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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.

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outline
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

how do we study
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).MeVGeVTeV (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
Super Photon Ring 8 GeV (SPring-8)in Osaka, Japan

Harima Science Garden City

Wen-Chen Chang

spring 8 beam lines
SPring-8 Beam-Lines

Wen-Chen Chang

synchrotron radiation
Synchrotron Radiation

Wen-Chen Chang

laser electron photon
Laser Electron Photon

Wen-Chen Chang

tagging of photon energy
Tagging of Photon Energy

Timing Counter

Energy Counter

Plastic scintillator ×20

(3mm(T),7.4mm(W),10 mm(H))

Silicon Strip Detector ×2

(Analog readout,100mm pitch 640 ch)

Accelerator chamber wall

Scattered electron

1cm

8GeV electron beam

Wen-Chen Chang

laser electron photon spectrum
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

Wen-Chen Chang

total cross section of hadronic interaction i
Total Cross Section of Hadronic Interaction (I)

Universal Scaling :

= 0.5,  = 0.08

Wen-Chen Chang

total cross section of hadronic interaction ii
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
Photo-Production of  Mesons

Pomeron Exchange

Boson Exchange

 Emission from Nucleon

(OZI Suppressed!)

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unpolarized differential cross section of p p
Unpolarized Differential Cross section of  p   p

(t=0)

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

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polarized photon beam disentangle exchanges of different parity
Polarized Photon Beam: disentangle exchanges of different parity

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

Experimentally we measure W’s functions

where density matrix  could be decomposed.

Parity Asymmetry

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

Wen-Chen Chang

strangeness inside nucleon
Strangeness Inside Nucleon

-knock out Process

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

Wen-Chen Chang

polarized photon polarized target
Polarized Photon + Polarized Target

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
LEPS Collaboration

RCNP, Osaka University, Japan

J.K. Ahn, M. Fujiwara, T. Hotta, N. Matsuoka, T. Matsumura, T. Mibe, T.Nakano, M. Nomachi, Y. Sugaya

Academia Sinica, Taiwan

W.C. Chang, C.W. Wang, D.Oshuev, S.C. Wang

Chiba University, Japan

H. Kawai, T. Ooba

Nagoya University, Japan

T. Iwata, A. Wakai

Ohio University, U.S.

K. Hicks

JAERI/Spring-8, Japan

H. Akimune, Y. Asano, S. Date,, N. Kumagai, Y. Ohashi, Ho. Toyokawa

Kyoto University, Japan

K. Imai, M. Yosoi, A. Ichikawa

Osaka University, Japan

T. Kishimoto, A. Sakaguchi, M. Sumihama

Wakayam Med. University, Japan

S. Makino

Yamagata University, Japan

H. Shimizu

Wen-Chen Chang

leps experiment
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 of 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

capability of leps detectors and daq
Capability of LEPS detectors and DAQ
  • DAQ
    • 1 kHz trigger rate.
  • LEP beam intensity
    • 5*106 photon/sec.
    • Yield of f1.72x10-2/sec with 0.1 radiation length target.
  • Mass resolution (f from CH2)
    • Tagging Gamma energy resolution:15 MeV.
    • Drift chamber resolution: 200 mm.
  • Particle ID
    • Time-of-Flight(TOF) timing resolution: 100 psec.
    • 4s separation of K/p/e at 2 GeV/c momentum.

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laser system
Laser System

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time of flight wall
Time-of-Flight Wall

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performance of time of flight detector
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 summary
Run Summary
  • 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

detector upgrade
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
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.

Wen-Chen Chang