jan. 18, 2008 hall c meeting l. yuan/hampton u.. outline hks experimental goals hks experimental...
DESCRIPTION
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 SiTRANSCRIPT
Jan. 18, 2008Hall 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: 12B,28
Al, 7He
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
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
BeamTarget
Hadron arm E-arm
Sieve Slit
Standard double arm spectrometerHKS spectrometer system
Beam
Target
Splitter
HKSEnge
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
M)|f(X=pmΔwχ fpiii
i22
222SSSSMMMMtot χw+χw=χ
Kinematics Scan for Beam Energy, the HKS and Enge Central Momentum Nominal values: E_beam=1.853 GeV, Pe0=0. 3417GeV, PK
0=1.2 GeV Scan beam energy, HKS and Enge central P ±100 keV Define
00EKbkin ΔPΔPΔE=V 0.0451.531.125 00 =ΔP,=ΔP,=ΔE EKb
222 )m(m+)m(m= PDGΣ
fΣ
PDGΛ
fΛpos
)σ+σ+σ+σ+σ+(σ+σ+σ=χ LHePSLAlGSLAlceLBPSLBGSLBΣΛwid2
72
282
282
1122
122
12222 9
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))σ+σ+σ+σ+σ+(σ+σ+σ=χ LHePSLAlGSLAlceLBPSLBGSLBΣΛwid
27
228
228
2112
212
212
222 0.70.50.01
)σ+σ+σ+σ+σ+(σ+σ+σ=χ LHePSLAlGSLAlceLBPSLBGSLBΣΛwid2
72
282
282
1122
122
12222 0.70.5
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 pi becomes constant 1
12B gs event selection gate
12B gs weight function
)exp()exp()exp(
2
2
iiii
iii M
Mp
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
Cou
nts
(0.3
MeV
/bin
)
0AccidentalsEvents from C
p(e,e’Kp(e,e’K++))&&00 used for kinematics and optics calibration used for kinematics and optics calibration
HKS-JLABHKS-JLABCH2 targetCH2 target~ 70 hours~ 70 hours
Preliminary
Preliminary
s
p
C.E. #1
C.E. #2
width: 380 keV FWHM
1212C(e,e’KC(e,e’K++))1212B used for kinematics and optics calibrationB used for kinematics and optics calibration
PreliminaryPreliminary
AccidentalsAccidentals
JLAB – HKSJLAB – HKS~ 120 hrs w/ 30~ 120 hrs w/ 30A A
77Li(e,e’KLi(e,e’K++))77He – First Observation of ½He – First Observation of ½++ G.S. of G.S. of 77
HeHeC
ount
s (0
.2 M
eV/b
in)
B- Binding Energy (MeV)
S (1/2+)
AccidentalsAccidentals
7He: added to a
neutron halo state 6He“glue role” of :
6He 7He
0++n+n ++n+n
½+
-0.69<r-n>=4.6
-6.12<rcore-n>=3.55 fm
PreliminaryPreliminary
* Hiyama 1997
PreliminaryPreliminaryS
p
d ?C.E. ?
2828Si(e,e’KSi(e,e’K++))2828Al – First Spectroscopy of Al – First Spectroscopy of 2828
AlAlC
ount
s (0
.15
MeV
/bin
)
B- Binding Energy (MeV)
JLAB – HKS JLAB – HKS ~ 140 hrs w/ 13~ 140 hrs w/ 13AA
AccidentalsAccidentals
Major shell structures seen Indication of core excited states
* Motoba 2003
Missing Mass Spectra of Li9L, He6L, Be10L
He
H6He 10
e 9Li
GS?
Binding Energy (300 keV/bin) Binding Energy (250 keV/bin)Binding Energy (250 keV/bin)
Simulated 10Be 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.)
10e Data
10e 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 12B gs
The gs and major shell structures of 28Al 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