First Study of Three-body Photodisintegration of with Double Polarizations at HI g S

First Study of Three-body Photodisintegration of with Double Polarizations at HIgS Ph.D. Dissertation Defense Xing Zong Committee members: Prof. Haiyan Gao (Advisor) Prof. Thomas Mehen Prof. John Thomas Prof. Henry Weller Prof. Ying Wu Feb 19th, 2010

Outline • Introduction and Physics Motivation • The Experiment • Overview • HIGS working principle • Polarized 3He Target • Neutron Detection • Data Analysis • Result and Discussion • Summary & Outlook

Introduction • Understanding Nuclear force has been a fundamental goal in nuclear physics: Hideki Yukawa: exchange of pion accounted for the force between two nucleons • Two nucleon (NN) system can be described by realistic NN potentials: • long range one-pion exchange, intermediate attraction, short-range repulsion • Modern NN potentials include: AV18[1] and CD Bonn[2]. • NN potentials reproduce NN scattering database up to 350 MeV with high precision. • They underbind triton [1] R.B.Wiringa et al. PRC 51, 38 (1995) [2] R.Machleidt et al. PRC 53, R1483 (1996)

Three-nucleon system • Excellent testing ground of theory • simplest non-trivial nuclear system • sufficient complex to test the details of theory • small enough to allow exact calculations • Hamiltonian is written as • . • Three-nucleon Force (3NF) • (a) Fujita and Miyazawa first introduced 3NF in 1957[1]; isobar yields an effective 3NF • (b) Urbana IX is one of the most widely used 3NFs[2] △ △ [1] J. Fujita and H. Miyazawa, Prog. Theor. Phys. 17, 360 (1957) [2] J. Carlson, et al. Nucl. Phys. A 401, 59 (1983)

Three-nucleon system: 3He ~90% ~2% ~8% Polarized 3He is an effective neutron target

Movitation I: Test 3-body calculations △ 2005 Nagai data @10.2 and 16 MeV (green)

Motivation II: Test GDH sum rule Fundamental Interpretation: any particle with a nonzero anomalous magnetic moment has internal structure 3He GDH Sum Rule HIgS @ DUKE Extrapolated from low Q23He GDH (E94-010) measurement @ JLab, (E97-110 much lower Q2) [1] M. Amarian, PRL 89, 242301(2002) [2] J. L. Friar et al. PRC 42, 2310 (1990) [3] N. Bianchi, et al. PLB 450, 439 (1999)

Few-body calculations of GDH integral up to np Compare to our simple estimation: It is crucial to carry out 3-body measurement to provide stringent test of the theories! Deltuva et al. PRC 72, 054004 (2005): Green (with △ isobar) and Blue (without △ isobar) Golak et al. PRC 67, 054002 (2003) (Black curve)

Experimental Overview • Beam: HIgS provides circularly polarized g-ray @ 11.4 MeV • Polarized 3He target: flip target spin to form helicity-dependent measurement • ONLY neutrons are detected! 7 detectors from 50 to 160 degs.

High Intensity g-ray source Progress in Particle and Nuclear Physics 62 (2009) 257, Henry R. Weller, et al.

Experimental Setup Polarization preserving mirror Liquid D2O target 22mm collimator Optics table

Experiment Setup@ Duke FEL

Spin Exchange Optical Pumping (SEOP) • Rb vapor in a weak B field is optically pumped • Spin exchange of hybrid alkali N2 buffer gas Rb only: Hybrid: Largest 3He cell ever made!

NMR Polarimetry gyromagnetic ratio • A magnetic moment when placed in an external B-field • Transform into a rotating frame rotates around the B field at frequency w • The motion of M in the rotating frame • Apply oscillating RF field • Effective field in the rotating frame at frequency

NMR - Adiabatic Fast Passage (AFP) • Ramp the holding field from below the resonance to above it • AFP line shape Amplitude of voltage at resonance, proportional to the sample polarization.

Water calibration to extract 3He Polarization rf frequency • The ratio of 3He signal to water signal • The definition of polarization • The polarization of proton in water is given by • The polarization of 3He is nuclear polarization number density volume of the cell magnetic moment pressure of cell temperature of cell W.Lorenzon et al. Phys. Rev. A, 47, 468 (1993) K.Kramer et al. Nucl. Inst. Method A, 582, 318 (2007)

Spin up/down curves The typical spin up/down curves: measurement every 3 hrs. 17 mV corresponds to ~40% polarization. During the run, the average polarization was 42%, and quite stable.

Neutron Detection Important info from the signal: ADC: Pulse-height (energy) TAC: Pulse-shape discrimination (particle separation) TDC: Time of flight (time) g n 1D TAC: Proportional to the length of the trailing edge of the detector signal, therefore measure the particle type. The traditional PSD working principle

11.4 MeV Run summary Run Summary: D2 run: used as a calibration of main experiment 3He run: took spin P and A alternatively to form asymmetry and to reduce systematic uncertainties. Al run: determine gamma peak position to obtain timing information N2 run: background subtraction • Data Analysis Overview: • Calibration: relate ADC and TDC to PH (energy) and TOF (timing) information. • Cuts: separate gammas and neutrons • Integrated flux determination • GEANT4 simulation to determine the acceptance

Calibration I: ADC Determine Pedestal (offset resulting from electronics bias) Compare Cs source runs with simulation to find tune gains (energy per channel)

Calibration II: TDC Determine Gamma peak TDC position Compare D2 run and simulation to determine C (TDC Calibration constant)

How to select neutrons? Gammas Neutron Candidates Note: 1. s roughly corresponds to 30 TAC channels, 2. ee means electron equivalent

Cut effects En=1.1 MeV

Monte Carlo Simulation • Geant4 Simulation helps to determine • the ADC, TDC calibration constant • The back detector efficiency (for flux determination) • Main detector acceptance • The acceptance is the convoluted effect of all the factors: the extended target effect and detecting efficiency of the detectors. • G4 simulation was ran twice under the same conditions first with a point target (Run 1), then with 40cm long target (Run 2). Then divide the number of detected neutrons from Run 2, by the number of neutrons into the detectors from Run 1.

Integrated flux determination Principle: • Note: • We use back detectors to monitor the gamma flux. • The info was used to extract DXS. • The D2 calibration run is based on the same principle.

Normalization Issue • Normalized Yields by back detectors: • Spin P (black), spin A (red) • A downward trend is observed, which gives rise to false asymmetry

Gamma peak normalization • Gamma peak method: • Only provide a relative (not absolute) photon measurement • Cell-dependent. • We use it to get relative integrated flux between spin P and A. Compare run-to-run stabilities between back detectors and gamma peak

Systematic uncertainty study • Uncertainty from analysis cuts PSD cut: vary from 5s to 7s PH cut: vary from 0.19 MeVee to 0.21 MeVee (5% change) TOF cut: vary the trailing edge by from 1.0 MeV to 1.2 MeV (+/- 3 ns). • Uncertainty from HIgS beam Integrated Photon Flux: different methods for asymmetry and DXS Beam polarization: we assume 5% relative uncertainty • Uncertainty from target Target polarization: 4% (NMR/EPR measurement) Target Thickness: 2%(uncertainty in the density measurement, temperature change)

Outline • Introduction • The Experiment • Overview • HIGS principle • Polarized 3He Target • Neutron Detector • Data Analysis • Result and Discussion • Summary & Outlook

D2 differential cross section • Goal of this run is consistency check: • calibration • data selection (cuts) • simulation • normalization B*sin2(q)+C The two fits give us very similar results. Using the Bsin2(q)+C fit result, we obtained total cross section :1247+/-45 mb in agreement with world data: s0 = (1257+/-36 mb) A*sin2(q)

I. Asymmetry Results Expression: Systematic study includes PSD, PH, TOF cuts variations, beam and target polarization, and integrated photon flux. Top two curves are from Deltuva (CD Bonn), bottom two from Golak (AV18). En starts from 1.1 MeV. The fitted average asymmetry agrees with theory within 2s.

II. Unpolarized differential cross section Expression: AV18 AV18+UIX CD Bonn CD Bonn+△ is the detector acceptance which includes both detector efficiency and the extended target effect. Data is from En=1.1 MeV, corrected by simulation (model-dependent) from 0. Statistical uncertainty:

III: Total Cross Section • Two methods: • Fit the data with a constant times the AV-18 curve (725mb), the constant is about 1.053 • Expand the DXS: Fit results: Total cross section result: 776±18(stat.) ±32(sys.)±11(mod)mb Compared with 05 Nagai data at 10.2 MeV, our datum agrees with theory much better!

Outline • Introduction & Physics Motivation • The Experiment • Overview • HIGS working principle • Polarized 3He Target • Neutron Detection • Data Analysis • Result and Discussion • Summary & Outlook

Summary • We carried out a first study of three-body photodisintegration of 3He at HIgS with 11.4 MeV circularly polarized photons. • We have extracted three sets of results: asymmetry, unpol DXS and TXS. • Results are compared to two sets of state-of-the-art three-body calculations from Deltuva and Golak using CD Bonn and AV18 potentials. • Fitted average asymmetry is within 2s of the theoretical value, unpolarized DXS agrees reasonably with theory. • Total cross section is obtained by two methods. The final result agrees with theoretical calculation much better than 2005 Nagai data.

Outlook • A new proposal was approved by HIGS physics advisory committee (PAC) in July 2009. • PAC granted us 180 hrs to run measurements at three photon energies. • Beam time could be as early as fall 2010.

3He Three-body Photodisintegration Collaboration @ Duke HIgS M. Ahmed, C. Arnold, M. Blackston, W. Chen, T. Clegg, D. Dutta, H. Gao(Spokesperson/ Contact Person), J. Kelley, K. Kramer, J. Li, R. Lu, B. Perdue, X. Qian, S. Stave, C. Sun, H. Weller(Co-Spokesperson), Y. Wu, Q.Ye, W. Zheng, X. Zhu, X. Zong Duke University, Durham, NC

Acknowledgement • U.S. DOE contract number DE-FG02-03ER41231 • Duke University School of Arts and Sciences • TUNL MEP group, Capture group, TUNL staff & FEL staff • Dr. Deltuva and Dr. Golak and their collaborators

Historical Background Nuclear interactions and Nobel Prizes • Hideki Yukawa: exchange of pion accounted for the force between two nucleons • Murray Gell-Mann: existence of more fundamental particles, ie. quarks • Gross/Politzer/Wilczek: discovery of asymptotic freedom in QCD Photos are from nobelprize.org

Mesons Pseudoscaler Mesons: quark and anti-quark spin antiparallel Vector Mesons: quark and anti-quark spin parallel

Baryons J=1/2 J=3/2

Nuclear force • Range of nuclear force is ~ radius of alpha particle, 1.7 fm • Intermediate attraction: nuclear binding • Repulsive core. Proof: NN scattering data, energies above 300 MeV, the s-wave phase shifts becomes negative • Nuclear force has a tensor component. Proof: the presence of the a quadrupole moment for the deuteron ground state • Nuclear force has a strong spin-orbit component. The triple p-waves from phase shift analysis at high energies can only be reproduced by adding a spin-orbit term to the central and tensor nuclear force component.

Yukawa potential Derived from Klein-Gordon eqn. With the increase of r, potential decreases very fast, which implies the short-range characteristics of nuclear force.

AV18: • It contains an EM interaction & a phenomenological short and intermediate range • NN interaction describe by V(r, p, s1, s2) where terms are the relative position, relative momentum, spin. • It is based on AV14, 14 operators not related to charge, • 4 charge operators

CD-Bonn 549 Exchange of mesons! It is based on field theoretical perturbation theory. Completely defined in terms of one-boson exchange! 770 782 s-meson describes multiple-meson contributions in the single boson exchange. Nonlocality: the potential acting at one point may depend on the the value of the wavefunction at a different point. It essentially describes the relativistic treatment. All mesons with mass below nucleon mass are included. Interaction between nucleons in the same spin-angular momentum is identical for pp, np, and nn system. ----charge independence.

Three-nucleon Force (3NF): UIX Fujita-Miyazawa term where Urbana IX potential: Short range repulsive term: Multiple-pion exchange and repulsive contributions

Nuclear current operator • One-body current with Siegert operator • Meson Exchange Currents (MEC) include non-relativistic In my calculations MEC means that meson exchange currents were included directly, i.e., (transversal) E and M multipoles were calculated from spatial 1-body and 2-body currents. In my all other calculations (RCO) Siegert theorem was used, that assumes current conservation and replaces dominant parts of electric multipoles by the Coulomb multipoles. In case of exact current conservation MEC and Siegert would be identical (and I verified this practically with simple meson exchange model). However, it is very hard to achieve exact current conservation with realistic NN models, especially if they are nonlocal like CD Bonn. Therefore MEC and Siegert yield different results. Since the charge operator is theoretically known better than MEC's, it is advantageous to use Siegert approach, where, in fact, dominant contribution of not well known MEC's are replaced by better known 1N charge (you probably know all that). Therefore our standard calculation is Siegert. The first relativistic corrections are of order (p/m)**2 and are charge corrections, i.e., they have entirely no effect on MEC results. The large difference between MEC and RCO results means that the considered observable is very sensitive to relativistic corrections. I remember, that when I did first calculations without RCO, MEC and Siegert were quite similar. Once again: my MEC does not includes 1N charge relativistic corrections, but others two do so. One more remark: the calculations named "Siegert" have different meaning in my and Golak calculations.

Nuclear current operators Siegert theorem: Electric multipoles = matrix elements of spatial current operator, Coulomb multipoles = matrix elements of charge operator. electric multipoles = Coulomb multipoles + higher order terms. The advantage of Siegert form is that Coulomb multipoles (charge), being strongly dominated by 1-body operators, are known better than spatial current operator. The uncertanties from spatial current operators enter then only in higher order terms and magnetic multipoles. Currents and nuclear forces are connected by continuity equation!!!

First Study of Three-body Photodisintegration of with Double Polarizations at HI g S