1. 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: 12  B, 28  Al, 7  He 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: A Z + e  A  (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: 6 Li, 7 Li, 9 Be, 10 Be, 12 C –High resolution spectroscopy beyond p-shell, possibly resolve spin-doublet splitting -- Target: 28 Si

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

6. Spectrometer System Calibration Strategy Using known masses of ,   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, Pe 0 =0. 3417GeV, P K 0 =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 w i determined by scan to find minimized  2 wid : Region I (exfp ≥ -12 cm) Region II (exfp < -12 cm)

9. Nonlinear Least Square Fitting Nonlinear Least Square fitting with event weight-- a weight factor is calculated for each calibration event according to function:  Noise cut-off parameter  : Annealing temperature parameter When  ∞, function p i becomes constant 1 12  B gs event selection gate 12  B gs weight function Excitation Energy (MeV)

10. Accidental Background Comparison Between Different Optics 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

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

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

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

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

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

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

20. Missing Mass Spectra of Li9L, He6L, Be10L He H 6  He 10   e 9  Li GS? Binding Energy (300 keV/bin)Binding Energy (250 keV/bin)

21. Simulated 10  Be Missing Mass Spectrum 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.) 10   e Data 10   e Theoretical 10   e Simulation

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 12  B gs The gs and major shell structures of 28  Al and 7  He 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