recent results and future prospects of the laser electron photon experiment at spring-8
DESCRIPTION
第六届中日核物理研讨会 , 上海 , 2006/05/18. Recent results and future prospects of the Laser Electron Photon experiment at SPring-8. T. Hotta (RCNP Osaka University) the LEPS collaboration. LEPS experiment Search for the Q + pentaquark Upgrade of the LEPS facilty LEPS2. - PowerPoint PPT PresentationTRANSCRIPT
Recent results and future prospects of the Laser Electron Photon experiment at SPring-8
T. Hotta (RCNP Osaka University)
the LEPS collaboration
第六届中日核物理研讨会 , 上海 , 2006/05/18
• LEPS experiment • Search for the pentaquark• Upgrade of the LEPS facilty LEPS2
• SPring-8: world’s largest synchrotron radiation facility (8 GeV)• LEPS beamline: ~3 GeV polarized photon beam
produced by backward Compton scattering of Laser photon.
Laser Electron Photon beamline at SPring-8
1m
Magnetic spectrometer in the forward direction(, K, p, d)
Beam: GeV photonTarget: p, d, A
LEPS Experiment
Research Center for Nuclear Physics, Osaka University : T. Nakano, D.S. Ahn, M. Fujiwara, K. Horie, T. Hotta, Y. Kato, K. Kino, H. Kohri, N. Muramatsu, T. Sawada, T. Tsunemi, M. Uchida, M. Yosoi, R.G.T. ZegersDepartment of Physics, Pusan National University : J.K. Ahn, J.Y. Park School of Physics, Seoul National University : H.C. Bhang, K.H. TshooDepartment of Physics, Konan University : H. Akimune Japan Atomic Energy Research Institute / SPring-8 : Y. Asano, A. Titov Institute of Physics, Academia Sinica : W.C. Chang, D.S. Oshuev, Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 : H. Ejiri, S. Date', N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa, T. Yorita Department of Physics and Astronomy, Ohio University : K. Hicks, T. MibeDepartment of Physics, Kyoto University : K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. NiiyamaDepartment of Physics, Chiba University : H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University : S. Makino Department of Physics and Astrophysics, Nagoya University : S. Fukui Department of Physics, Yamagata University : T. Iwata Department of Physics, Osaka University : S. Ajimura, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan : C. Rangacharyulu Department of Physics, Tohoku University : M. Sumihama Laboratory of Nuclear Science, Tohoku University : T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University : T. Matsuda, Y. Toi Institute for Protein Research, Osaka University : M. Yoshimura National Defense Academy in Japan : T. Matsumura
The LEPS Collaboration
Pentaquark
M1890-180*Y] MeV
D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A 359 (1997) 305.
• Exotic: S=+1• Low mass: 1530 MeV• Narrow width: ~ 15 MeV• Jp=1/2+
The antiquark has a different flavor than the other 4 quarks.
γ + d (n ) reactions
γ + p → p Ks0
γ + p → n K+ K- p+
K + (N) → p Ks0
lepton + D, A → p Ks0
p + A → pKs0 + X
p + p → pKs0 + +
Other + Upper Limits
BaBar
CLAS-d2
BELLE
ALEPH, ZSVD2
LEPS-d2LEPS-C CLAS-d1
DIANA
SAPHIR
SVD2
COSY-TOF
Hermes
JINR
CLAS-p
LEPS-d
BCZEUS
BES J,
CLAS g11
SPHINX HyperCP
HERA-B
FOCUS WA89CDF
: Positive result
: Negative result
2002 2003 2004 2005
• Both positive & negative results exist.• Confirmation of the existence is still most important.• Theoretical attempt to explain observation vs. non-observation. Hosaka: May 20, Session 15 in this symposium.
Time dependent experimental status of +
nKKnPhys.Rev.Lett. 91 (2003) 012002
hep-ex/0301020
+Low statistics: but
Tight cut: 85% of events are rejected by the exclusion cut.
Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections.
Correction: Fermi motion correction is necessary.
4.6S
B 3.2
S
S B
First evidence from LEPS
• Collected Data (LH2 and LD2 runs)
Dec.2000 – June 2001 LH2 50 mm ~5×1012 photons
published data (target: 5mm plastic scint.)
May 2002 – Apr 2003 LH2 150 mm ~1.4×1012 photons
Oct. 2002 – June 2003 LD2 150 mm ~2×1012 photons
• #neutrons × #photons in K + K - detection mode
LD2 runs ~ ×5 statistics
expected # of : 17 85
LEPS LD2 runs
MM (GeV) MM (GeV)
• A proton is a spectator (undetected).
• Fermi motion is corrected to get the missing mass spectra.
• Tight exclusion cut is essential.
• Background is estimated by mixed events.
preliminary
preliminary
(1520)
pK+K-p nK+K-n
Co
un
ts/1
2.5
MeV
Co
un
ts/1
2.5
MeV
Search for + in nK+K-n
• Θ + is identified by K -p missing mass from deuteron. ⇒ No Fermi correction is needed.
• K- n and pn final state interactions are suppressed.• Isospin selection: some reaction mechanism may favor specific isospin state. • CLAS(d)@JLAB: <450 pb.
– acceptance coverage is different from LEPS (forward).
+ search in d (1520) KN reaction
γ
p
n
Θ +
K -
p
(1520)
detected
?
A possible reaction mechanism
• + can be produced by re-scattering of K+.• K momentum spectrum is soft for forward going (1520).
γ
p/n
n/p
(1520)
K+/K0
missing momentum
Formation momentum
LD2
Pmiss GeV/c
• Exchanged kaon can be on-shell. • KN formation cross section.
Background process
• Quasi-free (1520) production must be the major background.
• The effect can be estimated from the LH2 data. γ
p
n
(1520)
K+
n
The other background processes which do not have a strong pK- invariant mass dependence can be removed by sideband subtraction.
Event selections in K - p mode
MMp(γ,K - p) GeV/c2
π - mis-ID as K -
K + mass : 0.40 – 0.62 GeV/c2
M(K - p) GeV/c2
Λ(1520) : 1.50 – 1.54 GeV/c2
Events with Λ(1520) production were selected.E > 1.75 GeV was also applied.
Non-resonantKKp + p + …
γp→K - pKπ
Sideband BG estimation
M(K - p) GeV/c2 MMd(γ,K - p) GeV/c2
correction for contribution
• 10-MeV E smearing has been applied to remove fine structure due to fluctuation.
• No visible signal.
• Validity of the sideband method with E smearing was checked by using two independent regions of the sideband.
Co
un
ts/5
MeVLD2
K - p missing mass spectrum
MMd(γ,K - p) GeV/c2
sideband
Quasi-free*
sum
Co
un
ts/5
MeV
C Excesses are seen at 1.53 GeV and at 1.6 GeV above the background level.
1.53-GeV peak:
pre
lim
inar
y
MMd(γ,K - p) GeV/c2
Co
un
ts/5
MeV
Normalization of * is obtained by fit in the region of MMd < 1.52 GeV.
(in the 5 bin = 25 MeV)
pre
lim
inar
y
No visible signal in sidebands.
+
5~BS
S
LD2
MM(K - p) GeV/c2MM(K - p) GeV/c2
Co
un
ts/5
MeV
Co
un
ts/5
MeV
pre
lim
inar
y
pre
lim
inar
y
Remove high frequency fluctuations by 10-MeV E smearing
All data & sideband BG data BG
Real peak or fluctuation? • Within existing data, robustness of the peak has been checked by E smearing (smoothing of the spectra).• Fine structure (< experimental resolution) must be statistical fluctuations.
•Normalization factor for LH2 data (green line) is 2.6. No large p/n asymmetry.
•Quasi-free process can be reproduced by free process. small effect from Fermi motion.
•Large cross-section compared with(1520).
•Missing Mass resolution is worse.
• No excess at 1.53 GeV nor at 1.6 GeV.
MMd(γ, - p) GeV/c2
Co
un
ts/5
MeV
preliminary
Search for d (1116) +
γ
pn
Θ +
-
p
(1116)
forward angle detection
Summary of search at LEPS
Confirmation of + by using LD2 data
• KK detection mode: – 1.53 GeV/c2 peak observed ~ expected # of events. – BG estimation is still underway.
• K-p detection mode in MMd(g,pK-) spectrum: – 1.53 GeV/c2 peak (4-5σ,preliminary) + 1.6 GeV/c2 bump
associated with (1520) production
– Signal-like behavior. [M(pK) gate, E dependence, & robustness of the peak under smearing.]
Prospects
Negative and positive results on • Negative results restrict the possibility of existence.
– New CLAS@JLAB data denied their evidence. But their kinematical condition is different from LEPS.
• There are still some positive evidences which cannot be excluded completely. – e.g. DIANA exp. (hep-ex/0603017)
• If exist, production mechanism should be also exotic.
Further measurements with wider kinematical coverage & high statistics are important.
• LEPS: Experiment w/ Large solid angle TPC will start soon.• LEPS2: New beamline is proposed.
Beamline map of Spring-8
BL31ID
Schematic view of the LEPS2 facilityBackward Compton Scattering
a) SPring-8 SR ring
b) Laser hutch
c) Experimental hutch
8 GeV electron
Recoil electron (Tagging)
Plan to move the BNL-E949 detector to Spring-8 (helped by RIKEN)
5 m
GeV -rayInsidebuilding Outside
building
30m long line
( LEPS 7.8m)
4 detector ( Tohoku U. )Large decay spectrometerForward spectrometerNew DAQ system
Laser or re-injected X-ray
High intensity : Multi laser LRNB Round beam ~10 7 photons/s ( LEPS ~10 6 )High energy : Re-injection of X-ray from undulator ( Tohoku U., JASRI ) E< 7.5GeV (LEPS < 3GeV)
modify :JASRI Acc. group
Schedule
2006 2007 2008 2009
Decomposition of E949 detector (BNL)
Moving E949 det.
Construction of the decay spectrometer
Construction of the forward spectrometer
High speed DAQ system
Modify SR ring
Construction of the beamline
Building Exp hutch
Infrastructure
Radiation shield
Laser injection system
R&D of polarized HD target Experiment with HD target
X-ray re-injection system
4 photon detector
Submit LEPS2 proposal
Apply BL modification
Beam
com
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Det
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Sta
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LEPS2 Collaboration
• Core institutes RCNP, Osaka U. LNS Tohoku U. JASRI (SPring-8) Accelerator group RIKEN Radiation Laboratory (new !)• Other LEPS members Kyoto U., Osaka U., Konan U., Chiba U., Yamagata U., Miyazaki U., Pusan U.(Korea), Seoul U.(Korea), Academia Sinica (Republic of China), Ohio U. (USA), Saskachewan U. (Canada) …etc.• New members National Defense Academy, … some members from the BNL-E949 experiment (domestic and foreign institutes (BNL, TRIUMF,…))
We are trying to expand the collaboration !!