Physics Prospects with the JLab 12 GeV Upgrade

Transcription

1 Physics Prospects with the JLab 12 GeV Upgrade Gluonic Excitations 3-dim view of the Nucleon Valence Structure of the Nucleon Elton S. Smith Jefferson Lab PANIC02 Osaka 1

2 JLab Today Main physics programs nucleon electromagnetic form factors (including strange form factors) N N* electromagnetic transition form factors spin structure functions of the nucleon form factors and structure of light nuclei Superconducting recirculating electron accelerator max. energy 5.7 GeV max current 200 µa e polarization 80% Simultaneous operation in 3 halls L[cm -2 s -1 ] 2 High Resolution Spectrometers (p max =4 GeV/c) spectrometers (p max =7 and 1.8 GeV/c) + special equipment Large Acceptance Spectrometer for e and γ induced reactions

3 126 GeV CEBAF add Hall D (and beam line) Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls Elton S. Smith PaNic02, Sep 30 Oct 4,

4 Gluonic Excitations Dynamical role of Glue Confinement 4

5 Lattice QCD Flux tubes realized Flux tube forms between qq Flux Tube Model Confinement arises from flux tubes and their excitation leads to a new spectrum of mesons From G. Bali 5

6 Understanding Confinement The Ideal Experiment Q Q quarks fixed E (GeV) 1 fm free gluons flux tube 2 1 Q The Real Experiment Q quark motion plus flux tube excitation 6

7 Hybrid Mesons Hybrid mesons 1 GeV mass difference (π/r) Normal mesons 7

8 Normal Mesons qq color singlet bound states Spin/angular momentum configurations & radial excitations generate our known spectrum of light quark mesons. Starting with u - d - s we expect to find mesons grouped in nonets - each characterized by a given J, P and C. S 1 L S 2 S = S + S 1 2 J = L + S P = (-1) L + 1 C = (-1) L + S J PC = Not-allowed: exotic J PC = Allowed combinations 8

9 Quantum Numbers of Hybrid Mesons Quarks Excited Flux Tube Hybrid Meson S = 0 L = 0 J PC = J PC = 0 + like π, K J PC = S = 1 L = 0 J PC = J PC = 1 like γ,ρ Exotic J PC = Flux tube excitation (and parallel quark spins) lead to exotic J PC 9

10 Meson Map Radial excitations Mass (GeV) qq Mesons Glueballs Each box corresponds to 4 nonets (2 for L=0) Hybrids exotic nonets Lattice GeV GeV GeV L = (L = qq angular momentum) 10

11 Exotic Signal J PC =1 + Events/(0.020 GeV/c ) 2 Events/(0.006 GeV/c ) 2 Acceptance E852 π 1 (1600) η π η π + π γγ M =1.60 ± 0.05 Γ = 0.34 ± a. b. η' η M (γγ) GeV/c M(ηπ π ) GeV/c M GeV/c ' (η π ) PRL 86, 3977 (2001) 11

12 Families of Exotics π 1 I G (J PC )=1 - (1 -+ ) 1 -+ nonet η 1 I G (J PC )=0 + (1 -+ ) K 1 I G (J PC )= ½ (1 - ) η 1 I G (J PC )=0 + (1 -+ ) X γ e N N γ ρ,ω,φ Couple to V.M + e π ρπ 1 η 1 ρb 1, ωφ η 1 φω 12

13 Strategy for Exotic Meson Search Use photons to produce meson final states tagged photon beam with 8 9 GeV linear polarization to constrain production mechanism Use large acceptance detector hermetic coverage for charged and neutral particles typical hadronic final states: f 1 η KKη KKπππ b 1 π ωπ ππππ ρπ πππ high data acquisition rate Perform partial-wave analysis identify quantum numbers as a function of mass check consistency of results in different decay modes 13

14 Coherent Bremsstrahlung This technique provides requisite energy, flux and polarization flux Incoherent & coherent spectrum 12 GeV electrons 40% polarization in peak electrons in photons out collimated spectrometer diamond crystal tagged with 0.1% resolution Eγ (GeV) 14

15 GlueX / Hall D Detector Barrel Calorimeter Lead Glass Detector Solenoid Coherent Bremsstrahlung Photon Beam Note that tagger is 80 m upstream of detector Target Time of Tracking Flight Cerenkov Counter Electron Beam from CEBAF 15

16 Finding an Exotic Wave An exotic wave (J PC = 1 -+ ) was generated at level of 2.5 % with 7 other waves. Events were smeared, accepted, passed to PWA fitter. Mass Input: 1600 MeV Output: /- 3 MeV Width X(exotic) ρπ 3π events/20 MeV generated PWA fit Input: 170 MeV Output: 173 +/- 11 MeV Statistics shown here correspond to a few days of running. Double-blind M. C. exercise Mass (3 pions) (GeV)

17 Detector Designed to do Partial Wave Analysis Double blind studies of 3π final states γ p ρ n π X π π a 2 π 2 Linear Polarization η=+1 η= 1 φ GJ η=+1 η= 1 η=+1 m 3π [GeV/c 2 ] 17

18 3-dimensional view of the Nucleon Deep Exclusive Scattering 18

19 Generalized Parton Distributions e γ e' x+ξ x-ξ ξ = γ, π, η, ρ, ω, Κ x B 2- x B H, H, E, E, H, H, E N N',, Λ (1+ ξ)p (1- ξ)p H, E - unpolarized, H, E - polarized GPD The GPDs Define Nucleon Structure GPD s provide access to fundamental quantities such as the quark orbital angular momentum that have not been accessible J = Σ + L = dxx H ( x, ξ, t = 0) + E ( x, ξ, t = 0) quark q 1 q and the GPD s unify the description of inclusive and exclusive processes, connecting directly to the normal parton distributions: + 1 G ( ) q (,, ) q E t = t dx H xξt + E 4 2 ( x, ξ, t M ) 1 q q (for example), 19

20 Limiting Cases for GPDs Ordinary Parton Distributions (, t, ξ 0) ~ H 0 (x,0) = q(x) unpolarized H 0 (x,0) = q(x) polarized x P P ξ = H, E, z P z (x-ξ) P ~ ~ H, E P t = 2 Nucleon Form Factors (Sum Rules) H ξ ( x, t) dx = F1 ( t) Dirac ~ Hξ ( x, t) dx = g A( t) Axial vector E ξ ( x, t) dx = F2 ( t) Pauli ~ Eξ ( x, t) dx = ha( t) Pseudoscalar 20

21 GPDs Contain Much More Information than DIS DIS only measures a cut at ξ=0 Quark distribution q(x) Antiquark distribution q(x) qq distribution 21

22 Measuring the GPD s Key experimental capabilities include: CW (100% duty factor) electron beams (permits fully exclusive reactions) modern detectors (permit exclusive reactions at high luminosity) adequate energy (~10 GeV to access the valence quark regime) Measurements of the GPD s are now feasible 22

23 r F( q) = H ( x, q d ) = Interpretation of the GPD s Analogy with form factors r iq r 3 ρ re d r ( ) r measured relative to r R cm = 2 iq b b e f ( x, b ξ Charge Form Factor miri M Parton Distribution GPD s = 0 b measured relative to R CM = x r i i where f ( x, b ) is a parton density of quarks with momentum fraction x at a distance b from R CM Ref. Burkardt 23

24 Meson Production as a Filter γ* Ψ(z)Γ j Ψ(y) Use quantum numbers of meson to select appropriate combinations of parton distributions in nucleon. Pseudo-scalars (polarized) π 0 : u v -½ d v η : u v -½ d v + 2 s v p Ψ(z)Γ i Ψ(y) p Vector Mesons (unpolarized) ρ L0 : u + u + ½ (d + d); g ω L0 : u + u - ½ (d + d); g φ L0 : s + s; g 24

25 Program to determine GPD s ep r e p r ep e ep ρ en π en pγ ep γ π π + π H ~ H H 2 H H ~ 2 2,, E 2 ~, E E 2 2, E, ~ E ~ 2, H, ~ ~ H, E ~ E 2 Other Channels r e p en (η,π) e π e Nω e (Λ,Σ) K 25

26 Deep Virtual Compton Scattering: A Window on Quark Correlations DIS is limited by the fact that it can only measure longitudinal distributions averaged over all quarks in the nucleon Deep Inclusive Scattering => Deep Compton Scattering N γ x x H, E, H, E 2 γ* N Im N x x H, E, H, E Deep Virtual Compton Scattering (DVCS) N γ x+ξ x ξ H, E, H, E dgpds γ ξ = momentum imbalance γ N γ* N hard processes DIS corresponds exactly to the imaginary part of the Deep Compton Scattering amplitude Add determination of the final state (by exclusive reactions such as DVCS) and we can (finally!) probe nucleon quark structure and correlations at the amplitude level 26

27 DVCS Single-Spin Asymmetry CLAS Q 2 = 5.4 Collaboration GeV 2 PRL x = , (2001) -t = 0.3 GeV 2 Measure interference between DVCS-BH CLAS experiment E e 0 = 11 GeV γ e P e = 80% L = cm -2 s -1 Run time: 2000 hrs p GPD s p A=(σ + -σ - )/(σ + +σ - ) A hours at L= cm -2 sec -1 ξ independent b val = 1.0, b sea = φ, deg Q 2 = 5.4 (GeV/c) 2 x B = t = 0.3 (GeV/c) φ γγ (degree) 27

28 Hard Meson Electroproduction (ρ o ) Physics issue: map out GPD s (need to isolate σ L ) e e ρ p GPD s p σ L ~ Q -6 Technique: determine σ L from ρ ππ decay angle distribution CLAS at 11 GeV 400 hrs at L = cm -2 s -1 σ T ~ Q -8 28

29 Valence Quark Structure of the Nucleon Parton Distributions at large x 29

30 Enhanced Access to the DIS Regime 12 GeV will access the valence quark regime for x > 0.3 where constituent quark properties are not masked by the sea quarks Q 2 [GeV 2 ] GeV 4 GeV W>2 GeV x=1 x=0.9 x=0.8 x=0.7 x= GeV x=0.5 x=0.4 x=0.3 x=0.2 Q 2 >2 GeV 2 x= Μν = (E-E )M [GeV 2 ] 30

31 Predictions for large x Bj Proton Wavefunction (Spin and Flavor Symmetric) p = 1 2 u ( ud) S= u ( ud) S = u ( ud) S = d ( uu) S = d ( uu) S = 1 Nucleon Model F 2n /F p 2 d/u A n 1 A p 1 SU(6) 2/3 1/2 0 5/9 Valence Quark 1/ pqcd 3/7 1/

32 Valence Quark Distribution Physics issue: compare behavior of u and d quarks as x Bj 1 Experimental problem: extract information from comparison of hydrogen and deuterium data need to correct for nuclear effects in D Solution for CEBAF upgrade: Valence Quark compare DIS off 3 He and 3 H (nuclear effects ~ same) SU(6) pqcd 32

33 The Neutron Spin Asymmetry A 1 n n A 1 Measures the Spin Response: n A 1 = γ * σ 1 / 2 - ~ q (x) _ partons Nucleon partons σ ~ q + 3 / 2 (x) Nucleon Study of spin structure functions has been limited to the low-x region JLab at 12 GeV with its high luminosity is a prime facility for measurements at large x γ * 1.0 CEBAF 11 GeV, W > 2 GeV Q 10 (GeV/c ) n CEBAF 11 GeV, W > 1.2 GeV 2 A TJNAF at 11GeV, 15 1 W GeV SLAC E142 ( 3 He) SLAC E143 ( 2 D) SLAC E154 ( 3 He) Hermes ( 3 He) SMC ( 2 D) Jlab E ( 3 He) preliminary pqcd-based light cone model valence quark models x 33

34 Flavor Decomposition: (e,e π + )/(e,e π - ) ( u+ u)/(u+u) ( d+ d)/(d+d) q / q 34

35 12 GeV Upgrade Project Status Developed by CEBAF User Community in collaboration with JLab Nuclear Science Advisory Committee, NSAC plan presented during last 5-year Long Range Plan recommended by NSAC for new construction Plan presented to Department of Energy presently waiting for CD-0 (determination of mission need ) Detailed report is being prepared to be reviewed by Jlab PAC in January Construction construction start expected in FY2007 (October 2006) 3 year construction project 35

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37 CLAS++ Detector Forward Cerenkov Forward DC Forward EC Inner Cerenkov Central Detector Preshower EC Torus Cold Ring Inner Calorimeter Forward TOF 37

38 SHMS - HMS Spectrometers After Upgrade Max. Central Momentum 11 GeV/c 9 GeV/c Min. Scattering Angle 5.5 deg 10 deg Momentum Resolution.15% -.2% Solid Angle 2.1 msr 4.4 msr Momentum Acceptance 20% 40% Target Length Acceptance 50 cm Opening Angle with HMS 25 deg 16 deg Configuration QQ(DQ) Bend Angle 18.4 deg 38

39 Physics Program at 12 GeV Gluonic Excitations Valence Structure of the Nucleon 3-dim view of the Nucleon Exciting Compelling In view of recent progress in lattice calculations Timely 39

40 Electron-Light Ion Collider Layout Ion Source RFQ DTL CCL Snake IR IR Snake Solenoids 5 GeV electrons 100 GeV light ions Injector 5 GeV CEBAF with Energy Recovery Beam Dump 100 MV cryomodules Luminosity = cm -2 s -1 Lia Merminga 40