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)