22 September 2005 Haw05 1
(1405) photoproduction at SPring-8/LEPS
H. Fujimura, Kyoto University
Kyoto University, JapanK. Imai, M. Niiyama
Research Center for Nuclear Physics, Osaka University, JapanT. Nakano
for the LEPS collabration
Collaborators1. Physics Motivation2. Mechanical Design of TPC3. Experiment Setup at SPring-8/LEPS4. Current status of Analysis5. Summary and Prospects
Contents
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Physics Motivation structure of Λ*(1405) JP =1/2-
• Chiral perturbation theory describe (1405) as a meson-bariyon resonance and predict its lineshape to be different in different decay channel , +.
→ J.K.Ahn et al
They predict the modification of invariant mass distribution of (1405) in nuclear matter.
E. Oset et al., Nucl. Lett. B455 55(1999)
Lutz…,
3-quark state or KN bound state ?
Large mass difference between (1520) JP=3/2- and (1405) JP =1/2- cannot be explained by quark model.
KN threshold
3/2-
1/2-
)
)30 MeV
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Physics Motivation Experimental Data• Thomas et al. Nucl. Phys. B56 15 (1973)
470 events
• Hemingway et al. Nucl. Phys. B253 742 (1985)
• J.K.Ahn et al. Nucl. Phys. A721 (2003)
It is necessary to detect to identify (1405)
develop Time Projection Chamber(TPC) as 4 detector to detect decay topology
pK
KKn
KKp
NKKKp
)1385(
)1385(
)1405(00
00 )1405( KKp
)()1405()1660(pK
KKp )1405(
Σ+π- 766 eventsΣ-π+ 1106 events
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880mm
585 mm
Up stream
Solenoid Magnet
Down stream view
600mm
TPC is designed to be installed in Solenoid Magnet.
Hexagonal cylinder 880mm in length 585 mm in diameter
Design of TPC
E // B
700mm
Target holder
High voltage plane
Wire & padplane
Drift field cage
Beam
Active volume (cylindrical shape) 700 mm in length 400 mm in diameter
Drift time → z position
To detect trajectory as close as a few cm from target, target holder is mounted in TPC.
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Design of TPC Pad Plane
Signals from TPC are read out through cathode pads and anode wires.
The position resolution (required value)Drift direction : 550 m (700 m)
Pad plane : 340 m (350m)
Invariant mass of (1405) → 1% accuracy
# of Cathode pads : 1055 # of Anode wires : 95
Beam
E // B
400mm
Large pads 8mm x 13mmSmall pads 4mm x 8mm
3-dimentional position information pad-plane → x-y position drift time → z positiondE/dX, momentum → PID
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Experimental setup at SPring-8/LEPS
E // B
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Solenoid Magnet
DipoleMagnet TPC
BufferCollimator 24Φ
Collimator 2 1 Φ
BeamBeam
TPC
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Beam Time
CH2 113Mtrig : 110k K+ in spectrometer
500 (1405) in K+-TPC+)
600 (1405) in K+spec+-)
C 60 Mtrig : 60k K+ in spectrometer
Cu 41 Mtrig : 12k K+ in spectrometer
Jan – Mar Commissioning runApr – Jul Physics runSep – Dec Physics run
2004
How to Identify (1405) events
Missing Mass of p ( , K+ + -)
Spectrometer TPC
nK
K
Kp )1405( Missing mass of p ( , K+ + -) → n Missing mass of p ( , K+ ) → ±
Select decay mode ( ) by the kinematical fit.
)1405(
In this talk, missing mass spectrum of p(, K+)X is shown by selecting + - in TPC to extract (1405) events.
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Proton
++
dE
/dx
(arb
itra
ry u
nit)
Momentum×charge (GeV/c)
PID by TPC
p
K+
K-
+-
Mass x Charge (GeV/c2)
Particle Identification
PID by Spectrometer
TOF, Momentum → Mass
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Missing mass of p ( , K+) X
CH2
C(1116)(1193) (1520)
(1405)/(1385)
CH2 - C
p (, K+) X (GeV/c2)
K+ were detected by Spectrometer PDG:1.115683 1.1155±0.0005 GeV0 PDG:1.1926421.1894±0.0005 GeV
(1502 PDG:1.5195 1.5192±0.006 GeV
E and Momentum calibration of LEPS Spectrometer system have been done.
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(1385) events
0
0)1116(
)1385(
pK
K
Kp
Spectrometer TPC
Invariant mass of (p, -) (GeV/c2)
Select (1116) by TPC
CH2
C
p (, K+) X (GeV/c2)
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CH2
C
CH2 - C
neutron
Missing mass p ( , K+ + -) (GeV/c2)
Event Selection by TPCMissing mass of p ( , K+ + -)
Missing Mass
p ( , K+ + -)
Spectrometer TPC
nK
K
Kp )1405(
Selection - Spectrometer
1 track, K+
2 prob 0.02≧ - TPC 2 tracks, + -
scattering angle of + - > 40°
Momentum calibration of TPC is underway
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CH2
C
p (, K+) X (GeV/c2)
Missing mass of p (, K+) Xselected by + - in TPC
CH2 - C
(1520)
Next step: select decay mode by identifying in p (, K+ )X.
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Summary and Prospects• (1405) is an unique object to study the dynamics of QCD. Some theoretical
models describing (1405) as meson-baryon molecular state あ and predict the different lineshape in different decay channel and the modification of lineshape of (1405) in nuclear matter.
• We have performed hyperon photoproduction experiment at SPring-8/LEPS. The CH2, C, and Cu targets were used. The energy range of the backward compton scattering photon was 1.5 – 2.4 GeV.
• To identify the (1405) from (1385), we have constructed a TPC as a 4 detector to measure decay topology.
• The physics run has been done in the year 2004. We identified 100K of K+
production events measured by forward spectrometer from CH2 target. Among K+ events tagged by spectrometer, 600 events of (1405) are expected.
• LEPS forward spectrometer system was used to detect forward going particles. E and momentum calibration of LEPS spectrometer system was finished.
• Momentum calibration of TPC is underway. We will extract (1405) lineshape from different decay mode by identifying in p (, K+ )X.
• The modification of invariant mass shape of (1405) in the nuclear matter will be studied.