GDH 　 sum rule experiment at SPring-8 　 LEPS

Nov. 19. 2002Japan-Italy Sympo. Miyazaki

Takahiro IwataYamagata Univ.

GDH sum ruleOverview of the SPring-8 LEPS facilityPlan of the GDH experiment at SPring-8

GDH sum rule• Gerasimov-Drell-Hearn sum rule

23/ 2 1/ 2 22

GDHN

I dm

p p

n n

,p ,

: photon energy: pion threshold energy

: anomalous magnetic moment( ) / 1.79

( 0) / 1.91

205 , 233

N N

N

GDH GDH nI b I b

•S.B.Gerasimov: Yad.Fiz. 2 (1965) 598 / Sov. J. Nucl. Phys. 2, 430(1966)•S.D.Drell and A.C.Hearn: Phys.Rev. Lett. 16, 430 (1966) •M.Hosoda and K.Yamamoto: Prog. Theor Phys. 36 (1966) No.2, Lett. to Editor 425 　　“ DHGHY sum rule” 　　　　　　 called by Jaffe （ SPIN200 ０ )

spin non-flip spin fli

†2

p

1

Forward Compton Amplitud

[ ]

e

f f i if if f if

22 2 2

0

unsubtracted dipersion relation

mfef P d

2lim 0f

2 3/ 2 1/ 2

optical theorem

8mf

222 2

0

low energy theo

2

rem

ff

m

23/ 2 1/ 2 22

N

dm

GDH sum rule

ASSUMPTION:spin flip amplitudevanishes at infinite energy

General Principles

Lorenz invariance, gauge invariance, causality, relativity, crossing symmetry, analytic amplitude

nucleon spin structure

SPring-8 (Super Photon ring-8 GeV)

• Third-generation synchrotron radiation facility

Circumference: 1436m

• Electron Energy: 8GeV

• Max. beam current: 100mA

• 62 beam lines

• LEPS beam line for high energy nuclear physics (RCNP beam line)

LEPS Beam Line• Backward Compton scattering of a laser light agai

nst 8GeV electrons in the storage ring• Laser Electron Photon at SPring-8 : LEPS• Photon energy :

Experiments in higher energy regions Polarized photons(linear & circular) available with

a polarized laser Polarization experiments

2.maxeEE

Polarization

Layout of the Beam Line

Laser Hutch(36m from I.R.)Interaction

RegionExperimental Hutch (69mfrom I.R.)

Laser System

laser

Gamma

Energy Spectrum

2.4 GeV

8 GeV

0

200

400

600

800

1000

1200

1400

1600

05 0 100 150 200 250 300 350 400

0

100

200

300

400

500

600

05 0 100 150 200 250 300 350 400

BCS

background

measured by PWO

Intensity(typ.)

2.5x106 　　

LEPS SpectrometerDipole Magnet (0.7 T)

Liquid HydrogenTarget (50mm thick)

TOFwall

AerogelCerenkov(n=1.03)

DC ｓ

beam

photo-production; further study with pol. target

　　（ ss-content in nucleon) K+ photo-production; beam asymmetry

• (1405) photo-production

– further study by TPC 　 to identify the decay products ()

GDH experiment at SPring-8

• Study of the GDH sum rule for proton (measurement of helicity dependent photo-absorption cross-sections)

• Approved in Oct. 2001(QPAC of RCNP)• Energy region: 1.8 ~ 2.8 GeV• Energy settings

– 1st phase: Emax=2.4GeV (λ=351nm, 1W)• 1.8<E<2.4GeV, I=106/s(full spectrum), <Pol.>=85%

– 2nd phase: Emax=2.8GeV (λ=275nm, 0.3W)• 2.3< E <2.8GeV, I=105/s(full spectrum), <Pol.>=80%

• Polarized polyethylene target • 4pi-detector system

SP8-GDH collaboration

• Yamagata Univ. T.Iwata, H.Yoshida, Y.Tajima, S.Kato 、　　　　　　　　　　　　　　 M.Moriya

• Nagoya Univ. N.Horikawa, I.Daito, S.Fukui, S.Hasegawa,　　　　　　　　　　　　 T.Kobayashi• Miyazaki Univ. T.Hasegawa, T.Mastuda, M.Iio, Y.Toi, R.Akashi• Melbourne Univ. M.Thompson, R.Rassool, M.Geso, L.Smith• UCLA G.Igo, S.Trentalange, V.Ghazikanian• University Bonn D.Menze• CUA F.Klein• KEK S.Ishimoto• SPring-8 Y.Ohashi

SP8-GDH SetupForward Detector(TOF wall)

InnerDetector

Gas Cerenkov

PT-Magnet

Polarized Target

Inner Gamma Detector

Gamma beam

Large AngleDetector

Forward GammaDetector(lead-glass, PWO)

Large AngleGamma Detector(lead-plastic)

1 m

geometrical acceptance97% of 4

Polarized Target for SP8-GDH Dynamic Nuclear Polarization(DNP) technique

microwave irradiation at low temperature(100mK) and high magnetic field(2.5T)

polarization reversal by change of microwave frequency

Target material stack of polyethylene(　　 ) foils(t=100μm )

new material developed by Nagoya Group target preparation at room temperature precise evaluation of thickness reducing systematic errors efficient cooling by foil shape

Target size: d=20mm, l=50mm, Polarization: P>60%

2CH

PT-Magnet

SuperconductingSolenoidB=2.5T(max=2.6T)B/B~130ppm(20x50mm)warm bore: 60cmlength: 100cmcooled by cryocooler(GM-refrigerator) no need of lid. He

KEK Dilution Cryostat

• Top part(still, heat-exchanger, mixing-chamber) to be modified• beam pipe to be rearranged(MW guide removed)

– diameter of the beam pipe is 24mm• beam size x: 40mm need an active collimator

Inner Gamma Detector

to PMT

clear fiber3m long

WLS fiberd=1mm

lead-plastic-scintillatorSandwich detector

18 sampling layers(lead:1.6mm, Scin.:8mm)total thickness~5X0

Test of Prototype

Eff. > 90%for EMeV

electron beam

photon beam

simulation

simulation

the results published:NIM A 481(2002) 188-199

• Charged particle detection• Surrounding target• Plastic-scintillator, 25mm thick• 10 segments x 8 sectors

– 80 modules– neighboring segments rotated by h

alf a sector

• Readout: WLS fiber(d=1mm) + clear fiber(3m long)• 4-dimensional readout• PMT: 16CH multi-anode-PMT• Melbourne group made prelimin

ary study

Inner Detector

40cm

Gas Cerenkov Counter

• Basic tests have been done by Nagoya group– Radiator: 90cm CO2 1atm

• n=1.00043(thre.=4.9GeV/c for pi, 17.5MeV/c for e)

– Eff. > 99.8% for a single electron track at 300MeV

• suppression of shower: 10-4

• Miyazaki group will construct the final version

300 MeV electron

<Np.e.>=6.7 thre.=1p.e.

Test Module

Status and time schedule

• Status– R&D in progress

– lack of budget for construction

• Possible time schedule– 2003 July, Aug.

Installation of detectors and pol. target

– 2003 Sep., tuning detectors

– 2003 Oct.,Nov., data taking(1st phase)

– 2004 Jan. Feb., data taking(2nd phase)

– 2004~2005 data taking with pol. deuteron target

Summary• The polarized photon beam facility at SPring8 has been es

tablished.

• The experiments with the common spectrometer are currently running. They are giving interesting results.

• The GDH sum 　 rule experiment at SPring-8 aims at the study of the GDH sum rule for proton in the energy region from 1.8 GeV to 2.8GeV.

• Preparation of the experiment is in progress although we have serious budget problem.

• Possible run time is from Oct. 2003.