector mesons were arranged in decuplets and could be constructed [1]. Gell-Mann and Zweig nonets, respectively, where “nonet” is the term had not only produced a theory of hadron for the combined group of the singlet and octet. classification, but also a theory of the hadronic This method of grouping hadrons proved to be constituents: a theory of subatomic particles. very successful, and even led to Gell-Mann The quark model divides hadrons into postulating the existence of a yet undiscovered two groups: baryons and mesons. Baryons - consist of three quarks (qqq) or antiquarks particle, which he named Ω .​ Only three years ​ later, the particle was discovered at (qqq) , and mesons are composed of a Brookhaven National Laboratory [1]! quark-antiquark pair (qq) . However, while all The success of the eightfold way paved of the particles detected prior to the turn of the the road for the next advancement in particle twenty-first century fit into one of these two physics. While Gell-Mann’s method showed categories, they are not exhaustive. In fact, promise categorizing hadrons into singlets, Gell-Mann himself postulated the existence of octets, and decuplets, it was missing an integral particles with a higher quark content [1]. part of the representation group: the triplet. Continued work in the field produced a This issue led to the formulation of the quark new theory of the strong nuclear force, quantum 1 chromodynamics (QCD), using the subatomic [5], but there are some theorists who believe the building blocks postulated by Gell-Mann and particles detected were more of a “meson Zweig along with eight new vector bosons molecule”. This configuration would consist of called gluons. In addition to the configurations two traditional mesons that are loosely joined of quarks given by the quark model, QCD together [3] (see fig. 2); the attractive force calculations shows that particles containing four between the mesons could come from a pion or five quarks could also exist [2]. exchange [1]. Similarly, it would be possible for a pentaquark signature to be created from a II. Exotic Hadron Structure joined system of a baryon and a meson, opposed to a true pentaquark. In QCD, a new quantum property called color charge is introduced. There are three colors, each with a corresponding anticolor: red, green, blue, antired, antigreen, and antiblue. Each quark carries a single color charge, and all particles composed of quarks must be colorless in total. Particles can be colorless by containing all three colors in equal amounts or with equal amounts of color and its anticolor. The rule that all quark particles must be colorless is referred to as color confinement. With color confinement, we recover the two families of hadrons from the quark model with an added twist. In traditional baryons, each quark must have a different color charge in order to be colorless in total; similarly, mesons must be composed of a colored quark and a quark of the corresponding anticolor. However, baryons and mesons are not the only colorless configurations III. Experimental detection of quarks. Colorless four-quark systems can be composed of two colored quarks and their Since their postulation in the antiquarks (qqqq) , or five-quark systems can mid-1960’s, there have been several exist with four quarks and an antiquark experiments attempting to discover them. Here, (qqqqq) . I will focus on a few experiments detecting Despite evidence for tetraquark and tetraquark candidates and the LCHb experiment pentaquark particles discussed in a later section, detecting pentaquark candidates. there is still some debate on the true structure of the detected systems. For example, four-quark systems were observed at the Belle experiment 2 III.1 Tetraquarks researchers claimed to have evidence of a 2 pentaquark of mass 1500 MeV/c .​ Additional ​ In the early 2010’s, two experiments data analyses from several other groups claimed published papers claiming discovery of to have reproduced the findings. These claims four-quark systems. One of these experiments did not hold, however, and after other repeated was the Belle collaboration. The Belle detector experiments of the same type failed to is located at the High Energy Accelerator reproduce the signature in the data, the Research Organization (KEK) in Tsukuba, pentaquark seemed to be ruled out of existence Japan. While analyzing electron-positron [2]. collisions, the detector recorded data consistent Over a decade later, the pentaquark with the decay of a four-quark system. These would make a resurgence. This time, the news systems were determined to consist of two came from researchers at the LHCb experiment charm quarks and two lighter quarks, denoted at the Large Hadron Collider (LHC) at the by Zc(3900) [3]. European Organization for Nuclear Research ​ ​ The Zc(3900) particle was also (CERN) in Geneva, Switzerland. Unlike the ​ ​ independently discovered by the Beijing previous particle colliders mentioned, the LHC Spectrometer III (BESIII) housed at the Beijing studies proton-proton collisions and operates at Electron Positron Collider. much higher energies. This allows the creation As mentioned in the previous section, of higher-mass particles. In 2015, the LHCb there is still some debate regarding the actual announced new evidence for the elusive internal structure of the detected four-quark pentaquark [4]; and this time, they weren’t even systems. Those in favor of true tetraquark looking for it! detection point out that the meson molecule While studying the decay of unstable should split apart upon decay, but this type of particles, researchers found something strange behavior has not been recorded. However, the in their data, collected between 2009 and 2012. 0 uncertainties in the measurements are consistent The surprise came from analyzing Λb decay. with both the molecule and tetraquark structures This the main decay channel is expected to be 0 * [3]. Λb → J/ψΛ (fig. 3a) with the further decay of Λ* → K−p being detected. However, there III.2 Pentaquarks could also be some exotic decay channels, such 0 + − as the one given by Λb → P c K (fig. 3b), Just as the search for tetraquarks had + where P c denotes the pentaquark with raised some skepticism, the history of the composition (uudcc) and referred to as pentaquark discoveries have not always been “charmonium” [2,4]. widely accepted. The first announcement of a While analyzing their data, researchers + pentaquark, named Θ , was put forth in 2002 noticed bump growing sticking out over their from data collected at the SPring-8 synchrotron expected curve (see fig. 4). Interestingly, due to in Harima, Japan. This experiment involved the infamous past of the pentaquark, the colliding high-energy photons and neutrons, and researchers originally ignored this anomalous 3 hump and continued their original research; The baryons and mesons of the quark model no however, they got to a point where they could longer encompassed all that was allowed in the no longer ignore their data. The bump was laws of particle physics, and since the very staring them right in the face, with an introduction of QCD, physicists have pondered astonishing significance of 9-sigma [2]! Not more exotic states of matter than those seen in only did the researchers find evidence for a new everyday life. Despite being postulated in the pentaquark particle, but the data showed mid-twentieth century, it wasn’t until the early evidence for two distinct short-lived objects twenty first that the first signs of tetra- and ​ 2 2 with masses of 4380 Mev/c 4450 Mev/c ,​ much pentaquarks were gathered. Results from 2011 ​ ​ higher masses than the Θ+ claimed to have been to 2015 showed significant evidence of exotic discovered previously [2].
Load more

Recommended publications
  • LHC Explore Pentaquark
    LHC Explore Pentaquark Scientists at the Large Hadron Collider have announced the discovery of a new particle called the pentaquark. [9] CERN scientists just completed one of the most exciting upgrades on the Large Hadron Collider—the Di-Jet Calorimeter (DCal). [8] As physicists were testing the repairs of LHC by zipping a few spare protons around the 17 mile loop, the CMS detector picked up something unusual. The team feverishly pored over the data, and ultimately came to an unlikely conclusion—in their tests, they had accidentally created a rainbow universe. [7] The universe may have existed forever, according to a new model that applies quantum correction terms to complement Einstein's theory of general relativity. The model may also account for dark matter and dark energy, resolving multiple problems at once. [6] This paper explains the Accelerating Universe, the Special and General Relativity from the observed effects of the accelerating electrons, causing naturally the experienced changes of the electric field potential along the moving electric charges. The accelerating electrons explain not only the Maxwell Equations and the Special Relativity, but the Heisenberg Uncertainty Relation, the wave particle duality and the electron’s spin also, building the bridge between the Classical and Relativistic Quantum Theories. The Big Bang caused acceleration created the radial currents of the matter and since the matter composed of negative and positive charges, these currents are creating magnetic field and attracting forces between the parallel moving electric currents. This is the gravitational force experienced by the matter, and also the mass is result of the electromagnetic forces between the charged particles.
    [Show full text]
  • Pentaquark Search Shows How Science Moves Forward
    Although initial results were encouraging, physicists searching for an exotic five-quark particle now think it probably doesn’t exist. The debate over the pentaquark search shows how science moves forward. The rise and fall of the PE NTAQUAR K by Kandice Carter, Jefferson Lab 16 Three years ago, research teams around the stars are made. Yet he and his peers had no world announced they had found data hinting at means to verify its existence. the existence of an exotic particle containing Luminaries of 16th-19th century physics, five quarks, more than ever observed in any other including Newton, Fresnel, Stokes, and Maxwell, quark-composite particle. More than two dozen debated at length the properties of their physi- experiments have since taken aim at the particle, cal version of the philosophical concept, which dubbed the pentaquark, and its possible partners, they called ether. in the quest to turn a hint into a discovery. It’s a The ether was a way to explain how light scenario that often plays out in science: an early could travel through empty space. In 1881, theory or observation points to a potentially Albert A. Michelson began to explore the ether important discovery, and experimenters race to concept with experimental tools. But his first corroborate or to refute the idea. experiments, which seemed to rule out the “Research is the process of going up alleys to existence of the ether, were later realized to be see if they are blind,” said Marston Bates, a zool- inconclusive. ogist whose research on mosquitoes led to Six years later, Michelson paired up with an understanding of how yellow fever is spread.
    [Show full text]
  • Introduction to Subatomic- Particle Spectrometers∗
    IIT-CAPP-15/2 Introduction to Subatomic- Particle Spectrometers∗ Daniel M. Kaplan Illinois Institute of Technology Chicago, IL 60616 Charles E. Lane Drexel University Philadelphia, PA 19104 Kenneth S. Nelsony University of Virginia Charlottesville, VA 22901 Abstract An introductory review, suitable for the beginning student of high-energy physics or professionals from other fields who may desire familiarity with subatomic-particle detection techniques. Subatomic-particle fundamentals and the basics of particle in- teractions with matter are summarized, after which we review particle detectors. We conclude with three examples that illustrate the variety of subatomic-particle spectrom- eters and exemplify the combined use of several detection techniques to characterize interaction events more-or-less completely. arXiv:physics/9805026v3 [physics.ins-det] 17 Jul 2015 ∗To appear in the Wiley Encyclopedia of Electrical and Electronics Engineering. yNow at Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723. 1 Contents 1 Introduction 5 2 Overview of Subatomic Particles 5 2.1 Leptons, Hadrons, Gauge and Higgs Bosons . 5 2.2 Neutrinos . 6 2.3 Quarks . 8 3 Overview of Particle Detection 9 3.1 Position Measurement: Hodoscopes and Telescopes . 9 3.2 Momentum and Energy Measurement . 9 3.2.1 Magnetic Spectrometry . 9 3.2.2 Calorimeters . 10 3.3 Particle Identification . 10 3.3.1 Calorimetric Electron (and Photon) Identification . 10 3.3.2 Muon Identification . 11 3.3.3 Time of Flight and Ionization . 11 3.3.4 Cherenkov Detectors . 11 3.3.5 Transition-Radiation Detectors . 12 3.4 Neutrino Detection . 12 3.4.1 Reactor Neutrinos . 12 3.4.2 Detection of High Energy Neutrinos .
    [Show full text]
  • Photoproduction of Exotic Hadrons Exotic Mesons Photoproduction + Photoproduction of LHCB Pentaquarks
    Introduction The MesonEx experiment The GlueX experiment Hidden-charm pentaquark search Conclusions Photoproduction of exotic hadrons Exotic mesons photoproduction + photoproduction of LHCB pentaquarks Andrea Celentano INFN-Genova Introduction The MesonEx experiment The GlueX experiment Hidden-charm pentaquark search Conclusions Introduction 1 Introduction 2 The MesonEx experiment 3 The GlueX experiment 4 Hidden-charm pentaquark search 5 Conclusions 2 / 24 Introduction The MesonEx experiment The GlueX experiment Hidden-charm pentaquark search Conclusions Exotic mesons QCD does not prohibit the existence of unconventional meson states such as hybrids (qqg), tetraquarks (qqqq), and glueballs. Exotic quantum numbers: J PC 6= qq The discovery of states with manifest gluonic component, behind the CQM, would be the opportunity to directly “look” inside hadron dynamics. Exotic quantum numbers would provide an unambiguous evidence of these states. Lattice QCD calculations1provided a first hint on the spectrum and mass range of exotics. Mass range: 1.4 GeV - 3.0 GeV CQM mesons Exotics Lightest exotic is a 1-+ state. Negative parity Positive parity 1 J. J. Dudek et al, Phys. Rev. D82, 034508 (2010) 3 / 24 Introduction The MesonEx experiment The GlueX experiment Hidden-charm pentaquark search Conclusions Exotic mesons photoproduction Traditionally, meson spectroscopy was studied trough different experimental techinques: peripheral hadron production, NN annihiliation, ... Photo-production measurements were limited by the lack of high-intensity, high-energy, high-quality photon beams. Today, this limitation is no longer present. Advantages: • Photon spin: exotic quantum numbers are more likely produced by S = 1 probe • Linear polarization: acts like a filter to disentangle the production mechanisms and suppress backgrounds • Production rate: for exotics is expected to be comparable as for regular meson 4 / 24 Introduction The MesonEx experiment The GlueX experiment Hidden-charm pentaquark search Conclusions Results from past experiments See P.
    [Show full text]
  • Review of Lepton Universality Tests in B Decays
    January 4, 2019 Review of Lepton Universality tests in B decays Simone Bifani∗, S´ebastienDescotes-Genony, Antonio Romero Vidalz, Marie-H´el`ene Schunex Abstract Several measurements of tree- and loop-level b-hadron decays performed in the recent years hint at a possible violation of Lepton Universality. This article presents an experimental and theoretical overview of the current status of the field. arXiv:1809.06229v2 [hep-ex] 3 Jan 2019 Published in Journal of Physics G: Nuclear and Particle Physics, Volume 46, Number 2 ∗University of Birmingham, School of Physics and Astronomy Edgbaston, Birmingham B15 2TT, United Kingdom yLaboratoire de Physique Th´eorique(UMR 8627), CNRS, Universit´eParis-Sud, Universit´eParis-Saclay, 91405 Orsay, France zInstituto Galego de F´ısicade Altas Enerx´ıas(IGFAE), Universidade de Santiago de Compostela, Santiago de Compostela, Spain xLaboratoire de l'Acc´el´erateurLin´eaire,CNRS/IN2P3, Universit´eParis-Sud, Universit´eParis-Saclay, 91440 Orsay, France Contents 1 Introduction 1 2 Lepton Universality in the Standard Model 2 3 Overview of Lepton Universality tests beyond the B sector 3 3.1 Electroweak sector . .4 3.2 Decays of pseudoscalar mesons . .5 3.3 Purely leptonic decays . .7 3.4 Quarkonia decays . .7 3.5 Summary . .7 4 Theoretical treatment of b-quark decays probing Lepton Universality 8 4.1 Effective Hamiltonian . .8 4.2 Hadronic quantities . 10 4.3 Lepton Universality observables . 13 5 Experiments at the B-factories and at the Large Hadron Collider 13 5.1 B-factories . 13 5.2 Large Hadron Collider . 16 5.3 Complementarity between the B-factories and the LHC .
    [Show full text]
  • Snowmass 2021 Letter of Interest: Hadron Spectroscopy at Belle II
    Snowmass 2021 Letter of Interest: Hadron Spectroscopy at Belle II on behalf of the U.S. Belle II Collaboration D. M. Asner1, Sw. Banerjee2, J. V. Bennett3, G. Bonvicini4, R. A. Briere5, T. E. Browder6, D. N. Brown2, C. Chen7, D. Cinabro4, J. Cochran7, L. M. Cremaldi3, A. Di Canto1, K. Flood6, B. G. Fulsom8, R. Godang9, W. W. Jacobs10, D. E. Jaffe1, K. Kinoshita11, R. Kroeger3, R. Kulasiri12, P. J. Laycock1, K. A. Nishimura6, T. K. Pedlar13, L. E. Piilonen14, S. Prell7, C. Rosenfeld15, D. A. Sanders3, V. Savinov16, A. J. Schwartz11, J. Strube8, D. J. Summers3, S. E. Vahsen6, G. S. Varner6, A. Vossen17, L. Wood8, and J. Yelton18 1Brookhaven National Laboratory, Upton, New York 11973 2University of Louisville, Louisville, Kentucky 40292 3University of Mississippi, University, Mississippi 38677 4Wayne State University, Detroit, Michigan 48202 5Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 6University of Hawaii, Honolulu, Hawaii 96822 7Iowa State University, Ames, Iowa 50011 8Pacific Northwest National Laboratory, Richland, Washington 99352 9University of South Alabama, Mobile, Alabama 36688 10Indiana University, Bloomington, Indiana 47408 11University of Cincinnati, Cincinnati, Ohio 45221 12Kennesaw State University, Kennesaw, Georgia 30144 13Luther College, Decorah, Iowa 52101 14Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 15University of South Carolina, Columbia, South Carolina 29208 16University of Pittsburgh, Pittsburgh, Pennsylvania 15260 17Duke University, Durham, North Carolina 27708 18University of Florida, Gainesville, Florida 32611 Corresponding Author: B. G. Fulsom (Pacific Northwest National Laboratory), [email protected] Thematic Area(s): (RF07) Hadron Spectroscopy 1 Abstract: The Belle II experiment at the SuperKEKB energy-asymmetric e+e− collider is a substantial upgrade of the B factory facility at KEK in Tsukuba, Japan.
    [Show full text]
  • Discovery Potential for the Lhcb Fully Charm Tetraquark X(6900) State Via P¯P Annihilation Reaction
    PHYSICAL REVIEW D 102, 116014 (2020) Discovery potential for the LHCb fully charm tetraquark Xð6900Þ state via pp¯ annihilation reaction † ‡ Xiao-Yun Wang,1,* Qing-Yong Lin,2, Hao Xu,3 Ya-Ping Xie,4 Yin Huang,5 and Xurong Chen4,6,7, 1Department of physics, Lanzhou University of Technology, Lanzhou 730050, China 2Department of Physics, Jimei University, Xiamen 361021, China 3Department of Applied Physics, School of Science, Northwestern Polytechnical University, Xi’an 710129, China 4Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 5School of Physical Science and Technology, Southwest Jiaotong University, Chendu 610031, China 6University of Chinese Academy of Sciences, Beijing 100049, China 7Guangdong Provincial Key Laboratory of Nuclear Science, Institute of Quantum Matter, South China Normal University, Guangzhou 510006, China (Received 2 August 2020; accepted 16 November 2020; published 18 December 2020) Inspired by the observation of the fully-charm tetraquark Xð6900Þ state at LHCb, the production of Xð6900Þ in pp¯ → J=ψJ=ψ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of Xð6900Þ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by the D0 experiment, which indicates that searching for the Xð6900Þ via antiproton-proton scattering may be a very important and promising way. Therefore, related experiments are suggested to be carried out. DOI: 10.1103/PhysRevD.102.116014 I. INTRODUCTION Γ ¼ 168 Æ 33 Æ 69 MeV; ð2Þ In recent decades, more and more exotic hadron states have been observed [1].
    [Show full text]
  • Detectors for Extreme Luminosity: Belle II
    Nuclear Inst. and Methods in Physics Research, A 907 (2018) 46–59 Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima Detectors for extreme luminosity: Belle II I. Adachi a,b , T.E. Browder c, P. Kriºan d,e, *, S. Tanaka a,b , Y. Ushiroda a,b,f , (on behalf of the Belle II Collaboration) a High Energy Accelerator Research Organization (KEK), Tsukuba, Japan b SOKENDAI (The Graduate University for Advanced Studies), Hayama 240-0193, Japan c University of Hawaii, Honolulu, HI, United States d Faculty of Mathematics and Physics, University of Ljubljana, Slovenia e Joºef Stefan Institute, Ljubljana, Slovenia f Department of Physics, Graduate School of Science, University of Tokyo, Japan ARTICLEINFO ABSTRACT Keywords: We describe the Belle II detector at the SuperKEKB electron–positron accelerator. SuperKEKB operates at the Belle II energy of the 훶 .4S/ resonance where pairs of B mesons are produced in a coherent quantum mechanical state Super B Factory with no additional particles. Belle II, the first Super B factory detector, aims to achieve performance comparable SuperKEKB to the original Belle and BaBar B factory experiments, which first measured the large CP violating effects in the Magnetic spectrometer B meson system, with much higher luminosity collisions and larger beam-induced backgrounds. Flavor physics Contents 1. Introduction .....................................................................................................................................................................................................
    [Show full text]
  • Front-End Electronic Readout System for the Belle II Imaging Time-Of- Propagation Detector
    Front-end electronic readout system for the Belle II imaging Time-Of- Propagation detector Dmitri Kotchetkova, Oskar Hartbricha,*, Matthew Andrewa, Matthew Barretta,1, Martin Bessnera, Vishal Bhardwajb,2, Thomas Browdera, Julien Cercillieuxa, Ryan Conradc, Istvan Dankod, Shawn Dubeya, James Fastc, Bryan Fulsomc, Christopher Kettera, Brian Kirbya,3, Alyssa Loosb, Luca Macchiaruloa, Boštjan Mačeka,4, Kurtis Nishimuraa, Milind Purohitb, Carl Rosenfeldb, Ziru Sanga, Vladimir Savinovd, Gary Varnera, Gerard Vissere, Tobias Webera,5, Lynn Woodc a. Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Road, Honolulu, HI 96822, USA b. Department of Physics and Astronomy, University of South Carolina, 712 Main Street, Columbia, SC 29208, USA c. Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99354, USA d. Department of Physics and Astronomy, University of Pittsburgh, 3941 O’Hara Street, Pittsburgh, PA 15260, USA e. Center for Exploration of Energy and Matter, Indiana University, 2401 North Milo B. Sampson Lane, Bloomington, IN 47408, USA * Corresponding author. Phone: 1-808-956-4097. Fax: 1-808-956-2930 E-mail address: [email protected] 1Present address: Department of Physics and Astronomy, Wayne State University, 666 W Hancock St, Detroit, MI 48201, USA 2Present address: Indian Institute of Science Education and Research Mohali, Knowledge city, Sector 81, SAS Nagar, Manauli PO 140306, India 3Present address: Physics Department, Brookhaven National Laboratory, Upton, NY 11973, USA 4Present address: Department of Experimental Particle Physics, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia 5Present address: Ruhr-Universität Bochum, 44780 Bochum, Germany Abstract The Time-Of-Propagation detector is a Cherenkov particle identification detector based on quartz radiator bars for the Belle II experiment at the SuperKEKB e+e– collider.
    [Show full text]
  • Observation of Structure in the J/Ψ-Pair Mass Spectrum
    EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN) CERN-EP-2020-115 LHCb-PAPER-2020-011 CERN-EP-2020-115June 30, 2020 22 June 2020 Observation of structure in the J= -pair mass spectrum LHCb collaborationy Abstract p Using proton-proton collision data at centre-of-mass energies of s = 7, 8 and 13 TeV recorded by the LHCb experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 9 fb−1, the invariant mass spectrum of J= pairs is studied. A narrow structure around 6:9 GeV/c2 matching the lineshape of a resonance and a broad structure just above twice the J= mass are observed. The deviation of the data from nonresonant J= -pair production is above five standard deviations in the mass region between 6:2 and 7:4 GeV/c2, covering predicted masses of states composed of four charm quarks. The mass and natural width of the narrow X(6900) structure are measured assuming a Breit{Wigner lineshape. Submitted to Science Bulletin c 2020 CERN for the benefit of the LHCb collaboration. CC BY 4.0 licence. yAuthors are listed at the end of this paper. ii 1 1 Introduction 2 The strong interaction is one of the fundamental forces of nature and it governs the 3 dynamics of quarks and gluons. According to quantum chromodynamics (QCD), the 4 theory describing the strong interaction, quarks are confined into hadrons, in agreement 5 with experimental observations. The quark model [1,2] classifies hadrons into conventional 6 mesons (qq) and baryons (qqq or qqq), and also allows for the existence of exotic hadrons 7 such as tetraquarks (qqqq) and pentaquarks (qqqqq).
    [Show full text]
  • The Belle II Experiment: Status and Prospects
    universe Article The Belle II Experiment: Status and Prospects Paolo Branchini † INFN Sezione di RomaTre Via Della Vasca Navale, 84, 00146 Roma, Italy; [email protected] † On behalf of the Belle II Collaboration. Received: 16 September 2018; Accepted: 29 September 2018; Published: 1 October2018 Abstract: The Belle II experiment is a substantial upgrade of the Belle detector and will operate at the SuperKEKBenergy-asymmetric e+e− collider. The accelerator has already successfully completed the first phase of commissioning in 2016. The first electron versus positron collisions in Belle II were delivered in April 2018. The design luminosity of SuperKEKB is 8 × 1035 cm−2 s−1, and the Belle II experiment aims to record 50 ab−1 of data, a factor of 50 more than the Belle experiment. This large dataset will be accumulated with low backgrounds and high trigger efficiencies in a clean e+e− environment. This contribution will review the detector upgrade, the achieved detector performance and the plans for the commissioning of Belle II. Keywords: flavor; dark matter 1. Introduction Even though the Standard Model (SM) is currently the best description of the subatomic world, it does not explain the complete picture. The theory incorporates only three out of the four fundamental forces, omitting gravity. Moreover, there are also important questions that it does not answer, such as the matter versus antimatter asymmetry in the number of quark and lepton generations. Many New Physics (NP) scenarios have been proposed. Experiments in high-energy physics search for NP using two complementary approaches. The first, at the energy frontier, is able to discover new particles directly produced in pp collisions (ATLAS, CMS).
    [Show full text]
  • Model-Independent Evidence for Exotic Hadron Contributions To#[Subscript B][Superscript 0]→J/#Pπ−Decays
    Model-Independent Evidence for Exotic Hadron Contributions to#[subscript b][superscript 0]→J/#pπ−Decays The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Aaij, R., C. Abellán Beteta, B. Adeva, M. Adinolfi, Z. Ajaltouni, S. Akar, J. Albrecht, et al. "Model-Independent Evidence for Exotic Hadron Contributions toΛ[subscript b][superscript 0]→J/ψpπ−Decays." Physical Review Letters 117, 082002 (August 2016): 1-9 © 2016 CERN for the LHCb Collaboration As Published http://dx.doi.org/10.1103/PhysRevLett.117.082002 Publisher American Physical Society Version Final published version Citable link http://hdl.handle.net/1721.1/110294 Terms of Use Creative Commons Attribution Detailed Terms http://creativecommons.org/licenses/by/3.0 week ending PRL 117, 082002 (2016) PHYSICAL REVIEW LETTERS 19 AUGUST 2016 0 − Model-Independent Evidence for J=ψp Contributions to Λb → J=ψpK Decays R. Aaij et al.* (LHCb Collaboration) (Received 19 April 2016; published 18 August 2016) 0 − The data sample of Λb → J=ψpK decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb−1, is inspected for the presence of J=ψp or J=ψK− contributions with minimal assumptions about K−p contributions. It is demonstrated at more than 0 − − nine standard deviations that Λb → J=ψpK decays cannot be described with K p contributions alone, and that J=ψp contributions play a dominant role in this incompatibility. These model-independent results þ support the previously obtained model-dependent evidence for Pc → J=ψp charmonium-pentaquark states in the same data sample.
    [Show full text]