The Investigation of Strangeness Photoproduction in the Threshold R egion at LNS-Tohoku

The Investigation of Strangeness

Photoproduction in the Threshold Region

at LNS-TohokuMasashi Kanetafor the NKS/NKS2 collaboration

Department of Physics, Tohoku University

INTRODUCTION序

Introduction• Motivation

– Understanding the mechanism of strangeness production• via photoproduction on nucleon• focusing on neutral channel

• Characteristics– Neutral channel

• K + data is not enough to make a model to predict cross section of neutral channel

• K 0 data is the KEY of the study– Threshold region

• No resonance decay effect in the final products

Masashi Kaneta: Workshop on "Hadron and Nuclear Physics (HNP09)“ Nov. 16-19, 2009, RCNP, Osaka University

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4








5

Channels of Strangeness Production


g+p K++Lg+p K++S0

g+p K0+S+

g+n K0+Lg+n K0+S0

g+n K++S-

g+N K+Y

6

The Cross-section


Proton target

Mainly K+ data

Figure:PRC74(2006)044004

No databefore NKSexperimenthad started

Data: SAPHIRLines: Kaon-MAID

model

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Different predictions by Models

0.9 1.0 1.1 1.2 1.3 1.4 1.5

Eg [GeV]0.9 1.0 1.1 1.2 1.3 1.4 1.5

g+p K++L g+p K++L

g+n K0+L g+n K0+L

cosq

1.0

1.0-1.0

-1.0 0.0

0.0

s [m

b]

3

2

1

0

s [m

b]

10

5

0

ds/dW

[mb/

sr]

ds/dW

[mb/

sr]

0

0

1

1

Kaon-MAIDSaclay-Lyon A

Eg=1.05[GeV]

Eg=1.05[GeV]

Both models show similar results

Huge differences

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10

MODELS模型


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Theoretical Study: Effective Lagrangian Approach

• 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

Y

- 0.45 in Kaon-MAID, estimated from gpK0S+ data Free parameter in SLA

53.1)()()( *

00** - g

ggKKgKKgKKr

)( 1 gKKr


Models• Kaon-MAID

– T.Mart, C.Bennhold, PRC61 (2000) 012201(R)– Input: gpK+L, gpK+S0, gpK0S+

– 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: gpK+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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EXPERIMENTALSTUDY BY NKS/NKS2

実験


The NKS (1998-) and NKS2 (2004-) collaboration• Akita University, Akita, Japan

A. Sasaki• Ichinoseki National college of Technology, Ichinoseki, Japan

O. Konno• Department of Physics, Tohoku University, Sendai, Japan

N. Chiga, B. Beckford, M. Ejima, T. Fujii, Y. Fujii, T.Fujibayashi, T. Gogami, K. Futatsukawa,O. Hashimoto, K. Hosomi, K. Hirose(a), A. Iguchi, S. Kameoka, H. Kanda, M. Kaneta, H. Kato,D. Kawama, T. Kawasaki, C. Kimura, S. Kiyokawa, T. Koike, T. Kon, Y. Ma, K. Maeda,N. Maruyama, A. Matsumura, Y. Miyagi, Y. Miura, K. Miwa, S.N. Nakamura, H. Nomura, A. Okuyama, A. Ohtani, T. Otani, M. Sato, A. Shichijo, K. Shirotori, T. Takahashi(b), H. Tamura, N. Taniya, H. Tsubota, K. Tsukada(c) N. Terada, M. Ukai(d), D. Uchida,T. Watanabe, T. Yamamoto, T. Yamamoto, H. Yamauchi, K. Yokota

• Laboratory of Nuclear Science, Tohoku University, Sendai, JapanT. Ishikawa, T. Kinoshita, H. Miyahara, T. Nakabayashi, H. Shimizu, K. Suzuki, T. Tamae, T. Terasawa, H. Yamazaki

• Department of Nuclear Science, Lanzhou University, Lanzhou, ChinaY.C. Han, T.S. Wang

• Nuclear Institute, Czech RepublicP. Bydzovsky, M. Sotona

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Student name is shown with underline(a)Now at LNS, Tohoku University, Japan(b)Now at KEK, Japan(c)Now at RIKEN, Japan(d)Now at Gifu University, Japan


Laboratory of Nuclear Science (LNS), Tohoku Univ. at Sendai

• Electron beam up-to 1.2 GeV• Two tagged-photon beam lines

– Bremsstrahlung– Eg=0.8-1.1 GeV (from Ee=1.2 GeV)– Tagged-photon beam rate > ~MHz

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Tagged Photon System

BM4 tagger

BM5 tagger

to the otherexperimental 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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Experimental Study at LNS, Tohoku• Neutral Kaon Spectrometer (NKS)

– The first measurement of the K0 cross section near the threshold• Published as PRC78(2008)014001

– The data prefers SLA model rather than Kaon-MAID• Backward peak in cos qCM distribution

• NKS2– Expanding the study using new spectrometer– Improving the acceptance

• K0, L single measurement• K0L coincidence measurement

– But the statistics is not enough• Detector upgrade project in progress

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Results of NKS

• The cross section of K0

– Eg =0.9-1.0 and 1.0-1.1 GeV– cos qKLab = 0.9-1.0

• The data prefer SLA– SLA suggests backward peak of K0 in CM

forwardbackward forwardbackward

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NKS to NKS2

• Extending the study– We needed new spectrometer

• Larger acceptance• better TOF resolution for the particle

identification– The second generation of study by

Neutral Kaon Spectrometer 2 (NKS2)

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NKS NKS2

Improved Acceptance by covering forward region

NKS to NKS2

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Particle Identification of NKS2• An example

– Liq. D2 target– two-tracks event– TOF resolution

~350ps– opening angle cut

is applied to reduce e+e-

• -0.9 < cosqOA < 0.8

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TOF(IHL2-OHVL4)

char

ge si

gn pp

p-


Decay Vertex Distribution

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g

Vacuumcellregion

Target Cell

Opening angle cut -0.9<cosqOA<0.8is required

Target Cell

Decay vertex point [cm]

num

ber o

f cou

nts

• Decay vertex is reconstructed from trajectories of positive and negative charged particle pair

This distribution is projectedon beam axis direction


Recent Results (K 0)• K0

S cross-section on Liq. D2 target– analyzed ~30% of recorded data– g+nK 0S+L is dominant– expanding angle

• New region: cos qKLab<0.9– Capability to discuss angular

dependence

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0.9<Eg<1.0 [GeV] 1.0<Eg<1.1 [GeV]

K 0 momentum [GeV/c]

ds/d

p [m

b c/

GeV]

Background is estimated by side-bands

pp- invariant mass

0.0

-0.2

0.2

0.4

0.6

0.8

0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6

0.0

-0.2

0.2

0.4

0.6

0.8

0.0

-0.2

0.2

0.4

0.6

0.8

0.0

-0.2

0.2

0.4

0.6

0.8

0.0

-0.2

0.2

0.4

0.6

0.8

1.0

0.0

-0.2

0.2

0.4

0.6

0.8

1.0

cos K

Lab

0.8

- 0.9

0.7

- 0.8

0.9

– 1.0

Prelim

inary


Recent Results (L)• L cross-section on

Liq. D2 target– Analyzed ~30% of

recorded data– g+n K0

S+L and– g+p K++L are

dominant

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0.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

L momentum [GeV/c]

cosq

LLa

b0.

90 -

0.95

0.80

- 0.

900.

95 –

1.00

0.9<Eg<1.0 [GeV] 1.0<Eg<1.1 [GeV]

Background is estimated by side-bands

pp- invariant mass

Preliminaryds

/dp

[mb

c/Ge

V]


Recent Results (cont’)• K 0 measurement

– Extends the study to discuss cosq dependence– Total number of the particle is similar to NKS

• statistics in each (Eg, p, cosq) bin are smaller.. • L measurement

– Large statistics (>10 times of NKS)– Data is from two reaction (g+p and g+n )

• need to separate to compare a model of elementally process

• K +L coincidence measurement– Four-track-event analyses– Need to increase the acceptance

• Detector upgrade project is on going

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pp- Invariant Mass [GeV/c2]

pp- I

nvar

iant

Mas

s [G

eV/c

2 ]

all of combinationsfrom ppp-p- event

WHAT IS THE NEXT?

次


The next stage of the study• KY coincidence measurement

– No Fermi motion correction of n in d– Reaction plane will be defined

• More information for study– Self polarization of L

• New inner detectors– to increase the acceptance

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L Polarization Measurement

qqq

cosP 1 )A(cos )(cos 0 LN

ddN

Acceptance as a function of cosq decay parameter

0.642(PDG)

polarization

pg

pLt = pg×pL t

LCM

q

pp

pp

Transverse polarization measurement

pK

qK

reaction planein CM

pN

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Model Predictions: L Polarization

q of Kaon in CM [degree]

L P

olar

izatio

nSLA

(rKK=

-2.0

87)

Kaon

MAI

DSA

1(P.

Byd

zolv

ski)

g+p K ++L g+n K 0+L

calculated by P. Bydzofvky

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NEW DETECTORS

新


NKS2+ Set-up with New Inner Detectors

A 3D trackerVertex Drift Chamber

Inner Hodoscope

Upgrade project

NKS2 to NKS2+

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Acceptance for K 0

S+L Events

• The acceptance will increase with the same trigger condition– ~8 times

(1): all K0S (p+ p- )+Lp-p) events

(2): the four daughters pass through VDC with two OH Hits

(3): four daughters pass through OH Note: No decay volume cut is applied

L p p- channel)K 0

S (p+ p- channel)

Note: single tracking efficiency: assumed to be 90%

Acceptance of new detectorsAcceptance of Current Detectors

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Vertex Drift Chamber Design• Requirements

– As possible as small cell• but limited by feedthrough

(f3mm)– At least 6 layers with stereo

wires• Decision

– Trapezoid (almost square) cell shape

– Half cell size: 4 mm– 8 layers– uu’ vv’ uu’ vv’

• increasing stereo angle with radius:6.0 - 11.1°

– Drift gas = Ar:Ethane(50:50)

55 mm

65 mm

137 mm

uu’uu’vv’

vv’


Vertex Drift Chamber

• >99% tracking efficiency for each layer– by Cosmic-ray test, using Ar:Ethane (50:50) gas

• Position resolution: ~400 mm (FWHM)35


Event Display

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g beam


Event Display

37

g beam

SUMMARY結


Summary• Investigation of Strangeness photoproduction

– focusing on the neutral channel: g+nK0+L– near the threshold

• using tagged photon beam (Eg=0.8-1.1GeV) Laboratory of Nuclear Science, Tohoku University

• KY coincidence measurement will open the next stage of the study

• Detector upgrade project is on going

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Documents

The Investigation of Strangeness Photoproduction in the Threshold R egion at LNS-Tohoku