LEPS Beam and Detector

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Recent results of LEPS at SPring-8T.
Nakano(RCNP)for LEPS collaboration

• LEPS Beam and Detector
• First physics run and
• results
• K photo-production
• f photo-production
• w photo-production
• L(1405) decay width
• Z in g n ? K- X
• Summary

PaNic02 October 3, 2002 _at_ Osaka
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SPring-8 (Super Photon ring-8 GeV)

• Third-generation synchrotron radiation facility
• Circumference 1436 m
• 8 GeV
• 100 mA
• 62 beamlines

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The LEPS collaboration

• Research Center for Nuclear Physics, Osaka
  University
• T. Nakano, M. Fujiwara, H. Fujimura, T. Hotta, K.
  Kino,
• H. Kohri, T. Matsumura, N. Matsuoka, T. Mibe, M.
  Morita
• Pusan National University
• J.K. Ahn, D.S. Ahn
• Konan University
• H. Akimune
• Japan Atomic Energy Research Institute / SPring-8
  
• Y. Asano, N. Muramatsu, R.G.T. Zegers
• Institute of Physics, Academia Sinica, Taiwan
• W.C. Chang, D.S. Oshuev, C.W. Wang, S.C. Wang
• Japan Synchrotron Radiation Research Institute
  (JASRI)
• / SPring-8
• S. Date, N. Kumagai, Y. Ohashi, H. Ookuma, H.
  Toyokawa,
• T. Yorita
• Ohio University
• K. Hicks
• Kyoto University
• K. Imai, T. Ishikawa, M. Miyabe, M. Niiyama, T.
  Sasaki,

Wakayama Medical University S. Makino Nagoya
University T. Iwata, Y. Miyachi, A. Wakai Osaka
University H. Nakamura, M. Nomachi, A.
Sakaguchi, Y. Sugaya, M. Sumihama University of
Saskatchewan C. Rangacharyulu Institute for
High Energy Physics (IHEP), Moscow P. Shagin
Laboratory of Nuclear Science, Tohoku University
H. Shimizu University of Michigan K. Yonehara
International Institute for Advanced Studies H.
Ejiri
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Laser electron Photon at SPring-8
g
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Energy Spectrum
Intensity (Typ.) 2.5 106 photons/sec
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Polarization of LEP Beam
Linear Polarization 95 at 2.4 GeV
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Tagging system
s 15 MeV
Tagging Region 1.5 GeVlt Eg lt 2.4 GeV
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LEPS detector
TOF wall
Aerogel Cerenkov (n1.03)
Dipole Magnet (0.7 T)
Start counter
Liquid Hydrogen Target (50mm thick)
MWDC 3
Silicon Vertex Detector
MWDC 2
MWDC 1
1m
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LH2 Target
Drift Chamber
g
SSD
Cerenkov Detector
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Trigger
about 30 Hz for 800 kHz_at_tagger

• Photon requirement
• Tagger hit
• No signal in charge veto
• Charged particle production
• Start counter
• TOF hit
• e e- veto
• AC (n 1.03)
• pp lt 0.6 GeV/c

Charge veto
AC
Target
Start counter
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Study of p(g,K)L,S0 reactions

• Available data is not sufficient
• to fix models and draw
• conclusions on the reaction
• process and presence
• of missing nucleon resonances
• e.g. D13(1900)

• Measurement of additional observables
• is needed
• At LEPS/SPring-8
• Single polarization observables
• Photon polarization asymmetry (S)
• Recoil polarization
• Double Polarization observables
• Beam-recoil asymmetry
• Cross sections
• Forward angles (tmaxgttgt-0.6)
• (t-channel K/K interference)

Saphir ?
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Photon polarization asymmetry
preliminary
K,L photon pol. Asym.
1.5ltEglt2.4 tmaxgttgt-0.6
ALSO S0
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Backward Photoproduction of w

• Proton detected in the forward LEPS detector
• Identify w in the missing mass spectrum.
• Sensitive to N ? Nw coupling
• Role of N in w photoproduction (different model
  predictions)
• Oh, Titov, Lee
• N(3/2)(1910) missing
• N(3/2)-(1960) PDG-listed
• Zhao et al.
• F15(2000) missing
• photon beam asymmetry Sx
• Sensitive to inclusion of N.
• No data for Eggt1.5 GeV

Oh, Titov, and Lee, nucl-th/0012012, Data from
SAPHIR('96)
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Missing mass spectrum and asymmetry

• Non-zero Sx observed.
• Analysis in progress.
• To be compared with theoretical predictions.

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photoproduction near production threshold
Titov, Lee, Toki Phys.Rev C59(1999) 2993
Data from SLAC('73), Bonn(74),DESY(78)
P2 2nd pomeron 0 glueball (Nakano, Toki
(1998))
Decay asymmetry helps to disentangle relative
contributions
?
?
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Reconstructed f events
KK event
t (GeV2)
Eg (GeV)
Kp event
t (GeV2)

• KK- decay mode
• High acceptance at forward angles
• 5000 fs (2000,Dec-2001,June)

Eg (GeV)
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Photoproducion by linearly polarized photon
In f rest frame (Helicity frame)
Decay Plane // g if natural parity exchange
(-1)J (Pomeron, Scaler mesons)
K
K
Polarization vector of g
K-
K-

• Decay Angular distribution of f
• Decomposition of
• natural parity exchange
• unnatural parity exchange

Decay Plane g if unnatural parity exchange
-(-1)J (Pseudoscaler mesons)
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Decay angular distribution of K in f rest frame
(Helicity frame)
-0.2lt t lt tmin GeV2 , 2.2 lt Eg lt 2.4 GeV w/o
Acceptance Correction
Raw data
Number of event
Helicity conserving amplitudes are dominant.
cos(qK)
Horizontally polarized beam
Vertically polarized beam
Raw data
Number of event
Major contribution from natural-parity exchange
Presented by W.C. Chang on Oct. 1. Poster session
6B-26 by T. Mibe
fK - Fpol (degree)
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(No Transcript)
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Invariant mass of pS
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Z Baryon

• Exotic S1
• Low mass 1530 MeV
• Narrow width lt 15 MeV
• Production
• p- p ? K- Z ? K- K n
• pp ? S Z ? S K0 p
• g n ? K- Z ? K- K n

D. Diakonov, V. Petrov, and M. Polakov, Z. Phys.
A 359 (1997) 305.
S(1890 )
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Identification of g n ? K S- ? K p- n
Start counter (CH2)
L
S-
MM(g,Kp-) GeV
Eglt1.65 GeV
MM(g,Kp-) GeV
MM(g,K) GeV
MM(g,K) GeV
MM(g,K) GeV
VTZ mm
LH2
MM(g,K) GeV
MM(g,K) GeV
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p ? K L(1520) ? K K- p g n ? K- Z ? K-
K n
MM(gN?KX)
MM(gN?K-X)
f cut

• KK- PID(3s)
• 0.935ltMMlt0.975
• Eglt2.35 GeV
• Edepgt1.5 MIP
• Vertex Cut

excluded
MM(g,K) GeV
MM(g,K-) GeV
KK invariant mass GeV
L(1520)
After f cut
MM(g,K) GeV
MM(g,K-) GeV
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N ? K- K N from LH2 and Start Counter
MM(gN?K-X)
LH2
Start counter
MM(gN?KX)
L(1520) cut
MM(g,K-) GeV
MM(g,K-) GeV
MM(g,K) GeV
After L(1520) cut
MM(g,K-) GeV
MM(g,K-) GeV
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Observation of Narrow Peak in Missing Mass of g
n ? K- X
After L(1520) cut
Preliminary
Start counter
LH2
LH2
MM(g,K-) GeV
MM(g,K-) GeV

• Statistical significance is 5 6 s depending on
  the assumption of the BG shape.
• The peak is consistent with a theoretical
  prediction of Z.
• Detailed BG study with MC and Real Data is
  underway.
• Crosscheck can/should be done at Jlab and
  elsewhere.
• New measurement with LD2 target is planned at
  LEPS.

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Summary

• Backscattered photon beam facility in Japan.
• 2.4 GeV linearly polarized photons.
• Forward-angle spectrometer .
• Physics programs and recent results.
• K Photo-production.
• Photon beam asymmetry sensitive to study missing
  N.
• Photo-production of f meson near threshold.
• Decay asymmetry measurement to separate various
  contributions.
• Photo-production of w in u-channel.
• sensitive to N and gwNN.
• Photo-production of L(1405) from a proton and in
  nuclei.
• Invariant mass of pS
• Pin down the nature of L(1405).
• Observation of Narrow Peak in Missing Mass of g
  n ? K- X.
• Exotic Z baryon signature.