Hadron physics with GeV photons at SPring-8/LEPS II
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Transcript Hadron physics with GeV photons at SPring-8/LEPS II
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 W16 W, 266 nm (for 2.9 GeV) 1 W2 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