Construction of �Laser-Electro-Photons (LEPS) �at Taiwan Photon Source (TPS)

Wen-Chen Chang

Institute of Physics, Academia Sinica

Outline

• Design parameters
• Physics motivation
• Experimental setup
• Cost estimation

Laser-Electron-PhotonS facility

b) Laser hutch

a) Storage Ring

c) Experimental hutch

Compton γ-ray

Laser light

3.3 GeV electron

Recoil electron

Tagging counter

Collision

Energy spectrum of

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BCS photons

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Bremsstrahlung

Backward-Compton scattering

Summary of Existing LEPS Facilities Worldwide

Backward-Compton-Scattering Spectra using 266nm Laser

Energy of Electrons

Minimum photon energy

for production

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Photon Flux

LEGS Exp in BNL

The LEPS facility according to the current parameters of TPS is most similar to the

LEGS exp in BNL, which was shutdown at the end of year 2006. The beam time

using polarized HD target in LEGS was rather limited.

The polarization degree was not high: P(H)=60% and P(D)=16.5%.

Physics Program

• High precision measurement of γN→πN and γ N→π π N with polarized photon beam and polarized targets. This will provide the data on the double-polarization variables E and G, as well as beam asymmetry, and cross section data for the neutron and the proton. The data are extremely important information for the low-energy GDH integral sum of these two reactions.
• Magnetic dipole moment of Delta(1232)

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Motivation

• Constructing a “LEPS” beamline in Taiwan is no more than a duplicate “LEGS” experiment at BNL IF WITHOUT POLARIZED TARGET. As mentioned before, the beam time with polarized target and comprehensive detectors in LEGS Exp was rather limited (about 2 months in year 2006).
• However recently we learned there is a big progress in developing the polarized HD target in Osaka University and the whole technique will become available in about 2-3 years. We start participating in this project. The combined use of high-degree polarized photon beam and HD target will bring up the extremely interesting physics program.
• The competition will come from the MAMIC at Mainz. The schedule of operation will be within a few years. However their focus is mainly on the high-energy side for strangeness meson production.
• We have the advantage of inheriting the experience and hardware from the LEPS experiment in Japan.

Experimental set-up

• Tagged photon beam: M _π< Eγ <500 MeV ; Flux 1 MHz.
• High-degree Linearly polarized photons: P(γ)>95%.
• Polarized HD target: P(H)=90%;P(D)=60%.
• Large acceptance detectors:
• Time Projection Chamber: charged pions. One is available at LEPS experiment and we can consider reuse it in Taiwan.
• Photon detector: photon and neutral pions. It needs to be constructed.

Dilution refrigerator

Leiden Cryogenics

DRS-3000　(He3-He4)

Cooling power 　　 　

　　　3000μW at 120 mK

Lowest temperature 　

　　　 6 mK

Magnetic Field 　　　　

　　　17 T

Homogeneity of Magnetic Field

　　　5×10^-4 for 15 cm

IBC（In Beam Cryostat） for BL33LEP

Al wire

2.5cm

Cost Estimate

• Laser: $200K USD / per unit.
• Target: Polarized HD target $1M.
• Time Projection Detector: $50K (if we cannot reuse the current one in LEPS).
• Photon Detector: crystal ball with 4π coverage, is $300K – 500K. (This might be an optional choice at the every beginning.)
• Electronics: $500K.
• In total: about USD$2.2M.