Transcript Recent results and future prospects of the , 2006/05/18 LEPS experiment

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
Laser Electron Photon beamline at SPring-8
•
•
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.
LEPS Experiment
Magnetic spectrometer in the
forward direction
(p±, K±, p, d)
Beam: GeV photon
Target: p, d, A
g
1m
The LEPS Collaboration
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. Zegers
Department of Physics, Pusan National University ：J.K. Ahn, J.Y. Park
School of Physics, Seoul National University ：H.C. Bhang, K.H. Tshoo
Department 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. Mibe
Department of Physics, Kyoto University ：K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. Niiyama
Department 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
Pentaquark Q+
The antiquark has a different flavor than the other 4 quarks.
D. Diakonov, V. Petrov, and M.
Polyakov, Z. Phys. A 359 (1997) 305.
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M = [1890-180*Y] MeV
Exotic: S=+1
Low mass: 1530 MeV
Narrow width: ~ 15 MeV
Jp=1/2+
Time dependent experimental status of Q+
γ + d (n ) reactions
CLAS-d1
LEPS-C
γ + p → p Ks0
LEPS-d2
LEPS-d
CLAS g11
SAPHIR
γ + p → n K+ K- p+
CLAS-d2
CLAS-p
BELLE
DIANA
K + (N) → p Ks0
lepton + D, A → p Ks0
SVD2
p + A → pKs0 + X
p + p → pKs0 + S+
Other Q+ Upper Limits
JINR SPHINX HyperCP
ALEPH, Z
COSY-TOF
HERA-B
BES J,Y
2002
2003
BaBar
ZEUS nBC
Hermes
2004
CDF
FOCUS
SVD2
WA89
2005
: Positive result
• Both positive & negative results exist.
: Negative result
• Confirmation of the existence is still most important.
• Theoretical attempt to explain observation vs. non-observation.
 Hosaka: May 20, Session 15 in this symposium.
First evidence from LEPS
g
Phys.Rev.Lett. 91 (2003) 012002
nK+K-n
Low statistics: S = 4.6
B
but
hep-ex/0301020
S
= 3.2
S+B
Tight cut: 85% of events are rejected
by the f 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.
Q+
LEPS LD2 runs
• 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 Q+ : 17  85
Search for Q+ in g nK+K-n
• A proton is a spectator (undetected).
• Fermi motion is corrected to get the missing mass spectra.
• Tight f exclusion cut is essential.
• Background is estimated by mixed events.
L(1520)
MMgK+ (GeV)
g nK+K-n
Counts/12.5 MeV
Counts/12.5 MeV
g pK+K-p
Q+
MMgK- (GeV)
Q+ search in g d  L(1520) KN reaction
• 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: s<450 pb.
– acceptance coverage is different from LEPS (forward).
γ
Θ＋
?
L(1520)
p
K－
n
detected
p
A possible reaction mechanism
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Q+ can be produced by re-scattering of K+.
K momentum spectrum is soft for forward going L(1520).
missing momentum
L(1520)
γ
LD2
p/n
n/p
K+/K0
Q+
• Exchanged kaon can be on-shell.
• KN  Q+ formation cross section.
Formation
momentum
Pmiss GeV/c
Background process
• Quasi-free L(1520) production must be the major
background.
• The effect can be estimated from the LH2 data.
γ
L(1520)
p
n
n
K+
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
K＋ mass : 0.40 – 0.62 GeV/c2
π－ mis-ID
as K－
γp→K－pKπ
MMp(γ,K－p) GeV/c2
Λ(1520) : 1.50 – 1.54 GeV/c2
Non-resonant
KKp + fp + …
M(K－p) GeV/c2
Events with Λ(1520) production were selected.
Eg > 1.75 GeV was also applied.
L(1520)
LD2
Counts/5 MeV
Sideband BG estimation
correction for
f contribution
M(K－p) GeV/c2
MMd(γ,K－p) GeV/c2
• 10-MeV Eg smearing has been applied to remove fine structure
due to fluctuation.
• No visible signal.
• Validity of the sideband method with Eg smearing was checked
by using two independent regions of the sideband.
MMd(γ,K－p) GeV/c2
Excesses are seen at 1.53
GeV and at 1.6 GeV above
the background level.
1.53-GeV peak:
(in the 5 bin = 25 MeV)
S
~5
S+B
preliminary
No visible signal in sidebands.
Counts/5 MeV
LD2
Q+
preliminary
Counts/5 MeVC
K－p missing mass spectrum
sideband
Quasi-free L*
sum
MMd(γ,K－p) GeV/c2
Normalization of L* is obtained by fit in the region of MMd < 1.52 GeV.
Remove high frequency fluctuations by 10-MeV
Eg smearing
Real peak or fluctuation?
MM(K－p) GeV/c2
data - BG
preliminary
Counts/5 MeV
All data & sideband BG
preliminary
Counts/5 MeV
• Within existing data, robustness of the peak has been checked by Eg
smearing (smoothing of the spectra).
• Fine structure (< experimental resolution) must be statistical fluctuations.
MM(K－p) GeV/c2
Search for g d  L(1116) Q+
γ
p
n
Θ＋
L(1116)
•Normalization factor for
LH2 data (green line) is 2.6.
 No large p/n asymmetry.
p－
Counts/5 MeV
p
forward
angle
detection
•Quasi-free process can be
reproduced by free process.
 small effect from Fermi
motion.
•Large cross-section
compared with L(1520).
•Missing Mass resolution is
worse.
• No excess at 1.53 GeV nor
at 1.6 GeV.
MMd(γ,p－p) GeV/c2
Summary of Q+ search at LEPS
Confirmation of Q+ by using LD2 data
• K+K- 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 L(1520) production
– Signal-like behavior. [M(pK-) gate, Eg dependence, &
robustness of the peak under smearing.]
Prospects
Negative and positive results on Q+:
• Negative results restrict the possibility of Q+ 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 Q+ 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 facility
Backward Compton Scattering
8 GeV electron
Recoil electron
(Tagging)
modify：
JASRI Acc. group
a) SPring-8 SR ring
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）
Eg < 7.5GeV (LEPS < 3GeV)
GeV g-ray
Inside
building
Outside
building
5m
b) Laser hutch
Plan to move the BNL-E949
detector to Spring-8
(helped by RIKEN)
4p g detector（Tohoku U.）
Large decay spectrometer
Forward spectrometer
New DAQ system
c) Experimental hutch
Schedule
Decomposition of
E949 detector (BNL)
2008
Moving
E949 det.
2009
Construction of the
decay spectrometer
Construction of the
forward spectrometer
Apply BL
modification
Modify
SR ring
Building
Exp hutch
High speed DAQ system
Construction of
the beamline
Infrastructure
Radiation shield
Laser injection
system
Beam
commisioning
Submit LEPS2
proposal
Start experiment
2007
Detector
commisioning
2006
4p photon detector
X-ray re-injection system
R&D of polarized HD target
Experiment with HD target
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 !!