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

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

3 He as effective n 0 target Precision of this approximation depends on the understanding of the structure of the 3 He. Precise test of understanding of the 3 He structure, nuclear forces between nucleons, FSI, MEC. n 0 Understand the structure of the n 0 3 He is a calculable nuclear system 3 He is a calculable nuclear system, where theoretical predictions of its nuclear structure can be compared with data to an increasingly accurate degree. uncertainty of the polarization 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 3 He.

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

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

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

Experimental Setup in Hall A

Experiment E in Hall-A θLθL pn p p n p θqθq γ*γ* Incident polarized electron Detected Electron Detected Deuterons and Protons AzAz AxAx Beam Helicity

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

Polarization of the 3 He 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.

High Resolution Spectrometers 2 Quadrupoles Quadrupole Dipole Detector package Particle Track

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

BigBite Spectrometer - Single normal-conducting dipole magnet spectrometer large solid anglelarge momentum acceptance. - 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

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

BigBite Optics Calibration - Purpose of optics calibration is to determine target variables (y Tg, φ Tg, θ Tg, δ Tg ) from focal plane variables (x Fp, y Fp, θ Fp, φ Fp ). - There are many parameterizations possible. We use polynomials:

What are the theoretical expectations? S’ D D S’ - The role of S’ is most evident in region of small recoil momenta where A x is large. A z is close to zero at small p r. This behavior is governed by the D-state. - Much stronger variation of A z at high p r. This behavior is governed by the D-state.

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

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

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