# Presentation: 474170

## Jan. 18, 2008
Hall C Meeting
L. Yuan/Hampton U.

- Jan. 18, 2008
- Hall C Meeting
- L. Yuan/Hampton U.

## 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

## 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  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:6Li, 7Li, 9Be, 10Be, 12C
- High resolution spectroscopy beyond p-shell, possibly resolve spin-doublet splitting --Target: 28Si

## HKS Experimental Setup

**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

##  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

- Standard double arm spectrometer

- HKS spectrometer system

- Beam

- Target

- Splitter

- HKS

- Enge

- Sieve Slit

- To beam dump

## 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

## Kinematics Scan for Beam Energy, the HKS and Enge Central Momentum

**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

## 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)

## Nonlinear Least Square Fitting  

**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)

## 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

## Background comparison: old optics

- Old optics: 05/18/07:

- Background: new optics

- Background: old optics

## Mean value difference for each bin

- Sigma of bins in new optics

- Sigma difference for each bin

## Background: new optics

- Background: old optics

- Mean value difference for each bin

- Sigma of bins in new optics

## Mean value difference for each bin

- Sigma of bins in new optics

## Mean value difference for each bin

## Preliminary

**Counts (0.3MeV/bin)**

****

******0**

**Accidentals**

**Events from C**

**p(e,e’K****+****)********&********0**** used for kinematics and optics calibration**

**HKS-JLAB**
**CH2 target**
**~ 70 hours**

**Preliminary**

## Preliminary

**s******

**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 **

## 7Li(e,e’K+)7He – First Observation of 1⁄2+ G.S. of 7He

**7****Li(e,e’K****+****)****7********He – First Observation of 1⁄2****+**** 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 6He

- “glue role” of :

- 6He

- 7He

- 0+

- +n+n

- ++n+n

- 1⁄2+

- -0.69
- <r-n>=4.6

- -6.12
- <rcore-n>=3.55 fm

**Preliminary**

- * Hiyama 1997

**Preliminary**

**S******

**p******

**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

## Missing Mass Spectra of Li9L, He6L, Be10L

**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)

- Binding Energy (250 keV/bin)

## 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**** **

## 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?

## Reconstructed correlations

**Reconstructed correlations**