Recent Results from LEPS/SPring-8
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Transcript of Recent Results from LEPS/SPring-8
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Recent Results from LEPS/SPring-8
Ken HicksOhio University, USA
Sept. 21, 2009
on behalf of LEPS collaboration
International Conference on Quark Nuclear Physics 2009, Beijing, ChinaInternational Conference on Quark Nuclear Physics 2009, Beijing, China
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Outline
• Short description of LEPS• Photoproduction of KY• Photoproduction of KY*• Photoproduction of K*Y• Search for the + using K+K- from deuterium
K. Hicks, Ohio U. QNP2009 2
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Schematic view of the LEPS facility
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b) Laser hutch
a) SPring-8 SR ring
c) Experimental hutch
Compton -ray
Laser light
8 GeV electron Recoil electron
Tagging counter
36m70m
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Backward-Compton Scattered Photon• 8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV )• E measured by tagging a recoil electron E ~10 MeV• Laser Power ~6 W Photon Flux ~1 Mcps• Laser linear polarization 95-100% ⇒ Highly polarized beam
QNP2009 4
PWO measurement
tagged
Linear Polarization of beam
photon energy [GeV] photon energy [MeV]
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K. Hicks, Ohio U. QNP2009 5
LEPS detector at SPring-8/LEPS
1.5
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Particle ID at LEPS
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TOF
Dipole Magnet 0.7 Tesla
Target
Start Counter DC2 DC3
DC1SVTX
AC(n=1.03)
Photons
Mo
men
tum
[G
eV/c
]
K/ separation
K++
Mass/Charge [GeV/c2]
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Strangeness Production
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Goals: data for (1020) , hyperons
Features:• Forward angle
measurement, including 0o
• Polarization observables
• Strangeness production
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(1116) & (1193)Reaction Detection Method
& MeasurementsMajor Authors
Reference
K+ missing;
beam asymmetry
R.G.T. Zegers,
M. Sumihama
PRL 91, 092001 (2003)
K+ missing;
beam asymmetry,
differential cross section
M. Sumihama PRC 73, 035214 (2006)
p-;
beam asymmetry,
differential cross section
K. Hicks,
T. Mibe,
M. Sumihama
PRC 76, 042201(R) (2007)
K+ missing;
beam asymmetry,
differential cross section
H. Kohri PRL 97, 082003 (2006)
K. Hicks, Ohio U. QNP2009 8
),( Kp
),( Kp
),( Kp
),( Kn
),( Kp
),( Kp
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(1385), (1405), (1520)Reaction Detection Method
& MeasurementsMajor Authors
Reference
;
differential cross section
M. Niiyama,
H. Fujimura
PRC 78, 035202 (2008)
K+ missing;
beam asymmetry,
differential cross section
K. Hicks,
D. Keller,
H. Kohri
PRL 102, 012501 (2009)
pK, KK;
beam asymmetry,
decay asymmetry,
differential cross section
N. Muramatsu,
J. Y. Chen,
W.C. Chang
PRL 103, 012001 (2009)
K+ missing;
beam asymmetry,
differential cross section
H. Kohri axXiv:0906.0197
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)1405(),( Kp
)1385(),( Kp
)1520(),( Kp
)1385(),( Kn
)1520(),( Kp
)1520(),( 0 Kn
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Born Diagrams
QNP2009 10
s-channel
t-channel contact term
u-channel
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Angular Distributions of pK+
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s-channel
t-channelu-channel
R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006)
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Angular Distributions of pK+
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s-channel
t-channelu-channel
R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006)
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Energy Distribution
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R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006)
LEPS LEPS
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Missing Mass of K+
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LH2 data
p(, K+) GeV/c2
0
(1520)(1405)(1385)
LD2 data
(1520)
(1405)0(1385)- (1385)
0, -
N(, K+) GeV/c2
spectrometer
K+
Y
p/d
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Invariant Mass and Its Missing Mass
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spectrometer
K-
K+
p
p
* K+
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Energy Dependence of Cross Sections
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K+K*-exchange by M. Guidal (Regge model).Isobar + Regge by T. Mart and C. Bennhold. Gent isobar model by T. Corthals
LEPS SAPHIR CLAS
0(1193)(1116)
M. Sumihama et al. (LEPS Collaboration), PRC 73, 035214 (2006)
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Differential Cross Sections
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No forward peaking.
0(1193)(1116)
Forward peaking. Need Regge poles.
LEPS CLAS
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Photon-Beam Asymmetry
• If the dominant contributions are from t-channel K and K* exchange, they can be further distinguished by photon-beam asymmetry using linearly polarized photon beam.
• A=(perp-para)/ (perp+para)• If A is negative (positive), the interaction is
dominated by the electric (magnetic) component induced by K (K*) exchange.
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Photon Beam Asymmetry
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0(1193)(1116)
Larger contribution from t-channel K* exchange.
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Uncertainties in the Theoretical Models
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T. Mart and A. SulaksonoPRC74 (2006) 055203
SAPHIR/LEPS
CLAS/LEPS
SAPHIR/CLAS/LEPS
Used data for fitting in models.
Photon asymmetry
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Backward K+ photoproduction
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Detect (p-) at forward angles
(1116)
p XK+
p p K+, K*, KY*
K. Hicks et al. (LEPS Collaboration), PRC 76, 042201(R) (2007)
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Theoretical Models
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T. Mart and A. SulaksonoPRC74 (2006) 055203
SAPHIR/LEPS
CLAS/LEPS
SAPHIR/CLAS/LEPS
Used data to fit models.
Photon asymmetry
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(1520) Experiments• LAMP2 (real photon) • CLAS (virtual photon)
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)1520( Kp )1520(' Kepe
D. P. Barber et al. (LAMP2 Collaboration), Z. Phys. C 7, 17 (1980).S. P. Barrow et al. (CLAS Collaboration), PRC 64, 044601 (2001).
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Toki, Garcia-Recio and Nieves, PRD, 77, 034001 (2008)
• The chiral unitary model predicts a small coupling between Λ(1520) and NK*.
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Main contribution comes from the K exchange process
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Nam, Hosaka, and Kim, PRD71, 114012 (2005)
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Production from ProtonProduction from Proton Production from NeutronProduction from Neutron
Large np isospin asymmetry.
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Photoproduction of Λ*
QNP2009 26
N. Muramatsu et al. (LEPS Collaboration), PRL 103, 012001 (2009)
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Cross sections on H and D
• The ratio between deuterons and protons was 1.02±0.11. Production from neutrons is strongly suppressed at LEPS kinematics.
• Large isospin asymmetry. K. Hicks, Ohio U. QNP2009 27
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Importance of Contact Term
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A. Hosaka, Workshop of “Challenge to New Exotic Hadrons with Heavy Quarks”.
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Isospin Asymmetry in + Production
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Cross Sections: n K+*-
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Calculations are from Oh, Ko & Nakayama, averaged over the bin size shown.
•Cross sections are only measured at forward angles: complementary to the CLAS data.
K. Hicks et al. (LEPS Collaboration), PRL 102, 012501 (2009)
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Beam Polarization Dependence
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Due to statistics, only three bins in beam energy (1.5-1.8, 1.8-2.1, 2.1-2.4 GeV) were used for the beam asymmetry fits.
The K+- final state (left), shows the opposite sign for the beam asymmetry when compared with the K+*- final state (right).
n K+- n K+*-
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Beam Asymmetries
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Present results (solid points) compared with previously published data (open points) from Kohri et al. (PRL, 2006)
Curve (Oh, Ko, Nakanyama) assumes 3-quark structure to the *. A 5-quark component would have asymmetry of -1 (model of B. Zou).
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K*0 photoproduction at LEPS
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K*K*
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K. Hicks (Ohio) Hyp-X Conf. 34
Theory: a) K*+ , b) K*0+
SOLID BLUE: no kappa form factor; DASHED RED: with kappa form factor
Y. Oh and H. Kim, hep-ph/0605105.
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K*+ and K*0 Beam Asymmetry
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Large sensitivity to the kappa meson for linear polarization.
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Experimental status of + Searches
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•Not seen in the most of the high energy experiments: The production rate of +/(1520) is less than 1%.
•No signal seen in CLAS p, KEK-PS (K+,+) experiments.
•The width must be less than 1 MeV. (DIANA and KEK-B).
•LEPS could be inconsistent with CLAS d experiment.
•Production rate depends on reaction mechanism.
•K* coupling should be VERY small.
•K coupling should be small.
•Strong angle or energy dependence.
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LEPS
Good forward angle coverage
Poor wide angle coverage
1.5 – 2.4 GeV photons
Symmetric acceptance for K+ and K-
MKK>1.04 GeV/c2
Select quasi-free process
CLAS
Poor forward angle coverage
Good wide angle coverage
1.0 – 3.5 GeV photons
Asymmetric acceptance
MKK > 1.07 GeV/c2
Require re-scattering or large
Fermi momentum of a spectator
~
Differences: LEPS and CLAS for n K-
K. Hicks, Ohio U. QNP2009 37
LEPS: LAB < 20 degree
CLAS: LAB > 20 degree
K- coverage:
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Minimum Momentum Spectator Approximation (MMSA)
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γ
d
K-
K+
Nucleon fromdecay or scattering
Spectatornucleon
p n
4 momentum of pn system
Mpn and ptot
|pCM| and vpn
pCM
- pCM
vpn
We know
Direction of pCM is assumed so that the spectator can have the minimum momentum for given |pCM| and vCM.
at rest
tagged
detected
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Double-role of MMSA
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coherent
inelastic
quasi-free
Clean-up Estimation of pF
pmin pmin
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Results of (1520) analysisSimple (,K+) missing mass: No correction on Fermi motion effect.pK- invariant mass with MMSA: Fermi motion effect corrected.
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(-2lnL) =55.1 for ndf=2 7.1
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Results of analysis
(-2lnL) =31.1 for ndf=2 5.2
Simple (,K-) missing mass: No correction on Fermi motion effect.nK+ invariant mass with MMSA: Fermi motion effect corrected.
2Peak position: 1.527 0.002 GeV/
Signal yeild: 116 21 events
Differential cross-section: 12 2 nb/sr
c
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Probability of 2 x 10-7 is not good enough. “Extraordinary claim requires extraordinary evidence.”
Higher statistics data was collected in 2006-2007 with the same experimental setup.
Blind analysis is under way to check the Θ+ peak
Next step
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Summary• LEPS data has had a significant effect on our
understanding of strangeness production.• Recent results on * reveals the importance of
the contact term in photoproduction.– Large isospin difference of production cross section.
• Recent results on * shows that SU(3) flavor symmetry works well for the baryon decuplet.– Beam asymmetry is more negative than expected.
• Search for + is still in progress.– There are many constraints from other data.
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K. Hicks, Ohio U. QNP2009 44
LEPS new beam line (LEPS2)
• Beam upgrade: Intensity --- High power laser, Multi laser(x4) --- Laser elliptic focus 2x106 107 /sec for 2.4 GeV 2x105 106 /sec for 3 GeV
Energy --- Laser with short , re-injected Soft X-ray+BCS (2nd stage), up to ~7.5 GeV
• Detector upgrade: (reaction process & decay process) Scale & --- General-purpose large 4 detector Flexibility Coincidence measurement of charged particles and neutral particles (photons) BNL/E949 detector
DAQ --- High speed for the minimum bias trigger
• Physics: Multi-quark (>3)
Workshop on LEPS2 (2005/7, 2007/1)
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Missing mass of p ( , K+) X
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H. Kohri et al. (LEPS Collaboration), arXiv:0906.0197
Possible bump structure at W~2.1 GeV? Better description of energy dependence
with the inclusion of a nucleon resonance
w/o N*with N*
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Beam Asymmetry of (1520)
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Contribution from t-channel K* exchange is dominant at W>2.2 GeV.