Lulin Yuan / Hampton University

HKS Collaboration Meeting

Jefferson Lab, May 16, 2008

Spectrometer System Calibration Strategy

Minimize Chisquare w.r.t reconstruction matrix M by an Nonlinear Least Square method

Kinematics calibration: important to determine correct binding energy, energy resolution Iteration

M)|f(X=pmmwχ fpiexpi

cali

ii

22 )(

Starting optics

Calculate missing mass

Select , and hypernuclear bound states events

Minimize Chisquare w.r.t reconstruction matrix M

New optics

Better signal to background ratio

More accurate bound state mass

Iteration procedure for optical calibration

Co

un

ts (

0.3M

eV/b

in)

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-JLAB

CH2 targetCH2 target

~ 70 hours~ 70 hours

Preliminary

Preliminary = 660 keV

M = -9 keVM = -18 keV

Analysis Status

Optical reconstruction matrices and kinematics almost finalHave quick estimate of B12

ground state (GS) cross section

Finished analysis for simulated HKS data. Results of blind analysis is being compared with correct optics

Better Fitting for and 0 peaks in CH2 spectrum result in shift in binding energy for hypernuclear spectrum

Need precise energy loss correction in CH2 target and other targets in order to determine binding energy correctly

Blind Analysis

Involved B12L bound states in calibrationThe expected position and relative weights of bound states are determined

by scan to find the minimized 2:2

122

12222

PSLBGSLBΣΛwid σ+σ+σ+σ=χ

2_wid at each stage of the calibration

Blind Analysis Step by Step Result

1. initial matrix

2. involving and 3. involving B12L 2 peaks at Excitation Ex~0 and Ex~-11.5

4. involving B12L "core excited" peak at Ex~9.0

5. involving B12L " 2nd core excited" peak at Ex~5.0B12L spectrum at each stage (Ex=0 at binding energy 11.37 MeV)

Blind Analysis: Final Result

● Final matrix: 6 states are identified from simulated C12 target data, their binding energy (MeV) and relative counts to "ground state "are

11.43 ('Ground state'): counts 491

23.70 and 23.04: combined counts relative to GS 0.83

20.35: 0.29

16.70: 0.39

13.63: 0.11

The and position and counts from

simulated CH2 target:: -0.031 from PDG value, 2291 count

: 0.022, 418 count

Ex : binding energy 11.37 MeV

BetterFitting for and 0

Better fitting for and 0 peaks to improve confidence level and binding energy precision. Three fitting methods:

– G+P: Gaussian + Polynomial– AV: Gaussian + Avoigtian

– ASAV: Gaussian + Asymmetric Avoigtian

MaximumhalfWidthHalfmeanxxx

y : ,: ,)(

1022

0

factorasymmetricaxx

xxay : ,

)(

)(122

0

0

Calibration by and 0

Fit Centroid (keV) p.d.f. Confi. Level

G+P -15 1.54 0

AV -8 1.12

ASAV -85 0.86 0.85

0Fit

Centroid (keV) p.d.f. Confi. Level

G+P -12 1.27 0

AV -11 1.18

ASAV -84 1.17 0.15

L Fit

Average Cross section: B12 GS

Quick estimate of B12 GS cross section as the average of 5 C12 run periods

Set# 1 2 3 4 5 6

HKS Tracking 0.93 0.90 0.93 0.89 0.90 0.92

Enge Tracking 0.72 0.66 0.85 0.91 0.92 0.91

AC Cut 0.81 0.82 0.86 0.90 0.95 0.97

WC Cut 0.90 (for all data sets)

Cut 0.93 0.87 0.95 0.93 0.98 0.98

Computer Live 0.90 0.90 0.94 0.92 0.90 0.93

K Absorption 0.975

K Decay 0.345

Beam Charge(mC) 618.5 0.115 0.184 0.158 0.210 0.226

GS Count 26 0 322 77 30 202

Integrated VPF 4.805E-6

Averaged HKS Solid angle 15 msr

Cross section ddL (nbar/sr)

135.5 0 115.7 161.7 94.0 85.6

*Correction factors, solid angle and VPF Based on Okayasu’s PhD Thesis

Average Cross section: B12GS

Averaged B12GS cross section (0-13 degree average)

ddL = 103.1±5.7 (stats)(nbar/sr)

HNSS (E89-009) (0-4.6 degree average):

ddL = 155.0±24 (stats)(nbar/sr)

C12 Run Period

dd

L(n

bar/

sr)

Average Cross section

K+ Scattering Angle(degree)