Transcript Hadronic Physics at LEPS/SPring-8

MESON 2010
CRACOW, POLAND
12 JUNE 2010
Hadron physics with meson
photoproduction at LEPS/SPring-8
Tomoaki Hotta (RCNP, Osaka University)
for
LEPS Collaboration
Outline
• LEPS (Laser-Electron Photon at SPring-8)
Experiment
• Brief summary of the recent results
• Some Selected topics
– Backward meson photoproduction
– Photoproduction of L(1405)
• Future prospects: LEPS2
Super Photon ring-8 GeV
SPring-8
• 8 GeV, 100 mA, e- ring
• Third-generation synchrotron radiation facility
• 62 beamlines
LEPS Beamline
Scattering
region
Compton Scatterin
g
BM1
BM2 CR2
Tagging counter
Eg Tagging
(SSD
+ Plastic Scint.)
Backscattered photon
LEP
Laser
8-GeV
e-
storage ring
UV Laser
l = 351 nm, 257 nm
Compton backscattering: 8 GeV e- + UV Laser
 Eg = 1.5 GeV (tagged) – 2.4 GeV, 3.0 GeV
~100 % polarized (direction can be changed easily).
Intensity: ~ 2x106/sec for Egmax = 2.4 GeV
~ 2x105/sec for Egmax = 3.0 GeV
Backward Compton : Small fraction of the low energy background
LEPS spectrometer (forward)
Charged particle spectrometer with forward acceptance
PID from momentum and time-of-flight measurements
SVTX
DC1
K/p separation
TOF
Momentum [GeV/c]
AC(n=1.03)
p+
Photons
K+
Target
Dipole Magnet
0.7 Tesla
Start Counter
DC2
DC3
Mass/Charge [GeV/c2]
P ~6 MeV/c for 1 GeV/c, TOF ~150 ps,
MASS ~30 MeV/c2 for 1 GeV/c Kaon
Summary of Results from LEPS
• Backward meson prod.
– h PRC 80:052001R(‘09)
– p0 PLB 657:32(‘07)
• Q+ pentaquark
– PRC79:025210(’09)
– PRL 91:012002(‘03)
• f photoproduction
– Proton target
PRL95:182001(‘05)
– Nuclear targets
PLB608:215(’05)
– D target (coherent)
PLB658:209(‘08)
– D target (indoherent)
PLB684:6 (‘10)
• Hyperon production
– L, S0 (forward K+)
PRC73:035214(‘06),
PRL91:092001(‘03)
– S- (forward K+)
PRL 97:082003(‘06)
– L(1520)
PRL 103:012001(‘09),
PRL 104:172001(‘10)
– S*-(1385)
PRL 102:012501(’09)
– Backward L
PRC 76:042201(’07)
– L(1405), S0(1385) (with TPC)
PRC 78:035202(‘08)
Q+
detected
K-
PRC79:025210(’09)
K+
γ
n
p
Q+
p
n
Peak at M(nK+) = 1.524 GeV/c2
Statistical Significance = 5.2 
Blind analysis for new data set
with x3 higher statistics is
underway
Experiment with TPC, LEPS2
Selected Topics
1. Backward meson photoproduction
Meson photoproduction
Tree-level diagrams:
g
t-channel
M
g
s-channel
g
M
M
p, N*, D*
p
p
Resonance term
+Born term
u-channel
p
meson exchange
p
p, N*, D*
resonances
Forward
p
p
gNNM
gNN*M
M
….
Nucleon
exchange
Backward
Present data
 W ( √s ) = 1.9 – 2.3 GeV
cosQcm = -1 ~ -0.6 (Qcm = 123o – 180o)
Motivation: Baryon resonances
Problems in the constituent quark models
• Mass-order-reverse problem for the lowest excited baryons.
S11(1535) uud(L=1) ½- should be the lowest
P11(1440) uud(n=1) ½+
L*(1405) uud(L=1) ½-
-
 introducing additional qq to solve the problem.
• Missing baryon resonances
The number of predicted states is much less than observed.
 coupling to (non-pN) rN, hN, h’N, wN channels?
Backward Meson Production
gp  p x
Proton (Forward) : measured
Meson (Backward): Missing mass
u-channel, s-channel
N, N* contributions
gp  p p p
gp  p p p p
gp  p p p p p
gp  p p0/h/h’/w
Data
Fitting result
p0
w/r
Eg = 2.3 - 2.4 GeV
cosQcm = -1 ~ -0.9
h’
f
h
Missing Mass2 (GeV2/c4)
Results: Differential cross sections
for h photoproduction
Jlab/CLAS data
LEPS data
PRL89:222002(2002)
Bonn/ELSA data
PRL94:012004(2005)
SAID -partial-wave analysis
Eta-MAID - isobar model
Bump-like structure is seen above W=2.0 GeV
Evidence for resonances
h photoproduction
CLAS : Evidence at W ~ 1850 MeV for S11(2090)
PRL 89, 222002(2002)
ELSA : Evidence at W ~ 2070 MeV for D15(2068)
PRL 94, 012004(2005)
No for S11(2090)
BES : N* from J/y decay, J/y  N*N  p NN
N*(1440)
N*(2070) PRL 97, 062001(2006)
N*(1535)..
N*(1650)..
Particle Data Group
P11(2100)
G(hN)/Gtot = 0.61
in Pitt-ANL model
Phys. Rep. 328, 181(2000)
13
Comparison of p0, h, h’ and w
photoproductions
h
h’
cosQcm = -0.8 ~ -0.7
PRC80
052201R (‘10)
w
p0
14
Selected Topics
2. Photoproduction of L(1405)
LEPS detector setup with TPC
1.5
g
E // B
TPC
Solenoid
Magnet
Buffer
Collimator 24Φ
Collimator
2１Φ
Dipole
Magnet
TPC
17
g p  K+ L(1405)  K+S p∓  K+ p+ p- n
Spectrometer TPC
cosq*p
The L(1405) lineshape
depends on the decay
angles at its rest frame?
cosq*p
19
0.8< cosq*K+< 1.0
S(1385)
S(1385)
t
L(1405)
L(1405)
Future prospects
LEPS2 Project
Polarized HD Target
New Beamline (LEPS2)
8-GeV e-
UV Laser
Detector
• Smaller (1/4)
• Multiple (x4) laser injection
beam divergence • 8W 16W / laser tube
• improved optics
• Much higher intensity beam
~ x 10 or higher
• Larger-acceptance detector
• Better tagged Eg resolution
• Smaller beam size
~50% of the total budget has been approved.
Construction of the beamline &detectors started!!
Design Concept of the Main detector
• Momentum resolution at forward angle Dp/p~1%.
 Good reaction tag.
• Large and smooth acceptance azimuthally 
Decay and polarization.
• Detection of decay product down to lower
momentum 100 MeV/c
• Detection of neutral particle (Photon)
LEPS2 detector
• BNL-E949 Solenoid Magnet
• Large Angle Coverage
• DP/P < 1.4% qlab > 10 degree
• TOF, DE/Dx , TOP, AC for PID
• Symmetric acceptance for positive
and negative particles
• Collaboration with Belle and J-PARC,
RIKEN
RPC, TOPcounter, DSSD, GEM-TPC…
Detailed design, R&D in progress
LEPS2 Schedule
• 2010 - 2011
–
–
–
–
Construction of Beamline
R&D of the detectors and DAQ
Construction of Experimental Hall
Transporting E949 magnet+detectors
• 2012
– Beam comissioning
– Construction of main detector
• 2013
– Start LEPS2 experiment
Polarized HD target
Polarize HD at 10 mK, 17 T at RCNP
 Transport to LEPS site
Longstanding R&D at Syracuse,
LEGS/BNL, and Orsay.
Polarized successfully.
Polarization measurement underway
2.5cm
In-Beam Cryostat
Al wire
Polarization Observables in
K +Y* 


+
K +Q 
 
g +N 
K+K +N
f + N 
 non - res. 
W.Roberts PRC73,035215(2006)


w/o Q+
T
Q+(1/2+)
BT
CZZ
BT
CZX
Q+(1/2-)
NK invariant mass (GeV)
Summary
• LEPS experiment
–
–
–
–
Linearly polarized real photon beam (~3 GeV)
Forward charged-particle spectrometer.
TPC+Solenoid, surrounding the target
Meson photproduction
• Production and decay of baryon resonances, Hyperon resonances,
and exotic Q+ pentaquark.
• Backward meson photoproduction
– evidence for N* contribution at w=2 GeV?
• Photoproduction of L(1405)
– line-shape analysis, L(1405) vs S*(1385) ratio
• Future Prospects
– LEPS2: higher intensity beam + Large acceptance detector.
– Pol. HD target
LEPS/LEPS2 Collaboration
RCNP / Osaka Univ.
Osaka Univ.
Tohoku Univ.
JASRI / SPring-8
Kyoto Univ.
Tohoku Univ.
JAEA
Chiba Univ.
Konan Univ.
Wakayama Med. College
RIKEN
KEK
Univ. of Tokyo
Nagoya Univ.
Yamagata Univ.
Miyazaki Univ.
National Defense Academy
Tokyo Institute of Technology
Academia Sinica (Taiwan)
Ohio Univ. (USA)
Pusan National Univ. (Korea)
Seoul National Univ. (Korea)
Univ. of Saskatchewan (Canada)
JINR Dubna (Russia)
Univ. of Connecticut (USA)
National Chung Cheng Univ. (Taiwan)