New (e,e’K+) hypernuclear spectroscopyNew (e,e’K+) hypernuclear spectroscopywith a high-resolution kaon spectrometerwith a high-resolution kaon spectrometer

Osamu HashimotoDepartment of Physics, Tohoku University

December 4-7EMI2001 at RCNP, Osaka

• Significance of the (e,e’K+) hypernuclear spectroscopy• Lessons from the previous E89-009 (e,e’K+) experiment• Optimization of the experimental condition• New high-resolution kaon spectrometer for (e,e’K+) spectroscopy

Current issues of hypernuclear physicsCurrent issues of hypernuclear physics

A new degrees of freedom– can examine deeply bound states– baryon structure in nuclear medium

New nuclear structure with strangeness– nucleus with a new quantum number– electromagnetic properties

Hyperon-nucleon, hyperon-hyperon interaction– Hyperon scattering and hypernuclear structure– S=-2 system and beyond

Weak interaction in nuclear medium– decay widths, polarization

high quality(high resolution & high statistics) spectroscopy plays a significant role

Reaction spectroscopy : From MeV to sub-MeV resolution-ray spectroscopy

１２１２Ｃ（Ｃ（＋＋，Ｋ，Ｋ＋＋）） 1212C spectra C spectra

by the SKS spectrometer at KEK 12 GeV PSby the SKS spectrometer at KEK 12 GeV PS

E3362 MeV(FWHM)

1.45 MeV(FWHM)

Hypernuclear mass spectra of Hypernuclear mass spectra of 8989Y, Y, 139139

La and La and 208208PbPb

by the (by the (++,K,K++) reaction) reaction

KEK SKS E140a

A A Hyperon in nuclear medium Hyperon in nuclear medium

The (e,e’KThe (e,e’K++) reaction for hypernuclear spectroscopy) reaction for hypernuclear spectroscopy

Proton to – Neutron rich hypernculei Large angular momentum transfer Spin-flip amplitude Higher energy resolution

Hyperon production reactions for spectroscopy

Z = 0 　 Z = -1 comment neutron to proton to

　　　 (+,K+) (-,K0) stretched, high-spin large momentum transfer

　　 In-flight (K-,-) in-flight (K-,0) substitutional

stopped (K-,-) stopped (K-,0) large momentum transfer (e,e'K0) (e,e'K+) spin-flip (K0) (,K+) & large momentum transfer

Comparison of the (KComparison of the (K--,,--),(),(++,K,K++), (e,e’K), (e,e’K++) reactions) reactions

q~100MeV/c l=0 substitutional statesS=0 J=0+

q~300MeV/c l=1,2 stretched statesS=0 J=1-,2+

q~300MeV/c l=1,2 stretched statesS=0,1 J=2-,3+

12

60

Rel

ativ

e S

tren

gth

1-

1-

1-+2-

1-

2- 3+

3++2+

2+

12C(e,e’K+)12B

12C(+,K+)12C

12C(-,-)12C

2+

0+

Ex(MeV)

FWHM 2MeV

FWHM 2MeV

FWHM 0.6MeV

0 6

12

1260

Physics goals of Jlab E01-011Physics goals of Jlab E01-011

• Hypernuclear structure up to medium-heavy mass region• 28

Si(e,e’K+) 28Al reaction and beyond

• N interaction in the p-shell region• 12C(e,e’K+)12

B reaction • Mirror symmetric hypernuclei 12

C vs. 12B

Explore hadronic many-body systems with strangenessthrough the reaction spectroscopy by the (e,e’K+) reaction

High-resolution and high hypernuclear yield rates are keys of the experiment

High-resolution 3-400 keVHigh yield rates > a few 100/day for 12

B ground state (comparable to the (+,K+) spectroscopy)

Immediate goals

New experiment designed based on the E89-009 experience

The E89-009 experimentThe E89-009 experiment

Beam Dump

Target

Electron beam

　　　　 Focal Plane( SSD + Hodoscope )

Splitter Magnet

K+

K+

QD

_D

0 1m

QD

_D

Side View

Top View

Target

SOS SpectrometerResolution 5 x 10-4

Solid angle 4 msr(with splitter)

ENGE SpectrometerResolution 2x10-4

(0.66 A@ 1.645 GeV/c)

-4

The first successful (e,e’K+)

hypernuclear spectroscopy 0 degree tagging method employed Low luminosity

K+ arm At very forward angle (2 degrees) Maximum hypernuclear production cross section

e’ arm At exactly zero degree Advantage : Maximum virtual photon flux Disadvantage : Huge backgrounds from Bremsstrahlung

e-

e’

K+

pK=1.2 GeV/c

pe=0.3GeV/cEe=1.8 GeV

E89-009 kinematicsE89-009 kinematics

Beam

Target nucleus

E=1.5 GeV

E89-009 resultsE89-009 results

Clean observation of 12B ground st

ate by the (e,e’K+) reaction About 600 keV(FWHM) resolution 0 degree tagging method employed

12C(e,e’K+)12B

p

p(e,e’K+) p(e,e’K+)

12C(e,e’K+) quasi-free

Accidental

s

What limited What limited the E89-009 hypernuclear physics experiment ?the E89-009 hypernuclear physics experiment ?

Energy resolution– Momentum resolution of the kaon spectrometer limited

hypernuclear mass resolution Hypernuclear yield rates

– Kaon spectrometer solid angle limited detection efficiency

– High count rates at the focal plane of the Enge spectrometer set the limit of maximum beam intensity

– High accidental background rate

A high-resolution large-solid-angle kaon spectrometer designed “Tilt method” proposed

E01-011 design principleE01-011 design principle

Optimize the experimental kinematics : Similar to E89-009

Avoid 0 degree Brems associated electrons in ENGE Avoid 0 degree positrons in the kaon arm

Maximize acceptance of the kaon spectrometer Higher energy resolution(down to a few 100 keV)

Tilt method

High resolution kaon spectrometer

Matching the momentum acceptances etc.

HKS overviewHKS overview

Side View

（）

Resolution 2 x 10 Solid angle 30 msr

BEAMQ1Q2

TOF

CHAMBERK

New QQD Spectrometer

0 1m

D

-4

1.4

GeV

/c

1.2

GeV

/c

1.0

GeV

/c

+

Beam Dump

Target

Electron Beam

　　　　 Focal Plane( SSD + Hodoscope )

Splitter

K+

K+

QD

_D

0 1m

QD

_D

Side View

Top View

Target

SOS SpectrometerResolution 5 x 10-4

Solid angle 6 msr(with splitter)

ENGE Spectrometer

Resolution 2x10-4

(1.645 GeV/c)

-

• Kaon spectrometerConfiguration QQD and horizontal bendCentral momentum 1.2 GeV/cMomentum acceptance 12.5 %Momentum resolution(p/p) 2 x 10-4(FWHM) (Beam spot size 0.1mm assumed)Solid angle 18 msr with the splitter

(30 msr without the splitter)Kaon detection angle Horizontal: 7 degrees

• Enge split-pole spectrometerCentral momentum 0.3 GeV/cMomentum acceptance 30 %Momentum resolution(p/p) 5 x 10-4(FWHM)Electron detection angle Horizontal: 0 degrees

Vertical : 4.5 degrees

Basic parameters of the E01-011 experimentBasic parameters of the E01-011 experiment

Beam condition Beam energy 1.8 GeV, Beam momentum stability < 1 x 10-4

Beam current 30 AGeneral configuration Splitter+Kaon spectrometer+Enge spectrometer

•Virtual Photon energy E1.5 GeV Elementary cross section:

constant from 1.1 to 1.5 GeVHigher E: Smaller momentum transfer Lower hypernuclear cross section

•Beam energy Ee ~ 1.8 GeVHigher Ee: Opens other kaon production channels

•e’ momentum Ee’~Ee-EGeV

Lower pe’: Better resolution

•Kaon momentum pK

E determines pK = 1.2 GeV/c ± 12.5 %Lower pK : Better resolution, particle ID Smaller K survival factor

Reaction Threshold(MeV)p KKKK*(892)

21 1.2 1.4 1.6 1.8

σto

tal(

b)

1.0

2.0

Eγ(GeV)

p(,K+) Total cross section

Phys. Lett. B 445, 20 (1998)M. Q. Tran et al.

General experimental conditionGeneral experimental condition

Ee’ = 0.285 GeV/c, e’ = 0, K = 0, K = 30 msr

Hypernuclear yield vs. electron energyHypernuclear yield vs. electron energy

Kaon momentum ( MeV/c )

Sur

viva

l rat

e of

kao

ns

5m 6m7m

10m 9m8m

Flight path 5-10m

K+ Angular distribution

Decay in flight

Correlation of kaon and electron momenta,Correlation of kaon and electron momenta,and hypernuclear massand hypernuclear mass

What is “Tilt method” ?What is “Tilt method” ?

Avoid Brems electron tail– The tail extends due to multi

ple scattering in the target Avoid Moeller scattering el

ectrons– Peak around 2.5 degrees for t

he beam energy around 1.8 GeV and momentum acceptance of 300 MeV+-30%

Allows us to run at 250 time higher luminocity

compared to E89-009.1.8 GeV electron beam on a 100mg/cm2 12C target

Moellerring

Bremselectron

Scattered electrons in the Enge acceptance

Optimization of the tilt angleOptimization of the tilt angle

Very forward peaked Long tail at the larger angle Brems electron angular distr

ibution is more forward peaked(dominated by multiple scattering in the target)

Virtual photon flux

The “Tilt method” requiresThe “Tilt method” requires

Optimization of “tilt” geometry Full tracking of scattered electrons

at the focal plane of the Enge spectrometer

– New tracking chamber Careful study of optics and

momentum reconstruction method – Simulation and calibration methods

Handling of higher singles rates– Pions, protons

Higher rejection efficiency against pions and protons

– Cerenkov counters– Better time resolution

For the kaon armFor the scattered electron arm

Optics of Electron Arm Optics of Electron Arm (Splitter + Split-Pole)(Splitter + Split-Pole)

Tilt 4.5o with respect to a virtual source point.

Optimize the figure of merit for S/A (e ~ 3o)

Maximize the average virtual photon acceptance (~1.5%) (HNSS ~ 35%)

Minimize the scattered electron rate (~3MHz) (HNSS ~ 200MHz)

Clean separation/blocking of the bremsstrahlung electrons

Improve momentum acceptance (~180 MeV/c) (HNSS ~ 120 MeV/c)

Full measurement of X, X’, Y and Y’ is needed (HNSS – X only)

Splitter + Enge energy resolutionSplitter + Enge energy resolution 5x105x10--44 (FWHM) (FWHM)

The HKS spectrometer system under constructionThe HKS spectrometer system under construction

Design specification of HKS

Configuration Q + Q + D

Maximum momentum 1.2 GeV/c

Dispersion 4.7 cm/%

Momentum resolution 2 10 -4 (FWHM)

Solid angle 30 msr w/o splitter18 msr w splitter

Flight path length 10 m

Angular acceptance 170 mrad vertical180 mrad horizontal

Momentum acceptance ±12.5 %

Maximum dipole field 1.5 T

Conductor normal

Transport StudyTransport Study

(R12=R34=0)

(R12=R44=0)

Horizontal Focusing & Vertical Focusing

Horizontal Focusing & Vertical Parallel

Chamber positionTwo DCs

50cm from 1st order focal plane(235cm downstream from D exit)

Momentum resolution = 270m p/p 210-4 FWHM

(SOS DC =160~180m)

Momentum resolution of HKSMomentum resolution of HKS

Solid angle of HKSSolid angle of HKS

QQD configuration flexible to adjust vertical and horizontal focusing

Horizontally thin Q1, Q2 design allows to minimize distance from the target without bumping to Enge magnet

%5.122.118 GeVovermsr

Expected performanceExpected performance

Resolution– 300 – 400 keV(FWHM) depending on target mass

Yield– More than factor of 50 gain over E89-009– Comparable to the present (+,K+) spectroscopy

Accidental background– 8 x 10-4/sec vs. 1.3 x 10-2/(100nb/sr)/sec per 100 keV bin ( an order of magnitude better than E89-009)– Can be further improved with the lower beam intensity

Singles ratesSingles rates

TargetHKS ENGE

e+

(Hz)+

(kHz)K+

(Hz)p

(kHz)e-

(MHz)-

(kHz)

12C - 800 340 280 2.6 2.8

28Si - 800 290 240 5.1 2.8

51V - 770 260 230 6.9 3.0

Ie = 30 A, 100 mg/cm2

High rejection efficiencies of Cerenkov counters against pions and protons required

• Scattered electron rate is considerably lower than E89-009• Pion and proton rates of the kaon arm are high

A comparison of the (A comparison of the (++,K,K++) reaction and ) reaction and the (e,e’Kthe (e,e’K++) reactions for the hypernuclear physics) reactions for the hypernuclear physics

(+,K+) (e,e’K+) (e,e’K+)/(+,K+)

SKS E89-009 RATIO E01-011/E89-009

Cross sections(12

Cgr or 12Bgr) 10 0.05 5x10-3

(b/sr) (,K+)

Target thickness 1 0.01 10-2 ~ 4.5 (g/cm2)

Beam intensity 106 109-10 103-4 ~ 45(particle/sec) (virtual photon)

K+ momentum 0.72 1.2 (GeV/c)

K+ solid angle ~ 60 % ~ 10 % 0.18 ~ 3coverage (%) (100 msr) (4 msr) K+ survival rate(%) ~ 0.4 ~ 0.4 1 ~ 0.8(Flight path) (5 m) (8 m)

Overall ~1 x 10-1~-2 ~ 100

SKS at KEK vs

HNSS at Jlab

Yield comparison of E01-011 and E89-009Yield comparison of E01-011 and E89-009

ItemE01-011

E89-009Gain factor

Virtual photon flux per

electron(x10-4)0.35 4 0.0875

Target thickness(mg/cm2) 100 22 4.5

Scattered electron momentum acceptance(MeV/c)

150 120 1.2

Kaon survival rate 0.35 0.4 0.88

Solid angle of K arm 18 4 4.5

Beam current(A) 30 0.66 45

Estimated yield (12Bgr:counts/h) 76

0.9(measured) 85

Expected hypernuclear production ratesExpected hypernuclear production ratesin the (e,e’Kin the (e,e’K++) reaction) reaction

TargetBeam Int

ensity

(A)

Counts per

100nb/sr/hour

Q-free K+ in

HKS(Hz)

12C 30 72 510

28Si 30 31 432

51V 30 16 342

TargetHypernucleu

s orbitalCross section

(nb/sr)

12C 12B

s1/2 112

p3/2 79

p1/2 45

28Si 28Al

s1/2 56

p3/2 95

p1/2 57

d5/2 131

d3/2 111

51V 51Ti

s1/2 18

p3/2 41

p1/2 26

d5/2 52

d3/2 48

1s1/2 16

f7/2 32

f5/2 38

Calculated hypernuclear cross sections

(Target thickness 100 mg/cm2 with HKS)

Hypernuclear production rates

Motoba

Expected energy resolutionExpected energy resolution

Item Contribution to the resolution(keV, FWHM)

Target C Si V Y

HKS momentum(2x10-4) 216

Beam momentum(<1x10-

4)< 180

Enge momentum(5x10-4) 150

K+ angle(mr 152 64 36 20

Target thickness(100mg/cm2) < 180 < 171 < 148 < 138

Overall < 400 < 370 < 350 < 350

2001.12.05.

Expected hypernuclear spectraExpected hypernuclear spectra

An installation plan of the new spectrometer system An installation plan of the new spectrometer system in Hall Cin Hall C

SummarySummary

New (e,e’K+) hypernuclear spectroscopy, E01-011, was proposed based on the experience of the pioneering E89-009 experiment at Jlab.

With the new “Tilt method” and with a new high-resolution kaon spectrometer(HKS), twice better resolution, more than an order of magnitude higher yield rates and an order of magnitude better signal to accidental ratios will be realized.

Design of the high-resolution kaon spectrometer (HKS) has been completed and construction of the spectrometer magnets and detector systems is under way supported by Monkasho.

The spectrometer system will be ready for installation by the beginning of 2003, although it is subject to Jlab scheduling.

HKS magnet detail designHKS magnet detail design

Dipole

Vacuum extension

Enge magnet

Q1 Q2

Splitter

Photon lineBeam

Expected accidental coincidence rateExpected accidental coincidence rate

Electron arm singles rate 2.6 MHzKaon singles rate 340 HzCoincidence time window 2 nsec ( Offline analysis )

Nacc = 1.8 /sec

At the beam current of 30 A, we expect

3H

4H,4

He 6He, 6

Li

7He, 7

Li, 7Be 9

Be

10Be,10

B 13C

hyperonNucleonAlpha

荷電対称ハイパー核とクラスター構造荷電対称ハイパー核とクラスター構造

　 Spin dependence of the (e,e’K+) reaction

Spin independent term f0

f0 spin nonflip

Spin dependent term ggo spin nonflipg1

g-1

spin flip

Natural parity states

Unnatural parity states

110 &1 gggf o

Elementary electroproduction of a hyperonElementary electroproduction of a hyperon

)cos()1(2)2cos(

''

3

kk

ILk

k

P

k

LL

k

T

keeE

Virtual photon fluxVirtual photon polarizationLongitudinal polarization

2

2

222

22

2tan/2(1

1

'

1)2/(

Q

Qq

E

EEQΓ

L

e

e

e

E = Ee - Ee’

Virtual photon becomes almost realat very forward electron scattering angle

Cross Section View of the Cross Section View of the HKSHKS

Photon line

Electron line

Basic experimental conditions of E89-Basic experimental conditions of E89-009009 Electron detection including 0 degrees

– greater photoproduction cross section of a hyperon– E > 1.2 GeV– E = Ee - Ee’, Ee = 1.645 GeV and Ee’~0.285 GeV

K+ detection at forward angle including 0 degrees– PK+ ~ 1.1 GeV/c– flight path as short as possible ~ 8 m

A splitter magnet for e’ and K+ separation at very forward angles

Beam intensity < 1A Target thickness ~ 10 mg/cm2

e’ (Degrees)

e’ vse’ (Degrees)

e’ is aimed about 3o . Virtual process is used in the optical simulation.

The long tails are from the features of tilted Split-pole and momentum dependent

Accepted e’ from virtual process

Collimator

Bremsstrahlung/Multiple scattered e’

- Bremsstrahlung separation

- Max. VPF

- Min. electron rate

Pe’ (%)

- Mom. acceptance ~ 180 MeV/c

- Average VPF acceptance: ~1.5%

RequirementProton rejection efficiency 410-

4of

Tohoku Univ.Florida Int. Univ.

two identical walls with =0.02

•Water Cherenkov n=1.33with and w/o WLS

•Lucite Cherenkov n=1.49with WLSw/o WLS(Total reflection type)

Prototypes were builtWaiting for R&D beamtime

HKS Water (or Lucite) Cherenkov counteHKS Water (or Lucite) Cherenkov counterr

Focal Plane Correlations Focal Plane Correlations Reconstruction from (XReconstruction from (Xff, X, Xff’, Y’, Yff and Y and Yff’) to (X’) to (Xtt’, X’, Xtt’, Y’, Ytt, Y, Ytt’ and ’ and

Xf vs Yf vs

Xf’ vs Yf’ vs