Takashi NAKANO

(RCNP, Osaka University)

for the LEPS collaboration

Bryons’10 @ Osaka, December 9th, 2010

Highlights and Prospects

from

LEPS and LEPS2LEPS

2

LEPS CollaborationResearch Center for Nuclear Physics, Osaka University ： D.S. Ahn, M. Fujiwara, T. Hotta, Y. Kato, H. Kohri, Y. Maeda, T. Mibe, N. Muramatsu, T. Nakano, S.Y. Ryu, T. Sawada, M. Yosoi, T. YoritaDepartment of Physics, Pusan National University ： J.K. AhnSchool of Physics, Seoul National University ： H.C. BhangDepartment of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. AsanoInstitute of Physics, Academia Sinica ： W.C. Chang, J.Y. ChenJapan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： S. Date', H. Ejiri, N. Kumagai,

Y. Ohashi, H. Ohkuma, H. ToyokawaDepartment of Physics and Astronomy, Ohio University ： K. HicksDepartment of Physics, Kyoto University ： M. Niiyama, K. Imai, H. Fujimura, M. Miyabe, T. TsunemiDepartment of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. IwataDepartment of Physics, Osaka University ： S. Ajimura, K. Horie, M. Nomachi, A. Sakaguchi,

S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura RIKEN ： Y. NakatsugawaDepartment of Education, Gifu University ： M. Sumihama,

Laser Electron Photon beamline at SPring-8

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Backward-Compton Scattered Photon 8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV ）

maximum 2.4 GeV photon Laser Power ~6 W Photon Flux ~1 Mcps E measured by tagging a recoil electron E>1.5 GeV, E ~10 MeV Laser linear polarization 95-100% ⇒ Highly polarized beam

PWO measurement

tagged

Linear Polarization of beam

photon energy [GeV] photon energy [MeV]

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1.5

Only FWD spectrometer　　　　　　　 ±20°x ±10°

Setup of LEPS Detectors

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E // B

1.5

Setup of LEPS Detectors

Polarized HD target will be ready soon.Talk by YOSOI (P4)

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PID in LEPS Spectrometer

TOF

Dipole Magnet　 0.7 Tesla

Target

Start Counter DC2 DC3

DC1SVTX

AC(n=1.03)

Photons

Mo

men

tum

[G

eV/c

]

K/ separation

K++

Mass/Charge [GeV/c2]

P ~6　MeV/c　for　1　GeV/cTOF ~150　psMASS ~30　MeV/c2　for　1　GeV/c　Kaon

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Features of LEPS facility

• High linear polarization• Flat energy spectrum• Good forward acceptance• Good /K separation

• Linear polarization can be used to study spin-parity of exchanged particle in t-channel.

• Forward spectrometer is suitable for studying reactions near production threshold.

• Tagged photon energy region is close to ss thresholds.

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(1020)

Diffractive Photoproduction of vector meson

• Vector Meson Dominance

• Meson Exchange

• Pomeron Exchange

N

N

(~ss)

q

_q

_qq =

Dominant at low energies

Slowly increasing with energy

uud

Pomeron

2nd Pomeron

Scattering amplitude

Total crosssection

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photoproduction near production threshold

Titov,　Lee,　Toki　Phys.Rev　C59(1999)　2993

P2 : 2nd pomeron ~ 0+ glueball (Nakano, Toki (1998))

Data from: SLAC('73), Bonn(’74),DESY(’78)

Decay　asymmetry

helps　to　disentangle　relative　contributions

unn

unn

//

// ⊥

⊥

Polarization observables with linearly polarized photon

Decay Plane // natural parity exchange (-1)J (Pomeron, Scalar Glueball, Scalar mesons)

Polarizationvector of

K+

K+

K-

meson rest frame

Decay Plane unnatural parity exchange -(-1)J

(Pseudoscalar mesons )

Relative contributions from natural, unnatural parity exchanges

Decay angular distribution of meson

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Differential cross section at t=-|t|min

Phys. Rev. Lett. 95, 182001 (2005)

Bump is confirmed by CLAS.Talk by DEY (EM1)

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Decay angular distribution

2.173<E<2.373　GeV

1.973<E<2.173　GeV

cos

WW

Curves　are　fit　to　the　data.

No　energy　dependence,　except　for　　distribution.Natural　parity　exchange　is　dominant.

PRL104,172001 (2010)PRL95,182001 (2005)

pp )1520( Kp

Bump structures around 2 GeV in some reactions

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(1116)

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Identification of Hyperon From p/d in LEPS: Missing Mass of K+

LH2 data

p(, K+) GeV/c2

0

(1520)(1405)(1385)

LD2 data

(1520)

(1405)0(1385)- (1385)

0, -

N(, K+) GeV/c2

spectrometer

K+

Y

p/d

Acceptance of close to 1. CM

K cos

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Born Diagrams for Hyperon Photoproduction

s-channel

t-channel

u-channel

contact term

For gauge invariance.KNg NKg *

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Photon Beam Asymmetry

K+K*-exchange by M. Guidal.Isobar + Regge by T. Mart and C. Bennhold. Gent isobar model by T. Corthals

0(1193)(1116)

Larger contribution from t-channel K* exchange.

M. Sumihama et al. (LEPS Collaboration), PRC 73, 035214 (2006)

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S. Ozaki, H. Naghiro, A. Hosaka, PLB 665, 178 (2008)

SU(3)

Wess–Zumino–Witten term

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(1520)

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Photoproduction of Λ(1520) from p/d KpKKp )1520(

0 (1520)n K p K

N. Muramatsu et al. (LEPS Collaboration), PRL 103, 012001 (2009)

( ) ( )

( ) ( )

pd

pn

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A Large Isospin Asymmetry in * Production

A. Hosaka, Workshop of “Challenge to New Exotic Hadrons with Heavy Quarks”.S.i. Nam, A. Hosaka, and H.-Ch. Kim,Phys. Rev. D, 71, 114012 (2005)

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p p

M

p, N*,,,

Backward mesonproductions

gMpp

in high energy region

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Missing mass spectra

Data

’

Missing Mass2 (GeV2/c4)

E= 2.3 - 2.4 GeVcoscm = 0.9

Fitting result

p p x

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Differential cross sections for photoproduction

LEPS data SAID -partial-wave analysis Eta-MAID - isobar model

I = ½, small J, strong coupling to heavy may contain large ss component

Jlab/CLAS dataBonn/ELSA data

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+(1530)

uudds

Quasi-free production of + and (1520)

np p

n

K-

K+

pn n

p

K+

K-

•Both reactions are quasi-free processes.

•Fermi-motion should be corrected.

•Existence of a spectator nucleon characterize both reactions.

detected

spectator

E=1.5~2.4 GeV

Data was taken in 2002-2003.

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Minimum Momentum Spectator Approximation

γ

d

K-

K+

Nucleon fromdecay or scattering

Spectatornucleon

p n

4 momentum of pn system

Mpn and ptot

|pCM| and vpn

vpn

We know

Direction of pCM is assumed so that the spectator can have the minimum momentum for given |pCM| and vCM.

at rest

tagged detected

Results of (1520) analysisSimple (,K+) missing mass: No correction on Fermi motion effect.

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Proton is assumed to be stopped in the Lab system.

Results of (1520) analysis

(-2lnL) =55.1 for ndf=2 7.1

Structure with a width less than 30 MeV/c2 requires a physics process or fluctuation.

The total cross section is ~1 b, which is consistent with the LAMP2 measurements.

10Prob(7.1 ) 1.2 10

Simple (,K+) missing mass: No correction on Fermi motion effect.pK- invariant mass with MMSA: Fermi motion effect corrected.

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Results of analysisSimple (,K-) missing mass: No correction on Fermi motion effect.

Neutron is assumed to be stopped in the Lab system.

Results of analysis

(-2lnL) =31.1 for ndf=2 5.2 7Prob(5.2 ) 2 10

Simple (,K-) missing mass: No correction on Fermi motion effect.nK+ invariant mass with MMSA: Fermi motion effect corrected.

“We DO NOT estimate the statistical significance by counting the number of events above background level”

2Peak position: 1.527 0.002 GeV/

Signal yeild: 116 21 events

Differential cross-section: 12 2 nb/sr

c

PRC 79, 025210 (2009)

Reflection of (1520)

LARGE fluctuations are required if the peak is not real.

High statistics data was already collected in 2006-2007 with the same experimental setup.

Blind analysis is under way to check the Θ+ peak

Next step

The result will tell us if the peak structure is due to statistical fluctuations or not unambiguously.

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LEPS2

LEPS2 Project at SPring-8

Backward Compton Scattering

Experimental hutch

8 GeV electron

Recoil electron (Tagging)

Better divergence beamcollimated photon beamDifferent focus points for multi CW laser injection

GeV -rayInsidebuilding Outside

building

30m long line

（ LEPS 7.8m)

Large 4spectrometer based on BNL-E949 detector system.Better resolutions are expected.New DAQ system will be adopted.

Laser orre-injected X-ray

High intensity ： Multi (ex. 4) laser injection w/ large aperture beam-line & Laser beam shaping　 ~10 7 photons/s （ LEPS ~10 6 ）High energy ： Re-injection of　　　 　　　 X-ray from undulator E < 7.5GeV (LEPS < 3GeV)

Detail will be given by YOSOI (P4)

Main Detector Setup

Target cell

CFRPSSD

E949 Solenoid Magnet size: Φ5m×3.5m weight: ~400 t Field: 1.0 T (1.1 MW at 4400 A)

Target and Vertex detector

Construction of LEPS2 has been started!Please join us!!

Summary1. LEPS is a Backward Compton gamma beam facility at SPring-8.

GeV beam with high polarization is available.

2. LEPS detector has a good forward angle acceptance which is complimentary to the CLAS acceptance.

3. A bump structure is observed inphoto-production near threshold.

4. Strong isospin dependence was observed in (1520) photo-production.

5. Evidence for new baryon resonance in photo-production, which may contain ss component.

6 + peak was observed in the nK+ invariant mass at 1.53 GeV/c2. New data set with 3 times more statistics was taken. Blind analysis is under way.

7. LEPS2 project is ongoing: 10 times stronger beam & 4 coverage.