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Search for Exotics at Jefferson Lab

Search for Exotics at Jefferson Lab. Raffaella De Vita INFN – Genova For the CLAS Collaboration. PINAN11 Partons in Nucleons and Nuclei Marrakesh, 27 September 2011. p. p. Why Hadron Spectroscopy. QCD is responsible for most of the visible mass of the universe

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Search for Exotics at Jefferson Lab

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  1. Search for Exotics at Jefferson Lab Raffaella De Vita INFN –Genova For the CLAS Collaboration PINAN11 Partons in Nucleons and Nuclei Marrakesh, 27 September 2011

  2. p p Why Hadron Spectroscopy • QCD is responsible for most of the visible mass of the universe • Understanding the origin of this mass, i.e. the mass of hadrons, is a necessary step to reach a deep understanding of QCD • Revealing the nature of the mass of the hadrons • Identify the relevant degrees of freedom • Understand the origin of confinement • Validate LQCD predictions • Meson spectroscopy is a key tool to investigate these issues << 0.1 fm 0.1 – 1 fm > 1 fm Quarks and Gluons Effective Degrees of Freedom Mesons & Baryons

  3. K0 p+ p- Meson Spectroscopy Mesons are the simplest quark bound state, i.e. the best benchmark to understand how quarks interact to form hadrons and what the role of gluons is Historically, the study of meson properties led to some of the most relevant discoveries in particles physics G.D. Rochester and C.C. Butler, Nature 160 (1947) 855. • in 1947 the discovery of the pion by Powell, Occhialini and Lattes • in the same year, the discovery of strange particles by Rochester and Butler • the interpretation of the φdecay to KK by Zweig and others in 1963 • the discovery of the J/ψ in 1974 • … The new frontier in meson spectroscopy is the search for unconventional states with quark-gluon configuration different from regular quark-antiquark states C.F.Powell, Nobel Lecture, 11th December 1950

  4. Unconventional States and Exotics • Known hadron configurations are baryons, made of three quarks, and mesons, made by a quark and antiquark pair • QCD does not prohibit the existence of other configuration and other color singlet states, such as tetraquarks, glueballs and hybrids can also exist • These unconventional configurations can have the same quantum numbers as regular mesons or have “exotic” quantum number • Finding a proof of their existence is a both a fundamental validation of the theory and a precious source of information • Many experiments in the world have searched and will search for these states … • proton-antiproton annihilation: Crystal Barrel at CERN, LHC, Panda at GSI, ... • e+ e- annihilation: LEP, Babar at SLAC, DAΦNE at Frascati, CLEO at Cornell, BES at Beijing, … • proton-proton scattering: WA experiments at CERN, GAMS at Protvino, … • pion beams on fixed target: E852 at BNL, COMPASS at Cern, VES … • photoproduction experiments: CLAS at Jefferson Lab, GlueX and CLAS12 at Jefferson Lab

  5. q q q q Search for Hybrid Mesons Understanding the role of gluons and the origin of confinement is crucial to complete our picture of strong interaction Regular meson Hybrid meson • At high energy experimental evidence is found in jet production • At lower energies the hadron spectrum carries information about the gluons that bind quarks • Can we find hints of the glue in the meson spectrum? Search for non-standard states with explicit gluonic degrees of freedom • Predicted by various models as the Flux Tube model, the Bag model, QCD Sum Rules, .. • Now predicted by lattice QCD calculations

  6. S1 L S2 Hybrids and Exotics The best option to identify unambiguously a meson as an hybrid state is to look for exotic quantum numbers • Normal mesons (qq) are classified according to their JPC where • P=(-1)L+1 • C=(-1)L+S JPC= 0-+ (π,K,η,η’) 1--(ρ,K*,ω,Φ) 1+- (b1,K1,h1,h1’) ... • Some combinations of JPC are not allowed for conventional qq systems but can exist for “unconventional” states as hybrids Normal meson:flux tube in ground state m=0, PC=(-1)S+1 Hybrid meson:flux tube in excited state m=1, PC=(-1)S q q q q • Excitation of the flux tube leads to a new spectrum of hadrons that can have exotic quantum numbersJPC = 0+- , 1-+ , 2+- ... • Masses are predicted to be around 2 GeV, a range that can be explored at Jefferson Lab

  7. Lattice QCD J. Dudek et al., Phys. Rev. D82, 034508 (2010) • Existence of exotics is supported by LQCD • Fully dynamical calculation by the JLab Hadron Spectrum Collaboration: • two flavors of light quarks and an heavier (strange) quark • two lattice volumes • large set of operators • stable dependence on quark masses 3S? 1-+ 1F 2P 1D 1P 2S 1S • Good agreement of regular meson spectrum with known states • Exotic multiplets with quantum numbers 1-+,0+- and 2-+ are predicted

  8. Exotic Candidates: Experimental Evidence • The lightest exotic hybrids are expected in the 1-+ wave: • π1(1400): observed in ηπ final states by several experiments( GAMS, KEK, E852, Crystal Barrel) with a width of few hundreds MeV. Mass lower than expectation and interpretation still unclear • π1(1600): observed in several decay modes (ρπ, η’π, f1π, b1π) by different experiments (E852,VES,COMPASS) but with different production mechanism; not observed in reanalysis of E852 data and by CLAS . Evidence of the state still controversial • π1(2000): seen by E852 in f1π and b1π final states produced in peripheral πp scattering. Further confirmation is desirable M. G. Alekseev et al.(COMPASS), PRL 104, 241803 (2010) • Most of experimental evidence comes from pion (S=0) beam experiments (E852, VES, COMPASS) • → collecting more data with different production mechanism (different probes) is crucial • Controversial evidence may arise from PWA ambiguities • → larger data sets, polarization information, more sophisticatedanalysis tools, large computing resources M. G. Alekseev et al.(COMPASS), PRL 104, 241803 (2010) π1(1600)

  9. Pion Beam Photon Beam Quark spins anti-aligned JPC = 1-- , 1++ Quark spinsalready aligned JPC = 0+- , 1-+ , 2+- regular mesons @ Eg = 5GeV X = a2 Exotic meson @ Eg = 8GeV X = p1(1600) Exotics in Photoproduction • Photoproduction: exotic JPC are more likely produced by S=1 probe • Knowledge of the photon polarization can be used as a filter in the PWA A. Szczepaniak and M. Swat, Phys. Lett. B516 (2001) 72 • Production rate for exotics is expected to be comparable to regular mesons Few data (so far) but expected similar production rate as regular mesons

  10. LINAC LINAC A C B Jefferson Laboratory • Continuous • Electron • Beam • Accelerator • Facility • E: 0.75 –6 GeV • Imax: 200mA • RF: 1499 MHz • Duty Cycle:  100% • s(E)/E: 2.5x10-5 • Polarization: 80% • Simultaneous distribution to 3 experimental Halls Injector Experimental Halls

  11. Construction of the new Hall D Upgrade of the arcmagnets CHL-2 Upgrade of the instrumentation of the existing Halls The 12 GeV Upgrade 6 GeV CEBAF Beam Power: 1MW Beam Current: 90 µA Max Pass energy: 2.2 GeV Max Enery Hall A-C: 10.9 GeV Max Energy Hall D: 12 GeV

  12. CLAS12 and GLUEX • Meson spectroscopy is one of the main topics that will be studied with the Jlab 12 GeV upgrade. Key elements are: • High intensity tagged photon beams • Detectors with large acceptance and good particle identification capabilities • GlueX in Hall D CLAS12 in Hall B

  13. The GlueX Detector 2.2 Tesla Solenoid • 2.2T superconducting solenoidal magnet • Fixed target (LH2) • 108 tagged g/s (8.4-9.0GeV) • hermetic TOF time of flight SC start counter • Charged particle tracking • Central drift chamber (straw tube) • Forward drift chamber (cathode strip) • Calorimetry • Barrel Calorimeter (lead, fiber sandwich) • Forward Calorimeter (lead-glass blocks) • PID • Time of Flight wall (scintillators) • Start counter • Barrel Calorimeter

  14. The Hall D Photo Beam • Photon Polarization: • 20 mm diamond radiator • Coherent peak is linearly polarized • ~40% polarization with peak @ 9GeV • Peak location tunable with diamond angle • Crucial to simplify PWA!! • Microscope: • Movable to cover different energy ranges • 100 x 5 scintillating fibers (2mm x 2mm) • 800MeV covered by whole microscope • 100MHz tagged g/sec on target • ~8MeV energy bite/column 12m long vacuum chamber 1.5 T dipole magnet coherent bremsstrahlung spectrum • Fixed array hodoscope: • 190 scintillators • 50% coverage below 9GeV g • 100% coverage above 9GeV g • Tags 3.0-11.7 GeVg • ~30MeV energy bite/counter • 3.5 – 17 MHz/counter e- 20mm diamond radiator

  15. The Hall D Complex3 electron beam ~100 meters Groundbreaking, April 2009 In the Hall, February 2011

  16. GlueX: expected performance Design Goal: high and uniform acceptance Comparison of acceptance plots between BNL E852 and GlueX in a sample channel: high and uniform acceptance in invariant mass and Gottfried-Jackson angles.

  17. CLAS12 1 • Forward Detector: • - TORUS magnet • - Forward SVT tracker • HT Cherenkov Counter • Drift chamber system • LT Cherenkov Counter • Forward ToF System • Preshower calorimeter • E.M. calorimeter (EC) • Central Detector: • SOLENOID magnet • Barrel Silicon Tracker • Central Time-of-Flight • Proposed upgrades: • Micromegas (CD) • Neutron detector (CD) • RICH detector (FD) • Forward Tagger (FD)

  18. The CLAS12 Forward Tagger 1 Electron detection via Calorimeter+Tracker+Veto Forward Tagger • calorimeterto determine the electron energy with few % accuracy → homogenous PbWO4 crystals • trackerto determine precisely the electron scattering plane and the photon polarization → MicroMegas • vetoto distinguish photons from electrons → scintillator tiles with WLS fiber readout CLAS12 e- γ* e- p PbWO4 Calorimeter 424 Crystals

  19. Experiment Layout Calorimeter Tracker ScintillationHodoscope MollerShield

  20. PWA in CLAS12 In preparation for the experiment, PWA tools are being developed and tested on pseudo data (Monte Carlo) for different reactions as γp→nπ+π+π- a2→ρπ D-wave a1→ρπ S-wave a1→ρπ S-wave π2→ρπ P-wave π2→ρπ F-wave π2→f2π S-wave • Test for 2 t bins: • line: generated wave • |t|=0.2 GeV2 • |t|=0.5 GeV2 • As a function of M3π π2→f2π D-wave 3π all wave π2→f2π P-wave The CLAS12 detector system is intrinsically capable of meson spectroscopy measurements

  21. Summary • Meson spectroscopy is a key field for the understanding of fundamental questions in hadronic physics as what is the origin of the nucleon mass and what is the role of gluons • Jefferson Lab has launched a broad and comprehensive program to study meson spectroscopy via photoproduction: • Study of meson spectroscopy in the light –quark sector for masses around 2 GeV • Two complementary experiments will run in Hall B and D • GlueX: bremsstrahlung tagged photon beam, hermetic detector with excellent coverage for neutral an charged particles • CLAS12: quasi-real photon beam, high resolution and large acceptance detector with excellent Pid capabilities • Analysis tools are being developed and usage of GPUs to reduce computing time is being explored • A series of workshops on Partial Wave Analysis involving theorists and experimentalists was started (INT Nov. 2009, ECT* Jan. 2011, Jlab June 2011,…) • Detector construction is in progress and first 12 GeV beam is expected in 2014

  22. Summary

  23. Quasi-Real Photoproduction Studies at large W (~100 GeV) show a smooth transition between Q2=0 and Q20 Technique used in high energy experiments: Q2 < W2 COMPASS: <1 GeV2 <Q2> ~ 10-1 GeV2 ZEUS: 10-7 – 0.02 GeV2 <Q2> ~5 10-5 GeV2 H1: <2 GeV2

  24. Quasi-Real Photoproduction Analysis of existing CLAS data shows clear peaks associated to known mesons in ep(e’)pp0p0 ep(e’)pp0h f0(980) a0(980) f2(1270) The Technique works!!

  25. Kinematics • Electron kinematics: • E=0.5-4 GeV • q=2-5 deg. •  • Q2=0.007-0.33 GeV2 • Eg=7-10.5 GeV • Photon Polarization: 10-65% (determined on an event-by-event basis)

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