Hadron physics with GeV photons at
SPring-8/LEPS II
M. Niiyama (Kyoto Univ.)
Contents
1.
2.
3.
4.
Introduction to SPring-8/LEPS I
Physics motivation for LEPS II
Status of LEPS II project
Summary
1
Super Photon Ring 8 GeV (SPring-8)
2
Schematic View of LEPS I Facility
8 GeV electron
Backward-Compton
Recoil electron
Collision
scattering
Tagging counter
36m
a) SPring-8 SR
b) Laser hutch
70m
Laser light
Compton g-ray
c) Experimental hutch
3
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)
Eg measured by tagging a recoil electron  Eg>1.5 GeV, Eg ~10 MeV
Laser linear polarization 95-100% ⇒ Highly polarized g beam
Linear Polarization of g beam
PWO measurement
tagged
photon energy [GeV]
photon energy [MeV]
4
Setup of LEPS I
1.5
Acceptance is limited in forward region
5
Physics motivation for LEPS II
Q+ LEPS vs CLAS
LEPS
forward
angle
PRC 79, 025210 (2009)
CLAS
large
angle
PRL 96, 212001(2006)
6
Proton rejection by using dE/dx in Start Counter
p
n
K-
K-
K+
SC
Pid = (Measured energy loss in SC)
– (Expectation of KK)
– (Half of expectation of proton)
K+
or
SC
SC
p
KK+
Proton not tagged
Proton tagged (e ~60%)
(Proton rejected)
Peak structure is seen in the
KKn and partM(nK+)
of KKp for proton rejected events.KKp only
Signal enhancement is
seen in data
proton will
rejected
(Further more
be taken
w/ larger events.
acceptance
for proton)
should be associated
with gn reaction.
at LEPS
p/n ratio:
1.6 before proton rejection
0.6 after proton rejection
7
Physics motivation for LEPS II
Q+ LEPS vs CLAS
Strong angular dependence of production rate?
LEPS
forward
angle
SVTX DC1
TOF
AC(n=1.03)
CLAS
large
angle
Angular dependence of production cross section
Photonsmay solve controversial situation.
→ 4p detector LEPS II.
Target
Dipole Magnet
Start Counter 0.7 Tesla DC2 DC3
PRC 79, 025210 (2009)
PRL 96, 212001(2006)
8
Physics motivation for LEPS II
L(1405) JP=1/2mass (MeV)
Mass spectrum of P-wave baryons
Meson
Baryon molecule
been proposed.
1/23/2Λ(1520)
N(1535)picture has
(ex. Dalitz Phys. Rev.153 1967)
N(1520)
1) -3 quark or meson-baryon
molecule?
3/2
2) If it is a Kbar N molecule, what is the binding energy?
h+N (1485)
1/2-
uud (or udd)
30 MeV
K+N (1430)
Λ(1405)
uds
9
Higher mass of Kbar N component of L(1405)
D. Jido, et al.
NPA725(2003)
Confirm by photoproduction.
V.K. Magas, E. Oset and A. Ramos, PRL 95
M.Niiyama. PRC78
10
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
11
Hyperon production with K*(892)
 Parity
filter with linearly polarized photon
E
g
K
K*
p
unatural parity ex.
P= -(-1)J
kaons
12
K*(890) Λ(1405) photoproduction
with linearly polarized photon
g
E
K
K*
p
High luminosity photon beam with Eg>2.4
GeV.
T.Hyodo et. al, PLB593
+  ppp
Detect
K*+→ K0s pKL(1405) → S0p0 → Lg gg
S(1385) → Lp0
Large acceptance charged / photon detector
p
L(1405)
S(1385)
13
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
14
Schematic view of the LEPS2 facility
Backward Compton Scattering
10 times high intensity：
8 GeV electron
Multi laser injection
Recoil electron &Laser beam shaping
(Tagging)
Laser
LEP
(GeV g -ray)
Best emittance e beam
 pencil photon beam
Two different exp. setup
BGO Gamma counter
Beam dump
Large 4p spectrometer
15
High Beam Intensity



LEP intensity  107 cps for Eg<2.4 GeV beam (355 nm)
 106 cps for Eg<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]
UV lasers
(355/266 nm)
400 um
laser
10 um
pris
m
expander
AR-coated mirror
w/ stepping motor
• 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
16
Laser injection system
4 lasers in the laser hatch
17
New experimental hatch
2011.12 SP8
18
2013.1.27 first beam
(1.5-2.4 GeV~4Mcps w/ a single 24W laser)
Energy spectra of photon beam
w/ Laser
mm
Beam size in the
experimental hatch
w/o Laser
mm
19
BGO EGG+TOF
RPC-TOF
BGO EGG
proton
target
g
g
g
charged particle
tracker

1320 BGO crystals



polar angle 24°～146°
ΔE=1.3% @ 1GeV
RPC-TOF wall
Δt ~ 50 ps
flight length 12m
 polar angle 0°～5°



LH2, LD2 nuclear target

Backward meson production
from this November.
20
Detector performance
BGO EGG
RPC prototype
1m
RPC prototype
Time resolution of RPC-TOF
π0 reconstructed with
BGO-EGG.
Further calibration is
underway.
21
Solenoid spectrometer
2.22 m
g counter
RPC
TOP
Magnet (BNL-E949)
B=1 T
p/p 〜 1-5%
for q >7 deg
detectors for
photon, charged particle
3σ K/p/p separation
< 2.7 GeV
using RPC, TOP, AC
g
TPC
DC
Detector construction is
underway
Physics run from 2015
22
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. 2013.
BGO EGG experiment from this November!
23