Wen-Chen Chang

Outline• Laser-Electron Photon from Synchrotron facility.• Uniqueness of SPring-8 LEPS experiment.

– Vector Meson Photo-Production near production threshold.

– Good polarization of photon beam.

– Ability of measuring the single and double polarization observables.

• Status of SPring-8 experiment.– Detector configurations and performance.

– Run summary and preliminary results.

• New Detector Upgrade and Physics proposals.– Time-Projection Chamber: Medium effect of vector mesons production in nuclei.

– Gamma detector: Search of resonance with 2 reconstruction.

– Polarized target.

• Summary.

Wen-Chen Chang

What the world is composed of?

Wen-Chen Chang

How do we study?

• Different probes: p, e, A, and , etc…

• Interaction at small distance scale: accelerate the particles to high energy and make something happen. (Accelerator and collisions at higher and higher energy: keV (103eV). MeVGeVTeV (1012eV).)

• “See” what happens: detectors+event constructions.

• Understand what happens: simulation work.

Wen-Chen Chang

Super Photon Ring 8 GeV (SPring-8)in Osaka, Japan

Harima Science Garden City

Wen-Chen Chang

SPring-8 Beam-Lines

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Synchrotron Radiation

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Laser Electron Photon

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Tagging of Photon Energy

Silicon Strip Detector ×2(Analog readout,100m pitch 640 ch)

1cm8GeV electron beam

Scattered electron

Plastic scintillator ×20(3mm(T),7.4mm(W),10 mm(H))

Energy Counter Timing Counter

Accelerator chamber wall

Wen-Chen Chang

Laser-Electron-Photon Spectrum

• Source: Polarized laser is directed into the storage ring and backward-Compton-scatters with 8 GeV/c electron bunches

• Emax: 2.4 GeV(3.5GeV)

• Flux:5*106 /sec

( 1*107 /sec)

• Polarization:100% at Emax

2.4 GeV

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BLP33 Experimental Hutch

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BLP33 Experimental Hutch

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Total Cross Section of Hadronic Interaction (I)

XsYsT

Universal Scaling : = 0.5, = 0.08

Wen-Chen Chang

Total Cross Section of Hadronic Interaction (II)

• Pomeron exhange:

– Positive power-law scaling of s.

– Dominating at large s.

– Natural parity (J=0+).

– Exchange particles unknown; successful phenomenology for diffractive process.

• Reggeon exchange: – Negative power-law scaling of s.

– Dominating at small s.

– Un-natural parity (J=0–).

– Exchange particles like ,; Vector Meson Dominated Model.

Wen-Chen Chang

Photo-Production of Mesons

Pomeron Exchange Boson Exchange Emission from Nucleon

(OZI Suppressed!)

Wen-Chen Chang

Unpolarized Differential Cross section of p p

A.I.Titov et. al., PRC 59, R2993

(t=0

)

Wen-Chen Chang

Polarized Photon Beam: disentangle exchanges of different parity

),(cos2sin),(cos2cos

),(cos),,(cos21

0

WPWP

WW L

: angle between the photon polarization vector and CMS production plane.

Experimentally we measure W’s functions where density matrix

could be decomposed.

100

1112

UN

UNPParity Asymmetry

• P= +1, only natural parity• P= –1, only un-natural parity

Wen-Chen Chang

Strangeness Inside Nucleon

-knock out Process

A.I.Titov et. al., PRL 79, 1634.

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Polarized Photon + Polarized Target

zBzT

zBzT

zBzT

zBzT

BTL

Double polarization variable LBT is sensitive to the strangeness content in nucleons.

A.I.Titov et. al., PRL 79, 1634.

Wen-Chen Chang

LEPS Collaboration

RCNP, Osaka University, JapanJ.K. Ahn, M. Fujiwara, T. Hotta, N. Matsuoka, T. Matsumura, T. Mibe, T.Nakano, M. Nomachi, Y. SugayaAcademia Sinica, TaiwanW.C. Chang, C.W. Wang, D.Oshuev, S.C. WangChiba University, JapanH. Kawai, T. OobaNagoya University, JapanT. Iwata, A. WakaiOhio University, U.S.K. HicksJAERI/Spring-8, JapanH. Akimune, Y. Asano, S. Date,, N. Kumagai, Y. Ohashi, Ho. ToyokawaKyoto University, JapanK. Imai, M. Yosoi, A. IchikawaOsaka University, JapanT. Kishimoto, A. Sakaguchi, M. SumihamaWakayam Med. University, JapanS. MakinoYamagata University, JapanH. Shimizu

Wen-Chen Chang

LEPS Experiment• Detector:

– Large acceptance at forward small |t| region, mostly diffractive production.

– Effective e+e- events suppression at trigger level.

– Good K/ separation with TOF detector.

• Physics Program:: photo-production around and beyond threshold: study interplay o

f Pomeron exchange and quark exchange. , photo-production in u channel at large |t| region..

– Strangeness content of the nucleon using polarized beam and target.

– Nuclear medium effect from vector meson photo-production in nuclei.

Wen-Chen Chang

LEPS Detector Configuration

Wen-Chen Chang

Capability of LEPS detectors and DAQ

• DAQ– 1 kHz trigger rate.

• LEP beam intensity– 5*106 photon/sec.– Yield of x10-2/sec with 0.1 radiation length

target.• Mass resolution ( from CH2)

– Tagging Gamma energy resolution:15 MeV.– Drift chamber resolution: 200 m.

• Particle ID – Time-of-Flight(TOF) timing resolution: 100 psec.

– 4 separation of K//e at 2 GeV/c momentum.

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Laser System

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Liquid Hydrogen Target

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Dipole Magnet and Drift Chambers

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Time-of-Flight Wall

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Performance of Time-of-Flight Detector

• Totally 40 scintillator slats of geometry: 12cm(W)x200cm(L) x4cm(T).

• Each slat with top and bottom PMTs readout.

• Timing resolution ~100 psec.

• Essential to 4 K/ separation up to 2 GeV/c momentum.

Wen-Chen Chang

Run SummaryRun Period Run Number Target Laser Polarization Laser wavelength2001/01/18-2001/01/31

20751-20960 LH2, C, Cu Linear 351 nm

2000/12/08-2000/12/20

20559-20743 LH2 Linear 351 nm

2000/06/01-2000/06/14

10195-10508 CH2, C Linear 351 nm, 488 nm,514 nm

2000/05/16-2000/05/24

10000-10193 CH2, C, Cu,Pb

Linear, Circular 351 nm

Events in AS group•AS group(C.W. Wang and S.C. Wang) built the TOF detector.•W.C. Chang, C.W.Wang and S.C. Wang participated the data-taking and data analysis mainly on •S.C. Wang left the group in the fall of 2000.•D.S. Oshuev joins the group on 02/08/2001.

Wen-Chen Chang

Particle Identification using TOF and Tracking

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Particle Identification in Mass

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Signal of K+K

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Detector Upgrade

Gamma Detector Time Projection Chamber

•Backward triggering.•Detection of resonance with 2 reconstruction.

•Vertex detection around the target.•Nuclear medium effect in vector mesons.•Photo-production of (1405).

Wen-Chen Chang

Summary

• The LEPS experiment at SPring-8 is unique in measuring the photo-production of vector mesons near threshold regions and the capability of high-flux polarized photons. The physics goal is clearly defined.

• The detector and DAQ system works and meet the need of physics measurement. Tasks of data-taking and analysis are currently intensively under way.

• It is a nice start for AS nuclear group to work on high-energy project with an international collaboration. Even with a lack of man-power, we would work on the TPC upgrade project aiming at detecting nuclear medium effect from the production of vector mesons in nuclei.