Photoproduction of Strangeness near the Threshold at Tohoku

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

Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6 5

Why Neutral?

Theoretical studies were based on

data of g+p K++Yand then there are huge discrepancies

in prediction of neutral channel

6

Neutral channel is requisite


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

7

Data


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

8Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6

Discrepancy


Why Threshold ?

Less effect of resonances than higher energy region

Simplicityto compare the data with a model


In the threshold region


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


• 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

13

Characteristics of Two Models


EXPERIMENTS

NKSand

16

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

17

NKS


2005-2007:Completely new spectrometer to cover full kinematical region

2008-: Upgrade project2010-: Taking physics data

18

NKS2Joint Meeting of JSPS+SHERE at Praha, 2010/Sep/4-6

Neutral Kaon Spectrometer 2


Place of the ExperimentLaboratory of Nuclear Science

(LNS)

19

Research Center for Electron Photon Science

(ELPH)

Tohoku Univ.


Accelerator of LNS/ELPH, Tohoku University

20


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

22

Sweep magnet


NKS NKS2

Improved Acceptance by covering forward region

NKS to NKS2



NKS

NKS2

Acceptance of NKS and NKS2(-2007)


Results of NKS


K. Tsukada et. al, Phys.Rev.C78(2008)014001


Results of NKS rK1Kg=-2.09 for SLA(Kaon-MAID’s value:-0.4474)


backward angular distribution in CM


Suggestion from NKS Results


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


after


30

Results of NKS2

~370 K0S

~360 K0S

~2000 L

~2400 L


Analyzed by K. Futatsukawa (Ph.D student)

31

New region


Results of NKS2


32

~90 eventsin the peak

+- Invariant Mass [GeV/c2]p

- Inv

aria

nt M

ass [

GeV

/c2 ]

all of combinationsfrom p+-- event

preliminary



Results of NKS2

FURTHER INVESTIGATION

The next targets

K0S+L coincidence events

with reasonable statistics, andDetermine the sign of L recoil polarization


K 0S+L coincidence events

Advantage: No.1

Less background in the invariant mass distribution

(Remember p.28)



+- Invariant Mass [GeV/c2]

p- I

nvar

iant

Mas

s [G

eV/c

2 ]

all of combinationsfrom p+-- event

preliminary


Advantage: No.2Elimination of Fermi motion correction

Direct comparison with model Separation of K0+L and K0+S0



g+n K 0+L

K 0S ++-

-+p

Extending the acceptance is essential

4 charged particlesin final state


L recoil polarizationThe information make a restriction to model


40

Upgrade Project

To increase acceptance Inner detectors are replaced by

Vertex Drift Chamber (VDC)New Inner Hodoscope (IH)


20 cm Target

IHVDC

41

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

42

VDC IH


An Event Display from the Last Run


44

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


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


THANKS FOR LISTENING

Photoproduction of Strangeness near the Threshold at Tohoku

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