Miha Mihovilovi č For the E05-102 Collaboration

1. Measurement of double-polarized asymmetries in quasi-elastic processes 3He(e,e’d) and 3He(e,e’p) Miha Mihovilovič For the E05-102 Collaboration

2. Why study 3He? • Proton is well known and its properties are precisely measured. • Neutron is relatively poorly understood. Only loose constraints on the charge, magnetism and spin distribution Problem: direct measurements not possible, no neutron target. Solution: indirect measurements using appropriate targets: 1.) Deuteron where neutron behaves almost as a free particle due to the small binding energy (~2MeV) 2.) Polarized 3He used as effective polarized neutron target. !!!

3. 3He as effective n0 target Precision of this approximation depends on the understanding of the structure of the 3He. Precise test of understanding of the 3He structure, nuclear forces between nucleons, FSI, MEC. Understand the structure of the n0 3He is a calculable nuclear system, where theoretical predictions of its nuclear structure can be compared with data to an increasingly accurate degree. Error budget for An1: aside statistical error, leading source of error is due to the uncertainty of the polarization of the proton and neutron in polarized 3He.

4. S p n n n S’ p p p p (L=0) p D (L=0) (L=2) 3He ground-state wave-function - A bound state of p,p,n: S = ½, T = ½ (MT = +½) - Calculations predict three dominant components: 1.) Spatially symmetric state S (90%): Protons are in spin-singlet state. 3He spin is dominated by spin of n. Therefore 3He can be used as an effective n target. 2.) State D (8%): Nucleon spins oriented in opposite to the 3He nuclear spin. Generated by tensor component of NN force. 3.) Mixed symmetry state S’ (2%): Arises from differences between T=0 and T=1 forces and hence reflects (spin-isospin)-space correlations.

5. Ax,Az Asymmetry Measurement Experiment E05-102 at Jefferson Lab • Understanding the role of the D and S' states in 3He is a very important aspect of the few-body theory. • Observables sensitive to the S' state constitute a stringent test of the theory. Among them are also asymmetriesAx and Az. • For polarized beam and polarized target, the cross-section for the 3He(e,e’d) is: The (±; ±) signs represent the beam helicities and the projections of the target spin. • Measuring asymmetries saves a lot of problems, because “all” the problems with normalization of cross-section disappear. !

6. Thomas Jefferson National Accelerator Facility • CEBAF center at JLab was built to investigate the structure of nuclei and hadrons at intermediate energies and underlying fundamental forces. North Linac South Linac Injector A C B 6 GeV polarized continuous beam with currents up to 100uA is delivered to three experimental Halls A, B and C.

7. Experimental Setup in Hall A

8. p n p p n Experiment E05-102 in Hall-A Detected Electron Incident polarized electron θL θq γ* Beam Helicity Ax Az p Detected Deuterons and Protons

9. Polarized 3He Target Polarized 3He Cell Oven with Mirrors 12C Optics Target Beam Direction Large Coil Vertical Coil Small Coil

10. Polarization of the 3He Target • Five High-Power IR-Diode lasers (~30W) are used to polarize the target in all three directions • Optical table with lenses, mirrors, λ-shifters is used to properly guide light from optical fibers to the target.

11. High Resolution Spectrometers Detector package Quadrupole Dipole 2 Quadrupoles Particle Track

12. HRS - Detector Package Electronics Shower Open Detector-Hut Pre-Shower Scintillators Cerenkov Scintillators VDCs

13. BigBite Spectrometer • Single normal-conducting dipole magnet spectrometer • Combines a large solid angle with a large momentum acceptance. • Two MWDCs for tracking; Each MWDC consists of 6 wire planes u,u’,v,v’,x,x’ • Two Scintillation planes E/dE for particle identification and Energy determination

14. Analysis of Measured Data • Experiment was done in June 2009. We accumulated ~15C and collected 7TB of data. • Now Analysis is now underway. At the moment we are doing calibration of BigBite. After the calibration the asymmetry determination will folow.

15. BigBite Optics Calibration • Purpose of optics calibration is to determine target variables • (yTg, φTg, θTg, δTg) from focal plane variables (xFp, yFp, θFp, φFp). • There are many parameterizations possible. We use polynomials:

16. S’ D D What are the theoretical expectations? • The role of S’ is most evident in region of small recoil momenta where Ax is large. Az is close to zero at small pr. • Much stronger variation of Az at high pr. This behavior is governed by the D-state.

17. S D n n p p (L=0) (L=2) 2H Results from NIKHEF • This was observed in NIKHEF in the experiment with 2H polarized target • Deuteron is S=1 particle made of two S=1/2 nucleons (p,n) • Sign-change of the Asymmetry is a clear sign that D-state component becomes important in the nucleus at high pmiss.

18. Conclusions • Experiments with polarized target and polarized beam are important step forward in the experimental nuclear physics. • Asymmetries give an insight to the properties of the nucleons that were not measurable with unpolarized experiments. • Many 3He experiments were already done. • Why is experiment E05-102 so special? • 1.) Double polarized experiment (3He, e ) • 2.) Measured all three (p,d,n) channels at same Q2 with ω • covering the whole q-e peak and more. • 3.) Measured asymmetries as function of pmiss. It is the first, where D-wave and S’-wave contributions to 3He will be inspected in detail in order to understand Spin, Iso-Spin structure of Nuclei, MEC, FSI. Very important for all further experiments on 3He.

19. Thank you for listening!