recent results from leps/spring-8

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

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

Schematic view of the LEPS facility


b) Laser hutch

a) SPring-8 SR ring

c) Experimental hutch

Compton -ray

Laser light

8 GeV electron Recoil electron

Tagging counter

36m70m

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]


LEPS detector at SPring-8/LEPS

1.5

Particle ID at LEPS


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]

Strangeness Production


Goals: data for (1020) , hyperons

Features:• Forward angle

measurement, including 0o

• Polarization observables

• Strangeness production

(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,


K. Hicks,

T. Mibe,

M. Sumihama

PRC 76, 042201(R) (2007)

K+ missing;

beam asymmetry,


H. Kohri PRL 97, 082003 (2006)


),( Kp

),( Kp

),( Kp

),( Kn

),( Kp

),( Kp

(1385), (1405), (1520)Reaction Detection　Method

&　MeasurementsMajor　Authors

Reference

;


M. Niiyama,

H. Fujimura

PRC 78, 035202 (2008)

K+ missing;

beam asymmetry,


K. Hicks,

D. Keller,

H. Kohri

PRL 102, 012501 (2009)

pK, KK;

beam asymmetry,

decay asymmetry,


N. Muramatsu,

J. Y. Chen,

W.C. Chang

PRL 103, 012001 (2009)

K+ missing;

beam asymmetry,


H. Kohri axXiv:0906.0197


)1405(),( Kp

)1385(),( Kp

)1520(),( Kp

)1385(),( Kn

)1520(),( Kp

)1520(),( 0 Kn

Born Diagrams

QNP2009 10

s-channel

t-channel contact term

u-channel

Angular Distributions of pK+


s-channel

t-channelu-channel

R. Bradford et al. (CLAS Collaboration), PRC 73, 035202 (2006)

Angular Distributions of pK+


s-channel

t-channelu-channel


Energy Distribution



LEPS LEPS

Missing Mass of K+


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

Invariant Mass and Its Missing Mass


spectrometer

K-

K+

p

p

* K+

Energy Dependence of Cross Sections


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)

Differential Cross Sections


No forward peaking.

0(1193)(1116)

Forward peaking. Need Regge poles.

LEPS CLAS

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.


Photon Beam Asymmetry


0(1193)(1116)

Larger contribution from t-channel K* exchange.

Uncertainties in the Theoretical Models


T. Mart and A. SulaksonoPRC74 (2006) 055203

SAPHIR/LEPS

CLAS/LEPS

SAPHIR/CLAS/LEPS

Used data for fitting in models.

Photon asymmetry

Backward K+ photoproduction


Detect (p-) at forward angles

(1116)

p XK+

p p K+, K*, KY*

K. Hicks et al. (LEPS Collaboration), PRC 76, 042201(R) (2007)

Theoretical Models


T. Mart and A. SulaksonoPRC74 (2006) 055203

SAPHIR/LEPS

CLAS/LEPS

SAPHIR/CLAS/LEPS

Used data to fit models.

Photon asymmetry

(1520) Experiments• LAMP2 (real photon) • CLAS (virtual photon)


)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).

Toki, Garcia-Recio and Nieves, PRD, 77, 034001 (2008)

• The chiral unitary model predicts a small coupling between Λ(1520) and NK*.


Main contribution comes from the K exchange process

Nam, Hosaka, and Kim, PRD71, 114012 (2005)


Production from ProtonProduction from Proton Production from NeutronProduction from Neutron

Large np isospin asymmetry.

Photoproduction of Λ*

QNP2009 26

N. Muramatsu et al. (LEPS Collaboration), PRL 103, 012001 (2009)

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

Importance of Contact Term


A. Hosaka, Workshop of “Challenge to New Exotic Hadrons with Heavy Quarks”.

Isospin Asymmetry in + Production


Cross Sections: n K+*-


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)

Beam Polarization Dependence


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+*-

Beam Asymmetries


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).

K*0 photoproduction at LEPS


K*K*

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.

K*+ and K*0 Beam Asymmetry


Large sensitivity to the kappa meson for linear polarization.

Experimental status of + Searches


•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.

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-


LEPS: LAB < 20 degree

CLAS: LAB > 20 degree

K- coverage:

Minimum Momentum Spectator Approximation (MMSA)


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

Double-role of MMSA


coherent

inelastic

quasi-free

Clean-up Estimation of pF

pmin pmin

Results of (1520) analysisSimple (,K+) missing mass: No correction on Fermi motion effect.pK- invariant mass with MMSA: Fermi motion effect corrected.

K. Hicks, Ohio U. QNP200940

(-2lnL) =55.1 for ndf=2 7.1

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

K. Hicks, Ohio U. QNP200941

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


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.



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)

Missing mass of p ( , K+) X


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*

Beam Asymmetry of (1520)


Contribution from t-channel K* exchange is dominant at W>2.2 GeV.

recent results from leps/spring-8

Documents

differential cross sectionk

differential cross sectionh

differential cross sectionn

pbeam asymmetry

decay asymmetry

kkbeam asymmetry

clas collaboration

polarized photon beam