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Hadron physics with GeV photons at SPring-8/LEPS II

M. Niiyama (Kyoto Univ.)

1. Introduction to SPring-8/LEPS I2. Physics motivation for LEPS II3. Status of LEPS II project4. Summary

Contents

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Super Photon Ring 8 GeV (SPring-8)

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b) Laser hutch

a) SPring-8 SR

c) Experimental hutch

Compton g-ray

Laser light

8 GeV electron Recoil electron

Tagging counter

CollisionBackward-Compton scattering

36m70m

Schematic View of LEPS I Facility

Backward-Compton Scattered Photon 8 GeV electrons in SPring-8

+ 351nm Ar laser (3.5eV ） 8W ~ 2.4 GeV photon + 266nm Solid+BBO (4.6eV ） 1W +3.0 GeV photon

Laser Power ~6 W (351nm) Photon Flux ~1 Mcps (2.4 GeV) E measured by tagging a recoil electron E>1.5 GeV, Eg ~10

MeV Laser linear polarization 95-100% ⇒ Highly polarized g beam

PWO measurement

tagged

Linear Polarization of g beam

photon energy [GeV] photon energy [MeV] 4

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1.5

Setup of LEPS I

Acceptance is limited in forward region

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PRC 79, 025210 (2009)

Q+ LEPS vs CLAS

LEPSforwardangle

CLASlarge angle

Physics motivation for LEPS II

PRL 96, 212001(2006)

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Proton rejection by using dE/dx in Start CounterPid = (Measured energy loss in SC) – (Expectation of KK) – (Half of expectation of proton)

KKp onlyKKn and part of KKp

Proton not tagged(Proton rejected) Proton tagged (e ~60%)

K+

K-

p

n

K+

K-

p

K+

K-

or

Preliminary

Preliminary

Signal enhancement is seen in proton rejected events. should be associated with gn reaction.

p/n ratio:1.6 before proton rejection0.6 after proton rejection

SC SCSC

Peak structure is seen in theM(nK+) for proton rejected events.

(Further more data will be taken at LEPS w/ larger acceptance for proton)

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TOF

Dipole Magnet　 0.7 　 Tesla

TargetStart Counter DC2 DC3

DC1SVTX

AC(n=1.03)

Photons

Strong angular dependence of production rate?

PRC 79, 025210 (2009)

Q+ LEPS vs CLAS

LEPSforwardangle

CLASlarge angle

Physics motivation for LEPS II

PRL 96, 212001(2006)

Angular dependence of production cross section may solve controversial situation. → 4p detector LEPS II.

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L(1405) JP=1/2-Mass spectrum of P-wave baryons

3/2-

1/2-

N(1520)

N(1535)

h+N 　 (1485)

3/2-

1/2-

Λ(1520)

Λ(1405)30 MeV

K+N 　 (1430)

Physics motivation for LEPS II

uud (or udd) uds

mas

s (M

eV)

Meson Baryon molecule picture has been proposed. (ex. Dalitz Phys. Rev.153 1967) 1) 3 quark or meson-baryon molecule? 2) If it is a Kbar N molecule, what is the binding energy?

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Higher mass of Kbar N component of L(1405)

D. Jido, et al. NPA725(2003)

M.Niiyama. PRC78Confirm by photoproduction.

V.K. Magas, E. Oset and A. Ramos, PRL 95

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Hyperon production with K*(892) Parity filter with linearly polarized photon

E g K*K

p

natural parity ex.P=(-1)J

K*(890),κ

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Hyperon production with K*(892) Parity filter with linearly polarized photon

E g K*K

p

unatural parity ex.P= -(-1)J

kaons

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Eg

K*K

p

p L(1405)S(1385)

K-

K*(890) Λ(1405) photoproduction with linearly polarized photon

T.Hyodo et. al, PLB593 High luminosity photon beam with Eg>2.4 GeV. Detect K*+→ K0s p+ 　→ ppp L(1405) → S0p0 → Lg gg S(1385) → Lp0 Large acceptance charged / photon detector

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Physics motivation for LEPS IIh, w, h’ meson in nuclear medium

Detection of scattered and decay particles simaltaneously

M.Kaskulov, H. Nagahiro, S. Hirenzaki, and E. OsetPRC75,064616

Magic momentum~2.7 GeV, 0 degree

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Recoil electron (Tagging)

LEP(GeV g -ray)

Laser roomInside SR bldg

30m long line

8 GeV electron

Laser

Outside SR bldg

Experimental bldg Beam dump

Backward Compton ScatteringSR ring

Schematic view of the LEPS2 facility

10 times high intensity ： Multi laser injection &Laser beam shaping

Large 4p spectrometer

Best emittance e beamÞ pencil photon beam

BGO Gamma counterTwo different exp. setup

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prism

UV lasers(355/266 nm)

expander

AR-coated mirrorw/ stepping motor

LEP intensity 107 cps for Eg<2.4 GeV beam (355 nm) 106 cps for Eg<2.9 GeV beam (266 nm) 4-laser injection [x4] Higher power CW lasers. 355 nm (for 2.4 GeV) 8 W16 W, 266 nm (for 2.9 GeV) 1 W2 W

[x2] Laser beam shaping with cylindrical expander

[x2]

10 um

400 umlaser

• Electron beam is horizontally wide. Þ BCS efficiency will be increased by elliptical laser beam.

Need large aperture of the laser injection line construct new BL chambers

High Beam Intensity

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Laser injection system

4 lasers in the laser hatch

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2011.12 SP8New experimental hatch

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2013.1.27 first beam (1.5-2.4 GeV~4Mcps w/ a single 24W laser)

Energy spectra of photon beam

w/ Laser

w/o Laser

mm

mm

Beam size in the experimental hatch

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1320 BGO crystals polar angle 24° ～ 146° ΔE=1.3% @ 1GeV

RPC-TOF wall Δt ~ 50 ps flight length 12m polar angle 0° ～ 5°

LH2, LD2 nuclear target Backward meson production from

this November.

g charged particletracker

targetg

g

BGO EGG+TOF

proton

BGO EGG

RPC-TOF

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Detector performance

π0 reconstructed with BGO-EGG.Further calibration is underway.

Time resolution of RPC-TOFRPC prototype

BGO EGG RPC prototype

1m

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Solenoid spectrometer2.22 m

g

TPC DC

g counter RPC

TOP

Magnet (BNL-E949)B=1 T p/p 〜 1-5% for q >7 degdetectors for

photon, charged particle

3σ K/p/p separation < 2.7 GeV using RPC, TOP, AC

Detector construction isunderwayPhysics run from 2015

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Summary Backward Compton g beam line for hadron physics.

Hadrons with s-quark. Recoilless production of light mesons in nucleus.

Highly polarized photon beam up to 3 GeV. x10 luminosity. ~10Mcps. Two different experimental setups.

BGO EGG + TOF Backward meson production from proton and nuclei

Solenoid spectrometer Θ+, Λ(1405)

First beam in Jan. 2013. BGO EGG experiment from this November!