1. Hadron physics with GeV photons at SPring-8/LEPS II
M. Niiyama (Kyoto Univ.)
Introduction to SPring-8/LEPS I
Physics motivation for LEPS II
Status of LEPS II project
Summary
Contents

2. Super Photon Ring 8 GeV (SPring-8)

3. Schematic View of LEPS I Facility
Backward-Compton scattering
8 GeV electron
Collision
Recoil electron
Tagging counter
36m
70m
a) SPring-8 SR
Laser light
b) Laser hutch
Compton g-ray
c) Experimental hutch

4. Backward-Compton Scattered Photon
8 GeV electrons in SPring-8
+ 351nm Ar laser (3.5eV） 8W ~ 2.4 GeV photon
+ 266nm Solid+BBO (4.6eV） 1W +3.0 GeV photon
Laser Power ~6 W (351nm)  Photon Flux ~1 Mcps (2.4 GeV)
E measured by tagging a recoil electron  E>1.5 GeV, E ~10 MeV
Laser linear polarization % ⇒ Highly polarized  beam
Linear Polarization of  beam
PWO measurement
tagged
photon energy [GeV]
photon energy [MeV]

5. Setup of LEPS I
Acceptance is limited in forward region
1.5

6. Physics motivation for LEPS II
Q+ LEPS vs CLAS
LEPS
forward
angle
CLAS
large angle
PRC 79, (2009)
PRL 96, (2006)

7. Proton rejection by using dE/dx in Start Counter
Pid = (Measured energy loss in SC)
– (Expectation of KK)
– (Half of expectation of proton) n K- K- K+ K+ SC p SC or SC K- K+
Proton not tagged
(Proton rejected)
Proton tagged (e ~60%)
Peak structure is seen in the
M(nK+) for proton rejected events.
(Further more data will be taken at LEPS
w/ larger acceptance for proton)
KKp only
KKn and part of KKp
Preliminary
Signal enhancement is seen in proton rejected events.
should be associated with gn reaction.
Preliminary
p/n ratio:
1.6 before proton rejection
0.6 after proton rejection

8. Physics motivation for LEPS II
Q+ LEPS vs CLAS
Strong angular dependence of production rate?
LEPS
forward
angle
CLAS
large angle
TOF
Dipole Magnet
　0.7　Tesla
Target
Start Counter
DC2
DC3
DC1
SVTX
AC(n=1.03)
Angular dependence of production cross section may solve controversial situation.
→ 4p detector LEPS II.
Photons
PRC 79, (2009)
PRL 96, (2006)

9. Physics motivation for LEPS II
L(1405) JP=1/2-
Mass spectrum of P-wave baryons
Meson Baryon molecule picture has been proposed.
(ex. Dalitz Phys. Rev )
1) 3 quark or meson-baryon molecule?
2) If it is a Kbar N molecule, what is the binding energy?
3/2-
1/2-
N(1520)
N(1535)
h+N　(1485)
3/2-
1/2-
Λ(1520)
Λ(1405)
30 MeV
K+N　(1430)
mass (MeV)
uud (or udd)
uds

10. Higher mass of Kbar N component of L(1405)
D. Jido, et al. NPA725(2003)
Confirm by photoproduction.
M.Niiyama. PRC78
V.K. Magas, E. Oset and A. Ramos, PRL 95

11. Hyperon production with K*(892)
Parity filter with linearly polarized photon E g K* K p
natural parity ex.
P=(-1)J
K*(890),κ

12. Hyperon production with K*(892)
Parity filter with linearly polarized photon K g K* E p
unatural parity ex.
P= -(-1)J
kaons

13. K*(890) Λ(1405) photoproduction with linearly polarized photon
T.Hyodo et. al, PLB593 g K K* E p
High luminosity photon beam with Eg>2.4 GeV.
Detect K*+→ K0s p+　→ ppp
L(1405) → S0p0 → Lg gg
S(1385) → Lp0
Large acceptance charged / photon detector K- p
L(1405)
S(1385)

14. Physics motivation for LEPS II
h, w, h’ meson in nuclear medium
Magic momentum
~2.7 GeV, 0 degree
M.Kaskulov, H. Nagahiro,
S. Hirenzaki, and E. Oset
PRC75,064616
Detection of scattered and decay particles simaltaneously

15. Schematic view of the LEPS2 facility
Recoil electron
(Tagging)
LEP
(GeV g -ray)
Laser room
Inside SR bldg
30m long line
8 GeV electron
Laser
Outside SR bldg
Experimental bldg
Beam dump
Backward Compton Scattering
SR ring
10 times high intensity：
Multi laser injection
&Laser beam shaping
Best emittance e beam
pencil photon beam
Two different exp. setup
BGO Gamma counter
Large 4p spectrometer

16. High Beam Intensity Need large aperture of the laser injection line
LEP intensity  107 cps for E<2.4 GeV beam (355 nm)
 106 cps for E<2.9 GeV beam (266 nm)
4-laser injection [x4]
Higher power CW lasers.
355 nm (for 2.4 GeV) 8 W16 W, 266 nm (for 2.9 GeV) 1 W2 W [x2]
Laser beam shaping with cylindrical expander [x2]
prism
UV lasers
(355/266 nm)
expander
AR-coated mirror
w/ stepping motor
10 um
400 um
laser
Electron beam is horizontally wide.
 BCS efficiency will be increased
by elliptical laser beam.
Need large aperture of the laser injection line
 construct new BL chambers

17. Laser injection system
4 lasers in the laser hatch

18. New experimental hatch
SP8

19. (1.5-2.4 GeV~4Mcps w/ a single 24W laser)
first beam
( GeV~4Mcps w/ a single 24W laser)
Energy spectra of photon beam
Beam size in the
experimental hatch
w/ Laser mm
w/o Laser

20. BGO EGG+TOF g g g RPC-TOF BGO EGG proton target charged particle
1320 BGO crystals
polar angle 24°～146°
1GeV
RPC-TOF wall
Δt ~ 50 ps
flight length 12m
polar angle 0°～5°
LH2, LD2 nuclear target
Backward meson production from this November. g
charged particle
tracker

21. Detector performance BGO EGG RPC prototype 1m RPC prototype
Time resolution of RPC-TOF
π0 reconstructed with BGO-EGG.
Further calibration is underway.

22. Solenoid spectrometer
Magnet (BNL-E949)
B=1 T
Dp/p 〜 1-5%
for q >7 deg
g counter
RPC
detectors for
photon, charged particle
3σ K/p/p separation
< 2.7 GeV
using RPC, TOP, AC
Detector construction is
underway
Physics run from 2015
TOP g
TPC DC

23. Summary Backward Compton g beam line for hadron physics.
Hadrons with s-quark.
Recoilless production of light mesons in nucleus.
Highly polarized photon beam up to 3 GeV.
x10 luminosity. ~10Mcps.
Two different experimental setups.
BGO EGG + TOF
Backward meson production from proton and nuclei
Solenoid spectrometer
Θ+, Λ(1405)
First beam in Jan
BGO EGG experiment from this November!