Photoproduction of Strangenessnear the Threshold
at Tohoku
Masashi Kaneta for the NKS/NKS2 collaboration
Department of Physics, Tohoku University
Outline of this talk
IntroductionExperiments
Further InvestigationSummary
INTRODUCTION
Understanding the process ofStrangeness production
Motivation
Neutral channel
4
Threshold region
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
Key:via g+n reaction
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Why Neutral?
Theoretical studies were based on
data of g+p K++Yand then there are huge discrepancies
in prediction of neutral channel
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Neutral channel is requisite
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
Phys.Lett.B464(1999)331SAPHIR
g+pK0+S+
g+nK0+L
NKS experiment:differencial cross sectionin Eg=0.8-1.1 GeVPRC78(2008)014001
g+nK0+S0
LEPS experiment:differencial cross sectionin Eg=1.5-2.4 GeVwith polarized photon beamPRL97 (2006)082003PPRC76(2007)042201(R)
Phys.Rev.C73(2006)035202
Phys.Rev.C73(2006)035202
g+nK++S-
LEPS experiment:differencial cross section in Eg=1.5-2.4 GeVwith polarized photon beamPRL97 (2006)082003
CLAS experiment:differencial cross section in Eg=1.1-3.6 GeVPLB688(2010)289
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Data
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
1.0 1.1 1.2 1.3 1.4 1.5
Eg [GeV]
g+p K++L g+p K++L
g+n K0+L g+n K0+L
cosq1.0-1.0 0.0
s [m
b]
3
2
1
0
s [m
b]
10
5ds
/dW
[mb/
sr]
ds/dW
[mb/
sr]
0
0
1
1
Kaon-MAIDSaclay-Lyon A
Eg=1.05[GeV]
Eg=1.05[GeV]
0.9
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Discrepancy
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Why Threshold ?
Less effect of resonances than higher energy region
Simplicityto compare the data with a model
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In the threshold region
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TheoreticalApproach
• Hadron coupling– Isospin symmetry
• Electromagnetic (photo) coupling– Helicity amplitude
• Charged and neutral nucleon resonances
– Decay width• Charged and neutral Kaon resonances• However, the decay width of K1
resonance is not known
g
g
g
N
N
N
K
K
K
s channel
t channel
u channel
YNN*
K,K*,K1
Y
YYY*
g
N
KContact term
Y12
r (K1 K g ) = - 0.45 in Kaon-MAID, estimated from gpK0S+ data Free parameter in SLA
r (K* K g ) = = -1.53
g (K*0 K0
g )g (K*+
K+ g )
Theoretical Study: Effective Lagrangian Approach
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
• Kaon-MAID– T.Mart, C.Bennhold, PRC61 (2000) 012201(R)– Input: g+pK++L, g+pK++S0, g+pK0+S+
– Resonances: • N(1650) S11, N(1710) P11, N(1720) P13, • (1900) S31, (1910) P31 • K*(892), K1(1270)
– Hadronic form factor, contact term• Saclay-Lyon A
– T. Mizutani et al. PRC58 (1998) 75– Input: g+pK++L– Resonances:
• N(1720) P13• L(1405), L(1670), L(1810), S(1660) • K*(892), K1(1270)
– No hadronic form factor
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Characteristics of Two Models
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EXPERIMENTS
NKSand
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Experiments to InvestigateStrangeness Photo-
Productionat LNS/ELPH
NKS2Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
2000-2004:Using TAGX spectrometer (INS, U. Tokyo)Reconstruct K0
S from +- decayThe first measurement of K0 cross sectionfrom n(g,K0)L reaction [Phys.Rev.C78(2008)014001]
Neutral Kaon Spectrometer
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NKS
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2005-2007:Completely new spectrometer to cover full kinematical region
2008-: Upgrade project2010-: Taking physics data
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NKS2Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
Neutral Kaon Spectrometer 2
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Place of the ExperimentLaboratory of Nuclear Science
(LNS)
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Research Center for Electron Photon Science
(ELPH)
Tohoku Univ.
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Accelerator of LNS/ELPH, Tohoku University
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Accelerator of LNS/ELPH, Tohoku University
Photon Beam Line
BM4 tagger
BM5 tagger
to the GeV gexperimental hall
NKS2
Radiator (Carbon wire) to make Bremsstrahlung
B
Photo
n Bea
mEl
ectro
n (1.2
GeV
)
Scattered electron (0.1-0.4 GeV)
Tag F
Tag B
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Sweep magnet
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NKS NKS2
Improved Acceptance by covering forward region
NKS to NKS2
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NKS
NKS2
Acceptance of NKS and NKS2(-2007)
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Results of NKS
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K. Tsukada et. al, Phys.Rev.C78(2008)014001
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Results of NKS rK1Kg=-2.09 for SLA(Kaon-MAID’s value:-0.4474)
K. Tsukada et. al, Phys.Rev.C78(2008)014001
backward angular distribution in CM
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Suggestion from NKS Results
K. Tsukada et. al, Phys.Rev.C78(2008)014001
Suggestion from NKS Results
1.0 1.1 1.2 1.3 1.4 1.5
Eg [GeV]
g+n K0+L
s [m
b]
10
5
Saclay-Lyon AKaon-MAID
0.9
before
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after
K. Tsukada et. al, Phys.Rev.C78(2008)014001
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Results of NKS2
~370 K0S
~360 K0S
~2000 L
~2400 L
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Analyzed by K. Futatsukawa (Ph.D student)
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New region
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Results of NKS2
Analyzed by K. Futatsukawa (Ph.D student)
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~90 eventsin the peak
+- Invariant Mass [GeV/c2]p
- Inv
aria
nt M
ass [
GeV
/c2 ]
all of combinationsfrom p+-- event
preliminary
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
Analyzed by K. Futatsukawa (Ph.D student)
Results of NKS2
FURTHER INVESTIGATION
The next targets
K0S+L coincidence events
with reasonable statistics, andDetermine the sign of L recoil polarization
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K 0S+L coincidence events
Advantage: No.1
Less background in the invariant mass distribution
(Remember p.28)
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+- Invariant Mass [GeV/c2]
p- I
nvar
iant
Mas
s [G
eV/c
2 ]
all of combinationsfrom p+-- event
preliminary
K 0S+L coincidence events
Advantage: No.2Elimination of Fermi motion correction
Direct comparison with model Separation of K0+L and K0+S0
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K 0S+L coincidence events
g+n K 0+L
K 0S ++-
-+p
Extending the acceptance is essential
4 charged particlesin final state
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L recoil polarizationThe information make a restriction to model
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Upgrade Project
To increase acceptance Inner detectors are replaced by
Vertex Drift Chamber (VDC)New Inner Hodoscope (IH)
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20 cm Target
IHVDC
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Gain of Acceptancefor K 0S+L coincidence events
(1) Produced(2) NKS2 with new detectors(3) NKS2 prior(4) ratio of (2)/(3)
about 7 times after upgradeJoint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
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VDC IH
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An Event Display from the Last Run
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Preliminary results from the last run (2010/June-July)
PID plot: Momentum vs. 1/bwith rough counter calibrationfor two track event
proton
pion
About 40 counts as Lambdaabove the background
Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6
SUMMARY
• Investigation of strangeness photoproduction at ELPH, Tohoku Univ. in Sendai– NKS/NKS2 is an unique experiment
• Focusing neutral channel• In the threshold region (Eg=0.9-1.1 GeV)
– NKS• The first measurement of n(g, K0)X cross section
– cosqK0 = 0.9-1.0 in CM– NKS2
• Covering forward region– cosqK0 = 0.8-1.0 in CM
– NKS2 upgraded• New detectors are added to increase the acceptance• Detector and the system is ready• Physics data taking is going to start soon
– Sep/6–26 and Oct/1-31– ~2.01012 photon will be achieved
» ~400 K0s+L coincidence events is expected
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THANKS FOR LISTENING