HLab meeting

10/14/08

K. Shirotori

Contents

• SksMinus status– SKS magnet trouble– Magnetic field study

IntroductionHypernuclear production via the (K-,-) and (+,K+) reaction

⇒Scattered - and K+ are analyzed by the magnetic spectrometer, using SKS.

Analysis method : Runge-Kutta calculation from the position of drift chambers and the precisely measured magnetic field map

SKS magnet problem

One of the SKS magnet coil was broken by the high voltage test.

(It cannot be repaired… )

Effects to experiments• Strength of filed : 5/6 (2.7

T 2.5 T @ 395A)⇒⇒Decreasing acceptance and

momentum resolution• Change of filed shape⇒Tracking and absolute

momentum valueThe innermost part of the coil

StudyCalculated field maps are compared with the measured map.

Simulation• Scattered particles tracks generated with

calculated maps (as a true magnetic filed) are analyzed by the measured map or calculated map.

Real data analysis• Real experimental data (KEK E566 data) are

analyzed by calculated maps.

Simulation

Simulated conditions

Particles generation in the simulation• - of 1.4 GeV/c with uniform scattering

angular distribution up to 20 degree • No multiple scattering

Analysis of simulated data• Tracking by using the hit positions of

drift chamber• Drift chamber resolution ~400 m

Magnetic field map

sksmap395a.dat (measured,) Measured 395A magnetic field map

SksQM4S395AFullC.dat (QM4F) Calculated field map Full coil version

SksQM5S395AFullC.dat (QM5F) Calculated field map Full coil version Different B-H curve from QM4F

QM4 Fis used as generated map in the simulation.

Field map and particle tracks

Particles pass the incomplete magnetic filed map region, but they are rejected and there are no large effects.

Measured

Calculated(QM4)

Meaning of observables

P : Momentum U0 : angel (dx/dz) of

production point V0 : angle (dy/dz) of

production point

(x,y,z belong local coordinate)

z

x

● y

Local coordinate (In)zx

●

y

Local coordinate (Out)

Calculated(QM4F) measured : U0,V0⇒QM4F→QM4F QM4F→measured

Large difference P vs U0, 2nd polynomial shape P vs V0, tracks near the SKS magnet coil gap

Momentum resolution : 1.7 MeV/c 2.4 MeV/c (to select good region)⇒ Tracking 2~1.6 (1.0 original)

Calculated(QM4F) calculated(QM5F) : U0,V0⇒QM4F→QM4F QM4F→QM5F

Large difference P vs U0, little 2nd polynomial shape P vs V0, almost flat

Momentum resolution : 1.7 MeV/c 2.3 MeV/c (no correction)⇒ Tracking 2~1.0 (1.0 original)

QM4F→Measured : P vs U0

Particles passing the circled region have large difference between measured andcalculated map.

Measured

QM4F

Analysis

Analysis method

To analyze E566 data : (+,K+) reaction data Correlation by measured map (sksmap272a.d

at) Correlation by calculated map Target thickness : 12C (3.4 g/cm2)(Resolution is determined by the target)

To checkMissing mass (binding energy) vs u0Missing mass (binding energy) vs v0

Measured map (sksmap272a.dat)Before correction After correction

U0 vs MM : 1st+2nd polynomial correlation V0 vs MM : 2nd polynomial correlation⇒Momentum resolution : 2.8 MeV (After correction)

Correction coefficientsU : -0.012*U-0.01*U2

V : +0.05*V2

Calculated map (SksQM12S272AFull.dat)

Correction coefficientsU : -0.012*U-0.01*U2

V : +0.05*V2

U0 vs MM : 1st+2nd polynomial correlation V0 vs MM : 2nd polynomial correlation⇒Momentum resolution : 3.1 MeV (After correction)Binding energy offset : -4 MeV

Before correction After correction

Correlation shape

U0 vs MM : 1st+2nd polynomial correlation

V0 vs MM : 2nd polynomial correlation

Correlation shapes are almost same between all maps. BE vs u0(dx/dz) : strong 1st+2nd polynomial correlation (The

correlation becomes larger to the inner tracks.) BE vs v0(dy/dz) : small 2nd polynomial correlation Offset : less than 10 MeV (Absolute value of magnetic field : ±1%)

SummaryStudy Simulation

Generated by calculated map Analyzed by measured or ⇒calculated map

Check the correlation between momentum and scattering angle⇒To check the difference of absolute values and angles

Real data analysis @ 272A map E566 thin 12C target data analyzed by measured or calculated map Check the correlation between binding energy and scattering

angle ⇒ Correlation shapes are almost same between all maps. ⇒ The correlation can be corrected.

For the experiments High resolution experiments

To correct the correlation by many binding energy data How to determine the absolute value ?

Coincidence experiment (Hypernuclear -ray spectroscopy, weak decay)

The correction is almost enough to select the binding state. (Momentum resolution is not need to be so high)