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Introduction Searching for Gluonic Excitations and the JLab 12 GeV Upgrade A Flux Tube Between Two Quarks The Hall D Project Alex R. Dzierba Indiana University Spokesman Hall D Collaboration Outline Confinement - flux tubes - gluonic excitations & QCD exotics The experimental evidence for gluonic excitations Looking for gluonic excitations in the light-quark sector with linearly polarized photons The technique Conclusions QCD and confinement Small Distance High Energy Large Distance Low Energy Strong QCD Perturbative QCD Spectroscopy High Energy Scattering Gluon Jets Observed Gluonic Degrees of Freedom Missing Flux Tubes and Confinement Color Field: Because of self interaction, confining flux tubes form between static color charges Notion of flux tubes comes about from model-independent general considerations. Idea originated with Nambu in the ‘70s Lattice QCD Flux tubes realized Flux tube From G. Bali forms between qq linear potential Hybrid mesons 1 GeV mass difference Normal mesons Confinement arises from flux tubes and their excitation leads to a new spectrum of mesons Normal Mesons Normal mesons occur when the flux tube is in its ground state Spin/angular momentum configurations & radial excitations generate our known spectrum of light quark mesons Nonets characterized by given JPC q q q q Not allowed: exotic combinations: JPC = 0-- 0+- 1-+ 2+- … Excited Flux Tubes q q How do we look for gluonic degrees of freedom in spectroscopy? First excited state of flux tube has J=1 and when combined with S=1 for quarks generate: JPC = 0-+ 0+- 1+- 1-+ 2-+ 2+exotic Exotic mesons are not generated when S=0 Mass (GeV) Meson Map Each box corresponds to 4 nonets (2 for L=0) qq Mesons 2.5 Glueballs 2.0 1.5 2 +– 2 –+ 1 –– 1– + 1 +– 1 ++ 0 +– 0 –+ Hybrids 2 –+ 0 –+ 2 ++ Radial excitations 0 ++ 1.0 L=0 1 2 3 4 (L = qq angular momentum) exotic nonets Current Evidence Have gluonic excitations been observed ? Glueballs Hybrids Overpopulation of the scalar nonet and LGT predictions suggest that the f0(1500) is a glueball JPC = 1-+ states reported 1(1400) 1(1600) See results from Crystal Barrel Complication is mixing with conventional qq states by BNL E852 & others Not without controversy Crystal Barrel Result pp 0 0 0 3 Evidence for fo(1500) Scalar Glueball m2(0 0) [GeV2] 2 1 0 0 1 2 3 E852 Results p p M( ) GeV / c 2 to partial wave analysis M( ) At 18 GeV/c GeV / c 2 suggests 0 p p p Results of Partial Wave Analysis a1 Benchmark resonances 2 a2 An Exotic Signal in E852 1 Leakage From Non-exotic Wave due to imperfectly understood acceptance Correlation of Phase & Intensity Exotic Signal M( ) GeV / c 2 Why Photoproduction ? beam after q before q q q q q q A pion or kaon beam, when scattering occurs, can have its flux tube excited Much data in hand but little evidence for gluonic excitations (and not expected) Quark spins aligned after beam before q Quark spins anti-aligned Almost no data in hand in the mass region where we expect to find exotic hybrids when flux tube is excited Compare p and p Data Compare statistics and shapes p p @ 18 GeV Events/50 MeV/c2 ca. 1998 BNL p n ca. 1993 @ 19 GeV 28 SLAC SLAC 4 1.0 M(3) 2 GeV / c 1.5 2.0 2.5 Hybrid Decays Hall D will be sensitive to a wide variety of decay modes - the measurements of which will be compared against theory predictions. Gluonic excitations transfer angular momentum in their decays to the internal angular momentum of quark pairs not to the relative angular momentum of daughter meson pairs - this needs testing. For example, for hybrids: X b1 X favored not-favored To certify PWA - consistency checks will be made among different final states for the same decay mode, for example: 0 3 b1 0 2 Should give same results What is Needed? PWA requires that the entire event be identified - all particles detected, measured and identified. • The detector should be hermetic for neutral and charged particles, with excellent resolution and particle ID capability. The beam energy should be sufficiently high to produce mesons in the desired mass range with excellent acceptance. • Too high an energy will introduce backgrounds, reduce cross-sections of interest and make it difficult to achieve above experimental goals. PWA also requires high statistics and linearly polarized photons. • Linear polarization will be discussed. At 108 photons/sec and a 30-cm LH2 target a 1 µb cross-section will yield 600M events/yr. We want sensitivity to sub-nanobarn production cross-sections. Review Executive Summary Highlights: The experimental program proposed in the Hall D Project is wellsuited for definitive searches of exotic states that are required according to our current understanding of QCD JLab is uniquely suited to carry out this program of searching for exotic states The basic approach advocated by the Hall D Collaboration is sound The Committee David Cassel Frank Close John Domingo Bill Dunwoodie Don Geesaman David Hitlin Martin Olsson Glenn Young Cornell (chair) Rutherford JLab SLAC Argonne Caltech Wisconsin ORNL Linear Polarization Linear polarization is: Essential to isolate the production mechanism (M) if X is known A JPC filter if M is known (via a kinematic cut) Related to the fact that states of linear polarization are eigenstates of parity. States of circular polarization are not. X Linear polarization is important in PWA - loss in degree of linear polarization can be compensated for by increase in statistics. M N N Optimal Photon Energy 1.0 Figure of merit based on: Optimum photon energy is about 9 GeV 0.8 relative yield relative yield 1. Beam flux and polarization 2. Production yields 3. Separation of meson/baryon production m[x] = 1.0 GeV = 1.5 GeV = 2.0 GeV = 2.5 GeV produced meson mass 0.6 Electron endpoint energy of 12 GeV 0.4 0.2 0.0 6 7 8 9 beam photon energy (GeV) Staying below 10 GeV allows us to use an all-solenoidal detector. 10 11 This technique provides requisite energy, flux and polarization flux Coherent Bremsstrahlung 12 GeV electrons Incoherent & coherent spectrum 40% polarization in peak photons out collimated electrons in spectrometer diamond crystal tagged 0.1% resolution photon energy (GeV) Detector Barrel Calorimeter Lead Glass Detector Solenoid Coherent Bremsstrahlung Photon Beam Note that tagger is 80 m upstream of detector Tracking Target Electron Beam from CEBAF Time of Flight Cerenkov Counter Event rate to processor farm: 10 kHz and later 180 kHz corresponding to data rates of 50 and 900 Mbytes/sec respectively Solenoid & Lead Glass Array At LANL At SLAC Now at JLab 0 -1 -0.8 -0.6 -0.4 -0.2 -0 0.2 Cos( GJ) Acceptance 0.4 0.6 0.8 1 0 -3 -2 p -> p 0 1 GJ 2 3 p Xn n 1 1 0.8 0.8 Acceptance in 0.6 0.6 Decay Angles 0.4 0.4 11 Gottfried-Jackson frame: 0.8 0.8 In the rest frame of X Mass(X) = 1.4 GeV = 1.4 GeV theMass(X) decay angles are Mass(X) = 1.7 GeV Mass(X) = 1.7 GeV theta, phi Mass [X] = 1.4 GeV 0.6 0.6 Mass [X] = 1.7 GeV 0.4 0.4 Mass [X] = 2.0 GeV Mass(X) = 2.0 GeV Mass(X) = 2.0 GeV GeV 85GeV 0.2 0.2 assuming 9 GeV photon beam -1 0 0 0.4 0.6 0.6 0.8 0.8 -1 -1 -0.8-0.8 -0.6-0.6 -0.4-0.4 -0.2-0.2-0 -0 0.20.2 0.4 Cos( Cos( )) GJGJ 0.2 0.2 11 00 -3 -3 0 0 11 0.8 0.8 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0 0 1 1 2 0 1 2 GJ GJ 3 3 0.4 0.4 8 GeV 12 GeV 0 -1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 Cos( GJ ) Cos( GJ) 1 1 0.2 0.2 0 0-3 -3 -2 -2 -1 -1 GJ 0 GJ 1 Acceptance is high and uniform 1 2 0.6 0.6 Mass(X) = 1.4 GeV Mass(X) = 1.4 GeV Mass(X) = 1.7 GeV Mass(X) = 1.7 GeV Mass(X) = 2.0 GeV Mass(X) = 2.0 GeV 0.2 0 -1 -1-1 p Xn n 1 1 -2-2 1 2 3 3 Finding the Exotic Wave Double-blind M. C. exercise An exotic wave (JPC = 1-+) was generated at level of 2.5 % with 7 other waves. Events were smeared, accepted, passed to PWA fitter. X(exotic ) 3 500 500 events/20 MeV Mass Input: 1600 MeV Output: 1598 +/- 3 MeV 400 400 Width 300 300 Input: 170 MeV Output: 173 +/- 11 MeV Statistics shown here correspond to a few days of running. generated PWA fit 200 200 100 100 00 1.2 1.2 1.4 1.4 1.6 1.6 1.8 1.8 Mass (3 pions) (GeV) Collaboration US Experimental Groups Carnegie Mellon University Catholic University of America A. Dzierba (Spokesperson) - IU C. Meyer (Deputy Spokesperson) - CMU E. Smith (JLab Hall D Group Leader) Collaboration Board L. Dennis (FSU) J. Kellie (Glasgow) G. Lolos (Regina) (chair) R. Jones (U Conn) A. Klein (ODU) A. Szczepaniak (IU) Christopher Newport University University of Connecticut Florida International University Florida State University Other Experimental Groups Indiana University University of Glasgow Jefferson Lab Institute for HEP - Protvino Los Alamos National Lab Moscow State University Norfolk State University Budker Institute - Novosibirsk Old Dominion University University of Regina Renssalaer Polytechnic Institute CSSM & University of Adelaide Carleton University Carnegie Mellon University Insitute of Nuclear Physics - Cracow Hampton University Indiana University Los Alamos Ohio University University of Pittsburgh Theory Group 90 collaborators 25 institutions North Carolina Central University University of Pittsburgh University of Tennessee/Oak Ridge Conclusion In the last decade we have seen much theoretical progress in using lattice gauge theory techniques in the confinement region of QCD. Low energy data on gluonic excitations are needed to understand the nature of confinement in QCD. Recent data in hand provide hints of these excitations - but a detailed map of the hybrid spectrum is essential. Photoproduction promises to be rich in hybrids - starting with those possessing exotic quantum numbers - little or no data exist. We are now in a position to use the energy-upgraded JLab to provide photon beams of the needed flux, duty factor, polarization along with a state-of-the-art detector to collect high-quality data of unprecedented statistics and precision.