Transcript Status of SPring-8 LEP project and the GDH experiment

Nov. 19. 2002
Japan-Italy Sympo.
Miyazaki
GDH sum rule experiment
at SPring-8 LEPS
Takahiro Iwata
Yamagata Univ.
GDH sum rule
Overview of the SPring-8 LEPS facility
Plan of the GDH experiment at SPring-8
GDH sum rule
• Gerasimov-Drell-Hearn sum rule
 3/ 2     1/ 2   2 2 2
  d



mN


I GDH
 : photon energy
  : pion threshold energy
 : anomalous magnetic moment
 p  ( p  N ) /  N  1.79
 n  ( n  0) /  N  1.91
I GDH ,p  205b, I GDH ,n  233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（SPIN200０)
Forward Compton Amplitude
f     [ f1      i  if 2        i ]i
†
f

f

f
spin non-flip
spin flip
ASSUMPTION:
General Principles
spin flip amplitude
vanishes at infinite energy
Lorenz invariance,
gauge invariance,
causality, relativity,
crossing symmetry,
analytic amplitude
lim f 2    0
 
optical theorem
mf 2   
nucleon spin structure

 3/ 2     1/ 2   
8
unsubtracted dipersion relation
  mf 2  
ef 2    P  2
d 
2

 0  
low energy theorem
GDH sum rule
f
 2
f 2    2


  0 2m2
 3/ 2     1/ 2   2 2 2


 d

mN


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
against 8GeV electrons in the storage ring
• Laser Electron Photon at SPring-8 : LEPS
• Photon energy : Emax.  Ee2
 Experiments in higher energy regions

Polarized photons(linear & circular) available with
a polarized laser
 Polarization experiments
Polarization
Layout of the Beam Line
Interaction
Region
Laser Hutch
(36m from I.R.)
Experimental
Hutch
(69mfrom I.R.)
Laser System
Gamma
laser
Energy Spectrum
measured by PWO
1600
1400
BCS
Intensity(typ.
)
2.5x106
1200
1000
800
600
400
200
0
background
8 GeV
05
0
100
150
200
250
300
350
400
05
0
100
150
200
250
300
350
400
600
500
400
300
200
100
0
2.4 GeV
LEPS Spectrometer
TOF
wall
Dipole Magnet
(0.7 T)
Liquid Hydrogen
Target (50mm thick)
beam
DCｓ
Aerogel
Cerenkov
(n=1.03)


•
f photo-production;

further study with pol. target
（ss-content in nucleon)
K+ photo-production; beam asymmetry
L(1405) photo-production
– further study by TPC to identify the
decay products (S)
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 Setup
Polarized Target
Large Angle
Detector
Forward
Detector
(TOF wall)
geometrical acceptance
97% of 4
Gas Cerenkov
Inner
Detector
Gamma
beam
PT-Magnet
Inner Gamma Detector
Large Angle
Gamma Detector
(lead-plastic)
Forward Gamma
Detector
(lead-glass, PWO)
1m
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( CH ) foils(t=100μm )

2






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%
PT-Magnet
Superconducting
Solenoid
B=2.5T(max=2.6T)
DB/B~130ppm
(f20x50mm)
warm bore: 60cm
length: 100cm
cooled 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
lead-plastic-scintillator
Sandwich detector
clear fiber
3m long
to PMT
WLS fiber
d=1mm
18 sampling layers
(lead:1.6mm, Scin.:8mm)
total thickness~5X0
Test of Prototype
electron beam
simulation
photon beam
simulation
Eff. > 90%
for E>50MeV
the results published:
NIM A 481(2002) 188-199
Inner Detector
•
•
•
•
Charged particle detection
Surrounding target
Plastic-scintillator, 25mm thick
10 segments x 8 sectors
– 80 modules
– neighboring segments rotated by
half a sector
• Readout: WLS fiber(d=1mm)
+ clear fiber(3m long)
• 4-dimensional readout
• PMT: 16CH multi-anode-PMT
• Melbourne group made
preliminary study
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
Test Module
300 MeV electron
<Np.e.>=6.7
thre.=1p.e.
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
established.
• 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.