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Neutral kaon photoproduction at LNS, Tohoku

Neutral kaon photoproduction at LNS, Tohoku. Masashi Kaneta f or the NKS/NKS2 collaboration Department of Physics Tohoku University. イントロダクション. Introduction. Physics Motivation. Investigation of strangeness production mechanism Threshold region of the production

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Neutral kaon photoproduction at LNS, Tohoku

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  1. Neutral kaon photoproduction at LNS, Tohoku Masashi Kaneta for the NKS/NKS2 collaboration Department of Physics Tohoku University

  2. イントロダクション Introduction

  3. 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K0+L

  4. Model dependence in cross-section • Models are based on K+ experimental data • There is large model dependence for K0 cross-section Solid-White: Kaon-MAID Dash-Red: Saclay-Lyon A (rkk=-0.45)

  5. 東北大学原子核理学研究施設での実験 The Experiments at LNS, Tohoku

  6. The Experiments • The series of experimentsby 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

  7. 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, Japan T. Ishikawa, T. Kinoshita, H. Miyahara, T. Nakabayashi, H. Shimizu, K. Suzuki, T. Tamae, T. Terasawa, H. Yamazaki • Department of Nuclear Science, Lanzhou University, Lanzhou, China Y.C. Han, T.S. Wang • Nuclear Institute, Czech Republic P. 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

  8. Tagged Photon Beam Line at LNS Neutral Kaon Spectrometer Neutral Kaon Spectrometer 2 150 MeV electron beam from LINAC Sweep magnet Photon tagging system 1.2 GeV Stretcher-Booster Ring

  9. Tagged Photon Beam at LNS g • Photon beam • Electron beam on carbon wire(11mm f) • Tagged by electron which has energy loss • E=0.8-1.1 GeV • from 1.2 GeV electron beam • 6 MeV coverage per tagging counter • Time resolution: ~240 ps e-on orbit Scattered e- Tagger Backup Tagger Finger Radiator

  10. NKS • There are two arms in one dipolemagnet IH: Inner Hodoscope SDC: Straw Drift Chamber CDD: Cylindrical Drift Chamber OH: Outer Hodoscope EV: Electron Veto No acceptance in forward region

  11. 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 1.0 m g beam A vertical cross section along beam

  12. NKS2 Photo

  13. Masashi Kaneta, Tohoku Univ. Comparison of Acceptances NKS NKS2 1.0 0.5 1.0 0.5 1.0 0.5 5 4 3 2 1 0 Eg = 0.9-1.0 GeV 1.0 0.5 1.0 0.5 1.0 0.5 efficiency [%] Eg=1.0-1.1 GeV 0.0 0.5 1.0 0.0 0.5 1.0 0.0 0.5 1.0 • Red contours: K0Scross-section • Kaon-MAID model calculation on a D2 target • Energy threshold 0.915 GeV in g+nK0+L • Eg=0.8-1.1 GeV at LNS cosθlab K0S momentum [GeV/c] Red contour: D2 target K0Sproduction cross-section (Kaon-MAID model) Gray contour: Acceptance of K0S(p+p-) in NKS and NKS2

  14. 第一世代実験 NKS の結果 Results from the 1st generation experiment NKS

  15. Particle Identification • Good pion/proton separation • DTOF: ~510ps

  16. Decay Volume Cut • Main background of K0S • e+e- from photon conversion  can be rejected by opening angle cut and Electron Veto counter • + - from r and w  can be rejected by decay volume cut • With the decay volume cut, the S/N increased

  17. Invariant Mass of p+p- • After applying decay volume cut and opening angle cut (-0.9<cosqOA<0.8), invariant mass of + - pair is obtained K0S K0S B.G.0 B.G.1 B.G.2 B.G.0: e+ e- (miss-ID as pions) B.G.1: p+ from K0S and p- from L B.G.2: p+p- from r and w

  18. Results of NKS: K 0S cross section • The first data of K0Scross section from g+nreaction near the threshold • vertical bar: statistical error • histogram: systematic error

  19. 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, K0S+ • 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

  20. p(g, K+)L reaction nn(g, K0)L reaction Hadronic coupling Isospin symmetry Electromagnetic coupling Helicity amplitude : photo-coupling of charged and neutral nucleon resonances. Decay width : photo-coupling of charged and neutral kaon resonances. However, the decay width of K1resonance is not known. Comparison ofp(g, K+)L with n(g, K0)L g(K*0K0g) r(K*K g) = = -1.53 g(K*+K+g) - 0.45 in Kaon-MAID from K0S+ reaction Free parameter in SLA r(K1K g) : r(K1Kg) represented as rkk from the next slide

  21. Comparison of K 0SCross-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

  22. Data prefer Saclay-Lyon A model and parametrization PH1 In the CM frame, the angle dependence of K0Scross sections are: Backward peak is suggested What is the model suggesting? backward forward backward forward

  23. 第二世代実験 NKS2 の結果 Results from the 2nd generationexperiment NKS2

  24. Particle Identification • An example • Liq. D2 target • two-tracks event • DTOF: ~350ps • opening angle cut is appliedto reduce e+e- • -0.9 < cosqOA < 0.8 charge sign  p+ p p- TOF(IHL2-OHVL4)

  25. Decay Vertex Distribution Target Cell Target Cell Opening angle cut -0.9<cosqOA<0.8 is required This distribution is projected on beam axis direction number of counts Vacuum cell region Decay vertex point [cm] • Decay vertex is reconstructed from trajectories of positive and negative charged particle pair g

  26. Recent Results (K0) • K0S cross-section on Liq. D2 target • analyzed ~30% of recorded data • g+nK0S+L is dominant • expanding angle • New region:cosqKLab<0.9 • Capability to discuss angular dependence 0.8 0.8 0.8 0.8 cosKLab 1.0<Eg<1.1 [GeV] 0.9<Eg<1.0 [GeV] 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.9 – 1.0 -0.2 -0.2 -0.2 -0.2 Preliminary 0.8 - 0.9 1.0 1.0 ds/dp [mbc/GeV] Background is estimatedby side-bands 0.8 0.8 0.6 0.2 0.4 0.0 0.6 0.6 0.4 0.4 0.2 0.2 0.7 - 0.8 0.0 0.0 -0.2 -0.2 0.6 0.2 0.4 0.0 p+p- invariant mass K0momentum [GeV/c]

  27. Recent Results (L) • Λ cross-section on Liq. D2 target • Analyzed ~30% of recorded data • g+nK0S+L and • g+pK++L are dominant cosqLLab 0.9<Eg<1.0 [GeV] 1.0<Eg<1.1 [GeV] 0.95 – 1.00 Preliminary 0.90 - 0.95 ds/dp [mbc/GeV] Background is estimatedby side-bands 0.80 - 0.90 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 pp- invariant mass L momentum [GeV/c]

  28. Recent Results (cont’) • K0 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.. •  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+ 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- invariant mass [GeV/c2] p+p- invariant mass [GeV/c2]

  29. 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

  30. Acceptance with New Detectors Note: single tracking efficiency: assumed to be 90% K0S (p+p- channel) L (pp-channel) (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 • The acceptance will increase • ~8 times

  31. New Inner Detectors Vertex Drift Chmaber 8 Layers u,u’,v,v’,u,u’,v,v’ structure Photo taken in Nov. 2008

  32. Event Display from the Last Run • Chamber commissioning and trigger study runs are held Sep. and Nov. 2008 g beam

  33. Event Display from the Last Run • Chamber commissioning and trigger study runs are held Sep. and Nov. 2008 g beam

  34. 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

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