Post on 30-Dec-2015
Hadron physics with meson photoproduction at LEPS/SPring-8
Tomoaki Hotta (RCNP, Osaka University)for
LEPS Collaboration
MESON 2010 CRACOW, POLAND
12 JUNE 2010
Outline
• LEPS (Laser-Electron Photon at SPring-8) Experiment
• Brief summary of the recent results• Some Selected topics
– Backward meson photoproduction– Photoproduction of (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
Compton backscattering: 8 GeV e- + UV Laser E = 1.5 GeV (tagged) – 2.4 GeV, 3.0 GeV
100 % polarized (direction can be changed easily).Intensity: 2x106/sec for Emax = 2.4 GeV
2x105/sec for Emax = 3.0 GeV
BM1 CR2BM2
Compton Scattering
Tagging counter (SSD + Plastic Scint.)
LEP
Laser
8-GeV e- storage ring
Scattering region E Tagging
UV Laser = 351 nm, 257 nm
Backscattered photon
Backward Compton : Small fraction of the low energy background Backward Compton : Small fraction of the low energy background
LEPS spectrometer (forward)
TOF
Dipole Magnet 0.7 Tesla
Target
Start Counter DC2 DC3
DC1SVTX
AC(n=1.03)
Charged particle spectrometer with forward acceptancePID from momentum and time-of-flight measurements
Photons
Mom
entu
m [G
eV/c
]
K/ separation
K++
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.
– PRC 80:052001R(‘09)– PLB 657:32(‘07)
• pentaquark– PRC79:025210(’09)– PRL 91:012002(‘03)
• 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– , (forward K+)
PRC73:035214(‘06), PRL91:092001(‘03)
– (forward K+) PRL 97:082003(‘06)– (1520) PRL 103:012001(‘09), PRL 104:172001(‘10)– (1385) PRL 102:012501(’09)– Backward PRC 76:042201(’07)– (1405), (1385) (with TPC) PRC 78:035202(‘08)
PRC79:025210(’09)γ
np p
n
K-
K+
detected
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
W ( √s ) = 1.9 – 2.3 GeV coscm = 1 ~ 0.6 (cm = 123o – 180o)
Resonance term+Born term
M
p pp, N*, *
s-channel
Forward Backward
meson exchange resonances Nucleon exchange
p
Mp
p, N*, *
u-channelt-channelM
pp
M
gNNM
gNN*M
….
Present data
Tree-level diagrams:
Motivation: Baryon resonances
Problems in the constituent quark models 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+*(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-N) N, N, ’N, N channels?
-
Backward Meson Production
Data
’
Missing Mass2 (GeV2/c4)
E= 2.3 - 2.4 GeVcoscm = 0.9
Fitting result
p p x
p p p p p p p p ’
Proton (Forward) : measuredMeson (Backward): Missing mass
u-channel, s-channel N, N* contributions
Results: Differential cross sections for photoproduction
LEPS data SAID -partial-wave analysis Eta-MAID - isobar model
Bump-like structure is seen above W=2.0 GeV
Jlab/CLAS data PRL89:222002(2002)
Bonn/ELSA data PRL94:012004(2005)
13
Evidence for resonances
CLAS : Evidence at W ~ 1850 MeV for S11(2090)
ELSA : Evidence at W ~ 2070 MeV for D15(2068) No for S11(2090)
PRL 89, 222002(2002)
PRL 94, 012004(2005)
BES : N* from J/ decay, J/ PRL 97, 062001(2006) N*(1440)
N*(1535)..
N*(1650)..
N*(2070)
Particle Data Group P11(2100) N)/tot = 0.61 in Pitt-ANL model
Phys. Rep. 328, 181(2000)
photoproduction photoproduction
14
’
Comparison of ’ and photoproductions
coscm = 0.8 ~ 0.7
PRC80052201R (‘10)
Selected Topics
2. Photoproduction of (1405)
E // B
1.5
LEPS detector setup with TPC
17
Solenoid Magnet
DipoleMagnet TPC
BufferCollimator 24Φ
Collimator 2 1 Φ
BeamBeam
TPC
Spectrometer TPC
p K++∓-n
The (1405) lineshape depends on the decay angles at its rest frame?
cos cos
19
0.8< cosK+< 1.0
t
Future prospects
LEPS2 ProjectPolarized HD Target
New Beamline (LEPS2)
8-GeV e8-GeV eDetectorDetector
UV LaserUV Laser
• Smaller (1/4) beam divergence
• Multiple (x4) laser injection• 8W 16W / laser tube• improved optics
• Much higher intensity beam x 10 or higher• Better tagged E resolution• Smaller beam size
• Larger-acceptance detector
~50% of the total budget has been approved.Construction of the beamline &detectors started!!~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 p/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)
• BNL-E949 Solenoid Magnet• Large Angle Coverage• P/P < 1.4% lab > 10 degree• TOF, E/x , 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 detector
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
Al wire
2.5cm
Polarized HD target
In-Beam Cryostat
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
W.Roberts PRC73,035215(2006)
NKKN
K
YK
N
res.-non
*
NK invariant mass (GeV)
BTZZCT BT
ZXC
Polarization Observables in
w/o
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 pentaquark.
• Backward meson photoproduction– evidence for N* contribution at w=2 GeV?
• Photoproduction of (1405)– line-shape analysis, (1405) vs *(1385) ratio
• Future Prospects– LEPS2: higher intensity beam + Large acceptance detector.– Pol. HD target
LEPS/LEPS2 CollaborationRCNP / Osaka Univ.Osaka Univ.Tohoku Univ.JASRI / SPring-8Kyoto Univ. Tohoku Univ. JAEAChiba Univ.Konan Univ. Wakayama Med. CollegeRIKENKEKUniv. of Tokyo
Nagoya Univ.Yamagata Univ.Miyazaki Univ.National Defense AcademyTokyo Institute of TechnologyAcademia 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)