1

Elementary Reactions at

LEPS/SPring-8

J. K. AhnPusan National University

HYP2006@Mainz, Oct. 11, 2006

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Research Center for Nuclear Physics, Osaka University ： D.S. Ahn, M. Fujiwara, T. Hotta, Y. Kato, K. Kino, H. Kohri, Y. Maeda, N. Muramatsu, T. Nakano, M. Niiyama, T. Sawada, M. Sumihama, M. Uchida, M. Yosoi, T. Yorita, R.G.T. ZegersDepartment of Physics, Pusan National University ： J.K. Ahn, S.H. HwangSchool of Physics, Seoul National University ： H.C. BhangDepartment of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano, A. Titov Institute of Physics, Academia Sinica ： W.C. Chang, J.Y. Chen, B.R. Lin, D.S. OshuevJapan 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. Hicks, T. MibeDepartment of Physics, Kyoto University ： K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, 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. Iwata Department 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

The LEPS Collaboration

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Outline

1. Introduction2. LEPS Facility3. Selected Recent Results

4. Status of the + Study

5. LEPS2 Future Facility

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1

1.5

N

N

N

K

KN

(1232)

N(1535)

N(1650)

(1405)

(1520)

N(940)

N(1440)

N(1710)

N

NGeV

Resonances and Coupled Channels

(A. Hosaka)

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t-Channel Process

• dominates in the forward angles.• can access to a baryon below MB. • Linearly polarized photon as a

parity filter.

N BM

M’

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Key Items are

1.linearly polarized beam.

2.good forward acceptance.

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Compton-Backscattered Photon Beam

8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV ） maximum 2.4 GeV photons

E measured by tagging a recoil electron E>1.5 GeV, E ~10 MeVLaser Power ~6 W Photon Flux ~1 McpsLaser linear polarization 95-100% ⇒ Highly polarized beam

PWO measurement

tagged

Linear Polarization of beam

photon energy [GeV] photon energy [MeV]

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LEPS Spectrometer

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

Mo

men

tum

[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

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Photoproduction near threshold

Titov, Lee, Toki PR 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

//

// ⊥

⊥

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Differential Cross Sections at -|t|min

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

Pomeron +π/η exchange

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Polarization Observables

Decay Plane || Natural parity exchange (-1)J (Pomeron, Scalar glueball or mesons)

meson rest frame

Decay Plane Unnatural parity exchange -(-1)J

(Pseudoscalar mesons )

Relative contributions from natural, unnatural parity exchanges

Decay angular distribution of

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Decay Angular Distributions

-0.2 < t+|t|min <0. GeV2

K ＋ polar angle at φ rest frame K ＋ azimuthal angle relative to pol. vector

Contribution from Natural Parity Exchange is dominant.

T. Mibe et. al., PRL 95 (2005), 182001

Coherent D D Reaction

Coherent production from deuterons, iso-scalar target, where iso-vector -exchange is forbidden.

Stronger asymmetry

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and Photoproduction from p/d

LH2 data LD2 data

p(, K+) GeV/c2

0

(1520)

(1520)(1405)(1385)

(1405)0(1385)- (1385)

0, -

N(, K+) GeV/c2

• Hyperons are identified in the K+ missing-mass spectrum • Differential cross sections & photon beam asymmetry

R.G.T. Zegers et. al., PRL 91 (2003), 092001M. Sumihama et. al., PRC 73 (2006), 035214

New!

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Differential cross sections

W (GeV)

LEPS SAPHIR CLASResonance-like structure

W (GeV)Phys. Rev. C68, 058201 (2003)

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Beam asymmetry for and 0

K+K*-exchange (K*-exchange is dominant) by M. GuidalIsobar + Regge by T. Mart and C. Bennhold. Gent isobar model by T. Corthals

Positive sign data

nucl-th 0412097 / SNP2004

Phys. Rev. C68, 058201 (2003)

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- photoproduction from LD2

Differential cross sections Enhancement in K+0 relative to K+- around W=2 GeV P31 * ?

Beam Asymmetries• Large asymmetries in K+-

K* exchange in t-channel. • Large difference of

asymmetries in K+- and K+0 channels. Inclusion of * resonance ? Or inclusion of additional

effects ?

Blue : K+-

Green: K+0

Lines: Regge model

Kohri et. al., PRL 97 (2006) 082003

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The Nature of the (1405)

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Two poles near 1405 MeV

1426 + 16i (KN)

1390 + 66i ()

Jido-Oller-Oset-Ramos-Meissner, Nucl.Phys.A725, 181 (2003)

KN or quasi-bound state

KN ~ 8 x 8 = 1, 8, 8, 10, 10, 27

attractive repulsive

Two Poles near the (1405)

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Lineshape of the (1405)

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p K*(1405)

The first data will be taken next year.

• K- must be virtual because (1405) is lighter than pK-.

• K- exchange can be enhanced by selecting events where is perpendicular to K*.

z1=1390+66iz2=1426+16i 　

by Hyodo

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(1405) Photoproduction with TPC

(1

405

)

(1

520

)

)1405( +- and -+

E (200 V/cm)

B (2 Tesla)

beam

chargedparticle

target

electron drift

Momentum×charge [GeV/c]

dE

/dx

[arb

itra

ry u

nit

]

p

nK

K

Kp )1405(

Missing mass p ( , K+) (GeV/c2)

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u-Channel Process

• dominates in the backward angles (forward angles in terms of a nucleon).

• is sensitive to gNNM.

M

NgNNM

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Missing-Mass Distribution for (, p)

t (G

eV2 )

Missing mass(GeV/c2)

η´

η

ω

π0

cosθ

ω

Missing mass(GeV/c2)

η’peak is clearly identified 　　　 by requiring t < -0.6~9000 events in the 2001 data

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First Evidence from LEPS nK+K-

nPhys.Rev.Lett. 91 (2003) 012002

+

•Low statistics: but

•Tight cut: 85% of events are rejected by the f exclusion cut.

•Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections.

•Correction: Fermi motion correction is necessary.

4.6S

B 3.2

S

S B

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LEPS LD2 Runs

• Collected Data (LH2 and LD2 runs)

Dec.2000 – June 2001 LH2 50 mm ~5×1012 　　　　　　　 published the first resultMay 2002 – Apr 2003 LH2 150 mm ~1.4×1012

　　Oct. 2002 – June 2003 LD2 150 mm ~2×1012

• #neutrons × #photons in K ＋K － detection mode LD2 runs = 5mm-thick STC in short LH2 runs × ~5

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Search in d (1520)KN Reaction

• ＋ is identified by K －p missing mass from deuteron. ⇒ No Fermi correction is needed.

• K- n and pn final state interactions are suppressed.

• If ss(I=0) component of a is dominant in the reaction, the final state KN has I=0. (Lipkin)

pn

＋

K －

p

detected

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A Possible Reaction Mechanism

• + can be produced by re-scattering of K+.• K momentum spectrum is soft for forward going

(1520).

γ

p/nn/p

K+/K0

Missing Momentum

Formation momentum

LD2

Pmiss GeV/c

•LEPS acceptance has little overlap with CLAS acceptance.•t-channel K exchanged is possible and an exchanged kaon can be on-shell. A. Titov et. al., nucl-th/0607054, accepted for PRC

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Background Processes

• Quasi-free (1520) production is the major background.

• The effect can be estimated from the LH2 data.γ

pn

K+

n

• The other background processes which do not have a strong pK- invariant mass dependence can be removed by side-band subtraction.

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A. Titov et. al., nucl-th/0607054

Enhancement at Forward Angle

Theoretical prediction for forward peaking D

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K － p Missing-Mass Spectrum

MM d(,K － p) GeV/c2

sideband * sum

Cou

nts

/5

MeV

An Excess of Events is seen at 1.53 GeV and at 1.6 GeV above the background level.1.53-GeV peak: 5 statistical significance

pre

lim

inar

y

Normalization of * is obtained by fit in the region of MMd < 1.52 GeV.

No Structure in Sidebands!

+

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Is the peak really associated with *?

BG level 1/10 * 1/5

Total # of events 1 / 7

1.50 < M(K-p) < 1.54

1.518 < M(K-p) < 1.522

MMd(γ,K － p) GeV/c2

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Focusing on the + at LEPS

• Just started new data taking with LD2 target and a forward spectrometer.

• Photon beam intensity is twice with two 355nm lasers. • Aim at 10 times higher statistics

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The LEPS2 Future FacilityBackward Compton Scattering

a) SPring-8 SR ring

b) Laser hutch

c) Experimental hutch

8 GeV electron

Recoil electron (Tagging)

the BNL-E949 detector

5 m

GeV -rayInsidebuilding Outside

building

30m long line

（ LEPS 7.8m)

detector （ Tohoku U. ）Large decay spectrometerForward spectrometerNew DAQ system

Laser or re-injected X-ray

High intensity ： Multi-laser　　　　　　 LRNB, round-beam　 ~10 7 photons/s （ LEPS ~10 6 ）High energy ： Re-injection of　　　　　　 X-ray from undulator E< 7.5GeV (LEPS < 3GeV)modify ：

JASRI Acc. group

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LEPS2 Working Group

• Beam upgrade Energy --- Laser with short (>200nm), re-

injected Soft X-ray,, Compact accelerator, XFEL Intensity --- High power laser, Multi laser, LRNB --- Round beam

106 107 /sec

• Detector upgrade Scale & --- General-purpose 4 detector Flexibility --- Coincidence measurement of

charged particles and neutral particles (photons)

(e.g., 0) DAQ --- High speed for the minimum bias

trigger

Virtual laboratory : http://www.hadron.jp