neutral kaon photoproduction at lns, tohoku

International Symposium on Strangeness in Nuclear and Hadronic Systems -SENDAI08- (Dec15-18)

Neutral kaon photoproduction at LNS, Tohoku

Masashi Kanetafor the NKS/NKS2

collaboration

Department of PhysicsTohoku University


イントロダクション

Introduction

2Masashi Kaneta, Tohoku Univ.


Physics Motivation• Investigation of strangeness production

mechanism–Threshold region of the production

• No resonance decay effect– Good for comparison with models

• Give theoreticians base data to address– Coupling constant– Resonance contribution

• Small cross-section, i.e. high statistics data is required–Neutral channel in the strangeness photo-production

• Past experiments studied by K + production until 2002• Not enough data of differential cross-section of

g+n K 0+L



Model dependence in cross-section• Models are based on K + experimental data• There is large model dependence for K 0 cross-

section

Solid-White: Kaon-MAIDDash-Red: Saclay-Lyon A (rkk=-0.45)



東北大学原子核理学研究施設での実験

Masashi Kaneta, Tohoku Univ. 5

The Experiments at LNS, Tohoku


The Experiments• The series of experiments by neutral kaon

spectrometer at LNS, Tohoku Univ.–The 1st generation (NKS)

• Used TAGX spectrometer of INS and successfully done in 2004• The first measurement of the cross-section of neutral channel near

the threshold– Carbon target results: PLB651(2007)269– Liquid D2 target results: PRC78(2008)014001

• It is found that some improvements are necessary:– the forward region, and– the vertical position information in the chambers

–The 2nd generation (NKS2)• Constructed in 2004-2006 from scratch• Commissioning run in 2006• The data taking with liquid D2 target in 2006-2007• An upgrade is on going



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


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


Tagged Photon Beam Line at LNS

150 MeV electron beamfrom LINAC

1.2 GeV Stretcher-Booster Ring

Photon taggingsystem

Sweep magnet

Neutral KaonSpectrometerNeutral Kaon

Spectrometer 2



Tagged Photon Beam at LNS

Radiator

• Photon beam– Electron beam on

carbon wire (11mm f)– Tagged by electron

which has energy loss– Eg=0.8-1.1 GeV• from 1.2 GeV electron

beam– 6 MeV coverage per

tagging counter– Time resolution: ~240

ps

TaggerBackup

TaggerFinger

g

Scattered e -

e- on orbit



NKS• There are two arms

in one dipole magnet IH: Inner HodoscopeSDC: Straw Drift ChamberCDD: Cylindrical Drift ChamberOH: Outer HodoscopeEV: Electron Veto

No acceptancein forward region



NKS2


• Dipole Magnet– B=0.42 [T] at the

center• Inner Hodoscope

– Trigger– Start timing of TOF

• Outer Hodoscope– Trigger– Stop timing of TOF

• Straw Drift Chamber– Tracking (2D)

• Cylindrical Drift Chamber

– Tracking (3D)• Electron Veto

Counter

g beam

1.0 m

A verticalcross sectionalong beam


NKS2 Photo



0.0 0.5 1.0

1.0

0.51.0

0.50.0 0.5 1.0

1.0

0.51.0

0.5

13

Red contour: D2 target K 0S

production cross-section (Kaon-MAID model)

Gray contour: Acceptance of K 0S (p+p-) in NKS and NKS2

K 0S momentum [GeV/c]

• Red contours: K 0S cross-section

– Kaon-MAID model calculation on a D2 target

– Energy threshold 0.915 GeV in g+nK0+L

– Eg=0.8-1.1 GeV at LNS

0.0 0.5 1.0

1.0

0.51.0

0.5

cosθ

lab

Eg = 0.9-1.0 GeV

Eg =1.0-1.1 GeV

NKS NKS2

5

4

3

2

1

0

efficiency [%]

Comparison of Acceptances


第一世代実験 NKS の結果


Results from the 1st generation experiment NKS


Particle Identification• Good pion/proton

separation–DTOF: ~510ps



Decay Volume Cut

• Main background of K 　 0S

– e+e- from photon conversion can be rejected by opening angle cut and Electron Veto counter

– p+ p- from r and w can be rejected by decay volume cut

• With the decay volume cut, the S/N increased



Invariant Mass of p+p-

B.G.1

B.G.2

B.G.0

B.G.0: e+ e- (miss-ID as pions)B.G.1: p+ from K0

S and p- from L B.G.2: p+ p- from r and w

• After applying decay volume cut and opening angle cut (-0.9<cosqOA<0.8),invariant mass of p+ p- pair is obtained

K 0S


K 0S


Results of NKS: K 0S cross section

• The first data of K 0S cross section from g+n reaction near the threshold

– vertical bar: statistical error– histogram: systematic error



Isobar models (Effective Lagrangian Approach)

• Kaon-MAID [T. Mart, C. Bennhold, PRC61 (2000) 012201(R)]– Resonances in coupling:

• N(1650) S11, N(1710) P11, N(1720) P13, N(1895) D13,K *(892), K1(1270)

– Reaction of input data:• K +L, K +S0, K 0S+

– including hadronic form factor and contact term• Saclay-Lyon A [T. Mizutani et al., PRC58 (1998) 75]

– Resonances in coupling:• N(1720) P13,

K *(892), K1(1270),L(1405) S01, L(1670) S01, L(1810) P01, S(1660) P11

– Reaction of input data:• K +L

– No hadronic form factor


International Symposium on Strangeness in Nuclear and Hadronic Systems -SENDAI08- (Dec15-18) 20

Comparison of p(g, K+)L with n(g, K0)Lp(g, K+)L reaction n n(g, K0)L reaction

1. Hadronic coupling• Isospin symmetry

2. Electromagnetic coupling① Helicity amplitude : photo-coupling of charged and neutral

nucleon resonances.② Decay width : photo-coupling of charged and neutral kaon

resonances. However, the decay width of K 1 resonance is not known.

- 0.45 in Kaon-MAID from K0S+ reaction Free parameter in SLA

r(K1K g) represented as rkk from the next slide

r(K* K g) =

r(K1 K g) :

Masashi Kaneta, Tohoku Univ.

g(K*0 K 0 g) g(K*+ K + g)

= -1.53


Comparison of K 0S Cross-section with

Models

• Fermi motion effect of neutron is included in the calculation– Non-relativistic Bonn OBEPQ (one-boson-exchange-potential in q-space)

deuteron wave function [R. Machleidt et al., Phys. Rept. 149 (1987) 1-89]• Data prefer Saclay-Lyon A model and phenomenological

parametrization PH1– Note: PH2 is the inverse angular distribution to that of PH1



What is the model suggesting?


• Data prefer Saclay-Lyon A model and parametrization PH1

• In the CM frame, the angle dependence of K 0S cross sections are:

Backward peak is suggested

forwardbackward forwardbackward


第二世代実験 NKS2 の結果

Results from the 2nd generationexperiment NKS2



Particle Identification• An example

– Liq. D2 target– two-tracks event– DTOF: ~350ps– opening angle cut

is applied to reduce e+e-

• -0.9 < cosqOA < 0.8


TOF(IHL2-OHVL4)

char

ge si

gn pp+

p-


Decay Vertex Distribution


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)


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

K 0 momentum [GeV/c]

ds/d

p [m

b c/

GeV]

• K 0S cross-section on Liq.

D2 target– analyzed ~30% of

recorded data– g+n K 0

S+L is dominant– expanding angle

• New region: cosqKLab<0.9– Capability to discuss

angular dependenceBackground is estimated by side-bands

p+p- 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)


• Λ cross-section on Liq. D2 target

– Analyzed ~30% of recorded data

– g+n K 0S+L and

g+p K ++L are dominant

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 is important– Three/Four tracks event analyses

• Recent results will be shown by Kenta Futatsukawa in the poster session– Need to increase the acceptance

• Detector upgrade project is on going


pp- in

varia

nt m

ass [

GeV/

c2]

p+p- invariant mass [GeV/c2]


Expanding the Study• Physics motivation

–K+Y coincidence measurement• Advantage

– No Fermi motion correction• Differentials cross section• Lambda polarization

• Detector upgrade–Replacing inner detector

• Replace straw drift chamber by a 3D tracker– increase the acceptance

• Two-side-read-out hodoscope– increase TOF resolution to have better particle separation



Acceptance with New Detectors


• The acceptance will increase– ~8 times

(1): all K0S (p+ p- )+L(p-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 (pp- channel)K 0

S (p+p- channel)

Note: single tracking efficiency: assumed to be 90%


New Inner Detectors


Vertex Drift Chmaber8 Layersu,u’,v,v’,u,u’,v,v’ structure

Photo taken in Nov. 2008


Event Display from the Last Run• Chamber

commissioning and trigger study runs are held Sep. and Nov. 2008


g beam


Summary• The investigation of neutral kaon photoproduction at LNS,

Tohoku– Tagged photon beam (Eg=0.8-1.1 GeV)at LNS, Tohoku

• The first measurement of neutral kaon via g+n reaction near the threshold by NKS

– Carbon target: PLB651(2007)269– Liquid D2 target: PRC78(2008)014001

• The new spectrometer NKS2 covers larger acceptance– Over all kinematic region– Capability to discuss angular dependence of cross-section

• The upgrade– New inner detectors– Expanding the solid angle– Coincidence measurement of K+L

• ~8 times acceptance– The performance is tested by commissioning run


neutral kaon photoproduction at lns, tohoku

Documents

data of neutral channel

neutral kaon spectrometer

production crosssection

k0 lambda channel

hadronic systems sendai08

requiredneutral channel

kaon angle dependence

total crosssection