1. Pentaquark search at SPring-8 LEPS Norihito Muramatsu RCNP, Osaka University For the LEPS Collaboration DIS06 @Tsukuba, 22 Apr. 2006 ～～～ Today’s menu ～～～ - Overview of  + status and standpoint of LEPS experiment -  + search in  d  +  (1520) - Future prospects at LEPS, new beamline and J-PARC

2. Overview of  + status searched mass width statistical mode [MeV/c 2 ] [MeV/c 2 ] significance LEPS(C)  C  K + K - X 1540  10 < 25 4.6  DIANA K + Xe  K S 0 pX 1539  2 < 9 4.4  Belle ? CLAS(d)  d  K + K - p(n) 1542  5 < 21 5.2  CLAS(d) SAPHIR  p  K + K 0 (n) 1540  6 < 25 4.8  CLAS(p) ITEP A  K S 0 pX 1533  5 < 20 6.7  CLAS(p)  p   + K - K + (n) 1555  10 < 26 7.8  HERMES e + d  K S 0 pX 1528  3 13  9 ~5  ZEUS e + p  e’K S 0 pX 1522  3 8  4 ~5  COSY pp  K S 0 p  + 1530  5 < 18 4-6  SVD(2004) pA  K S 0 pX 1526  4 < 24 5.6  SVD(2005) pA  K S 0 pX 1523  4 < 14 8.0  independent sample KEK E522  - p  K - X 1531  3 < 10 ~2.5  P  =1.92 GeV/c only New results will appear from LEPS(d), DIANA, COSY, … Negative results in high energy experiments. (BES, BaBar, Belle, LEP, HERA-B, SPHINX, HyperCP, CDF, FOCUS, PHENIX)  d  + K - p  <450 pb, but acceptance coverage is different from LEPS (forward region). ⇒  + is not killed.

3. LEPS LD 2 runs Still need to confirm  + existence Collected Data (LH 2 and LD 2 runs) Dec.2000 – June 2001 LH 2 50 mm ~5×10 12 photons published data set [using 5 mm-thick plastic counter] May 2002 – Apr. 2003 LH 2 150 mm ~1.4×10 12 photons Oct. 2002 – June 2003 LD 2 150 mm ~2×10 12 photons #neutrons×#photons in K ＋ K － detection mode (  n→  ＋ K －  K + nK － ) = 5×short LH 2 runs K － p detection mode :γd→  ＋ K － p  ＋ is identified by pK － missing mass from deuteron. ⇒ No Fermi correction is needed. γ p n ＋＋ K－K－ p  (1520)

4. LEPS Experiment － 8 GeV electrons in SPring-8 + 351nm Ar laser (3.5eV ） ⇒ 1.5-2.4 GeV photons (Backward Compton Scattering) － Photon Flux ~10 6 cps, Photon Energy Resolution ~10 MeV － Charged particle spectrometer with forward acceptance － PID from momentum and time-of-flight measurements PWO measurement tagged TOF Dipole Magnet 0.7 Tesla Target Start Counter DC2DC3 DC1SVTX AC(n=1.03) 

5. Research Center for Nuclear Physics, Osaka University ： T. Nakano, D.S. Ahn, M. Fujiwara, K. Horie, T. Hotta, Y. Kato, K. Kino, H. Kohri, N. Muramatsu, T. Sawada, T. Tsunemi, M. Uchida, M. Yosoi, R.G.T. Zegers Department of Physics, Pusan National University ： J.K. Ahn, J.Y. Park School of Physics, Seoul National University ： H.C. Bhang, K.H. Tshoo Department of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano, A. Titov Institute of Physics, Academia Sinica ： W.C. Chang, D.S. Oshuev, Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： H. Ejiri, S. Date', N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa, T. Yorita Department of Physics and Astronomy, Ohio University ： K. Hicks, T. Mibe Department of Physics, Kyoto University ： K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, M. Niiyama Department of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. Iwata Department of Physics, Osaka University ： S. Ajimura, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Department of Physics, Tohoku University ： M. Sumihama Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura The LEPS Collaboration

6. Event selections in K － p mode MMp(γ,K － p) GeV/c 2 π － mis-ID as K － K ＋ mass : 0.40 – 0.62 GeV/c 2 M(K － p) GeV/c 2 Λ(1520) : 1.50 – 1.54 GeV/c 2 Events with Λ(1520) production were selected. E  > 1.75 GeV was also applied. Non-resonant KKp +  p + … γp→K － pKπ

7. Fluctuation or not? ⇒ Two complementary BG estimations (MC-based & real data-based) ⇒ smoothening missing mass spectrum by smearing E  resolution K － p missing mass in 1.50<M(pK － )<1.54 GeV/c 2 MMd(γ,K － p) GeV/c 2 Θ ＋ signal ？ ~1.53 GeV/c 2 preliminary MMd(γ,K － p) GeV/c 2 5 MeV bins 3 MeV bins preliminary ?? ??

8. MM(K － p) GeV/c 2 Counts/5 MeV preliminary 10-MeV E  smearing to remove fluctuations Any structure which is finer than detector resolution is due to fluctuations. ⇒ A magnitude which roughly equals to detector resolution was smeared with 100 times more statistics. side-band averaged spectrum E  -smeared spectrum [1.50<M(K - p)<1.54 GeV/c 2 ]  (1520) production [side-band subtracted]

9. M(KK) GeV/c 2 M(pK － ) GeV/c 2 MC-based BG estimation by using LH 2 data Quasi-Free BG in LD 2 data= K  (1520) +  p + Non-resonant KKp + … - BGs were simulated by including Fermi motion. (MC ~ 20 x real data) - Kinematics at CMS were adjusted to real LH 2 data.  ‘Filters’ in E CMS,  CMS (pK － ),  CMS (proton), P CMS (proton), P CMS (K － ) - Non-resonant KKp ⇒ K +  * ⇒  p were adjusted step by step. KKp K*K* pp  (1520)  Fermi-corrected MMp( ,p) LH 2 data

10. MMd( ,pK － ) in  (1520) region  2 test at 1.4-1.7 GeV/c 2  2 = 34.154 ndf = 30 prob. = 0.275 MMd( ,pK － ) GeV/c 2 Assuming dueteron mass MMd( ,pK － ) GeV/c 2 ++ 1.6 GeV bump mass ~1.53 GeV/c 2 s/sqrt[s+b] ~ 4  Possibility of model variations LH 2 data (preliminary) 1.50< M(pK － )<1.54 GeV/c 2 LD 2 data (preliminary) 1.50< M(pK － )<1.54 GeV/c 2

11. MMd( ,pK － ) below/above  (1520) region [LD 2 ] MMd( ,pK － ) GeV/c 2 M(pK － )<1.50 GeV/c 2 M(pK － )>1.54 GeV/c 2 Preliminary

12. Real data-based BG estimation LD 2 data M(K － p) GeV/c 2 ** Non-resonant BGs +  p + … - Non-resonant BGs +  p : Deduced by 0.4 x sum of spectra in side bands - K  (1520) : LH 2 data after sideband subtraction Linearity was checked by comparing two independent sideband regions. MMd(γ,K － p) GeV/c 2 correction for  contribution red : inside blue: outside 10-MeV E  smeared K  * MC black: Fermi off red : Fermi on

13. K － p missing mass spectrum MMd(γ,K － p) GeV/c 2 Counts/5 MeV preliminary  * fitted in MM<1.52 GeV/c 2 ++ 1.6 GeV bump ** from sidebands MMd(γ,K － p) GeV/c 2 preliminary Counts/5 MeV K  (1520) fit to all MMd( ,pK － ) region - BG level : 6.5% more. -  2 /ndf=2.8 mass ~1.53 GeV/c 2 s/sqrt[s+b] ~ 5  Possibility to be affected by statistics in real data

14.  (1520) mass gate dependence & photon energy dependence MMd(γ,K － p) GeV/c 2  10 MeV/c 2  20 MeV/c 2 (Standard)  50 MeV/c 2  100 MeV/c 2 MMd( ,pK － ) GeV/c 2 E  < 2.1 GeV E   > 2.1 GeV

15. Prospects at LEPS Planning to take another data set with LD2 target and forward spectrometer this year. Photon beam intensity will be twice by injecting two lasers. Time Projection Chamber is being prepared to increase acceptance coverage. CLAS region can be covered.

16. New beamline at SPring-8 Started to discussing about constructing new beamline at SPring-8. Upgrades of beam intensity (multi-laser injection, Long Range Non-diffractive Beam) and energy (deep-UV laser with =257 nm, x-ray injection) are planned. 4π detector with good resolutions are under considerations (BNL-E949 detector). Better kinematical coverage and energy extension in  + photoproduction are expected. 8 GeV electron 100 eV photon

17. Pentaquark Search with E949 Detector (possible extension at J-PARC) π ＋ π － detection at UTC M(π ＋ π － )=M(K S 0 ) M(  + )=M(K ＋ n)- [MM(K ＋,π ＋ π － )-M(p)] Fermi-correction π ＋ π － detection at UTC & proton detection at Sci. Tgt. M(π ＋ π － )=M(K S 0 ) M(Θ ＋ )=M(K S 0 p) TOF Δv/v=Δt/t, v=L/t, Δt=200 psec ⇒ L=4 m is equivalent to σ=8.4 MeV K/π separation : ~6 nsec π＋π＋ π－π－ proton K ＋ beam 417 MeV/c σ=8.4 MeV ΔP/P=1.3% Important to confirm the existence and to extract width, (spin), … K ＋ n→  + →K S 0 p→π ＋ π － p (26 mb for Γ=1 MeV) vs. CEX BG is forward peaked. (7 mb in PRD15 (1977) 1846)

18. Summary Confirmation of  + by using LD 2 data with K － p detection mode in MMd( ,pK － ) spectrum - Two methods in BG shape estimation (MC-based & sideband method) are complementary. - 1.53 GeV/c 2 peak (4-5σ,preliminary) + 1.6 GeV/c 2 bump associated with  (1520) production - Signal-like behavior [M(pK － ) gate & E  dependence] Differential cross section is being measured. Luminosity(LD 2 ) ~0.6 pb -1. Efforts for further confirmations are in progress. Better kinematical coverage and energy extension are expected in future.