Spin Physics in Jefferson Lab s Hall C

Transcription

1 Spin Physics in Jefferson Lab s Hall C Frank R. Wesselmann Norfolk State University

2 Outline Introduction Jefferson Lab, Hall C Concepts & Definitions Experiments & Measurements Spin as Goal Spin as Tool Summary & Outlook

3 CEBAF: Continuous Electron Beam Accelerator Facility at the Thomas Jefferson National Accelerator Facility Newport News, Virginia, USA

4

5 Introduction Hall C 2 Spectrometer High Momentum Spectrometer, Short Orbit Spectrometer Cryogenic Target:,, solids or: UVa Polarized Target, other options Møller Polarimeter for Beam Compton Polarimeter being added target & detectors

6 High Momentum Spectrometer movable: 1 dipole magnet, 3 quadrupoles acceptance Q1 Q2 Q3 Dipole 27m shielded detector package scintillator hodoscopes, wire drift chambers gas Cerenkov, segmented Pb glass calorimeter well-studied tracking, reconstruction provides electron ID, event time, momentum & energy determines track position & direction at target

7 UVa Polarized Target frozen NH, ND He evaporation refrigerator polarizing field remotely movable insert, LiD dynamic nuclear polarization driven by microwaves NMR system for polarization measurement e Beam 4-94 LN 2 Microwave Input To Pumps Magnet Liquid Helium Target (inside coil) 1 K NMR Signal Out NMR Coil B 5T Refrigerator To Pumps Liquid Helium Signal LN A1 Frequency

8 Spin Experiments in Hall C Two Basic Categories of Experiments: Spin is the Goal Polarization Measurements ( ) Spin Structure Functions (RSS, SANE) Spin is a Tool Form Factor Measurements ( Parity Experiments (, ), ) omitting some subjects, e.g. spin-dependent transitions in hyperon nuclear spectroscopy (E , E )

9 Experiments Spin as Goal (E ): Deuteron Tensor Polarization published RSS (E ): Resonance Region Spin Structure Functions ongoing analysis SANE (E ): Spin Asymmetries of the Nucleon Experiment planned, 2007?

10 E : Measurement of the Deuteron Tensor Polarization at Large Momentum Transfers in Scattering Ran in 1997 published Coincidence Measurement of Deuteron Tensor Polarization Observables, and Used Target, HMS & Custom Polarimeter Via Analyzing Interaction Target in Secondary Relate to Deuteron Form Factors (monopole), (magnetic dipole) and (quadrupole)

11 E : : Measurement via Efficiency of Analyzing Interaction independently from SATURNE and polarization direction of Analyzing Power

12 Setup: POLDER

13 Results NRIA NRIA+MEC+RC - Relativistic I Relativistic II pqcd I pqcd II

14 Results

15 E : RSS Nucleon Spin Structure in the Resonance Region Inclusive Scattering, Polarized Beam & Target Proton & Deuteron, & or & or consistent setup, minimal model input ran January March 2002 Dependence Polarized Local Duality GDH Sum Rule Higher Twist Effects &

16 Asymmetries and Spin Structure #" $ % & ' $ ( ) #* +, - ( ) #* +., / : 6 3; 8 < = 1 0 > 8 3; 8?1 A B8 C 1 D E 3; 8 F > 8 G > 1 H I > J > A K A L MN O P MN K A QSR TU > P V > Q

17 RSS Kinematics Example: longitudinal

18 RSS Results " PRELIMINARY (Uncorrected) RSS A deuterons protons x charge normalized: PRELIMINARY (Uncorrected) RSS A _ _ deuterons protons #%$ & Beam Polarization Target Polarization Dilution Factor Radiative Corrections x

19 RSS Results based on Hall C fits for and

20 E : SANE Spin Asymmetries of the Nucleon Experiment Proton SSF at Large for Resonance Region Systematically Related, Kinematic Dependence Polarized Local Duality Twist-3 Contributions

21 SANE Proton vs.

22 SANE Expectations

23 SANE Setup UVa Polarized Target Big Electron Telescope Array HMS only for Background Studies

24 BigCal 1744 Pb Glass Blks, 56 Event Time, Energy & Position

25 Experiments: Spin as Tool Form Factor Measurements Neutron E (Gen98, Gen01), E published Proton E (GEp-III), E ( ) planned Parity Experiments E ( ) ongoing analysis, more planned E ( planned )

26 Form Factors Spacial Extent of Charge & Current (Sub-Structure) Anomalous Magnetic Moment Fundamental Quantities Test of QCD Required for Study of Other Physics e.g. Few-Body Structure Functions

27 Form Factor Measurements Traditional Methods: Cross Section Based Rosenbluth Separation Highly Sensitive to Wavefunction Models Spin-Based Methods: Polarization Observables (asymmetry, LT-ratio) Complex Setups Asymmetry Measurements Require Absolute Polarization

28 Formalism Sachs Form Factors for Elastic Scattering Intuitive Interpretation ) point-like probe ( " " Breit frame (NR limit) Fourier Transform of Charge, Current Distribution

29 " & Basic Approximation: Dipole Fit Phys. Rev. 139, B458 (1965) Based on Exponential Charge Distribution FT fitted to Data: " +-, *) (' "$#% corresp. to

30 Structure Functions * Form Factors for Elastic Scattering Only More General: Structure Functions and In the Limit of Elastic Scattering ( ):

31 : Neutron Charge Form Factor " E ran in 1998 (Gen98) and in 2001 (Gen01) doubly polarized quasi-elastic scattering: polarized off polarized in measured at and E ran in 2000 recoil polarization: polarized scattering off measured at, " and "

32 *,+ *,+ 1 0 Asymmetry Measurement Formalism - (*) %'& $ #* " * - / - )., 2*5 243 Measurement via Vector Asymmetry

33 Asymmetry Measurement Formalism " " " for quasi-free, u y Spin Orientation Plane LAB Frame: ( and ) in scattering plane ( ), k θe k Q= h e Scattering Plane (ω, q) P t θ* φ * u z (along q)

34 1 0 at QE Kinematics 1 0 For Scattering Quasi-Elastically off Deuterium: G E n =0.5 Galster G E n =1.0 Galster G E n =1.5 Galster Born N N+MEC N+MEC+IC N+MEC+IC+REL Large Sensitivity to Small Model Dependence Based on Calculations by H. Arenhövel

35 Gen01 Neutron Detector High Momentum Spectrometer Polarized Target Incoming Beam Line, Chicane Magnet

36 Gen98, Gen01 Neutron Detector 3 * segmented scintillator 2 VETO layers 6 conversion layers high rate: Protons vertically extended for symmetric proton acceptance (2001) provides 3 space coords, time & energy Beam Height Neutrons 11cm 10 cm 1.0 cm 10 cm (length:160cm)

37 Recoil Polarimetry Formalism " " Electron scattering plane e e' θ e n t Secondary scattering plane n(p) l θ φ Direct measurement of form factor ratio by measuring the ratio of the transfered polarization and

38 + Recoil Polarimetry E Top Rear Array Bottom Rear Array Front Veto/Tagger Rear Veto/Tagger Lead Curtain Front Array Charybdis To HMS e e Target LD2, LH2 rotate longitudinal pol with Charybdis magnet want to determine and at target polarimeter sensitive to transverse pol only 90 deg. P X = PL, P L, Z (Momentum Direction) δ P, S Polarization Vector + 90 deg. P + X = P, L X

39 Results G E n E (01) E (98) E Sick and Schiavilla Golak et al (01) Bermuth (00) Ostrick (99) Galster Q 2 (GeV/c) 2 Plans for recoil polarization up to

40 E : GEp-III Measurement of Recoil Polarization Expands on Hall A Work: Higher :,, ' Different Systematics Planned 2005/2006

41 E : GEp-III Measurement of Recoil Polarization Expands on Hall A Work: Higher :,, ' Different Systematics Planned 2005/2006

42 in Hall A

43 Recoil Polarimetry E Detect Scattered in BigCal Protons in HMS with new Focal Plane Polarimeter HMS Dipole Rotates Polarization Vector y z B χ P fpp x y x P z

44 E : TPEX Measurement of the Two-Photon Exchange Contribution in Elastic Scattering Using Recoil Polarization Resolve pol unpol Discrepancy Generalization of Form Factors Examine -Dependence at Fixed Significant New Theory To Run after GEp-III (same setup)

45 " " " # * 5 E : TPEX Recoil Polarization: Traditional Extended for TPEX: $ % $ #*

46 " Form Factors Current Status Data: All Form Factors Measured (,,, ) Models: Several QCD-based Models Vector Meson Dominance pqcd light front CQM, Goldstone Boson Exchange CQM Solitons None Well Describe all Form Factors over Entire Measured Range

47 G p M / µg D G n M / µg D Q 2 [GeV 2 ] VMD + pqcd (Lomon 2002) Soliton (Holzwarth b1) Soliton (Holzwarth b2) µg p E /G p M G n E Q 2 [GeV 2 ] PFSA CQM GBE LF CQM qff (Cardarelli) LF CQM π (Miller) Q 2 [GeV 2 ] Q 2 [GeV 2 ]

48 Parity Experiments Theory Include Weak Interaction in Scattering:,,, Cross Section Interference Term Violates Parity *

49 Parity Experiments Theory " " " " With Measurements at 2 Different, can Extract and Separately 5 %

50 " Flavor Singlet " " Assuming Isospin Symmetry, get Weak Part of Quark Form Factors in Proton:

51

52 Expectations

53 E : The Experiment A Search for Physics at the TeV Scale Via a Measurement of the Proton s Weak Charge Recall Polarized Scattering Asymmetry: For Forward Scattering (, ", " ): "

54 Expectations " " SLAC E158 Result for

55 Setup

56 Summary & Outlook Hall C Well Situated & Equipped to Utilize Jefferson Lab s Polarized CW Beam Extensive Experimental Program Measuring & Using Spin: Deuteron Tensor Polarization Spin Structure Functions Proton & Neutron Form Factors Ongoing Efforts and Planned Measurements: up to ', up to Measure TPEX, Resolve pol unpol Ground-Breaking Parity Experiments Planned and Upgrade to Accelerator...