Current Status of HKS Data analysis

1. Current Status of HKS Data analysis Jan. 18, 2008 Hall C Meeting L. Yuan/Hampton U.

2. Outline • HKS experimental goals • HKS experimental setup • Issues on spectrometer system calibration • Calibration strategy and procedures • Calibration consistency check -- accidental background comparison between different optics • Current spectra: 12LB,28LAl, 7LHe • Summary and work to do

3. HKS Experimental Goals • JLab HKS experiment: Hypernuclear spectroscopy from lower p-shell to medium-heavy systems with ~400 keV resolution by electroproduction • Electroproduction: AZ + e  AL(Z-1) + e’+ K+ • A few hundred keV binding energy resolution achievable by utilizing high precision electron beam • Focus: • High spin, unnatural parity states complementary to hadronic reactions; Neutron rich systems -- Targets:6Li, 7Li, 9Be, 10Be, 12C • High resolution spectroscopy beyond p-shell, possibly resolve spin-doublet splitting --Target: 28Si

4. HKS Experimental Setup Experimental setup: Increasing yield and reduce accidental background • Accept very forward angle e’: using Splitter magnet on target • Vertically tilt electron spectrometer Beam energy 1.8 GeV

5. Issues on Spectrometer System Calibration Hadron arm E-arm Sieve Slit Target Beam Spectrometer system calibration: • On-target splitter field – no single arm elastic scattering, delta scan data available • High accidental background in calibration data HKS spectrometer system Standard double arm spectrometer To beam dump HKS Enge Sieve Slit Splitter Target Beam

6. Spectrometer System Calibration Strategy • Using known masses of L, S0 from CH2 target and identified hypernuclear bound states • Angle calibration uses both the constraints of missing mass and Sieve Slit data • Kinematics scan: important to determine absolute missing mass, energy resolution • Nonlinear Least Square fitting with event weight function p--reduce effect of background events in calibration • Iteration

7. Kinematics Scan for Beam Energy, the HKS and Enge Central Momentum • Nominal values: E_beam=1.853 GeV, Pe0=0. 3417GeV, PK0=1.2 GeV • Scan beam energy, HKS and Enge central P ±100 keV • Define

8. Relative Weight Scan and Momentum Calibration • Relative weights of different states wi determined by scan to find minimized 2 wid: Region I (exfp ≥ -12 cm) • Region II (exfp < -12 cm)

9. Nonlinear Least Square Fitting 12LB gs weight function • Nonlinear Least Square fitting with event weight-- a weight factor is calculated for each calibration event according to function: l: Noise cut-off parameter b: Annealing temperature parameter • Whenl∞, function pibecomes constant 1 12LB gs event selection gate Excitation Energy (MeV)

10. Two optics: 05/18/2007 first optics after divide region and current optics Procedure: Select events from 4 accidental coincidence windows. In missing mass spectrum of the old optics, cut events into 1 MeV bins For events in each bin of the old optics, calculate missing mass with the new optics, fit its centre and width. The width and sigma from the old and new optics are compared bin by bin Accidental Background Comparison Between Different Optics

11. Background comparison: old optics Background: new optics Background: old optics Old optics: 05/18/07:

12. Background comparison: C12 Mean value difference for each bin Sigma of bins in new optics Sigma difference for each bin

13. Background comparison: CH2 Background: new optics Background: old optics Mean value difference for each bin Sigma of bins in new optics

14. Background comparison: Si28 Mean value difference for each bin Sigma of bins in new optics

15. Background comparison: Li7 Mean value difference for each bin

16. p(e,e’K+)&0 used for kinematics and optics calibration  HKS-JLAB CH2 target ~ 70 hours Preliminary Counts (0.3MeV/bin) 0 Events from C Accidentals

17. 12C(e,e’K+)12B used for kinematics and optics calibration JLAB – HKS ~ 120 hrs w/ 30A sL Preliminary pL width: 380 keV FWHM C.E. #1 C.E. #2 Accidentals

18. 7Li(e,e’K+)7He – First Observation of ½+ G.S. of 7He SL (1/2+) Preliminary • 7LHe: L added to a neutron halo state 6He Counts (0.2 MeV/bin) “glue role” of L: 6He 7LHe a+n+n a+L+n+n 0+ Accidentals -0.69 <ra-n>=4.6 ½+ -6.12 <rcore-n>=3.55 fm B- Binding Energy (MeV) * Hiyama 1997

19. 28Si(e,e’K+)28Al – First Spectroscopy of 28Al JLAB – HKS ~ 140 hrs w/ 13A Preliminary pL SL dL? C.E. ? • Major shell structures seen • Indication of core excited states Counts (0.15 MeV/bin) Accidentals * Motoba 2003 B- Binding Energy (MeV)

20. Missing Mass Spectra of Li9L, He6L, Be10L H 6LHe 10LBe 9LLi He GS? Binding Energy (250 keV/bin) Binding Energy (300 keV/bin) Binding Energy (250 keV/bin)

21. Generated simulated Be10L missing mass spectrum according to the statistics and S/A in the real spectrum and the resolution of the B12L GS: 0.161 keV. The peak positions and strength from theoretical calculation (T. Motoba, Prog. Theo. Phys.) Simulated 10LBe Missing Mass Spectrum 10LBe Simulation 10LBe Theoretical 10LBe Data

22. Summary • A special designed calibration procedure for HKS spectrometer system has been carried out • The preliminary spectrum has a resolution ~380 keV (FWHM) for 12LB gs • The gs and major shell structures of 28LAl and 7LHe have been observed • Work to do: • Missing mass linearity check / Estimate systematic error due to the calibration process -- by calibrating simulated events with same procedure • Cross section calculation – virtual photon flux?

23. Reconstructed correlations